ASAP Chem. Mater., ASAP Article, 10.1021/cm702523d Web Release Date: February 29, 2008 Copyright © 2008 American Chemical Society
Determination and Quantification of the Local Environments in Stoichiometric and Defect Jarosite by Solid-State 2H NMR Spectroscopy
Ulla Gro Nielsen,†‡ Juraj Majzlan,§ and Clare P. Grey*†
Abstract:
The nature and concentrations of the local environments in a series of deuterated jarosite (nominally AFe3(SO4)2(OD)6 with A = K, Na, and D3O) samples with different levels of iron and cation vacancies have been determined by 2H MAS NMR spectroscopy at ambient temperatures. Three different local deuteron environments, Fe2OD, FeOD2, and D2O/D3O+, can be separated based on their very different Fermi contact shifts of δ ≈ 237, 70, and 0 ppm, respectively. The FeOD2 group arises from the charge compensation of the Fe3+ vacancies, allowing the concentrations of the vacancies to be readily determined. Analysis of the 2H quadrupole interaction indicates that the FeOD2 groups are mobile, undergoing rapid 180° flips on the NMR time scale; the D2O/D3O+ species (located on the A sites) undergo close to isotropic motion, whereas the Fe2OD groups are rigid and are hydrogen-bonded to nearby sulfate O atoms, with a (Fe)OD−O(S) distance of 2.79(4) Å. No evidence for the intrinsic protonation reaction Fe2OH + H3O+ → Fe2OH2 + H2O is found in the hydronium jarosite, suggesting that this mechanism is not the cause of the anomalous magnetic behavior of this material. The results illustrate that 2H MAS NMR spectroscopy is an excellent probe of the local environments and defects, on the atomic/molecular level, providing information that is complementary to diffraction techniques and that will help to rationalize the magnetic properties of these materials.
J. Am. Chem. Soc., ASAP Article 10.1021/ja709975z S0002-7863(70)09975-4 Web Release Date: February 23, 2008 Copyright © 2008 American Chemical Society
Direct NMR Detection of Alkali Metal Ions Bound to G-Quadruplex DNA
Ramsey Ida and Gang Wu*
Abstract:
We describe a general multinuclear (1H, 23Na, 87Rb) NMR approach for direct detection of alkali metal ions bound to G-quadruplex DNA. This study is motivated by our recent discovery that alkali metal ions (Na+, K+, Rb+) tightly bound to G-quadruplex DNA are actually "NMR visible" in solution (Wong, A.; Ida, R.; Wu, G. Biochem. Biophys. Res. Commun. 2005, 337, 363). Here solution and solid-state NMR methods are developed for studying ion binding to the classic G-quadruplex structures formed by three DNA oligomers: d(TG4T), d(G4T3G4), and d(G4T4G4). The present study yields the following major findings. (1) Alkali metal ions tightly bound to G-quadruplex DNA can be directly observed by NMR in solution. (2) Competitive ion binding to the G-quadruplex channel site can be directly monitored by simultaneous NMR detection of the two competing ions. (3) Na+ ions are found to locate in the diagonal T4 loop region of the G-quadruplex formed by two strands of d(G4T4G4). This is the first time that direct NMR evidence has been found for alkali metal ion binding to the diagonal T4 loop in solution. We propose that the loop Na+ ion is located above the terminal G-quartet, coordinating to four guanine O6 atoms from the terminal G-quartet and one O2 atom from a loop thymine base and one water molecule. This Na+ ion coordination is supported by quantum chemical calculations on 23Na chemical shifts. Variable-temperature 23Na NMR results have revealed that the channel and loop Na+ ions in d(G4T4G4) exhibit very different ion mobilities. The loop Na+ ions have a residence lifetime of 220 s at 15 C, whereas the residence lifetime of Na+ ions residing inside the G-quadruplex channel is 2 orders of magnitude longer. (4) We have found direct 23Na NMR evidence that mixed K+ and Na+ ions occupy the d(G4T4G4) G-quadruplex channel when both Na+ and K+ ions are present in solution. (5) The high spectral resolution observed in this study is unprecedented in solution 23Na NMR studies of biological macromolecules. Our results strongly suggest that multinuclear NMR is a viable technique for studying ion binding to G-quadruplex DNA.
Friday, February 29, 2008
Thursday, February 28, 2008
Joel's Journal Update
Spin-counting NMR experiments for the spectral editing of structural motifs in solids
Michaël Deschamps, Franck Fayon, Julien Hiet, Geoffroy Ferru, Marc Derieppe, Nadia Pellerin and Dominique Massiot
PCCP(2008)10,1298.
Abstract:
Scalar couplings, recoupled or full dipolar interactions can be used to characterize multinuclear structural molecular motifs in solids, by counting the neighbouring spins in solid-state NMR, opening new ways for the differentiation of overlapping spectral responses which is a limiting factor in many high resolution experiments carried out on disordered systems.
Experimental and Computational Characterization of the 17O Quadrupole Coupling and Magnetic Shielding Tensors or p-Nitrobenzaldehyde and Formaldehyde.
Gang Wu, Peter Mason, Xin Mo, and Victor Terskikh
JPCA(2008)112,1024.
Abstract:
We have used solid-state 17O NMR experiments to determine the 17O quadrupole coupling (QC) tensor and chemical shift (CS) tensor for the carbonyl oxygen in p-nitro-[1-17O]benzaldehyde. Analyses of solid-state 17O NMR spectra obtained at 11.75 and 21.15 T under both magic-angle spinning (MAS) and stationary conditions yield the magnitude and relative orientation of these two tensors: CQ = 10.7 ± 0.2 MHz, Q = 0.45 ± 0.10, 11 = 1050 ± 10, 22 = 620 ± 10, 33 = -35 ± 10, = 90 ± 10, = 90 ± 2, = 90 ± 10. The principal component of the 17O CS tensor with the most shielding, 33, is perpendicular to the H-C=O plane, and the tensor component with the least shielding, 11, lies along the C=O bond. For the 17O QC tensor, the largest (zz) and smallest (xx) components are both in the H-C=O plane being perpendicular and parallel to the C=O bond, respectively. This study represents the first time that these two fundamental 17O NMR tensors have been simultaneously determined for the carbonyl oxygen of an aldehyde functional group by solid-state 17O NMR. The reported experimental solid-state 17O NMR results provide the first set of reliable data to allow evaluation of the effect of electron correlation on individual CS tensor components. We found that the electron correlation effect exhibits significant influence on 17O chemical shielding in directions within the H-C=O plane. We have also carefully re-examined the existing experimental data on the 17O spin-rotation tensor for formaldehyde and proposed a new set of best "experimental" 17O chemical shielding tensor components: 11 = -1139 ± 80, 22 = -533 ± 80, 33 = 431 ± 5, and iso = -414 ± 60 ppm. Using this new set of data, we have evaluated the accuracy of quantum chemical calculations of the 17O CS tensors for formaldehyde at the Hartree-Fock (HF), density-functional theory (DFT), Mller-Plesset second-order perturbation (MP2), and coupled-cluster singles and doubles (CCSD) levels of theory. The conclusion is that, while results from HF and DFT tend to underestimate the electron correlation effect, the MP2 method overestimates its contribution. The CCSD results are in good agreement with the experimental data.
Proton Spin Diffusion in Polyethylene as a Function of Magic-Angle Spinning Rate. A Phenomenological Approach.
Zhenlong Jia, Lili Zhang, Qun Chen, and E. W. Hansen
JPCA(2008)112,1228.
Abstract:
Starting from the phenomenological Bloembergen-Purcell-Pound equation a relation between magic-angle spinning (MAS) rate and spin diffusion is derived. The resulting model equation was fitted to observed spin diffusion versus MAS rate data obtained at 298 K on an high-density polyethylene sample, revealing a reduction in the effective spin diffusivity by (65 + 5)% when increasing the MAS rate from 2 to 12 kHz. The same model equation enabled the rigid-lattice diffusivity to be estimated and was found to be only slightly higher, by approximately 10%, compared to the spin diffusivity observed at the lowest MAS rate applied (2 kHz). Moreover, the model equation predicts a reduction in the effective spin diffusivity by more than 90% when increasing the MAS rate to more than 30 kHz.
Michaël Deschamps, Franck Fayon, Julien Hiet, Geoffroy Ferru, Marc Derieppe, Nadia Pellerin and Dominique Massiot
PCCP(2008)10,1298.
Abstract:
Scalar couplings, recoupled or full dipolar interactions can be used to characterize multinuclear structural molecular motifs in solids, by counting the neighbouring spins in solid-state NMR, opening new ways for the differentiation of overlapping spectral responses which is a limiting factor in many high resolution experiments carried out on disordered systems.
Experimental and Computational Characterization of the 17O Quadrupole Coupling and Magnetic Shielding Tensors or p-Nitrobenzaldehyde and Formaldehyde.
Gang Wu, Peter Mason, Xin Mo, and Victor Terskikh
JPCA(2008)112,1024.
Abstract:
We have used solid-state 17O NMR experiments to determine the 17O quadrupole coupling (QC) tensor and chemical shift (CS) tensor for the carbonyl oxygen in p-nitro-[1-17O]benzaldehyde. Analyses of solid-state 17O NMR spectra obtained at 11.75 and 21.15 T under both magic-angle spinning (MAS) and stationary conditions yield the magnitude and relative orientation of these two tensors: CQ = 10.7 ± 0.2 MHz, Q = 0.45 ± 0.10, 11 = 1050 ± 10, 22 = 620 ± 10, 33 = -35 ± 10, = 90 ± 10, = 90 ± 2, = 90 ± 10. The principal component of the 17O CS tensor with the most shielding, 33, is perpendicular to the H-C=O plane, and the tensor component with the least shielding, 11, lies along the C=O bond. For the 17O QC tensor, the largest (zz) and smallest (xx) components are both in the H-C=O plane being perpendicular and parallel to the C=O bond, respectively. This study represents the first time that these two fundamental 17O NMR tensors have been simultaneously determined for the carbonyl oxygen of an aldehyde functional group by solid-state 17O NMR. The reported experimental solid-state 17O NMR results provide the first set of reliable data to allow evaluation of the effect of electron correlation on individual CS tensor components. We found that the electron correlation effect exhibits significant influence on 17O chemical shielding in directions within the H-C=O plane. We have also carefully re-examined the existing experimental data on the 17O spin-rotation tensor for formaldehyde and proposed a new set of best "experimental" 17O chemical shielding tensor components: 11 = -1139 ± 80, 22 = -533 ± 80, 33 = 431 ± 5, and iso = -414 ± 60 ppm. Using this new set of data, we have evaluated the accuracy of quantum chemical calculations of the 17O CS tensors for formaldehyde at the Hartree-Fock (HF), density-functional theory (DFT), Mller-Plesset second-order perturbation (MP2), and coupled-cluster singles and doubles (CCSD) levels of theory. The conclusion is that, while results from HF and DFT tend to underestimate the electron correlation effect, the MP2 method overestimates its contribution. The CCSD results are in good agreement with the experimental data.
Proton Spin Diffusion in Polyethylene as a Function of Magic-Angle Spinning Rate. A Phenomenological Approach.
Zhenlong Jia, Lili Zhang, Qun Chen, and E. W. Hansen
JPCA(2008)112,1228.
Abstract:
Starting from the phenomenological Bloembergen-Purcell-Pound equation a relation between magic-angle spinning (MAS) rate and spin diffusion is derived. The resulting model equation was fitted to observed spin diffusion versus MAS rate data obtained at 298 K on an high-density polyethylene sample, revealing a reduction in the effective spin diffusivity by (65 + 5)% when increasing the MAS rate from 2 to 12 kHz. The same model equation enabled the rigid-lattice diffusivity to be estimated and was found to be only slightly higher, by approximately 10%, compared to the spin diffusivity observed at the lowest MAS rate applied (2 kHz). Moreover, the model equation predicts a reduction in the effective spin diffusivity by more than 90% when increasing the MAS rate to more than 30 kHz.
Friday, February 22, 2008
Hiyam's Journal Update
Low-lying excitations at the rare-earth site due to the rattling motion in the filled skutterudite LaOs4Sb12 revealed by 139La NMR and 121/123Sb NQR
Yusuke Nakai,1 Kenji Ishida,1 Hitoshi Sugawara,2 Daisuke Kikuchi,3 and Hideyuki Sato3
Abstract
We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the Sb site in the filled skutterudite LaOs4Sb12. We found that the nuclear spin-lattice relaxation rate divided by temperature 1/T1T at the La site exhibits a different temperature dependence from that at the Sb site. Although 1/T1T at the Sb site is explained by the Korringa mechanism, 1/T1T at the La site exhibits a broad maximum around 50 K, showing the presence of an additional contribution at the La site. The additional low-lying excitations observed at the La site can be understood with the relaxation from anharmonic phonons due to the rattling motion of the La atoms.
Phys. Rev. B 77, 014412 (2008) (10 pages)
17O and 51V NMR for the zigzag spin-1 chain compound CaV2O4
X. Zong,1,2 B. J. Suh,1 A. Niazi,1 J. Q. Yan,1 D. L. Schlagel,3 T. A. Lograsso,3 and D. C. Johnston1,2
1Ames Laboratory, Ames, Iowa 50011, USA
Abstract
51V NMR studies on CaV2O4 single crystals and 17O NMR studies on 17O-enriched powder samples are reported. The temperature dependences of the 17O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at TN=78 K in the powder. Magnetic susceptibility measurements show that TN=69 K in the crystals. A zero-field 51V NMR signal was observed at low temperatures (f237 MHz at 4.2 K) in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is collinear, with the easy axes of the two substructures separated by an angle of 19(1)°, and with their average direction pointing approximately along the b axis of the crystal structure. The two spin substructures contain equal numbers of spins. The temperature dependence of the ordered moment, measured up to 45 K, shows the presence of an energy gap EG in the antiferromagnetic spin wave excitation spectrum. Antiferromagnetic spin wave theory suggests that EG/kB lies between 64 and 98 K.
J. Am. Chem. Soc., ASAP Article 10.1021/ja0778803 S0002-7863(07)07880-8 Web Release
Solid-State Deuterium NMR Studies Reveal s-ns Motions in the HIV-1 Transactivation Response RNA Recognition Site
Greg L. Olsen, Dorothy C. Echodu, Zahra Shajani, Michael F. Bardaro, Jr., Gabriele Varani, and Gary P. Drobny*
Abstract:
Solution and solid-state NMR measurements were used together to examine motion in three sites in the HIV-1 TAR RNA. We wished to investigate the dynamics facilitating the conformational rearrangements the TAR RNA must undergo for Tat binding and in particular to characterize the full range of motional time scales accessible to this RNA. Our results demonstrate that the dynamics in TAR involving residues essential to Tat binding include not only the faster motions detected by solution relaxation measurements but also a significant component in the s-ns time scale.
J. Am. Chem. Soc., 130 (8), 2667 -2675, 2008. 10.1021/ja078337p S0002-7863(07)08337-0 Web Release Date: February 1, 2008 Copyright © 2008 American Chemical Society
Probing Chemical Shifts of Invisible States of Proteins with Relaxation Dispersion NMR Spectroscopy: How Well Can We Do?
D. Flemming Hansen, Pramodh Vallurupalli, Patrik Lundström, Philipp Neudecker, and Lewis E. Kay*
Abstract:
Carr-Purcell-Meiboom-Gill relaxation dispersion NMR spectroscopy has evolved into a powerful approach for the study of low populated, invisible conformations of biological molecules. One of the powerful features of the experiment is that chemical shift differences between the exchanging conformers can be obtained, providing structural information about invisible excited states. Through the development of new labeling approaches and NMR experiments it is now possible to measure backbone 13C and 13CO relaxation dispersion profiles in proteins without complications from 13C-13C couplings. Such measurements are presented here, along with those that probe exchange using 15N and 1HN nuclei. A key experimental design has been the choice of an exchanging system where excited-state chemical shifts were known from independent measurement. Thus it is possible to evaluate quantitatively the accuracy of chemical shift differences obtained in dispersion experiments and to establish that in general very accurate values can be obtained. The experimental work is supplemented by computations that suggest that similarly accurate shifts can be measured in many cases for systems with exchange rates and populations that fall within the range of those that can be quantified by relaxation dispersion. The accuracy of the extracted chemical shifts opens up the possibility of obtaining quantitative structural information of invisible states of the sort that is now available from chemical shifts recorded on ground states of proteins.
J. Am. Chem. Soc., 130 (8), 2432 -2433, 2008. 10.1021/ja710477h S0002-7863(71)00477-3 Web Release Date: February 5, 2008 Copyright © 2008 American Chemical Society
Accurately Probing Slow Motions on Millisecond Timescales with a Robust NMR Relaxation Experiment
Dong Long, Maili Liu, and Daiwen Yang*
Abstract:
A new pulse scheme is proposed for the accurate measurement of relaxation dispersion, which cycles the phases of CPMG pulses. Numerical simulations show that systematic errors in the measured relaxation rates mainly result from off-resonance and radio frequency inhomogeneity effects and they can be significantly suppressed with the method proposed here. The method has been demonstrated on human liver fatty acid binding protein. It allows the reliable identification of residues undergoing conformational exchange on millisecond timescales and accurate extraction of kinetics parameters. The relaxation dispersion data indicate that human liver fatty acid binding protein is highly flexible on millisecond timescales.
J. Am. Chem. Soc., 130 (8), 2412 -2413, 2008. 10.1021/ja710557t S0002-7863(71)00557-2 Web Release Date: February 1, 2008 Copyright © 2008 American Chemical Society
A High-Resolution 43Ca Solid-State NMR Study of the Calcium Sites of Hydroxyapatite
Danielle Laurencin, Alan Wong, John V. Hanna, Ray Dupree, and Mark E. Smith*
Abstract:
High resolution 43Ca solid-state NMR studies of hydroxyapatite (Ca10(PO4)6(OH)2) were performed at 14.1 T. The two crystallographically distinct calcium sites were unequivocally resolved by a triple-quantum magic angle spinning experiment, and the unambiguous assignment of the signals was possible using 1H-43Ca rotational echo double resonance and 1H-43Ca cross polarization magic angle spinning experiments.
J. Am. Chem. Soc., ASAP Article 10.1021/
Probing Local Structure in Zeolite Frameworks: Ultrahigh-Field NMR Measurements and Accurate First-Principles Calculations of Zeolite 29Si Magnetic Shielding Tensors
Darren H. Brouwer* and Gary D. Enright
Abstract:
The principal components of zeolite 29Si magnetic shielding tensors have been accurately measured and calculated for the first time. The experiments were performed at an ultrahigh magnetic field of 21.1 T in order to observe the small anisotropies of the 29Si shielding interactions that arise for Si atoms in near-tetrahedral geometries. A robust two-dimensional (2D) chemical shift anisotropy (CSA) recoupling pulse sequence was employed that enables quasi-static powder patterns to be resolved according to the isotropic chemical shifts. For the zeolites Sigma-2 and ZSM-12, it is demonstrated that the 29Si chemical shift (CS) tensor components measured by the recoupling experiment are in excellent agreement with those determined from spinning sidebands in slow magic-angle spinning (MAS) experiments. For the zeolite ZSM-5, the principal components of the 29Si CS tensors of 15 of the 24 Si sites were measured using the 2D CSA recoupling experiment, a feat that would not be possible with a slow MAS experiment due to the complexity of the spectrum. A simple empirical relationship between the 29Si CS tensors and local structural parameters could not be established. However, the 29Si magnetic shielding tensors calculated using Hartree-Fock ab initio calculations on clusters derived from the crystal structures are in excellent agreement with the experimental results. The accuracy of the calculations is strongly dependent on the quality of the crystal structure used in the calculation, indicating that the 29Si magnetic shielding interaction is extremely sensitive to the local structure around each Si atom. It is anticipated that the measurement and calculation of 29Si shielding tensors could be incorporated into the "NMR crystallography" of zeolites and other related silicate materials, possibly being used for structure refinements that may lead to crystal structures with very accurate Si and O atomic coordinates.
ASAP Chem. Mater., ASAP Article, 10.1021/cm0717763 Web Release Date: February 16, 2008 Copyright © 2008 American Chemical Society
A Solid-State NMR, X-ray Diffraction, and Ab Initio Investigation into the Structures of Novel Tantalum Oxyfluoride Clusters
Todd M. Alam,*† Jacalyn S. Clawson,†‡ François Bonhomme,† Steven G. Thoma,† Mark A. Rodriguez,† Shaohui Zheng,§ and Jochen Autschbach§
Abstract:
A series of tantalum oxyfluoride materials containing the [Ta4F16O4]4− and [Ta8F24O12]8− anion clusters have been synthesized and characterized using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (SSNMR) spectroscopy. The structure of both tantalum oxyfluoride materials display octahedrally bonded tantalum atoms with bridging oxygen and terminal fluoride atoms. The [Ta4F16O4]4− cluster is an eight-membered ring, whereas the [Ta8F24O12]8- cluster forms a cagelike structure. Solid-state dynamics of these clusters were explored by monitoring the impact of temperature on the one-dimensional (1D) 19F magic angle spinning (MAS) NMR, 13C cross-polarization (CP) MAS NMR, and two-dimensional (2D) double quantum (DQ) 19F MAS NMR spectra. The DQ 19F NMR correlation experiments allowed the through space connectivity between the different resolved fluorine environments to be determined, thus aiding in the spectral assignment and structural refinement of these materials. Ab initio 19F NMR chemical shift calculations were used to assist in the interpretation of the 19F NMR spectra. The influence of scalar relativistic and Ta−F spin–orbit coupling on the 19F NMR shielding calculation arising from bonding to tantalum atoms is also addressed.
Yusuke Nakai,1 Kenji Ishida,1 Hitoshi Sugawara,2 Daisuke Kikuchi,3 and Hideyuki Sato3
Abstract
We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the Sb site in the filled skutterudite LaOs4Sb12. We found that the nuclear spin-lattice relaxation rate divided by temperature 1/T1T at the La site exhibits a different temperature dependence from that at the Sb site. Although 1/T1T at the Sb site is explained by the Korringa mechanism, 1/T1T at the La site exhibits a broad maximum around 50 K, showing the presence of an additional contribution at the La site. The additional low-lying excitations observed at the La site can be understood with the relaxation from anharmonic phonons due to the rattling motion of the La atoms.
Phys. Rev. B 77, 014412 (2008) (10 pages)
17O and 51V NMR for the zigzag spin-1 chain compound CaV2O4
X. Zong,1,2 B. J. Suh,1 A. Niazi,1 J. Q. Yan,1 D. L. Schlagel,3 T. A. Lograsso,3 and D. C. Johnston1,2
1Ames Laboratory, Ames, Iowa 50011, USA
Abstract
51V NMR studies on CaV2O4 single crystals and 17O NMR studies on 17O-enriched powder samples are reported. The temperature dependences of the 17O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at TN=78 K in the powder. Magnetic susceptibility measurements show that TN=69 K in the crystals. A zero-field 51V NMR signal was observed at low temperatures (f237 MHz at 4.2 K) in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is collinear, with the easy axes of the two substructures separated by an angle of 19(1)°, and with their average direction pointing approximately along the b axis of the crystal structure. The two spin substructures contain equal numbers of spins. The temperature dependence of the ordered moment, measured up to 45 K, shows the presence of an energy gap EG in the antiferromagnetic spin wave excitation spectrum. Antiferromagnetic spin wave theory suggests that EG/kB lies between 64 and 98 K.
J. Am. Chem. Soc., ASAP Article 10.1021/ja0778803 S0002-7863(07)07880-8 Web Release
Solid-State Deuterium NMR Studies Reveal s-ns Motions in the HIV-1 Transactivation Response RNA Recognition Site
Greg L. Olsen, Dorothy C. Echodu, Zahra Shajani, Michael F. Bardaro, Jr., Gabriele Varani, and Gary P. Drobny*
Abstract:
Solution and solid-state NMR measurements were used together to examine motion in three sites in the HIV-1 TAR RNA. We wished to investigate the dynamics facilitating the conformational rearrangements the TAR RNA must undergo for Tat binding and in particular to characterize the full range of motional time scales accessible to this RNA. Our results demonstrate that the dynamics in TAR involving residues essential to Tat binding include not only the faster motions detected by solution relaxation measurements but also a significant component in the s-ns time scale.
J. Am. Chem. Soc., 130 (8), 2667 -2675, 2008. 10.1021/ja078337p S0002-7863(07)08337-0 Web Release Date: February 1, 2008 Copyright © 2008 American Chemical Society
Probing Chemical Shifts of Invisible States of Proteins with Relaxation Dispersion NMR Spectroscopy: How Well Can We Do?
D. Flemming Hansen, Pramodh Vallurupalli, Patrik Lundström, Philipp Neudecker, and Lewis E. Kay*
Abstract:
Carr-Purcell-Meiboom-Gill relaxation dispersion NMR spectroscopy has evolved into a powerful approach for the study of low populated, invisible conformations of biological molecules. One of the powerful features of the experiment is that chemical shift differences between the exchanging conformers can be obtained, providing structural information about invisible excited states. Through the development of new labeling approaches and NMR experiments it is now possible to measure backbone 13C and 13CO relaxation dispersion profiles in proteins without complications from 13C-13C couplings. Such measurements are presented here, along with those that probe exchange using 15N and 1HN nuclei. A key experimental design has been the choice of an exchanging system where excited-state chemical shifts were known from independent measurement. Thus it is possible to evaluate quantitatively the accuracy of chemical shift differences obtained in dispersion experiments and to establish that in general very accurate values can be obtained. The experimental work is supplemented by computations that suggest that similarly accurate shifts can be measured in many cases for systems with exchange rates and populations that fall within the range of those that can be quantified by relaxation dispersion. The accuracy of the extracted chemical shifts opens up the possibility of obtaining quantitative structural information of invisible states of the sort that is now available from chemical shifts recorded on ground states of proteins.
J. Am. Chem. Soc., 130 (8), 2432 -2433, 2008. 10.1021/ja710477h S0002-7863(71)00477-3 Web Release Date: February 5, 2008 Copyright © 2008 American Chemical Society
Accurately Probing Slow Motions on Millisecond Timescales with a Robust NMR Relaxation Experiment
Dong Long, Maili Liu, and Daiwen Yang*
Abstract:
A new pulse scheme is proposed for the accurate measurement of relaxation dispersion, which cycles the phases of CPMG pulses. Numerical simulations show that systematic errors in the measured relaxation rates mainly result from off-resonance and radio frequency inhomogeneity effects and they can be significantly suppressed with the method proposed here. The method has been demonstrated on human liver fatty acid binding protein. It allows the reliable identification of residues undergoing conformational exchange on millisecond timescales and accurate extraction of kinetics parameters. The relaxation dispersion data indicate that human liver fatty acid binding protein is highly flexible on millisecond timescales.
J. Am. Chem. Soc., 130 (8), 2412 -2413, 2008. 10.1021/ja710557t S0002-7863(71)00557-2 Web Release Date: February 1, 2008 Copyright © 2008 American Chemical Society
A High-Resolution 43Ca Solid-State NMR Study of the Calcium Sites of Hydroxyapatite
Danielle Laurencin, Alan Wong, John V. Hanna, Ray Dupree, and Mark E. Smith*
Abstract:
High resolution 43Ca solid-state NMR studies of hydroxyapatite (Ca10(PO4)6(OH)2) were performed at 14.1 T. The two crystallographically distinct calcium sites were unequivocally resolved by a triple-quantum magic angle spinning experiment, and the unambiguous assignment of the signals was possible using 1H-43Ca rotational echo double resonance and 1H-43Ca cross polarization magic angle spinning experiments.
J. Am. Chem. Soc., ASAP Article 10.1021/
Probing Local Structure in Zeolite Frameworks: Ultrahigh-Field NMR Measurements and Accurate First-Principles Calculations of Zeolite 29Si Magnetic Shielding Tensors
Darren H. Brouwer* and Gary D. Enright
Abstract:
The principal components of zeolite 29Si magnetic shielding tensors have been accurately measured and calculated for the first time. The experiments were performed at an ultrahigh magnetic field of 21.1 T in order to observe the small anisotropies of the 29Si shielding interactions that arise for Si atoms in near-tetrahedral geometries. A robust two-dimensional (2D) chemical shift anisotropy (CSA) recoupling pulse sequence was employed that enables quasi-static powder patterns to be resolved according to the isotropic chemical shifts. For the zeolites Sigma-2 and ZSM-12, it is demonstrated that the 29Si chemical shift (CS) tensor components measured by the recoupling experiment are in excellent agreement with those determined from spinning sidebands in slow magic-angle spinning (MAS) experiments. For the zeolite ZSM-5, the principal components of the 29Si CS tensors of 15 of the 24 Si sites were measured using the 2D CSA recoupling experiment, a feat that would not be possible with a slow MAS experiment due to the complexity of the spectrum. A simple empirical relationship between the 29Si CS tensors and local structural parameters could not be established. However, the 29Si magnetic shielding tensors calculated using Hartree-Fock ab initio calculations on clusters derived from the crystal structures are in excellent agreement with the experimental results. The accuracy of the calculations is strongly dependent on the quality of the crystal structure used in the calculation, indicating that the 29Si magnetic shielding interaction is extremely sensitive to the local structure around each Si atom. It is anticipated that the measurement and calculation of 29Si shielding tensors could be incorporated into the "NMR crystallography" of zeolites and other related silicate materials, possibly being used for structure refinements that may lead to crystal structures with very accurate Si and O atomic coordinates.
ASAP Chem. Mater., ASAP Article, 10.1021/cm0717763 Web Release Date: February 16, 2008 Copyright © 2008 American Chemical Society
A Solid-State NMR, X-ray Diffraction, and Ab Initio Investigation into the Structures of Novel Tantalum Oxyfluoride Clusters
Todd M. Alam,*† Jacalyn S. Clawson,†‡ François Bonhomme,† Steven G. Thoma,† Mark A. Rodriguez,† Shaohui Zheng,§ and Jochen Autschbach§
Abstract:
A series of tantalum oxyfluoride materials containing the [Ta4F16O4]4− and [Ta8F24O12]8− anion clusters have been synthesized and characterized using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (SSNMR) spectroscopy. The structure of both tantalum oxyfluoride materials display octahedrally bonded tantalum atoms with bridging oxygen and terminal fluoride atoms. The [Ta4F16O4]4− cluster is an eight-membered ring, whereas the [Ta8F24O12]8- cluster forms a cagelike structure. Solid-state dynamics of these clusters were explored by monitoring the impact of temperature on the one-dimensional (1D) 19F magic angle spinning (MAS) NMR, 13C cross-polarization (CP) MAS NMR, and two-dimensional (2D) double quantum (DQ) 19F MAS NMR spectra. The DQ 19F NMR correlation experiments allowed the through space connectivity between the different resolved fluorine environments to be determined, thus aiding in the spectral assignment and structural refinement of these materials. Ab initio 19F NMR chemical shift calculations were used to assist in the interpretation of the 19F NMR spectra. The influence of scalar relativistic and Ta−F spin–orbit coupling on the 19F NMR shielding calculation arising from bonding to tantalum atoms is also addressed.
Tuesday, February 12, 2008
J. Chem. Phys.: SPECIAL TOPIC: NEW DEVELOPMENTS IN MAGNETIC RESONANCE (OVERVIEW ARTICLES)
The Journal of Chemical Physics -- 7 February 2008
SPECIAL TOPIC: NEW DEVELOPMENTS IN MAGNETIC RESONANCE (OVERVIEW ARTICLES)
This edition of JCP features an excellent selection of "overview" articles on a variety of topics in NMR. Please have a close look. A list of authors and titles is presented below:
SPECIAL TOPIC: NEW DEVELOPMENTS IN MAGNETIC RESONANCE (OVERVIEW ARTICLES)
Introduction to Special Topic: New Developments in Magnetic Resonance
Robert Tycko
J. Chem. Phys. 128, 052101 (2008) (2 pages)
Ab initio calculations of NMR chemical shifts
Leah B. Casabianca and Angel C. de Dios
J. Chem. Phys. 128, 052201 (2008) (10 pages)
High-resolution liquid- and solid-state nuclear magnetic resonance of nanoliter sample volumes using microcoil detectors
A. P. M. Kentgens, J. Bart, P. J. M. van Bentum, A. Brinkmann, E. R. H. van Eck, J. G. E. Gardeniers, J. W. G. Janssen, P. Knijn, S. Vasa, and M. H. W. Verkuijlen
J. Chem. Phys. 128, 052202 (2008) (17 pages)
Optically pumped nuclear magnetic resonance of semiconductors
Sophia E. Hayes, Stacy Mui, and Kannan Ramaswamy
J. Chem. Phys. 128, 052203 (2008) (16 pages)
Conformational distributions of unfolded polypeptides from novel NMR techniques
Sebastian Meier, Martin Blackledge, and Stephan Grzesiek
J. Chem. Phys. 128, 052204 (2008) (14 pages)
Symmetry in the design of NMR multiple-pulse sequences
Malcolm H. Levitt
J. Chem. Phys. 128, 052205 (2008) (25 pages)
Spins as qubits: Quantum information processing by nuclear magnetic resonance
Dieter Suter and T. S. Mahesh
J. Chem. Phys. 128, 052206 (2008) (14 pages)
Multidimensional solid state NMR of anisotropic interactions in peptides and proteins
Benjamin J. Wylie and Chad M. Rienstra
J. Chem. Phys. 128, 052207 (2008) (16 pages)
Advances in mechanical detection of magnetic resonance
Seppe Kuehn, Steven A. Hickman, and John A. Marohn
J. Chem. Phys. 128, 052208 (2008) (19 pages)
Spatial encoding strategies for ultrafast multidimensional nuclear magnetic resonance
Yoav Shrot and Lucio Frydman
J. Chem. Phys. 128, 052209 (2008) (14 pages)
Progress in 13C and 1H solid-state nuclear magnetic resonance for paramagnetic systems under very fast magic angle spinning
Nalinda P. Wickramasinghe, Medhat A. Shaibat, Christopher R. Jones, Leah B. Casabianca, Angel C. de Dios, John S. Harwood, and Yoshitaka Ishii
J. Chem. Phys. 128, 052210 (2008) (15 pages)
Dynamic nuclear polarization at high magnetic fields
Thorsten Maly, Galia T. Debelouchina, Vikram S. Bajaj, Kan-Nian Hu, Chan-Gyu Joo, Melody L. Mak–Jurkauskas, Jagadishwar R. Sirigiri, Patrick C. A. van der Wel, Judith Herzfeld, Richard J. Temkin, and Robert G. Griffin
J. Chem. Phys. 128, 052211 (2008) (19 pages)
Magnetic resonance in porous media: Recent progress
Yi-Qiao Song, H. Cho, Tim Hopper, Andrew E. Pomerantz, and Phillip Zhe Sun
J. Chem. Phys. 128, 052212 (2008) (12 pages)
ARTICLES
Special Topic: New Developments in Magnetic Resonance
Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition
Carl A. Michal, Simon P. Hastings, and Lik Hang Lee
J. Chem. Phys. 128, 052301 (2008) (8 pages)
High-frequency dynamic nuclear polarization using biradicals: A multifrequency EPR lineshape analysis
Kan-Nian Hu, Changsik Song, Hsiao-hua Yu, Timothy M. Swager, and Robert G. Griffin
J. Chem. Phys. 128, 052302 (2008) (17 pages)
Physical insights from a penetration depth model of optically pumped NMR
Stacy Mui, Kannan Ramaswamy, and Sophia E. Hayes
J. Chem. Phys. 128, 052303 (2008) (7 pages)
Observable effects of mechanical stress induced by sample spinning in solid state nuclear magnetic resonance
M. Jochum, U. Werner-Zwanziger, and J. W. Zwanziger
J. Chem. Phys. 128, 052304 (2008) (7 pages)
Entangled electron and nuclear spin states in 15N@C60: Density matrix tomography
Werner Scherer and Michael Mehring
J. Chem. Phys. 128, 052305 (2008) (11 pages)
Electron paramagnetic resonance investigation of metalloendofullerene derived carbon nanotube peapods
P. Jakes, A. Gembus, K.-P. Dinse, and K. Hata
J. Chem. Phys. 128, 052306 (2008) (5 pages)
NMR study of liquid to solid transition in a glass forming metallic system
Lilong Li and Yue Wu
J. Chem. Phys. 128, 052307 (2008) (4 pages)
Two-dimensional homonuclear chemical shift correlation established by the cross-relaxation driven spin diffusion in solids
Jiadi Xu, Jochem Struppe, and Ayyalusamy Ramamoorthy
J. Chem. Phys. 128, 052308 (2008) (11 pages)
Supercycled homonuclear dipolar decoupling in solid-state NMR: Toward cleaner 1H spectrum and higher spinning rates
Michal Leskes, P. K. Madhu, and Shimon Vega
J. Chem. Phys. 128, 052309 (2008) (11 pages)
High field 207Pb spin-lattice relaxation in solid lead nitrate and lead molybdate
Peter J. de Castro, Christopher A. Maher, Robert L. Vold, and Gina L. Hoatson
J. Chem. Phys. 128, 052310 (2008) (6 pages)
Spatially resolved 195Pt NMR of carbon-supported PtRu electrocatalysts: Local electronic properties, elemental composition, and catalytic activity
Bingchen Du, Aaron L. Danberry, In-Su Park, Yung-Eun Sung, and YuYe Tong
J. Chem. Phys. 128, 052311 (2008) (7 pages)
Shiftless nuclear magnetic resonance spectroscopy
Chin H. Wu and Stanley J. Opella
J. Chem. Phys. 128, 052312 (2008) (5 pages)
Non-negative matrix factorization of two-dimensional NMR spectra: Application to complex mixture analysis
David A. Snyder, Fengli Zhang, Steven L. Robinette, Lei Bruschweiler-Li, and Rafael Brüschweiler
J. Chem. Phys. 128, 052313 (2008) (4 pages)
Determination of methyl 13C–15N dipolar couplings in peptides and proteins by three-dimensional and four-dimensional magic-angle spinning solid-state NMR spectroscopy
Jonathan J. Helmus, Philippe S. Nadaud, Nicole Höfer, and Christopher P. Jaroniec
J. Chem. Phys. 128, 052314 (2008) (16 pages)
Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field
Elie Belorizky, Pascal H. Fries, Lothar Helm, Jozef Kowalewski, Danuta Kruk, Robert R. Sharp, and Per-Olof Westlund
J. Chem. Phys. 128, 052315 (2008) (17 pages)
Measurement of 15N-T1 relaxation rates in a perdeuterated protein by magic angle spinning solid-state nuclear magnetic resonance spectroscopy
Veniamin Chevelkov, Anne Diehl, and Bernd Reif
J. Chem. Phys. 128, 052316 (2008) (5 pages)
51V solid-state NMR and density functional theory studies of vanadium environments in V(V)O2 dipicolinic acid complexes
Stephanie E. Bolte, Kristopher J. Ooms, Tatyana Polenova, Bharat Baruah, Debbie C. Crans, and Jason J. Smee
J. Chem. Phys. 128, 052317 (2008) (11 pages)
Solid-state nuclear magnetic resonance in the rotating tilted frame
Nicole M. Trease and Philip J. Grandinetti
J. Chem. Phys. 128, 052318 (2008) (12 pages)
13C–13C and 15N–13C correlation spectroscopy of membrane-associated and uniformly labeled human immunodeficiency virus and influenza fusion peptides: Amino acid-type assignments and evidence for multiple conformations
Michele L. Bodner, Charles M. Gabrys, Jochem O. Struppe, and David P. Weliky
J. Chem. Phys. 128, 052319 (2008) (11 pages)
A triple resonance hyperfine sublevel correlation experiment for assignment of electron-nuclear double resonance lines
Alexey Potapov, Boris Epel, and Daniella Goldfarb
J. Chem. Phys. 128, 052320 (2008) (10 pages)
Radio frequency-driven recoupling at high magic-angle spinning frequencies: Homonuclear recoupling sans heteronuclear decoupling
Marvin J. Bayro, Ramesh Ramachandran, Marc A. Caporini, Matthew T. Eddy, and Robert G. Griffin
J. Chem. Phys. 128, 052321 (2008) (11 pages)
SPECIAL TOPIC: NEW DEVELOPMENTS IN MAGNETIC RESONANCE (OVERVIEW ARTICLES)
This edition of JCP features an excellent selection of "overview" articles on a variety of topics in NMR. Please have a close look. A list of authors and titles is presented below:
SPECIAL TOPIC: NEW DEVELOPMENTS IN MAGNETIC RESONANCE (OVERVIEW ARTICLES)
Introduction to Special Topic: New Developments in Magnetic Resonance
Robert Tycko
J. Chem. Phys. 128, 052101 (2008) (2 pages)
Ab initio calculations of NMR chemical shifts
Leah B. Casabianca and Angel C. de Dios
J. Chem. Phys. 128, 052201 (2008) (10 pages)
High-resolution liquid- and solid-state nuclear magnetic resonance of nanoliter sample volumes using microcoil detectors
A. P. M. Kentgens, J. Bart, P. J. M. van Bentum, A. Brinkmann, E. R. H. van Eck, J. G. E. Gardeniers, J. W. G. Janssen, P. Knijn, S. Vasa, and M. H. W. Verkuijlen
J. Chem. Phys. 128, 052202 (2008) (17 pages)
Optically pumped nuclear magnetic resonance of semiconductors
Sophia E. Hayes, Stacy Mui, and Kannan Ramaswamy
J. Chem. Phys. 128, 052203 (2008) (16 pages)
Conformational distributions of unfolded polypeptides from novel NMR techniques
Sebastian Meier, Martin Blackledge, and Stephan Grzesiek
J. Chem. Phys. 128, 052204 (2008) (14 pages)
Symmetry in the design of NMR multiple-pulse sequences
Malcolm H. Levitt
J. Chem. Phys. 128, 052205 (2008) (25 pages)
Spins as qubits: Quantum information processing by nuclear magnetic resonance
Dieter Suter and T. S. Mahesh
J. Chem. Phys. 128, 052206 (2008) (14 pages)
Multidimensional solid state NMR of anisotropic interactions in peptides and proteins
Benjamin J. Wylie and Chad M. Rienstra
J. Chem. Phys. 128, 052207 (2008) (16 pages)
Advances in mechanical detection of magnetic resonance
Seppe Kuehn, Steven A. Hickman, and John A. Marohn
J. Chem. Phys. 128, 052208 (2008) (19 pages)
Spatial encoding strategies for ultrafast multidimensional nuclear magnetic resonance
Yoav Shrot and Lucio Frydman
J. Chem. Phys. 128, 052209 (2008) (14 pages)
Progress in 13C and 1H solid-state nuclear magnetic resonance for paramagnetic systems under very fast magic angle spinning
Nalinda P. Wickramasinghe, Medhat A. Shaibat, Christopher R. Jones, Leah B. Casabianca, Angel C. de Dios, John S. Harwood, and Yoshitaka Ishii
J. Chem. Phys. 128, 052210 (2008) (15 pages)
Dynamic nuclear polarization at high magnetic fields
Thorsten Maly, Galia T. Debelouchina, Vikram S. Bajaj, Kan-Nian Hu, Chan-Gyu Joo, Melody L. Mak–Jurkauskas, Jagadishwar R. Sirigiri, Patrick C. A. van der Wel, Judith Herzfeld, Richard J. Temkin, and Robert G. Griffin
J. Chem. Phys. 128, 052211 (2008) (19 pages)
Magnetic resonance in porous media: Recent progress
Yi-Qiao Song, H. Cho, Tim Hopper, Andrew E. Pomerantz, and Phillip Zhe Sun
J. Chem. Phys. 128, 052212 (2008) (12 pages)
ARTICLES
Special Topic: New Developments in Magnetic Resonance
Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition
Carl A. Michal, Simon P. Hastings, and Lik Hang Lee
J. Chem. Phys. 128, 052301 (2008) (8 pages)
High-frequency dynamic nuclear polarization using biradicals: A multifrequency EPR lineshape analysis
Kan-Nian Hu, Changsik Song, Hsiao-hua Yu, Timothy M. Swager, and Robert G. Griffin
J. Chem. Phys. 128, 052302 (2008) (17 pages)
Physical insights from a penetration depth model of optically pumped NMR
Stacy Mui, Kannan Ramaswamy, and Sophia E. Hayes
J. Chem. Phys. 128, 052303 (2008) (7 pages)
Observable effects of mechanical stress induced by sample spinning in solid state nuclear magnetic resonance
M. Jochum, U. Werner-Zwanziger, and J. W. Zwanziger
J. Chem. Phys. 128, 052304 (2008) (7 pages)
Entangled electron and nuclear spin states in 15N@C60: Density matrix tomography
Werner Scherer and Michael Mehring
J. Chem. Phys. 128, 052305 (2008) (11 pages)
Electron paramagnetic resonance investigation of metalloendofullerene derived carbon nanotube peapods
P. Jakes, A. Gembus, K.-P. Dinse, and K. Hata
J. Chem. Phys. 128, 052306 (2008) (5 pages)
NMR study of liquid to solid transition in a glass forming metallic system
Lilong Li and Yue Wu
J. Chem. Phys. 128, 052307 (2008) (4 pages)
Two-dimensional homonuclear chemical shift correlation established by the cross-relaxation driven spin diffusion in solids
Jiadi Xu, Jochem Struppe, and Ayyalusamy Ramamoorthy
J. Chem. Phys. 128, 052308 (2008) (11 pages)
Supercycled homonuclear dipolar decoupling in solid-state NMR: Toward cleaner 1H spectrum and higher spinning rates
Michal Leskes, P. K. Madhu, and Shimon Vega
J. Chem. Phys. 128, 052309 (2008) (11 pages)
High field 207Pb spin-lattice relaxation in solid lead nitrate and lead molybdate
Peter J. de Castro, Christopher A. Maher, Robert L. Vold, and Gina L. Hoatson
J. Chem. Phys. 128, 052310 (2008) (6 pages)
Spatially resolved 195Pt NMR of carbon-supported PtRu electrocatalysts: Local electronic properties, elemental composition, and catalytic activity
Bingchen Du, Aaron L. Danberry, In-Su Park, Yung-Eun Sung, and YuYe Tong
J. Chem. Phys. 128, 052311 (2008) (7 pages)
Shiftless nuclear magnetic resonance spectroscopy
Chin H. Wu and Stanley J. Opella
J. Chem. Phys. 128, 052312 (2008) (5 pages)
Non-negative matrix factorization of two-dimensional NMR spectra: Application to complex mixture analysis
David A. Snyder, Fengli Zhang, Steven L. Robinette, Lei Bruschweiler-Li, and Rafael Brüschweiler
J. Chem. Phys. 128, 052313 (2008) (4 pages)
Determination of methyl 13C–15N dipolar couplings in peptides and proteins by three-dimensional and four-dimensional magic-angle spinning solid-state NMR spectroscopy
Jonathan J. Helmus, Philippe S. Nadaud, Nicole Höfer, and Christopher P. Jaroniec
J. Chem. Phys. 128, 052314 (2008) (16 pages)
Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field
Elie Belorizky, Pascal H. Fries, Lothar Helm, Jozef Kowalewski, Danuta Kruk, Robert R. Sharp, and Per-Olof Westlund
J. Chem. Phys. 128, 052315 (2008) (17 pages)
Measurement of 15N-T1 relaxation rates in a perdeuterated protein by magic angle spinning solid-state nuclear magnetic resonance spectroscopy
Veniamin Chevelkov, Anne Diehl, and Bernd Reif
J. Chem. Phys. 128, 052316 (2008) (5 pages)
51V solid-state NMR and density functional theory studies of vanadium environments in V(V)O2 dipicolinic acid complexes
Stephanie E. Bolte, Kristopher J. Ooms, Tatyana Polenova, Bharat Baruah, Debbie C. Crans, and Jason J. Smee
J. Chem. Phys. 128, 052317 (2008) (11 pages)
Solid-state nuclear magnetic resonance in the rotating tilted frame
Nicole M. Trease and Philip J. Grandinetti
J. Chem. Phys. 128, 052318 (2008) (12 pages)
13C–13C and 15N–13C correlation spectroscopy of membrane-associated and uniformly labeled human immunodeficiency virus and influenza fusion peptides: Amino acid-type assignments and evidence for multiple conformations
Michele L. Bodner, Charles M. Gabrys, Jochem O. Struppe, and David P. Weliky
J. Chem. Phys. 128, 052319 (2008) (11 pages)
A triple resonance hyperfine sublevel correlation experiment for assignment of electron-nuclear double resonance lines
Alexey Potapov, Boris Epel, and Daniella Goldfarb
J. Chem. Phys. 128, 052320 (2008) (10 pages)
Radio frequency-driven recoupling at high magic-angle spinning frequencies: Homonuclear recoupling sans heteronuclear decoupling
Marvin J. Bayro, Ramesh Ramachandran, Marc A. Caporini, Matthew T. Eddy, and Robert G. Griffin
J. Chem. Phys. 128, 052321 (2008) (11 pages)
Friday, February 01, 2008
Phys. Rev. B 77, 024311 (2008)
Li jump process in h-Li0.7TiS2 studied by two-time 7Li spin-alignment echo NMR and comparison with results on two-dimensional diffusion from nuclear magnetic relaxation
M. Wilkening and P. Heitjans
Abstract
7Li spin-alignment NMR is used to trace ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 (x=0.7). Two-time correlation functions were recorded for fixed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identified as Li jump rates −1 ranging from 10−1 to 103 s−1 between temperatures T=148 K and 213 K. The jump rates obtained directly from spin-alignment echo NMR and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, are consistent with each other and follow an Arrhenius law with an activation energy of 0.41(1) eV and a preexponential factor of 6.3(1)×1012 s−1. Altogether, a solitary Li diffusion process was found between 148 and 510 K. Li diffusion was investigated in a dynamic range of about 10 orders of magnitude, i.e., 0.1−17.8×108 s−1. Additionally, the analysis of final-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process is present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap are involved in the overall two-dimensional diffusion process.
M. Wilkening and P. Heitjans
Abstract
7Li spin-alignment NMR is used to trace ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 (x=0.7). Two-time correlation functions were recorded for fixed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identified as Li jump rates −1 ranging from 10−1 to 103 s−1 between temperatures T=148 K and 213 K. The jump rates obtained directly from spin-alignment echo NMR and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, are consistent with each other and follow an Arrhenius law with an activation energy of 0.41(1) eV and a preexponential factor of 6.3(1)×1012 s−1. Altogether, a solitary Li diffusion process was found between 148 and 510 K. Li diffusion was investigated in a dynamic range of about 10 orders of magnitude, i.e., 0.1−17.8×108 s−1. Additionally, the analysis of final-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process is present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap are involved in the overall two-dimensional diffusion process.
J. Am. Chem. Soc.,
ASAP Article 10.1021/ja710557t S0002-7863(71)00557-2 Web Release Date: February 1, 2008 Copyright © 2008 American Chemical Society
A High-Resolution 43Ca Solid-State NMR Study of the Calcium Sites of Hydroxyapatite
Danielle Laurencin, Alan Wong, John
Abstract:
High resolution 43Ca solid-state NMR studies of hydroxyapatite (Ca10(PO4)6(OH)2) were performed at 14.1 T. The two crystallographically distinct calcium sites were unequivocally resolved by a triple-quantum magic angle spinning experiment, and the unambiguous assignment of the signals was possible using 1H-43Ca rotational echo double resonance and 1H-43Ca cross polarization magic angle spinning experiments.
A High-Resolution 43Ca Solid-State NMR Study of the Calcium Sites of Hydroxyapatite
Danielle Laurencin, Alan Wong, John
Abstract:
High resolution 43Ca solid-state NMR studies of hydroxyapatite (Ca10(PO4)6(OH)2) were performed at 14.1 T. The two crystallographically distinct calcium sites were unequivocally resolved by a triple-quantum magic angle spinning experiment, and the unambiguous assignment of the signals was possible using 1H-43Ca rotational echo double resonance and 1H-43Ca cross polarization magic angle spinning experiments.
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