Friday, August 29, 2008

Chemical Physics Volume 352, Issues 1-3, Pages 320-326

Indirect spin–spin coupling constants in CH4, SiH4 and GeH4 – Gas-phase NMR experiment and ab initio calculations

Andrej Antušeka, Dariusz Ke¸dzierab, Karol Jackowskic, Michał Jaszuńskid, , and Włodzimierz Makulskic

New values of the indirect spin–spin coupling constants in CH4, SiH4 and GeH4, derived from experiment and ab initio calculations, are reported. The new experimental values of 1J(CH), 1J(SiH) and 1J(GeH) are obtained from gas-phase NMR spectra. The dependence of the measured one-bond coupling constants on the density is analysed and the results are extrapolated to zero-density point to eliminate the effects due to intermolecular forces. In the calculation of the coupling constants, at the nonrelativistic level coupled cluster singles and doubles (CCSD) perturbation theory is used and the basis set convergence of the results is discussed. The relativistic corrections are estimated from Dirac–Hartree–Fock (DHF) calculations. The final theoretical values are obtained adding available estimates of the vibrational and temperature corrections. The agreement of the calculated and experimental 1J(XH), X = C, Si, Ge, constants is very satisfying, the differences are approximately 1–3%.

J. Am. Chem. Soc., 130 (33), 11056–11065, 2008.

Application of Solid-State 35Cl NMR to the Structural Characterization of Hydrochloride Pharmaceuticals and their Polymorphs

Hiyam Hamaed, Jenna M. Pawlowski, Benjamin F.T. Cooper, Riqiang Fu, S. Holger Eichhorn, and Robert W. Schurko

Solid-state 35Cl NMR (SSNMR) spectroscopy is shown to be a useful probe of structure and polymorphism in HCl pharmaceuticals, which constitute ca. 50% of known pharmaceutical salts. Chlorine NMR spectra, single-crystal and powder X-ray diffraction data, and complementary ab initio calculations are presented for a series of HCl local anesthetic (LA) pharmaceuticals and some of their polymorphs. 35Cl MAS SSNMR spectra acquired at 21.1 T and spectra of stationary samples at 9.4 and 21.1 T allow for extraction of chlorine electric field gradient (EFG) and chemical shift (CS) parameters. The sensitivity of the 35Cl EFG and CS tensors to subtle changes in the chlorine environments is reflected in the 35Cl SSNMR powder patterns. The 35Cl SSNMR spectra are shown to serve as a rapid fingerprint for identifying and distinguishing polymorphs, as well as a useful tool for structural interpretation. First principles calculations of 35Cl EFG and CS tensor parameters are in good agreement with the experimental values. The sensitivity of the chlorine NMR interaction tensor parameters to the chlorine chemical environment and the potential for modeling these sites with ab initio calculations hold much promise for application to polymorph screening for a wide variety of HCl pharmaceuticals.

J. Am. Chem. Soc., 130 (33), 10850–10851, 2008.

Evidence for Dynamics on a 100 ns Time Scale from Single- and Double-Quantum Nitrogen-14 NMR in Solid Peptides

Simone Cavadini, Anuji Abraham, Simone Ulzega, and Geoffrey Bodenhausen

The indirect detection of 14N spectra via protons in the manner of heteronuclear multiple-quantum correlation (HMQC) allows one to obtain single- (SQ) and double-quantum (DQ) 14N spectra in solids. A comparison of the SQ and DQ line widths as a function of temperature with simulations reveals motions in the tripeptide AAG with rates on the order of 107 s−1 at 49 °C.

Science Vol. 321. no. 5885, pp. 113 - 117

Mg/Al Ordering in Layered Double Hydroxides Revealed by Multinuclear NMR Spectroscopy

Paul J. Sideris, Ulla Gro Nielsen, Zhehong Gan, Clare P. Grey

The anion-exchange ability of layered double hydroxides (LDHs) has been exploited to create materials for use in catalysis, drug delivery, and environmental remediation. The specific cation arrangements in the hydroxide layers of hydrotalcite-like LDHs, of general formula Mg2+1–xAl3+xOH2(Anionn–x/n)·yH2O, have, however, remained elusive, and their elucidation could enhance the functional optimization of these materials. We applied rapid (60 kilohertz) magic angle spinning (MAS) to obtain high-resolution hydrogen-1 nuclear magnetic resonance (1H NMR) spectra and characterize the magnesium and aluminum distribution. These data, in combination with 1H-27Al double-resonance and 25Mg triple-quantum MAS NMR data, show that the cations are fully ordered for magnesium:aluminum ratios of 2:1 and that at lower aluminum content, a nonrandom distribution of cations persists, with no Al3+-Al3+ close contacts. The application of rapid MAS NMR methods to investigate proton distributions in a wide range of materials is readily envisaged.

J. Am. Chem. Soc., 130 (34), 11282–11283, 2008.

Mismatched Hartmann−Hahn Conditions Cause Proton-Mediated Intermolecular Magnetization Transfer between Dilute Low-Spin Nuclei in NMR of Static Solids

Alexander A. Nevzorov*

Mismatched Hartmann−Hahn conditions between the protons and dilute spins (such as 15N) are found to cause intermolecular magnetization transfer between the low-gamma nuclei over long distances. This transfer is purely proton mediated and occurs even in the absence of direct 15N−15N couplings. This has been demonstrated experimentally using a static single crystal of n-acetyl Leucine with intermolecular distances between the 15N nuclei exceeding 6.5 Å. A quantum-mechanical explanation of this phenomenon is given based on the average-Hamiltonian theory which was confirmed by detailed numerical many-spin simulations. The theory and experiment presented in the present paper may help in the development of solid-state NMR methods for studying interhelical contacts in membrane proteins, as well as for their spectral assignment.

Journal Update

Rapid Analysis of Organic Compounds by Proton-Detected Heteronuclear Correlation NMR Spectroscopy with 40-kHz Magic-Angle Spinning
Donghua H. Zhou, Chad M. Rienstra
Angwandte (2008), Article ASAP

High-sensitivity proton detection enabled acquisition of well-resolved two-dimensional spectra in only 30 min for less than 5 mg of organic compounds at natural abundance. Besides faster resonance assignment, rapid analysis of crystal polymorphism, molecular dynamics, and H-bonding is possible. This method is applicable to both pure and dosage forms of solid pharmaceuticals, such as ibuprofen

Wednesday, August 27, 2008

Journal of Solid State Chemistry Vol. 181, Iss. 8

Solid-state 27Al and 29Si NMR characterization of hydrates formed in calcium aluminate–silica fume mixtures
Journal of Solid State Chemistry Volume 181, Issue 8,Pages 1744-1752
P. Pena, J.M. Rivas Mercury, A.H. de Aza, X. Turrillas, I. Sobrados, J. Sanz

Partially deuterated Ca3Al2(SiO4)y(OH)12−4y–Al(OH)3 mixtures, prepared by hydration of Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7) and CaAl2O4 (CA) phases in the presence of silica fume, have been characterized by 29Si and 27Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca3Al2(OH)12 and Al(OH)3 phases were detected. From the quantitative analysis of 27Al NMR signals, the Al(OH)3/Ca3Al2(OH)12 ratio was deduced. The incorporation of Si into the katoite structure, Ca3Al2(SiO4)3−x(OH)4x, was followed by 27Al and 29Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of 27Al MAS–NMR components associated with Al(OH)6 and Al(OSi)(OH)5 environments. The 29Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C–S–H and C–A–S–H for short. From 29Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures.

Solid-state NMR and EPR study of fluorinated carbon nanofibers
Journal of Solid State Chemistry Volume 181, Issue 8, Pages 1915-1924
Wei Zhang, Marc Dubois, Katia Guérin, André Hamwi, Jérôme Giraudet, Francis Masin
Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF4 during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C2F)n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O2), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.

Tuesday, August 26, 2008

JACS: The Long-Lived Nuclear Singlet State of 15N-Nitrous Oxide in Solution

Not a solid-state NMR article, but a very neat result from Malcolm Levitt's group.

ASAP J. Am. Chem. Soc., ASAP Article, 10.1021/ja803601d
Web Release Date: August 26, 2008

The Long-Lived Nuclear Singlet State of 15N-Nitrous Oxide in Solution

Giuseppe Pileio, Marina Carravetta, Eric Hughes, and Malcolm H. Levitt*

School of Chemistry, University of Southampton, SO17 1BJ, Southampton, U.K., and Nestlé Research Centre, NESTEC LTD, 1000 Lausanne 26, Switzerland

Received May 14, 2008


A 15N nuclear singlet lifetime of over 26 min has been observed in a solution of 15N2O, by using a field-cycling NMR pulse sequence. This observation suggests applications of hyperpolarized 15N2O in medical imaging and for flow and diffusion studies.

Monday, August 25, 2008

Cows: An interesting (and tenuous) analogy for NMR spins

Cows Have A Magnetic Connection
from NPR Programs: All Things Considered

A team of researchers sorting through satellite images of cows in 300 pastures make a surprising discovery: Cows tend to face either magnetic north or south when grazing or resting.

MRC up to August 25, 2008

Magnetic Resonance in Chemistry, up to August 25, 2008
and Volume 46 Issue 9 (September 2008)

Heteronuclear dipolar decoupling effects on multiple-quantum and satellite-transition magic-angle spinning NMR spectra
from Magnetic Resonance in Chemistry by S. Ganapathy, L. Delevoye, J. P. Amoureux, P. K. Madhu (Early View)

We here report on the influence of heteronuclear dipolar decoupling on the 27Al 3QMAS, 5QMAS, and the double-quantum filter-satellite-transition magic-angle spinning (DQF-STMAS) spectra of a strongly dipolar-coupled system, gibbsite. The requirements for heteronuclear dipolar decoupling increase with the order of coherence evolving in the indirect dimension of a two-dimensional (2D) experiment. The isotropic line width of the high-resolution 2D spectra, in samples like gibbsite, is composed of four parts: the distribution of isotropic shifts ([delta]ISO, [delta]QIS), the homogeneous broadening related to the proton-proton flip-flop terms, the 27Al[bond]27Al homonulcear dipolar couplings, and the 1H[bond]27Al heteronuclear dipolar couplings. It is shown that, even in the case of gibbsite, where a strong proton-proton bath exists, the main resolution limiting factor in these experiments resides in the 1H[bond]27Al dipolar interaction. Copyright © 2008 John Wiley & Sons, Ltd.
solid-state NMR • quadrupolar nuclei • MQMAS • STMAS • homogeneous broadening • heteronuclear broadening • heteronuclear decoupling • TPPM


Magnetic Resonance in Chemistry
Volume 46 Issue 9, Pages 803 - 810
Multi-nuclear magnetic resonance study of Na3AlF6AlPO4 molten and solidified mixtures
M. Keppert, A. Rakhmatullin, F. Simko, Michael Deschamps, G. M. Haarberg, C. Bessada
Phosphorus is one of the predominant impurities in the Hall-Heroult process for industrial aluminium production. The nature of the dissolved phosphorus species in the Na3AlF6AlPO4 system has been investigated by in situ high-temperature (HT) 19F, 23Na, 27Al, 17O, and 31P NMR. The combination of these experiments enables to define the presence of PO43-, AlF52- and (AlF4OPO3)4- anions in the melt, and then the formation of AlOP bonding. Melts solidified at different cooling rates were characterised using various solid-state NMR techniques including multiple quantum magic angle spinning (MQMAS), rotational echo double resonance (REDOR) and heteronuclear single quantum correlation (HSQC). The glass obtained by the rapid quenching of the hypereutectic melt has been carefully described in order to better understand the structure of the melt. Copyright © 2008 John Wiley & Sons, Ltd.
high-temperature NMR • solid-state NMR • molten salts • cryolite • aluminium fluoride • phosphate glasses • MQMAS • REDOR • HSQC

Progress in Nuclear Magnetic Resonance Spectroscopy up to Nov. 2008

Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 53, Issue 4, November 2008, Pages 249-268

The quantum-chemical calculation of NMR indirect spin–spin coupling constants

Trygve Helgaker, Michał Jaszuński and Magdalena Pecul

Keywords: Spin-spin coupling constants; Electronic-structure theory; Quantum chemistry; Ab initio calculations; Density-functional theory

Tuesday, August 19, 2008

J. Am. Chem. Soc., 130 (32), 10625–10632, 2008.

Methyl Proton Contacts Obtained Using Heteronuclear Through-Bond Transfers in Solid-State NMR Spectroscopy
Antoine Loquet,† Ségolène Laage,‡ Carole Gardiennet,† Bénédicte Elena,‡ Lyndon Emsley,‡ Anja Böckmann,*† and Anne Lesage*‡

A two-dimensional proton-mediated carbon−carbon correlation experiment that relies on through-bond heteronuclear magnetization transfers is demonstrated in the context of solid-state NMR of proteins. This new experiment, dubbed J-CHHC by analogy to the previously developed dipolar CHHC techniques, is shown to provide selective and sensitive correlations in the methyl region of 2D spectra of crystalline organic compounds. The method is then demonstrated on a microcrystalline sample of the dimeric protein Crh (2 × 10.4 kDa). A total of 34 new proton−proton contacts involving side-chain methyl groups were observed in the J-CHHC spectrum, which had not been observed with the conventional experiment. The contacts were then used as additional distance restraints for the 3D structure determination of this microcrystalline protein. Upon addition of these new distance restraints, which are in large part located in the hydrophobic core of the protein, the root-mean-square deviation with respect to the X-ray structure of the backbone atom coordinates of the 10 best conformers of the new ensemble of structures is reduced from 1.8 to 1.1 Å.

J. Am. Chem. Soc., 130 (32), 10596–10604, 2008.

NMR Structure of the Complex between the Tfb1 Subunit of TFIIH and the Activation Domain of VP16: Structural Similarities between VP16 and p53

Chantal Langlois, Caroline Mas, Paola Di Lello, Lisa M. Miller Jenkins, Pascale Legault, and James G. Omichinski

The Herpes Simplex Virion Protein 16 (VP16) activates transcription through a series of protein/protein interactions involving its highly acidic transactivation domain (TAD). The acidic TAD of VP16 (VP16TAD) has been shown to interact with several partner proteins both in vitro and in vivo, and many of these VP16 partners also bind the acidic TAD of the mammalian tumor suppressor protein p53. For example, the TADs of VP16 and p53 (p53TAD) both interact directly with the p62/Tfb1 (human/yeast) subunit of TFIIH, and this interaction correlates with their ability to activate both the initiation and elongation phase of transcription. In this manuscript, we use NMR spectroscopy, isothermal titration calorimetery (ITC) and site-directed mutagenesis studies to characterize the interaction between the VP16TAD and Tfb1. We identify a region within the carboxyl-terminal subdomain of the VP16TAD (VP16C) that has sequence similarity with p53TAD2 and binds Tfb1 with nanomolar affinity. We determine an NMR structure of a Tfb1/VP16C complex, which represents the first high-resolution structure of the VP16TAD in complex with a target protein. The structure demonstrates that like p53TAD2, VP16C forms a 9-residue α-helix in complex with Tfb1. Comparison of the VP16/Tfb1and p53/Tfb1 structures clearly demonstrates how the viral activator VP16C and p53TAD2 shares numerous aspects of binding to Tfb1. Despite the similarities, important differences are observed between the p53TAD2/Tfb1 and VP16C/Tfb1 complexes, and these differences demonstrate how selected activators such as p53 depend on phosphorylation events to selectively regulate transcription.

J. Am. Chem. Soc., 130 (32), 10490–10491, 2008.

Double-Quantum 13C Nuclear Magnetic Resonance of Bathorhodopsin, the First Photointermediate in Mammalian Vision

Maria Concistrè, Axel Gansmüller, Neville McLean, Ole G. Johannessen, Ildefonso Marín Montesinos, Petra H. M. Bovee-Geurts, Peter Verdegem, Johan Lugtenburg, Richard C. D. Brown, Willem J. DeGrip, and Malcolm H. Levitt

The 13C chemical shifts of the primary visual photointermediate bathorhodopsin have been observed by performing double-quantum magic-angle-spinning NMR at low temperature in the presence of illumination. Strong isomerization shifts have been observed upon the conversion of rhodopsin into bathorhodopsin.

J. Am. Chem. Soc., 130 (32), 10486–10487, 2008.

A Dipicolinic Acid Tag for Rigid Lanthanide Tagging of Proteins and Paramagnetic NMR Spectroscopy

Xun-Cheng Su, Bradley Man, Sophie Beeren, Haobo Liang, Shane Simonsen, Christophe Schmitz,Thomas Huber, Barbara A. Messerle, and Gottfried Otting

A new lanthanide tag was designed for site-specific labeling of proteins with paramagnetic lanthanide ions. The tag, 4-mercaptomethyl-dipicolinic acid, binds lanthanide ions with nanomolar affinity, is readily attached to proteins via a disulfide bond, and avoids the problems of diastereomer formation associated with most of the conventional lanthanide tags. The high lanthanide affinity of the tag opens the possibility to measure residual dipolar couplings in a single sample containing a mixture of paramagnetic and diamagnetic lanthanides. Using the DNA-binding domain of the E. coli arginine repressor as an example, it is demonstrated that the tag allows immobilization of the lanthanide ion in close proximity of the protein by additional coordination of the lanthanide by a carboxyl group of the protein. The close proximity of the lanthanide ion promotes accurate determinations of magnetic susceptibility anisotropy tensors. In addition, the small size of the tag makes it highly suitable for studies of intermolecular interactions.

J. Am. Chem. Soc., 130 (32), 10452–10453, 2008.

Spatially Resolved NMR Thermometry of an Operating Fixed-Bed Catalytic Reactor
Igor V. Koptyug,* Alexey V. Khomichev, Anna A. Lysova, and Renad Z. Sagdeev

An MRI-based approach for the thermometry of an operating packed-bed catalytic reactor was implemented. It was employed for the spatially resolved NMR thermometry of the bed of Pd/γ-Al2O3 catalyst beads in the course of propylene hydrogenation reaction. This was achieved by detecting the spatially resolved axial 1D profiles of the 27Al NMR signal intensity of Al2O3 in the course of the reaction. The experimental results demonstrate a clear correlation between the 27Al NMR signal intensity and the catalyst temperature measured with a thermocouple (25−250 °C), and reveal the existence of pronounced temperature gradients along the catalyst bed.

Monday, August 18, 2008

Physical Review B - Up to vol 78 no 4

Multinuclear NMR studies of mixed Ca1−xSrxF2 crystals
R. E. Youngman and C. M. Smith
The local environments of fluorine and calcium ions in Ca1−xSrxF2 single crystals have been studied using 19F and 43Ca magic-angle spinning (MAS) NMR spectroscopies. The fluorine speciation is found to depend on both the distribution of cations (Ca and Sr) around each fluorine site in the fluorite lattice, as well as fluctuations in the ionic character of bonding between fluorine and these cations. The natural abundance 43Ca MAS NMR results show a clear relation between 43Ca chemical shielding and bond distances in halides, with increasing shielding as the fluorite lattice expands and Ca-F distances lengthen. When taken together, the results from 19F and 43Ca NMR are consistent with a random substitution of Sr for Ca in the mixed fluoride system.

Similar glassy features in the 139La NMR response of pure and disordered La1.88Sr0.12CuO4
V. F. Mitrović, M.-H. Julien, C. de Vaulx, M. Horvatić, C. Berthier, T. Suzuki, and K. Yamada
High Tc superconductivity in La2−xSrxCuO4 coexists with (striped and glassy) magnetic order. Here, we report NMR measurements of the 139La spin-lattice relaxation, which displays a stretched-exponential time dependence, in both pure and disordered x=0.12 single crystals. An analysis in terms of a distribution of relaxation rates 139T indicates that: (i) the spin-freezing temperature is spatially inhomogeneous with an onset at T=20 K for the pristine samples and (ii) the width of the T distribution in the vicinity of T is insensitive to an ~1% level of atomic disorder in CuO2 planes. This suggests that the stretched-exponential 139La relaxation, considered as a manifestation of the system's glassiness, may not arise from quenched disorder.

77Se NMR investigation of the field-induced spin-density-wave transitions in (TMTSF)2ClO4
L. L. Lumata, J. S. Brooks, P. L. Kuhns, A. P. Reyes, S. E. Brown, H. B. Cui, and R. C. Haddon
Complementary 77Se nuclear magnetic resonance (NMR) and electrical transport have been used to correlate the spin-density dynamics with the subphases of the field-induced spin-density wave (FISDW) ground state in (TMTSF)2ClO4. We have found that the peaks in the spin-lattice relaxation rate 1/T1 appear within the metal-FISDW phase boundary and/or at first-order subphase transitions. In the quantum limit above 25 T, the NMR data have given an insight into the FISDW electronic structure.

Comparative NMR investigation of the Re-based borides
C. S. Lue, Y. F. Tao, and T. H. Su
We report a systematic study of the rhenium-based borides, ReB2, Re7B3, and Re3B, by means of the 11B nuclear magnetic resonance (NMR) spectroscopy. While Re7B3 and Re3B are superconductors, ReB2 exhibits no superconducting signature but is of current interest due to its superhard mechanical property. Since the major focus of this investigation is their electronic characteristics in the normal states, we performed the measurements at temperatures between 77 and 295 K. For Re7B3 and Re3B, s-character electrons were found to be responsible for the observed 11B NMR Knight shift and spin-lattice relaxation rate (1/T1). From T1 analysis, we thus deduce the partial B s Fermi-level density of states (DOS) of both borides. On the other hand, the relaxation rate of ReB2 is mainly associated with p electrons, similar to the cases of OsB2 and RuB2. In addition, the extracted B 2p Fermi-level DOS is in good agreement with the theoretical prediction from band-structure calculations.

Physical Review Letters - Up to vol 101, no 7

NMR Evidence for the Persistence of a Spin Superlattice Beyond the 1/8 Magnetization Plateau in SrCu2(BO3)2
M. Takigawa, S. Matsubara, M. Horvatić, C. Berthier, H. Kageyama, and Y. Ueda
We present 11B NMR studies of the 2D frustrated dimer spin system SrCu2(BO3)2 in the field range 27–31 T covering the upper phase boundary of the 1/8 magnetization plateau, identified at 28.4 T. Our data provide a clear evidence that above 28.4 T the spin superlattice of the 1/8 plateau is modified but does not melt even though the magnetization increases. Although this is precisely what is expected for a supersolid phase, the microscopic nature of this new phase is much more complex. We discuss the field-temperature phase diagram on the basis of our NMR data.

75As NMR Studies of Superconducting LaFeAsO0.9F0.1
H.-J. Grafe, D. Paar, G. Lang, N. J. Curro, G. Behr, J. Werner, J. Hamann-Borrero, C. Hess, N. Leps, R. Klingeler, and B. Büchner
We have performed 75As nuclear magnetic resonance measurements on aligned powders of the new LaFeAsO0.9F0.1 superconductor. In the normal state, we find a strong temperature dependence of the spin shift and Korringa behavior of the spin lattice relaxation rate. In the superconducting state, we find evidence for line nodes in the superconducting gap and spin-singlet pairing. Our measurements reveal a strong anisotropy of the spin lattice relaxation rate, which suggests that superconducting vortices contribute to the relaxation rate when the field is parallel to the c axis but not for the perpendicular direction.

Coherent Precession of Magnetization in the Superfluid 3He A-Phase
T. Sato, T. Kunimatsu, K. Izumina, A. Matsubara, M. Kubota, T. Mizusaki, and Yu. M. Bunkov
We report the first observation of coherent precession of magnetization in superfluid 3He A-like phase (CP-A) in aerogel. The coherent precession in bulk 3He A-phase is unstable due to the positive feedback of spin supercurrent to the gradient of phase of precession. It was predicted that the homogeneous precession will be stable if the orbital momentum of the 3He A-phase can be oriented along the magnetic field. We have succeeded to prepare this configuration by emerging 3He in uniaxially deformed anisotropic aerogel. The dissipation rate of coherent precession states in aerogel is much larger than that in bulk 3He B-phase. We propose a mechanism of this dissipation.

Universal Long-Time Behavior of Nuclear Spin Decays in a Solid
S. W. Morgan, B. V. Fine, and B. Saam
Magnetic resonance studies of nuclear spins in solids are exceptionally well suited to probe the limits of statistical physics. We report experimental results indicating that isolated macroscopic systems of interacting nuclear spins possess the following fundamental property: spin decays that start from different initial configurations quickly evolve towards the same long-time behavior. This long-time behavior is characterized by the shortest ballistic microscopic time scale of the system and therefore falls outside of the validity range for conventional approximations of statistical physics. We find that the nuclear free-induction decay and different solid echoes in hyperpolarized solid xenon all exhibit sinusoidally modulated exponential long-time behavior characterized by identical time constants. This universality was previously predicted on the basis of analogy with resonances in classical chaotic systems.

Spin Dynamics in Iron-Based Layered Superconductor (La0.87Ca0.13)FePO Revealed by 31P and 139La NMR Studies
Yusuke Nakai, Kenji Ishida, Yoichi Kamihara, Masahiro Hirano, and Hideo Hosono
We report 31P and 139La NMR studies of (La0.87Ca0.13)FePO, which is a family member of the recently discovered superconductor LaFeAs(O1-xFx). In the normal state, Knight shift and nuclear spin-lattice relaxation rate divided by T (1/T1T) show that a Fermi-liquid state with moderate ferromagnetic fluctuations emerges below 30 K. From 1/T1T of 31P and 139La, a quasi-two- dimensional electronic structure is suggested, in which the FeP layer is more conductive than the LaO layer. In the superconducting (SC) state, although a clear Meissner signal was observed, 1/T1T increases below Tc, in contrast to a decrease of 1/T1T due to the opening of a SC gap, suggesting that novel low-energy spin dynamics develop in the SC state.

Applied Magnetic Resonance - Vol 34, No 1 & 2

Preparation and NMR Characterization of Polyethyl-2-cyanoacrylate Nanocapsules
M. Bogdan, A. Nan, C. V. L. Pop, L. Barbu-Tudoran and I. Ardelean
The aim of this work was to prepare a nanocapsule by interfacial polymerization of ethyl-2-cyanoacrylate monomer in an oil-in-water emulsion. The chemical nature of the individual system components and the nanocapsule was investigated by high-resolution 1H and 13C nuclear magnetic resonance. The nanocapsule mean size and polydispersity were determined by photon correlation spectroscopy. The effect of different variables such as the organic solvent, oil concentration and stirring rate on the nanocapsule size was evaluated. The oil concentration was found to play a major role in controlling the size of the emulsified droplets.

Study of Thermal Mobility by Means of 1H NMR Magic-Angle Spinning Sideband Analysis
Ö. F. Erdem and D. Michel
1H nuclear magnetic resonance (NMR) magic-angle spinning (MAS) sideband patterns of molecules adsorbed in zeolites or related materials both depend on the MAS frequency and the thermal mobility. By using a statistical NMR line shape theory a valuable information on the thermal motion can be derived from the MAS sidebands. The conclusions are compared with the results of longitudinal proton spin relaxation studies at different temperatures and Larmor frequencies. The measurements are performed on samples of ethylene glycol molecules adsorbed in zeolites of the NaX and sodalite type which were prepared under well-defined conditions in vacuum. It is shown that the comparison of the respective results is very suitable for a deeper understanding of the dynamics of the adsorbed molecules.

1H NMR Relaxation Studies of Proton-Conducting Imidazolium Salts of Dicarboxylic Acids
A. Rachocki, K. Pogorzelec-Glaser and J. Tritt-Goc
The proton nuclear magnetic resonance spin–lattice relaxation time has been successfully used to evidence the reorientation of the imidazolium rings in carboxylic acid salts of imidazole: imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate. The process occurs in the temperature range between 325 K and the melting point of the salts (523, 379 and 360 K) and is described by a single activation energy of 20, 48 and 66 kJ/mol for imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate, respectively. The studied salts are considered as possible candidate materials for fuel-cell membranes.

Molecular Motion in the Biocopolymer Sequence of Glycolide and Lactide Studied by Solid-State NMRF. Nozirov, Z. Fojud, M. Jancelewicz, A. Nazirov and S. Jurga
This paper reports a nuclear magnetic resonance study of the molecular motion in copolymers derived from glycolide and L-lactide in the solid state. Variation of T 1 relaxation times with temperature reflects a local disorder and the fast segment conformational motions which can be quantified in terms of correlation times predicted by the Bloembergen–Purcell–Pound and Davidson–Cole models. At low temperatures, spin relaxation is dominated by the axial methyl rotation in lactide units described by an asymmetry parameter of the correlation time δ which takes a value of about 0.45 for all systems. Above the devitrification points the trans and gauche isomerization in glycolide segments occurs. In addition to the chemical structure characterization, solid-state magic-angle spinning spectroscopy gives an insight into the role of glycol segments in the chain mobility.

Marcel's Update

REDOR recoupling in polymer-stabilized liquid crystals undergoing MAS — Two-dimensional NMR applications with strongly aligned proteins

Jean-François Trempe, Ekaterina Pomerantseva, and Kalle Gehring

Can. J. Chem. 86(6): 608–615 (2008)

Abstract: We recently introduced a technique, termed SAD-REDOR, for recoupling residual dipolar couplings in a single-domain polymer-stabilized liquid crystal (PSLC) undergoing magic-angle spinning (MAS). The experiment was demonstrated with 1H–15N dipolar couplings in a small molecule. Here, we show the applicability of the technique to a strongly aligned protein and we describe a novel two-dimensional experiment to generate in-phase and anti-phase (IPAP) doublets in the 1H dimension of an HSQC NMR spectrum. This pulse sequence, SAD-IPAP, was tested on a sample of 15N-labeled ubiquitin (5 mmol/L) in a polyacrylamide-stabilized Pf1 phage liquid crystal (20 mg/mL). 15N–1H residual dipolar couplings (RDCs) were measured with the SAD-IPAP pulse sequence at spinning speeds of 1000 and 1250 Hz. RDSs were also measured using the conventional HSQC-IPAP method in a sample of 15N-ubiquitin dissolved in a solution of Pf1 phage (1 mg/mL). The resulting RDCs were fitted to the solution structure of ubiquitin to estimate the alignment tensor and to determine the accuracy of the measured couplings. The results highlight the benefits of SAD-REDOR for the measurement of RDCs in strongly aligned macromolecules.

Carbon and silicon substitution in (4, 4) aluminum nitride nanotube — Density functional study of 27Al and 14N electric field gradient tensors

Ahmad Seif, Mehran Aghaie, and Hossein Aghaie

Can. J. Chem. 86(8): 745–750 (2008)

Abstract: A computational study at the level of density functional theory (DFT) was performed to investigate the influence of Si and C substitution on the 14N and 27Al quadrupole coupling constants (CQ) in the armchairsingle-walled aluminum nitride nanotube (SWAlNNT). To this aim, a 1 nm AlNNT consisting of 28 Al and 28 N atoms was considered in which both mouths of the nanotube are capped by hydrogen atoms. Additionally, two other forms of this model of AlNNT were considered in which five Si and five C atoms were substituted in place of the five Al and five N atoms, with two rings in the length of nanotube, like a wire, in the first form; and three Si and three C atoms were substituted in place of three Al and three N atoms as a central ring on the surface of the AlNNT in the second form. The calculated CQ values for three optimized AlNNT systems (raw and Si- and C-substituted) reveal diverse electronic environments in the above-mentioned systems. All the calculations were carried out using the Gaussian 98 software pac

Tuesday, August 12, 2008

Wine chemistry - Chem. Soc. Rev. 2008

There is a little bit of NMR in this article - but an article on the chemistry of wines is just interesting anyhow.

Critical Review

Article citation: Pavla Polášková, Chem. Soc. Rev., 2008, DOI: 10.1039/b714455p

Wine flavor: chemistry in a glass

Pavla Poláková, Julian Herszage and Susan E. Ebeler

Although hundreds of chemical compounds have been identified in grapes and wines, only a few compounds actually contribute to sensory perception of wine flavor. This critical review focuses on volatile compounds that contribute to wine aroma and provides an overview of recent developments in analytical techniques for volatiles analysis, including methods used to identify the compounds that make the greatest contributions to the overall aroma. Knowledge of volatile composition alone is not enough to completely understand the overall wine aroma, however, due to complex interactions of odorants with each other and with other nonvolatile matrix components. These interactions and their impact on aroma volatility are the focus of much current research and are also reviewed here. Finally, the sequencing of the grapevine and yeast genomes in the past 10 years provides the opportunity for exciting multidisciplinary studies aimed at understanding the influences of multiple genetic and environmental factors on grape and wine flavor biochemistry and metabolism (147 references).

Thursday, August 07, 2008

J Phys Chem B, J Phys Chem C, Organometallics and Macromolecules, End of June to Beginning of August

J. Phys. Chem. C, 112 (26), 9808–9821, 2008. 10.1021/jp8010348
7Li NMR Spectroscopy and Multiquantum Relaxation as a Probe of the Microstructure and Dynamics of Confined Li+ Cations: An Application to Dense Clay Sediments

Patrice Porion,* Anne Marie Faugère, and Alfred Delville*
Centre de Recherche sur la Matière Divisée, CNRS - Université d’Orléans, 1b rue de la Férollerie, 45071 Orléans Cedex 02, France

Abstract: 7Li NMR spectroscopy and relaxometry are exploited to obtain structural and dynamical information within heterogeneous systems resulting from aqueous dispersion of clay platelets. In addition to the specific orientation of the clay platelets detected by the splitting of the 7Li resonance line, multiquantum relaxation measurements are used to determine the relative contributions from the quadrupolar and dipolar relaxation mechanisms responsible for the detected broadening of the 7Li resonance line. Intrinsic spectral densities are further extracted from the variation of these apparent relaxation rates as a function of the orientation of the clay sediment within the static magnetic field. A semiquantitative interpretation of the intrinsic quadrupolar and dipolar relaxation behavior is performed by a multiscale modeling of the Li+ ions’ diffusion in relation to the structure of the clay dispersions. Equivalent structural and dynamical investigations can be performed within a broad class of material containing electrically charged solid/liquid interfaces by exploiting the sensitivity of 7Li NMR spectroscopy.

J. Phys. Chem. C, 112 (26), 9962, 2008. 10.1021/jp802847m
Comment on “27Al, 47,49Ti, 31P, and 13C MAS NMR Study of VX, GD, and HD Reactions with Nanosize Al2O3, Conventional Al2O3 and TiO2, and Aluminum and Titanium Metal”

George W. Wagner* and Boris Itin

Wagner et al.1 recently reported 47,49Ti MAS NMR spectra for TiO2 (anatase) at 14, 17.5, and 21 T to assess anticipated line-narrowing for these nuclei at high magnetic field. As quadrupolar nuclei, 49Ti (I = 7/2, Q = 0.24) and 47Ti (I = 5/2, Q = 0.29) are susceptible to broadening by the second-order quadrupolar interactions that diminish with respect to the dominant NMR Zeeman interaction at higher magnetic fields.2 Although the lineshapes of both 49Ti and 47Ti were clearly evident in the 14 and 17.5 T spectra, only the 49Ti peak was detected in the 21 T spectrum because of the poor signal-to-noise ratio. By 21 T, the 49Ti resonance had narrowed to less than half of its width at 14 T, but the extent of narrowing of the 47Ti could not be ascertained.
As shown in Figure
1, much better signal-to-noise 47,49Ti MAS NMR spectra have now been obtained3 for anatase at 21 T, which allow the line shape of the much broader 47Ti resonance to be observed. The better sensitivity was evidently provided by use of a larger-diameter 5 mm probe rather than the previous 3.2 mm probe.1 Spectra previously reported1 at 14 and 17.5 T are also shown for comparison. At 21 T, the line width of the 47Ti peak narrows to less than half of its width at 14 T, in agreement with the results previously noted1 for the sharper 49Ti resonance.

J. Phys. Chem. C, 112 (27), 9996–10003, 2008. 10.1021/jp801992d

Tuning Metal Nanostructures in Mesoporous Silica by a Simple Change of Metal Complexes and by Reduction with Grafted Imines and Hemiaminals
Youwei Xie, Sean Quinlivan, and Tewodros Asefa*

Abstract: We report synthetic methods to produce silver (Ag) or gold (Au) monodisperse nanoparticles with different loadings as well as Ag and Au nanorods with tunable aspect ratios and optical properties. This is achieved inside externally functionalized mesoporous SBA-15 material by utilizing a simple change of the type of metal complex that is reduced with imines or hemiaminals that were anchored within the channel walls of the mesoporous material. The imine and hemiaminal groups were produced by reacting grafted 3-aminopropyl groups with CH3CHO or HCHO, respectively. Upon using lower concentrations of aqueous AgNO3 or ammonical [Ag(NH3)2]NO3 solution as the metal source, Ag monodisperse nanoparticles formed. Interestingly, when the concentration of ammonical [Ag(NH3)2]NO3 solution was increased, this resulted exclusively in nanoparticles with a higher loading and with no formation of nanorods; while increasing the concentration of aqueous AgNO3 solution resulted in silver nanorods with higher aspect ratios and tunable optical absorption and color. A possible mechanism for the growth of nanoparticles versus nanorods in the mesoporous materials by using ammonical instead of aqueous silver complexes, respectively, was proposed. The synthesis of gold nanoparticles or tunable gold nanorods was also carried out by changing the concentration of aqueous HAuCl4 in the same material. The synthesis of Ag nanostructures with grafted imines and Au nanostructures with grafted imines and hemiaminals are to be reported for the first time. The functionalized mesoporous materials, the Ag and Au nanoparticles, and nanorods inside the mesoporous materials were characterized by UV−vis absorption and reflectance spectroscopy, small-angle and wide-angle X-ray diffraction, solid-state NMR spectroscopy, and transmission electron microscopy.

J. Phys. Chem. C, 112 (28), 10462–10471, 2008. 10.1021/jp800721e

Structural Role of Fluoride in the Ion-Conducting Glass System B2O3−PbO−LiF Studied by Single- and Double-Resonance NMR

A. S. Cattaneo,†‡ R. P. Lima,§ C. E. Tambelli,§ C. J. Magon,§ V. R. Mastelaro,§ A. Garcia,§ J. E. de Souza,§ A. S. S. de Camargo,§ C. C. de Araujo,† J. F. Schneider,§ J. P. Donoso,§ and H. Eckert*†

Abstract: The local structure of an ion-conducting glass with nominal composition 50B2O3−10PbO−40LiF has been investigated by complementary 7Li, 11B, 19F, and 207Pb single- and double-resonance experiments. The results give insight into the structural role of the lithium fluoride additive in borate glasses: (1) LiF is seen to actively participate in the network transformation process contributing to the conversion of three- into four-coordinate boron units, as shown by 11B single-resonance as well as by 11B{19F} and 19F{11B} double-resonance experiments. (2) 19F signal quantification experiments suggest substantial fluoride loss, presumably caused by formation of volatile BF3. A part of the fluoride remains in the dopant role, possibly in the form of small LiF-like cluster domains, which serve as a mobile ion supply. (3) The extent of lithium−fluorine and lead−fluorine interactions has been characterized by 7Li{19F} and 207Pb{19F} REDOR and SEDOR experiments. On the basis of these results, a quantitative structural description of this system has been developed.

J. Phys. Chem. C, 112 (29), 10899–10908, 2008. 10.1021/jp803037u
Evidence of Multiple Cation Site Occupation in Zeolite NaY with High Si/Al Ratio

Laurent Gueudré, Anne Agathe Quoineaud, Gerhard Pirngruber, and Philibert Leflaive*

Abstract: 23Na MAS NMR and 23Na 2D MQMAS NMR spectra of dehydrated NaY zeolite with different Si/Al ratios were analyzed. Particularly, the cation distribution was examined in both as synthesized NaY with a Si/Al ratio of 2.7 and a dealuminated NaY with a framework Si/Al ratio of 8.6, prepared by ion-exchange of a dealuminated NH4Y zeolite CBV712. This is, to the best of our knowledge, the first experimental investigation of the cation distribution in dealuminated NaY. Careful analysis of 23Na MAS NMR and 23Na 2D MQMAS NMR spectra of dealuminated NaY revealed the occupation of at least three different sites, contrary to what was expected from previous computational studies where site II was the only occupied site. Moreover, two new features could be observed. First, a split of the contribution of site I into two relatively close and similar narrow peaks in the MQMAS NMR spectra, and second a new narrow signal, interpreted in terms of fast cation movement inside the sodalite cage. This work also allows a clear identification of the contribution of site II to the 23Na MAS and MQMAS NMR spectra of as synthesized NaY (Na52Y). This was hardly possible in previous 23Na MAS NMR studies of NaX or NaY due to strong overlap of the broad quadrupolar pattern of site II with the one of the cations located in site I′.

-13C Solid-State NMR
J. Phys. Chem. B, 112 (29), 8443–8446, 2008. 10.1021/jp804447r

Spectroscopic Observation of Critical Guest Concentration Appearing in tert-Butyl Alcohol Clathrate Hydrate

Youngjune Park, Minjun Cha, Woongchul Shin, Huen Lee,* and John A. Ripmeester*

Abstract: The tert-butyl alcohol (TBA) is the most hydrophobic of the simple alcohol and by itself does not form a clathrate hydrate with water. A genuine clathrate hydrate is synthesized by exposing a gaseous guest to solid TBA + H2O powders. Here, we examine three consecutive spectroscopic approaches of (1) the occurrence of a “free” OH stretching band (ν(OH)) signal of TBA molecules representing an absence of hydrogen bonding between the host water and guest TBA, (2) a tuning effect for creating fresh cages via the rearrangement of the host−water lattice, and finally (3) the existence of a critical guest concentration (CGC) that appears only when the TBA concentration is dilute. The present findings from this simple three-step approach can be extended to other alcoholic guest species with the specific modifications to provide the new insights into inclusion chemistry.

-14N CQ measured via EPR
J. Phys. Chem. B, 112 (29), 8549–8557, 2008. 10.1021/jp800222c

Electron Spin Resonance Investigation of Microscopic Viscosity, Ordering, and Polarity in Nafion Membranes Containing Methanol−Water Mixtures

Jamie S. Lawton, Eugene S. Smotkin, and David E. Budil*

Abstract: Electron spin resonance (ESR) was used to monitor the local environment of 2,2,6,6-tetramethyl-4-piperidone N-oxide (Tempone) spin probe in water and methanol mixtures in solution and in Li+ ion exchanged Nafion 117 membranes. Solution spectra were analyzed using the standard fast-motion line width parameters, while membrane spectra were fitted using the microscopic order macroscopic disorder (MOMD) slow-motional line shape program of Freed and co-workers. The 14N hyperfine splitting, aN, which reflects the local polarity of the nitroxide probe, decreases with increasing methanol concentration, consistent with the decrease in solvent polarity. The polarity depended only weakly on composition in the Nafion membrane, but was noticeably more temperature-dependent. The microviscosity of the membrane aqueous phase as reflected by the rotational correlation time (τc) of the probe, was nearly 2 orders of magnitude longer in the membrane than in solution and varied by an order of magnitude over the composition range studied. The probe exhibits significant local ordering in the aqueous phase of Nafion membranes that is diminished with increasing methanol concentration.

J. Phys. Chem. B, 112 (30), 9079–9090, 2008. 10.1021/jp711640p

High-Field EPR and ESEEM Investigation of the Nitrogen Quadrupole Interaction of Nitroxide Spin Labels in Disordered Solids: Toward Differentiation between Polarity and Proticity Matrix Effects on Protein Function

A. Savitsky, A. A. Dubinskii, M. Plato, Y. A. Grishin,§ H. Zimmermann, and K. Möbius*

Abstract: The combination of high-field electron paramagnetic resonance (EPR) with site-directed spin labeling (SDSL) techniques employing nitroxide radicals has turned out to be particularly powerful in revealing subtle changes of the polarity and proticity profiles in proteins enbedded in membranes. This information can be obtained by orientation-selective high-field EPR resolving principal components of the nitroxide Zeeman (g) and hyperfine (A) tensors of the spin labels attached to specific molecular sites. In contrast to the g- and A-tensors, the 14N (I = 1) quadrupole interaction tensor of the nitroxide spin label has not been exploited in EPR for probing effects of the microenvironment of functional protein sites. In this work it is shown that the W-band (95 GHz) high-field electron spin echo envelope modulation (ESEEM) method is well suited for determining with high accuracy the 14N quadrupole tensor principal components of a nitroxide spin label in disordered frozen solution. By W-band ESEEM the quadrupole components of a five-ring pyrroline-type nitroxide radical in glassy ortho-terphenyl and glycerol solutions have been determined. This radical is the headgroup of the MTS spin label widely used in SDSL protein studies. By DFT calulations and W-band ESEEM experiments it is demonstrated that the Qyy value is especially sensitive to the proticity and polarity of the nitroxide environment in H-bonding and nonbonding situations. The quadrupole tensor is shown to be rather insensitive to structural variations of the nitroxide label itself. When using Qyy as a testing probe of the environment, its ruggedness toward temperature changes represents an important advantage over the gxx and Azz parameters which are usually employed for probing matrix effects on the spin labeled molecular site. Thus, beyond measurenments of gxx and Azz of spin labeled protein sites in disordered solids, W-band high-field ESEEM studies of 14N quadrupole interactions open a new avenue to reliably probe subtle environmental effects on the electronic structure. This is a significant step forward on the way to differentiate between effects from matrix polarity and hydrogen-bond formation.

-Some solution NMR for the solids blog

J. Phys. Chem. B, 112 (30), 9174–9181, 2008. 10.1021/jp8030545

Remarkable Metal Counterion Effect on the Internucleotide J-Couplings and Chemical Shifts of the N−H···N Hydrogen Bonds in the W−C Base Pairs

Huifang Li, Robert I. Cukier, and Yuxiang Bu*

Abstract: The effects of metal ion binding on the 2hJNN-coupling and δ(1H)/Δδ(15N) chemical shifts of N−H···N H-bond units in internucleotide base pairs were explored by a combination of density functional theory calculations and molecular dynamics (MD) simulations. Results indicate that the NMR parameters vary considerably upon cation binding to the natural GC or AT base pairs, and thus can be used to identify the status of the base pairs, if cation-perturbed. The basic trend is that cation perturbation causes 2hJNN to increase, Δδ(15N) to decrease, and δ(1H) to shift upfield for GC, and in the opposite directions for AT. The magnitudes of variation are closely related to the Lewis acidity of the metal ions. For both base pair series (Mz+GC and Mz+AT), these NMR parameters are linearly correlated among themselves. Their values depend strongly on the energy gaps (ΔELP→σ*) and the second-order interaction energies (E(2)) between the donor N lone pair (LPN) and the acceptor σ*N−H localized NBO orbitals. In addition, the 2hJNN changes are also sensitive to the amount of σ charge transfer from LPN to σ*N−H NBOs or from the purine to the pyrimidine moieties. The different trends are a consequence of the different H-bond patterns combined with the polarization effect of the metal ions in the cationized Mz+AT series, Mz+ ← A → T, and the cationized GC series, Mz+ ← G ← C. The predicted cation-induced systematic trends of 2hJNN and δ(15N,1H) in N−H···N H-bond units may provide a new approach to the determination of H-bond structure and strength in Watson−Crick base pairs, and provide an alternative probe of the heterogeneity of DNA sequences.

J. Phys. Chem. B, 112 (32), 9625–9629, 2008. 10.1021/jp801128x Web Release Date: July 17, 2008

Study of the Adsorption of Organic Molecules on Transition Metal Exchanged Zeolites via Solid State NMR. Part 1: Theoretical Aspects

Kristof Houthoofd,* Piet J. Grobet, and Pierre A. Jacobs

Abstract: A theoretical study is performed of the 1H relaxation behavior of an organic molecule that is adsorbed in a zeolite exchanged with transition metal ions. An expression is derived for the spin−lattice and spin−spin relaxation rate constant of a uniform proton ensemble, while the occurrence of molecular exchange is taken into account. The influence is analyzed of an approach of a uniform proton ensemble toward the nearest neighboring paramagnetic ion system. It is shown that there exists a signal extinction effect, for which the critical distance was estimated.

J. Phys. Chem. B, 112 (32), 9630–9640, 2008. 10.1021/jp801133x

Study of the Adsorption of Organic Molecules on Transition Metal Exchanged Zeolites via Solid State NMR. Part 2: Adsorption of Organic Molecules on Zeolite NaX, CaX, and CaCoX

Kristof Houthoofd,* Piet J. Grobet, and Pierre A. Jacobs

Abstract: Literature [Denayer et al. Microporous Mesoporous Mater. 2007, 103, 1 and Denayer et al. Microporous Mesoporous Mater. 2007, 103, 11] shows that zeolite NaX exchanged with Ca2+ and Co2+ ions is able to remove cyclopentadiene (CPD) impurities from a 1-octene feed with high selectivity. In the present work, the adsorption of dicyclopentadiene (DCPD), CPD, 1-octene, and n-octane on zeolite X, exchanged with Ca2+ and/or Co2+ ions, has been investigated via 1H magic-angle spinning (MAS) NMR spectroscopy. The liquid adsorbate was dosed under inert atmosphere in an MAS rotor filled with dry adsorbent, at a pore filling degree of 70%. Next, the evolution in time was recorded of the 1H MAS NMR spectrum and the 1H spin−lattice and spin−spin relaxation times of the adsorbed components. For the various adsorbate−adsorbent systems, a plot is made of the signal intensity versus the square root of the contact time. It is found that, over the considered time interval, Fickian diffusion takes place. On the basis of the change in time of the spin−lattice relaxation time, a transport diffusion coefficient ranging between 1 and 2 × 10−15 m2·s−1 is calculated. Moreover, there appear to be two sorption regimes, with different diffusivities. A comparison is made between the 1H spin−lattice relaxation behavior of DCPD, 1-octene, and n-octane, indicating that 1-octene and n-octane are located closer to the paramagnetic ions than DCPD. The average distance between the adsorbate molecules and the paramagnetic ions is derived from relaxometric data. By analyzing the chemical shifts of the resonance lines, it is found that the π-interaction of CPD and 1-octene is stronger than that of DCPD.

Macromolecules, 41 (12), 4290–4295, 2008. 10.1021/ma8002483

NMR Characterization of Low Hard Segment Thermoplastic Polyurethane/Carbon Nanofiber Composites

Daniel S. Powers,† Richard A. Vaia,† Hilmar Koerner,‡ Jennifer Serres,§ and Peter A. Mirau*†

Abstract:Solid-state proton nuclear magnetic resonance (NMR) has been used to investigate the structure and dynamics of a thermoplastic polyurethane elastomer (TPE) filled with carbon nanofibers (CNF’s) for shape-memory applications. The TPE soft segments are above their glass transition temperature (Tg) at ambient temperature and give rise to relatively narrow (~2 kHz) signals in the solid-state proton spectrum. The introduction of CNF’s leads to a concentration-dependent shifting and broadening of the signals, while the proton spin−lattice and spin−spin relaxation times are not significantly altered, showing that the broadening is inhomogeneous and related to the difference in magnetic susceptibility between the TPE and the CNF’s. Proton spin diffusion experiments reveal the onset of stress-induced crystallinity as the samples are stretched to 60%, and stretching to 1000% leads to crystallization at the CNF surface and increased separation between the CNF’s and the mobile amorphous phase of the TPE. The implications for the mixing of polymers and CNF’s are considered.

Macromolecules, 41 (14), 5313–5321, 2008. 10.1021/ma702771s

From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Low and High Molecular Weight Limit

S. Kariyo, A. Brodin,§ C. Gainaru,§ A. Herrmann,§ H. Schick,§ V. N. Novikov, and E. A. Rössler*§

Abstract: Fast field cycling (FFC) NMR is applied to study the dispersion of the 1H spin−lattice relaxation in the low molecular weight glass-formers o-terphenyl, tristyrene, and oligomeric polybutadiene (PB, with M/gmol−1 = 355 and 466) over a broad temperature range (203−401 K). Differing from previous FFC NMR works, we analyze the relaxation data in the susceptibility form ω/T1(ω), and applying frequency−temperature superposition, master spectra are obtained covering up to 8 decades in frequency. In all cases solely the glassy dynamics (α-process) determines the relaxation behavior, and the Rouse unit is estimated to MR @ 500 g/mol. The time constant τα(T) in the range 10−11−10−6 s is extracted, which agrees well with those measured at the same time by dielectric spectroscopy. For the high molecular weight PB (M/gmol−1 = 56 500, 87 000, 314 000, and 817 000) pronounced polymer effects are observed at low frequencies (ωτα ≪ 1) which are isolated from the total spectrum by subtracting the “glass spectrum” as obtained from low molecular PB. We argue that unless the underlying α-relaxation is properly accounted for, the apparent power law spectrum does not reflect the actual polymer dynamics.

Macromolecules, 41 (14), 5322–5332, 2008. 10.1021/ma702758j

From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Rouse Regime

S. Kariyo, A. Brodin,§ C. Gainaru,§ A. Herrmann,§ J. Hintermeyer,§ H. Schick,§ V. N. Novikov, and E. A. Rössler*§

Abstract: We apply fast field cycling NMR to study the dispersion of the 1H spin−lattice relaxation time T1(ω) of linear 1,4-polybutadienes with molecular weight M (g/mol) ranging from M = 355 to 817 000. By this, the crossover from glassy dynamics through Rouse to reptation becomes accessible. Analyzing the data in the susceptibility form ω/T1(ω) and applying frequency−temperature superposition, spectra extending over up to 8 decades in ω are obtained. Characteristic polymer spectra are revealed when the underlying glassy dynamics are accounted for. Instead of describing the unentangled melt by the full Rouse mode spectrum, the emergence of a limited number of modes is identified which saturates when entanglement sets in. A quantitative analysis yields the molecular weight of a Rouse unit MR @ 500, and the entanglement weight Me @ 2000, at which first entanglement effects are observed. Moreover, the dynamic order parameter S(M) and the behavior of the terminal time τmax(M) are obtained. Both quantities allow to identify three dynamic regimes, namely simple liquid, Rouse, and reptation dynamics. The temperature dependence of the segmental relaxation time τs(T) coincides with the corresponding dielectric relaxation times which were measured additionally, and the M dependence of the glass transition temperature Tg shows distinctive kinks at MR and Me, indicating that glassy dynamics are modified by polymer dynamics.

Organometallics, 27 (15), 3633–3634, 2008. 10.1021/om800399x

Quantitative Tin Loading Determination of Supported Catalysts by 119Sn HRMAS NMR using a Calibrated Internal Signal (ERETIC)
Vanja Pinoie, Monique Biesemans,
* and Rudolph Willem

Abstract: As an alternative to tedious elemental analysis, tin loading of a grafted organotin catalyst is quantified using an electronic reference (ERETIC) in 119Sn HRMAS NMR. The results are in excellent agreement with elemental analysis data and display a significantly higher precision.

Monday, August 04, 2008

Al's Update

Quantitative prediction of gas-phase 19F nuclear magnetic shielding constants
J. Chem. Phys. 128, 244111 (2008)
Michael E. Harding, Michael Lenhart, Alexander A. Auer, and Jürgen Gauss
Benchmark calculations of 19F nuclear magnetic shielding constants are presented for a set of 28 molecules. Near-quantitative accuracy (ca. 2 ppm deviation from experiment) is achieved if (1) electron correlation is adequately treated by employing the coupled-cluster singles and doubles (CCSD) model augmented by a perturbative correction for triple excitations [CCSD(T)], (2) large (uncontracted) basis sets are used, (3) gauge-including atomic orbitals are used to ensure gauge-origin independence, (4) calculations are performed at accurate equilibrium geometries [obtained from CCSD(T)/cc-pVTZ calculations correlating all electrons], and (5) vibrational averaging and temperature corrections via second-order vibrational perturbation theory (VPT2) are included. For the CCSD(T)/13s9p4d3f calculations corrected for vibrational effects, mean and standard deviation from experiment are −1.9 and 1.6 ppm, respectively. Less elaborate theoretical treatments result in larger errors. Consideration of relative shifts can reduce the mean deviation (through an appropriately chosen reference compound), but does not change the standard deviation. Density-functional theory calculations of absolute and relative 19F nuclear magnetic shielding constants are found to be, at best, as accurate as the corresponding Hartree–Fock self-consistent-field calculations and are not improved by consideration of vibrational effects. Molecular systems containing fluorine-oxygen, fluorine-nitrogen, and fluorine-fluorine bonds are found to be more challenging than the other investigated molecules for the considered theoretical methods.

Structural and Spectroscopic Impact of Tuning the Stereochemical Activity of the Lone Pair in Lead(II) Cyanoaurate Coordination Polymers via Ancillary Ligands
Inorg. Chem., 47 (14), 6353–6363, 2008
Michael J. Katz, Vladimir K. Michaelis, Pedro M. Aguiar, Renante Yson, Haiyan Lu, Harini Kaluarachchi, Raymond J. Batchelor, Georg Schreckenbach, Scott Kroeker, Howard H. Patterson, and Daniel B. Leznoff
The reaction of Pb(ClO4)2·xH2O, an ancillary ligand L, and two equivalents of Au(CN)2− gave a series of crystalline coordination polymers, which were structurally characterized. The ligands were chosen to represent a range of increasing basicity, to influence the stereochemical activity (i.e., p-orbital character) of the Pb(II) lone pair. The Pb(II) center in [Pb(1,10-phenanthroline)2][Au(CN)2]2 (1) is 8-coordinate, with a stereochemically inactive lone pair; all 8 Pb−N bonds are similar. The Au(CN)2− units propagate a 2-D brick-wall structure. In [Pb(2,2′-bipyridine)2][Au(CN)2]2 (2), the 8-coordinate Pb(II) center has asymmetric Pb−N bond lengths, indicating moderate lone pair stereochemical activity; the supramolecular structure forms a 1-D chain/ribbon motif. For [Pb(ethylenediamine)][Au(CN)2]2 (3), the Pb(II) is only 5-coordinate and extremely asymmetric, with Pb−N bond lengths from 2.123(7) to 3.035(9) Å; a rare Pb−Au contact of 3.5494(5) Å is also observed. The Au(CN)2− units connect the Pb(ethylenediamine) centers to form 1-D zigzag chains which stack via Au−Au interactions of 3.3221(5) Å to yield a 2-D sheet. 207Pb MAS NMR of the polymers indicates an increase in both the chemical shielding span and isotropic chemical shift with increasing Pb(II) coordination sphere anisotropy (from δiso = −2970 and Ω = 740 for 1 to δiso = −448 and Ω = 3980 for 3). The shielding anisotropy is positively correlated with Pb(II) p-character, and reflects a direct connection between the NMR parameters and lone-pair activity. Solid-state variable-temperature luminescence measurements indicate that the emission bands at 520 and 494 nm, for 1 and 2, respectively, can be attributed to Pb → L transitions, by comparison with simple [Pb(L)2](ClO4)2 salts. In contrast, two emission bands for 3 at 408 and 440 nm are assignable to Au−Au and Pb−Au-based transitions, respectively, as supported by single-point density-functional theory calculations on models of 3.

Cupric Siliconiobate. Synthesis and Solid-State Studies of a Pseudosandwich-Type Heteropolyanion
Inorg. Chem., 47 (17), 7834–7839, 2008

Travis M. Anderson, Todd M. Alam, Mark A. Rodriguez, Joel N. Bixler, Wenqian Xu, John B. Parise, and May Nyman
The Na+ and [Cu(en)2(H2O)2]2+ (en = ethylenediamine) salt of a pseudosandwich-type heteropolyniobate forms upon prolonged heating of Cu(NO3)2 and hydrated Na14[(SiOH)2Si2Nb16O54] in a mixed water−en solution. The structure [a = 14.992(2) Å, b = 25.426(4) Å, c = 30.046(4) Å, orthorhombic, Pnn2, R1 = 6.04%, based on 25869 unique reflections] consists of two [Na(SiOH)2Si2Nb16O54]13− units linked by six sodium cations, and this sandwich is charge-balanced by five [Cu(en)2(H2O)2]2+ complexes, seven protons, and three additional sodium atoms (all per a sandwich-type cluster). Diffuse-reflectance UV−vis indicates that there is a λmax at 383 nm for the CuII d−d transition and the 29Si MAS NMR spectrum has two peaks at −78.2 ppm (151 Hz) and −75.5 ppm (257 Hz) for the two pairs of symmetry-equivalent internal [SiO4]4– and external [SiO3(OH)]3− tetrahedra, respectively. Unlike tungsten-based sandwich-type complexes, the [Na(SiOH)2Si2Nb16O54]13− units are linked exclusively by Na+ instead of one or more d-electron metals.

On the Structure of Amorphous Calcium Carbonate—A Detailed Study by Solid-State NMR Spectroscopy
Inorg. Chem., 47 (17), 7874–7879, 2008

Holger Nebel, Markus Neumann, Christian Mayer, and Matthias Epple
The calcium carbonate phases calcite, aragonite, vaterite, monohydrocalcite (calcium carbonate monohydrate), and ikaite (calcium carbonate hexahydrate) were studied by solid-state NMR spectroscopy (1H and 13C). Further model compounds were sodium hydrogencarbonate, potassium hydrogencarbonate, and calcium hydroxide. With the help of these data, the structure of synthetically prepared additive-free amorphous calcium carbonate (ACC) was analyzed. ACC contains molecular water (as H2O), a small amount of mobile hydroxide, and no hydrogencarbonate. This supports the concept of ACC as a transient precursor in the formation of calcium carbonate biominerals.

Binding Properties of Solvatochromic Indicators [Cu(X)(acac)(tmen)] (X = PF6− and BF4−, acac− = Acetylacetonate, tmen = N,N,N′,N′-Tetramethylethylenediamine) in Solution and the Solid State
ASAP Inorg. Chem., ASAP Article, 10.1021/ic800685z Web Release Date: July 25, 2008
Shin-ichiro Noro, Nobuhiro Yanai, Susumu Kitagawa, Tomoyuki Akutagawa, and Takayoshi Nakamura
The solvatochromic indicator [Cu(acac)(tmen)(H2O)]·PF6 (1·H2O) has been synthesized and crystallographically characterized. 1·H2O binds an H2O molecule at the Cu(II) axial site, while the PF6− anion is coordination free. The binding properties of [Cu(PF6)(acac)(tmen)] (1) and [Cu(BF4)(acac)(tmen)] (2) have been investigated in solution and the solid state. The donor number of the PF6− anion (DNPF6) was determined from the UV−vis spectra of 1 in 1,2-dichloroethane. The value of DNPF6 of the PF6− anion is slightly larger than that of the tetraphenylborate anion (BPh4−), which is known as a noncoordinating anion. In the solid state, 1 and 2 reversibly bind and release H2O molecules at the Cu(II) axial sites. The coordinated H2O molecules in 2 are more easily removed than those in 1 because of the strong Lewis basicity of the BF4− anion compared to the PF6− ion. The lower melting point of 1 versus 2 is attributed to the loose binding of the PF6− anions to the Cu(II) centers, which induces the dynamic nature of the crystal.

17O Solid-State NMR and First-Principles Calculations of Sodium Trimetaphosphate (Na3P3O9), Tripolyphosphate (Na5P3O10), and Pyrophosphate (Na4P2O7)
Inorg. Chem., 47 (16), 7327–7337, 2008

Filipe Vasconcelos, Sylvain Cristol, Jean-Francois Paul, Grégory Tricot, Jean-Paul Amoureux, Lionel Montagne, Francesco Mauri, and Laurent Delevoye
The assignment of high-field (18.8 T) 17O MAS and 3QMAS spectra has been completed by use of first-principles calculations for three crystalline sodium phosphates, Na3P3O9, Na5P3O10, and Na4P2O7. In Na3P3O9, the calculated parameters, quadrupolar constant (CQ), quadrupolar asymmetry (ηQ), and the isotropic chemical shift (δcs) correspond to those deduced experimentally, and the calculation is mandatory to achieve a complete assignment. For the sodium tripolyphosphate Na5P3O10, the situation is more complex because of the free rotation of the end-chain phosphate groups. The assignment obtained with ab initio calculations can however be confirmed by the 17O{31P} MAS-J-HMQC spectrum. Na4P2O7 17O MAS and 3QMAS spectra show a complex pattern in agreement with the computed NMR parameters, which indicate that all of the oxygens exhibit very similar values. These results are related to structural data to better understand the influence of the oxygen environment on the NMR parameters. The findings are used to interpret those results observed on a binary sodium phosphate glass.

Sunday, August 03, 2008

Magn. Reson. Chem. (MRC) up to July 30, 2008

Magn. Reson. Chem. up to July 30, 2008

Correlating sideband patterns with powder patterns for accurate determination of chemical shift parameters in solid-state NMR
from Magnetic Resonance in Chemistry by M. S. Ironside, D. G. Reid, M. J. Duer

Powder patterns and sideband patterns have different strengths when it comes to using them to determine chemical shift parameters. Here, we show that chemical shift parameters can be determined with high accuracy by analysing the correlation pattern from a 2D experiment which correlates a powder pattern in the indirect dimension with a sideband pattern in the direct dimension. The chemical shift parameters so determined have greater accuracy than those obtained by analysing a sideband or powder pattern alone, for the same signal-to-noise ratio. This method can be applied for both resolved correlation patterns and to cases where two components share similar isotropic chemical shifts. The methodology is demonstrated in this paper, both theoretically and experimentally, on the 31P signals of the bis-phosphonate drug, pamidronate. Copyright © 2008 John Wiley & Sons, Ltd.
Digital Object Identifier (DOI)

Swept-frequency two-pulse phase modulation (SWf-TPPM) sequences with linear sweep profile for heteronuclear decoupling in solid-state NMR
from Magnetic Resonance in Chemistry by C. Vinod Chandran, P. K. Madhu, Narayanan D. Kurur, Thomas Bräuniger

Recently, a pulse scheme for heteronuclear spin decoupling in solid-state NMR, called swept-frequency two-pulse phase modulation (SWf-TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency-sweep profile can be varied to achieve optimal efficiency for crystalline and liquid-crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SWf-TPPM sequences with tangential sweep profiles (SWftan-TPPM) and linear sweep profiles (SWflin-TPPM). Using the 13CH2 resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut-off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise. Copyright © 2008 John Wiley & Sons, Ltd.
Digital Object Identifier (DOI)

Progress in NMR Spectroscopy - up to V. 53, iss.3 2008

Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 53, Issue 3, October 2008, Pages 128-191

Practical aspects of 51V and 93Nb solid-state NMR spectroscopy and applications to oxide materials

O.B. Lapina, D.F. Khabibulin, A.A. Shubin and V.V. Terskikh
Keywords: Solid-state NMR; Modern NMR techniques; NMR in catalysis; Vanadium oxide catalysts; Niobium oxide catalysts; Vanadia; Niobia; NMR of Group VB elements; 51V NMR; 93Nb NMR; 181Ta NMR

Abbreviations: CP, cross polarization; CS, chemical shielding; CSA, chemical shift anisotropy; CT, central transition; CW, continuous wave; CW-NMR, continuous wave nuclear magnetic resonance; DAS, dynamic-angle spinning; DeNOx, nitrogen oxide abatement; DFT, density functional theory; DOR, double rotation; DQ, double-quantum; DQ STMAS, double-quantum satellite transition magic-angle spinning; EDAX, energy dispersive X-ray spectroscopy; EFG, electric field gradient; ESR, electron spin resonance; FID, free induction decay; FT-NMR, Fourier transform nuclear magnetic resonance; GIPAW, gauge-including projected augmented-wave; HETCOR, heteronuclear correlation spectroscopy; HFI, hyperfine interaction tensor; HFMAS, high-field magic-angle spinning; HREM, high resolution electron microscopy; HSMAS, high-speed magic-angle spinning; KTN, KTa(1−x)NbxO3; MAS, magic-angle spinning; MASSA, magic-angle spinning and static spectra analysis; MQMAS, multiple quantum magic-angle spinning; MQ, multiple quantum; NMR, nuclear magnetic resonance; NQR, nuclear quadrupolar resonance; QCPMG, quadrupolar Carr-Purcell Meiboom-Gill; PBN, Ba-substituted Pb(Mg1/3Nb2/3)O3; PMN, Pb(Mg1/3Nb2/3)O3; PMN/PT, (1−x)Pb(Mg1/3Nb2/3)O3/xPbTiO3; PSN, Sc-substituted Pb(Mg1/3Nb2/3)O3; PZN, Zr-substituted Pb(Mg1/3Nb2/3)O3; REAPDOR, rotational echo adiabatic passage double resonance; REDOR, rotational echo double resonance; RF, radio frequency; SATRAS, satellite transition spectroscopy; SBV, Strongly bound vanadium; SEDOR, spin–echo double resonance; ST, satellite transition; STMAS, satellite transition magic-angle spinning; SSTMAS, spinning sidebands analysis of selected transitions; TRAPDOR, transfer of population in double resonance; VOCS, variable offset cumulative spectrum

Friday, August 01, 2008

Joel's Journal Update

Improved Description of Nuclear Magnetic Resonance Chemical Shielding Constants Using the M06-L Meta-Generalized-Gradient-Approximation Density Functional
Yan Zhao and Donald g. Truhlar
The performance of the M06-L density functional has been tested for four databases of NMR isotropic chemical shielding constants. Comparison with the B3LYP, BLYP, HCTH, KT1, KT2, LSDA, OPBE, OLYP, PBE, TPSS, and VSXC functionals shows that M06-L has improved performance for calculating NMR chemical shielding constants, especially for highly correlated systems. We also found that VSXC and M06-L have encouraging accuracy for calculating 13C chemical shielding constants, and both functionals perform very well for the chemical shielding constants in the o-benzyne molecule.

Polymorphism in an Amyloid-Like Fibril-Forming Model Peptide
René Verel, Ivan T. Tomka, Carlo Bertozzi, Riccardo Cadalbert, Richard A. Kammerer, Michel O. Steinmetz, Beat H. Meier
Angwandte (2008)47,5842.
The structural basis for polymorphism in amyloids is unraveled with a model system. The hydrogen-bonding pattern within the sheets of fibrils is strongly influenced by the pH of the solution from which the fibrils are formed. Solid-state NMR spectroscopy experiments allow quantification of the relative amounts of two different -sheet structures over the pH range 2.0-7.3.