-General interest 31P NMR. Nice distance measurements via spin diffusion.
Chem. Mater., 18 (26), 6333 -6338, 2006. 10.1021/cm0613410 S0897-4756(06)01341-X Web Release Date: November 24, 2006
Detection of Nanometer-Scale Mixing in Phosphate-Glass/Polyamide-6 Hybrids by 1H-31P NMR
A. Rawal, K. Urman, J. U. Otaigbe,* and K. Schmidt-Rohr*
Abstract: The size of phosphate-glass (Pglass) particles dispersed in a polyamide-6 (PA6) matrix by melt blending has been characterized by 1H-31P solid-state nuclear magnetic resonance (NMR). 1H spin diffusion from ~75% of the 1H in the glass to the polyamide is observed within 50 ms, indicating proximity on a 30 nm scale. Fast dephasing of a quarter of the 31P magnetization by dipolar couplings to polyamide protons in 31P{1H} heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP) NMR shows that ~25% of the Pglass is within 0.5 nm from the polyamide. This is confirmed by 1H-31P heteronuclear correlation NMR spectra with inverse T2,H filtering, which document relatively fast (1 ms) cross polarization from PA6 protons, identified by their upfield chemical shift and short transverse relaxation time T2,H, to a significant fraction of 31P in the glass. The 31P spectrum associated with the polyamide 1H reveals that the phosphate sites near the polyamide matrix are chemically altered but differently than previously observed in Pglass-polyethylene hybrids, where no such contact was proven. As expected, the 31P sites that cross-polarize from the polyamide protons also exhibit pronounced dephasing in 31P{1H} HARDSHIP experiments. HARDSHIP experiments after cross polarization and 31P spin diffusion experiments indicate that the ~25% of phosphate that is within 0.5 nm from the polyamide is not dispersed in the polymer but on the surface of ~10 nm diameter Pglass particles. This study represents the first conclusive evidence of intimate mixing of the hybrid components. Further, it suggests that this is an excellent model system for exploring new routes for driving organic polymers and inorganic glass to self-assemble into useful organic/inorganic hybrid materials
-Interesting study on a drug inside microporous materials
Chem. Mater., 18 (26), 6382 -6390, 2006. 10.1021/cm061551c S0897-4756(06)01551-1 Web Release Date: December 19, 2006
Solid-State NMR Study of Ibuprofen Confined in MCM-41 Material
Thierry Azaïs,* Corine Tourné-Péteilh, Fabien Aussenac, Niki Baccile, Cristina Coelho, Jean-Marie Devoisselle,* and Florence Babonneau
Abstract: Ibuprofen (an anti-inflammatory drug that is a crystalline solid at ambient temperature) has been encapsulated in MCM-41 silica matrices with different pore diameters (35 and 116 Å). Its behavior has been investigated by magic angle spinning (MAS) 1H, 13C, and 29Si solid-state NMR spectroscopy at ambient and low temperature. This study reveals an original physical state of the drug in such materials. At ambient temperature, ibuprofen is not in a solid state (crystalline or amorphous) and is extremely mobile inside the pores, with higher mobility in the largest pores (116 Å). The interaction between ibuprofen and the silica surface is weak, which favors fast drug release from this material in a simulated intestinal or gastric fluid. The quasi-liquid behavior of ibuprofen allows the use of NMR pulse sequences issued from solution-state NMR, such as the INEPT sequence, to characterize these solid-state samples. The solid-state MAS NMR study shows that the proton of the carboxylic acid group of ibuprofen is in a chemical exchange at ambient temperature. Furthermore, at low temperature (down to 223 K), NMR spectroscopy results show that ibuprofen is able to crystallize inside the largest pores (116 Å), whereas a glassy state is obtained for the smallest ones (35 Å).
-91Zr and 29Si studies of surface coated metal oxides. A couple of cites of our work on 91Zr. NMR done by Klaus Muller
Chem. Mater., 18 (25), 6019 -6030, 2006. 10.1021/cm061403m S0897-4756(06)01403-7 Structural Evolution upon Thermal Heating of Nanostructured Inorganic-Organic Hybrid Materials to Binary Oxides MO2-SiO2 (M = Hf, Zr) as Evaluated by Solid-State NMR and FTIR Spectroscopy
Lidia Armelao, Silvia Gross,* Klaus Müller,* Giuseppe Pace, Eugenio Tondello, Otgontuul Tsetsgee, and Andrea Zattin
Abstract:
The structural and compositional evolution of inorganic-organic silica-based hybrid materials and their conversion to mixed oxides, consisting of host silica with variable amounts of zirconia or hafnia (1:1 Si:M, 40:1 Si:M, M = Zr, Hf), was studied by multinuclear solid-state NMR spectroscopy, FTIR spectroscopy, and thermogravimetry. It is shown that the as-prepared materials, composed of M4O2(OMc)12 oxoclusters (M = Zr, Hf; OMc = methacrylate) and methacryloxymethyltriethoxysilane (MAPTMS), are not completely polymerized. Rather, a finite number of double bonds remain independent of the actual sample composition. Thermolysis between 300 and 500 C is accompanied by drastic changes in the structural composition, as reflected by the complete loss of all organic components. The incorporation of oxoclusters is found to catalyze the cleavage of Si-C bonds. At the same time, continuous alterations in the inorganic/oxide part are registered. The degree of condensation, as derived from the 29Si NMR data, increases steadily with calcination temperature and is found to depend on the oxocluster amount. Thus, for the samples with the highest oxocluster content, a pronounced temperature dependence for the degree of condensation is observed that is absent for the samples with a small oxocluster content or for pure MAPTMS. 91Zr NMR measurements on the sample with the highest zirconium content indicate that upon calcination at 1000 C, only a small amount of crystalline zirconia with tetragonal coordination exists. The major zirconia fraction distributed in the silica matrix is therefore in an amorphous state.
-Rod, 55Mn studies on Manganese Carbonyls
Inorg. Chem., 45 (21), 8492 -8499, 2006. 10.1021/ic0608445 S0020-1669(06)00844-5
Ultrahigh-Field NMR Spectroscopy of Quadrupolar Transition Metals: 55Mn NMR of Several Solid Manganese Carbonyls
Kristopher J. Ooms, Kirk W. Feindel, Victor V. Terskikh, and Roderick E. Wasylishen*
Abstract: 55Mn NMR spectra acquired at 21.14 T ( L(55Mn) = 223.1 MHz) are presented and demonstrate the advantages of using ultrahigh magnetic fields for characterizing the chemical shift tensors of several manganese carbonyls: 5-CpMn(CO)3, Mn2(CO)10, and (CO)5MnMPh3 (M = Ge, Sn, Pb). For the compounds investigated, the anisotropies of the manganese chemical shift tensors are less than 250 ppm except for 5-CpMn(CO)3, which has an anisotropy of 920 ppm. At 21.14 T, one can excite the entire mI = 1/2 mI = -1/2 central transition of 5-CpMn(CO)3, which has a breadth of approximately 700 kHz. The breadth arises from second-order quadrupolar broadening due to the 55Mn quadrupolar coupling constant of 64.3 MHz, as well as the anisotropic shielding. Subtle variations in the electric field gradient tensors at the manganese are observed for crystallographically unique sites in two of the solid pentacarbonyls, resulting in measurably different CQ values. MQMAS experiments are able to distinguish four magnetically unique Mn sites in (CO)5MnPbPh3, each with slightly different values of iso, CQ, and Q.
-Solid-state 119Sn NMR
Inorg. Chem., 45 (22), 9132 -9136, 2006. 10.1021/ic060983m S0020-1669(06)00983-9
Solid-State 119Sn NMR and Mössbauer Spectroscopy of "Distannynes": Evidence for Large Structural Differences in the Crystalline Phase
Geoffrey H. Spikes, Jason R. Giuliani, Matthew P. Augustine, Israel Nowik, Rolfe H. Herber, and Philip P. Power*
Abstract: The "distannynes" Ar'SnSnAr' (Ar' = C6H3-2,6(C6H3-2,6-Pri2)2) and Ar*SnSnAr* (Ar* = C6H3-2,6(C6H2-2,4,6-Pri3)2) were examined by solid-state 119Sn NMR and Mössbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar'SnSnAr') or presence (Ar*SnSnAr*) of a para-Pri group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn-Sn bond for Ar*SnSnAr* in comparison to the wider Sn-Sn-C angle (125.24(7) ) and shorter Sn-Sn bond length (2.6675(4)Å) determined from the crystal structure of Ar'SnSnAr'. The differences are consistent with previously published calculations by Nagase and Takagi for Ar*SnSnAr*.
-23Na, 27Al, and 19F SSNMR. WIEN2K calculations.
Inorg. Chem., 45 (25), 10215 -10223, 2006. 10.1021/ic061348j S0020-1669(06)01348-6
Multinuclear High-Resolution NMR Study of Compounds from the Ternary System NaF-CaF2-AlF3: from Determination to Modeling of NMR Parameters
C. Martineau,* M. Body, C. Legein, G. Silly, J.-Y. Buzaré, and F. Fayon
Abstract:27Al and 23Na NMR satellite transition spectroscopy and 3Q magic-angle-spinning spectra are recorded for three compounds from the ternary NaF-CaF2-AlF3 system. The quadrupolar frequency Q, asymmetry parameter Q, and isotropic chemical shift iso are extracted from the spectrum reconstructions for five aluminum and four sodium sites. The quadrupolar parameters are calculated using the LAPW-based ab initio code WIEN2k. It is necessary to perform a structure optimization of all compounds to ensure a fine agreement between experimental and calculated parameters. By a comparison of experimental and calculated values, an attribution of all of the 27Al and 23Na NMR lines to the crystallographic sites is achieved. High-speed 19F NMR MAS spectra are recorded and reconstructed for the same compounds, leading to the determination of 18 isotropic chemical shifts. The superposition model developed by Bureau et al. is used, allowing a bijective assignment of the 19F NMR lines to the crystallographic sites.
-Dave Bryce, 31P NMR.
Inorg. Chem., 45 (25), 10293 -10299, 2006. 10.1021/ic061021i S0020-1669(06)01021-4
A Chelate-Stabilized Ruthenium( -pyrrolato) Complex: Resolving Ambiguities in Nuclearity and Coordination Geometry through 1H PGSE and 31P Solid-State NMR Studies
Heather M. Foucault, David L. Bryce,* and Deryn E. Fogg*
Abstract: Reaction of RuCl2(PPh3)3 with LiNN' (NN' = 2-[(2,6-diisopropylphenyl)imino]pyrrolide) affords a single product, with the empirical formula RuCl[(2,6-iPr2C6H3)N=CHC4H3N](PPh3)2. We identify this species as a -pyrrolato complex, [Ru(NN')(PPh3)2]2( -Cl)2 (3b), rather than mononuclear RuCl(NN')(PPh3)2 (3a), on the basis of detailed 1D and 2D NMR characterization in solution and in the solid state. Retention of the chelating, -bound iminopyrrolato unit within 3b, despite the presence of labile (dative) chloride and PPh3 donors, indicates that the chelate effect is sufficient to inhibit isomerization of 3b to a piano-stool, -pyrrolato structure. 2D COSY, SECSY, and J-resolved solid-state 31P NMR experiments confirm that the PPh3 ligands on each metal center are magnetically and crystallographically inequivalent, and 31P CP/MAS NMR experiments reveal the largest 99Ru-31P spin-spin coupling constant (1J(99Ru,31P) = 244 ± 20 Hz) yet measured. Finally, 31P dipolar-chemical shift spectroscopy is applied to determine benchmark phosphorus chemical shift tensors for phosphine ligands in hexacoordinate ruthenium complexes.
-Massiot has some crazy 19F NMR specra!!
Inorg. Chem., 45 (26), 10636 -10641, 2006. 10.1021/ic061339a S0020-1669(06)01339-5
19F High Magnetic Field NMR Study of -ZrF4 and CeF4: From Spectra Reconstruction to Correlation between Fluorine Sites and 19F Isotropic Chemical Shifts
C. Legein,* F. Fayon, C. Martineau, M. Body, J.-Y. Buzaré, D. Massiot, E. Durand, A. Tressaud, A. Demourgues, O. Péron, and B. Boulard
Abstract:High magnetic field and high spinning frequency one- and two-dimensional one-pulse MAS 19F NMR spectra of -ZrF4 and CeF4 were recorded and reconstructed allowing the accurate determination of the 19F chemical shift tensor parameters for the seven different crystallographic fluorine sites of each compound. The attributions of the NMR resonances are performed using the superposition model for 19F isotropic chemical shift calculation initially proposed by Bureau et al. (Bureau, B.; Silly, G.; Emery, J.; Buzaré, J.-Y. Chem. Phys. 1999, 249, 85-104). A satisfactory reliability is reached with a root-mean-square (rms) deviation between calculated and measured isotropic chemical shift values equal to 1.5 and 3.5 ppm for -ZrF4 and CeF4, respectively.
-27Al and 19F SSNMR
Inorg. Chem., 45 (26), 10807 -10814, 2006. 10.1021/ic061493x S0020-1669(06)01493-5
F/Cl-Exchange on AlCl3-Pyridine Adducts: Synthesis and Characterization of trans-Difluoro-tetrakis-pyridine-aluminum-chloride, [AlF2(Py)4]+Cl-
Anton Dimitrov, Detlef Heidemann, and Erhard Kemnitz*
Abstract: Whereas liquid CCl3F reacts with solid AlCl3 exothermically under chlorine-fluorine-exchange already above -20 C, no reaction takes place between CCl3F and the pyridine complexes of AlCl3 (AlCl3·Py, AlCl3·2Py, or AlCl3·3Py) up to 100 C. The desired chlorine by fluorine substitution on the monomer AlCl3-pyridine adducts occurs, however, easily using Me3SiF as fluorinating agent. By reacting AlCl3·3Py with Me3SiF (even up to 10-fold stoichiometric excess) in pyridine as a solvent, only two of the three Cl atoms can be substituted by fluorine, leading in good yield to the new "mixed aluminum halide", AlF2Cl·4Py. Actually, it represents the first example of a stable solid donor-acceptor adduct of an aluminum-III halide with two different halogens of defined stoichiometry. It was characterized by multinuclear solid-state NMR (27Al and 19F), IR spectroscopy, as well as single-crystal structure analysis. The new compound has an ionic solid-state structure with helical trans-octahedral [(Py)4AlF2]+ cations and isolated Cl- anions. The comparison of its 27Al MAS solid-state NMR spectra with those of a compound bearing the analogous [(Py)4AlCl2]+ cation reveals an extreme increase in the quadrupolar coupling constants, from 0.24 MHz in case of the chlorine cation to about 16 MHz in case of the new [(Py)4AlF2]+ cation.
-Some cool 14N spectra, Hans Jakobsen of course
Inorg. Chem., 45 (26), 10873 -10881, 2006. 10.1021/ic061197k S0020-1669(06)01197-9
Probing Crystal Structures and Transformation Reactions of Ammonium Molybdates by 14N MAS NMR Spectroscopy
Anders R. Hove, Henrik Bilds e, J rgen Skibsted, Michael Brorson, and Hans J. Jakobsen*
Abstract:The unique high-resolution feature offered by 14N magic-angle spinning (MAS) NMR spectroscopy of ammonium ions has been used to characterize the crystal structures of various ammonium molybdates by their 14N quadrupole coupling parameters, i.e., CQ, the quadrupole coupling constant, and Q, the asymmetry parameter. Two polymorphs of diammonium monomolybdate, (NH4)2MoO4, recently structurally characterized by single-crystal X-ray diffraction (XRD) and named mS60 and mP60, show distinct but different 14N MAS NMR spectra from each of which two sets of characteristic 14N CQ and Q values have been obtained. Similarly, the well-characterized ammonium polymolybdates (NH4)2Mo2O7, (NH4)6Mo7O24·4H2O, and (NH4)6Mo8O27·4H2O also give rise to distinct and characteristic 14N MAS NMR spectra. In particular, it is noted that simulation of the experimental (NH4)6Mo7O24·4H2O spectrum requires an iterative fit with six independent NH4+ sites. For the slow spinning frequencies employed ( r = 1500-3000 Hz), all 14N MAS NMR spectra of the ammonium molybdates in this study are fingerprints of their identity. These different 14N MAS NMR fingerprints are shown to be an efficient tool in qualitative and quantitative assessment of the decomposition of (NH4)2MoO4 in humid air. Finally, by a combination of the 14N and 95Mo MAS NMR experiments performed here, it has become clear that a recent report of the 95Mo MAS spectra and data for the mS60 and mP60 polymorphs of (NH4)2MoO4 are erroneous because the sample examined had decomposed to (NH4)2Mo2O7.
-Ripmeester and Igor
J. Phys. Chem. B, 111 (3), 491 -495, 2007. 10.1021/jp0667994 S1520-6106(06)06799-X
39K NMR of Solid Potassium Salts at 21 T: Effect of Quadrupolar and Chemical Shift Tensors
Igor L. Moudrakovski* and John A. Ripmeester
Abstract:39K Solid State NMR spectra (static and magic angle spinning (MAS)) on a set of potassium salts measured at 21.14 T show that the chemical shift range for K+ ions in diamagnetic salts is well in excess of 100 ppm contrary to previous assumptions that it was quite small. Inequivalent potassium sites in crystals can be resolved through differences in chemical shifts, with chemically similar sites showing differences of over 10 ppm. The quadrupolar coupling constants obtained from MAS and solid echo experiments on powders cover the range from zero for potassium in cubic environments in halides to over 3 MHz for the highly asymmetric sites in K2CO3. Although the quadrupolar effects generally dominate the 39K spectra, in several instances, we have observed subtle but significant contributions of chemical shift anisotropy with values up to 45 ppm, a first such observation. Careful analysis of static and MAS spectra allows the observation of the various chemical shift and quadrupole coupling tensor components as well as their relative orientations, thereby demonstrating that high-field 39K NMR spectroscopy in the solid state has a substantial sensitivity to the local environment with parameters that will be of considerable value in materials characterization and electronic structure studies.
-Solid-state 15N NMR to observe phase transitions
J. Phys. Chem. B, 111 (4), 677 -681, 2007. 10.1021/jp0649347 S1520-6106(06)04934-0
High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order-Disorder and Displacive Behavior
O. Gunaydin-Sen, R. Achey, N. S. Dalal,* A. Stowe, and T. Autrey
Department of Chemistry and Biochemistry and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, 32306, and Pacific Northwest National Laboratory, Richland, Washington 99352
Received: August 1, 2006
In Final Form: November 16, 2006
Abstract:
We report high resolution 15N NMR probing of the solid-solid phase transition of 15N-labeled ammonia borane (NH3BH3) at 225 K. Both the 15N isotropic chemical shift ( iso) and the spin-lattice relaxation rate (T1-1) exhibited strong anomalies around 225 K. The analysis of T1-1 using the Bloembergen, Purcell, and Pound model showed that the motional correlation time, , increased from about 1 to 100 ps and the corresponding Arrhenius activation energy increased from 6 to 14.5 kJ/mol on going through the transition toward lower temperatures. The temperature dependence of iso was interpreted by an extension of the Bayer model. The time scale of the underlying motion was found to be in a reasonable agreement with the T1-1 data. These results imply that the NH3 rotor motion plays a pivotal role in the transition mechanism and that the transition is of both order-disorder and displacive type
-Multi-nuclear NMR study. REDOR with quadrupoles.
J. Phys. Chem. B, 111 (5), 968 -978, 2007. 10.1021/jp065201p S1520-6106(06)05201-1
Structural Description of the Na2B4O7-Na3AlF6-TiO2 System. 2. A Multinuclear NMR Approach of Melts and Solids
Pierre Florian, Elena M. Anghel, and Catherine Bessada*
Abstract:A quantitative structural investigation of pseudo-binary Na2B4O7-[Na3AlF6-TiO2]11 was carried out by NMR spectroscopy. We applied high-resolution solid-state NMR on quenched samples and in situ high-temperature NMR spectroscopy on molten compositions to obtain a more accurate description of the melts. Consistent with our previous findings, two compositional ranges can be evidenced. Below 50 mol % Na2B4O7, the TiIV TiVI valence conversion prevails, leading to the formation of B(O,F)3 species at the expense of B(O,F)4 ones and a low average coordination number of aluminum; above 50 mol %, the system behaves mainly like the binary Na2B4O7-Na3AlF6 where Na3AlF6 is playing a network former role. The dominant oxyfluoro-species evidenced by double-resonance NMR in the quenched samples are BO2F2, BO3F, BO2F, BOF2, NaO7F, NaO6F2, and AlO4F with sodium in various coordination states, Na(O,F)8, Na(O,F)7, and Na(O,F)6. F-Ti bonds were found to be almost negligible whereas F-Al2, F-B, F-Na, and F-Al-Na bonds were clearly observed in the solid state
-27Al and 29Si studies of Mesopourous Silicates, Marek Pruski
J. Phys. Chem. C, 111 (3), 1480 -1486, 2007. 10.1021/jp0659913 S1932-7447(06)05991-7
Mesoporous Aluminum Silicate Catalyst with Single-Type Active Sites: Characterization by Solid-State NMR and Studies of Reactivity for Claisen Rearrangement Reactions
Yang Cai, Rajeev Kumar, Wei Huang, Brian G. Trewyn, Jerzy W. Wiench, Marek Pruski,* and Victor S.-Y. Lin*
Abstract:A mesoporous aluminum silicate (Al-MS) material has been successfully synthesized via a base-catalyzed co-condensation reaction. Solid-state NMR studies showed that the aluminum atoms are tetrahedrally coordinated and are stable up to at least 400 C. The double resonance 27Al-29Si NMR experiment provided first direct evidence that all Al atoms are surrounded by Si atoms forming Al-O-Si bonds in the framework. The silicon to aluminum atomic ratio at the surface (Si/Al)s is estimated at around 100, which exceeds the overall Si/Al ratio of 60. Reactivity study of the mesoporous aluminosilicate shows an excellent catalytic reactivity for the Claisen rearrangement of allyl phenyl ether despite the low surface concentration of Al
-27Al of Al2O3. Of interest to Joel?
J. Phys. Chem. C, 111 (4), 1579 -1583, 2007. 10.1021/jp0651945 S1932-7447(06)05194-6
27Al Triple-Quantum Magic-Angle Spinning Nuclear Magnetic Resonance Characterization of Nanostructured Alumina Materials
Hae Jin Kim,* Hyun Chul Lee, and Jae Sung Lee
Abstract:The nanostructured transition aluminas were synthesized from an aluminum alkoxide precursor in the presence of various surfactants under hydrothermal conditions without any organic additives. The synthesized nanostructured alumina materials showed different morphologies depending on surfactants with high surface area, thermal stability, and aluminum sites of different coordination. The 27Al triple-quantum (3Q) magic-angle spinning (MAS) NMR results showed that the samples prepared with cationic and nonionic surfactants consisted of mainly -Al2O3 phase and a small amount of -Al2O3 phase due to the presence of the distorted tetrahedral site, but that the samples with anionic and neutral surfactants were predominantly in the -Al2O3 phase. The experimental and calculated values of the electric field gradient (EFG) definitely suggested that cation vacancies were preferentially located at the octahedral sites in -Al2O3 whereas at the tetrahedral sites in -Al2O3.
-More SSNMR of zeolites
J. Phys. Chem. C, 111 (4), 1830 -1839, 2007. 10.1021/jp066498u S1932-7447(06)06498-3
Characterization of Cr-MCM-41 and Al,Cr-MCM-41 Mesoporous Catalysts for Gas-Phase Oxidative Dehydrogenation of Cyclohexane
Maria Lezanska,* Grzegorz S. Szymanski, Piotr Pietrzyk, Zbigniew Sojka, and Johannes A. Lercher
Abstract:The effects of the Cr concentration in hydrothermally synthesized Cr-MCM-41 and the impact of various postsynthesis treatments including grafting with alumina were investigated. Using physicochemical characterization by XRD, diffuse reflectance UV-vis spectroscopy, EPR spectroscopy, 29Si MAS NMR spectroscopy, H2 TPR, and acidity measurements, formation of mono- and dichromate surface species as well as CrV, dispersed CrIII, and clustered CrIII was detected, confirming the high speciation and valence versatility of the surface chromium. The roles of each species in the preparation stage, calcination, leaching, and grafting are discussed. Leaching resulted in removal of all isolated CrIII species, suggesting that CrIII is attached to the MCM-41 surface via silanol groups. The resulting materials exhibited low acidity, with both Lewis and Br nsted acid sites being present. The oxidative dehydrogenation (ODH) of cyclohexane was catalyzed by Cr-MCM-41 with a conversion of up to 25.7% in the temperature range of 533-633 K. The CrIII sites have been concluded to be responsible for cyclohexane ODH, but total activity was influenced by the presence of easily reducible CrVI at the beginning of the reaction. During the reaction, high-valence Cr ions were reduced to clustered Cr2O3 species.
- 13C SSNMR of methane hydrates.
J. Phys. Chem. C, 111 (5), 2341 -2346, 2007. 10.1021/jp066536+ S1932-7447(06)06536-8
NMR Investigation of Methane Hydrate Dissociation
Arvind Gupta, Steven F. Dec,* Carolyn A. Koh, and E. D. Sloan, Jr.
Abstract:The methane hydrate dissociation mechanism was studied on the molecular scale using 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Analysis of time-resolved 13C MAS NMR spectra for methane Structure I (sI) hydrate dissociation obtained by raising the temperature above the hydrate equilibrium conditions permitted the cage occupancy and pressure to be determined during this process. The relationship between NMR methane gas chemical shift, pressure, and temperature was developed, which allows estimating the system pressure in the sealed glass tube sample at any temperature. The large to small cage occupancy ratio remained constant during hydrate dissociation suggesting that there is no preferential dissociation of hydrate cavities and the whole unit cell decomposes during dissociation. This decomposition rate is virtually the same for both the large and the small cages in methane hydrate on a per cage basis. The similar decomposition rate of both cage types shows that the sI methane hydrate dissociation mechanism differs from the formation process where preferential formation of specific hydrate cages has been observed.
-J Phys Chem C: A Zeolite Journal
J. Phys. Chem. C, 111 (6), 2520 -2524, 2007. 10.1021/jp066578y S1932-7447(06)06578-2
Distribution of Aluminum in the Periodical Building Units of Faujasites
Tam s I. Kor nyi* and J nos B.Nagy
Abstract: Four NH4-Y faujasites (FAU) with different Si/Al ratios were characterized by 27Al and 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The quantitative contributions of the Al sites, defect-free Si(nAl), and silanol groups to the different double-six-ring (D6R) periodical building units (PerBUs) of the zeolite framework were calculated from the various Si/Al ratios and relative 27Al and 29Si NMR signal intensities. Four different PerBU systems were assumed in the FAU structure, but only the distribution of PerBUs containing three, two, or one Al atom pairs in body-diagonal positions of D6Rs followed the composition of the framework with appropriate precision in the studied composition range (Si/Al = 2.6-19.5). Contrary to BEA, FER, and MOR zeolites, the PerBUs of FAU do not contain Al atoms in unpaired "lone" positions.
-15N NMR of organic species interacting with TiO2, Raftery
J. Phys. Chem. C, 111 (6), 2738 -2748, 2007. 10.1021/jp0652289 S1932-7447(06)05228-9
15N Solid State NMR and EPR Characterization of N-Doped TiO2 Photocatalysts
Enrique A. Reyes-Garcia, Yanping Sun, Karla Reyes-Gil, and Daniel Raftery*
Abstract:The solid-state nuclear magnetic resonance (SSNMR) analysis and structural characterization of N-doped TiO2 nanoparticle and monolayer materials suitable for visible photocatalysis is reported. The SSNMR analysis of 15N-doped TiO2 synthesized using 15N-urea before calcination indicates formation of various amino functionalities of the type NH, NH2, NH3, and probably NH4+, while the NMR spectrum of the yellow powder that results from high-temperature calcination shows that these nitrogen species oxidize to form nitrate. These and nonisotopically labeled materials were characterized also by X-ray diffraction, UV-vis, and electron paramagnetic resonance spectroscopy. Monitoring the oxidation of 1,2-13C-trichloroethylene (TCE), photochemical activity was confirmed by monitoring the production of CO2 by 13C NMR analysis. The powdered form of N-doped TiO2 proved to be a highly efficient visible light catalyst by oxidizing all of the TCE to chlorinated alkyl and acyl containing molecules along with CO2. The performance of a TiO2-N-TiO2/porous Vycor 7930 borosilicate glass monolayer catalyst was in turn evaluated by monitoring the photochemical oxidation of ethanol and acetone with UV-vis light, and it was found to perform better than TiO2-only monolayers. Direct nitridation of TiO2 powders and monolayers also was conducted to compare the 15N SSNMR and to discern if there is a nitridic bond in these materials. The SSNMR results provide more evidence supporting the hypothesis that the nitrogen atom in N-doped TiO2 is present in interstitial sites when N is in a highly oxidized state.
-Calculation of 19F and 29Si shifts
J. Phys. Chem. C, 111 (9), 3584 -3590, 2007. 10.1021/jp065695q S1932-7447(06)05695-0
Calculation of 19F and 29Si NMR Shifts and Stabilities of F- Encapsulating Silsesquioxanes
J. A. Tossell*
Abstract:Hartree-Fock and density functional theory techniques have been used to calculate the structures, the stabilities in aqueous and toluene solutions, and the 19F and 29Si NMR shifts of F- encapsulating double-ring geometry silsesquixoanes DnR with n = 3-6. We find for the fluorides that the encapsulation free energy is most negative for the double four-ring (D4R) cage, in which the most stable geometry has F- in the center. For n = 5, 6 (and for an opened version of the double five-ring, D5R, cage), the most stable geometry has F- bonded to a single apex Si atom, with a bond distance around 1.76 Å. The 19F NMR is somewhat deshielded relative to that of the Si(OH)4F- monomer for all of the apex bonded F- DnR species and is very strongly deshielded for the central F- encapsulating DnR species with n = 3, 4. The Si is slightly deshielded by the presence of F- for the DnR with central F- ions, while in the apex-bonded larger double rings, n = 5, 6, the Si directly bonded to F- is substantially shielded. The energetic results help to explain why fluorides, as mineralizing agents, increase the yield of zeolites and mesoporous silicas with D4R rings, and the NMR results provide a means for ascertaining double-ring size and the position of F- within the double-ring cage.
- 2H NMR of molecules inside zeolites (Andy?)
J. Phys. Chem. C, 111 (11), 4393 -4403, 2007. 10.1021/jp066959b S1932-7447(06)06959-7
Dynamics of Linear n-C6-n-C22 Alkanes Inside 5A Zeolite Studied by 2H NMR
Daniil I. Kolokolov, Sergei S. Arzumanov, Alexander G. Stepanov,* and Hervé Jobic*
Abstract:The dynamic behavior of deuterated analogues of linear alkanes, n-C6-n-C22, adsorbed in zeolite 5A has been studied by deuterium solid-state NMR (2H NMR). Temperature dependences of spin-lattice (T1) and spin-spin (T2) relaxation times of the deuterium located in the CD3 groups of the adsorbed n-alkanes were rationalized on the basis of a model derived for the motion of n-alkanes located in the pores of the zeolite. The model implies that the adsorbed molecules consist of two ensembles: diffusing (or stretched) and temporarily blocked from diffusion (or coiled). The possible intramolecular motions for the alkane chains were taken into account based on both the finite size of the zeolite cage and the allowable hydrocarbon chain conformations. The coiled molecules are involved in two modes of motion: isotropic reorientation and intramolecular conformational isomerization, whereas the stretched molecules are additionally involved in a diffusion process. Dynamics parameters for different modes of motion and a proportion of the blocked and stretched molecules were derived from the analysis of relaxation data. The estimated proportion of the diffusing molecules correlates with the alkanes diffusivities earlier obtained by neutron spin echo measurements.
-19F-27Al HETCOR
J. Phys. Chem. C, 111 (12), 4495 -4498, 2007. 10.1021/jp070739w S1932-7447(07)00739-X
Direct Solid-State NMR Observation of Tetrahedral Aluminum Fluorides in Zeolite HY Fluorinated by Ammonium Fluoride
Hsien-Ming Kao* and Yi-Chen Liao
Abstract:19F to 27Al CPMAS and 27Al{19F} 2D HETCOR NMR experiments provide direct evidence of the formation of tetrahedral Al-F species in zeolite HY fluorinated by an aqueous solution of ammonium fluoride at 80 C. On the basis of these NMR observations, a NMR peak assignment for the 19F signals at -173 and -182 ppm to the tetrahedral Al-F species corresponding to an 27Al signal at 50 ppm is made for the first time.
-13C-17O REAPDOR Spectroscopy
Macromolecules, 40 (5), 1363 -1365, 2007. 10.1021/ma062835l S0024-9297(06)02835-X
13C-17O REAPDOR NMR as a Tool for Determining Secondary Structure in Polyamides
Terry Gullion,* Kazuo Yamauchi, Michi Okonogi, and Tetsuo Asakura*
Secondary structure of polyamides is determined largely by hydrogen bonding between the carbonyl oxygen and the amide proton. Nylon-6, with its and crystalline forms, is the classic example of a synthetic polyamide where hydrogen bonding has a significant influence on structure, and the secondary structure of natural proteins and peptides is very much governed by hydrogen bonding.1 X-ray crystallography is the primary tool for determining structures in crystalline macromolecules, but not all polyamides can be suitably prepared for X-ray diffraction experiments. For such samples solid-state NMR has been widely used for structural studies, including 13C chemical shift analysis, 13C-13C spin-diffusion, and REDOR experiments.2 Because the carbonyl oxygen serves as the proton acceptor and, consequently, plays such an important role in hydrogen bonding and formation of the secondary structure, we have begun to explore 17O NMR as a structural tool in polyamides. This paper illustrates 13C-17O REAPDOR NMR as a structural tool for characterizing polyamides.
-Gillian Goward, studies of Nafion/SiO2 systems
Macromolecules, 40 (5), 1529 -1537, 2007. 10.1021/ma0621876 S0024-9297(06)02187-5
Proton Dynamics of Nafion and Nafion/SiO2 Composites by Solid State NMR and Pulse Field Gradient NMR
G. Ye, C. A. Hayden, and G. R. Goward*
Abstract:
Proton mobilities in Nafion and Nafion/SiO2 composites have been studied using high-resolution solid-state MAS NMR. High-resolution solid-state 1H NMR show that low concentrations of TEOS or short permeation times are necessary to allow complete hydrolysis of TEOS in Nafion. Incomplete hydrolysis of TEOS leaves residual ethyl groups on the surface of silica, which not only reduces the amount of water adsorbed by silica but also blocks the pathway of proton transport in the Nafion/SiO2 composites. The diffusion coefficients established using PFG NMR show that the best Nafion/SiO2 composite can be obtained from synthesis with a low concentration of TEOS in a methanol solution. This composite gives a higher diffusion coefficient than pure Nafion under dry conditions, although no differentiation in performance is observed when the membranes are hydrated. 29Si NMR shows that this composite has a high ratio of Q3/Q4 sites, consistent with a small particle size and many surface hydroxyl groups. Together, these data demonstrate the role of high-surface-area SiO2 particles in trapping water and building a pathway for structural (Grotthuss mechanism) proton diffusion. Good proton transport under low relative humidity is the holy grail of the PEM-FC community, and this molecular level study shows how conditions can be iteratively optimized to target desirable structure-property relationships.
-13C SSNMR studies of spider silk
Macromolecules, 40 (6), 1995 -2001, 2007. 10.1021/ma062452n S0024-9297(06)02452-1
Molecular Disorder and Structure of Spider Dragline Silk Investigated by Two-Dimensional Solid-State NMR Spectroscopy
Isabelle Marcotte, Jacco D. van Beek, and Beat H. Meier*
Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
Received October 24, 2006
Revised Manuscript Received December 18, 2006
Abstract:
We have studied the molecular disorder in (13C)Ala- and (13C)Gly-labeled dragline silk from Nephila edulis through the distributions of isotropic chemical shifts in one- and two-dimensional 13C-13C NMR spectra obtained under MAS. The alanine residues were found to be present in two distinct major structural environments, in agreement with previous studies, where -sheets and 31-helices were found. The distributions in chemical shift within each residue were found to be uncorrelated, even between spins in the same amino acid residue, and were of similar widths for both the crystalline and noncrystalline parts. Upon long-term mechanical stretching of the silk, the NMR spectra showed no significant changes in conformation nor changes in the degree of disorder but did show increasing structural damage to the silk threads.
Thursday, March 22, 2007
Tuesday, March 20, 2007
Progress in NMR, update to March 2007
Progress in Nuclear Magnetic Resonance Spectroscopy
Volume 50, Issues 2-3 , 30 March 2007, Pages 87-174
doi:10.1016/j.pnmrs.2006.12.001
Solid-state Li NMR with applications to the translational dynamics in ion conductors
R. Böhmer a,K.R. Jeffrey b and M. Vogel c
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Received 13 October 2006. Available online 9 February 2007.
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow dynamics
Volume 50, Issues 2-3 , 30 March 2007, Pages 87-174
doi:10.1016/j.pnmrs.2006.12.001
Solid-state Li NMR with applications to the translational dynamics in ion conductors
R. Böhmer a,K.R. Jeffrey b and M. Vogel c
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Received 13 October 2006. Available online 9 February 2007.
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow dynamics
MRC: Magnetic Resonance in Chemistry, updated to April 2007
1-Cyclohepta-2,4,6-trienyl-selanes - a 77Se NMR study: Indirect nuclear 77Se13C spin-spin coupling constants and application of density functional theory (DFT) calculations
Bernd Wrackmeyer *, Zureima García Hernández, Max Herberhold
Anorganische Chemie II, Universität Bayreuth, D-95440 Bayreuth, Germany
*Correspondence to Bernd Wrackmeyer, Anorganische Chemie II, Universität Bayreuth, D-95440 Bayreuth, Germany.
Keywords
cylohepta-2,4,6-trienes • selenium • NMR • coupling constants • DFT calculations
Abstract
1-Cyclohepta-2,4,6-trienyl-selanes Se(C7H7)2 (2c), RSeC7H7 with R = Bu, tBu, Ph, 4-FC6H4 (12a,b,c,d) were prepared by the reaction of the corresponding silanes, Si(SeMe3)2 and RSeSiMe3, respectively, with tropylium bromide C7H7Br. In spite of the low stability of the selanes even in dilute solutions and at low temperature, they could be characterised by their 1H, 13C and 77Se NMR parameters. Coupling constants 1J(77Se,13C) were measured and calculated by DFT methods at the B3LYP/6-311+G(d,p) level of theory. The comparison of experimental and calculated coupling constants 1J(77Se,13C) included numerous selenium carbon compounds with largely different SeC bonds, revealing a satisfactory agreement. Both the spin-dipole (SD) and the paramagnetic spin-orbital (PSO) terms contributed significantly to the spin-spin coupling interaction, in addition to the Fermi contact (FC) term. Copyright © 2006 John Wiley & Sons, Ltd.
Received: 23 October 2006; Revised: 3 November 2006; Accepted: 7 November 2006
Digital Object Identifier (DOI)
10.1002/mrc.1946
Bernd Wrackmeyer *, Zureima García Hernández, Max Herberhold
Anorganische Chemie II, Universität Bayreuth, D-95440 Bayreuth, Germany
*Correspondence to Bernd Wrackmeyer, Anorganische Chemie II, Universität Bayreuth, D-95440 Bayreuth, Germany.
Keywords
cylohepta-2,4,6-trienes • selenium • NMR • coupling constants • DFT calculations
Abstract
1-Cyclohepta-2,4,6-trienyl-selanes Se(C7H7)2 (2c), RSeC7H7 with R = Bu, tBu, Ph, 4-FC6H4 (12a,b,c,d) were prepared by the reaction of the corresponding silanes, Si(SeMe3)2 and RSeSiMe3, respectively, with tropylium bromide C7H7Br. In spite of the low stability of the selanes even in dilute solutions and at low temperature, they could be characterised by their 1H, 13C and 77Se NMR parameters. Coupling constants 1J(77Se,13C) were measured and calculated by DFT methods at the B3LYP/6-311+G(d,p) level of theory. The comparison of experimental and calculated coupling constants 1J(77Se,13C) included numerous selenium carbon compounds with largely different SeC bonds, revealing a satisfactory agreement. Both the spin-dipole (SD) and the paramagnetic spin-orbital (PSO) terms contributed significantly to the spin-spin coupling interaction, in addition to the Fermi contact (FC) term. Copyright © 2006 John Wiley & Sons, Ltd.
Received: 23 October 2006; Revised: 3 November 2006; Accepted: 7 November 2006
Digital Object Identifier (DOI)
10.1002/mrc.1946
Concepts in NMR, updated to March 2007
Coherence pathway selection by cogwheel phase cycling in liquid-state NMR
Gerhard Zuckerstätter, Norbert Müller *
Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria
*Correspondence to Norbert Müller, Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria
Keywords
cogwheel phase cycling • coherence order • coherence transfer pathways • coherence selection • phase cycling • triple resonance
Abstract
Coherence selection as an integral element of most multipulse NMR methods also represents a bottleneck to the efficiency of multidimensional NMR methods. In particular, phase cycling often requires total scan numbers in excess of signal-to-noise demands. M. H. Levitt and coworkers have recently introduced cogwheel phase cycling in solid-state NMR, which improves on this problem. In this article we recapitulate the principles of coherence selection in multipulse and multidimensional NMR. The fundamental differences between various coherence selection strategies are discussed, and examples of implementing cogwheel phase cycling in liquid-state NMR experiments commonly used for biopolymers are given. Design guidelines are suggested for incorporating cogwheel phase cycles into other pulsed NMR techniques. For experiments with multiple coherence transfer steps, cogwheel phase cycling is more efficient in spectrometer time usage than traditional nested phase cycling, as the scan numbers can be adjusted in smaller steps. Even compared with pulsed field gradient selection methods advantages exist, especially for fast relaxing resonances. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 81-99, 2007.
Received: 21 September 2006; Revised: 21 December 2006; Accepted: 21 December 2006
Digital Object Identifier (DOI)
10.1002/cmr.a.20079
A practical guide for solid-state NMR distance measurements in proteins
Frank A. Kovacs, Daniel J. Fowler, Gregory J. Gallagher, Lynmarie K. Thompson *
Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts
*Correspondence to Lynmarie K. Thompson, Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts
Keywords
rotational resonance • R2 • REDOR • MAS • solid-state NMR • site-directed distance measurements
Abstract
Rotational resonance (R2) and rotational echo double resonance (REDOR) are powerful solid-state NMR techniques that can be applied in a site-directed fashion for precise distance measurements in proteins. These tools are well suited for systems in which a few precise distance measurements are needed to understand a mechanism or map a binding site, particularly if this information is unavailable from x-ray crystallography or solution NMR, as is often the case for membrane proteins. Strategies and challenges in the design and implementation of such experiments are described and illustrated with experiments probing mechanisms of transmembrane signaling in bacterial chemotaxis receptors. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 21-39, 2007.
Received: 27 July 2006; Accepted: 28 August 2006
Digital Object Identifier (DOI)
10.1002/cmr.a.20071
Gerhard Zuckerstätter, Norbert Müller *
Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria
*Correspondence to Norbert Müller, Institute of Organic Chemistry, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz, Austria
Keywords
cogwheel phase cycling • coherence order • coherence transfer pathways • coherence selection • phase cycling • triple resonance
Abstract
Coherence selection as an integral element of most multipulse NMR methods also represents a bottleneck to the efficiency of multidimensional NMR methods. In particular, phase cycling often requires total scan numbers in excess of signal-to-noise demands. M. H. Levitt and coworkers have recently introduced cogwheel phase cycling in solid-state NMR, which improves on this problem. In this article we recapitulate the principles of coherence selection in multipulse and multidimensional NMR. The fundamental differences between various coherence selection strategies are discussed, and examples of implementing cogwheel phase cycling in liquid-state NMR experiments commonly used for biopolymers are given. Design guidelines are suggested for incorporating cogwheel phase cycles into other pulsed NMR techniques. For experiments with multiple coherence transfer steps, cogwheel phase cycling is more efficient in spectrometer time usage than traditional nested phase cycling, as the scan numbers can be adjusted in smaller steps. Even compared with pulsed field gradient selection methods advantages exist, especially for fast relaxing resonances. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 81-99, 2007.
Received: 21 September 2006; Revised: 21 December 2006; Accepted: 21 December 2006
Digital Object Identifier (DOI)
10.1002/cmr.a.20079
A practical guide for solid-state NMR distance measurements in proteins
Frank A. Kovacs, Daniel J. Fowler, Gregory J. Gallagher, Lynmarie K. Thompson *
Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts
*Correspondence to Lynmarie K. Thompson, Department of Chemistry, University of Massachusetts Amherst, Amherst, Massachusetts
Keywords
rotational resonance • R2 • REDOR • MAS • solid-state NMR • site-directed distance measurements
Abstract
Rotational resonance (R2) and rotational echo double resonance (REDOR) are powerful solid-state NMR techniques that can be applied in a site-directed fashion for precise distance measurements in proteins. These tools are well suited for systems in which a few precise distance measurements are needed to understand a mechanism or map a binding site, particularly if this information is unavailable from x-ray crystallography or solution NMR, as is often the case for membrane proteins. Strategies and challenges in the design and implementation of such experiments are described and illustrated with experiments probing mechanisms of transmembrane signaling in bacterial chemotaxis receptors. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 21-39, 2007.
Received: 27 July 2006; Accepted: 28 August 2006
Digital Object Identifier (DOI)
10.1002/cmr.a.20071
Tuesday, March 13, 2007
Solid State NMR update, Feb 2007 issue
Solid State Nuclear Magnetic Resonance
Volume 31, Issue 1 , February 2007, Pages 1-9
doi:10.1016/j.ssnmr.2006.09.002
Comparison of high-resolution solid-state NMR MQMAS and STMAS methods for half-integer quadrupolar nuclei
Julien Trebosc a, Jean-Paul Amoureux a, and Zhehong Gan b
a UCCS, CNRS-8181, University of Lille-1, C7-ENSCL, 59652 Villeneuve d’Ascq, France
b NHMFL, 32310 Tallahassee, FL, USA
Received 15 May 2006; revised 18 September 2006. Available online 28 September 2006.
Abstract
Several different amplitude-modulated two-dimensional high-resolution methods, based on MQMAS and STMAS, are compared. They include 3QMAS, 5QMAS, DQ-STMAS, and DQF-STMAS experiments. A new method, called t1-split-STMAS, is also proposed for spin-3/2 nuclei. The comparison is performed in terms of isotropic resolution and spectral-width, efficiency, and sensitivity to magic-angle offset and spinning speed fluctuations.
Solid State Nuclear Magnetic Resonance
Volume 31, Issue 1 , February 2007, Pages 55-61
doi:10.1016/j.ssnmr.2007.01.001
Double-quantum filtered heteronuclear correlation spectroscopy under magic angle spinning
Yao-Hung Tseng a, Yi-Ling Tsai a, Tim W.T . Tsai a, Chun-Pin Lin a, b, Shih-Hao Huang a, b, Chung-Yuan Mou a, c and Jerry C.C. Chan a, Corresponding Author Contact Information, E-mail The Corresponding Author
a Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei, Taiwan
b Graduate Institute of Clinical Dentistry, National Taiwan University, Taipei
c Center of Condensed Matter, National Taiwan University, Taipei, Taiwan
Received 30 September 2006; revised 29 December 2006. Available online 8 January 2007.
Abstract
We present a simple experimental method to extract the van Vleck second moment of a multiple-spin system under high-resolution condition. The idea is to incorporate a double-quantum (DQ) filter into the pulse sequence of heteronuclear correlation spectroscopy so that a DQ excitation profile can be obtained by measuring a series of 2D spectra. The effects of spinning frequency and proton decoupling are demonstrated on the measurements of two model compounds, viz. hydroxyapatite and brushite. Based on the results obtained for the model compounds, the P-31 homonuclear second moment of the apatite component in rat dentin is characterized. The method is generally suited for the study of bone, enamel and dentin.
Keywords: Brushite; Calcium phosphate; HAp; NMR; Double-quantum filter; HETCOR; Second moment; Dentin; Teeth
Volume 31, Issue 1 , February 2007, Pages 1-9
doi:10.1016/j.ssnmr.2006.09.002
Comparison of high-resolution solid-state NMR MQMAS and STMAS methods for half-integer quadrupolar nuclei
Julien Trebosc a, Jean-Paul Amoureux a, and Zhehong Gan b
a UCCS, CNRS-8181, University of Lille-1, C7-ENSCL, 59652 Villeneuve d’Ascq, France
b NHMFL, 32310 Tallahassee, FL, USA
Received 15 May 2006; revised 18 September 2006. Available online 28 September 2006.
Abstract
Several different amplitude-modulated two-dimensional high-resolution methods, based on MQMAS and STMAS, are compared. They include 3QMAS, 5QMAS, DQ-STMAS, and DQF-STMAS experiments. A new method, called t1-split-STMAS, is also proposed for spin-3/2 nuclei. The comparison is performed in terms of isotropic resolution and spectral-width, efficiency, and sensitivity to magic-angle offset and spinning speed fluctuations.
Solid State Nuclear Magnetic Resonance
Volume 31, Issue 1 , February 2007, Pages 55-61
doi:10.1016/j.ssnmr.2007.01.001
Double-quantum filtered heteronuclear correlation spectroscopy under magic angle spinning
Yao-Hung Tseng a, Yi-Ling Tsai a, Tim W.T . Tsai a, Chun-Pin Lin a, b, Shih-Hao Huang a, b, Chung-Yuan Mou a, c and Jerry C.C. Chan a, Corresponding Author Contact Information, E-mail The Corresponding Author
a Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei, Taiwan
b Graduate Institute of Clinical Dentistry, National Taiwan University, Taipei
c Center of Condensed Matter, National Taiwan University, Taipei, Taiwan
Received 30 September 2006; revised 29 December 2006. Available online 8 January 2007.
Abstract
We present a simple experimental method to extract the van Vleck second moment of a multiple-spin system under high-resolution condition. The idea is to incorporate a double-quantum (DQ) filter into the pulse sequence of heteronuclear correlation spectroscopy so that a DQ excitation profile can be obtained by measuring a series of 2D spectra. The effects of spinning frequency and proton decoupling are demonstrated on the measurements of two model compounds, viz. hydroxyapatite and brushite. Based on the results obtained for the model compounds, the P-31 homonuclear second moment of the apatite component in rat dentin is characterized. The method is generally suited for the study of bone, enamel and dentin.
Keywords: Brushite; Calcium phosphate; HAp; NMR; Double-quantum filter; HETCOR; Second moment; Dentin; Teeth
Monday, March 12, 2007
Dalton Transactions from Jan 2007
Complexation of the triphosphate anion: tunigh the structure of cyclen based bacrotricycles with 1,3-dimethylbenzene and 2,6-dimethylpyridine linkers. A potentiometric and NMR study
Stéphanie Develay, Raphaël Tripier, Nicolas Bernier, Michel Le Baccon, Véronique Patinec, Guy Serratrice and Henri Handel
Dalton Trans., 2007, 1038 - 1046, DOI: 10.1039/b616862k
Abstract: The host–guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range.
Multidimensional NMR spectroscopy of the study of histone H4-Ni(II) interaction
Maria Antonietta Zoroddu, Massimiliano Peana and Serenella Medici
Dalton Trans., 2007, 379 - 384, DOI: 10.1039/b610725g
Abstract: The N-terminal 30-amino acid tail of histone H4, a nuclear protein, was studied as a model for the interaction of this protein with Ni(II) ions. The behaviour of the ends-blocked Ac-SGRGKGGKGLGKGGA15K16R17H18R19KVLRDNIQGIT-Am fragment towards Ni(II) was analyzed with multidimensional NMR (1D, 2D TOCSY, NOESY) and UV-Vis spectroscopy. As expected, the coordination involved the imidazolic nitrogen of the His18 residue and the three deprotonated amidic nitrogens of the His18, Arg17 and Lys16 residues, respectively. A model for the structure of the complex was calculated from the inter-residual NOEs recorded in 2D NOESY spectra. The structure obtained shows that the interaction with the metal is responsible for deep changes in the conformation of the peptide, blocking the side chain of Arg17 and Lys16 residues above the coordination plane. These structural modifications may be physiologically relevant to the mechanism of nickel carcinogenesis.
Stéphanie Develay, Raphaël Tripier, Nicolas Bernier, Michel Le Baccon, Véronique Patinec, Guy Serratrice and Henri Handel
Dalton Trans., 2007, 1038 - 1046, DOI: 10.1039/b616862k
Abstract: The host–guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range.
Multidimensional NMR spectroscopy of the study of histone H4-Ni(II) interaction
Maria Antonietta Zoroddu, Massimiliano Peana and Serenella Medici
Dalton Trans., 2007, 379 - 384, DOI: 10.1039/b610725g
Abstract: The N-terminal 30-amino acid tail of histone H4, a nuclear protein, was studied as a model for the interaction of this protein with Ni(II) ions. The behaviour of the ends-blocked Ac-SGRGKGGKGLGKGGA15K16R17H18R19KVLRDNIQGIT-Am fragment towards Ni(II) was analyzed with multidimensional NMR (1D, 2D TOCSY, NOESY) and UV-Vis spectroscopy. As expected, the coordination involved the imidazolic nitrogen of the His18 residue and the three deprotonated amidic nitrogens of the His18, Arg17 and Lys16 residues, respectively. A model for the structure of the complex was calculated from the inter-residual NOEs recorded in 2D NOESY spectra. The structure obtained shows that the interaction with the metal is responsible for deep changes in the conformation of the peptide, blocking the side chain of Arg17 and Lys16 residues above the coordination plane. These structural modifications may be physiologically relevant to the mechanism of nickel carcinogenesis.
Chem Commun from Jan 2007
A simple NMR analysis of the Protonation equilibrium that accompanies aminoglycoside recognition: Dramatc alterations in the neomycin-B protonation state upon binding to a 23-mer RNA aptamer
Felix Freire, Igor Cuesta, Francisco Corzana, Julia Revuelta, Carlos González, Milos Hricovini, Agatha Bastida, Jesús Jiménez-Barbero and Juan Luis Asensio
Chem. Commun., 2007, 174 - 176, DOI: 10.1039/b611597g
Abstract: A complete characterisation of the protonation equilibrium that accompanies the molecular recognition of neomycin-B by a specific RNA receptor has been achieved by employing simple NMR measurements.
Only para-hydrogen spectroscopy (OPSY), a technique for the selective observation of para-hydrogen enhanced NMR signals
Juan A. Aguilar, Paul I. P. Elliott, Joaquín López-Serrano, Ralph W. Adams and Simon B. Duckett
Chem. Commun., 2007, 1183 - 1185, DOI:10.1039/b616307fAbstract: An NMR method is reported for the efficient removal of signals derived from nuclei with thermally equilibrated spin state populations whilst leaving, intact, signals derived from para-hydrogen induced polarisation (PHIP) through gradient assisted coherence selection.
Advancements in natural abundance solid-state 33S MAS NMR: characterizaton of transition-metal M=S bonds in ammonium tetrathiometallates
Hans J. Jakobsen, Anders R. Hove, Henrik Bildsoe, Jorgen Skibsted, Michael Brorson
Chem. Commun., 2007 DOI: 10.1039/b618497a
Abstract: We report the first 33S chemical shift anisotropy (CSA) data as obtained from a combined determination of 33S CSA and quadrupole coupling parameters utilizing the observation of both the 33S (I = 3/2) central and satellite transitions in a natural abundance 33S MAS NMR study aimed at characterizing the two important tetrathiometallates (NH4)2MoS4 and (NH4)2WS4.
Felix Freire, Igor Cuesta, Francisco Corzana, Julia Revuelta, Carlos González, Milos Hricovini, Agatha Bastida, Jesús Jiménez-Barbero and Juan Luis Asensio
Chem. Commun., 2007, 174 - 176, DOI: 10.1039/b611597g
Abstract: A complete characterisation of the protonation equilibrium that accompanies the molecular recognition of neomycin-B by a specific RNA receptor has been achieved by employing simple NMR measurements.
Only para-hydrogen spectroscopy (OPSY), a technique for the selective observation of para-hydrogen enhanced NMR signals
Juan A. Aguilar, Paul I. P. Elliott, Joaquín López-Serrano, Ralph W. Adams and Simon B. Duckett
Chem. Commun., 2007, 1183 - 1185, DOI:10.1039/b616307fAbstract: An NMR method is reported for the efficient removal of signals derived from nuclei with thermally equilibrated spin state populations whilst leaving, intact, signals derived from para-hydrogen induced polarisation (PHIP) through gradient assisted coherence selection.
Advancements in natural abundance solid-state 33S MAS NMR: characterizaton of transition-metal M=S bonds in ammonium tetrathiometallates
Hans J. Jakobsen, Anders R. Hove, Henrik Bildsoe, Jorgen Skibsted, Michael Brorson
Chem. Commun., 2007 DOI: 10.1039/b618497a
Abstract: We report the first 33S chemical shift anisotropy (CSA) data as obtained from a combined determination of 33S CSA and quadrupole coupling parameters utilizing the observation of both the 33S (I = 3/2) central and satellite transitions in a natural abundance 33S MAS NMR study aimed at characterizing the two important tetrathiometallates (NH4)2MoS4 and (NH4)2WS4.
Can. J. Chem. Vol 85 Number 1-2 Update
Biradical radiationless decay channel in adenine and its derivativesMarek Z. Zgierski, Serguei Patchkovskii, and Edward C. Lim Can. J. Chem./Rev. can. chim. 85(2): 124-134 (2007)
Full text (PDF 443 kb)
Abstract: Coupled-cluster calculations of increasing accuracy (approximate doubles: CC2; doubles: EOM-CCSD; connected triples: CR-EOM-CCSD(T)) for CIS-optimized potential energy profiles of adenine and its derivatives indicate that the ultrafast internal conversion of the optically excited π π* state occurs through a state switch to a biradical state, which intersects the ground state at a lower energy. The electronic nature of the biradical state is defined by an electronic configuration in which one unpaired electron occupies a π* orbital confined to the five-membered ring. The second unpaired electron is localized very strongly on a p-type C2 atomic orbital of the six-membered ring. The biradical state minimum has a strongly puckered six-membered ring and a C2–H bond, which is twisted nearly perpendicular to the average ring plane. Consistent with the biradical-mediated internal conversion, the π π* state lifetime is extremely short in adenine and 9-methyladenine, which have barrierless crossing to the biradical state. The lifetime is slightly longer in N,N-dimethyladenine, which has a small barrier for the state switch. In 2-aminopurine the biradical state is found above the π π* state, preventing the biradical state switch and dramatically increasing the lifetime. These results, combined with an earlier work on pyrimidine bases, strongly suggest the importance of a direct decay of the doorway π π* state via a biradical state switch in the photophysics of DNA, even though the nature of the biradical state is somewhat different in purines and pyrimidines.
Key words: adenine, guanine, DNA damage, radiationless decay, biradical, ab initio, coupled clusted.
Heterogeneities in sol–gel-derived paramagnetics-doped forsterites and willemites — Electron microprobe analysis and stretched-exponential 29Si MAS NMR spin–lattice relaxation studiesJ. Stephen Hartman, Arjun Narayanan, Suzie S. Rigby, David R. Sliwinski, Norman M. Halden, and Alex D. Bain Can. J. Chem./Rev. can. chim. 85(1): 56-65 (2007)
Full text (PDF 379 kb)
Abstract: We report the synthesis and analysis of sol–gel-derived samples of forsterite (Mg2SiO4) and willemite (Zn2SiO4), doped with paramagnetic Cu2+, Ni2+, and Co2+, at a range of dopant concentrations. Electron probe microanalysis and backscattered electron imaging show the presence of major micrometre-scale heterogeneities in the distribution of paramagnetic centres. Despite the inhomogeneities, the 29Si NMR spin–lattice relaxation behaviour is well-behaved and is consistent with the stretched-exponential expression Mz(t)=Mz(∞){1 – a exp[–(t/T′)n]}. The exponent n is 0.5 within the experimental error in some samples. This value is consistent with relaxation by immobile isolated paramagnetic impurities with negligible 29Si spin diffusion from the impurity centres, but careful curve fitting confirms that n is significantly larger than 0.5 in other samples. Relaxation efficiency is highly dependent on the dopant ion and its concentration. Although the purely empirical stretched-exponential function does not provide a unique physical picture, it is noteworthy that it is sufficiently robust to describe spin–lattice relaxation even in highly inhomogeneous systems. Spin–lattice relaxation is a useful probe of paramagnetics-doped solid samples, but NMR does not provide information on homogeneity. Careful sample characterization on the micrometre scale is highly desirable, as a complement to NMR studies.
Key words: MAS NMR, spin–lattice relaxation, 29Si, forsterite, willemite, stretched-exponential relaxation, sol–gel, minor-component heterogeneity, backscattered electron analysis.
Full text (PDF 443 kb)
Abstract: Coupled-cluster calculations of increasing accuracy (approximate doubles: CC2; doubles: EOM-CCSD; connected triples: CR-EOM-CCSD(T)) for CIS-optimized potential energy profiles of adenine and its derivatives indicate that the ultrafast internal conversion of the optically excited π π* state occurs through a state switch to a biradical state, which intersects the ground state at a lower energy. The electronic nature of the biradical state is defined by an electronic configuration in which one unpaired electron occupies a π* orbital confined to the five-membered ring. The second unpaired electron is localized very strongly on a p-type C2 atomic orbital of the six-membered ring. The biradical state minimum has a strongly puckered six-membered ring and a C2–H bond, which is twisted nearly perpendicular to the average ring plane. Consistent with the biradical-mediated internal conversion, the π π* state lifetime is extremely short in adenine and 9-methyladenine, which have barrierless crossing to the biradical state. The lifetime is slightly longer in N,N-dimethyladenine, which has a small barrier for the state switch. In 2-aminopurine the biradical state is found above the π π* state, preventing the biradical state switch and dramatically increasing the lifetime. These results, combined with an earlier work on pyrimidine bases, strongly suggest the importance of a direct decay of the doorway π π* state via a biradical state switch in the photophysics of DNA, even though the nature of the biradical state is somewhat different in purines and pyrimidines.
Key words: adenine, guanine, DNA damage, radiationless decay, biradical, ab initio, coupled clusted.
Heterogeneities in sol–gel-derived paramagnetics-doped forsterites and willemites — Electron microprobe analysis and stretched-exponential 29Si MAS NMR spin–lattice relaxation studiesJ. Stephen Hartman, Arjun Narayanan, Suzie S. Rigby, David R. Sliwinski, Norman M. Halden, and Alex D. Bain Can. J. Chem./Rev. can. chim. 85(1): 56-65 (2007)
Full text (PDF 379 kb)
Abstract: We report the synthesis and analysis of sol–gel-derived samples of forsterite (Mg2SiO4) and willemite (Zn2SiO4), doped with paramagnetic Cu2+, Ni2+, and Co2+, at a range of dopant concentrations. Electron probe microanalysis and backscattered electron imaging show the presence of major micrometre-scale heterogeneities in the distribution of paramagnetic centres. Despite the inhomogeneities, the 29Si NMR spin–lattice relaxation behaviour is well-behaved and is consistent with the stretched-exponential expression Mz(t)=Mz(∞){1 – a exp[–(t/T′)n]}. The exponent n is 0.5 within the experimental error in some samples. This value is consistent with relaxation by immobile isolated paramagnetic impurities with negligible 29Si spin diffusion from the impurity centres, but careful curve fitting confirms that n is significantly larger than 0.5 in other samples. Relaxation efficiency is highly dependent on the dopant ion and its concentration. Although the purely empirical stretched-exponential function does not provide a unique physical picture, it is noteworthy that it is sufficiently robust to describe spin–lattice relaxation even in highly inhomogeneous systems. Spin–lattice relaxation is a useful probe of paramagnetics-doped solid samples, but NMR does not provide information on homogeneity. Careful sample characterization on the micrometre scale is highly desirable, as a complement to NMR studies.
Key words: MAS NMR, spin–lattice relaxation, 29Si, forsterite, willemite, stretched-exponential relaxation, sol–gel, minor-component heterogeneity, backscattered electron analysis.
J. Phys. Chem. - journal update
Antusek, A., M. Jaszunski, et al. (2007).
"Ab initio study of interaction-induced NMR shielding constants in mixed rare gas dimers."
The Journal of Chemical Physics 126(7): 074303-9.
The interaction-induced contribution to the NMR shielding constants in homonuclear A2 and heteronuclear AB (A,B=He,Ne,Ar) dimers is obtained ab initio by employing a coupled cluster singles and doubles with perturbative treatment of triples wave function model and extended correlation-consistent basis sets. The second virial coefficients entering the expansion of the property with the density are then computed in a fully quantum mechanical approach, for temperatures ranging from the limit of dissociation of the dimer to well above standard conditions. The results can be used to describe the density and temperature dependence of the shielding constants in binary mixtures of helium, neon, and argon. The predicted effects should be observable for the interaction of 21Ne with other rare gases.
Schmidt-Rohr, K., A. Rawal, et al. (2007).
"A new NMR method for determining the particle thickness in nanocomposites, using T[sub 2,H]-selective X{[sup 1]H} recoupling."
The Journal of Chemical Physics 126(5): 054701-16.
A new nuclear magnetic resonance approach for characterizing the thickness of phosphate, silicate, carbonate, and other nanoparticles in organic-inorganic nanocomposites is presented. The particle thickness is probed using the strongly distant-dependent dipolar couplings between the abundant protons in the organic phase and X nuclei (31P, 29Si, 13C, 27Al, 23Na, etc.) in the inorganic phase. This approach requires pulse sequences with heteronuclear dephasing only by the polymer or surface protons that experience strong homonuclear interactions, but not by dispersed OH or water protons in the inorganic phase, which have long transverse relaxation times T2,H. This goal is achieved by heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP). The pulse sequence alternates heteronuclear recoupling for ~0.15 ms with periods of homonuclear dipolar dephasing that are flanked by canceling 90° pulses. The heteronuclear evolution of the long-T2,H protons is refocused within two recoupling periods, so that 1H spin diffusion cannot significantly dephase these coherences. For the short-T2,H protons of a relatively immobile organic matrix, the heteronuclear dephasing rate depends simply on the heteronuclear second moment. Homonuclear interactions do not affect the dephasing, even though no homonuclear decoupling is applied, because long-range 1H–X dipolar couplings approximately commute with short-range 1H–1H couplings, and heteronuclear recoupling periods are relatively short. This is shown in a detailed analysis based on interaction representations. The algorithm for simulating the dephasing data is described. The new method is demonstrated on a clay-polymer nanocomposite, diamond nanocrystals with protonated surfaces, and the bioapatite-collagen nanocomposite in bone, as well as pure clay and hydroxyapatite. The diameters of the nanoparticles in these materials range between 1 and 5 nm. Simulations show that spherical particles of up to 10 nm diameter can be characterized quite easily.
Teale, A. M., A. J. Cohen, et al. (2007).
"Transition metal NMR chemical shifts from optimized effective potentials."
The Journal of Chemical Physics 126(7): 074101-7.
Metal shielding constants and chemical shifts are determined for nine transition metal complexes using an uncoupled formalism with orbitals and eigenvalues determined using the Yang-Wu implementation [W. Yang and Q. Wu, Phys. Rev. Lett. 89, 143002 (2002)] of the optimized effective potential approach in density functional theory. Preliminary calculations using generalized gradient approximation functionals quantify the influence of the variables in the optimized effective potential implementation. In particular, a flexible potential expansion is necessary for a precise calculation of these quantities. Hybrid functionals are then considered. Expanding the potential in the primary orbital basis yields chemical shifts that are a notable improvement over conventional hybrid values, and which are a marginal improvement over those obtained using a high-quality generalized gradient approximation. Similar shifts are obtained using a more flexible potential expansion, although care is required to avoid unphysical structure in the exchange-correlation potential.
Tycko, R. (2007).
"Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR."
The Journal of Chemical Physics 126(6): 064506-9.
Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. 13C NMR data for singly-13C-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. 15N-detected and 13C-detected measurements of intramolecular 15N–15N distances in peptides with alpha-helical and beta-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone psi torsion angles in peptides containing uniformly 15N- and 13C-labeled amino acids.
Iuga, A., D. Iuga, et al. (2007).
"Observation of satellite signals due to scalar coupling to spin-1/2 isotopes in solid-state nuclear magnetic resonance spectroscopy."
The Journal of Chemical Physics 126(5): 054305-10.
A method is introduced to select the signal from a spin-1/2 nucleus I specifically bound to another spin-1/2 nucleus S for solid-state magic angle spinning nuclear magnetic resonance (NMR) spectroscopy via correlation through the heteronuclear J coupling. This experiment is analogous to the bilinear rotation decoupling (BIRD) sequence in liquid-state NMR spectroscopy which selects for signals from 1H directly bound to 13C. The spin dynamics of this modified BIRD experiment is described using the product-operator formalism, where experimental considerations such as rotor synchronization and the effect of large chemical shielding anisotropies on I and S are discussed. Two experiments are proposed that accommodate large chemical shielding anisotropies on S: (1) by stepping the inversion pulse frequency through the entire S spectral range or (2) by adiabatically inverting the S spins. Both these experiments are shown to successfully select the signal of 19F bound to 129Xe in XeF+ salts, removing the contributions from isotopomers containing non-spin-1/2 Xe isotopes. The feasibility in obtaining isotope-selective 19F spectra of inorganic fluoride compounds is discussed, and further modifications are proposed to expand the application to other chemical systems.
"Ab initio study of interaction-induced NMR shielding constants in mixed rare gas dimers."
The Journal of Chemical Physics 126(7): 074303-9.
The interaction-induced contribution to the NMR shielding constants in homonuclear A2 and heteronuclear AB (A,B=He,Ne,Ar) dimers is obtained ab initio by employing a coupled cluster singles and doubles with perturbative treatment of triples wave function model and extended correlation-consistent basis sets. The second virial coefficients entering the expansion of the property with the density are then computed in a fully quantum mechanical approach, for temperatures ranging from the limit of dissociation of the dimer to well above standard conditions. The results can be used to describe the density and temperature dependence of the shielding constants in binary mixtures of helium, neon, and argon. The predicted effects should be observable for the interaction of 21Ne with other rare gases.
Schmidt-Rohr, K., A. Rawal, et al. (2007).
"A new NMR method for determining the particle thickness in nanocomposites, using T[sub 2,H]-selective X{[sup 1]H} recoupling."
The Journal of Chemical Physics 126(5): 054701-16.
A new nuclear magnetic resonance approach for characterizing the thickness of phosphate, silicate, carbonate, and other nanoparticles in organic-inorganic nanocomposites is presented. The particle thickness is probed using the strongly distant-dependent dipolar couplings between the abundant protons in the organic phase and X nuclei (31P, 29Si, 13C, 27Al, 23Na, etc.) in the inorganic phase. This approach requires pulse sequences with heteronuclear dephasing only by the polymer or surface protons that experience strong homonuclear interactions, but not by dispersed OH or water protons in the inorganic phase, which have long transverse relaxation times T2,H. This goal is achieved by heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP). The pulse sequence alternates heteronuclear recoupling for ~0.15 ms with periods of homonuclear dipolar dephasing that are flanked by canceling 90° pulses. The heteronuclear evolution of the long-T2,H protons is refocused within two recoupling periods, so that 1H spin diffusion cannot significantly dephase these coherences. For the short-T2,H protons of a relatively immobile organic matrix, the heteronuclear dephasing rate depends simply on the heteronuclear second moment. Homonuclear interactions do not affect the dephasing, even though no homonuclear decoupling is applied, because long-range 1H–X dipolar couplings approximately commute with short-range 1H–1H couplings, and heteronuclear recoupling periods are relatively short. This is shown in a detailed analysis based on interaction representations. The algorithm for simulating the dephasing data is described. The new method is demonstrated on a clay-polymer nanocomposite, diamond nanocrystals with protonated surfaces, and the bioapatite-collagen nanocomposite in bone, as well as pure clay and hydroxyapatite. The diameters of the nanoparticles in these materials range between 1 and 5 nm. Simulations show that spherical particles of up to 10 nm diameter can be characterized quite easily.
Teale, A. M., A. J. Cohen, et al. (2007).
"Transition metal NMR chemical shifts from optimized effective potentials."
The Journal of Chemical Physics 126(7): 074101-7.
Metal shielding constants and chemical shifts are determined for nine transition metal complexes using an uncoupled formalism with orbitals and eigenvalues determined using the Yang-Wu implementation [W. Yang and Q. Wu, Phys. Rev. Lett. 89, 143002 (2002)] of the optimized effective potential approach in density functional theory. Preliminary calculations using generalized gradient approximation functionals quantify the influence of the variables in the optimized effective potential implementation. In particular, a flexible potential expansion is necessary for a precise calculation of these quantities. Hybrid functionals are then considered. Expanding the potential in the primary orbital basis yields chemical shifts that are a notable improvement over conventional hybrid values, and which are a marginal improvement over those obtained using a high-quality generalized gradient approximation. Similar shifts are obtained using a more flexible potential expansion, although care is required to avoid unphysical structure in the exchange-correlation potential.
Tycko, R. (2007).
"Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR."
The Journal of Chemical Physics 126(6): 064506-9.
Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. 13C NMR data for singly-13C-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. 15N-detected and 13C-detected measurements of intramolecular 15N–15N distances in peptides with alpha-helical and beta-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone psi torsion angles in peptides containing uniformly 15N- and 13C-labeled amino acids.
Iuga, A., D. Iuga, et al. (2007).
"Observation of satellite signals due to scalar coupling to spin-1/2 isotopes in solid-state nuclear magnetic resonance spectroscopy."
The Journal of Chemical Physics 126(5): 054305-10.
A method is introduced to select the signal from a spin-1/2 nucleus I specifically bound to another spin-1/2 nucleus S for solid-state magic angle spinning nuclear magnetic resonance (NMR) spectroscopy via correlation through the heteronuclear J coupling. This experiment is analogous to the bilinear rotation decoupling (BIRD) sequence in liquid-state NMR spectroscopy which selects for signals from 1H directly bound to 13C. The spin dynamics of this modified BIRD experiment is described using the product-operator formalism, where experimental considerations such as rotor synchronization and the effect of large chemical shielding anisotropies on I and S are discussed. Two experiments are proposed that accommodate large chemical shielding anisotropies on S: (1) by stepping the inversion pulse frequency through the entire S spectral range or (2) by adiabatically inverting the S spins. Both these experiments are shown to successfully select the signal of 19F bound to 129Xe in XeF+ salts, removing the contributions from isotopomers containing non-spin-1/2 Xe isotopes. The feasibility in obtaining isotope-selective 19F spectra of inorganic fluoride compounds is discussed, and further modifications are proposed to expand the application to other chemical systems.
Thursday, March 08, 2007
JACS Journal update- January 2007 -Present, continued
J. Am. Chem. Soc., 129 (8), 2398 -2407, 2007.
Probing Hydrogen Bonding and Ion-Carbonyl Interactions by Solid-State 17O NMR Spectroscopy: G-Ribbon and G-Quartet
Irene C. M. Kwan, Xin Mo, and Gang Wu*
Abstract:
We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1·2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6···H-N2 and N7···H-N7 hydrogen bonds in a zigzag fashion. In addition, the keto carbonyl oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1·2H2O are: Molecule A, CQ = 7.8 ± 0.1 MHz, Q = 0.45 ± 0.05, iso = 263 ± 2, 11 = 460 ± 5, 22 = 360 ± 5, 33 = -30 ± 5 ppm; Molecule B, CQ = 7.7 ± 0.1 MHz, Q = 0.55 ± 0.05, iso = 250 ± 2, 11 = 440 ± 5, 22 = 340 ± 5, 33 = -30 ± 5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6···H-N1 and N7···H-N2 hydrogen bonds in a cyclic fashion. In addition, each O6 atom is simultaneously coordinated to two K+ ions. For G1/K+ gel, the experimental 17O NMR tensors are: CQ = 7.2 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2, 11 = 400 ± 5, 22 = 300 ± 5, 33 = -20 ± 5 ppm. In the presence of divalent cations such as Sr2+, Ba2+, and Pb2+, G2 molecules form discrete octamers containing two stacking G-quartets and a central metal ion, that is, (G2)4-M2+-(G2)4. In this case, each O6 atom of the G-quartet is coordinated to only one metal ion. For G2/M2+ octamers, the experimental 17O NMR parameters are: Sr2+, CQ = 6.8 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm; Ba2+, CQ = 7.0 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2 ppm; Pb2+, CQ = 7.2 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm. We also perform extensive quantum chemical calculations for the 17O NMR tensors in both G-ribbons and G-quartets. Our results demonstrate that the 17O chemical shift tensor and quadrupole coupling tensor are very sensitive to the presence of hydrogen bonding and ion-carbonyl interactions. Furthermore, the effect from ion-carbonyl interactions is several times stronger than that from hydrogen-bonding interactions. Our results establish a basis for using solid-state 17O NMR as a probe in the study of ion binding in G-quadruplex DNA and ion channel proteins.
Probing Hydrogen Bonding and Ion-Carbonyl Interactions by Solid-State 17O NMR Spectroscopy: G-Ribbon and G-Quartet
Irene C. M. Kwan, Xin Mo, and Gang Wu*
Abstract:
We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1·2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6···H-N2 and N7···H-N7 hydrogen bonds in a zigzag fashion. In addition, the keto carbonyl oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1·2H2O are: Molecule A, CQ = 7.8 ± 0.1 MHz, Q = 0.45 ± 0.05, iso = 263 ± 2, 11 = 460 ± 5, 22 = 360 ± 5, 33 = -30 ± 5 ppm; Molecule B, CQ = 7.7 ± 0.1 MHz, Q = 0.55 ± 0.05, iso = 250 ± 2, 11 = 440 ± 5, 22 = 340 ± 5, 33 = -30 ± 5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6···H-N1 and N7···H-N2 hydrogen bonds in a cyclic fashion. In addition, each O6 atom is simultaneously coordinated to two K+ ions. For G1/K+ gel, the experimental 17O NMR tensors are: CQ = 7.2 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2, 11 = 400 ± 5, 22 = 300 ± 5, 33 = -20 ± 5 ppm. In the presence of divalent cations such as Sr2+, Ba2+, and Pb2+, G2 molecules form discrete octamers containing two stacking G-quartets and a central metal ion, that is, (G2)4-M2+-(G2)4. In this case, each O6 atom of the G-quartet is coordinated to only one metal ion. For G2/M2+ octamers, the experimental 17O NMR parameters are: Sr2+, CQ = 6.8 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm; Ba2+, CQ = 7.0 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2 ppm; Pb2+, CQ = 7.2 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm. We also perform extensive quantum chemical calculations for the 17O NMR tensors in both G-ribbons and G-quartets. Our results demonstrate that the 17O chemical shift tensor and quadrupole coupling tensor are very sensitive to the presence of hydrogen bonding and ion-carbonyl interactions. Furthermore, the effect from ion-carbonyl interactions is several times stronger than that from hydrogen-bonding interactions. Our results establish a basis for using solid-state 17O NMR as a probe in the study of ion binding in G-quadruplex DNA and ion channel proteins.
Progress in NMR
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 71–85
Solid state NMR studies of molecular recognition at protein–mineral interfaces
Gil Goobes a,1, Patrick S. Stayton b,2, Gary P. Drobny a,*
a Department of Chemistry, University of Washington, Box 351700, Seattle WA 98195, USA
b Department of Bioengineering, University of Washington, Box 355061, Seattle WA 98195, USA
Available online 26 January 2007
Keywords: Adsorbed protein; Structure determination; Recoupling; Magic angle spinning; Biomineralization
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 87–174
R. Böhmer,, K.R. Jeffrey and M. Vogel
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Solid-state Li NMR with applications to the translational dynamics in ion conductors
Available online 9 February 2007
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow
dynamics
Solid state NMR studies of molecular recognition at protein–mineral interfaces
Gil Goobes a,1, Patrick S. Stayton b,2, Gary P. Drobny a,*
a Department of Chemistry, University of Washington, Box 351700, Seattle WA 98195, USA
b Department of Bioengineering, University of Washington, Box 355061, Seattle WA 98195, USA
Available online 26 January 2007
Keywords: Adsorbed protein; Structure determination; Recoupling; Magic angle spinning; Biomineralization
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 87–174
R. Böhmer,, K.R. Jeffrey and M. Vogel
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Solid-state Li NMR with applications to the translational dynamics in ion conductors
Available online 9 February 2007
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow
dynamics
Tuesday, March 06, 2007
General Interest
1) High resolution NMR of water absorbed in single-wall carbon nanotubes
Sekhaneh, Wassef; Kotecha, Mrignayani; Dettlaff-Weglikowska, Urszula; Veeman, Wiebren S.
Abstract
1H MAS NMR study of water absorbed in open single-wall carbon nanotubes (SWCNTs) of average diameter 1.0 nm, synthesized with a Fe catalyst, was performed. Magic angle spinning significantly increases the spectral resolution and the spectrum shows that there are at least two distinct chemical shift regions for the water proton. From temperature dependent measurements, we assign the two chemical shift ranges to water absorbed inside and outside the nanotube. The spectra as a function of the water content show that the first water molecules that are absorbed by the dry material are absorbed inside the tubes.
CPL vol. 428 p 143
2) Characterization of violet emission from Rb optical pumping cells used in laser-polarized xenon NMR experiments
Indrajit Saha, Panayiotis Nikolaou, Nicholas Whiting, Boyd M. Goodson
Abstract
Visible emission from Rb optical pumping cells was characterized under a range of conditions relevant to the production of laserpolarized xenon (including temperature, partial pressures, and D1-resonant 795 nm laser power). Bright 421 nm (6P ! 5S) emission was consistent with energy-pooling processes of the type: Rb*(5P1/2) + Rb*(5P1/2,3/2)!Rb*(6P1/2,3/2) + Rb(5S1/2), with processes transiting through 5D states likely contributing at higher temperatures/lower N2 partial pressures. Under such conditions a number of Rb lines may be observed, indicating population of Rb states to P9D (31822 cm1). Such energies exceed those required for efficient production of laser-induced plasma.
CPL vol. 428 p 268
3) Double-quantum-filtered intermolecular single-quantum coherences in nuclear magnetic resonance spectroscopy and imaging
Zhong Chen, Xiaoqin Zhu, Bingwen Zheng, Shuhui Cai, Jianhui Zhong
Abstract
Based on the double-quantum-filtered technique, a three-pulse sequence was designed to effectively eliminate contamination of residual conventional single-quantum coherences (SQC) from intermolecular SQC signals in single-resonance spin-1/2 samples such as water. Analytical expressions were derived from the modified Bloch equations with dipolar fields. All experimental observations and numerical simulation results are in excellent agreement with the theoretical predictions. Compared to the CRAZED sequence, the sequence can effectively suppress residual conventional SQC signals even with great imperfection of radio-frequency pulse flip angles. For the first time, signals from pure intermolecular SQCs were selectively observed in forms of spectrum or image.
CPL vol 429 p 611
4) STARTMAS: A MAS-based method for acquiring isotropic NMR spectra of spin I = 3/2 nuclei in real time
Michael J. Thrippleton, Thomas J. Ball, Stefan Steuernagel, Sharon E. Ashbrook, Stephen Wimperis
Abstract
We describe a novel method, which we call STARTMAS, that allows acquisition of high-resolution or ‘isotropic’ spin I = 3/2 NMR spectra in solids in real time. Unlike the DOR technique of Samoson et al. [Mol. Phys. 65 (1988) 1013], STARTMAS is performed on a standard MAS probe and fast spinning rates are possible. The method consists of a multiple-pulse sequence interleaved with real-time data acquisition and exploits satellite (mI = ±3/2M±1/2) and double-quantum (±3/2M «1/2) transitions. We show that STARTMAS experiments can be used to obtain one-dimensional DOR-like spectra or provide an ‘ultrafast’ route to high-resolution two-dimensional spectra.
CPL vol 431 p 390
5) Improved double-quantum NMR correlation spectroscopy of dipolar-coupled quadrupolar spins
Mattias Ede´n a,*, Dan Zhou b, Jihong Yu
Abstract
We show that symmetry-based zero-quantum dipolar recoupling sequences sandwiched between central transition selective p/2-pulses may be used to excite double-quantum coherences (2QC) between the central transitions of homonuclear half-integer quadrupolar spins undergoing magic-angle spinning. The 2QC excitation is explored experimentally by 23Na and 27Al NMR on Na2SO3 and a-Al2O3 model compounds. When incorporated into 2Q–1Q 2D correlation protocols, the new recoupling method established all expected 27Al-27Al connectivities over 6A ˚ in the open-framework aluminophosphate AlPO–J19 [(NH4)2Al4(PO4)4HPO4 Æ H2O] and the layer mineral chlorite [Mg9Al6Si5O20(OH)16].
CPL vol 431 p 397
6) 27Al double rotation two-dimensional spin diffusion NMR: Complete unambiguous assignment of aluminium sites in 9Al2O3 Æ 2B2O3
I. Hung, A.P. Howes, T. Anupold, A. Samoson, D. Massiot, M.E. Smith, S.P. Brown, R. Dupree
Abstract
High-resolution two-dimensional 27Al spin diffusion NMR spectra of 9Al2O3 Æ 2B2O3 recorded under double rotation for different mixing times are presented. The two crystallographically distinct pentahedral Al sites are distinguished by the presence or absence of correlation peaks with neighboring tetrahedral sites.
CPL vol. 432 p 152
7) Solid-state 17O NMR in carbohydrates
T.H. Sefzik, J.B. Houseknecht, T.M. Clark, S. Prasad, T.L. Lowary, Z. Gan, P.J. Grandinetti
Abstract
Solid-state 17O magic-angle spinning nuclear magnetic resonance measurements at 19.5 Tesla were performed on 17O-enriched methyl a-D-galactopyranoside (4-17O), methyl b-D-glucopyranoside (2-17O), methyl a-D-glucopyranoside (4-17O), methyl a-D-glucopyranoside (6-17O), and a-D-glucopyranosyl (1 !6) a-D-glucopyranoside (6-17O). The 17O quadrupolar coupling constants and asymmetry parameters measured can be predicted with a model based entirely on the first-coordination sphere around oxygen. For the hydroxyl sites observed in the methyl glucosides, the quadrupolar coupling parameters are nearly identical, within 10% as predicted, given their nearly identical first-coordination sphere structures.
CPL 434 p 312
8) Fast adiabatic pulses for solid-state NMR of paramagnetic systems
Gwendal Kervern, Guido Pintacuda, Lyndon Emsley
Abstract
We present a simple framework for determining the parameters for efficient adiabatic pulses in solids with very large shift anisotropies under very fast MAS. We introduce the notion of the effective adiabatic quality factor to describe the spin dynamics. We then demonstrate the use of short, high-power adiabatic pulses (SHAPs) for population inversion in paramagnetic solids, and show its application to various systems with differing proton anisotropies in iron, ytterbium, and terbium complexes, from 400 to more than 1000 ppm. We then show how these pulses yield improvements in refocusing schemes and TEDOR NMR experiments on paramagnetic solids.
CPL vol 435 p 157
9) Proton-detected 14N MAS NMR using homonuclear decoupled rotary resonance
Zhehong Gan, Jean Paul Amoureux, Julien Trebosc
Abstract
A robust sensitivity-enhanced 1H/14N MAS HMQC experiment is described for proton-detected 14N NMR of solids. The sensitivity enhancement is achieved by using dipolar recoupling for coherence transfer with a so-called n = 2 rotary resonance. Rotary resonance occurs when a cw rf field matches certain ratios with the sample spinning frequency, n = x1/xr. The theory of rotary resonance for chemical shift anisotropy, heteronuclear and homonuclear dipolar interactions is presented in the irreducible representation. It is shown that the n = 2 rotary resonance decouples the homonuclear dipolar interactions while recoupling the heteronuclear dipolar interaction for proton-detected 14N NMR. The dipolar recoupling, T 02 lengthening, and 1H/14N HMQC experiment under the n = 2 rotary resonance are demonstrated.
CPL vol 435 p 163
10) High-resolution two-dimensional NMR spectra of half-integer-spin quadrupolar nuclei from one-dimensional projections
Thomas Vosegaard a,*, Dominique Massiot
Abstract
We present a technique providing high-resolution spectra of quadrupolar nuclei with half-integer nuclear spin displaying significant second-order linebroadening. The technique, dubbed chemical shift – quadrupolar projection-reconstruction of one-dimensional spectra (CQ-PRODI) exploits the different magnetic field dependence of the chemical shift and second-order quadrupolar effect. One-dimensional spectra recorded at different magnetic field strengths are represented as projections along different directions in the two-dimensional spectrum that correlates the chemical shift and the second-order quadrupolar lineshape. We present CQ-PRODI spectra for 27Al in 9Al2O3 Æ 2B2O3 and for 71Ga in b-Ga2O3 which display resolution of all sites in the chemical shift dimension.
CPL vol 437 p 120
11) Gas-Phase NMR Measurements, Absolute Shielding Scales, and Magnetic Dipole Moments
of 29Si and 73Ge Nuclei
W. Makulski, K. Jackowski, A. Antusek, and M. Jaszunski
Abstarct
New gas-phase NMR measurements of the shielding constants of 29Si, 73Ge, and 1H nuclei in SiH4 and GeH4 are reported. The results, extrapolated to zero density, provide accurate isolated molecule values, best suited for comparison with theoretical calculations. Using the recent ab initio results for these molecules and the measured chemical shifts, we determine the absolute shielding scales for 29Si and 73Ge. This allows us to provide new values of the nuclear magnetic dipole moments for these two nuclei; in addition, we examine the dipole moments of 13C and 119Sn.
JPCA vol 110 p 11462
12) An ab Initio Study of 15N-11B Spin-Spin Coupling Constants for Borazine and Selected
Derivatives
Janet E. Del Bene, Jose Elguero, Ibon Alkorta, Manuel Yanez, and Otilia Mo
Abstract
Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond 11B-15N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on 13C-13C coupling constants for benzene.
JPCA vol 110 p 9959
13) Proton NMR measurements of the local magnetic field in the paramagnetic metal
and antiferromagnetic insulator phases of lamda-(BETS)2FeCl4
Guoqing Wu, P. Ranin, W. G. Clark, S. E. Brown, L. Balicas, and L. K. Montgomery
Abstract
Measurements of the 1H-NMR spectrum of a small 4g single crystal of the organic conductor BETS2FeCl4 are reported with an applied magnetic field B0=9 T parallel to the a axis in the ac plane over a temperature T range 2.0–180 K. They provide the distribution of the static local magnetic field at the proton sites in the paramagnetic metal PM and antiferromagnetic insulator AFI phases, along with the changes that occur at the PM-AFI phase transition. The spectra have six main peaks that are significantly broadened and shifted at low T. The origin of these features is attributed to the large dipolar field from the
3d Fe3+ ion moments spin Sd=5/2. Their amplitude and T dependence are modeled using a modified Brillouin function that includes a mean field approximation for the total exchange interaction J0 between one Fe3+ ion and its two nearest neighbors. A good fit is obtained using J0=−1.7 K. At temperatures below the PM-AFI transition temperature TMI=3.5 K, an extra peak appears on the high frequency side of the spectrum and the details of the spectrum become smeared. Also, the rms linewidth and the frequency shift of the spectral distribution are discontinuous, consistent with the transition being first order. These measurements verify that the dominant local magnetic field contribution is from the Fe3+ ions and indicate that there is a significant change in the static local magnetic field distribution at the proton sites on traversing the PM to AFI phase transition.
PRB vol 74 p 064428
14) Structural, Solid-State NMR and Theoretical Studies of the Inverse- Coordination of Lithium Chloride Using Group 13 Phosphide Hosts
Melinda J. Duer, Felipe Garc1a, Jonathan M. Goodman, Jçrg P. Hehn, Richard A. Kowenicki, Vesal Naseri, Mary McPartlin, Matthew L. Stead, Robin Stein, and Dominic S. Wright
Abstract: The reaction of MeAlCl2 with ’PhPLi2’ in THF gives [{MeAl-(PPh)3Li4·3THF}4ACHTUNGTRENUNG(m4-Cl)]Li+ (1). The GaIII and InIII analogues, [{MeEACHTUNGTRENUNG(PPh)3Li4·3THF}4ACHTUNGTRENUNG(m4-Cl)]Li+·(THF)3 (E=Ga (2), In (3)), are obtained by the in situ reactions of MeECl2 with PhPLi2 in THF. For all of the complexes, the cage anions have an unusual cubic arrangement that is similar to a zeolite, and contain large voids (ca. 17 8). The location of the Li+ counterions in 1–3 and their coordination environment appears to subtly reflect variations in packing and lattice energy. Whereas in 1 highly mobile, loosely coordinated Li+ counterions are present, 2 and 3 contain less mobile THF-solvated counterions within the cavities. X-ray crystallographic and solid-state NMR studies are reported on 1–3, together with model DFT calculations on the selectivity of halide coordination.
CEJ vol 13 p 1251
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