A Solid-State 11B NMR and Computational Study of Boron Electric Field Gradient and Chemical Shift Tensors in Boronic Acids and Boronic Esters
Joseph W. E. Weiss and David L. Bryce
Abstract
The results of a solid-state 11B NMR study of a series of 10 boronic acids and boronic esters with aromatic substituents are reported. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. Data collected at 21.1 T clearly show the effects of chemical shift anisotropy (CSA), with tensor spans (Ω) on the order of 10−40 ppm. Signal enhancements of up to 2.95 were achieved with a DFS-modified QCPMG pulse sequence. To understand the relationship between the measured tensors and the local structure better, calculations of the 11B EFG and magnetic shielding tensors for these compounds were conducted. The best agreement was found between experimental results and those obtained from GGA revPBE DFT calculations. A positive correlation was found between Ω and the dihedral angle (CCBO), which describes the orientation of the boronic acid/ester functional group relative to an aromatic system bound to boron. The small boron CSA is discussed in terms of paramagnetic shielding contributions as well as diamagnetic shielding contributions. Although there is a region of overlap, both Ω and the 11B quadrupolar coupling constants tend to be larger for boronic acids than for the esters. We conclude that the span is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters, and show that the values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of CCBO, and the electron-donating or withdrawing substituents bound to the aromatic ring.
Monday, April 26, 2010
J. Am. Chem. Soc., 2010, 132 (16), pp 5779–5788
Proton-Evolved Local-Field Solid-State NMR Studies of Cytochrome b5 Embedded in Bicelles, Revealing both Structural and Dynamical Information
Ronald Soong, Pieter E. S. Smith, Jiadi Xu, Kazutoshi Yamamoto, Sang-Choul Im, Lucy Waskell and Ayyalusamy Ramamoorthy
Abstract
Structural biology of membrane proteins has rapidly evolved into a new frontier of science. Although solving the structure of a membrane protein with atomic-level resolution is still a major challenge, separated local field (SLF) NMR spectroscopy has become an invaluable tool in obtaining structural images of membrane proteins under physiological conditions. Recent studies have demonstrated the use of rotating-frame SLF techniques to accurately measure strong heteronuclear dipolar couplings between directly bonded nuclei. However, in these experiments, all weak dipolar couplings are suppressed. On the other hand, weak heteronuclear dipolar couplings can be measured using laboratory-frame SLF experiments, but only at the expense of spectral resolution for strongly dipolar coupled spins. In the present study, we implemented two-dimensional proton-evolved local-field (2D PELF) pulse sequences using either composite zero cross-polarization (COMPOZER-CP) or windowless isotropic mixing (WIM) for magnetization transfer. These PELF sequences can be used for the measurement of a broad range of heteronuclear dipolar couplings, allowing for a complete mapping of protein dynamics in a lipid bilayer environment. Experimental results from magnetically aligned bicelles containing uniformly 15N-labeled cytochrome b5 are presented and theoretical analyses of the new PELF sequences are reported. Our results suggest that the PELF-based experimental approaches will have a profound impact on solid-state NMR spectroscopy of membrane proteins and other membrane-associated molecules in magnetically aligned bicelles.
Ronald Soong, Pieter E. S. Smith, Jiadi Xu, Kazutoshi Yamamoto, Sang-Choul Im, Lucy Waskell and Ayyalusamy Ramamoorthy
Abstract
Structural biology of membrane proteins has rapidly evolved into a new frontier of science. Although solving the structure of a membrane protein with atomic-level resolution is still a major challenge, separated local field (SLF) NMR spectroscopy has become an invaluable tool in obtaining structural images of membrane proteins under physiological conditions. Recent studies have demonstrated the use of rotating-frame SLF techniques to accurately measure strong heteronuclear dipolar couplings between directly bonded nuclei. However, in these experiments, all weak dipolar couplings are suppressed. On the other hand, weak heteronuclear dipolar couplings can be measured using laboratory-frame SLF experiments, but only at the expense of spectral resolution for strongly dipolar coupled spins. In the present study, we implemented two-dimensional proton-evolved local-field (2D PELF) pulse sequences using either composite zero cross-polarization (COMPOZER-CP) or windowless isotropic mixing (WIM) for magnetization transfer. These PELF sequences can be used for the measurement of a broad range of heteronuclear dipolar couplings, allowing for a complete mapping of protein dynamics in a lipid bilayer environment. Experimental results from magnetically aligned bicelles containing uniformly 15N-labeled cytochrome b5 are presented and theoretical analyses of the new PELF sequences are reported. Our results suggest that the PELF-based experimental approaches will have a profound impact on solid-state NMR spectroscopy of membrane proteins and other membrane-associated molecules in magnetically aligned bicelles.
J. Am. Chem. Soc., 2010, 132 (14), pp 5179–5185
Elucidation of Structure and Dynamics in Solid Octafluoronaphthalene from Combined NMR, Diffraction, And Molecular Dynamics Studies
Andrew J. Ilott, Sebastian Palucha, Andrei S. Batsanov, Mark R. Wilson and Paul Hodgkinson
Abstract
X-ray diffraction (XRD), molecular dynamics simulations (MD), and 19F NMR have been used to investigate structure and dynamics in solid octafluoronaphthalene, C10F8. Two distinct processes are observed via measurements of 19F relaxation times as a function of temperature; a faster process from T1 relaxation with a correlation time of the order of ns at ambient temperature (fitting to Arrhenius-type parameters Ea = 20.6 ± 0.4 kJ mol−1 and τ0 = 8 ± 1 × 10−14 s) and a much slower process from T1ρ relaxation with a correlation time of the order of μs (fitting to Ea = 55.1 ± 1.3 kJ mol−1 and τ0 = 4 ± 2 × 10−16 s). Atomistic molecular dynamics reveals the faster process to involve a small angle jump of 40° of the molecules, which is in perfect agreement with the X-ray diffraction study of the material at ambient temperature. The MD study reveals the existence of more extreme rotations of the molecules, which are proposed to enable the full rotation of the octafluoronaphthalene molecules. This explains both the T1ρ results and previous wide-line 19F NMR studies. The experimental measurements (NMR and XRD) and the MD computations are found to be strongly complementary and mutally essential. The reasons why a process on the time scale of microseconds, and associated with such a large activation barrier, can be accessed via classical molecular dynamics simulations are also discussed.
Andrew J. Ilott, Sebastian Palucha, Andrei S. Batsanov, Mark R. Wilson and Paul Hodgkinson
Abstract
X-ray diffraction (XRD), molecular dynamics simulations (MD), and 19F NMR have been used to investigate structure and dynamics in solid octafluoronaphthalene, C10F8. Two distinct processes are observed via measurements of 19F relaxation times as a function of temperature; a faster process from T1 relaxation with a correlation time of the order of ns at ambient temperature (fitting to Arrhenius-type parameters Ea = 20.6 ± 0.4 kJ mol−1 and τ0 = 8 ± 1 × 10−14 s) and a much slower process from T1ρ relaxation with a correlation time of the order of μs (fitting to Ea = 55.1 ± 1.3 kJ mol−1 and τ0 = 4 ± 2 × 10−16 s). Atomistic molecular dynamics reveals the faster process to involve a small angle jump of 40° of the molecules, which is in perfect agreement with the X-ray diffraction study of the material at ambient temperature. The MD study reveals the existence of more extreme rotations of the molecules, which are proposed to enable the full rotation of the octafluoronaphthalene molecules. This explains both the T1ρ results and previous wide-line 19F NMR studies. The experimental measurements (NMR and XRD) and the MD computations are found to be strongly complementary and mutally essential. The reasons why a process on the time scale of microseconds, and associated with such a large activation barrier, can be accessed via classical molecular dynamics simulations are also discussed.
J. Am. Chem. Soc., 2010, 132 (15), pp 5357–5363
Sensitivity Enhanced Heteronuclear Correlation Spectroscopy in Multidimensional Solid-State NMR of Oriented Systems via Chemical Shift Coherences
T. Gopinath, Nathaniel J. Traaseth, Kaustubh Mote and Gianluigi Veglia
Abstract
We present new sensitivity enhanced schemes for heteronuclear correlation spectroscopy (HETCOR) in solid-state NMR of oriented systems. These schemes will enhance the sensitivity of the HETCOR by 40% for the two-dimensional experiments (SE-HETCOR) and up to 180% for the 3D HETCOR-separated local field version (SE-PISEMAI-HETCOR). The signal enhancement is demonstrated for a single crystal of (15N)N-acetylleucine and the integral membrane protein sarcolipin oriented in lipid bicelles. These methods will significantly reduce the time needed to acquire multidimensional experiments for membrane proteins oriented in magnetically or mechanically aligned lipid bilayers as well as liquid crystalline materials.
T. Gopinath, Nathaniel J. Traaseth, Kaustubh Mote and Gianluigi Veglia
Abstract
We present new sensitivity enhanced schemes for heteronuclear correlation spectroscopy (HETCOR) in solid-state NMR of oriented systems. These schemes will enhance the sensitivity of the HETCOR by 40% for the two-dimensional experiments (SE-HETCOR) and up to 180% for the 3D HETCOR-separated local field version (SE-PISEMAI-HETCOR). The signal enhancement is demonstrated for a single crystal of (15N)N-acetylleucine and the integral membrane protein sarcolipin oriented in lipid bicelles. These methods will significantly reduce the time needed to acquire multidimensional experiments for membrane proteins oriented in magnetically or mechanically aligned lipid bilayers as well as liquid crystalline materials.
J. Am. Chem. Soc., 2010, 132 (14), pp 5143–5155
Solid-State 17O NMR and Computational Studies of C-Nitrosoarene Compounds
Gang Wu, Jianfeng Zhu, Xin Mo, Ruiyao Wang and Victor Terskikh
Abstract
We report the first solid-state 17O NMR determination of the 17O quadrupole coupling (QC) tensor and chemical shift (CS) tensor for four 17O-labeled C-nitrosoarene compounds: p-[17O]nitroso-N,N-dimethylaniline ([17O]NODMA), SnCl2(CH3)2([17O]NODMA)2, ZnCl2([17O]NODMA)2, and [17O]NODMA·HCl. The 17O quadrupole coupling constants (CQ) observed in these C-nitrosoarene compounds are on the order of 10−15 MHz, among the largest values found to date for organic compounds. The 17O CS tensor in these compounds exhibits remarkable sensitivity toward the nitroso bonding scheme with the chemical shift anisotropy (δ11 − δ33) ranging from just 350 ppm in [17O]NODMA·HCl to over 2800 ppm in [17O]NODMA. This latter value is among the largest 17O chemical shift anisotropies reported in the literature. These extremely anisotropic 17O NMR interactions make C-nitrosoarene compounds excellent test cases that allow us to assess the detection limit of solid-state 17O NMR. Our results suggest that, at 21.14 T, solid-state 17O NMR should be applicable to all oxygen-containing organic functional groups. We also show that density functional theory (DFT) calculations can reproduce reasonably well the experimental 17O QC and CS tensors for these challenging molecules. By combining quantum chemical calculations with experimental solid-state 17O NMR results, we are able to determine the 17O QC and CS tensor orientations in the molecular frame of reference for C-nitrosoarenes. We present a detailed analysis illustrating how magnetic field-induced mixing between individual molecular orbitals (MOs) contributes to the 17O shielding tensor in C-nitrosoarene compounds. We also perform a Townes−Dailey analysis for the observed 17O QC tensors and show that 17O CS and QC tensors are intrinsically related through the π bond order of the N═O bond. Furthermore, we are able for the first time to examine the parallelism between individual 17O and 15N CS tensor components in C-nitrosoarenes.
Gang Wu, Jianfeng Zhu, Xin Mo, Ruiyao Wang and Victor Terskikh
Abstract
We report the first solid-state 17O NMR determination of the 17O quadrupole coupling (QC) tensor and chemical shift (CS) tensor for four 17O-labeled C-nitrosoarene compounds: p-[17O]nitroso-N,N-dimethylaniline ([17O]NODMA), SnCl2(CH3)2([17O]NODMA)2, ZnCl2([17O]NODMA)2, and [17O]NODMA·HCl. The 17O quadrupole coupling constants (CQ) observed in these C-nitrosoarene compounds are on the order of 10−15 MHz, among the largest values found to date for organic compounds. The 17O CS tensor in these compounds exhibits remarkable sensitivity toward the nitroso bonding scheme with the chemical shift anisotropy (δ11 − δ33) ranging from just 350 ppm in [17O]NODMA·HCl to over 2800 ppm in [17O]NODMA. This latter value is among the largest 17O chemical shift anisotropies reported in the literature. These extremely anisotropic 17O NMR interactions make C-nitrosoarene compounds excellent test cases that allow us to assess the detection limit of solid-state 17O NMR. Our results suggest that, at 21.14 T, solid-state 17O NMR should be applicable to all oxygen-containing organic functional groups. We also show that density functional theory (DFT) calculations can reproduce reasonably well the experimental 17O QC and CS tensors for these challenging molecules. By combining quantum chemical calculations with experimental solid-state 17O NMR results, we are able to determine the 17O QC and CS tensor orientations in the molecular frame of reference for C-nitrosoarenes. We present a detailed analysis illustrating how magnetic field-induced mixing between individual molecular orbitals (MOs) contributes to the 17O shielding tensor in C-nitrosoarene compounds. We also perform a Townes−Dailey analysis for the observed 17O QC tensors and show that 17O CS and QC tensors are intrinsically related through the π bond order of the N═O bond. Furthermore, we are able for the first time to examine the parallelism between individual 17O and 15N CS tensor components in C-nitrosoarenes.
J. Am. Chem. Soc., 2010, 132 (13), pp 4653–4668
DFT-NMR Investigation and 51V 3QMAS Experiments for Probing Surface OH Ligands and the Hydrogen-Bond Network in a Polyoxovanadate Cluster: The Case of Cs4[H2V10O28]·4H2O
Lionel A. Truflandier, Florent Boucher, Christophe Payen, Redouane Hajjar, Yannick Millot, Christian Bonhomme and Nathalie Steunou
Abstract
This work shows that the combination of first-principles calculations and 51V NMR experiments is a powerful tool to elucidate the location of surface hydroxyl groups and to precisely describe the hydrogen bond network in the complex decavanadate cluster Cs4[H2V10O28].4H2O, enhancing the strength of NMR crystallography. The detailed characterization of H-bond networks for these kinds of inorganic compounds is of primary importance and should benefit from the DFT-NMR predictions by considering explicitly the periodic boundary conditions. The determination of the Cs4[H2V10O28]·4H2O structure by single-crystal X-ray diffraction was not sufficiently accurate to provide the location of protons. From available diffraction data, five different protonated model structures have been built and optimized using DFT-based methods. The possible interconversion of two decavanadate isomers through a proton exchange is evaluated by calculating the energy barrier and recording variable-temperature 1H MAS NMR spectra. First-principles calculations of 51V NMR parameters clearly indicate that these parameters are very sensitive to the local intermolecular hydrogen-bonding interactions. Considering the DFT error limits, the fairly good agreement between calculated and experimental NMR parameters arising from the statistical modeling of the data allows the unambiguous assignment of the five 51V NMR signals and, thus, the location of OH surface ligands in the decavanadate cluster. In particular, first-principles calculations accurately reproduce the 51V quadrupolar parameters. These results are fully consistent with 51V 3QMAS NMR spectra recorded with and without 1H decoupling. Finally, correlations are established between local octahedral VO6 deformations and 51V NMR parameters (Cq and Δδ), which will be useful for the characterization of a wide range of chemical species containing vanadium(V).
Lionel A. Truflandier, Florent Boucher, Christophe Payen, Redouane Hajjar, Yannick Millot, Christian Bonhomme and Nathalie Steunou
Abstract
This work shows that the combination of first-principles calculations and 51V NMR experiments is a powerful tool to elucidate the location of surface hydroxyl groups and to precisely describe the hydrogen bond network in the complex decavanadate cluster Cs4[H2V10O28].4H2O, enhancing the strength of NMR crystallography. The detailed characterization of H-bond networks for these kinds of inorganic compounds is of primary importance and should benefit from the DFT-NMR predictions by considering explicitly the periodic boundary conditions. The determination of the Cs4[H2V10O28]·4H2O structure by single-crystal X-ray diffraction was not sufficiently accurate to provide the location of protons. From available diffraction data, five different protonated model structures have been built and optimized using DFT-based methods. The possible interconversion of two decavanadate isomers through a proton exchange is evaluated by calculating the energy barrier and recording variable-temperature 1H MAS NMR spectra. First-principles calculations of 51V NMR parameters clearly indicate that these parameters are very sensitive to the local intermolecular hydrogen-bonding interactions. Considering the DFT error limits, the fairly good agreement between calculated and experimental NMR parameters arising from the statistical modeling of the data allows the unambiguous assignment of the five 51V NMR signals and, thus, the location of OH surface ligands in the decavanadate cluster. In particular, first-principles calculations accurately reproduce the 51V quadrupolar parameters. These results are fully consistent with 51V 3QMAS NMR spectra recorded with and without 1H decoupling. Finally, correlations are established between local octahedral VO6 deformations and 51V NMR parameters (Cq and Δδ), which will be useful for the characterization of a wide range of chemical species containing vanadium(V).
Friday, April 16, 2010
Journal of Physical Chemistry B and C, Vol. 114, Issues 14 and 15
7Li NMR Knight Shifts in Li−Sn Compounds: MAS NMR Measurements and Correlation with DFT Calculations
Emilie Bekaert†, Florent Robert‡, Pierre Emmanuel Lippens‡ and Michel Mntrier*†
J. Phys. Chem. C, 2010, 114 (14), pp 6749–6754
DOI: 10.1021/jp100365u
Abstract: Several Li−Sn crystalline phases, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, and Li22Sn5, were prepared by ball-milling and studied by 7Li MAS NMR spectroscopy with silica as a diluting agent to avoid field penetration limitations. All phases except for LiSn exhibit exchanged NMR signals at room temperature for the various types of Li present in the unit cells, in the 10 to 100 ppm range. Electronic structure calculations based on first-principles method led to a rather good correlation between the participation of the Li 2s orbital to the density of states (DOS) at the Fermi level and the corresponding NMR Knight shift for the two Li crystallographic types in the case of LiSn, and for the weighted average of the different crystallographic types in the case of the NMR-exchanged signals for the other compounds.
A Novel Phase Transformation Phenomenon in Mesostructured Aluminophosphate
Wanling Shen†, Shenhui Li†, Jun Xu†, Hailu Zhang†, Wei Hu†, Dan Zhou‡, Jianan Zhang‡, Jihong Yu‡, Wujun Xu§, Yao Xu§ and Feng Deng*†
J. Phys. Chem. C, 2010, 114 (15), pp 7076–7084
DOI: 10.1021/jp911959u
Abstract: A novel phase transformation phenomenon that involves two successive phase transformation events was found for the first time in the synthesis of mesostructured aluminophosphate and studied by XRD, TEM, and multinuclear solid-state NMR techniques. The results showed that a hexagonal phase Hex and two lamellar phases, L1 and L2, were formed after hydrothermal treatment for 1, 3, and 50 h, respectively. The status of the surfactant was found to be arrayed interdigitated in a bilayer with a tilt angle in L1 phase but upright in L2 phase. A mechanism that the exciting of the alkane tail of the surfactant together with the condensation of aluminophosphate cooperatively promoted the phase transformation was proposed for the observed phenomenon. Additionally, a ZON microporous structure was found for the first time existing in the framework of the mesostructured aluminophosphate.
Emilie Bekaert†, Florent Robert‡, Pierre Emmanuel Lippens‡ and Michel Mntrier*†
J. Phys. Chem. C, 2010, 114 (14), pp 6749–6754
DOI: 10.1021/jp100365u
Abstract: Several Li−Sn crystalline phases, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, and Li22Sn5, were prepared by ball-milling and studied by 7Li MAS NMR spectroscopy with silica as a diluting agent to avoid field penetration limitations. All phases except for LiSn exhibit exchanged NMR signals at room temperature for the various types of Li present in the unit cells, in the 10 to 100 ppm range. Electronic structure calculations based on first-principles method led to a rather good correlation between the participation of the Li 2s orbital to the density of states (DOS) at the Fermi level and the corresponding NMR Knight shift for the two Li crystallographic types in the case of LiSn, and for the weighted average of the different crystallographic types in the case of the NMR-exchanged signals for the other compounds.
A Novel Phase Transformation Phenomenon in Mesostructured Aluminophosphate
Wanling Shen†, Shenhui Li†, Jun Xu†, Hailu Zhang†, Wei Hu†, Dan Zhou‡, Jianan Zhang‡, Jihong Yu‡, Wujun Xu§, Yao Xu§ and Feng Deng*†
J. Phys. Chem. C, 2010, 114 (15), pp 7076–7084
DOI: 10.1021/jp911959u
Abstract: A novel phase transformation phenomenon that involves two successive phase transformation events was found for the first time in the synthesis of mesostructured aluminophosphate and studied by XRD, TEM, and multinuclear solid-state NMR techniques. The results showed that a hexagonal phase Hex and two lamellar phases, L1 and L2, were formed after hydrothermal treatment for 1, 3, and 50 h, respectively. The status of the surfactant was found to be arrayed interdigitated in a bilayer with a tilt angle in L1 phase but upright in L2 phase. A mechanism that the exciting of the alkane tail of the surfactant together with the condensation of aluminophosphate cooperatively promoted the phase transformation was proposed for the observed phenomenon. Additionally, a ZON microporous structure was found for the first time existing in the framework of the mesostructured aluminophosphate.
Tuesday, April 13, 2010
Solid State Nuclear Magnetic Resonance
The partial 1H NMR spectra of Al-OH and H2Omol in hydrous aluminosilicate glasses: Component-Resolved analysis of 27Al-1H cross polarization and 1H spin-echo spectra
Publication year: 2010Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 9 April 2010
Wim J., Malfait , Xianyu, Xue
The Component-Resolved methodology was applied to 1H spin-echo and 27Al-1H cross polarization data of aluminosilicate glasses. The method was able to resolve two components with different T2 relaxation rates, hydroxyl groups (OH) and molecular water (H2Omol), from the spin-echo data and to determine partial spectra and the relative abundances of OH and H2Omol. The algorithm resolved two to three components with different 27Al-1H CP dynamics from the 27Al-1H cross polarization data; the obtained partial NMR spectra for Al-OH are in excellent agreement with those obtained previously from the difference spectra and confirm previous quantitative results and models for the Al-OH, Si-OH and H2Omol speciation (Malfait and Xue, 2010).
Nuclear hyperpolarization in solids and the prospects for nuclear spintronics
Publication year: 2010Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 7 April 2010
Jeffrey A., Reimer
Nuclear hyperpolarization can be achieved in a number of ways. This article focuses on the use of coupling of nuclei to (nearly) pure quantum states, with particular emphasis on those states obtained by optical excitation in bulk semiconductors. I seek an answer to this question: ”What is to prevent the design and analysis of nuclear spintronics devices that use the extremely long-lived hyperpolarized nuclear spin states, and their weak couplings to each other, to affect computation, memory, or informational technology schemes?” The answer, I argue, is in part because there remains a lack of fundamental understanding of how to generate and control nuclear polarization with schemes other than with rf coils.
Tuesday, April 06, 2010
PCCP, vol. 12, Issues 10 - 15
Phys. Chem. Chem. Phys., 2010, 12, 2895 - 2914, DOI: 10.1039/b915587b
The conformation and orientational order of a 1,2-disubstituted ethane nematogenic molecule (I22) in liquid crystalline and isotropic phases studied by NMR spectroscopy
James W. Emsley, Philippe Lesot, Anne Lesage, Giuseppina De Luca, Denis Merlet and Giuseppe Pileio
The structure, conformation and orientational order of the mesogen I22 have been studied by proton, carbon-13 and deuterium 1D and 2D-NMR spectroscopies at natural abundance and at various magnetic fields when in the nematic phase, the isotropic phase close to the nematic-isotropic phase transition, and as a solute in the chiral nematic solution comprised of the polypeptide PBLG dissolved in chloroform. It is concluded that 95% of conformers have a trans arrangement about the central C–C bond of the ethane fragment in all phases
Phys. Chem. Chem. Phys., 2010, 12, 2989 - 2998, DOI: 10.1039/b924666e
Dynamics on the microsecond timescale in hydrous silicates studied by solid-state 2H NMR spectroscopy
John M. Griffin, Andrew J. Miller, Andrew J. Berry, Stephen Wimperis and Sharon E. Ashbrook
Solid-state 2H NMR spectroscopy has been used to probe the dynamic disorder of hydroxyl deuterons in a synthetic sample of deuterated hydroxyl-clinohumite (4Mg2SiO4·Mg(OD)2), a proposed model for the incorporation of water within the Earths mantle. Both static and magic angle spinning (MAS) NMR methods were used. Static 2H NMR appears to reveal little evidence of the dynamic process, yielding results similar to those obtained from deuterated brucite (Mg(OD)2), where no dynamics on the relevant timescale are expected to be present. However, in 2H MAS NMR spectra, considerable line broadening is observed for hydroxyl-clinohumite and a 2H double-quantum (DQ) MAS NMR spectrum confirms that this is due to motion on the microsecond timescale. Using a model for dynamic exchange of the hydroxyl deuterons between two sites identified in previous diffraction studies, first-principles density functional theory (DFT) calculations of 2H (spin I = 1) quadrupolar NMR parameters, and a simple analytical model for dynamic line broadening in MAS NMR experiments, we were able to reproduce the observed motional line broadening and use this to estimate a rate constant for the dynamic process. From analysis of the observed 2H linewidths in variable-temperature MAS experiments, an activation energy for the exchange process was also determined. A simulated static 2H NMR lineshape based on our dynamic model is consistent with the observed experimental static NMR spectrum, confirming that the motion present in this system is not easily detectable using a static NMR approach. Finally, a 2H DQMAS NMR spectrum of fluorine-substituted 2H-enriched hydroxyl-clinohumite shows how the dynamic exchange process is inhibited by O–DF- hydrogen-bonding interactions.
Phys. Chem. Chem. Phys., 2010, 12, 3254 - 3259, DOI: 10.1039/b925326b
14N NQR and proton NMR study of ferroelectric phase transition and proton exchange in organic ferroelectric (H2-TPPZ)(Hca)2
Janez Seliger, Veselko agar, Tetsuo Asaji and Yumi Hasegawa
The complete 14N nuclear quadrupole resonance spectrum has been measured in ferroelectric (H2-TPPZ)(Hca)2 using nuclear quadrupole double resonance. The quadrupole coupling tensors are assigned to various nitrogen positions in the crystal structure. Two types of asymmetric N–H+N hydrogen bonds are observed in the ferroelectric phase. A slow dynamics influencing the 14N NQR spectrum and relaxation has been observed in the paraelectric phase. The analysis of the 14N NQR spectra in the paraelectric phase shows that above Tc each hydrogen bond exchanges between the two types observed in the ferroelectric phase. The change of the type of hydrogen bond is associated with the transfer of protons within the bond.
Phys. Chem. Chem. Phys., 2010, 12, 3895 - 3903, DOI: 10.1039/b915401a
Extra-framework aluminium species in hydrated faujasite zeolite as investigated by two-dimensional solid-state NMR spectroscopy and theoretical calculations
Shenhui Li, Anmin Zheng, Yongchao Su, Hanjun Fang, Wanling Shen, Zhiwu Yu, Lei Chen and Feng Deng
Extra-framework aluminium (EFAL) species in hydrated dealuminated HY zeolite were thoroughly investigated by various two-dimensional solid-state NMR techniques as well as density functional theoretical calculations. 27Al MQ MAS NMR experiments demonstrated that five-coordinated and four-coordinated extra-framework aluminium subsequently disappeared with the increase of water loading, and the quadrupole interaction of each aluminium species decreased gradually during the hydration process. 1H double quantum MAS NMR revealed that the EFAL species in the hydrated zeolite consisted of three components: a hydroxyl AlOH group, and two types of water molecule (rigid and mobile water). 1H–27Al LG-CP HETCOR experiments indicated that both the extra-framework and the framework Al atoms were in close proximity to the rigid water in the fully rehydrated zeolite. The experimental results were further confirmed by DFT theoretical calculations. Moreover, theoretical calculation results further demonstrated that the EFAL species in the hydrated zeolite consisted of the three components and the calculated 1H NMR chemical shift for each component agreed well with our NMR observations. It is the rigid water that connects the extra-framework aluminium with the four-coordinated framework aluminium through strong hydrogen bonds
The conformation and orientational order of a 1,2-disubstituted ethane nematogenic molecule (I22) in liquid crystalline and isotropic phases studied by NMR spectroscopy
James W. Emsley, Philippe Lesot, Anne Lesage, Giuseppina De Luca, Denis Merlet and Giuseppe Pileio
The structure, conformation and orientational order of the mesogen I22 have been studied by proton, carbon-13 and deuterium 1D and 2D-NMR spectroscopies at natural abundance and at various magnetic fields when in the nematic phase, the isotropic phase close to the nematic-isotropic phase transition, and as a solute in the chiral nematic solution comprised of the polypeptide PBLG dissolved in chloroform. It is concluded that 95% of conformers have a trans arrangement about the central C–C bond of the ethane fragment in all phases
Phys. Chem. Chem. Phys., 2010, 12, 2989 - 2998, DOI: 10.1039/b924666e
Dynamics on the microsecond timescale in hydrous silicates studied by solid-state 2H NMR spectroscopy
John M. Griffin, Andrew J. Miller, Andrew J. Berry, Stephen Wimperis and Sharon E. Ashbrook
Solid-state 2H NMR spectroscopy has been used to probe the dynamic disorder of hydroxyl deuterons in a synthetic sample of deuterated hydroxyl-clinohumite (4Mg2SiO4·Mg(OD)2), a proposed model for the incorporation of water within the Earths mantle. Both static and magic angle spinning (MAS) NMR methods were used. Static 2H NMR appears to reveal little evidence of the dynamic process, yielding results similar to those obtained from deuterated brucite (Mg(OD)2), where no dynamics on the relevant timescale are expected to be present. However, in 2H MAS NMR spectra, considerable line broadening is observed for hydroxyl-clinohumite and a 2H double-quantum (DQ) MAS NMR spectrum confirms that this is due to motion on the microsecond timescale. Using a model for dynamic exchange of the hydroxyl deuterons between two sites identified in previous diffraction studies, first-principles density functional theory (DFT) calculations of 2H (spin I = 1) quadrupolar NMR parameters, and a simple analytical model for dynamic line broadening in MAS NMR experiments, we were able to reproduce the observed motional line broadening and use this to estimate a rate constant for the dynamic process. From analysis of the observed 2H linewidths in variable-temperature MAS experiments, an activation energy for the exchange process was also determined. A simulated static 2H NMR lineshape based on our dynamic model is consistent with the observed experimental static NMR spectrum, confirming that the motion present in this system is not easily detectable using a static NMR approach. Finally, a 2H DQMAS NMR spectrum of fluorine-substituted 2H-enriched hydroxyl-clinohumite shows how the dynamic exchange process is inhibited by O–DF- hydrogen-bonding interactions.
Phys. Chem. Chem. Phys., 2010, 12, 3254 - 3259, DOI: 10.1039/b925326b
14N NQR and proton NMR study of ferroelectric phase transition and proton exchange in organic ferroelectric (H2-TPPZ)(Hca)2
Janez Seliger, Veselko agar, Tetsuo Asaji and Yumi Hasegawa
The complete 14N nuclear quadrupole resonance spectrum has been measured in ferroelectric (H2-TPPZ)(Hca)2 using nuclear quadrupole double resonance. The quadrupole coupling tensors are assigned to various nitrogen positions in the crystal structure. Two types of asymmetric N–H+N hydrogen bonds are observed in the ferroelectric phase. A slow dynamics influencing the 14N NQR spectrum and relaxation has been observed in the paraelectric phase. The analysis of the 14N NQR spectra in the paraelectric phase shows that above Tc each hydrogen bond exchanges between the two types observed in the ferroelectric phase. The change of the type of hydrogen bond is associated with the transfer of protons within the bond.
Phys. Chem. Chem. Phys., 2010, 12, 3895 - 3903, DOI: 10.1039/b915401a
Extra-framework aluminium species in hydrated faujasite zeolite as investigated by two-dimensional solid-state NMR spectroscopy and theoretical calculations
Shenhui Li, Anmin Zheng, Yongchao Su, Hanjun Fang, Wanling Shen, Zhiwu Yu, Lei Chen and Feng Deng
Extra-framework aluminium (EFAL) species in hydrated dealuminated HY zeolite were thoroughly investigated by various two-dimensional solid-state NMR techniques as well as density functional theoretical calculations. 27Al MQ MAS NMR experiments demonstrated that five-coordinated and four-coordinated extra-framework aluminium subsequently disappeared with the increase of water loading, and the quadrupole interaction of each aluminium species decreased gradually during the hydration process. 1H double quantum MAS NMR revealed that the EFAL species in the hydrated zeolite consisted of three components: a hydroxyl AlOH group, and two types of water molecule (rigid and mobile water). 1H–27Al LG-CP HETCOR experiments indicated that both the extra-framework and the framework Al atoms were in close proximity to the rigid water in the fully rehydrated zeolite. The experimental results were further confirmed by DFT theoretical calculations. Moreover, theoretical calculation results further demonstrated that the EFAL species in the hydrated zeolite consisted of the three components and the calculated 1H NMR chemical shift for each component agreed well with our NMR observations. It is the rigid water that connects the extra-framework aluminium with the four-coordinated framework aluminium through strong hydrogen bonds
Monday, April 05, 2010
J. Mag. Reson.
Optimal transfer of spin-order between a singlet nuclear pair and a heteronucleus
from ScienceDirect Publication: Journal of Magnetic ResonancePublication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 6 March 2010
Stephen, Kadlecek , Kiarash, Emami , Masaru, Ishii , Rahim, Rizi
Intramolecular spin-order transfer is a useful technique for signal enhancement of insensitive and low-concentration molecular species. We present a closed-form, optimized pulse sequence which maximizes the efficiency of transfer between a singlet (para) nuclear pair and a vicinal heteronucleus. Neglecting the decay of coherences while the nuclei are in the transverse plane, the scheme is unity efficient for all combinations of internuclear scalar couplings. Efficiency loss due to T2-like decay is also minimized by keeping the sequence as short as possible. We expect this result to be useful for hyperpolarization experiments in which the spin-order originates in parahydrogen, as well as studies of singlet state decay aimed at longer-term storage of spin-order in hyperpolarized Magnetic Resonance Imaging.
Carbon-13 NOESY and equivalent protons: methyl iodide dynamics
from ScienceDirect Publication: Journal of Magnetic ResonancePublication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript,Dmytro Kotsyubynskyy, Jozef Kowalewski, Pekka Tallavaara, Ville-Veikko Telkki, Jukka Jokisaari,and Evgeny Polyakov
We have shown that proton-coupled carbon-13 2D NOESY experiments, performed on degenerate spin systems, can provide unique quantitative information about anisotropic reorientational motions and molecular geometry. Relevant theory for AX2 and AX3 spin systems is presented, assuming the dipole–dipole and random field relaxation mechanisms of 13C nucleus, and demonstrated on methyl iodide solution in chloroform. Agreement with experimental intensities of all the six independent peaks is very good in the whole range of mixing times (up to 45 s).
Quantitative determination of NOE rates in perdeuterated and protonated proteins: practical and theoretical aspects
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 March 2010
Beat, Vögeli , Michael, Friedmann , Dominik, Leitz , Alexander, Sobol , Roland, Riek
Precision and accuracy are the limiting factors in extracting structural and dynamic information from experimental NOEs. In this study, error sources at all stages of such an analysis are identified and errors are estimated. The data set of HN-HN cross-relaxation rates obtained from triple labeled ubiquitin presented in [Vögeli, B.; Segawa, T.F.; Leitz, D., Sobol, A.; Choutko, A.; Trzesniak, D.; van Gunsteren, W.; Riek, R., J. Am. Chem. Soc. 131 (47), 17215–17225, 2009] is extended to rates obtained from a double labeled sample. Analog data sets are presented for GB3. It is shown that quantitative NOE rates can be determined with high accuracy from both triple-labeled as well as double-labeled samples. The quality of experimental cross-relaxation rates obtained from 3D HXQC-NOESY and NOESY-HXQC experiments is discussed. It is shown that NOESY-HXQC experiments provide rates of the same quality as HXQC-NOESY if both diagonal and cross peaks for a spin pair can be resolved. Expressions for cross-relaxation rates for anisotropically tumbling molecules exhibiting fast and slow motion are derived. The impact of anisotropy on the prediction of cross-relaxation rates and on the conversion of experimental rates into effective distances is discussed. For molecules with anisotropy DII/D
up to 5 the distance error is smaller than 2%. Finally, “averaged order parameters” are calculated for specific secondary structural elements showing similar trends for ubiquitin and GB3.NMR q-Space Imaging of Macroscopic Pores using Singlet Spin States
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 19 March 2010
Nirbhay N., Yadav , Allan M., Torres , William S., Price
NMR q-space imaging is a powerful non-invasive technique used to determine structural characteristics of pores in applications ranging from medical to material science. To date, the application of q-space imaging has primarily been limited to microscopic pores in part because of limitations of the effective observation time due to relaxation. Here we report on the use of singlet spin states for NMR q-space imaging, which allow significantly greater observation times. This opens the way for studying larger pores in materials such as biological tissue, emulsions, and rocks.
Quantitative Rapid Scan EPR Spectroscopy at 258 MHz
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 21 March 2010
Richard W., Quine , George A., Rinard , Sandra S., Eaton , Gareth R., Eaton
Experimental data obtained with an electron paramagnetic resonance (EPR) rapid scan spectrometer were translated through the reverse transfer functions of the spectrometer hardware to the sample position. Separately, theoretical calculations were performed to predict signal and noise amplitudes at the sample position for specified experimental conditions. A comparison was then made between the translated experimental values and the calculated values. Excellent agreement was obtained.
Solid State Nuclear Magnetic Resonance
Controversy about the reference compound for correct chemical shift determination of 195Pt nuclei
Publication year: 2010
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 27 March 2010
Bogdan, Nowak
Several groups exploring the 195Pt NMR in solids, including metallic and magnetic materials, use different standards for chemical shift (Knight shift) determination. Commonly applied H2PtCl6 and Na2PtCl6 (IUPAC δ scale) lead to considerable underestimation of the shifts since H2PtCl6 has considerable own 195Pt NMR shift due to its Van Vleck paramagnetism.In this Letter new results on 195Pt NMR in heavy fermion system CeInPt4 are presentedand rationalized scale for the Knight shift determination is discussed.
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 March 2010
Mariusz, Maćkowiak , Nicolay, Sinyavsky
Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 27 March 2010
Bogdan, Nowak
Several groups exploring the 195Pt NMR in solids, including metallic and magnetic materials, use different standards for chemical shift (Knight shift) determination. Commonly applied H2PtCl6 and Na2PtCl6 (IUPAC δ scale) lead to considerable underestimation of the shifts since H2PtCl6 has considerable own 195Pt NMR shift due to its Van Vleck paramagnetism.In this Letter new results on 195Pt NMR in heavy fermion system CeInPt4 are presentedand rationalized scale for the Knight shift determination is discussed.
Off-resonance effects in two-dimensional exchange NMR at zero- field
Publication year: 2010Source: Solid State Nuclear Magnetic Resonance, In Press, Accepted Manuscript, Available online 15 March 2010
Mariusz, Maćkowiak , Nicolay, Sinyavsky
The effects of off-resonance irradiation in 2D exchange NMR at zero-field are analysed. A theoretical treatment of the 2D exchange NMR pulse sequence is presented and applied to the quantitative study of exchange processes in molecular crystals. It takes into account the off-resonance irradiation, which critically influences the spin dynamics. The response of a system of spins I=3/2 in zero applied field to the three-pulse sequence is analysed. The mixing dynamics by exchange and the expected cross-peak intensities as a function of the frequency offset has been derived. It is shown that the off-resonance effects are of crucial importance for the quantitative description of the exchange spectra. The theory is successfully tested for the exchange spectra of hindered trichloromethyl groups of p-chloroanilinium trichloroacetate, where the conventional approach without taking into account the off-resonance phenomena has failed.
Thursday, April 01, 2010
J. Phys. Chem. B and C, v114, Issues 13
Distinguishing Polymorphs of the Semiconducting Pigment Copper Phthalocyanine by Solid-State NMR and Raman Spectroscopy
Medhat A. Shaibat†, Leah B. Casabianca†, Diana Y. Siberio-Prez§‡, Adam J. Matzger*‡ and Yoshitaka Ishii*†
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, and Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109
J. Phys. Chem. B, 2010, 114 (13), pp 4400–4406
Abstract: Cu(II)(phthalocyanine) (CuPc) is broadly utilized as an archetypal molecular semiconductor and is the most widely used blue printing pigment. CuPc crystallizes in six different forms; the chemical and physical properties are substantially modulated by its molecular packing among these polymorphs. Despite the growing importance of this system, spectroscopic identification of different polymorphs for CuPc has posed difficulties. This study presents the first example of spectroscopic distinction of α- and β-forms of CuPc, the most widely used polymorphs, by solid-state NMR (SSNMR) and Raman spectroscopy. 13C high-resolution SSNMR spectra of α- and β-CuPc using very-fast magic angle spinning (VFMAS) at 20 kHz show that hyperfine shifts sensitively reflect polymorphs of CuPc. The experimental results were confirmed by ab initio chemical shift calculations. 13C and 1H SSNMR relaxation times of α- and β-CuPc under VFMAS also showed marked differences, presumably because of the difference in electronic spin correlation times in the two forms. Raman spectroscopy also provided another reliable method of differentiation between the two polymorphs.
Medhat A. Shaibat†, Leah B. Casabianca†, Diana Y. Siberio-Prez§‡, Adam J. Matzger*‡ and Yoshitaka Ishii*†
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, and Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109
J. Phys. Chem. B, 2010, 114 (13), pp 4400–4406
Abstract: Cu(II)(phthalocyanine) (CuPc) is broadly utilized as an archetypal molecular semiconductor and is the most widely used blue printing pigment. CuPc crystallizes in six different forms; the chemical and physical properties are substantially modulated by its molecular packing among these polymorphs. Despite the growing importance of this system, spectroscopic identification of different polymorphs for CuPc has posed difficulties. This study presents the first example of spectroscopic distinction of α- and β-forms of CuPc, the most widely used polymorphs, by solid-state NMR (SSNMR) and Raman spectroscopy. 13C high-resolution SSNMR spectra of α- and β-CuPc using very-fast magic angle spinning (VFMAS) at 20 kHz show that hyperfine shifts sensitively reflect polymorphs of CuPc. The experimental results were confirmed by ab initio chemical shift calculations. 13C and 1H SSNMR relaxation times of α- and β-CuPc under VFMAS also showed marked differences, presumably because of the difference in electronic spin correlation times in the two forms. Raman spectroscopy also provided another reliable method of differentiation between the two polymorphs.
Monday, March 29, 2010
Acc. Chem. Res.: Noninvasive Testing of Art and Cultural Heritage by Mobile NMR
Noninvasive Testing of Art and Cultural Heritage by Mobile NMR
Bernhard Blmich, Federico Casanova, Juan Perlo, Federica Presciutti, Chiara Anselmi and Brenda Doherty
Acc. Chem. Res., Article ASAP
DOI: 10.1021/ar900277h
Publication Date (Web): March 26, 2010
Bernhard Blmich, Federico Casanova, Juan Perlo, Federica Presciutti, Chiara Anselmi and Brenda Doherty
Acc. Chem. Res., Article ASAP
DOI: 10.1021/ar900277h
Publication Date (Web): March 26, 2010
Thursday, March 25, 2010
J. Phys. Chem B and C, vol. 114, Issues 12
Measurement of the Reactive Surface Area of Clay Minerals Using Solid-State NMR Studies of a Probe Molecule†
Rebecca L. Sanders, Nancy M. Washton and Karl T. Mueller*
J. Phys. Chem. C, 2010, 114 (12), pp 5491–5498
Abstract: Understanding the surface reactivity of clay minerals is necessary for accurate prediction of natural weathering rates due to the ubiquity of clays in the environment as weathering products of primary minerals. However, the reactivity of the heterogeneous surfaces of a clay can be difficult to characterize as clay mineral edge sites often react at different rates or via different mechanisms than sites on the basal planes. Ultimately, a method is needed to probe quantitatively the reactive surface sites in order to predict clay mineral dissolution rates. In this study, solid-state NMR spectroscopy has been utilized to investigate surface hydroxyl species and their relation to clay surface reactivity. The surfaces of two kaolinite samples (KGa-1b and KGa-2) and two montmorillonite samples (STx-1b and SWy-2) were reacted with the probe molecule (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS), which binds selectively to reactive non-hydrogen bonded Q3Si hydroxyl sites. Quantification of 19F spins in the TFS-treated samples using 19F magic angle spinning NMR peak intensities provides a sensitive measure of the number of reactive hydroxyl sites on a mass normalized (per gram) basis. The reactive surface site densities of KGa-1b and KGa-2 were found to be proportional to published atomic force microscopy edge site fractions. An example from KGa-1b dissolution after 10 days at pH 2.9 and 21 °C revealed no significant change in Brunauer−Emmett−Teller specific surface area, but a 25% decrease in reactive surface site density. We posit this site density determined by solid-state NMR is proportional to the reactive surface area of each clay mineral and its use in future dissolution studies is warranted to investigate how changes in reactive surface area can be tied to decreases in rates of silicon and aluminum release into solution.
Rebecca L. Sanders, Nancy M. Washton and Karl T. Mueller*
J. Phys. Chem. C, 2010, 114 (12), pp 5491–5498
Abstract: Understanding the surface reactivity of clay minerals is necessary for accurate prediction of natural weathering rates due to the ubiquity of clays in the environment as weathering products of primary minerals. However, the reactivity of the heterogeneous surfaces of a clay can be difficult to characterize as clay mineral edge sites often react at different rates or via different mechanisms than sites on the basal planes. Ultimately, a method is needed to probe quantitatively the reactive surface sites in order to predict clay mineral dissolution rates. In this study, solid-state NMR spectroscopy has been utilized to investigate surface hydroxyl species and their relation to clay surface reactivity. The surfaces of two kaolinite samples (KGa-1b and KGa-2) and two montmorillonite samples (STx-1b and SWy-2) were reacted with the probe molecule (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS), which binds selectively to reactive non-hydrogen bonded Q3Si hydroxyl sites. Quantification of 19F spins in the TFS-treated samples using 19F magic angle spinning NMR peak intensities provides a sensitive measure of the number of reactive hydroxyl sites on a mass normalized (per gram) basis. The reactive surface site densities of KGa-1b and KGa-2 were found to be proportional to published atomic force microscopy edge site fractions. An example from KGa-1b dissolution after 10 days at pH 2.9 and 21 °C revealed no significant change in Brunauer−Emmett−Teller specific surface area, but a 25% decrease in reactive surface site density. We posit this site density determined by solid-state NMR is proportional to the reactive surface area of each clay mineral and its use in future dissolution studies is warranted to investigate how changes in reactive surface area can be tied to decreases in rates of silicon and aluminum release into solution.
Monday, March 22, 2010
J. Phys. Chem B and C, vol. 114, issues 11
Chemisorbed Thiols on Silica Particles: Characterization of Reactive Sulfur Species
Paula Caregnato*†, Malcolm D. E. Forbes‡, Delia B. Soria§, Daniel O. Mrtire† and Mnica C. Gonzalez†
J. Phys. Chem. C, 2010, 114 (11), pp 5080–5087
DOI: 10.1021/jp911253f
Abstract: Silica particles with surface thiol groups (Sil−SH) were prepared by silylation of silanol groups using 3-mercaptopropyltrimethoxysilane. The particles were characterized by FTIR, Raman, and XPS spectroscopies; thermogravimetry; and solid state 13C and 29Si NMR spectroscopy. Laser flash excitation at 266 nm of Sil−SH water suspensions in the presence of sodium peroxodisulfate generated sulfur-centered radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (330 nm) by transient optical techniques. Absorbance decay signals were fit to first- and second-order decay kinetics and were assigned to thiyl radicals. Formation of disulfide radicals, a major decay channel for free thiyl radicals in solution, was not observed for surface-grafted thiyl radicals.
Reversibility and Improved Hydrogen Release of Magnesium Borohydride
Rebecca J. Newhouse†‡, Vitalie Stavila*‡, Son-Jong Hwang§, Leonard E. Klebanoff‡ and Jin Z. Zhang†
J. Phys. Chem. C, 2010, 114 (11), pp 5224–5232
DOI: 10.1021/jp9116744
Abstract: Desorption and subsequent rehydrogenation of Mg(BH4)2 with and without 5 mol % TiF3 and ScCl3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(BxHy)n intermediates were formed at 300 °C, whereas MgB2 was the major product when heated to 600 °C. These samples were then rehydrogenated and subsequently characterized with powder X-ray diffraction (pXRD), Raman, and NMR spectroscopy. We confirmed significant conversion of MgB2 to fully hydrogenated Mg(BH4)2 for the sample with and without additives. TPD and NMR studies revealed that the additives have a significant effect on the reaction pathway during both dehydrogenation and rehydrogenation reactions. This work suggests that the use of additives may provide a valid pathway for improving intrinsic hydrogen storage properties of magnesium borohydride.
Comparison of Different Theory Models and Basis Sets in the Calculations of Structures and 13C NMR Spectra of [Pt(en)(CBDCA−O, O′)], an Analogue of the Antitumor Drug Carboplatin
Hongwei Gao*, Xiujuan Wei, Xuting Liu and Tingxia Yan
J. Phys. Chem. B, 2010, 114 (11), pp 4056–4062
DOI: 10.1021/jp912005a
Abstract: Comparisons of various density functional theory (DFT) methods at different basis sets in predicting the molecular structures and 13C NMR spectra for [Pt(en)(CBDCA−O, O′)], an analogue of the antitumor drug carboplatin, are reported. DFT methods including B3LYP, B3PW91, mPW1PW91, PBE1PBE, BPV86, PBEPBE, and LSDA are examined. Different basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G, and CEP-121G are also considered. It is remarkable that the LSDA/SDD level is clearly superior to all of the remaining density functional methods in predicting the structure of [Pt(en)(CBDCA−O, O′)]. The results also indicate that the B3LYP/SDD level is the best to predict 13C NMR spectra for [Pt(en)(CBDCA−O, O′)] among all DFT methods.
Paula Caregnato*†, Malcolm D. E. Forbes‡, Delia B. Soria§, Daniel O. Mrtire† and Mnica C. Gonzalez†
J. Phys. Chem. C, 2010, 114 (11), pp 5080–5087
DOI: 10.1021/jp911253f
Abstract: Silica particles with surface thiol groups (Sil−SH) were prepared by silylation of silanol groups using 3-mercaptopropyltrimethoxysilane. The particles were characterized by FTIR, Raman, and XPS spectroscopies; thermogravimetry; and solid state 13C and 29Si NMR spectroscopy. Laser flash excitation at 266 nm of Sil−SH water suspensions in the presence of sodium peroxodisulfate generated sulfur-centered radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (330 nm) by transient optical techniques. Absorbance decay signals were fit to first- and second-order decay kinetics and were assigned to thiyl radicals. Formation of disulfide radicals, a major decay channel for free thiyl radicals in solution, was not observed for surface-grafted thiyl radicals.
Reversibility and Improved Hydrogen Release of Magnesium Borohydride
Rebecca J. Newhouse†‡, Vitalie Stavila*‡, Son-Jong Hwang§, Leonard E. Klebanoff‡ and Jin Z. Zhang†
J. Phys. Chem. C, 2010, 114 (11), pp 5224–5232
DOI: 10.1021/jp9116744
Abstract: Desorption and subsequent rehydrogenation of Mg(BH4)2 with and without 5 mol % TiF3 and ScCl3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(BxHy)n intermediates were formed at 300 °C, whereas MgB2 was the major product when heated to 600 °C. These samples were then rehydrogenated and subsequently characterized with powder X-ray diffraction (pXRD), Raman, and NMR spectroscopy. We confirmed significant conversion of MgB2 to fully hydrogenated Mg(BH4)2 for the sample with and without additives. TPD and NMR studies revealed that the additives have a significant effect on the reaction pathway during both dehydrogenation and rehydrogenation reactions. This work suggests that the use of additives may provide a valid pathway for improving intrinsic hydrogen storage properties of magnesium borohydride.
Comparison of Different Theory Models and Basis Sets in the Calculations of Structures and 13C NMR Spectra of [Pt(en)(CBDCA−O, O′)], an Analogue of the Antitumor Drug Carboplatin
Hongwei Gao*, Xiujuan Wei, Xuting Liu and Tingxia Yan
J. Phys. Chem. B, 2010, 114 (11), pp 4056–4062
DOI: 10.1021/jp912005a
Abstract: Comparisons of various density functional theory (DFT) methods at different basis sets in predicting the molecular structures and 13C NMR spectra for [Pt(en)(CBDCA−O, O′)], an analogue of the antitumor drug carboplatin, are reported. DFT methods including B3LYP, B3PW91, mPW1PW91, PBE1PBE, BPV86, PBEPBE, and LSDA are examined. Different basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G, and CEP-121G are also considered. It is remarkable that the LSDA/SDD level is clearly superior to all of the remaining density functional methods in predicting the structure of [Pt(en)(CBDCA−O, O′)]. The results also indicate that the B3LYP/SDD level is the best to predict 13C NMR spectra for [Pt(en)(CBDCA−O, O′)] among all DFT methods.
Friday, March 12, 2010
J. Phys Chem. B and C. Volume 114, Issues 10
EPR, ENDOR, and HYSCORE Study of the Structure and the Stability of Vanadyl−Porphyrin Complexes Encapsulated in Silica: Potential Paramagnetic Biomarkers for the Origin of Life
Gourier*†, Olivier Delpoux†, Audrey Bonduelle†, Laurent Binet†, Ilaria Ciofini‡ and Herv Vezin§
J. Phys. Chem. B, 2010, 114 (10), pp 3714–3725
Abstract: The possibility of using vanadyl ions as paramagnetic biomarkers for the identification of traces of primitive life fossilized in silica rocks is studied by cw-EPR, ENDOR, HYSCORE, and DFT calculations. It is well-known that porphyrins, which are common to all living organisms, form vanadyl−porphyrin complexes in sediments deposited in oceans. However, the stability of these complexes over a very long time (more than 3 billion years) is not known. By encapsulating vanadyl−porphyrin complexes in silica synthesized by a sol−gel method to mimic SiO2 sediments, we studied the structure and stability of these complexes upon step heating treatments by monitoring the evolution of the g factor and of the hyperfine interactions with 51V, 1H, 14N, 13C, and 29Si nuclei. It is found that vanadyl−porphyrin complexes are progressively transformed into oxygenated vanadyl complexes by transfer of the VO2+ ion from the porphyrin ring to the mineral matrix. The organic component is transformed into carbonaceous matter which contains paramagnetic centers (IOM• centers). To test the validity of this approach, we studied by EPR a 3490 million years old chert (polycrystalline SiO2 rock) containing some of the oldest putative traces of life. This rock contains oxygenated vanadyl complexes and IOM• centers very similar to those found in the synthetic analogues.
Confinement of NaAlH4 in Nanoporous Carbon: Impact on H2 Release, Reversibility, and Thermodynamics
Jinbao Gao†, Philipp Adelhelm†, Margriet H. W. Verkuijlen‡, Carine Rongeat§, Monika Herrich§, P. Jan M. van Bentum‡, Oliver Gutfleisch§, Arno P. M. Kentgens‡, Krijn P. de Jong† and Petra E. de Jongh*†
J. Phys. Chem. C, 2010, 114 (10), pp 4675–4682
Abstract: Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH4 is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H2. The slow kinetics and poor reversibility of the hydrogen desorption can be combatted by the addition of a Ti-based catalyst. In an alternative approach we studied the influence of a reduced NaAlH4 particle size and the presence of a carbon support. We focused on NaAlH4/porous carbon nanocomposites prepared by melt infiltration. The NaAlH4 was confined in the mainly 2−3 nm pores of the carbon, resulting in a lack of long-range order in the NaAlH4 structure. The hydrogen release profile was modified by contact with the carbon; even for 10 nm NaAlH4 on a nonporous carbon material the decomposition of NaAlH4 to NaH, Al, and H2 now led to hydrogen release in a single step. This was a kinetic effect, with the temperature at which the hydrogen was released depending on the NaAlH4 feature size. However, confinement in a nanoporous carbon material was essential to not only achieve low H2 release temperatures, but also rehydrogenation at mild conditions (e.g., 24 bar H2 at 150 °C). Not only had the kinetics of hydrogen sorption improved, but the thermodynamics had also changed. When hydrogenating at conditions at which Na3AlH6 would be expected to be the stable phase (e.g., 40 bar H2 at 160 °C), instead nanoconfined NaAlH4 was formed, indicating a shift of the NaAlH4↔Na3AlH6 thermodynamic equilibrium in these nanocomposites compared to bulk materials.
Solid-State NMR Studies of the Local Structure of NaAlH4/C Nanocomposites at Different Stages of Hydrogen Desorption and Rehydrogenation
Margriet H. W. Verkuijlen†, Jinbao Gao‡, Philipp Adelhelm‡, P. Jan M. van Bentum*†, Petra E. de Jongh‡ and Arno P. M. Kentgens*†
J. Phys. Chem. C, 2010, 114 (10), pp 4683–4692
Abstract: Structural properties of NaAlH4/C nanocomposites were studied using 23Na and 27Al solid-state NMR. The samples were synthesized by melt infiltration of a highly porous carbon support, with typical pore sizes of 2−3 nm. Physical mixtures of high surface carbon with alanates in different stages of hydrogen desorption show somewhat broadened resonances and a small negative chemical shift compared to pure alanates. This is most likely caused by a susceptibility effect of the carbon support material, which shields and distorts the applied magnetic field. After melt infiltration, 23Na and 27Al spectra are broadened with a small downfield average shift, which is mainly caused by a chemical shift distribution and is explained by a larger disorder in the nanoconfined materials and a possible charge transfer to the carbon. Our measurements show that the local structure of the nanoconfined alanate is the similar to bulk alanate because a comparable chemical shift and average quadrupolar coupling constant is found. In contrast to bulk alanates, in partly desorbed nanocomposite samples no Na3AlH6 is detected. Together with a single release peak observed by dehydrogenation experiments, this points toward a desorption in one single step. 23Na spectra of completely desorbed NaAlH4/C and NaH/C nanocomposites confirm the formation of metallic sodium at lower temperatures than those observed for bulk alanates. The structural properties observed with solid-state NMR of the nanoconfined alanate are restored after a rehydrogenation cycle. This demonstrates that the dehydrogenation of the NaAlH4/C nanocomposite is reversible, even without a Ti-based catalyst.
Transferred Hyperfine Interaction between a Tetrahedral Transition Metal and Tetrahedral Lithium: Li6CoO4
Dany Carlier*, Michel Mntrier and Claude Delmas
J. Phys. Chem. C, 2010, 114 (10), pp 4749–4755
Abstract: Li6CoO4 presents an antifluorite-type structure, with both the Co and Li ions in tetrahedral oxygen coordination. 7Li MAS NMR shows remarkably different shifts (+885 and −232 ppm) for the two different crystallographic types of Li. In order to assign the signals and to understand the mechanisms whereby the electron spins on the e orbitals of Co2+ ions (e4 t23 electronic configuration) are transferred toward the two different types of Li with opposite polarization, we have carried out GGA and GGA+U calculations of the electronic structure using the VASP code. Spin density maps in selected planes of the structure reveal (as expected) that lobes of the t2 orbitals point toward the faces of the CoO4 tetrahedra and can thus overlap with the neighboring Li(2) through empty square pyramidal sites. As concerns Li(1), a mechanism is evidenced where the (filled) e orbitals of Co2+ are polarized by the electron spins in the t2 ones. These polarized e orbitals overlap with Li(1) through the common edge of the tetrahedra. The relative magnitude of the experimental shifts for the two types of Li are however not fully reproduced by the calculations, and the influence of the U parameter as well as of the pseudopotential method used is discussed.
A Combined Hydrogen Storage System of Mg(BH4)2−LiNH2 with Favorable Dehydrogenation
X. B. Yu*†‡, Y. H. Guo‡, D. L. Sun‡, Z. X. Yang§, A. Ranjbar†, Z. P. Guo†, H. K. Liu† and S. X. Dou†
J. Phys. Chem. C, 2010, 114 (10), pp 4733–4737
Abstract: The decomposition properties of Mg(BH4)2−LiNH2 mixtures were investigated. Apparent NH3 release appeared from 50 to 300 °C for the Mg(BH4)2−LiNH2 mixtures with mole ratios of 1:1.5, 1:2, and 1:3, while only hydrogen release was detected for the mixture with a mole ratio of 1:1. In the case of the Mg(BH4)2−LiNH2 (1:1) sample, the onset of the first-step dehydrogenation starts at 160 °C, with a weight loss of 7.2 wt % at 300 °C, which is improved significantly compared to the pure Mg(BH4)2 alone. From Kissinger’s method, the activation energy, Ea, for the first and second step dehydrogenation in Mg(BH4)2−LiNH2 (1:1) was estimated to be about 121.7 and 236.6 kJ mol−1, respectively. The improved dehydrogenation in the combined system may be ascribed to a combination reaction between [BH4] and [NH2], resulting in the formation of Li−Mg alloy and amorphous B−N compound.
Gourier*†, Olivier Delpoux†, Audrey Bonduelle†, Laurent Binet†, Ilaria Ciofini‡ and Herv Vezin§
J. Phys. Chem. B, 2010, 114 (10), pp 3714–3725
Abstract: The possibility of using vanadyl ions as paramagnetic biomarkers for the identification of traces of primitive life fossilized in silica rocks is studied by cw-EPR, ENDOR, HYSCORE, and DFT calculations. It is well-known that porphyrins, which are common to all living organisms, form vanadyl−porphyrin complexes in sediments deposited in oceans. However, the stability of these complexes over a very long time (more than 3 billion years) is not known. By encapsulating vanadyl−porphyrin complexes in silica synthesized by a sol−gel method to mimic SiO2 sediments, we studied the structure and stability of these complexes upon step heating treatments by monitoring the evolution of the g factor and of the hyperfine interactions with 51V, 1H, 14N, 13C, and 29Si nuclei. It is found that vanadyl−porphyrin complexes are progressively transformed into oxygenated vanadyl complexes by transfer of the VO2+ ion from the porphyrin ring to the mineral matrix. The organic component is transformed into carbonaceous matter which contains paramagnetic centers (IOM• centers). To test the validity of this approach, we studied by EPR a 3490 million years old chert (polycrystalline SiO2 rock) containing some of the oldest putative traces of life. This rock contains oxygenated vanadyl complexes and IOM• centers very similar to those found in the synthetic analogues.
Confinement of NaAlH4 in Nanoporous Carbon: Impact on H2 Release, Reversibility, and Thermodynamics
Jinbao Gao†, Philipp Adelhelm†, Margriet H. W. Verkuijlen‡, Carine Rongeat§, Monika Herrich§, P. Jan M. van Bentum‡, Oliver Gutfleisch§, Arno P. M. Kentgens‡, Krijn P. de Jong† and Petra E. de Jongh*†
J. Phys. Chem. C, 2010, 114 (10), pp 4675–4682
Abstract: Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH4 is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H2. The slow kinetics and poor reversibility of the hydrogen desorption can be combatted by the addition of a Ti-based catalyst. In an alternative approach we studied the influence of a reduced NaAlH4 particle size and the presence of a carbon support. We focused on NaAlH4/porous carbon nanocomposites prepared by melt infiltration. The NaAlH4 was confined in the mainly 2−3 nm pores of the carbon, resulting in a lack of long-range order in the NaAlH4 structure. The hydrogen release profile was modified by contact with the carbon; even for 10 nm NaAlH4 on a nonporous carbon material the decomposition of NaAlH4 to NaH, Al, and H2 now led to hydrogen release in a single step. This was a kinetic effect, with the temperature at which the hydrogen was released depending on the NaAlH4 feature size. However, confinement in a nanoporous carbon material was essential to not only achieve low H2 release temperatures, but also rehydrogenation at mild conditions (e.g., 24 bar H2 at 150 °C). Not only had the kinetics of hydrogen sorption improved, but the thermodynamics had also changed. When hydrogenating at conditions at which Na3AlH6 would be expected to be the stable phase (e.g., 40 bar H2 at 160 °C), instead nanoconfined NaAlH4 was formed, indicating a shift of the NaAlH4↔Na3AlH6 thermodynamic equilibrium in these nanocomposites compared to bulk materials.
Solid-State NMR Studies of the Local Structure of NaAlH4/C Nanocomposites at Different Stages of Hydrogen Desorption and Rehydrogenation
Margriet H. W. Verkuijlen†, Jinbao Gao‡, Philipp Adelhelm‡, P. Jan M. van Bentum*†, Petra E. de Jongh‡ and Arno P. M. Kentgens*†
J. Phys. Chem. C, 2010, 114 (10), pp 4683–4692
Abstract: Structural properties of NaAlH4/C nanocomposites were studied using 23Na and 27Al solid-state NMR. The samples were synthesized by melt infiltration of a highly porous carbon support, with typical pore sizes of 2−3 nm. Physical mixtures of high surface carbon with alanates in different stages of hydrogen desorption show somewhat broadened resonances and a small negative chemical shift compared to pure alanates. This is most likely caused by a susceptibility effect of the carbon support material, which shields and distorts the applied magnetic field. After melt infiltration, 23Na and 27Al spectra are broadened with a small downfield average shift, which is mainly caused by a chemical shift distribution and is explained by a larger disorder in the nanoconfined materials and a possible charge transfer to the carbon. Our measurements show that the local structure of the nanoconfined alanate is the similar to bulk alanate because a comparable chemical shift and average quadrupolar coupling constant is found. In contrast to bulk alanates, in partly desorbed nanocomposite samples no Na3AlH6 is detected. Together with a single release peak observed by dehydrogenation experiments, this points toward a desorption in one single step. 23Na spectra of completely desorbed NaAlH4/C and NaH/C nanocomposites confirm the formation of metallic sodium at lower temperatures than those observed for bulk alanates. The structural properties observed with solid-state NMR of the nanoconfined alanate are restored after a rehydrogenation cycle. This demonstrates that the dehydrogenation of the NaAlH4/C nanocomposite is reversible, even without a Ti-based catalyst.
Transferred Hyperfine Interaction between a Tetrahedral Transition Metal and Tetrahedral Lithium: Li6CoO4
Dany Carlier*, Michel Mntrier and Claude Delmas
J. Phys. Chem. C, 2010, 114 (10), pp 4749–4755
Abstract: Li6CoO4 presents an antifluorite-type structure, with both the Co and Li ions in tetrahedral oxygen coordination. 7Li MAS NMR shows remarkably different shifts (+885 and −232 ppm) for the two different crystallographic types of Li. In order to assign the signals and to understand the mechanisms whereby the electron spins on the e orbitals of Co2+ ions (e4 t23 electronic configuration) are transferred toward the two different types of Li with opposite polarization, we have carried out GGA and GGA+U calculations of the electronic structure using the VASP code. Spin density maps in selected planes of the structure reveal (as expected) that lobes of the t2 orbitals point toward the faces of the CoO4 tetrahedra and can thus overlap with the neighboring Li(2) through empty square pyramidal sites. As concerns Li(1), a mechanism is evidenced where the (filled) e orbitals of Co2+ are polarized by the electron spins in the t2 ones. These polarized e orbitals overlap with Li(1) through the common edge of the tetrahedra. The relative magnitude of the experimental shifts for the two types of Li are however not fully reproduced by the calculations, and the influence of the U parameter as well as of the pseudopotential method used is discussed.
A Combined Hydrogen Storage System of Mg(BH4)2−LiNH2 with Favorable Dehydrogenation
X. B. Yu*†‡, Y. H. Guo‡, D. L. Sun‡, Z. X. Yang§, A. Ranjbar†, Z. P. Guo†, H. K. Liu† and S. X. Dou†
J. Phys. Chem. C, 2010, 114 (10), pp 4733–4737
Abstract: The decomposition properties of Mg(BH4)2−LiNH2 mixtures were investigated. Apparent NH3 release appeared from 50 to 300 °C for the Mg(BH4)2−LiNH2 mixtures with mole ratios of 1:1.5, 1:2, and 1:3, while only hydrogen release was detected for the mixture with a mole ratio of 1:1. In the case of the Mg(BH4)2−LiNH2 (1:1) sample, the onset of the first-step dehydrogenation starts at 160 °C, with a weight loss of 7.2 wt % at 300 °C, which is improved significantly compared to the pure Mg(BH4)2 alone. From Kissinger’s method, the activation energy, Ea, for the first and second step dehydrogenation in Mg(BH4)2−LiNH2 (1:1) was estimated to be about 121.7 and 236.6 kJ mol−1, respectively. The improved dehydrogenation in the combined system may be ascribed to a combination reaction between [BH4] and [NH2], resulting in the formation of Li−Mg alloy and amorphous B−N compound.
Friday, March 05, 2010
J. Phys. Chem. B. and J. Phys. Chem. C, Volumes 114, Issues 9
LiBH4 in Carbon Aerogel Nanoscaffolds: An NMR Study of Atomic Motions
David T. Shane†, Robert L. Corey†‡, Charlie McIntosh†, Laura H. Rayhel†, Robert C. Bowman, Jr.§, John J. Vajo, Adam F. Gross and Mark S. Conradi*†
J. Phys. Chem. C, 2010, 114 (9), pp 4008–4014
DOI: 10.1021/jp9107365
Hydrogen NMR of LiBH4 in the pores of carbon aerogel nanoscaffolds shows the coexistence of motionally narrowed and broad components. The fraction of mobile, diffusing hydrogen, already evident at room temperature, increases continuously with temperature. Thus, a broad distribution of environments is present, as in some ball-milled hydrides. With decreasing pore size from 25 to 13 nm, the narrowed fraction increases, suggesting that the narrow resonance is from the most defective regions, the grain boundaries. The broad component eventually exhibits narrowing in the same temperature window as for bulk material, confirming the bulk-like structure of those regions. Hole-burning measurements reveal magnetization exchange between the broad and narrow resonance lines, confirming the close spatial proximity of the atoms in each line. The solid−solid transition is clearly evident in 7Li line shapes, with a 10−15 °C depression from the bulk. More rapid decay of the quadrupolar satellite signals in spin echoes, compared to the central transition, is due to lithium atoms diffusing between differently oriented nanocrystallites. Our results suggest that crystallites in neighboring pores have similar orientations but are incoherent for diffraction. Remarkably, the T1 data of hydrogen and 7Li are continuous in the vicinity of the transition, in contrast with the bulk T1 data, suggesting that some rapid lithium motion remains below the transition.
Metal Carbonation of Forsterite in Supercritical CO2 and H2O Using Solid State 29Si, 13C NMR Spectroscopy
Ja Hun Kwak, Jian Zhi Hu*, David W. Hoyt, Jesse A. Sears, Chongming Wang, Kevin M. Rosso and Andrew R. Felmy
J. Phys. Chem. C, 2010, 114 (9), pp 4126–4134
DOI: 10.1021/jp1001308
Ex situ natural abundance magic angle spinning (MAS) NMR was used for the first time to study fundamental mineral carbonation processes and reaction extent relevant to geologic carbon sequestration (GCS) using a model silicate mineral forsterite (Mg2SiO4)+supercritical CO2 with and without H2O. Run conditions were 80 °C and 96 atm. With H2O but without CO2, 29Si MAS NMR reveals that the reaction products contain only two peaks of similar intensities located at about −84.8 and −91.8 ppm, which can be assigned to surface Q1 and Q2 species, i.e., SiO4 tetrahedra sharing one and two corners with other tetrahedra, respectively. Using scCO2 without H2O, no reaction is observed within 7 days. Using both scCO2 and H2O, the surface reaction products for silica are mainly Q4 species (−111.6 ppm) accompanied by a lesser amount of Q3 (−102 ppm) and Q2 (−91.8 ppm) species. No surface Q1 species were detected, indicating the carbonic acid formation and magnesite (MgCO3) precipitation reactions are faster than the forsterite hydrolysis process. Thus, it can be concluded that the Mg2SiO4 hydrolysis process is the rate limiting step of the overall mineral carbonation process. 29Si NMR combined with XRD, TEM, SAED, and EDX further reveals that the reaction is a surface reaction with the Mg2SiO4 crystallite in the core and with condensed Q2, Q3, and Q4 species forming highly porous amorphous surface layers. 13C MAS NMR unambiguously identified a reaction intermediate as Mg5(CO3)4(OH)2·5H2O, i.e., the dypingite.
Solid State 2H NMR Analysis of Furanose Ring Dynamics in DNA Containing Uracil
Monica N. Kinde-Carson†, Crystal Ferguson§, Nathan A. Oyler‡, Gerard S. Harbison† and Gary A. Meints*§
J. Phys. Chem. B, 2010, 114 (9), pp 3285–3293
DOI: 10.1021/jp9091656
Abstract: DNA damage has been implicated in numerous human diseases, particularly cancer, and the aging process. Single-base lesions, such as uracil, in DNA can be cytotoxic or mutagenic and are recognized by a DNA glycosylase during the process of base excision repair. Increased dynamic properties in lesion-containing DNAs have been suggested to assist recognition and specificity. Deuterium solid-state nuclear magnetic resonance (SSNMR) has been used to directly observe local dynamics of the furanose ring within a uracil:adenine (U:A) base pair and compared to a normal thymine:adenine (T:A) base pair. Quadrupole echo lineshapes, T1Z, and T2e relaxation data were collected, and computer modeling was performed. The results indicate that the relaxation times are identical within the experimental error, the solid lineshapes are essentially indistinguishable above the noise level, and our lineshapes are best fit with a model that does not have significant local motions. Therefore, U:A base pair furanose rings appear to have essentially identical dynamic properties as a normal T:A base pair, and the local dynamics of the furanose ring are unlikely to be the sole arbiter for uracil recognition and specificity in U:A base pairs.
David T. Shane†, Robert L. Corey†‡, Charlie McIntosh†, Laura H. Rayhel†, Robert C. Bowman, Jr.§, John J. Vajo, Adam F. Gross and Mark S. Conradi*†
J. Phys. Chem. C, 2010, 114 (9), pp 4008–4014
DOI: 10.1021/jp9107365
Hydrogen NMR of LiBH4 in the pores of carbon aerogel nanoscaffolds shows the coexistence of motionally narrowed and broad components. The fraction of mobile, diffusing hydrogen, already evident at room temperature, increases continuously with temperature. Thus, a broad distribution of environments is present, as in some ball-milled hydrides. With decreasing pore size from 25 to 13 nm, the narrowed fraction increases, suggesting that the narrow resonance is from the most defective regions, the grain boundaries. The broad component eventually exhibits narrowing in the same temperature window as for bulk material, confirming the bulk-like structure of those regions. Hole-burning measurements reveal magnetization exchange between the broad and narrow resonance lines, confirming the close spatial proximity of the atoms in each line. The solid−solid transition is clearly evident in 7Li line shapes, with a 10−15 °C depression from the bulk. More rapid decay of the quadrupolar satellite signals in spin echoes, compared to the central transition, is due to lithium atoms diffusing between differently oriented nanocrystallites. Our results suggest that crystallites in neighboring pores have similar orientations but are incoherent for diffraction. Remarkably, the T1 data of hydrogen and 7Li are continuous in the vicinity of the transition, in contrast with the bulk T1 data, suggesting that some rapid lithium motion remains below the transition.
Metal Carbonation of Forsterite in Supercritical CO2 and H2O Using Solid State 29Si, 13C NMR Spectroscopy
Ja Hun Kwak, Jian Zhi Hu*, David W. Hoyt, Jesse A. Sears, Chongming Wang, Kevin M. Rosso and Andrew R. Felmy
J. Phys. Chem. C, 2010, 114 (9), pp 4126–4134
DOI: 10.1021/jp1001308
Ex situ natural abundance magic angle spinning (MAS) NMR was used for the first time to study fundamental mineral carbonation processes and reaction extent relevant to geologic carbon sequestration (GCS) using a model silicate mineral forsterite (Mg2SiO4)+supercritical CO2 with and without H2O. Run conditions were 80 °C and 96 atm. With H2O but without CO2, 29Si MAS NMR reveals that the reaction products contain only two peaks of similar intensities located at about −84.8 and −91.8 ppm, which can be assigned to surface Q1 and Q2 species, i.e., SiO4 tetrahedra sharing one and two corners with other tetrahedra, respectively. Using scCO2 without H2O, no reaction is observed within 7 days. Using both scCO2 and H2O, the surface reaction products for silica are mainly Q4 species (−111.6 ppm) accompanied by a lesser amount of Q3 (−102 ppm) and Q2 (−91.8 ppm) species. No surface Q1 species were detected, indicating the carbonic acid formation and magnesite (MgCO3) precipitation reactions are faster than the forsterite hydrolysis process. Thus, it can be concluded that the Mg2SiO4 hydrolysis process is the rate limiting step of the overall mineral carbonation process. 29Si NMR combined with XRD, TEM, SAED, and EDX further reveals that the reaction is a surface reaction with the Mg2SiO4 crystallite in the core and with condensed Q2, Q3, and Q4 species forming highly porous amorphous surface layers. 13C MAS NMR unambiguously identified a reaction intermediate as Mg5(CO3)4(OH)2·5H2O, i.e., the dypingite.
Solid State 2H NMR Analysis of Furanose Ring Dynamics in DNA Containing Uracil
Monica N. Kinde-Carson†, Crystal Ferguson§, Nathan A. Oyler‡, Gerard S. Harbison† and Gary A. Meints*§
J. Phys. Chem. B, 2010, 114 (9), pp 3285–3293
DOI: 10.1021/jp9091656
Abstract: DNA damage has been implicated in numerous human diseases, particularly cancer, and the aging process. Single-base lesions, such as uracil, in DNA can be cytotoxic or mutagenic and are recognized by a DNA glycosylase during the process of base excision repair. Increased dynamic properties in lesion-containing DNAs have been suggested to assist recognition and specificity. Deuterium solid-state nuclear magnetic resonance (SSNMR) has been used to directly observe local dynamics of the furanose ring within a uracil:adenine (U:A) base pair and compared to a normal thymine:adenine (T:A) base pair. Quadrupole echo lineshapes, T1Z, and T2e relaxation data were collected, and computer modeling was performed. The results indicate that the relaxation times are identical within the experimental error, the solid lineshapes are essentially indistinguishable above the noise level, and our lineshapes are best fit with a model that does not have significant local motions. Therefore, U:A base pair furanose rings appear to have essentially identical dynamic properties as a normal T:A base pair, and the local dynamics of the furanose ring are unlikely to be the sole arbiter for uracil recognition and specificity in U:A base pairs.
Wednesday, February 24, 2010
PCCP, vol. 11 issues, Issues 45 - 48 and vol. 12, Issues 1 - 9
Phys. Chem. Chem. Phys., 2009, 11, 10331 - 10339, DOI: 10.1039/b822560e
NMR shielding as a probe of intermolecular interactions: ab initio and density functional theory studies
James A. Platts and Konstantinos Gkionis
Ab initio and density functional theory (DFT) calculations of nuclear magnetic resonance shielding tensors in benzene–methane and two isomers of the benzene dimer are reported, with the aim of probing the changes in shielding induced by the formation of supramolecular complexes from isolated molecules. It is shown that the changes in shielding (and hence of chemical shift) for hydrogen nuclei are broadly in line with expectations from shielding cones based on aromatic ring current, but that changes for carbon nuclei are rather more subtle. More detailed analysis indicates that the change in isotropic shielding results from much larger changes in individual components of the shielding tensor and in diamagnetic/paramagnetic shielding contributions. Benchmark data were obtained using Møller–Plesset 2nd order perturbation theory with a medium-sized basis set, but it is shown that Hartree–Fock and most density functional theory methods reproduce all essential changes in shielding, and do so in a reasonably basis set independent fashion. The chosen method is then applied to a DNA–intercalator complex
Phys. Chem. Chem. Phys., 2009, 11, 10391 - 10395, DOI: 10.1039/b914468d
Double-quantum 19F–19F dipolar recoupling at ultra-fast magic angle spinning NMR: application to the assignment of 19F NMR spectra of inorganic fluorides
Qiang Wang, Bingwen Hu, Franck Fayon, Julien Trébosc, Christophe Legein, Olivier Lafon, Feng Deng and Jean-Paul Amoureux
A broadband dipolar recoupling method robust to chemical shift is introduced to observe 19F–19F proximities in fluoroaluminates in high magnetic field and at ultra-fast magic angle spinning (>60 kHz).
Phys. Chem. Chem. Phys., 2009, 11, 11404 - 11414, DOI: 10.1039/b919860a
NMR tensors in planar hydrocarbons of increasing size
Suvi Ikäläinen, Perttu Lantto, Pekka Manninen and Juha Vaara
13C nuclear shielding and 13C–13C spin–spin coupling tensors were calculated using density functional theory linear response methods for a series of planar hydrocarbons. As calculation of the spin–spin coupling is computationally demanding for large molecules due to demands placed on basis-set quality, novel, compact completeness-optimized (co) basis sets of high quality were employed. To maximize the predictive value of the data, the convergence of the co basis sets was compared to well-known basis-set families. The selection of the exchange–correlation functional was performed based on the available experimental data and coupled-cluster calculations for ethene and benzene. The series of hydrocarbons, benzene, coronene, circumcoronene and circumcircumcoronene, was chosen to simulate increasingly large fragments of carbon nanosheets. It was found that the nuclear shielding and the one-, two-, and three-bond spin–spin coupling constants, as well as the corresponding anisotropies with respect to the direction normal to the plane, approach convergence as the number of carbon atoms in the fragment is increased. Predictions of the investigated properties can then be done for the limit of large planar hydrocarbons or carbon nanosheets. From the results obtained with a judicious choice of the functional, PBE, and co basis close to convergence, limiting values are estimated as follows: = 54 ± 1 ppm [corresponding to the chemical shift of 134 ppm with methane (CH4) as a reference], = 207 ± 4 ppm, 1J = 59.0 ± 0.5 Hz, 1J = -1.5 ± 0.5 Hz, 2J = 0.2 ± 0.4 Hz, 2J = -4.6 ± 0.2 Hz, 3J = 6 ± 1 Hz, and 3J = 3 ± 1 Hz
Phys. Chem. Chem. Phys., 2009, 11, 11487 - 11500, DOI: 10.1039/b916076k
Mg-25 ultra-high field solid state NMR spectroscopy and first principles calculations of magnesium compounds
Peter J. Pallister, Igor L. Moudrakovski and John A. Ripmeester
Due to sensitivity problems, 25Mg remains a largely under-explored nucleus in solid state NMR spectroscopy. In this work at an ultrahigh magnetic field of 21.1 T, we have studied at natural abundance the 25Mg solid state (SS) NMR spectra for a number of previously unreported magnesium compounds with known crystal structures. Some previously reported compounds have been revisited to clarify the spectra that were obtained at lower fields and were either not sufficiently resolved, or misinterpreted. First principles calculations of the 25Mg SS NMR parameters have been carried out using plane wave basis sets and periodic boundary conditions (CASTEP) and the results are compared with experimental data. The calculations produce the 25Mg absolute shielding scale and give us insight into the relationship between the NMR and structural parameters. At 21.1 T the effects of the quadrupolar interactions are reduced significantly and the sensitivity and accuracy in determining chemicals shifts and quadrupole coupling parameters improve dramatically. Although T1 measurements were not performed explicitly, these proved to be longer than assumed in much of the previously reported work. We demonstrate that the chemical shift range of magnesium in diamagnetic compounds may approach 200 ppm. Most commonly, however, the observed shifts are between -15 and +25 ppm. Quadrupolar effects dominate the 25Mg spectra of magnesium cations in non-cubic environments. The chemical shift anisotropy appears to be rather small and only in a few cases could the contribution of the CSA be detected reliably. A good correspondence between the calculated shielding constants and experimental chemical shifts was obtained, demonstrating the good potential of computational methods in spectroscopic assignments of solid state 25Mg NMR spectroscopy
Phys. Chem. Chem. Phys., 2010, 12, 583 - 603, DOI: 10.1039/b909870d
Calculation of NMR parameters in ionic solids by an improved self-consistent embedded cluster method
Johannes Weber and Jörn Schmedt auf der Günne
A new embedded cluster method (extended embedded ion method = EEIM) for the calculation of NMR properties in non-conducting crystals is presented. It is similar to the Embedded Ion Method (EIM) (ref. 1) in the way of embedding the quantum chemically treated part in an exact, self-consistent Madelung potential, but requires no empirical parameters. The method is put in relation to already existing cluster models which are classified in a brief review. The influence of the cluster boundary and the cluster charge is investigated, which leads to a better understanding of deficiencies in EIM. A recipe for an improved semi-automated cluster setup is proposed which allows the treatment of crystals composed of highly charged ions and covalent networks. EIM and EEIM results for 19F and 31P shielding tensors in NaF and in four different magnesium phosphates are compared with experimental values from solid state MAS NMR, some of which are measured here for the first time. The quantum part of the clusters is treated at hybrid DFT level (mPW1PW) with atomic basis sets up to 6-311G(3df,3pd). The improved agreement of EEIM allows new signal assignments for the different P-sites in Mg2P4O12, -Mg2P2O7 and MgP4O11. Conversion equations of the type = A + B between calculated absolute magnetic shieldings and the corresponding experimental chemical shifts are obtained independently from linear regressions of plots of isotropically averaged versus values on 19 31P signals of small molecules
Phys. Chem. Chem. Phys., 2010, 12, 1535 - 1542, DOI: 10.1039/b919118f
31P solid-state NMR studies of the short-range order in phosphorus–selenium glasses
Aleksei Bytchkov, Franck Fayon, Dominique Massiot, Louis Hennet and David L. Price
The local structure of P-rich and Se-rich phosphorus–selenium glasses was studied using high-resolution 31P solid-state MAS NMR. Two-dimensional 31P homonuclear through-bond correlation MAS experiments and 2D homonuclear J-resolved MAS measurements were performed at high spinning frequency to probe P–P and P–Se–P connectivities between the different P sites for the compounds in two glass-forming regions, P2.5Se97.5–P50Se50 and P67Se33–P84Se16. Amorphous phosphorus and crystalline -P4Se3 and -P4Se3 were also studied as reference materials. Glasses from the Se-rich region contain mainly three- and four-coordinated P sites linked together by Sen chains, whereas P-rich glasses contain a mixture of P4Se3 molecular units and possibly other structural units embedded in a red-phosphorus-like polymeric network
NMR shielding as a probe of intermolecular interactions: ab initio and density functional theory studies
James A. Platts and Konstantinos Gkionis
Ab initio and density functional theory (DFT) calculations of nuclear magnetic resonance shielding tensors in benzene–methane and two isomers of the benzene dimer are reported, with the aim of probing the changes in shielding induced by the formation of supramolecular complexes from isolated molecules. It is shown that the changes in shielding (and hence of chemical shift) for hydrogen nuclei are broadly in line with expectations from shielding cones based on aromatic ring current, but that changes for carbon nuclei are rather more subtle. More detailed analysis indicates that the change in isotropic shielding results from much larger changes in individual components of the shielding tensor and in diamagnetic/paramagnetic shielding contributions. Benchmark data were obtained using Møller–Plesset 2nd order perturbation theory with a medium-sized basis set, but it is shown that Hartree–Fock and most density functional theory methods reproduce all essential changes in shielding, and do so in a reasonably basis set independent fashion. The chosen method is then applied to a DNA–intercalator complex
Phys. Chem. Chem. Phys., 2009, 11, 10391 - 10395, DOI: 10.1039/b914468d
Double-quantum 19F–19F dipolar recoupling at ultra-fast magic angle spinning NMR: application to the assignment of 19F NMR spectra of inorganic fluorides
Qiang Wang, Bingwen Hu, Franck Fayon, Julien Trébosc, Christophe Legein, Olivier Lafon, Feng Deng and Jean-Paul Amoureux
A broadband dipolar recoupling method robust to chemical shift is introduced to observe 19F–19F proximities in fluoroaluminates in high magnetic field and at ultra-fast magic angle spinning (>60 kHz).
Phys. Chem. Chem. Phys., 2009, 11, 11404 - 11414, DOI: 10.1039/b919860a
NMR tensors in planar hydrocarbons of increasing size
Suvi Ikäläinen, Perttu Lantto, Pekka Manninen and Juha Vaara
13C nuclear shielding and 13C–13C spin–spin coupling tensors were calculated using density functional theory linear response methods for a series of planar hydrocarbons. As calculation of the spin–spin coupling is computationally demanding for large molecules due to demands placed on basis-set quality, novel, compact completeness-optimized (co) basis sets of high quality were employed. To maximize the predictive value of the data, the convergence of the co basis sets was compared to well-known basis-set families. The selection of the exchange–correlation functional was performed based on the available experimental data and coupled-cluster calculations for ethene and benzene. The series of hydrocarbons, benzene, coronene, circumcoronene and circumcircumcoronene, was chosen to simulate increasingly large fragments of carbon nanosheets. It was found that the nuclear shielding and the one-, two-, and three-bond spin–spin coupling constants, as well as the corresponding anisotropies with respect to the direction normal to the plane, approach convergence as the number of carbon atoms in the fragment is increased. Predictions of the investigated properties can then be done for the limit of large planar hydrocarbons or carbon nanosheets. From the results obtained with a judicious choice of the functional, PBE, and co basis close to convergence, limiting values are estimated as follows: = 54 ± 1 ppm [corresponding to the chemical shift of 134 ppm with methane (CH4) as a reference], = 207 ± 4 ppm, 1J = 59.0 ± 0.5 Hz, 1J = -1.5 ± 0.5 Hz, 2J = 0.2 ± 0.4 Hz, 2J = -4.6 ± 0.2 Hz, 3J = 6 ± 1 Hz, and 3J = 3 ± 1 Hz
Phys. Chem. Chem. Phys., 2009, 11, 11487 - 11500, DOI: 10.1039/b916076k
Mg-25 ultra-high field solid state NMR spectroscopy and first principles calculations of magnesium compounds
Peter J. Pallister, Igor L. Moudrakovski and John A. Ripmeester
Due to sensitivity problems, 25Mg remains a largely under-explored nucleus in solid state NMR spectroscopy. In this work at an ultrahigh magnetic field of 21.1 T, we have studied at natural abundance the 25Mg solid state (SS) NMR spectra for a number of previously unreported magnesium compounds with known crystal structures. Some previously reported compounds have been revisited to clarify the spectra that were obtained at lower fields and were either not sufficiently resolved, or misinterpreted. First principles calculations of the 25Mg SS NMR parameters have been carried out using plane wave basis sets and periodic boundary conditions (CASTEP) and the results are compared with experimental data. The calculations produce the 25Mg absolute shielding scale and give us insight into the relationship between the NMR and structural parameters. At 21.1 T the effects of the quadrupolar interactions are reduced significantly and the sensitivity and accuracy in determining chemicals shifts and quadrupole coupling parameters improve dramatically. Although T1 measurements were not performed explicitly, these proved to be longer than assumed in much of the previously reported work. We demonstrate that the chemical shift range of magnesium in diamagnetic compounds may approach 200 ppm. Most commonly, however, the observed shifts are between -15 and +25 ppm. Quadrupolar effects dominate the 25Mg spectra of magnesium cations in non-cubic environments. The chemical shift anisotropy appears to be rather small and only in a few cases could the contribution of the CSA be detected reliably. A good correspondence between the calculated shielding constants and experimental chemical shifts was obtained, demonstrating the good potential of computational methods in spectroscopic assignments of solid state 25Mg NMR spectroscopy
Phys. Chem. Chem. Phys., 2010, 12, 583 - 603, DOI: 10.1039/b909870d
Calculation of NMR parameters in ionic solids by an improved self-consistent embedded cluster method
Johannes Weber and Jörn Schmedt auf der Günne
A new embedded cluster method (extended embedded ion method = EEIM) for the calculation of NMR properties in non-conducting crystals is presented. It is similar to the Embedded Ion Method (EIM) (ref. 1) in the way of embedding the quantum chemically treated part in an exact, self-consistent Madelung potential, but requires no empirical parameters. The method is put in relation to already existing cluster models which are classified in a brief review. The influence of the cluster boundary and the cluster charge is investigated, which leads to a better understanding of deficiencies in EIM. A recipe for an improved semi-automated cluster setup is proposed which allows the treatment of crystals composed of highly charged ions and covalent networks. EIM and EEIM results for 19F and 31P shielding tensors in NaF and in four different magnesium phosphates are compared with experimental values from solid state MAS NMR, some of which are measured here for the first time. The quantum part of the clusters is treated at hybrid DFT level (mPW1PW) with atomic basis sets up to 6-311G(3df,3pd). The improved agreement of EEIM allows new signal assignments for the different P-sites in Mg2P4O12, -Mg2P2O7 and MgP4O11. Conversion equations of the type = A + B between calculated absolute magnetic shieldings and the corresponding experimental chemical shifts are obtained independently from linear regressions of plots of isotropically averaged versus values on 19 31P signals of small molecules
Phys. Chem. Chem. Phys., 2010, 12, 1535 - 1542, DOI: 10.1039/b919118f
31P solid-state NMR studies of the short-range order in phosphorus–selenium glasses
Aleksei Bytchkov, Franck Fayon, Dominique Massiot, Louis Hennet and David L. Price
The local structure of P-rich and Se-rich phosphorus–selenium glasses was studied using high-resolution 31P solid-state MAS NMR. Two-dimensional 31P homonuclear through-bond correlation MAS experiments and 2D homonuclear J-resolved MAS measurements were performed at high spinning frequency to probe P–P and P–Se–P connectivities between the different P sites for the compounds in two glass-forming regions, P2.5Se97.5–P50Se50 and P67Se33–P84Se16. Amorphous phosphorus and crystalline -P4Se3 and -P4Se3 were also studied as reference materials. Glasses from the Se-rich region contain mainly three- and four-coordinated P sites linked together by Sen chains, whereas P-rich glasses contain a mixture of P4Se3 molecular units and possibly other structural units embedded in a red-phosphorus-like polymeric network
Tuesday, February 02, 2010
Journal of Magnetic Resonance
Mechanism of 1H-14N cross-relaxation in immobilized proteins
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 25 January 2010
Erik P., Sunde , Bertil, Halle
A resonant enhancement of the water-1H relaxation rate at three distinct frequencies in 0.5 – 3 MHz range has been observed in a wide range of aqueous biological systems. These so-called quadrupole (Q) peaks have been linked to a dipolar flip-flop polarization transfer from 1H nuclei to rapidly relaxing amide 14N nuclei in rotationally immobilized proteins. While the Q-peak frequencies conform to the known amide 14N quadrupole coupling parameters, a molecular model that accounts for the intensity and shape of the Q peaks has not been available. Here, we present such a model and test it against an extensive set of Q-peak data from two fully hydrated crosslinked proteins under conditions of variable temperature, pH and H/D isotope composition. We propose that polarization transfer from bulk water to amide 14N occurs in three steps: from bulk water to a so-called intermediary proton via material diffusion/exchange, from intermediary to amide proton by cross-relaxation driven by exchange-mediated orientational randomization of their mutual dipole coupling, and from amide proton to 14N by resonant dipolar relaxation ’of the second kind’, driven by 14N spin fluctuations, which, in turn, are induced by restricted rigid-body motions of the protein. An essentially equivalent description of the last step can be formulated in terms of coherent 1H→14N polarization transfer followed by fast 14N relaxation. Using independent structural and kinetic information, we show that the Q peaks from these two proteins involve
7 intermediary protons in internal water molecules and side-chain hydroxyl groups with residence times of order 10–5 s. The model not only accounts quantitatively for the extensive data set, but also explains why Q peaks are not observed from gelatin gels.PGSE-NMR Measurement of the non-local dispersion tensor for flow in porous media
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 28 January 2010
M.W., Hunter , A.N., Jackson , P.T., Callaghan
The purpose of this work was to design and implement constant adiabadicity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood, 1997) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (Frequency Offset Corrected Inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of line-shapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy.
Spectroscopic Imaging with Improved Gradient Modulated Constant Adiabadicity Pulses on High-Field Clinical Scanners
Publication year: 2010Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 28 January 2010 Ovidiu C. Andronesia,
, 
, Saadallah Ramadanb, Eva-Maria Rataia, Dominique Jenningsa, Carolyn E. Mountfordb and A. Gregory SorensenaThe purpose of this work was to design and implement constant adiabadicity gradient modulated pulses that have improved slice profiles and reduced artifacts for spectroscopic imaging on 3T clinical scanners equipped with standard hardware. The newly proposed pulses were designed using the gradient offset independent adiabaticity (GOIA, Tannus and Garwood, 1997) method using WURST modulation for RF and gradient waveforms. The GOIA-WURST pulses were compared with GOIA-HSn (GOIA based on nth-order hyperbolic secant) and FOCI (Frequency Offset Corrected Inversion) pulses of the same bandwidth and duration. Numerical simulations and experimental measurements in phantoms and healthy volunteers are presented. GOIA-WURST pulses provide improved slice profile that have less slice smearing for off-resonance frequencies compared to GOIA-HSn pulses. The peak RF amplitude of GOIA-WURST is much lower (40% less) than FOCI but slightly higher (14.9% more) to GOIA-HSn. The quality of spectra as shown by the analysis of line-shapes, eddy currents artifacts, subcutaneous lipid contamination and SNR is improved for GOIA-WURST. GOIA-WURST pulse tested in this work shows that reliable spectroscopic imaging could be obtained in routine clinical setup and might facilitate the use of clinical spectroscopy.
Measurement of Vorticity Diffusion by NMR Microscopy
Publication year: 2010
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 1 February 2010
Jennifer R., Brown , Paul T., Callaghan
In a Newtonian fluid, vorticity diffuses at a rate determined by the kinematic viscosity. Here we use rapid NMR velocimetry, based on a RARE sequence, to image the time-dependent velocity field on start-up of a fluid-filled cylinder and therefore measure the diffusion of vorticity. The results are consistent with the solution to the vorticity diffusion equation where the angular velocity on the outside surface of the fluid, at the cylinder’s rotating wall, is fixed. This method is a means of measuring kinematic viscosity for low viscosity fluids without the need to measure stress.
Source: Journal of Magnetic Resonance, In Press, Accepted Manuscript, Available online 1 February 2010
Jennifer R., Brown , Paul T., Callaghan
In a Newtonian fluid, vorticity diffuses at a rate determined by the kinematic viscosity. Here we use rapid NMR velocimetry, based on a RARE sequence, to image the time-dependent velocity field on start-up of a fluid-filled cylinder and therefore measure the diffusion of vorticity. The results are consistent with the solution to the vorticity diffusion equation where the angular velocity on the outside surface of the fluid, at the cylinder’s rotating wall, is fixed. This method is a means of measuring kinematic viscosity for low viscosity fluids without the need to measure stress.
Solid State Nuclear Magnetic Resonance
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