EFGShield — A program for parsing and summarizing the results of electric field gradient and nuclear magnetic shielding tensor calculations
Samyuktha Adiga, Dominic Aebi, and David L. Bryce Can. J. Chem./Rev. can. chim. 85(7-8): 496-505 (2007)
Full text (PDF 666 kb)
Abstract: A computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient (EFG) and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical software. In addition to summarizing tensor magnitudes according to conventions commonly used by solid-state NMR spectroscopists, the program provides Euler angles relating the orientations of the EFG and shielding tensor principal axis systems (PAS). An atomic coordinate file is generated that also contains dummy atoms representing the orientations of the EFG and shielding tensor PASs in the molecular framework. We demonstrate the functionality of the program using calculations of the chlorine EFG and shielding tensors for strontium chloride dihydrate and calcium chloride dihydrate. Several models of the chloride environment in these compounds are tested, including those where point charges are used to represent the extended three-dimensional lattices within the self-consistent charge field perturbation approach. The results highlight both the shortcomings and successes of traditional localized orbital-based basis sets in the description of the NMR properties of extended systems. We anticipate that EFGShield will be a useful tool for spectroscopists using quantum chemical software to aid in the interpretation of experimental data.
Key words: quantum chemical calculations, computer program, electric field gradient tensor, quadrupolar coupling constant, nuclear magnetic shielding tensor, Euler angles, alkaline earth chloride hydrates.
Friday, August 10, 2007
Thursday, August 09, 2007
J Phys Chem C, Macromolecules and Organometallics
J Phys. Chem. C
-J. Phys. Chem. C, 111 (21), 7605 -7611, 2007. 10.1021/jp070321y S1932-7447(07)00321-4
Pores in Nanostructured TiO2 Films. Size Distribution and Pore Permeability
Dulce Vargas-Florencia, Tomas Edvinsson, Anders Hagfeldt, and Istv n Furó*
Division of Physical Chemistry, Department of Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden
Abstract: Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical <2> values where is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle-particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.
-J. Phys. Chem. C, 111 (21), 7720 -7726, 2007. 10.1021/jp068738b S1932-7447(06)08738-3
NMR Study of Proton Sites in Group I Salts of 12-Tungstophosphoric Acid
Steven F. Dec,* George M. Jacobsen, James L. Horan, and Andrew M. Herring
Department of Chemistry and Geochemistry and Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 8040
Abstract: The Group I salts of 12-tungstophosphoric acid were studied in their limiting hydration state with use of both1H and 31P solid-state nuclear magnetic resonance (NMR). The bulk proton structures of the Li, Na, and Rb salts consist of both lone protons and water molecule protons. The K and Cs salts contain similar proton structures that reside in surface sites. Nonspinning 1H NMR results indicate that all protons in the limiting hydration state in each of the Group I salts are highly mobile at room temperature. 1H spin-lattice relaxation times obtained as a function of temperature indicate that the dominant mechanism responsible for proton relaxation in the Li, Na, and Rb salts is restricted rotation of water molecules while the K and Cs salts have proton spin-lattice relaxation that is dominated by translation of protons through surface sites of the material. Two stable Rb salt phases are crystallized when a stoichiometric amount of RbCl is added to aqueous 12-tungstophosphoric acid at room temperature.
-J. Phys. Chem. C, 111 (26), 9066 -9071, 2007. 10.1021/jp071490l S1932-7447(07)01490-2
Speciation of Silanol Groups in Precipitated Silica Nanoparticles by 1H MAS NMR Spectroscopy
Geoffrey Hartmeyer, Claire Marichal,* Bénédicte Lebeau, Séverinne Rigolet, Philippe Caullet, and Julien Hernandez
Laboratoire de Matériaux à Porosité Contrôlée, ENSCMu, Université de Haute Alsace, UMR 7016, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France, and Centre de Recherches d'Aubervilliers, RHODIA, 52 rue de la Haie Coq, 93308 Aubervilliers, France
Abstract: Speciation of the various proton species present in precipitated silica samples by 1H high-spinning frequency magic-angle spinning (MAS) NMR (25 kHz) is achieved. External standards are used for the calibration of the absolute amount of protons, the relevance of the proton spin counting being checked by comparison with the data deduced from classical thermogravimetric (TG) and 29Si MAS NMR experiments. The method also allows to follow postsynthesis modifications of silica, corresponding for instance to fluorination or deuteration treatments. In particular, a 1H resonance occurring at 1.1 ppm/TMS and corresponding to a constant proton amount whatever the applied treatment is tentatively assigned for the first time to inaccessible isolated silanol groups.
-J. Phys. Chem. C, 111 (28), 10624 -10629, 2007. 10.1021/jp0728757 S1932-7447(07)02875-0
Methane Carbonylation with CO on Sulfated Zirconia: Evidence from Solid-State NMR for the Selective Formation of Acetic Acid
Mikhail V. Luzgin, Vladimir A. Rogov, Nina S. Kotsarenko, Vera P. Shmachkova, and Alexander G. Stepanov*
Boreskov Institute of Catalysis, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia
Abstract: Using 13C and 1H solid-state NMR it has been shown, that methane can be carbonylated with carbon monoxide to give acetic acid on solid acid catalyst, sulfated zirconia. The carbonylation occurs at 473-573 K with high selectivity and essential conversion. The reaction proceeds both in the absence and in the presence of molecular oxygen. In the presence of oxygen, the catalyst can be used for the carbonylation of further portion of methane without reactivation in air. The mechanism of the reaction is discussed. The reaction observed opens up new possibilities of using sulfated zirconia-based solid catalysts for the synthesis of acetic acid from methane and carbon monoxide.
Macromolecules
-Macromolecules, 40 (14), 4736 -4739, 2007. 10.1021/ma0700025 S0024-9297(07)00002-2
Probing Chain Interpenetration in Polymer Glasses by 1H Dipolar Filter Solid-State NMR under Fast Magic Angle Spinning
Xiaoliang Wang, Fangfang Tao, Pingchuan Sun,* Dongshan Zhou, Zhaoqun Wang, Qiang Gu, Jinlei Hu, and Gi Xue*
Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071, P. R. China
Introduction. The concept of chain entanglement provides the basis of our current understanding of the flow behavior of polymer melts and solutions.1,2 The interpenetration process is a very important step for polymer chain condensation from the dilute solution to the aggregation state. Such a condensed multiple chain systems possess a structure where polymer chains form an entangled network, which thus establishes the mechanical property of polymers.1-3 Information about interpenetration regions would provide significant insight into intermolecular coupling and the dynamics of local segmental relaxation, which issues remain unclear for glassy polymer physics. However, compared to those in solution and in the rubber state, an intriguing question concerning the characterization of the degree of interpenetration below and around the glass transition temperature (Tg) of a polymer has still not been tackled.4-7 Atomic force microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and scattering methods (visible light, X-ray, neutron) are frequently used to investigate chain interpenetration.8-10 One drawback of these methods is that they yield information on length scales of a few to tens of nanometers; thus, they cannot be used to directly identify the individual structure in the interpenetration regions at a molecular level. Nonradiative energy transfer (NET) fluorescence spectroscopy has been used to observe the memory of the chain interpenetration that had existed in the original solution, and many interesting conclusions have been reported.11,12 On the other hand, 13C solid-state NMR and small-angle neutron scattering (SANS) studies have cast doubt on the conclusions regarding the memory of the chain interpenetration for the freeze-dried polymer reported by NET.13-16 Developing new strategies to characterize the chain interpenetration in polymer glasses on a short length scale of 0.5 nm is still a challenge.
-Macromolecules, 40 (14), 4953 -4962, 2007. 10.1021/ma0620924 S0024-9297(06)02092-4
Investigation of Network Heterogeneities in Filled, Trimodal, Highly Functional PDMS Networks by 1H Multiple Quantum NMR
Erica Gjersing, Sarah Chinn, Jason R. Giuliani, Julie Herberg, Robert S. Maxwell,* Eric Eastwood, Dan Bowen, and Tom Stephens
Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94551, Honeywell Federal Manufacturing and Technologies Plant, Kansas City, Missouri, Los Alamos National Laboratory, Los Alamos, New Mexico, and Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California
Abstract: The segmental order and dynamics of polymer network chains in a filled, trimodal silicone foam network have been studied by static 1H multiple quantum (MQ) NMR methods to gain insight into the structure property relationships. The foam materials were synthesized with two different types of cross-links, with functionalities, , of 4 and near 60. The network chains were composed of distributions of high, low, and medium molecular weight chains. Cross-linking was accomplished by standard acid-catalyzed reactions. MQ NMR methods have detected domains with residual dipolar couplings (<>) of near 4 and 1 krad/s assigned to (a) the shorter polymer chains and chains near the multifunctional ( = 60) cross-linking sites and to (b) the longer polymer chains far from these sites. Three structural variables were systematically varied and the mechanical properties via compression and distributions of residual dipolar couplings measured in order to gain insight into the network structural motifs that contribute significantly to the composite properties. The partitioning and average values of the residual dipolar couplings for the two domains were observed to be dependent on formulation variables and provided increased insight into the network structure of these materials which are unavailable from swelling and spin-echo methods. The results of this study suggest that the domains with high cross-link density contribute significantly to the high strain modulus, while the low cross-link density domains do not. This is in agreement with theories and experimental studies on silicone bimodal networks over the last 20 years. In situ MQ-NMR of swollen samples suggests that the networks deform heterogeneously and nonaffinely. The heterogeneity of the deformation process was observed to depend on the amount of the high functionality cross-linking site PMHS. The NMR experiments shown here provide increased ability to characterize multimodal networks of typical engineering silicone foam materials and to gain significant insight into structure-property relationships.
-Macromolecules, 40 (14), 5001 -5013, 2007. 10.1021/ma062507l S0024-9297(06)02507-1
Solid-State Organization and Morphological Partitioning in Polyoxymethylene-Based Copolymers: A Solid-State NMR and WAXS Study
Cédric Lorthioir,* Françoise Lauprêtre, Karthikeyan Sharavanan, Ronald F. M. Lange, Philippe Desbois, Michel Moreau, and Jean-Pierre Vairon
Laboratoire de Recherche sur les Polymères (CNRS-UMR 7581), 2-8 rue Henri Dunant, 94320 Thiais, France; Laboratoire de Chimie des Polymères (CNRS-UMR 7610), Université Pierre et Marie Curie, Case 185 T44 E1, 4 Place Jussieu, 75252 Paris Cedex 05, France; and BASF Research, GKT/U B1, D-67056 Ludwigshafen, Germany
Abstract: The solid-state organization of copolymers based on methylene oxide (MO) units and tetramethylene oxide (T) units, with T unit contents ranging between 0.9 and 10.0 mol %, is investigated by the combined use of solid-state NMR, WAXS, and DSC experiments. In these semicrystalline copolymers, the T units can be viewed as linear defects inserted along linear poly(oxymethylene) chains. As expected, the insertion of T units induces a significant decrease of both crystallinity and crystallite size: a large part of T units is located in the amorphous domains. However, some T units can also be detected within the crystalline domains and/or the interfacial regions with the amorphous phase. More precisely, the amount of T units at both sides of the noncrystalline/crystalline interfaces seems to be much higher than the T units in the interior of the crystallites. At the lowest T unit content (0.9 mol %), the composition averaged over both interfacial and crystalline phases appears to be identical to the composition of the amorphous phase. When the comonomer content increases, the amount of T units in the interfacial and crystalline zones becomes higher and higher while the partitioning coefficient of the T units in these domains tends to a limiting value of 0.40.
-Macromolecules, 40 (15), 5411 -5419, 2007. 10.1021/ma0707786 S0024-9297(07)00778-4
Quantitative Determination of Phase Content in Multiphase Polymers by Combining Spin-Diffusion and CP-MAS NMR
L. Zhang, Z. Liu, Q. Chen,* and E. W. Hansen*
Physics Department and the State Key Laboratory of Precision Spectroscopy, East China Normal University, 3663 Northern Zhongshan Road, Shanghai 200062, People's Republic of China, and Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
Abstract: We present a new approach to determine quantitatively the phase content of multiphase polymers by applying a spin-diffusion pulse sequence (filter) prior to cross-polarization (CP) in a 13C-CPAS experiment. The technique is exemplified for two rather different polymer systems, a high-density polyethylene (HDPE) and four styrene-isoprene diblock copolymers, all of known phase contents. In principle, the technique should be applicable to any multiphase system in which spin-diffusion between different regions/phases exists and where the magnetization of phases can selectively be filtered out
-Macromolecules, 40 (15), 5420 -5423, 2007. 10.1021/ma070790y S0024-9297(07)00790-5
Investigation of Dynamics of Poly(dimethylsilane) in the Mesophase by Solid-State 29Si NMR: Evidence for Rotator Phase
Hironori Kaji* and Fumitaka Horii
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Abstract: The dynamics of poly(dimethylsilane) (PDMS) in the mesophase was investigated by DSC and 29Si solid-state NMR. A solid-solid transition is observed at 166 C based on DSC measurements. Below the transition temperature, typical chemical shift anisotropy (CSA) spectra are obtained by the 29Si solid-state NMR with cross-polarization (CP) preparation for the static PDMS sample. In contrast, the intensities at the isotropic chemical shift are suppressed for the CSA spectra above the transition temperature. The intensity attenuation, termed "magic angle hole", in the CSA spectra is theoretically derived for uniaxially rotating solids. Therefore, it was found that PDMS undergoes a uniaxial rotation motion above the transition temperature. Theoretically, both the direct polarization (DP) experiments without the CP process and ultraslow magic angle spinning (MAS) experiments retrieve standard CSA line shapes. Our DP and ultraslow MAS experiments confirm the theoretical consideration. The retrieved CSA spectra have axially symmetric line shapes, which also confirm the above uniaxial dynamics. On the basis of the solid-state NMR, we clearly show that the solid-solid transition at 166 C is a rigid monoclinic-mobile rotator phase transition.
-Macromolecules, 40 (16), 5776 -5786, 2007. 10.1021/ma070485c S0024-9297(07)00485-8
Various Types of Hydrogen Bonds, Their Temperature Dependence and Water-Polymer Interaction in Hydrated Poly(Acrylic Acid) as Revealed by 1H Solid-State NMR Spectroscopy
Baohui Li, Lu Xu, Qiang Wu, Tiehong Chen, Pingchuan Sun,* Qinghua Jin, Datong Ding, Xiaoliang Wang, Gi Xue,* and An-Chang Shi
Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry and College of Physics, Nankai University, Tianjin, 300071, P. R. China, Department of Polymer Science and Engineering, The School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Abstract: Various types of hydrogen bonds, their temperature dependence and water-polymer interaction in hydrated poly(acrylic acid) (PAA) were systematically investigated using 1H CRAMPS solid-state NMR techniques in the temperature range from 25 to 110 C. The 1H CRAMPS NMR methods are based on a recently developed continuous phase modulation technique for 1H-1H homonuclear dipolar decoupling. The 1H CRAMPS experiments revealed four types of protons in hydrated PAA which are assigned to protons from the mutually hydrogen-bonded COOH groups (1), from the free COOH groups (2), from the COOH groups bounded with water or from water bounded with COOH groups which are undergoing fast chemical exchange mutually (3), and from main chain groups (4), respectively. Furthermore, we proposed double-quantum filtered and dipolar filtered 1H CRAMPS experiments to further assign the protons according to their dipolar coupling strength. In addition, high-resolution spin echo 1H CRAMPS experiments were further employed to accurately determine the chemical shift of these protons. These NMR techniques were also used to elucidate the molecular mobility of the different groups. It was found that dehydration in PAA promotes the formation of hydrogen bonds between COOH groups. Variable-temperature 1H CRAMPS experiments demonstrated that the dissociation of the hydrogen bonds between COOH groups occurs dramatically at lower temperature in hydrated PAA and slowly over a wide range of temperature in dehydrated PAA. It was also found that the dehydration of water bounded with COOH groups in hydrated PAA occurs significantly at high temperature. The NMR results were compared with previous work using DSC and other techniques. Besides undergoing fast chemical exchange, the adsorbed water was also demonstrated in proximity with the free COOH groups and far from the hydrogen bonds between COOH groups by using two-dimensional 1H-1H spin-exchange NMR experiments.
-Macromolecules, 40 (16), 5787 -5790, 2007. 10.1021/ma070793a S0024-9297(07)00793-0
Cross-Link Density of a Dispersed Rubber Measured by 129Xe Chemical Shift
Wallace O. Parker, Jr.,* Angelo Ferrando, Dino Ferri, and Valentino Canepari
Physical Chemistry, Refining & Marketing Division, Eni S.p.A., via Maritano 26, 20097 San Donato Milanese, Italy, and Polymer Research Center "C. Buonerba", Polimeri Europa, via Taliercio 14, 46100 Mantova, Italy
Abstract: 129Xe NMR chemical shifts of adsorbed xenon (natural isotopic abundance) were used to probe the free volume in a cross-linked rubber, polybutadiene (PB), alone and occluded within high impact polystyrene (HIPS). Shift dependency on cross-link density, or Nm (average number of monomer units between chemical cross-links) determined by the classical solvent swelling method, was detailed for high-cis-1,4-PB. A decrease in Nm from 262 to 4 caused the shift to increase 4 ppm. A curve inflection, evident at 218 ppm (and Nm = 30), corresponded to a free volume with an average spherical diameter of 0.49 nm using the empirical (shift-pore size) relation known for zeolites. This diameter is essentially equal to that of the PB chain (0.48 nm) at its Tg (glass transition temperature). Tg plotted against Nm showed the same inflection (at Nm = 25), corroborating a regime with more severe interchain contacts when the free volume diameter is inferior to the chain diameter. The empirical relation between 129Xe shift and Nm observed for pure PB was used to estimate the cross-link density of PB dispersed in HIPS as a function of cure time. Cross-linkage was greatly slowed after 8 h of curing, when Nm estimated by NMR spectroscopy was 10.
-J. Phys. Chem. C, 111 (21), 7605 -7611, 2007. 10.1021/jp070321y S1932-7447(07)00321-4
Pores in Nanostructured TiO2 Films. Size Distribution and Pore Permeability
Dulce Vargas-Florencia, Tomas Edvinsson, Anders Hagfeldt, and Istv n Furó*
Division of Physical Chemistry, Department of Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden
Abstract: Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical <2> values where is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle-particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.
-J. Phys. Chem. C, 111 (21), 7720 -7726, 2007. 10.1021/jp068738b S1932-7447(06)08738-3
NMR Study of Proton Sites in Group I Salts of 12-Tungstophosphoric Acid
Steven F. Dec,* George M. Jacobsen, James L. Horan, and Andrew M. Herring
Department of Chemistry and Geochemistry and Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 8040
Abstract: The Group I salts of 12-tungstophosphoric acid were studied in their limiting hydration state with use of both1H and 31P solid-state nuclear magnetic resonance (NMR). The bulk proton structures of the Li, Na, and Rb salts consist of both lone protons and water molecule protons. The K and Cs salts contain similar proton structures that reside in surface sites. Nonspinning 1H NMR results indicate that all protons in the limiting hydration state in each of the Group I salts are highly mobile at room temperature. 1H spin-lattice relaxation times obtained as a function of temperature indicate that the dominant mechanism responsible for proton relaxation in the Li, Na, and Rb salts is restricted rotation of water molecules while the K and Cs salts have proton spin-lattice relaxation that is dominated by translation of protons through surface sites of the material. Two stable Rb salt phases are crystallized when a stoichiometric amount of RbCl is added to aqueous 12-tungstophosphoric acid at room temperature.
-J. Phys. Chem. C, 111 (26), 9066 -9071, 2007. 10.1021/jp071490l S1932-7447(07)01490-2
Speciation of Silanol Groups in Precipitated Silica Nanoparticles by 1H MAS NMR Spectroscopy
Geoffrey Hartmeyer, Claire Marichal,* Bénédicte Lebeau, Séverinne Rigolet, Philippe Caullet, and Julien Hernandez
Laboratoire de Matériaux à Porosité Contrôlée, ENSCMu, Université de Haute Alsace, UMR 7016, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France, and Centre de Recherches d'Aubervilliers, RHODIA, 52 rue de la Haie Coq, 93308 Aubervilliers, France
Abstract: Speciation of the various proton species present in precipitated silica samples by 1H high-spinning frequency magic-angle spinning (MAS) NMR (25 kHz) is achieved. External standards are used for the calibration of the absolute amount of protons, the relevance of the proton spin counting being checked by comparison with the data deduced from classical thermogravimetric (TG) and 29Si MAS NMR experiments. The method also allows to follow postsynthesis modifications of silica, corresponding for instance to fluorination or deuteration treatments. In particular, a 1H resonance occurring at 1.1 ppm/TMS and corresponding to a constant proton amount whatever the applied treatment is tentatively assigned for the first time to inaccessible isolated silanol groups.
-J. Phys. Chem. C, 111 (28), 10624 -10629, 2007. 10.1021/jp0728757 S1932-7447(07)02875-0
Methane Carbonylation with CO on Sulfated Zirconia: Evidence from Solid-State NMR for the Selective Formation of Acetic Acid
Mikhail V. Luzgin, Vladimir A. Rogov, Nina S. Kotsarenko, Vera P. Shmachkova, and Alexander G. Stepanov*
Boreskov Institute of Catalysis, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia
Abstract: Using 13C and 1H solid-state NMR it has been shown, that methane can be carbonylated with carbon monoxide to give acetic acid on solid acid catalyst, sulfated zirconia. The carbonylation occurs at 473-573 K with high selectivity and essential conversion. The reaction proceeds both in the absence and in the presence of molecular oxygen. In the presence of oxygen, the catalyst can be used for the carbonylation of further portion of methane without reactivation in air. The mechanism of the reaction is discussed. The reaction observed opens up new possibilities of using sulfated zirconia-based solid catalysts for the synthesis of acetic acid from methane and carbon monoxide.
Macromolecules
-Macromolecules, 40 (14), 4736 -4739, 2007. 10.1021/ma0700025 S0024-9297(07)00002-2
Probing Chain Interpenetration in Polymer Glasses by 1H Dipolar Filter Solid-State NMR under Fast Magic Angle Spinning
Xiaoliang Wang, Fangfang Tao, Pingchuan Sun,* Dongshan Zhou, Zhaoqun Wang, Qiang Gu, Jinlei Hu, and Gi Xue*
Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071, P. R. China
Introduction. The concept of chain entanglement provides the basis of our current understanding of the flow behavior of polymer melts and solutions.1,2 The interpenetration process is a very important step for polymer chain condensation from the dilute solution to the aggregation state. Such a condensed multiple chain systems possess a structure where polymer chains form an entangled network, which thus establishes the mechanical property of polymers.1-3 Information about interpenetration regions would provide significant insight into intermolecular coupling and the dynamics of local segmental relaxation, which issues remain unclear for glassy polymer physics. However, compared to those in solution and in the rubber state, an intriguing question concerning the characterization of the degree of interpenetration below and around the glass transition temperature (Tg) of a polymer has still not been tackled.4-7 Atomic force microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and scattering methods (visible light, X-ray, neutron) are frequently used to investigate chain interpenetration.8-10 One drawback of these methods is that they yield information on length scales of a few to tens of nanometers; thus, they cannot be used to directly identify the individual structure in the interpenetration regions at a molecular level. Nonradiative energy transfer (NET) fluorescence spectroscopy has been used to observe the memory of the chain interpenetration that had existed in the original solution, and many interesting conclusions have been reported.11,12 On the other hand, 13C solid-state NMR and small-angle neutron scattering (SANS) studies have cast doubt on the conclusions regarding the memory of the chain interpenetration for the freeze-dried polymer reported by NET.13-16 Developing new strategies to characterize the chain interpenetration in polymer glasses on a short length scale of 0.5 nm is still a challenge.
-Macromolecules, 40 (14), 4953 -4962, 2007. 10.1021/ma0620924 S0024-9297(06)02092-4
Investigation of Network Heterogeneities in Filled, Trimodal, Highly Functional PDMS Networks by 1H Multiple Quantum NMR
Erica Gjersing, Sarah Chinn, Jason R. Giuliani, Julie Herberg, Robert S. Maxwell,* Eric Eastwood, Dan Bowen, and Tom Stephens
Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94551, Honeywell Federal Manufacturing and Technologies Plant, Kansas City, Missouri, Los Alamos National Laboratory, Los Alamos, New Mexico, and Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California
Abstract: The segmental order and dynamics of polymer network chains in a filled, trimodal silicone foam network have been studied by static 1H multiple quantum (MQ) NMR methods to gain insight into the structure property relationships. The foam materials were synthesized with two different types of cross-links, with functionalities, , of 4 and near 60. The network chains were composed of distributions of high, low, and medium molecular weight chains. Cross-linking was accomplished by standard acid-catalyzed reactions. MQ NMR methods have detected domains with residual dipolar couplings (<>) of near 4 and 1 krad/s assigned to (a) the shorter polymer chains and chains near the multifunctional ( = 60) cross-linking sites and to (b) the longer polymer chains far from these sites. Three structural variables were systematically varied and the mechanical properties via compression and distributions of residual dipolar couplings measured in order to gain insight into the network structural motifs that contribute significantly to the composite properties. The partitioning and average values of the residual dipolar couplings for the two domains were observed to be dependent on formulation variables and provided increased insight into the network structure of these materials which are unavailable from swelling and spin-echo methods. The results of this study suggest that the domains with high cross-link density contribute significantly to the high strain modulus, while the low cross-link density domains do not. This is in agreement with theories and experimental studies on silicone bimodal networks over the last 20 years. In situ MQ-NMR of swollen samples suggests that the networks deform heterogeneously and nonaffinely. The heterogeneity of the deformation process was observed to depend on the amount of the high functionality cross-linking site PMHS. The NMR experiments shown here provide increased ability to characterize multimodal networks of typical engineering silicone foam materials and to gain significant insight into structure-property relationships.
-Macromolecules, 40 (14), 5001 -5013, 2007. 10.1021/ma062507l S0024-9297(06)02507-1
Solid-State Organization and Morphological Partitioning in Polyoxymethylene-Based Copolymers: A Solid-State NMR and WAXS Study
Cédric Lorthioir,* Françoise Lauprêtre, Karthikeyan Sharavanan, Ronald F. M. Lange, Philippe Desbois, Michel Moreau, and Jean-Pierre Vairon
Laboratoire de Recherche sur les Polymères (CNRS-UMR 7581), 2-8 rue Henri Dunant, 94320 Thiais, France; Laboratoire de Chimie des Polymères (CNRS-UMR 7610), Université Pierre et Marie Curie, Case 185 T44 E1, 4 Place Jussieu, 75252 Paris Cedex 05, France; and BASF Research, GKT/U B1, D-67056 Ludwigshafen, Germany
Abstract: The solid-state organization of copolymers based on methylene oxide (MO) units and tetramethylene oxide (T) units, with T unit contents ranging between 0.9 and 10.0 mol %, is investigated by the combined use of solid-state NMR, WAXS, and DSC experiments. In these semicrystalline copolymers, the T units can be viewed as linear defects inserted along linear poly(oxymethylene) chains. As expected, the insertion of T units induces a significant decrease of both crystallinity and crystallite size: a large part of T units is located in the amorphous domains. However, some T units can also be detected within the crystalline domains and/or the interfacial regions with the amorphous phase. More precisely, the amount of T units at both sides of the noncrystalline/crystalline interfaces seems to be much higher than the T units in the interior of the crystallites. At the lowest T unit content (0.9 mol %), the composition averaged over both interfacial and crystalline phases appears to be identical to the composition of the amorphous phase. When the comonomer content increases, the amount of T units in the interfacial and crystalline zones becomes higher and higher while the partitioning coefficient of the T units in these domains tends to a limiting value of 0.40.
-Macromolecules, 40 (15), 5411 -5419, 2007. 10.1021/ma0707786 S0024-9297(07)00778-4
Quantitative Determination of Phase Content in Multiphase Polymers by Combining Spin-Diffusion and CP-MAS NMR
L. Zhang, Z. Liu, Q. Chen,* and E. W. Hansen*
Physics Department and the State Key Laboratory of Precision Spectroscopy, East China Normal University, 3663 Northern Zhongshan Road, Shanghai 200062, People's Republic of China, and Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway
Abstract: We present a new approach to determine quantitatively the phase content of multiphase polymers by applying a spin-diffusion pulse sequence (filter) prior to cross-polarization (CP) in a 13C-CPAS experiment. The technique is exemplified for two rather different polymer systems, a high-density polyethylene (HDPE) and four styrene-isoprene diblock copolymers, all of known phase contents. In principle, the technique should be applicable to any multiphase system in which spin-diffusion between different regions/phases exists and where the magnetization of phases can selectively be filtered out
-Macromolecules, 40 (15), 5420 -5423, 2007. 10.1021/ma070790y S0024-9297(07)00790-5
Investigation of Dynamics of Poly(dimethylsilane) in the Mesophase by Solid-State 29Si NMR: Evidence for Rotator Phase
Hironori Kaji* and Fumitaka Horii
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Abstract: The dynamics of poly(dimethylsilane) (PDMS) in the mesophase was investigated by DSC and 29Si solid-state NMR. A solid-solid transition is observed at 166 C based on DSC measurements. Below the transition temperature, typical chemical shift anisotropy (CSA) spectra are obtained by the 29Si solid-state NMR with cross-polarization (CP) preparation for the static PDMS sample. In contrast, the intensities at the isotropic chemical shift are suppressed for the CSA spectra above the transition temperature. The intensity attenuation, termed "magic angle hole", in the CSA spectra is theoretically derived for uniaxially rotating solids. Therefore, it was found that PDMS undergoes a uniaxial rotation motion above the transition temperature. Theoretically, both the direct polarization (DP) experiments without the CP process and ultraslow magic angle spinning (MAS) experiments retrieve standard CSA line shapes. Our DP and ultraslow MAS experiments confirm the theoretical consideration. The retrieved CSA spectra have axially symmetric line shapes, which also confirm the above uniaxial dynamics. On the basis of the solid-state NMR, we clearly show that the solid-solid transition at 166 C is a rigid monoclinic-mobile rotator phase transition.
-Macromolecules, 40 (16), 5776 -5786, 2007. 10.1021/ma070485c S0024-9297(07)00485-8
Various Types of Hydrogen Bonds, Their Temperature Dependence and Water-Polymer Interaction in Hydrated Poly(Acrylic Acid) as Revealed by 1H Solid-State NMR Spectroscopy
Baohui Li, Lu Xu, Qiang Wu, Tiehong Chen, Pingchuan Sun,* Qinghua Jin, Datong Ding, Xiaoliang Wang, Gi Xue,* and An-Chang Shi
Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry and College of Physics, Nankai University, Tianjin, 300071, P. R. China, Department of Polymer Science and Engineering, The School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Abstract: Various types of hydrogen bonds, their temperature dependence and water-polymer interaction in hydrated poly(acrylic acid) (PAA) were systematically investigated using 1H CRAMPS solid-state NMR techniques in the temperature range from 25 to 110 C. The 1H CRAMPS NMR methods are based on a recently developed continuous phase modulation technique for 1H-1H homonuclear dipolar decoupling. The 1H CRAMPS experiments revealed four types of protons in hydrated PAA which are assigned to protons from the mutually hydrogen-bonded COOH groups (1), from the free COOH groups (2), from the COOH groups bounded with water or from water bounded with COOH groups which are undergoing fast chemical exchange mutually (3), and from main chain groups (4), respectively. Furthermore, we proposed double-quantum filtered and dipolar filtered 1H CRAMPS experiments to further assign the protons according to their dipolar coupling strength. In addition, high-resolution spin echo 1H CRAMPS experiments were further employed to accurately determine the chemical shift of these protons. These NMR techniques were also used to elucidate the molecular mobility of the different groups. It was found that dehydration in PAA promotes the formation of hydrogen bonds between COOH groups. Variable-temperature 1H CRAMPS experiments demonstrated that the dissociation of the hydrogen bonds between COOH groups occurs dramatically at lower temperature in hydrated PAA and slowly over a wide range of temperature in dehydrated PAA. It was also found that the dehydration of water bounded with COOH groups in hydrated PAA occurs significantly at high temperature. The NMR results were compared with previous work using DSC and other techniques. Besides undergoing fast chemical exchange, the adsorbed water was also demonstrated in proximity with the free COOH groups and far from the hydrogen bonds between COOH groups by using two-dimensional 1H-1H spin-exchange NMR experiments.
-Macromolecules, 40 (16), 5787 -5790, 2007. 10.1021/ma070793a S0024-9297(07)00793-0
Cross-Link Density of a Dispersed Rubber Measured by 129Xe Chemical Shift
Wallace O. Parker, Jr.,* Angelo Ferrando, Dino Ferri, and Valentino Canepari
Physical Chemistry, Refining & Marketing Division, Eni S.p.A., via Maritano 26, 20097 San Donato Milanese, Italy, and Polymer Research Center "C. Buonerba", Polimeri Europa, via Taliercio 14, 46100 Mantova, Italy
Abstract: 129Xe NMR chemical shifts of adsorbed xenon (natural isotopic abundance) were used to probe the free volume in a cross-linked rubber, polybutadiene (PB), alone and occluded within high impact polystyrene (HIPS). Shift dependency on cross-link density, or Nm (average number of monomer units between chemical cross-links) determined by the classical solvent swelling method, was detailed for high-cis-1,4-PB. A decrease in Nm from 262 to 4 caused the shift to increase 4 ppm. A curve inflection, evident at 218 ppm (and Nm = 30), corresponded to a free volume with an average spherical diameter of 0.49 nm using the empirical (shift-pore size) relation known for zeolites. This diameter is essentially equal to that of the PB chain (0.48 nm) at its Tg (glass transition temperature). Tg plotted against Nm showed the same inflection (at Nm = 25), corroborating a regime with more severe interchain contacts when the free volume diameter is inferior to the chain diameter. The empirical relation between 129Xe shift and Nm observed for pure PB was used to estimate the cross-link density of PB dispersed in HIPS as a function of cure time. Cross-linkage was greatly slowed after 8 h of curing, when Nm estimated by NMR spectroscopy was 10.
Andre's Journal Update: Inorganic Chem. - up to Issue 16 (Aug 06, 2007)
Inorg. Chem., 46 (15), 6069-6077, 2007.
"Solid-State NMR Spectroscopic Study of Coordination Compounds of XeF2 with Metal Cations and the Crystal Structure of [Ba(XeF2)5][AsF6]2"
Michael Gerken, Paul Hazendonk, Adriana Iuga, Jared Nieboer, Melita Tramek, Evgeny Goreshnik, Boris emva, Shaohui Zheng, and Jochen Autschbach
Abstract:
The coordination compounds [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were characterized by solid-state 19F and 129Xe magic-angle spinning NMR spectroscopy. The 19F and 129Xe NMR data of [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, and [Ca(XeF2)2.5][AsF6]2 were correlated with the previously determined crystal structures. The isotropic 19F chemical shifts and 1J(129Xe-19F) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF2. Chemical-shift and coupling-constant calculations for [Mg(XeF2)4][AsF6]2 confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF2)3][AsF6]2 and [Ba(XeF2)5][AsF6]2 indicate the absence of any terminal XeF2 ligands, which was verified for [Ba(XeF2)5][AsF6]2 by its X-ray crystal structure. The adduct [Ba(XeF2)5][AsF6]2 crystallizes in the space group Fmmm, with a = 11.6604(14) Å, b = 13.658(2) Å, c = 13.7802(17) Å, V = 2194.5(5) Å3 at -73 C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF2 molecules and one nonligating XeF2 molecule. The AsF6- anions in [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.
"Solid-State NMR Spectroscopic Study of Coordination Compounds of XeF2 with Metal Cations and the Crystal Structure of [Ba(XeF2)5][AsF6]2"
Michael Gerken, Paul Hazendonk, Adriana Iuga, Jared Nieboer, Melita Tramek, Evgeny Goreshnik, Boris emva, Shaohui Zheng, and Jochen Autschbach
Abstract:
The coordination compounds [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were characterized by solid-state 19F and 129Xe magic-angle spinning NMR spectroscopy. The 19F and 129Xe NMR data of [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, and [Ca(XeF2)2.5][AsF6]2 were correlated with the previously determined crystal structures. The isotropic 19F chemical shifts and 1J(129Xe-19F) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF2. Chemical-shift and coupling-constant calculations for [Mg(XeF2)4][AsF6]2 confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF2)3][AsF6]2 and [Ba(XeF2)5][AsF6]2 indicate the absence of any terminal XeF2 ligands, which was verified for [Ba(XeF2)5][AsF6]2 by its X-ray crystal structure. The adduct [Ba(XeF2)5][AsF6]2 crystallizes in the space group Fmmm, with a = 11.6604(14) Å, b = 13.658(2) Å, c = 13.7802(17) Å, V = 2194.5(5) Å3 at -73 C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF2 molecules and one nonligating XeF2 molecule. The AsF6- anions in [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.
Progress in NMR Spectroscopy, up to Vol. 51 Iss. 2 October 2007
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 2, October 18, 2007
pp. 103-137
Title: Chemical shift anisotropy amplification
Authors: Shao, L.; Titman, J.J.
Keywords: Magic angle spinning; Sideband manipulation; Chemical shift anisotropy; CSA amplification; CSA tensor; Orientational order; Molecular dynamics
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00009-X
Publication Type: Miscellaneous
ISSN: 0079-6565
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 2, October 18, 2007
pp. 139-154
Title: Heterogeneous catalysis in solid acids
Authors: White, J.L.; Truitt, M.J.
Keywords: NMR; Solid state NMR; MAS NMR; Zeolites; Silicoaluminophosphates; Catalysis; Bronsted acid; Solid acids; Mesoporous; In situ NMR; Methanol; MTO; MTG; Hydrocarbon; Mechanism
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00023-4
Publication Type: Miscellaneous
ISSN: 0079-6565
Vol: 51, Issue: 2, October 18, 2007
pp. 103-137
Title: Chemical shift anisotropy amplification
Authors: Shao, L.; Titman, J.J.
Keywords: Magic angle spinning; Sideband manipulation; Chemical shift anisotropy; CSA amplification; CSA tensor; Orientational order; Molecular dynamics
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00009-X
Publication Type: Miscellaneous
ISSN: 0079-6565
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 2, October 18, 2007
pp. 139-154
Title: Heterogeneous catalysis in solid acids
Authors: White, J.L.; Truitt, M.J.
Keywords: NMR; Solid state NMR; MAS NMR; Zeolites; Silicoaluminophosphates; Catalysis; Bronsted acid; Solid acids; Mesoporous; In situ NMR; Methanol; MTO; MTG; Hydrocarbon; Mechanism
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00023-4
Publication Type: Miscellaneous
ISSN: 0079-6565
Solid-State NMR, Vol. 32, August 2007
Solid-State NMR, Vol. 32, August 2007
Using liquid and solid state NMR and photoluminescence to study the synthesis and solubility properties of amine capped silicon nanoparticles
J.R. Giuliani1, a, S.J. Harleya, R.S. Cartera, P.P. Powera and M.P. Augustine
Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA
Received 12 December 2006. Available online 29 May 2007.
doi:10.1016/j.ssnmr.2007.02.006
Abstract
Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H–29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.
Keywords: Nanoparticles; 29Si nuclear magnetic resonance; Nuclear spin relaxation; Photoluminescence
A computational investigation of 17O quadrupolar coupling parameters and structure in α-quartz phase GeO2
Travis H. Sefzika, Ted M. Clarka and Philip J. Grandinetti
aDepartment of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Received 12 March 2007; revised 4 June 2007. Available online 10 July 2007.
doi:10.1016/j.ssnmr.2007.07.002
Abstract
Ab initio band-structure calculations based on density functional theory have been completed for α-quartz phase GeO2 to obtain electric-field gradients (efg) for oxygen atoms, including those for GeO2 at elevated pressure and temperature. To interpret the resulting efg values and examine correlations between structure and 17O quadrupolar coupling parameters, additional ab initio self-consistent Hartree-Fock molecular orbital calculations were completed. The quadrupolar coupling constant was found to have a strong dependence on Ge–O distance and angleGe–O–Ge, with the quadrupolar asymmetry parameter being primarily dependent on angleGe–O–Ge. Analytical expressions describing these dependencies consistent with earlier investigations of analogous silicate compounds are also reported.
Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR
K.J. Mallikarjunaiah a, K.C. Paramita b, K.P. Ramesh b and R. Damle a
aDepartment of Physics, Bangalore University, Bangalore 560 056, India
bDepartment of Physics, Indian Institute of Science, Bangalore 560 012, India
Received 27 April 2007. Available online 10 July 2007.
doi:10.1016/j.ssnmr.2007.07.003
Abstract
1H NMR spin–lattice relaxation time measurements have been carried out in [(CH3)4N]2SeO4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T1 minimum observed around 280 K is attributed to the simultaneous motions of CH3 and (CH3)4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.
Keywords: 1H NMR; Internal motions; Magnetization recovery; Spin–lattice relaxation time; Quantum rotational tunneling
Using liquid and solid state NMR and photoluminescence to study the synthesis and solubility properties of amine capped silicon nanoparticles
J.R. Giuliani1, a, S.J. Harleya, R.S. Cartera, P.P. Powera and M.P. Augustine
Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA
Received 12 December 2006. Available online 29 May 2007.
doi:10.1016/j.ssnmr.2007.02.006
Abstract
Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H–29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.
Keywords: Nanoparticles; 29Si nuclear magnetic resonance; Nuclear spin relaxation; Photoluminescence
A computational investigation of 17O quadrupolar coupling parameters and structure in α-quartz phase GeO2
Travis H. Sefzika, Ted M. Clarka and Philip J. Grandinetti
aDepartment of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Received 12 March 2007; revised 4 June 2007. Available online 10 July 2007.
doi:10.1016/j.ssnmr.2007.07.002
Abstract
Ab initio band-structure calculations based on density functional theory have been completed for α-quartz phase GeO2 to obtain electric-field gradients (efg) for oxygen atoms, including those for GeO2 at elevated pressure and temperature. To interpret the resulting efg values and examine correlations between structure and 17O quadrupolar coupling parameters, additional ab initio self-consistent Hartree-Fock molecular orbital calculations were completed. The quadrupolar coupling constant was found to have a strong dependence on Ge–O distance and angleGe–O–Ge, with the quadrupolar asymmetry parameter being primarily dependent on angleGe–O–Ge. Analytical expressions describing these dependencies consistent with earlier investigations of analogous silicate compounds are also reported.
Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR
K.J. Mallikarjunaiah a, K.C. Paramita b, K.P. Ramesh b and R. Damle a
aDepartment of Physics, Bangalore University, Bangalore 560 056, India
bDepartment of Physics, Indian Institute of Science, Bangalore 560 012, India
Received 27 April 2007. Available online 10 July 2007.
doi:10.1016/j.ssnmr.2007.07.003
Abstract
1H NMR spin–lattice relaxation time measurements have been carried out in [(CH3)4N]2SeO4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T1 minimum observed around 280 K is attributed to the simultaneous motions of CH3 and (CH3)4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.
Keywords: 1H NMR; Internal motions; Magnetization recovery; Spin–lattice relaxation time; Quantum rotational tunneling
Wednesday, August 08, 2007
J Phys. Chem. B Updates
-ADF calculations of 31P chemical shift tensors
Inorg. Chem., ASAP Article 10.1021/ic700514u S0020-1669(70)00514-1 Web Release Date: August 3, 2007
Ethylenebis(triphenylphosphine)platinum as a Probe for Niobium-Mediated Diphosphorus Chemistry
Nicholas A. Piro and Christopher C. Cummins*
Abstract: Ethylenebis(triphenylphosphine)platinum is used as a trap for the P2-containing molecule W(CO)5(P2), which is eliminated at room temperature from a niobium-complexed diphosphaazide ligand. The rate of W(CO)5(P2) elimination is unaffected by the presence of the platinum species. Attempts to generate and trap free P2 with the platinum ethylene complex were hindered by the direct reaction between the platinum starting material and the P2 generator, (Mes*NPP)Nb(N[Np]Ar)3. In this case, reductive cleavage of the P-P bond in the diphosphaazide ligand is induced by platinum coordination, resulting in the formation of a trimetallic system with two bridging, three-coordinate phosphorus atoms.
J Phys. Chem. B
-23Na NMR
J. Phys. Chem. B, 111 (25), 7092 -7097, 2007. 10.1021/jp070533v S1520-6106(07)00533-0 Nonergodic Arrested State in Diluted Clay Suspensions Monitored by Triple-Quantum 23Na Nuclear Magnetic Resonance
T. Gili,* S. Capuani, and B. Maraviglia
CNR-INFM CRS-SOFT, Universit di Roma "La Sapienza",P.zle A. Moro 5, I-00185 Roma, Italy, Dipartimento di Fisica, Universit di Roma "La Sapienza", P.zle A. Moro 5, I-00185 Roma, Italy, Enrico Fermi Center, Compendio Viminale, I-00184 Roma, Italy, and Fondaziona Santa Lucia IRCCS, I-00179 Roma, Italy
Abstract: The aging of water suspension of the synthetic clay Laponite has been studied by liquid-state triple-quantum filter nuclear magnetic resonance techniques, in a range of clay weight concentration (Cw = 0.012-0.028) known as the isotropic phase. Counterions dynamic parameters (rotational correlation time c and quadrupolar coupling constant e2qQ/h) have been extracted from sodium triple-quantum filtered experimental data within the multi-exponential quadrupolar relaxation theory in the fast exchange approximation. By monitoring quadrupolar sodium ions dynamical ( c and e2qQ/h) and static (counterion concentration pb) properties during the aging, we find two different mechanisms of transition toward an arrested state. Our experimental findings match with the description which states, at low concentration, the formation of clusters of Laponite disks trigger the reaching of the arrested state, while at high concentration, single disks are the basic units of the arrested phase. The procedure proposed in this paper, based on multiple quantum filtered NMR data analysis, results to be a useful means to study the routes to arrested states in aqueous colloidal dispersions.
-31P and 27Al spectroscopy
J. Phys. Chem. B, 111 (25), 7105 -7113, 2007. 10.1021/jp0710133 S1520-6106(07)01013-9
Crystallization of AlPO4-5 Aluminophosphate Molecular Sieve Prepared in Fluoride Medium: A Multinuclear Solid-State NMR Study
Jun Xu, Lei Chen, Danlin Zeng, Jun Yang, Minjin Zhang, Chaohui Ye, and Feng Deng*
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, People's Republic of China
Abstract: In the present work, multinuclear solid-state NMR techniques, combined with powder X-ray diffraction (PXRD) and infrared (IR) spectroscopy, are employed to monitor the crystallization of AlPO4-5 aluminophosphate prepared in the presence of HF under hydrothermal condition. The crystallization process is characterized by the evolution of intermediate gels, in which the long-rang ordering arrangement is probed by PXRD, revealing the threshold of the crystallization around 120 min. The appearance of 31P signals at ca. -22 and -29 ppm due to the structural P-O-Al unit and 19F signal at -120 ppm due to the structural F-Alpen-O-P unit in the NMR spectra of the series gels indicates that the crystalline framework is starting to form. The onset of the crystallization is also evidenced by the presence of the pentacoordinated Al in the structural F-Alpen-O-P unit which is considered to be associated with the ordered framework. More information about the local ordering of the gels is obtained from two-dimensional 27Al 31P heteronuclear correlation (HETCOR) and 31P/27Al double-resonance experiments. In combination with 1H 31P cross-polarization/magic-angle spinning (CP/MAS) experiments, two microdomains can be identified in the 120 min heated gel. A possible evolution mechanism of the gels consisting of three successive stages is proposed for the crystallization process
-J. Phys. Chem. B, 111 (26), 7529 -7534, 2007. 10.1021/jp070692e S1520-6106(07)00692-X
Structural Changes above the Glass Transition and Crystallization in Aluminophosphate Glasses: An in Situ High-Temperature MAS NMR Study
Leo van Wüllen,* Sebastian Wegner, and Gregory Tricot
Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30-36, D-48149 Münster, Germany
Abstract: We present an in situ high-temperature nuclear magnetic resonance study on the structural changes in aluminophosphate glasses occurring in the temperature range between the glass transition temperature Tg and the crystallization temperature Tc, Tg < T < Tc. Decisive changes in the network organization between Tg and Tc in potassium aluminophosphate glasses in the compositional range 50K2O-xAl2O3-(50 - x)P2O5 with 2.5 < x < 20 could be monitored for the first time employing 1D 31P- and 27Al-MAS NMR. Accompanying ex situ NMR experiments (31P-RFDR NMR and 31P-{27Al} CP-HETCOR NMR) on devitrified samples were performed at room temperature to further characterize the phases formed during the crystallization process. The structural role of boron-which is known to inhibit the crystallization process in these aluminophosphate glasses-on short and intermediate length scales was analyzed employing 11B-MQMAS, 11B-{27Al} TRAPDOR and 11B-{31P} REDOR NMR spectroscopy
-J. Phys. Chem. B, 111 (27), 7802 -7811, 2007. 10.1021/jp072504q S1520-6106(07)02504-7
Boltzmann Statistics Rotational-Echo Double-Resonance Analysis
John D. Gehman, Frances Separovic, Kun Lu, and Anil K. Mehta*
School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia, and Department of Chemistry, Emory University, Atlanta, Georgia 30322
Abstract: A new approach to rotational-echo double-resonance (REDOR) data analysis, analogous to Boltzmann maximum entropy statistics, is reported. This Boltzmann statistics REDOR (BS-REDOR) approach is useful for reconstructing an unbiased internuclear distance distribution for multiple internuclear distances from experimentally limited REDOR data sets on isolated spin pairs. The analysis is characterized by exploring reconstructions on model data and applied to both [1-13C,15N]-glycine and a long intramolecular distance in A (16-22) peptide nanotubes. The approach also provides insight into the minimal number of REDOR data points required to allow faithful determination of dipolar couplings in systems with multiple internuclear distances.
-3Q-QCPMG MAS experiments.
J. Phys. Chem. B, 111 (28), 8014 -8019, 2007. 10.1021/jp071539n S1520-6106(07)01539-8
Order and Disorder in Titanosilicate Glass by 17O MAS, off-MAS, and 3Q-QCPMG-MAS Solid-State NMR
Flemming H. Larsen,* Stéphanie Rossano, and Ian Farnan
Department of Food Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, Université Paris-Est Laboratoire Géomatériaux et Géologie de l'Ingénieur (G2I), EA 4119, 5 bd Descartes, 77454 Marne la Vallée Cedex 2, France, and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
Abstract: An 17O-enriched version of the titanosilicate glass, KTS2 (K2O·TiO2·2SiO2), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO5 units. Therefore, the structure must consist of linkages between TiO5 units and SiO4 tetrahedra and linkages between SiO4 tetrahedra.
-J. Phys. Chem. B, 111 (30), 8691 -8694, 2007. 10.1021/jp0734979 S1520-6106(07)03497-9
Microscopic Access to Long-Range Diffusion Parameters of the Fast Lithium Ion Conductor Li7BiO6 by Solid State 7Li Stimulated Echo NMR
Martin Wilkening,* Claus Mühle, Martin Jansen, and Paul Heitjans
Institute of Physical Chemistry and Electrochemistry, and Center for Solid State Chemistry and New Materials, Leibniz University Hannover, Callinstr. 3a, 30167 Hannover, Germany, and Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
Abstract: Li self-diffusion in rhombohedral Li7BiO6, being a promising basic material for cathodes of rechargeable ion batteries, is studied by means of 7Li stimulated echo NMR. Using the pulse sequence introduced by Jeener and Broekaert, a spin-alignment echo is created whose amplitude decay is recorded as a function of mixing time. The so-obtained two-time correlation functions follow stretched exponential behavior and lead to decay rates which can be identified directly with microscopic Li motional correlation rates ( -1). Using a jump distance of about 0.2 nm, this results in a diffusion coefficient (D) of about 0.5 × 10-16 m2 s-1 at 294 K. The activation energy turned out to be 0.53(3) eV which is in very good agreement with recently obtained results by means of dc-conductivity measurements probing long-range diffusion parameters. This shows that stimulated echo NMR, due to its inherent time scale, gives microscopic access to long-range transport. The prefactor 0-1 of the corresponding Arrhenius law lies in the typical range of phonon frequencies, 0-1 = 3 × 1012 s-1.
-J. Phys. Chem. B, 111 (30), 8860 -8867, 2007. 10.1021/jp070782j S1520-6106(07)00782-1
1H NMR and Viscometric Studies on Cationic Gemini Surfactants in Presence of Aromatic Acids and Salts
Kabir-ud-Din,* Waseefa Fatma, Ziya Ahmad Khan, and Aijaz Ahmad Dar
Department of Chemistry, Aligarh Muslim University, Aligarh - 202 002, India, and Department of Chemistry, University of Kashmir, Srinagar - 190 006, Jammu and Kashmir, India
Abstract: In this paper, we are reporting the influence of addition of aromatic acids (anthranilic and benzoic acid) and their sodium salts on the micellar morphological changes in three cationic gemini surfactant solutions, viz. 5 mM tetramethylene-1,4-bis(N-hexadecyl-N,N-dimethylammonium bromide), 10 mM pentamethylene-1,5-bis(N-hexadecyl-N,N-dimethylammonium bromide), and 10 mM hexamethylene-1,6-bis(N,-hexadecyl-N,N-dimethylammonium bromide). The solubilization site of the counterions (obtained from the additives) near the micellar surface are inferred by 1H NMR. The behavior is explained in the light of binding of counterions to the micelle as well as the nature of the functional group attached to the additive.
-J. Phys. Chem. B, 111 (30), 9172 -9178, 2007. 10.1021/jp072755z S1520-6106(07)02755-1
High-Field 1H MAS and 15N CP-MAS NMR Studies of Alanine Tripeptides and Oligomers: Distinction of Antiparallel and Parallel -Sheet Structures and Two Crystallographically Independent Molecules
Yu Suzuki, Michi Okonogi, Kazuo Yamauchi, Hiromichi Kurosu, Masataka Tansho, Tadashi Shimizu, Hazime Saitô, and Tetsuo Asakura*
Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16, Nakacho, Koganei, Tokyo 184-8588, Japan, Graduate School of Humanities and Sciences, Nara Women's University, Kitauoya-Nishimachi, Nara 630-8506, Japan, and National Institute for Material Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
Abstract: -Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) -sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H···O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used.
Inorg. Chem., ASAP Article 10.1021/ic700514u S0020-1669(70)00514-1 Web Release Date: August 3, 2007
Ethylenebis(triphenylphosphine)platinum as a Probe for Niobium-Mediated Diphosphorus Chemistry
Nicholas A. Piro and Christopher C. Cummins*
Abstract: Ethylenebis(triphenylphosphine)platinum is used as a trap for the P2-containing molecule W(CO)5(P2), which is eliminated at room temperature from a niobium-complexed diphosphaazide ligand. The rate of W(CO)5(P2) elimination is unaffected by the presence of the platinum species. Attempts to generate and trap free P2 with the platinum ethylene complex were hindered by the direct reaction between the platinum starting material and the P2 generator, (Mes*NPP)Nb(N[Np]Ar)3. In this case, reductive cleavage of the P-P bond in the diphosphaazide ligand is induced by platinum coordination, resulting in the formation of a trimetallic system with two bridging, three-coordinate phosphorus atoms.
J Phys. Chem. B
-23Na NMR
J. Phys. Chem. B, 111 (25), 7092 -7097, 2007. 10.1021/jp070533v S1520-6106(07)00533-0 Nonergodic Arrested State in Diluted Clay Suspensions Monitored by Triple-Quantum 23Na Nuclear Magnetic Resonance
T. Gili,* S. Capuani, and B. Maraviglia
CNR-INFM CRS-SOFT, Universit di Roma "La Sapienza",P.zle A. Moro 5, I-00185 Roma, Italy, Dipartimento di Fisica, Universit di Roma "La Sapienza", P.zle A. Moro 5, I-00185 Roma, Italy, Enrico Fermi Center, Compendio Viminale, I-00184 Roma, Italy, and Fondaziona Santa Lucia IRCCS, I-00179 Roma, Italy
Abstract: The aging of water suspension of the synthetic clay Laponite has been studied by liquid-state triple-quantum filter nuclear magnetic resonance techniques, in a range of clay weight concentration (Cw = 0.012-0.028) known as the isotropic phase. Counterions dynamic parameters (rotational correlation time c and quadrupolar coupling constant e2qQ/h) have been extracted from sodium triple-quantum filtered experimental data within the multi-exponential quadrupolar relaxation theory in the fast exchange approximation. By monitoring quadrupolar sodium ions dynamical ( c and e2qQ/h) and static (counterion concentration pb) properties during the aging, we find two different mechanisms of transition toward an arrested state. Our experimental findings match with the description which states, at low concentration, the formation of clusters of Laponite disks trigger the reaching of the arrested state, while at high concentration, single disks are the basic units of the arrested phase. The procedure proposed in this paper, based on multiple quantum filtered NMR data analysis, results to be a useful means to study the routes to arrested states in aqueous colloidal dispersions.
-31P and 27Al spectroscopy
J. Phys. Chem. B, 111 (25), 7105 -7113, 2007. 10.1021/jp0710133 S1520-6106(07)01013-9
Crystallization of AlPO4-5 Aluminophosphate Molecular Sieve Prepared in Fluoride Medium: A Multinuclear Solid-State NMR Study
Jun Xu, Lei Chen, Danlin Zeng, Jun Yang, Minjin Zhang, Chaohui Ye, and Feng Deng*
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, People's Republic of China
Abstract: In the present work, multinuclear solid-state NMR techniques, combined with powder X-ray diffraction (PXRD) and infrared (IR) spectroscopy, are employed to monitor the crystallization of AlPO4-5 aluminophosphate prepared in the presence of HF under hydrothermal condition. The crystallization process is characterized by the evolution of intermediate gels, in which the long-rang ordering arrangement is probed by PXRD, revealing the threshold of the crystallization around 120 min. The appearance of 31P signals at ca. -22 and -29 ppm due to the structural P-O-Al unit and 19F signal at -120 ppm due to the structural F-Alpen-O-P unit in the NMR spectra of the series gels indicates that the crystalline framework is starting to form. The onset of the crystallization is also evidenced by the presence of the pentacoordinated Al in the structural F-Alpen-O-P unit which is considered to be associated with the ordered framework. More information about the local ordering of the gels is obtained from two-dimensional 27Al 31P heteronuclear correlation (HETCOR) and 31P/27Al double-resonance experiments. In combination with 1H 31P cross-polarization/magic-angle spinning (CP/MAS) experiments, two microdomains can be identified in the 120 min heated gel. A possible evolution mechanism of the gels consisting of three successive stages is proposed for the crystallization process
-J. Phys. Chem. B, 111 (26), 7529 -7534, 2007. 10.1021/jp070692e S1520-6106(07)00692-X
Structural Changes above the Glass Transition and Crystallization in Aluminophosphate Glasses: An in Situ High-Temperature MAS NMR Study
Leo van Wüllen,* Sebastian Wegner, and Gregory Tricot
Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30-36, D-48149 Münster, Germany
Abstract: We present an in situ high-temperature nuclear magnetic resonance study on the structural changes in aluminophosphate glasses occurring in the temperature range between the glass transition temperature Tg and the crystallization temperature Tc, Tg < T < Tc. Decisive changes in the network organization between Tg and Tc in potassium aluminophosphate glasses in the compositional range 50K2O-xAl2O3-(50 - x)P2O5 with 2.5 < x < 20 could be monitored for the first time employing 1D 31P- and 27Al-MAS NMR. Accompanying ex situ NMR experiments (31P-RFDR NMR and 31P-{27Al} CP-HETCOR NMR) on devitrified samples were performed at room temperature to further characterize the phases formed during the crystallization process. The structural role of boron-which is known to inhibit the crystallization process in these aluminophosphate glasses-on short and intermediate length scales was analyzed employing 11B-MQMAS, 11B-{27Al} TRAPDOR and 11B-{31P} REDOR NMR spectroscopy
-J. Phys. Chem. B, 111 (27), 7802 -7811, 2007. 10.1021/jp072504q S1520-6106(07)02504-7
Boltzmann Statistics Rotational-Echo Double-Resonance Analysis
John D. Gehman, Frances Separovic, Kun Lu, and Anil K. Mehta*
School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia, and Department of Chemistry, Emory University, Atlanta, Georgia 30322
Abstract: A new approach to rotational-echo double-resonance (REDOR) data analysis, analogous to Boltzmann maximum entropy statistics, is reported. This Boltzmann statistics REDOR (BS-REDOR) approach is useful for reconstructing an unbiased internuclear distance distribution for multiple internuclear distances from experimentally limited REDOR data sets on isolated spin pairs. The analysis is characterized by exploring reconstructions on model data and applied to both [1-13C,15N]-glycine and a long intramolecular distance in A (16-22) peptide nanotubes. The approach also provides insight into the minimal number of REDOR data points required to allow faithful determination of dipolar couplings in systems with multiple internuclear distances.
-3Q-QCPMG MAS experiments.
J. Phys. Chem. B, 111 (28), 8014 -8019, 2007. 10.1021/jp071539n S1520-6106(07)01539-8
Order and Disorder in Titanosilicate Glass by 17O MAS, off-MAS, and 3Q-QCPMG-MAS Solid-State NMR
Flemming H. Larsen,* Stéphanie Rossano, and Ian Farnan
Department of Food Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, Université Paris-Est Laboratoire Géomatériaux et Géologie de l'Ingénieur (G2I), EA 4119, 5 bd Descartes, 77454 Marne la Vallée Cedex 2, France, and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom
Abstract: An 17O-enriched version of the titanosilicate glass, KTS2 (K2O·TiO2·2SiO2), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO5 units. Therefore, the structure must consist of linkages between TiO5 units and SiO4 tetrahedra and linkages between SiO4 tetrahedra.
-J. Phys. Chem. B, 111 (30), 8691 -8694, 2007. 10.1021/jp0734979 S1520-6106(07)03497-9
Microscopic Access to Long-Range Diffusion Parameters of the Fast Lithium Ion Conductor Li7BiO6 by Solid State 7Li Stimulated Echo NMR
Martin Wilkening,* Claus Mühle, Martin Jansen, and Paul Heitjans
Institute of Physical Chemistry and Electrochemistry, and Center for Solid State Chemistry and New Materials, Leibniz University Hannover, Callinstr. 3a, 30167 Hannover, Germany, and Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
Abstract: Li self-diffusion in rhombohedral Li7BiO6, being a promising basic material for cathodes of rechargeable ion batteries, is studied by means of 7Li stimulated echo NMR. Using the pulse sequence introduced by Jeener and Broekaert, a spin-alignment echo is created whose amplitude decay is recorded as a function of mixing time. The so-obtained two-time correlation functions follow stretched exponential behavior and lead to decay rates which can be identified directly with microscopic Li motional correlation rates ( -1). Using a jump distance of about 0.2 nm, this results in a diffusion coefficient (D) of about 0.5 × 10-16 m2 s-1 at 294 K. The activation energy turned out to be 0.53(3) eV which is in very good agreement with recently obtained results by means of dc-conductivity measurements probing long-range diffusion parameters. This shows that stimulated echo NMR, due to its inherent time scale, gives microscopic access to long-range transport. The prefactor 0-1 of the corresponding Arrhenius law lies in the typical range of phonon frequencies, 0-1 = 3 × 1012 s-1.
-J. Phys. Chem. B, 111 (30), 8860 -8867, 2007. 10.1021/jp070782j S1520-6106(07)00782-1
1H NMR and Viscometric Studies on Cationic Gemini Surfactants in Presence of Aromatic Acids and Salts
Kabir-ud-Din,* Waseefa Fatma, Ziya Ahmad Khan, and Aijaz Ahmad Dar
Department of Chemistry, Aligarh Muslim University, Aligarh - 202 002, India, and Department of Chemistry, University of Kashmir, Srinagar - 190 006, Jammu and Kashmir, India
Abstract: In this paper, we are reporting the influence of addition of aromatic acids (anthranilic and benzoic acid) and their sodium salts on the micellar morphological changes in three cationic gemini surfactant solutions, viz. 5 mM tetramethylene-1,4-bis(N-hexadecyl-N,N-dimethylammonium bromide), 10 mM pentamethylene-1,5-bis(N-hexadecyl-N,N-dimethylammonium bromide), and 10 mM hexamethylene-1,6-bis(N,-hexadecyl-N,N-dimethylammonium bromide). The solubilization site of the counterions (obtained from the additives) near the micellar surface are inferred by 1H NMR. The behavior is explained in the light of binding of counterions to the micelle as well as the nature of the functional group attached to the additive.
-J. Phys. Chem. B, 111 (30), 9172 -9178, 2007. 10.1021/jp072755z S1520-6106(07)02755-1
High-Field 1H MAS and 15N CP-MAS NMR Studies of Alanine Tripeptides and Oligomers: Distinction of Antiparallel and Parallel -Sheet Structures and Two Crystallographically Independent Molecules
Yu Suzuki, Michi Okonogi, Kazuo Yamauchi, Hiromichi Kurosu, Masataka Tansho, Tadashi Shimizu, Hazime Saitô, and Tetsuo Asakura*
Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16, Nakacho, Koganei, Tokyo 184-8588, Japan, Graduate School of Humanities and Sciences, Nara Women's University, Kitauoya-Nishimachi, Nara 630-8506, Japan, and National Institute for Material Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
Abstract: -Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) -sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H···O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used.
Friday, August 03, 2007
Hiyam's Journal Update
J. Am. Chem. Soc., 129 (21), 6670 -6671, 2007.
Solid-State NMR Reveals Structural and Dynamical Properties of a Membrane-Anchored Electron-Carrier Protein, Cytochrome b5
Ulrich H. N. Dürr, Kazutoshi Yamamoto, Sang-Choul Im, Lucy Waskell, and Ayyalusamy Ramamoorthy
Abstract:
Cytochrome b5 (cyt b5) is a membrane-anchored electron-carrier protein containing a heme in its soluble domain. It enhances the enzymatic turnover of selected members of the cytochrome P450 superfamily of catabolic enzymes, localized in the endoplasmic reticulum of liver cells. Remarkably, its -helical membrane-anchoring domain is indispensable for the cyt b5/cyt P450 interaction. Here, we present the first solid-state NMR studies on holo-cyt b5 in a membrane environment, namely, macroscopically oriented DMPC:DHPC bicelles. We have presented approaches to selectively investigate different domains of the protein using spectral editing NMR techniques that utilize the unique motional properties of each domain. Two-dimensional 1H-15N HIMSELF spectra showed PISA-wheel patterns reporting on the structure and dynamics of the membrane anchor of the protein.
J. Am. Chem. Soc., 129 (21), 6682 -6683, 2007.
J-Deconvolution Using Maximum Entropy Reconstruction Applied to 13C-13C Solid-State Cross-Polarization Magic-Angle-Spinning NMR of Proteins
Ingo Scholz, Stefan Jehle, Peter Schmieder, Matthias Hiller, Frank Eisenmenger, Hartmut Oschkinat, and Barth-Jan van Rossum
Abstract:
Scalar couplings between 13C spins can impair both resolution and sensitivity in 13C-labeled preparations. It is demonstrated that deconvolution of magic-angle-spinning NMR data with maximum entropy (MaxEnt) reconstruction allows the removal of splittings due to J-couplings without expenses in sensitivity. A combination of MaxEnt reconstruction in t2 with selective pulses in t1 produces fully J-resolved data in both dimensions. The possibility to obtain J-resolved 13C-13C data without compromising the sensitivity is particularly important for solid-state NMR of "difficult" biological samples, like membrane proteins, where sacrifices in signal-to-noise are fatal. The method is demonstrated using preparations of -spectrin SH3 domain (62 residues) as small test system and of outermembrane protein G as example of a membrane protein with higher molecular weight (281 residues). Both preparations were obtained using [2-13C]-glycerol as the carbon source during the bacterial growth.
Solid-State NMR Reveals Structural and Dynamical Properties of a Membrane-Anchored Electron-Carrier Protein, Cytochrome b5
Ulrich H. N. Dürr, Kazutoshi Yamamoto, Sang-Choul Im, Lucy Waskell, and Ayyalusamy Ramamoorthy
Abstract:
Cytochrome b5 (cyt b5) is a membrane-anchored electron-carrier protein containing a heme in its soluble domain. It enhances the enzymatic turnover of selected members of the cytochrome P450 superfamily of catabolic enzymes, localized in the endoplasmic reticulum of liver cells. Remarkably, its -helical membrane-anchoring domain is indispensable for the cyt b5/cyt P450 interaction. Here, we present the first solid-state NMR studies on holo-cyt b5 in a membrane environment, namely, macroscopically oriented DMPC:DHPC bicelles. We have presented approaches to selectively investigate different domains of the protein using spectral editing NMR techniques that utilize the unique motional properties of each domain. Two-dimensional 1H-15N HIMSELF spectra showed PISA-wheel patterns reporting on the structure and dynamics of the membrane anchor of the protein.
J. Am. Chem. Soc., 129 (21), 6682 -6683, 2007.
J-Deconvolution Using Maximum Entropy Reconstruction Applied to 13C-13C Solid-State Cross-Polarization Magic-Angle-Spinning NMR of Proteins
Ingo Scholz, Stefan Jehle, Peter Schmieder, Matthias Hiller, Frank Eisenmenger, Hartmut Oschkinat, and Barth-Jan van Rossum
Abstract:
Scalar couplings between 13C spins can impair both resolution and sensitivity in 13C-labeled preparations. It is demonstrated that deconvolution of magic-angle-spinning NMR data with maximum entropy (MaxEnt) reconstruction allows the removal of splittings due to J-couplings without expenses in sensitivity. A combination of MaxEnt reconstruction in t2 with selective pulses in t1 produces fully J-resolved data in both dimensions. The possibility to obtain J-resolved 13C-13C data without compromising the sensitivity is particularly important for solid-state NMR of "difficult" biological samples, like membrane proteins, where sacrifices in signal-to-noise are fatal. The method is demonstrated using preparations of -spectrin SH3 domain (62 residues) as small test system and of outermembrane protein G as example of a membrane protein with higher molecular weight (281 residues). Both preparations were obtained using [2-13C]-glycerol as the carbon source during the bacterial growth.
Joel's Journal Update: JPCA
NMR Mearsurements and Density Functional Calculations of the 199Hg-13C Spin-Spin Coupling Tensor in Methylmercury Halides.
J. Autschbach, A.M. Kantola, J. Jokisaari.
JPCA(2007)111,5343.
Abstract:
The isotropic average,JisoHgC , and the anisotropy, DJHgC, of the 199Hg-13C spin-spin coupling tensor in methylmercury halides, CH3HgX (X = Cl, Br, I), were determined for the first time by utilizing the NMR spectra of these molecules dissolved in liquid crystals. Furthermore, density functional calculations were performed using the zeroth-order regular approximation, including also dimethylmercury. The temperature-dependence of the JisoHgC couplings in the isotropic phase was studied in each case in order to extrapolate their values into the liquid crystal state. Good agreement is found between the experimental and the calculated DJHgC values as long as solvent effects are considered in the computations. Most of the magnitude of DJ can be attributed to the spin mechanism of J-coupling, with additional sizable spin-orbital cross terms due to electronic spin-orbit coupling.
Nuclear Magnetic Resonance and ab initio Studies of Small Cmplexes Formed between Water and Pyridine Derivatives in Solid and Liquid Phases.
S. Sharif, I.G. Shenderovich, L. Gonzalez, G.S. Denisov, D.N. Silverman, H.H. Limbach
JPCA(2007)111,6084.
Abstract:
The structure and geometry of hydrogen-bonded complexes formed between heterocyclic bases, namely, pyridine and 2,4,6-trimethylpyridine (collidine), and water were experimentally studied by NMR spectroscopy in frozen phase and in highly polar aprotic liquefied freon mixtures and theoretically modeled for gas phase. Hydrogen-bonded species in frozen heterocycle-water mixtures were characterized experimentally using 15N NMR. When base was in excess, one water molecule was symmetrically bonded to two heterocyclic molecules. This complex was characterized by the rHN distances of 1.82 Å for pyridine and 1.92 Å for collidine. The proton-donating ability of water in such complexes was affected by an anticooperative interaction between the two coupled hydrogen bonds and exhibited an apparent pKa value of about 6.0. When water was in excess, it formed water clusters hydrogen bonded to base. Theoretical analysis of binding energies of small model heterocycle-water clusters indicated that water in such clusters was oriented as a chain. The NMR estimated rHN distances in these species were 1.69 Å for pyridine and 1.64 Å for collidine. Here, the proton-donating ability of the hydroxyl group bonded to the heterocycle was affected by a mutual cooperative interaction with other water molecules in the chain and became comparable to the proton-donating ability of a fictitious acid, exhibiting an apparent pKa value of about 4.9. This value seems to depend only slightly on the length of the water chain and on the presence of another base at the other end of the chain if more than two water molecules are involved. Thus, the proton-donating ability of the outer hydroxyl groups of biologically relevant water bridges should be comparable to the proton-donating ability of a fictitious acid exhibiting a pKa value of about 4.9 in water. Driven by the mixing entropy, monomeric water presented in the aprotic freonic mixtures above 170 K but completely precipitated upon further cooling. Traces of water could be suspended in the mixtures down to 130 K in the presence of about 20-fold excess of heterocyclic bases. The obtained experimental data indicated that at these conditions water trended to form the symmetric 2:1 heterocycle-water complexes, whose bridge protons resonated around 6.7 ppm.
J. Autschbach, A.M. Kantola, J. Jokisaari.
JPCA(2007)111,5343.
Abstract:
The isotropic average,JisoHgC , and the anisotropy, DJHgC, of the 199Hg-13C spin-spin coupling tensor in methylmercury halides, CH3HgX (X = Cl, Br, I), were determined for the first time by utilizing the NMR spectra of these molecules dissolved in liquid crystals. Furthermore, density functional calculations were performed using the zeroth-order regular approximation, including also dimethylmercury. The temperature-dependence of the JisoHgC couplings in the isotropic phase was studied in each case in order to extrapolate their values into the liquid crystal state. Good agreement is found between the experimental and the calculated DJHgC values as long as solvent effects are considered in the computations. Most of the magnitude of DJ can be attributed to the spin mechanism of J-coupling, with additional sizable spin-orbital cross terms due to electronic spin-orbit coupling.
Nuclear Magnetic Resonance and ab initio Studies of Small Cmplexes Formed between Water and Pyridine Derivatives in Solid and Liquid Phases.
S. Sharif, I.G. Shenderovich, L. Gonzalez, G.S. Denisov, D.N. Silverman, H.H. Limbach
JPCA(2007)111,6084.
Abstract:
The structure and geometry of hydrogen-bonded complexes formed between heterocyclic bases, namely, pyridine and 2,4,6-trimethylpyridine (collidine), and water were experimentally studied by NMR spectroscopy in frozen phase and in highly polar aprotic liquefied freon mixtures and theoretically modeled for gas phase. Hydrogen-bonded species in frozen heterocycle-water mixtures were characterized experimentally using 15N NMR. When base was in excess, one water molecule was symmetrically bonded to two heterocyclic molecules. This complex was characterized by the rHN distances of 1.82 Å for pyridine and 1.92 Å for collidine. The proton-donating ability of water in such complexes was affected by an anticooperative interaction between the two coupled hydrogen bonds and exhibited an apparent pKa value of about 6.0. When water was in excess, it formed water clusters hydrogen bonded to base. Theoretical analysis of binding energies of small model heterocycle-water clusters indicated that water in such clusters was oriented as a chain. The NMR estimated rHN distances in these species were 1.69 Å for pyridine and 1.64 Å for collidine. Here, the proton-donating ability of the hydroxyl group bonded to the heterocycle was affected by a mutual cooperative interaction with other water molecules in the chain and became comparable to the proton-donating ability of a fictitious acid, exhibiting an apparent pKa value of about 4.9. This value seems to depend only slightly on the length of the water chain and on the presence of another base at the other end of the chain if more than two water molecules are involved. Thus, the proton-donating ability of the outer hydroxyl groups of biologically relevant water bridges should be comparable to the proton-donating ability of a fictitious acid exhibiting a pKa value of about 4.9 in water. Driven by the mixing entropy, monomeric water presented in the aprotic freonic mixtures above 170 K but completely precipitated upon further cooling. Traces of water could be suspended in the mixtures down to 130 K in the presence of about 20-fold excess of heterocyclic bases. The obtained experimental data indicated that at these conditions water trended to form the symmetric 2:1 heterocycle-water complexes, whose bridge protons resonated around 6.7 ppm.
Joel' Journal Update: ChemPhysChem
Probing the Evolution of Adsorption on Nanoporous Solids by In Situ Solid-State NMR Spectroscopy.
M. Xu, K. D.M. Harris, J.M. Thomas, D.E.W. Vaughan.
ChemPhysChem(2007)8(7),1311.
Summary:
A rotor-spinning technique is developed for carrying out in situ studies of adsorption processes by solid-state NMR spectroscopy. The method is suitable for the study of adsorption at the liquid/solid interface, does not require any modification of the NMR instrumentation, and allows spectra to be recorded immediately from the start of the adsorption process (see picture).
Indirect Detection of Nitrogen-14 in Solid-State NMR Spectroscopy.
S. Cavadini, S. Antonijevic, A. Lupulescu, G. Bodenhausen
ChemPhysChem(2007)8(7),1363.
Abstract:
NMR spectra of 14N (spin I=1) are obtained by indirect detection in powders spinning at the magic angle. The method relies on the transfer of coherence from a neighboring spy nucleus with S=1/2, such as 13C or 1H, to single- or double-quantum transitions of 14N nuclei. The transfer of coherence can occur through a combination of scalar and residual dipolar splittings (RDS); the latter are also known as second-order quadrupole-dipole cross terms. The two-dimensional NMR spectra reveal powder patterns determined by second- and third-order quadrupolar couplings. These spectra depend on the quadrupolar coupling constant CQ (typically a few megahertz), on the asymmetry parameter Q of the 14N nucleus, and on the orientation of the internuclear vector rIS between the I (14N) and S (spy) nuclei with respect to the quadrupolar tensor. These parameters, which can be subject to motional averaging, can reveal valuable information about the structure and dynamics of nitrogen-containing solids. Application of this technique to various amino acids, either enriched in 13C or with natural carbon isotope abundance, with spectra recorded at various magnetic fields, illustrates the scope of the method.
M. Xu, K. D.M. Harris, J.M. Thomas, D.E.W. Vaughan.
ChemPhysChem(2007)8(7),1311.
Summary:
A rotor-spinning technique is developed for carrying out in situ studies of adsorption processes by solid-state NMR spectroscopy. The method is suitable for the study of adsorption at the liquid/solid interface, does not require any modification of the NMR instrumentation, and allows spectra to be recorded immediately from the start of the adsorption process (see picture).
Indirect Detection of Nitrogen-14 in Solid-State NMR Spectroscopy.
S. Cavadini, S. Antonijevic, A. Lupulescu, G. Bodenhausen
ChemPhysChem(2007)8(7),1363.
Abstract:
NMR spectra of 14N (spin I=1) are obtained by indirect detection in powders spinning at the magic angle. The method relies on the transfer of coherence from a neighboring spy nucleus with S=1/2, such as 13C or 1H, to single- or double-quantum transitions of 14N nuclei. The transfer of coherence can occur through a combination of scalar and residual dipolar splittings (RDS); the latter are also known as second-order quadrupole-dipole cross terms. The two-dimensional NMR spectra reveal powder patterns determined by second- and third-order quadrupolar couplings. These spectra depend on the quadrupolar coupling constant CQ (typically a few megahertz), on the asymmetry parameter Q of the 14N nucleus, and on the orientation of the internuclear vector rIS between the I (14N) and S (spy) nuclei with respect to the quadrupolar tensor. These parameters, which can be subject to motional averaging, can reveal valuable information about the structure and dynamics of nitrogen-containing solids. Application of this technique to various amino acids, either enriched in 13C or with natural carbon isotope abundance, with spectra recorded at various magnetic fields, illustrates the scope of the method.
Joel' Journal Update: PCCP
Quantifying hydrogen-bonding strength: the measure of 2hJNN coupling in self-assembled guanosines by solid-state 15N spin-echo MAS NMR.
T.N. Pham, J.M. Griffin, S. Masiero, S. Lena, G. Gottarelli, P. Hodgkinson, C. Filip, S.P. Brown.
PCCP(2007)9,3416.
Abstract:
2hJNN hydrogen-bond mediated J couplings are measured in the solid state for two synthetic deoxyguanosine derivatives by 15N MAS NMR spin-echo experiments. The use of rotor-synchronised Hahn-echo pulse train (RS-HEPT) 1H decoupling, with a duty cycle of 6%, allows spin-echo durations out to 200 ms, hence enabling the accurate determination of J couplings as small as 3.8 Hz. A single-crystal X-ray diffraction structure exists for the shorter alkyl chain derivative dG(C3)2: the observation of significantly different 2hJNN couplings, 6.2 ± 0.4 and 7.4 ± 0.4 Hz, for the two resolved N7 resonances is to be expected given the NHN hydrogen-bonding distances of 2.91 and 2.83 for the two distinct molecules in the asymmetric unit cell. For the longer alkyl chain derivative, dG(C10)2, for which there is no single-crystal diffraction structure, a 15N refocused INADEQUATE spectrum (Pham et al., J. Am. Chem. Soc., 2005, 127, 16018–16019) has demonstrated the presence of N2–HN7 intermolecular hydrogen-bonds indicative of a quartet-like structure. The 2hJNN hydrogen-bond mediated J coupling of 5.9 ± 0.2 Hz is at the lower end of the range (5.9–8.2 Hz) of 2hJNN couplings determined from solution-state NMR of guanosine quartets in quadruplex DNA. A full discussion of the determination of error bars on the fitted parameters is given; specifically, error bars determined by a non-linear fitting (using the covariance matrix) or in a Monte-Carlo fashion are found to give effectively identical results.
Spatial distribution of lithium ions in glasses studied by 7Li{6Li} spin echo double resonance.
S.P. Puls and H. Eckert.
PCCP(2007)9,3992.
Abstract:
This manuscript introduces 7Li{6Li} spin echo double resonance (SEDOR) spectroscopy as a novel approach for studying the spatial distribution of lithium ions in solid electrolytes. Theoretical simulations using density operator theory as well as experimental validation on the model compound lithium carbonate reveal that this method affords a selective measurement of 7Li–6Li heteronuclear dipole–dipole couplings. Dipolar second moments characterizing internuclear lithium–lithium interactions have been measured in lithium silicate (Li2O)x(SiO2)1–x, (0.1 x 0.4) and lithium borate (Li2O)x(B2O3)1–x, (0.1 x 0.3) glasses. The results indicate that the spatial distributions of the lithium ions in these two glass systems are decidedly different. In the lithium silicate glass system, the results give clear evidence of strong cation clustering for x 0.3, providing quantitative support for a previously proposed model of a one-dimensional channel structure. In contrast, in the lithium borate glass system, the cations seem to be more or less randomly distributed. Nevertheless, an observed superlinear dependence of M2(7Li–6Li) as a function of ion concentration indicates subtle changes of the lithium arrangement principles, which are discussed in relation to the previously proposed ring structure of borate glasses.
T.N. Pham, J.M. Griffin, S. Masiero, S. Lena, G. Gottarelli, P. Hodgkinson, C. Filip, S.P. Brown.
PCCP(2007)9,3416.
Abstract:
2hJNN hydrogen-bond mediated J couplings are measured in the solid state for two synthetic deoxyguanosine derivatives by 15N MAS NMR spin-echo experiments. The use of rotor-synchronised Hahn-echo pulse train (RS-HEPT) 1H decoupling, with a duty cycle of 6%, allows spin-echo durations out to 200 ms, hence enabling the accurate determination of J couplings as small as 3.8 Hz. A single-crystal X-ray diffraction structure exists for the shorter alkyl chain derivative dG(C3)2: the observation of significantly different 2hJNN couplings, 6.2 ± 0.4 and 7.4 ± 0.4 Hz, for the two resolved N7 resonances is to be expected given the NHN hydrogen-bonding distances of 2.91 and 2.83 for the two distinct molecules in the asymmetric unit cell. For the longer alkyl chain derivative, dG(C10)2, for which there is no single-crystal diffraction structure, a 15N refocused INADEQUATE spectrum (Pham et al., J. Am. Chem. Soc., 2005, 127, 16018–16019) has demonstrated the presence of N2–HN7 intermolecular hydrogen-bonds indicative of a quartet-like structure. The 2hJNN hydrogen-bond mediated J coupling of 5.9 ± 0.2 Hz is at the lower end of the range (5.9–8.2 Hz) of 2hJNN couplings determined from solution-state NMR of guanosine quartets in quadruplex DNA. A full discussion of the determination of error bars on the fitted parameters is given; specifically, error bars determined by a non-linear fitting (using the covariance matrix) or in a Monte-Carlo fashion are found to give effectively identical results.
Spatial distribution of lithium ions in glasses studied by 7Li{6Li} spin echo double resonance.
S.P. Puls and H. Eckert.
PCCP(2007)9,3992.
Abstract:
This manuscript introduces 7Li{6Li} spin echo double resonance (SEDOR) spectroscopy as a novel approach for studying the spatial distribution of lithium ions in solid electrolytes. Theoretical simulations using density operator theory as well as experimental validation on the model compound lithium carbonate reveal that this method affords a selective measurement of 7Li–6Li heteronuclear dipole–dipole couplings. Dipolar second moments characterizing internuclear lithium–lithium interactions have been measured in lithium silicate (Li2O)x(SiO2)1–x, (0.1 x 0.4) and lithium borate (Li2O)x(B2O3)1–x, (0.1 x 0.3) glasses. The results indicate that the spatial distributions of the lithium ions in these two glass systems are decidedly different. In the lithium silicate glass system, the results give clear evidence of strong cation clustering for x 0.3, providing quantitative support for a previously proposed model of a one-dimensional channel structure. In contrast, in the lithium borate glass system, the cations seem to be more or less randomly distributed. Nevertheless, an observed superlinear dependence of M2(7Li–6Li) as a function of ion concentration indicates subtle changes of the lithium arrangement principles, which are discussed in relation to the previously proposed ring structure of borate glasses.
Joel's Journal Update: Angewandte
Magnetic Resonance at or Below the Earth's Magnetic Field
Christina M. Thiele
Angewandte (2007)46,4820.
Summary:
NMR resonances of two nuclei can be obtained in one spectrum at ultralow magnetic fields. At such low fields, chemical shifts become negligible and heteronuclear couplings dominate the NMR spectra. The Highlight gives an overview of pure J-coupling spectroscopy and (functional) imaging applications at magnetic-field strengths in the range of the Earth's magnetic field.
Christina M. Thiele
Angewandte (2007)46,4820.
Summary:
NMR resonances of two nuclei can be obtained in one spectrum at ultralow magnetic fields. At such low fields, chemical shifts become negligible and heteronuclear couplings dominate the NMR spectra. The Highlight gives an overview of pure J-coupling spectroscopy and (functional) imaging applications at magnetic-field strengths in the range of the Earth's magnetic field.
Thursday, August 02, 2007
Hiyam's Journal Update
J. Am. Chem. Soc., 129 (29), 8932 -8933, 2007.
Resolving Structures from Powders by NMR Crystallography Using Combined Proton Spin Diffusion and Plane Wave DFT Calculations
Chris J. Pickard, Elodie Salager, Guido Pintacuda, Bénédicte Elena, and Lyndon Emsley*
Abstract:
We report a method that combines measured solid-state NMR chemical shifts and first principles calculations to resolve the crystal structure of a powdered crystalline solid to within 0.13 Å of the known structure. The validity of this process is confirmed by comparing the DFT calculated chemical shifts with the experimentally measured shifts, where we observe a substantial improvement in the agreement between the calculations and experiments before and after the DFT structure optimization.
Resolving Structures from Powders by NMR Crystallography Using Combined Proton Spin Diffusion and Plane Wave DFT Calculations
Chris J. Pickard, Elodie Salager, Guido Pintacuda, Bénédicte Elena, and Lyndon Emsley*
Abstract:
We report a method that combines measured solid-state NMR chemical shifts and first principles calculations to resolve the crystal structure of a powdered crystalline solid to within 0.13 Å of the known structure. The validity of this process is confirmed by comparing the DFT calculated chemical shifts with the experimentally measured shifts, where we observe a substantial improvement in the agreement between the calculations and experiments before and after the DFT structure optimization.
Friday, July 20, 2007
Hiyam Journal Update
J. Am. Chem. Soc., 129 (21), 6704 -6705, 2007.
Ultrahigh-Field Solid-State 59Co NMR Studies of Co(C2B9H11)2- and Co(C5H5)2+ Salts
Kristopher J. Ooms, Victor V. Terskikh, and Roderick E. Wasylishen*
Abstract:
Cobalt-59 NMR spectra of stationary powder samples of salts containing Co(C2B9H11)2- and Co(C5H5)2+ have been acquired at 21.14 T using single-echo stepped-frequency experiments. The resulting central transition, mI = 1/2 mI = -1/2, line shapes span more than 2.0 MHz and are dominated by the second-order quadrupolar interaction. Analysis of the spectra leads to CQ values of ca. 163 MHz for both ions, among the largest 59Co CQ values reported. In addition, 59Co chemical shift anisotropies are significant for Co(C2B9H11)2- and Co(C5H5)2+, with values of 4500-4700 and 5650 ppm, respectively. Isotropic 59Co chemical shifts for the cobalticarborane anion are unavailable from NMR measurements of solution samples, probably because of the extremely short relaxation times anticipated for this complex.
Ultrahigh-Field Solid-State 59Co NMR Studies of Co(C2B9H11)2- and Co(C5H5)2+ Salts
Kristopher J. Ooms, Victor V. Terskikh, and Roderick E. Wasylishen*
Abstract:
Cobalt-59 NMR spectra of stationary powder samples of salts containing Co(C2B9H11)2- and Co(C5H5)2+ have been acquired at 21.14 T using single-echo stepped-frequency experiments. The resulting central transition, mI = 1/2 mI = -1/2, line shapes span more than 2.0 MHz and are dominated by the second-order quadrupolar interaction. Analysis of the spectra leads to CQ values of ca. 163 MHz for both ions, among the largest 59Co CQ values reported. In addition, 59Co chemical shift anisotropies are significant for Co(C2B9H11)2- and Co(C5H5)2+, with values of 4500-4700 and 5650 ppm, respectively. Isotropic 59Co chemical shifts for the cobalticarborane anion are unavailable from NMR measurements of solution samples, probably because of the extremely short relaxation times anticipated for this complex.
Thursday, July 19, 2007
JMR up to Volume 187, Issue 2, August 2007
Journal of Magnetic Resonance
Volume 187, Issue 2, August 2007, Pages 343-351
doi:10.1016/j.jmr.2007.05.020
Title: Use of SPAM and FAM pulses in high-resolution MAS NMR spectroscopy of quadrupolar nuclei
Thomas J. Ball and Stephen Wimperis
Department of Chemistry and WestCHEM, University of Glasgow, Glasgow G12 8QQ, UK
Received 15 March 2007; revised 18 May 2007. Available online 9 June 2007.
Abstract
The merits of SPAM and FAM pulses for enhancing the conversion of triple- to single-quantum coherences in the two-dimensional MQMAS experiment are compared using 87Rb (spin I = 3/2) and 27Al (I = 5/2) NMR of crystalline and amorphous materials. Although SPAM pulses are more easily optimized, our experiments and simulations suggest that FAM pulses yield greater signal intensity in all cases. In conclusion, we argue that, as originally suggested, SPAM and FAM pulses are best implemented in phase-modulated whole-echo MQMAS experiments and that the use of SPAM pulses to record separate echo and antiecho data sets, which are then combined, generally yields lower signal-to-noise ratios.
Keywords: NMR; Solid-state NMR; MAS NMR; Composite pulses; MQMAS; STMAS; FAM; SPAM
Journal of Magnetic Resonance
Vol: 187, Issue: 1, July, 2007
Title: First principles NMR calculations of phenylphosphinic acid C6H5HPO(OH): Assignments, orientation of tensors by local field experiments and effect of molecular motion
Authors: Gervais, C.a; Coelho, C.a; Azai¨s, T.a; Maquet, J.a; Laurent, G.a; Pourpoint, F.a; Bonhomme, C.a; Florian, P.b; Alonso, B.c; Guerrero, G.d; Mutin, P.H.d; Mauri, F.e
Keywords: Solid state NMR; 1H CSA; GIPAW calculations; Tensors
Abstract (English):
The complete set of NMR parameters for 17O enriched phenylphosphinic acid C6H5HP*O(*OH) is calculated from first principles by using the Gauge Including Projected Augmented Wave (GIPAW) approach [C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101/1–245101/13]. The analysis goes beyond the successful assignment of the spectra for all nuclei (1H, 13C, 17O, 31P), as: (i) the 1H CSA (chemical shift anisotropy) tensors (magnitude and orientation) have been interpreted in terms of H bonding and internuclear distances. (ii) CSA/dipolar local field correlation experiments have allowed the orientation of the direct P–H bond direction in the 31P CSA tensor to be determined. Experimental and calculated data were compared. (iii) The overestimation of the calculated 31P CSA has been explained by local molecular reorientation and confirmed by low temperature static 1H31P CP experiments.
Journal of Magnetic Resonance
Vol: 187 Issue: 1, July, 2007 pp: 19-26
DOI: 10.1016/j.jmr.2007.03.017
Title: matNMR: A flexible toolbox for processing, analyzing and visualizing magnetic resonance data in Matlab®
Jacco D. van Beek, Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
Received 9 March 2007; revised 23 March 2007
Abstract
matNMR (matnmr.sourceforge.net) is a toolbox for processing, analyzing and visualizing magnetic-resonance data within the Matlab® environment ( www.mathworks.com ) that aims for control, flexibility and extendability. Processing can be done using either a graphical user interface or with command-line scripts, both of which allow user-defined processing or analysis functions to be incorporated at any time. The direct access to data points during processing, and the extensive library of mathematical and visualization routines provided by Matlab, afford the high degree of control and flexibility needed in modern magnetic-resonance research.
Keywords: Magnetic resonance; Processing toolbox; Matlab; Visualization; Data analysis.
Journal of Magnetic Resonance
Vol: 186 Issue: 2, June, 2007 pp: 220-227
DOI: 10.1016/j.jmr.2007.02.015
Title: Through-space R3 -HETCOR experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR
J. Trebosc a, B. Hu a, J.P. Amoureux a, , Email Address, Z. Gan b
a UCCS, CNRS-8181, Université de Lille, FR-59652 Villeneuve d'Ascq, France
b National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL 32310, USA
Received 25 January 2007 Abstract
We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n /2 (n > 1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up.
Keywords: Solid-state NMR; Quadrupolar nuclei; HETCOR; Dipolar coupling; HMQC; R-INEPT.
Volume 187, Issue 2, August 2007, Pages 343-351
doi:10.1016/j.jmr.2007.05.020
Title: Use of SPAM and FAM pulses in high-resolution MAS NMR spectroscopy of quadrupolar nuclei
Thomas J. Ball and Stephen Wimperis
Department of Chemistry and WestCHEM, University of Glasgow, Glasgow G12 8QQ, UK
Received 15 March 2007; revised 18 May 2007. Available online 9 June 2007.
Abstract
The merits of SPAM and FAM pulses for enhancing the conversion of triple- to single-quantum coherences in the two-dimensional MQMAS experiment are compared using 87Rb (spin I = 3/2) and 27Al (I = 5/2) NMR of crystalline and amorphous materials. Although SPAM pulses are more easily optimized, our experiments and simulations suggest that FAM pulses yield greater signal intensity in all cases. In conclusion, we argue that, as originally suggested, SPAM and FAM pulses are best implemented in phase-modulated whole-echo MQMAS experiments and that the use of SPAM pulses to record separate echo and antiecho data sets, which are then combined, generally yields lower signal-to-noise ratios.
Keywords: NMR; Solid-state NMR; MAS NMR; Composite pulses; MQMAS; STMAS; FAM; SPAM
Journal of Magnetic Resonance
Vol: 187, Issue: 1, July, 2007
Title: First principles NMR calculations of phenylphosphinic acid C6H5HPO(OH): Assignments, orientation of tensors by local field experiments and effect of molecular motion
Authors: Gervais, C.a; Coelho, C.a; Azai¨s, T.a; Maquet, J.a; Laurent, G.a; Pourpoint, F.a; Bonhomme, C.a; Florian, P.b; Alonso, B.c; Guerrero, G.d; Mutin, P.H.d; Mauri, F.e
Keywords: Solid state NMR; 1H CSA; GIPAW calculations; Tensors
Abstract (English):
The complete set of NMR parameters for 17O enriched phenylphosphinic acid C6H5HP*O(*OH) is calculated from first principles by using the Gauge Including Projected Augmented Wave (GIPAW) approach [C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101/1–245101/13]. The analysis goes beyond the successful assignment of the spectra for all nuclei (1H, 13C, 17O, 31P), as: (i) the 1H CSA (chemical shift anisotropy) tensors (magnitude and orientation) have been interpreted in terms of H bonding and internuclear distances. (ii) CSA/dipolar local field correlation experiments have allowed the orientation of the direct P–H bond direction in the 31P CSA tensor to be determined. Experimental and calculated data were compared. (iii) The overestimation of the calculated 31P CSA has been explained by local molecular reorientation and confirmed by low temperature static 1H31P CP experiments.
Journal of Magnetic Resonance
Vol: 187 Issue: 1, July, 2007 pp: 19-26
DOI: 10.1016/j.jmr.2007.03.017
Title: matNMR: A flexible toolbox for processing, analyzing and visualizing magnetic resonance data in Matlab®
Jacco D. van Beek, Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
Received 9 March 2007; revised 23 March 2007
Abstract
matNMR (matnmr.sourceforge.net) is a toolbox for processing, analyzing and visualizing magnetic-resonance data within the Matlab® environment ( www.mathworks.com ) that aims for control, flexibility and extendability. Processing can be done using either a graphical user interface or with command-line scripts, both of which allow user-defined processing or analysis functions to be incorporated at any time. The direct access to data points during processing, and the extensive library of mathematical and visualization routines provided by Matlab, afford the high degree of control and flexibility needed in modern magnetic-resonance research.
Keywords: Magnetic resonance; Processing toolbox; Matlab; Visualization; Data analysis.
Journal of Magnetic Resonance
Vol: 186 Issue: 2, June, 2007 pp: 220-227
DOI: 10.1016/j.jmr.2007.02.015
Title: Through-space R3 -HETCOR experiments between spin-1/2 and half-integer quadrupolar nuclei in solid-state NMR
J. Trebosc a, B. Hu a, J.P. Amoureux a, , Email Address, Z. Gan b
a UCCS, CNRS-8181, Université de Lille, FR-59652 Villeneuve d'Ascq, France
b National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL 32310, USA
Received 25 January 2007 Abstract
We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n /2 (n > 1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up.
Keywords: Solid-state NMR; Quadrupolar nuclei; HETCOR; Dipolar coupling; HMQC; R-INEPT.
Thursday, July 12, 2007
Inorganic Chemistry - up to Issue 14 (July 2007)
Kuhn, A.; Azcondo, M. T.; Amador, U.; Boulahya, K.; Sobrados, I.; Sanz, J.; Garcia-Alvarado, F.
"Structural Characterization and NMR Study of NaNbWO6 and Its Proton-Exchanged Derivatives." Inorg. Chem. 2007, 46(13), 5390-5397.
Abstract: The structural characterization of NaNbWO6, prepared by the ceramic route, has been performed. Electron diffraction has shown the presence of two related phases in a 1:1 ratio, whose lattice parameters correspond to those of the well-known tetragonal tungsten bronzes (TTB) and those of a monoclinically distorted phase. In addition to basic unit cells, the morphology of the two phases has been found to be similar, but they present a slight difference in the W/Nb ratio. 1H and 23Na magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectra of NaNbWO6 and its proton-exchanged derivatives have been interpreted on the basis of the ideal TTB structure. The average structure and the morphology remain unchanged in Na1 - xHxNbWO6 derivatives. 1H and 23Na MAS-NMR spectroscopies have been used to monitor changes produced during exchange processes. It has been shown that the exchange of Na ions is mainly produced, but not exclusively, at tetragonal channels. However, a large amount of Na ions at the pentagonal channels do not exchange with protons, suggesting that these ions are needed to stabilize the TTB-like structure. A tentative distribution of sodium ions in the most-exchanged oxide, deduced from NMR results, ~(Na0.46)p(Na0.08)sH0.46NbWO6, has been proposed. NMR spectra of Na1 - xHxNbWO6 indicate that two different OH groups are formed upon exchanging. The study of samples hydrated with D2O allowed us to conclude that deuterons of adsorbed water exchange with protons of the two OH groups. The proton-deuteron exchange is slow at room temperature but is strongly enhanced at 90 C. This observation relates to the proton conductivity displayed by exchanged products under a humid atmosphere.
"Structural Characterization and NMR Study of NaNbWO6 and Its Proton-Exchanged Derivatives." Inorg. Chem. 2007, 46(13), 5390-5397.
Abstract: The structural characterization of NaNbWO6, prepared by the ceramic route, has been performed. Electron diffraction has shown the presence of two related phases in a 1:1 ratio, whose lattice parameters correspond to those of the well-known tetragonal tungsten bronzes (TTB) and those of a monoclinically distorted phase. In addition to basic unit cells, the morphology of the two phases has been found to be similar, but they present a slight difference in the W/Nb ratio. 1H and 23Na magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectra of NaNbWO6 and its proton-exchanged derivatives have been interpreted on the basis of the ideal TTB structure. The average structure and the morphology remain unchanged in Na1 - xHxNbWO6 derivatives. 1H and 23Na MAS-NMR spectroscopies have been used to monitor changes produced during exchange processes. It has been shown that the exchange of Na ions is mainly produced, but not exclusively, at tetragonal channels. However, a large amount of Na ions at the pentagonal channels do not exchange with protons, suggesting that these ions are needed to stabilize the TTB-like structure. A tentative distribution of sodium ions in the most-exchanged oxide, deduced from NMR results, ~(Na0.46)p(Na0.08)sH0.46NbWO6, has been proposed. NMR spectra of Na1 - xHxNbWO6 indicate that two different OH groups are formed upon exchanging. The study of samples hydrated with D2O allowed us to conclude that deuterons of adsorbed water exchange with protons of the two OH groups. The proton-deuteron exchange is slow at room temperature but is strongly enhanced at 90 C. This observation relates to the proton conductivity displayed by exchanged products under a humid atmosphere.
Solid-State NMR, up to Issue 4 (July 2007)
Solid-State NMR
Indirect covariance NMR spectroscopy of through-bond homo-nuclear correlations for quadrupolar nuclei in solids under high-resolution - doi:10.1016/j.ssnmr.2007.03.002
Bingwen Hu, Jean-Paul Amoureux and Julien Trebosc
UCCS, CNRS-8181, Lille University, FR-59652 Villeneuve d'Ascq, France
Received 20 November 2006; revised 26 February 2007. Available online 1 April 2007.
Abstract
Indirect covariance NMR spectroscopy is demonstrated in solids, and we show that it can be used to obtain through-bond 2D homo-nuclear correlation spectra for quadrupolar nuclei under high-resolution. These spectra, generated with indirect covariance from a hetero-nuclear correlation spectrum, are equivalent to those recorded with the through-bond homo-nuclear hetero-nuclear single-quantum correlation (H-HSQC) method very recently proposed. However, the indirect covariance method can save a lot of experiment time, compared to the H-HSQC experiments, which allows introducing a high-resolution quadrupolar filter, thus providing a much better resolution, even on medium-field spectrometers. The covariance concept can be used to generate many different ‘indirectly-detected' high-resolution homo-nuclear correlation spectra with through-space or through-bond correlations for spin Click to view the MathML source or quadrupolar nuclei. We also propose a simple method that decreases the noise in all (direct or indirect) covariance methods.
Keywords: Indirect-covariance; GEN2D; H-HSQC experiment; J-coupling; MQ-HETCOR; ST-HETCOR; MQ-HOMCOR; ST-HOMCOR
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A 27Al MAS NMR study of a sol–gel produced alumina: Identification of the NMR parameters of the theta-Al2O3 transition alumina phase - doi:10.1016/j.ssnmr.2007.05.002
L.A. O'Dell, S.L.P. Savin, A.V. Chadwick and M.E. Smith
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH, UK
Received 29 December 2006; revised 6 April 2007. Available online 13 May 2007.
Abstract
27Al MAS NMR has been used to study a sol–gel prepared alumina annealed at various temperatures. Two-field simulation of the sample heated to 1200 °C confirmed the presence of corundum, as suggested by XRD, and also the presence of nanocrystalline ?-Al2O3. 27Al MAS NMR chemical shifts, quadrupolar coupling constants and asymmetry parameters are reported for the tetrahedral and octahedral aluminium sites within ?-Al2O3.
Keywords: 27Al MAS NMR; theta-alumina; NMR interaction parameters
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Phosphorus-31 spin–lattice NMR relaxation in bone apatite and its mineral standards - doi:10.1016/j.ssnmr.2007.04.005
Agnieszka Kaflak and Waclaw
Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warszawa, Poland
Received 9 February 2007; revised 25 April 2007. Available online 16 May 2007.
Abstract
Phosphorus-31 spin–lattice relaxation, both in the laboratory (B0=4.7 T) and rotating frame (B1=2.2 mT), was studied in the following samples: mineral of whole human bone (samples B1–B6), apatite prepared from bone (BHA), natural brushite (BRU), synthetic hydroxyapatite hydrated (HAh) and calcined (HAc), and synthetic carbonatoapatite of type B (CHA-B) with 9 wt% of CO32-. The T1P relaxation time was determined directly using the saturation recovery technique, while the Click to view the MathML source relaxation time was measured via 1H?31P CP by incrementing the 31P spin-lock. In order to avoid an effect of magic-angle spinning (MAS) on CP and relaxation, the experiments were carried out on static samples. The 31P spin–lattice relaxation was discussed for trabecular and cortical bone tissue from adult subjects in comparison to the synthetic mineral standards. None of the reference materials has matched accurately the relaxation behaviour of the bone mineral.
The most striking differences between the examined substances were observed for T1P, which for human bone was sample dependent and appeared in the range 55–100 s, while for HAh, HAc, and CHA-B was 7.2, 10.0, and 25.8 s, respectively. Possible reasons of so large relaxation diversity were discussed. It has been suggested that T1P of apatites is to some extent dependent on the concentration of the structural hydroxyl groups, and this in turn is controlled by the material crystallinity. It was also found that T1P decreased on hydration by ca. 30%.
Keywords: Bone; Mineral; Apatite; 31P NMR; Cross-polarization; Relaxation
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Letter to the Editor: Two-dimensional 11B–11B exchange NMR study in mesoporous boron carbon nitride at 21.8 T - doi:10.1016/j.ssnmr.2007.04.003
Miwa Murakami, Tadashi Shimizu, Masataka Tansho, Ajayan Vinu, Katsuhiko Ariga, Toshiyuki Mori and K. Takegoshi
National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
Indirect covariance NMR spectroscopy of through-bond homo-nuclear correlations for quadrupolar nuclei in solids under high-resolution - doi:10.1016/j.ssnmr.2007.03.002
Bingwen Hu, Jean-Paul Amoureux and Julien Trebosc
UCCS, CNRS-8181, Lille University, FR-59652 Villeneuve d'Ascq, France
Received 20 November 2006; revised 26 February 2007. Available online 1 April 2007.
Abstract
Indirect covariance NMR spectroscopy is demonstrated in solids, and we show that it can be used to obtain through-bond 2D homo-nuclear correlation spectra for quadrupolar nuclei under high-resolution. These spectra, generated with indirect covariance from a hetero-nuclear correlation spectrum, are equivalent to those recorded with the through-bond homo-nuclear hetero-nuclear single-quantum correlation (H-HSQC) method very recently proposed. However, the indirect covariance method can save a lot of experiment time, compared to the H-HSQC experiments, which allows introducing a high-resolution quadrupolar filter, thus providing a much better resolution, even on medium-field spectrometers. The covariance concept can be used to generate many different ‘indirectly-detected' high-resolution homo-nuclear correlation spectra with through-space or through-bond correlations for spin Click to view the MathML source or quadrupolar nuclei. We also propose a simple method that decreases the noise in all (direct or indirect) covariance methods.
Keywords: Indirect-covariance; GEN2D; H-HSQC experiment; J-coupling; MQ-HETCOR; ST-HETCOR; MQ-HOMCOR; ST-HOMCOR
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A 27Al MAS NMR study of a sol–gel produced alumina: Identification of the NMR parameters of the theta-Al2O3 transition alumina phase - doi:10.1016/j.ssnmr.2007.05.002
L.A. O'Dell, S.L.P. Savin, A.V. Chadwick and M.E. Smith
Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NH, UK
Received 29 December 2006; revised 6 April 2007. Available online 13 May 2007.
Abstract
27Al MAS NMR has been used to study a sol–gel prepared alumina annealed at various temperatures. Two-field simulation of the sample heated to 1200 °C confirmed the presence of corundum, as suggested by XRD, and also the presence of nanocrystalline ?-Al2O3. 27Al MAS NMR chemical shifts, quadrupolar coupling constants and asymmetry parameters are reported for the tetrahedral and octahedral aluminium sites within ?-Al2O3.
Keywords: 27Al MAS NMR; theta-alumina; NMR interaction parameters
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Phosphorus-31 spin–lattice NMR relaxation in bone apatite and its mineral standards - doi:10.1016/j.ssnmr.2007.04.005
Agnieszka Kaflak and Waclaw
Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warszawa, Poland
Received 9 February 2007; revised 25 April 2007. Available online 16 May 2007.
Abstract
Phosphorus-31 spin–lattice relaxation, both in the laboratory (B0=4.7 T) and rotating frame (B1=2.2 mT), was studied in the following samples: mineral of whole human bone (samples B1–B6), apatite prepared from bone (BHA), natural brushite (BRU), synthetic hydroxyapatite hydrated (HAh) and calcined (HAc), and synthetic carbonatoapatite of type B (CHA-B) with 9 wt% of CO32-. The T1P relaxation time was determined directly using the saturation recovery technique, while the Click to view the MathML source relaxation time was measured via 1H?31P CP by incrementing the 31P spin-lock. In order to avoid an effect of magic-angle spinning (MAS) on CP and relaxation, the experiments were carried out on static samples. The 31P spin–lattice relaxation was discussed for trabecular and cortical bone tissue from adult subjects in comparison to the synthetic mineral standards. None of the reference materials has matched accurately the relaxation behaviour of the bone mineral.
The most striking differences between the examined substances were observed for T1P, which for human bone was sample dependent and appeared in the range 55–100 s, while for HAh, HAc, and CHA-B was 7.2, 10.0, and 25.8 s, respectively. Possible reasons of so large relaxation diversity were discussed. It has been suggested that T1P of apatites is to some extent dependent on the concentration of the structural hydroxyl groups, and this in turn is controlled by the material crystallinity. It was also found that T1P decreased on hydration by ca. 30%.
Keywords: Bone; Mineral; Apatite; 31P NMR; Cross-polarization; Relaxation
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Letter to the Editor: Two-dimensional 11B–11B exchange NMR study in mesoporous boron carbon nitride at 21.8 T - doi:10.1016/j.ssnmr.2007.04.003
Miwa Murakami, Tadashi Shimizu, Masataka Tansho, Ajayan Vinu, Katsuhiko Ariga, Toshiyuki Mori and K. Takegoshi
National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
Tuesday, July 10, 2007
CPL Update
Single-scan 2D NMR spectroscopy on a 25 T bitter magnet
vol.442, iss 4-6, Pages 478-482
Boaz Shapira, Kiran Shetty, William W. Brey, Zhehong Gan and Lucio Frydman
Abstract:
2D NMR relies on monitoring systematic changes in the phases incurred by spin coherences as a function of an encoding time t1, whose value changes over the course of independent experiments. The intrinsic multi-scan nature of such protocols implies that resistive and/or hybrid magnets, capable of delivering the highest magnetic field strengths but possessing poor temporal stabilities, become unsuitable for 2D NMR acquisitions. It is here shown with a series of homo- and hetero-nuclear examples that such limitations can be bypassed using recently proposed 2D ‘ultrafast’ acquisition schemes, which correlate interactions along all spectral dimensions within a single-scan.
vol.442, iss 4-6, Pages 478-482
Boaz Shapira, Kiran Shetty, William W. Brey, Zhehong Gan and Lucio Frydman
Abstract:
2D NMR relies on monitoring systematic changes in the phases incurred by spin coherences as a function of an encoding time t1, whose value changes over the course of independent experiments. The intrinsic multi-scan nature of such protocols implies that resistive and/or hybrid magnets, capable of delivering the highest magnetic field strengths but possessing poor temporal stabilities, become unsuitable for 2D NMR acquisitions. It is here shown with a series of homo- and hetero-nuclear examples that such limitations can be bypassed using recently proposed 2D ‘ultrafast’ acquisition schemes, which correlate interactions along all spectral dimensions within a single-scan.
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