Nonaromatic Core−Shell Structure of Nanodiamond from Solid-State NMR Spectroscopy
XiaoWen Fang, JingDong Mao, E. M. Levin and Klaus Schmidt-Rohr
J. Am. Chem. Soc., 2009, 131 (4), pp 1426–1435
DOI: 10.1021/ja8054063
Publication Date (Web): January 9, 2009
The structure of synthetic nanodiamond has been characterized by 13C nuclear magnetic resonance (NMR) spectral editing combined with measurements of long-range 1H−13C dipolar couplings and 13C relaxation times. The surface layer of these ∼4.8-nm diameter carbon particles consists mostly of sp3-hybridized C that is protonated or bonded to OH groups, while sp2-hybridized carbon makes up less than 1% of the material. The surface protons surprisingly resonate at 3.8 ppm, but their direct bonding to carbon is proved by fast dipolar dephasing under homonuclear decoupling. Long-range 1H−13C distance measurements, based on 13C{1H} dipolar dephasing by surface protons, show that seven carbon layers, in a shell of 0.63 nm thickness that contains ∼60% of all carbons, predominantly resonate more than +8 ppm from the 37-ppm peak of bulk diamond (i.e., within the 45−80 ppm range). Nitrogen detected in 15N NMR spectra is mostly not protonated and can account for some of the high-frequency shift of carbon. The location of unpaired electrons (∼40 unpaired electrons per particle) was studied in detail, based on their strongly distance-dependent effects on T1,C relaxation. The slower relaxation of the surface carbons, selected by spectral editing, showed that the unpaired electrons are not dangling bonds at the surface. This was confirmed by detailed simulations, which indicated that the unpaired electrons are mostly located in the disordered shell, at distances between 0.4 and 1 nm from the surface. On the basis of these results, a nonaromatic core−shell structural model of nanodiamond particles has been proposed.
Tuesday, February 03, 2009
MRI at the nanoscale
An interesting description of nanoscale magnetic resonance imaging at Chemistry World, RSC.
http://www.rsc.org/chemistryworld/News/2009/January/14010901.asp
http://www.rsc.org/chemistryworld/News/2009/January/14010901.asp
Monday, February 02, 2009
MRC: Magn. Reson. Chem. (Wiley) up to Feb. 2, 2009
MRC: Magn. Reson. Chem. (Wiley) up to Feb. 2, 2009
13C CP MAS NMR of halogenated (Cl, Br, I) pharmaceuticals at ultrahigh magnetic fields
from Magnetic Resonance in Chemistry by Victor V. Terskikh, Stephen J. Lang, Peter G. Gordon, Gary D. Enright, John A. Ripmeester
1 Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, Canada K1A 0R6
2 Department of Chemistry, Carleton University, Ottawa, Canada K1S 5B6
This work reports significantly improved spectral resolution of 13C CP MAS NMR spectra of chlorinated, brominated and iodinated solid organic compounds when such spectra are recorded at ultrahigh magnetic field strengths. The cause of this is the residual dipolar coupling between carbon atoms and quadrupolar halogen nuclides (chlorine-35/37, bromine-79/81 or iodine-127), an effect inversely proportional to the magnetic field strength which declines in importance markedly at 21.1 T as compared to lower fields. In favorable cases, the fine structure observed can be used for spectral assignment, e.g. for Cl-substituted aromatics where the substituted carbon as well as the ortho-carbons show distinct doublets. The experimental results presented are supported by theoretical modeling and calculations. The improved spectral resolution in the studied systems and similar halogenated materials will be of particular interest and importance for polymorph identification, drug discovery and quality control in the pharmaceutical industry.
Digital Object Identifier (DOI) 10.1002/mrc.2399
Studies on drug-DNA complexes, adriamycin-d-(TGATCA)2 and 4[prime]-epiadriamycin-d-(CGATCG)2, by phosphorus-31 nuclear magnetic resonance spectroscopy
from Magnetic Resonance in Chemistry by Prashansa Agrawal, Girjesh Govil, Ritu Barthwal
1 Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India
2 Chemical Physics Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Navy Nagar, Colaba, Mumbai 400 005, India
The complexes of adriamycin-d-(TGATCA)2 and 4[prime]-epiadriamycin-d-(CGATCG)2 are studied by one- and two-dimensional 31P nuclear magnetic resonance spectroscopy (NMR) at 500 MHz in the temperature range 275-328 K and as a function of drug to DNA ratio (0.0-2.0). The binding of drug to DNA is clearly evident in 31P[bond]31P exchange NOESY spectra that shows two sets of resonances in slow chemical exchange. The phosphate resonances at the intercalating steps, T1pG2/C1pG2 and C5pA6/C5pG6, shift downfield up to 1.7 ppm and that at the adjacent step shift downfield up to 0.7 ppm, whereas the central phosphate A3pT4 is relatively unaffected. The variations of chemical shift with drug to DNA ratio and temperature as well as linewidths are different in each of the two complexes. These observations reflect change in population of BI/BII conformation, stretching of backbone torsional angle [zeta], and distortions in O[bond]P[bond]O bond angles that occur on binding of drug to DNA. To the best of our knowledge, there are no solution studies on 4[prime]-epiadriamycin, a better tolerated drug, and binding of daunomycin or its analogue to d-(TGATCA)2 hexamer sequence. The studies report the use of 31P NMR as a tool to differentiate various complexes. The specific differences may well be the reasons that are responsible for different antitumor action of these drugs due to different binding ability and distortions in DNA. Copyright © 2009 John Wiley & Sons, Ltd.
Digital Object Identifier (DOI) 10.1002/mrc.2398
13C CP MAS NMR of halogenated (Cl, Br, I) pharmaceuticals at ultrahigh magnetic fields
from Magnetic Resonance in Chemistry by Victor V. Terskikh, Stephen J. Lang, Peter G. Gordon, Gary D. Enright, John A. Ripmeester
1 Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, Canada K1A 0R6
2 Department of Chemistry, Carleton University, Ottawa, Canada K1S 5B6
This work reports significantly improved spectral resolution of 13C CP MAS NMR spectra of chlorinated, brominated and iodinated solid organic compounds when such spectra are recorded at ultrahigh magnetic field strengths. The cause of this is the residual dipolar coupling between carbon atoms and quadrupolar halogen nuclides (chlorine-35/37, bromine-79/81 or iodine-127), an effect inversely proportional to the magnetic field strength which declines in importance markedly at 21.1 T as compared to lower fields. In favorable cases, the fine structure observed can be used for spectral assignment, e.g. for Cl-substituted aromatics where the substituted carbon as well as the ortho-carbons show distinct doublets. The experimental results presented are supported by theoretical modeling and calculations. The improved spectral resolution in the studied systems and similar halogenated materials will be of particular interest and importance for polymorph identification, drug discovery and quality control in the pharmaceutical industry.
Digital Object Identifier (DOI) 10.1002/mrc.2399
Studies on drug-DNA complexes, adriamycin-d-(TGATCA)2 and 4[prime]-epiadriamycin-d-(CGATCG)2, by phosphorus-31 nuclear magnetic resonance spectroscopy
from Magnetic Resonance in Chemistry by Prashansa Agrawal, Girjesh Govil, Ritu Barthwal
1 Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India
2 Chemical Physics Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Navy Nagar, Colaba, Mumbai 400 005, India
The complexes of adriamycin-d-(TGATCA)2 and 4[prime]-epiadriamycin-d-(CGATCG)2 are studied by one- and two-dimensional 31P nuclear magnetic resonance spectroscopy (NMR) at 500 MHz in the temperature range 275-328 K and as a function of drug to DNA ratio (0.0-2.0). The binding of drug to DNA is clearly evident in 31P[bond]31P exchange NOESY spectra that shows two sets of resonances in slow chemical exchange. The phosphate resonances at the intercalating steps, T1pG2/C1pG2 and C5pA6/C5pG6, shift downfield up to 1.7 ppm and that at the adjacent step shift downfield up to 0.7 ppm, whereas the central phosphate A3pT4 is relatively unaffected. The variations of chemical shift with drug to DNA ratio and temperature as well as linewidths are different in each of the two complexes. These observations reflect change in population of BI/BII conformation, stretching of backbone torsional angle [zeta], and distortions in O[bond]P[bond]O bond angles that occur on binding of drug to DNA. To the best of our knowledge, there are no solution studies on 4[prime]-epiadriamycin, a better tolerated drug, and binding of daunomycin or its analogue to d-(TGATCA)2 hexamer sequence. The studies report the use of 31P NMR as a tool to differentiate various complexes. The specific differences may well be the reasons that are responsible for different antitumor action of these drugs due to different binding ability and distortions in DNA. Copyright © 2009 John Wiley & Sons, Ltd.
Digital Object Identifier (DOI) 10.1002/mrc.2398
Progress in NMR: Review: solid-state selenium-77 (77Se) NMR
Progress in NMR: Review: solid-state selenium-77 (77Se) NMR
doi:10.1016/j.pnmrs.2008.10.002
Solid-state selenium-77 NMR
Bryan A. Demko and Roderick E. Wasylishen
Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, AB, Canada T6G 2G2
Keywords: Solid-state NMR; 77Se NMR; Chemical shift tensors; Indirect spin–spin coupling constants
doi:10.1016/j.pnmrs.2008.10.002
Solid-state selenium-77 NMR
Bryan A. Demko and Roderick E. Wasylishen
Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, AB, Canada T6G 2G2
Keywords: Solid-state NMR; 77Se NMR; Chemical shift tensors; Indirect spin–spin coupling constants
Monday, January 26, 2009
J Phys Chem C, vol. 113, Issue 4
Effect of Al−Si−Al and Al−Si−Si−Al Pairs in the ZSM-5 Zeolite Framework on the 27Al NMR Spectra. A Combined High-Resolution 27Al NMR and DFT/MM Study
Jiří Dědeček†, Stepan Sklenak*†, Chengbin Li†, Blanka Wichterlová†, Vendula Gábová†, Jiří Brus‡, Marek Sierka§ and Joachim Sauer§
J. Phys. Chem. C, 2009, 113 (4), pp 1447–1458
Publication Date (Web): January 8, 2009
J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic.,
* Corresponding author. E-mail: stepan.sklenak@jh-inst.cas.cz.,
Abstract: The effect of the presence of Al−O−Si−O−Al and Al−O−Si−O−Si−O−Al sequences in the ZSM-5 zeolite framework on the local geometry of AlO4− tetrahedra and the 27Al NMR parameters was investigated employing 27Al 3Q MAS NMR spectroscopy and DFT/MM calculations. The presence of an Al atom as a next-nearest (Al−O−Si−O−Al) and next-next-nearest (Al−O−Si−O−Si−O−Al) neighbor can significantly affect both the local geometry of AlO4− tetrahedra as well as 27Al NMR isotropic chemical shift (up to 4 ppm). There is no systematic contribution of Al in Al−O−Si−O−Al or Al−O−(Si−O)2−Al chains to the 27Al isotropic chemical shift, and not even the direction can be predicted without explicit DFT calculations. Our combined experimental and computational approach employing 27Al (3Q) MAS NMR spectroscopy supported by DFT/MM calculations ( Sklenak, S.; Dědeček, J.; Li, C.; Wichterlová, B.; Gábová, V.; Sierka, M.; Sauer, J. Angew. Chem., Int. Ed. 2007, 46, 7286.) can be employed only for ZSM-5 samples having a low or negligible concentration of Al−O−(Si−O)n−Al (n = 1 and 2) sequences in the zeolite matrix, otherwise 27Al (3Q) MAS NMR spectroscopy cannot be used to even identify the number of framework T sites occupied by Al.
Jiří Dědeček†, Stepan Sklenak*†, Chengbin Li†, Blanka Wichterlová†, Vendula Gábová†, Jiří Brus‡, Marek Sierka§ and Joachim Sauer§
J. Phys. Chem. C, 2009, 113 (4), pp 1447–1458
Publication Date (Web): January 8, 2009
J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic.,
* Corresponding author. E-mail: stepan.sklenak@jh-inst.cas.cz.,
Abstract: The effect of the presence of Al−O−Si−O−Al and Al−O−Si−O−Si−O−Al sequences in the ZSM-5 zeolite framework on the local geometry of AlO4− tetrahedra and the 27Al NMR parameters was investigated employing 27Al 3Q MAS NMR spectroscopy and DFT/MM calculations. The presence of an Al atom as a next-nearest (Al−O−Si−O−Al) and next-next-nearest (Al−O−Si−O−Si−O−Al) neighbor can significantly affect both the local geometry of AlO4− tetrahedra as well as 27Al NMR isotropic chemical shift (up to 4 ppm). There is no systematic contribution of Al in Al−O−Si−O−Al or Al−O−(Si−O)2−Al chains to the 27Al isotropic chemical shift, and not even the direction can be predicted without explicit DFT calculations. Our combined experimental and computational approach employing 27Al (3Q) MAS NMR spectroscopy supported by DFT/MM calculations ( Sklenak, S.; Dědeček, J.; Li, C.; Wichterlová, B.; Gábová, V.; Sierka, M.; Sauer, J. Angew. Chem., Int. Ed. 2007, 46, 7286.) can be employed only for ZSM-5 samples having a low or negligible concentration of Al−O−(Si−O)n−Al (n = 1 and 2) sequences in the zeolite matrix, otherwise 27Al (3Q) MAS NMR spectroscopy cannot be used to even identify the number of framework T sites occupied by Al.
J Phys Chem B, vol. 113, Issue 4
Solid-State NMR Studies of Aminocarboxylic Salt Bridges in l-Lysine Modified Cellulose
Ricardo Manríquez†‡, Fernando A. López-Dellamary‡, Jaroslaw Frydel†, Thomas Emmler†, Hergen Breitzke§, Gerd Buntkowsky§, Hans-Heinrich Limbach† and Ilja G. Shenderovich*†#
J. Phys. Chem. B, 2009, 113 (4), pp 934–940
DOI: 10.1021/jp8081968
Abstract: LysCel is a cellulose-based material in which l-lysine molecules are grafted with their amino side chains to the cellulose hydroxyl groups. This modification increases considerably the mechanical strength and resistance of cellulosic structures toward water. It has been attributed to the formation of double salt bridges between lysine aminocarboxyl groups in the zwitterionic state. In order to characterize this unusual structure, we have performed high-resolution solid-state 15N and 13C CPMAS NMR experiments on LysCel samples labeled with 15N in the α-position or ε-position. Furthermore, 13C−15N REDOR experiments were performed on LysCel where half of the aminocarboxyl groups were labeled in 1-position with 13C and the other half in α-position with 15N. The comparison with the 13C and 15N chemical shifts of l-leucine lyophilized at different pH shows that the aminocarboxyl groups of LysCel are indeed zwitterionic. The REDOR experiments indicate distances of about 3.5 Å between the carboxyl carbon and the nitrogen atoms of different aminocarboxyl groups, indicating that the latter are in close contact with each other. However, the data are not compatible with isolated aminocarboxyl dimers but indicate the assembly of zwitterionic aminocarboxyl dimers either in a flat ribbon or as tetramers, exhibiting similar intra- and interdimer 13C···15N distances. This interaction of several aminocarboxyl groups is responsible for the zwitterionic state, in contrast to the gas phase, where amino acid dimers exhibiting two OHN hydrogen bonds are neutral.
Ricardo Manríquez†‡, Fernando A. López-Dellamary‡, Jaroslaw Frydel†, Thomas Emmler†, Hergen Breitzke§, Gerd Buntkowsky§, Hans-Heinrich Limbach† and Ilja G. Shenderovich*†#
J. Phys. Chem. B, 2009, 113 (4), pp 934–940
DOI: 10.1021/jp8081968
Abstract: LysCel is a cellulose-based material in which l-lysine molecules are grafted with their amino side chains to the cellulose hydroxyl groups. This modification increases considerably the mechanical strength and resistance of cellulosic structures toward water. It has been attributed to the formation of double salt bridges between lysine aminocarboxyl groups in the zwitterionic state. In order to characterize this unusual structure, we have performed high-resolution solid-state 15N and 13C CPMAS NMR experiments on LysCel samples labeled with 15N in the α-position or ε-position. Furthermore, 13C−15N REDOR experiments were performed on LysCel where half of the aminocarboxyl groups were labeled in 1-position with 13C and the other half in α-position with 15N. The comparison with the 13C and 15N chemical shifts of l-leucine lyophilized at different pH shows that the aminocarboxyl groups of LysCel are indeed zwitterionic. The REDOR experiments indicate distances of about 3.5 Å between the carboxyl carbon and the nitrogen atoms of different aminocarboxyl groups, indicating that the latter are in close contact with each other. However, the data are not compatible with isolated aminocarboxyl dimers but indicate the assembly of zwitterionic aminocarboxyl dimers either in a flat ribbon or as tetramers, exhibiting similar intra- and interdimer 13C···15N distances. This interaction of several aminocarboxyl groups is responsible for the zwitterionic state, in contrast to the gas phase, where amino acid dimers exhibiting two OHN hydrogen bonds are neutral.
Thursday, January 22, 2009
MRC: Magn. Reson. Chem. (Wiley) up to Jan. 20, 2009
Magn. Reson. Chem. (Wiley) up to Jan. 20, 2009
Magnetic Resonance in Chemistry
Volume 47 Issue 1, Pages 9 - 15
Published Online: 4 Nov 2008
Solid-state natural abundance 25Mg NMR studies of Na2MgEDTA·4H2O - a possible new reference compound for 25Mg NMR spectroscopy
from Magnetic Resonance in Chemistry by Jair C. C. Freitas, Alan Wong, Mark E. Smith
Natural abundance solid-state 25Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na2MgEDTA·4H2O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (Cq) and the asymmetry parameter ([eta]q) of the electric field gradient (EFG) tensor associated with 25Mg in this compound, giving the values Cq = 1.675(5) MHz and [eta]q = 0.15(1). The isotropic chemical shift was determined to be [delta]iso = 0.25(10) ppm (relative to 11 M MgCl2 aqueous solution) and a small chemical shift anisotropy (CSA) contribution ([sim]- 13 ppm) was detected, one of the first CSA reports in 25Mg NMR. This compound exhibited remarkably good 25Mg NMR sensitivity, due to its fast spin-lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal-enhancement methods in 25Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 47 Issue 2, Pages 97 - 99
Published Online: 21 Oct 2008
Electronic structure and biological activity of chosen DDT-type insecticides studied by 35Cl-NQR
from Magnetic Resonance in Chemistry by Maciej Jad[zdot]yn, Boles[lstrok]aw Nogaj
A correlation between the electronic structure and biological activity of chosen dichlorodiphenyltrichloroethane (DDT)-type insecticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene, 2,2-bis(4-chlorophenyl)ethanoic acid and 4,4[prime]-dichlorobenzophenone (used in agriculture) has been analysed on the basis of the 35Cl-nuclear quadrupole resonance (NQR) spectroscopy. The 35Cl-NQR resonance frequencies measured at 77 K have been correlated with the lethal dose (LD50) parameter that characterises the biological activity of these insecticides. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 46 Issue S1, Pages S36 - S44
Special Issue: Diffusion ordered and heteronuclear NMR spectroscopy applied to inorganic and organometallic chemistry. Special Issue dedicated to Professor Paul S. Pregosin on the occasion of his 65th birthday
Published Online: 14 Oct 2008
Density-functional computation of 99Tc NMR chemical shifts
from Magnetic Resonance in Chemistry by Michael Bühl, Volodymyr Golubnychiy
99Tc chemical shifts of TcO4-, TcH92-, TcOF5, TcO2F4-, TcOCl4-, Tc2(CO)10, and Tc(CO)3L3+ (L = CO, MeCN, H2O) are computed using geometries optimized with the gradient-corrected BP86 and hybrid B3P86 density functionals, at the gauge-including atomic orbitals (GIAO), -BPW91 and -B3LYP levels. For this set of compounds, substituent effects on [delta](99Tc) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. A rough, qualitative correlation is found between computed electric-field gradients at the Tc nuclei and the corresponding 99Tc NMR line widths. Thermal and solvation effects on magnetic shielding constants of aqueous TcO4-, as assessed by averaging these properties over trajectories from Car-Parrinello molecular dynamics simulations, are indicated to be small and comparable to those of MnO4-. Complexation to aqueous uranyl, UO22+, is predicted to affect [delta](99Tc) of TcO4- only slightly; somewhat larger complexation shifts are obtained for the oxygen nuclei of pertechnetate, suggesting that 17O NMR could be a useful probe for the extent of association between both radionuclides in solution. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 46 Issue S1, Pages S45 - S55
Special Issue: Diffusion ordered and heteronuclear NMR spectroscopy applied to inorganic and organometallic chemistry. Special Issue dedicated to Professor Paul S. Pregosin on the occasion of his 65th birthday
Published Online: 14 Oct 2008
Analyzing Pt chemical shifts calculated from relativistic density functional theory using localized orbitals: The role of Pt 5d lone pairs
from Magnetic Resonance in Chemistry by Jochen Autschbach, Shaohui Zheng
Pt chemical shifts were calculated from two-component relativistic density functional theory (DFT). The shielding tensors were analyzed by using a recently developed method to decompose the spin-orbit DFT results into contributions from spin-free localized orbitals (here: natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs)). Seven chemical shifts in six Pt complexes with Pt oxidation states II, III, and IV; and halide, amino, and amidate ligands were analyzed, with particular focus on the role of nonbonding Pt 5d orbitals. A simple d-orbital 'rotation' model has been used to rationalize some of the observed trends such as the main difference between Pt(II) and Pt(IV) chemical shifts. The localized orbital analysis data showed that most of this difference as well as trends among different Pt complexes with similar coordination can be rationalized by comparing properties of the nonbonding Pt 5d orbitals. We have also analyzed the spin-orbit effects on the chemical shifts of [PtCl4]2- compared to [PtBr4]2-. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 46 Issue 11, Pages 1045 - 1050
Published Online: 19 Sep 2008
DFT calculations as a powerful technique to probe the crystal structure of Al(acac)3
from Magnetic Resonance in Chemistry by S. K. Amini, M. Tafazzoli
27Al, 17O and 13C chemical shieldings of aluminum acetylacetonate complex, Al(acac)3, were calculated at some Density Functional Theory (DFT) levels of theory. In these calculations the X-ray structures of its different polymorphs were used. Using these calculated data observed discrepancies between the X-ray crystallography and solid state NMR experiment were explained in terms of the quality of the NMR data. In this survey we resorted to the simulated spectra using our calculated chemical shifts. In order to confirm our conclusions, electric field gradient (EFG) tensors of the 27Al and 17O nuclei were calculated at the same levels of theory as used in the chemical shielding calculations. On the other hand, these calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs) made a correlation between X-ray crystallography and solid state NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Volume 47 Issue 1, Pages 9 - 15
Published Online: 4 Nov 2008
Solid-state natural abundance 25Mg NMR studies of Na2MgEDTA·4H2O - a possible new reference compound for 25Mg NMR spectroscopy
from Magnetic Resonance in Chemistry by Jair C. C. Freitas, Alan Wong, Mark E. Smith
Natural abundance solid-state 25Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na2MgEDTA·4H2O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (Cq) and the asymmetry parameter ([eta]q) of the electric field gradient (EFG) tensor associated with 25Mg in this compound, giving the values Cq = 1.675(5) MHz and [eta]q = 0.15(1). The isotropic chemical shift was determined to be [delta]iso = 0.25(10) ppm (relative to 11 M MgCl2 aqueous solution) and a small chemical shift anisotropy (CSA) contribution ([sim]- 13 ppm) was detected, one of the first CSA reports in 25Mg NMR. This compound exhibited remarkably good 25Mg NMR sensitivity, due to its fast spin-lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal-enhancement methods in 25Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 47 Issue 2, Pages 97 - 99
Published Online: 21 Oct 2008
Electronic structure and biological activity of chosen DDT-type insecticides studied by 35Cl-NQR
from Magnetic Resonance in Chemistry by Maciej Jad[zdot]yn, Boles[lstrok]aw Nogaj
A correlation between the electronic structure and biological activity of chosen dichlorodiphenyltrichloroethane (DDT)-type insecticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene, 2,2-bis(4-chlorophenyl)ethanoic acid and 4,4[prime]-dichlorobenzophenone (used in agriculture) has been analysed on the basis of the 35Cl-nuclear quadrupole resonance (NQR) spectroscopy. The 35Cl-NQR resonance frequencies measured at 77 K have been correlated with the lethal dose (LD50) parameter that characterises the biological activity of these insecticides. Copyright © 2008 John Wiley & Sons, Ltd.
--
Magnetic Resonance in Chemistry
Volume 46 Issue S1, Pages S36 - S44
Special Issue: Diffusion ordered and heteronuclear NMR spectroscopy applied to inorganic and organometallic chemistry. Special Issue dedicated to Professor Paul S. Pregosin on the occasion of his 65th birthday
Published Online: 14 Oct 2008
Density-functional computation of 99Tc NMR chemical shifts
from Magnetic Resonance in Chemistry by Michael Bühl, Volodymyr Golubnychiy
99Tc chemical shifts of TcO4-, TcH92-, TcOF5, TcO2F4-, TcOCl4-, Tc2(CO)10, and Tc(CO)3L3+ (L = CO, MeCN, H2O) are computed using geometries optimized with the gradient-corrected BP86 and hybrid B3P86 density functionals, at the gauge-including atomic orbitals (GIAO), -BPW91 and -B3LYP levels. For this set of compounds, substituent effects on [delta](99Tc) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. A rough, qualitative correlation is found between computed electric-field gradients at the Tc nuclei and the corresponding 99Tc NMR line widths. Thermal and solvation effects on magnetic shielding constants of aqueous TcO4-, as assessed by averaging these properties over trajectories from Car-Parrinello molecular dynamics simulations, are indicated to be small and comparable to those of MnO4-. Complexation to aqueous uranyl, UO22+, is predicted to affect [delta](99Tc) of TcO4- only slightly; somewhat larger complexation shifts are obtained for the oxygen nuclei of pertechnetate, suggesting that 17O NMR could be a useful probe for the extent of association between both radionuclides in solution. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 46 Issue S1, Pages S45 - S55
Special Issue: Diffusion ordered and heteronuclear NMR spectroscopy applied to inorganic and organometallic chemistry. Special Issue dedicated to Professor Paul S. Pregosin on the occasion of his 65th birthday
Published Online: 14 Oct 2008
Analyzing Pt chemical shifts calculated from relativistic density functional theory using localized orbitals: The role of Pt 5d lone pairs
from Magnetic Resonance in Chemistry by Jochen Autschbach, Shaohui Zheng
Pt chemical shifts were calculated from two-component relativistic density functional theory (DFT). The shielding tensors were analyzed by using a recently developed method to decompose the spin-orbit DFT results into contributions from spin-free localized orbitals (here: natural localized molecular orbitals (NLMOs) and natural bond orbitals (NBOs)). Seven chemical shifts in six Pt complexes with Pt oxidation states II, III, and IV; and halide, amino, and amidate ligands were analyzed, with particular focus on the role of nonbonding Pt 5d orbitals. A simple d-orbital 'rotation' model has been used to rationalize some of the observed trends such as the main difference between Pt(II) and Pt(IV) chemical shifts. The localized orbital analysis data showed that most of this difference as well as trends among different Pt complexes with similar coordination can be rationalized by comparing properties of the nonbonding Pt 5d orbitals. We have also analyzed the spin-orbit effects on the chemical shifts of [PtCl4]2- compared to [PtBr4]2-. Copyright © 2008 John Wiley & Sons, Ltd.
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Magnetic Resonance in Chemistry
Volume 46 Issue 11, Pages 1045 - 1050
Published Online: 19 Sep 2008
DFT calculations as a powerful technique to probe the crystal structure of Al(acac)3
from Magnetic Resonance in Chemistry by S. K. Amini, M. Tafazzoli
27Al, 17O and 13C chemical shieldings of aluminum acetylacetonate complex, Al(acac)3, were calculated at some Density Functional Theory (DFT) levels of theory. In these calculations the X-ray structures of its different polymorphs were used. Using these calculated data observed discrepancies between the X-ray crystallography and solid state NMR experiment were explained in terms of the quality of the NMR data. In this survey we resorted to the simulated spectra using our calculated chemical shifts. In order to confirm our conclusions, electric field gradient (EFG) tensors of the 27Al and 17O nuclei were calculated at the same levels of theory as used in the chemical shielding calculations. On the other hand, these calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs) made a correlation between X-ray crystallography and solid state NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd.
Faraday Discussions (RSC) - up to Jan. 20, 2009
Faraday Disc. (RSC) - up to Jan. 20, 2009
Faraday Discuss., 2009, 140, 139 - 153, DOI: 10.1039/b803073a
A comparative in situ195Pt electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials
Fatang Tan, Bingchen Du, Aaron L. Danberry, In-Su Park, Yung-Eun Sung and YuYe Tong
This paper reports a detailed in situ195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman–Kittel–Kasuya–Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (Ef-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.
--
Faraday Discuss., 2009, 140, 69 - 80, DOI: 10.1039/b802919a
Bridging the gap between nanoparticles and single crystal surfaces
Payam Kaghazchi, Felice C. Simeone, Khaled A. Soliman, Ludwig A. Kibler and Timo Jacob
Using density functional theory calculations and the extended ab initio atomistic thermodynamics approach, we studied the adsorption of oxygen on the different surface faces, which are involved in the faceting of Ir(210). Constructing the (p,T)-surface phase diagrams of the corresponding surfaces in contact with an oxygen atmosphere, we find that at high temperatures the planar surfaces are stable, while lowering the temperature stabilizes those nano-facets found experimentally. Afterwards, we constructed the (a,T,)-phase diagram for Ir(210) in contact with an aqueous electrolyte and found that the same nano-facets should be stable under electrochemical conditions. Motivated by this prediction from theory, experiments were performed using cyclic voltammetry and in-situ scanning tunneling microscopy. The presence of nanofacets for Ir(210) gives rise to a characteristic current-peak in the hydrogen adsorption region for sulfuric acid solution. Furthermore, first results on the electrocatalytic behavior of nano-faceted Ir(210) are presented.
Faraday Discuss., 2009, 140, 139 - 153, DOI: 10.1039/b803073a
A comparative in situ195Pt electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials
Fatang Tan, Bingchen Du, Aaron L. Danberry, In-Su Park, Yung-Eun Sung and YuYe Tong
This paper reports a detailed in situ195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman–Kittel–Kasuya–Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (Ef-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.
--
Faraday Discuss., 2009, 140, 69 - 80, DOI: 10.1039/b802919a
Bridging the gap between nanoparticles and single crystal surfaces
Payam Kaghazchi, Felice C. Simeone, Khaled A. Soliman, Ludwig A. Kibler and Timo Jacob
Using density functional theory calculations and the extended ab initio atomistic thermodynamics approach, we studied the adsorption of oxygen on the different surface faces, which are involved in the faceting of Ir(210). Constructing the (p,T)-surface phase diagrams of the corresponding surfaces in contact with an oxygen atmosphere, we find that at high temperatures the planar surfaces are stable, while lowering the temperature stabilizes those nano-facets found experimentally. Afterwards, we constructed the (a,T,)-phase diagram for Ir(210) in contact with an aqueous electrolyte and found that the same nano-facets should be stable under electrochemical conditions. Motivated by this prediction from theory, experiments were performed using cyclic voltammetry and in-situ scanning tunneling microscopy. The presence of nanofacets for Ir(210) gives rise to a characteristic current-peak in the hydrogen adsorption region for sulfuric acid solution. Furthermore, first results on the electrocatalytic behavior of nano-faceted Ir(210) are presented.
Chem. Soc. Rev. - Chemical Society Reviews (RSC) - up to Jan. 21, 2009
Chemical Society Reviews (RSC) - up to Jan. 21, 2009
Some interesting Chem. Soc. Rev. articles that might be of interest to the group
(no NMR here, but some interesting topics)
Critical Review
Chem. Soc. Rev., 2009, 38, 185 - 196, DOI: 10.1039/b802262n
Photosynthetic energy conversion: natural and artificial
James Barber
Photosystem II (PSII) is the water splitting enzyme of photosynthesis. Its appearance during evolution dramatically changed the chemical composition of our planet and set in motion an unprecedented explosion in biological activity. Powered by sunlight, PSII supplies biology with the hydrogen needed to convert carbon dioxide into organic molecules. The questions now are can we continue to exploit this photosynthetic process through increased use of biomass as an energy source and, more importantly, can we address the energy/CO2 problem by developing new photochemical technologies which mimic the natural system? (Critical review, 82 references)
--
Tutorial Review
Chem. Soc. Rev., 2009, 38, 25 - 35, DOI: 10.1039/b800582f
Biology and technology for photochemical fuel production
Michael Hambourger, Gary F. Moore, David M. Kramer, Devens Gust, Ana L. Moore and Thomas A. Moore
Sunlight is the ultimate energy source for the vast majority of life on Earth, and organisms have evolved elegant machinery for energy capture and utilization. Solar energy, whether converted to wind, rain, biomass or fossil fuels, is also the primary energy source for human-engineered energy transduction systems. This tutorial review draws parallels between biological and technological energy systems. Aspects of biology that might be advantageously incorporated into emerging technologies are highlighted, as well as ways in which technology might improve upon the principles found in biological systems. Emphasis is placed upon artificial photosynthesis, as well as the use of protonmotive force in biology.
--
Tutorial Review
Chem. Soc. Rev., 2009, 38, 73 - 82, DOI: 10.1039/b718842k
New approaches to hydrogen storage
Jason Graetz
The emergence of a Hydrogen Economy will require the development of new media capable of safely storing hydrogen in a compact and light weight package. Metal hydrides and complex hydrides, where hydrogen is chemically bonded to the metal atoms in the bulk, offer some hope of overcoming the challenges associated with hydrogen storage. The objective is to find a material with a high volumetric and gravimetric hydrogen density that can also meet the unique demands of a low temperature automotive fuel cell. Currently, there is considerable effort to develop new materials with tunable thermodynamic and kinetic properties. This tutorial review provides an overview of the different types of metal hydrides and complex hydrides being investigated for on-board (reversible) and off-board (non-reversible) hydrogen storage along with a few new approaches to improving the hydrogenation–dehydrogenation properties.
--
Tutorial Review
Chem. Soc. Rev., 2008, 37, 2383 - 2392, DOI: 10.1039/b710347f
Current state for the development of metallopharmaceutics and anti-diabetic metal complexes
Hiromu Sakurai, Yutaka Yoshikawa and Hiroyuki Yasui
This tutorial review introduces the current state of metallopharmaceutics development by focusing on the topics of anti-diabetic vanadium and zinc complexes. Over thousands of years, people have produced many types of inorganic compounds, and the modern concept of chemotherapy was achieved by Ehrlich, who used an arsenic-containing compound to treat syphilis. Since then, many metallopharmaceutics have been developed worldwide. This review will be helpful to researchers who are interested in the current states of not only metallopharmaceutics but also anti-diabetic metal complexes.
--
Critical Review
Chem. Soc. Rev., 2008, 37, 2274 - 2309, DOI: 10.1039/b719149a
In-silico investigations in heterogeneous catalysis—combustion and synthesis of small alkanes
Oliver R. Inderwildi and Stephen J. Jenkins
In this critical review, we cover first-principles density functional calculations relevant to alkane oxidation and synthesis over transition metal catalysts. For oxidation, we focus upon Pt, Rh, Pd and Ni surfaces, while for synthesis we consider Co, Ru, Fe and Ni. Throughout, we emphasise the insight to be gained by thinking of each kind of reaction as the inverse of the other, with the directionality determined simply by the choice of metal catalyst and the reaction conditions. We highlight particularly the role of low-coordination sites (steps, kinks, etc.) and the emerging consensus over the importance of the formyl intermediate in facilitating the rate-determining step (249 references).
--
Editorial
Chem. Soc. Rev., 2008, 37, 2153 - 2154, DOI: 10.1039/b814437k
Chemistry at surfaces
Hans-Peter Steinrück, Jörg Libuda and Sir David A. King
--
Tutorial Review
Chem. Soc. Rev., 2008, 37, 2204 - 2211, DOI: 10.1039/b719206c
Automotive catalysis studied by surface science
Michael Bowker
In this tutorial review I discuss the significant impact that surface science has had on our understanding of the catalytic phenomena associated with automobile exhaust depollution catalysis. For oxidation reactions it has generally been found that reactions are self-poisoned at low temperatures by the presence of strongly adsorbed reactants (such as molecular CO and NO), and that the rapid acceleration in rate at elevated temperatures (often called light-off) is due to the desorption of such adsorbates, which then frees up sites for dissociation and hence for oxidation reactions. In some circumstances such autocatalytic phenomena can then manifest themselves as oscillatory reactions which can vary in rate in both space and time. For NO reduction, the efficiency of depollution (by production of molecular nitrogen) is strongly affected by the nature of the metal used. Rh is extremely effective because it can dissociate NO much more readily than metals such as Pd and Pt, enabling oxygen removal (by reaction with CO to CO2) even at room temperature. Rh is also very selective in producing predominantly N2, rather than N2O. NOx storage and reduction (NSR) is an important recent development for removal of NOx under the highly oxidising conditions of a lean-burn engine exhaust, and the strategy involves storing NOx on BaO under oxidising conditions followed by the creation of reducing conditions to de-store and reduce it to nitrogen. By the use of STM it has been shown that this storage process is extremely facile, occurring fast even under UHV conditions, and that the storage occurs on BaO in the vicinity of Pt, with most of the oxide being converted to nitrate.
--
Critical Review
Chem. Soc. Rev., 2008, 37, 2224 - 2242, DOI: 10.1039/b718768h
Oxide ultra-thin films on metals: new materials for the design of supported metal catalysts
Hans-Joachim Freund and Gianfranco Pacchioni
Ultrathin oxide films on metals offer new opportunities for the design of supported nanoclusters with potential use in catalysis. This requires a characterization at the atomistic level of the structure and composition of the thin film, of its morphology and defect structure. A proper selection of metal/oxide interface, film thickness, lattice mismatch, etc. makes it possible to prepare collections of supported metal particles with novel properties. This critical review describes some illustrative examples, emphasizes the role of the interplay between theory and experiment, and relates some recent findings related to the possibility to control the charge state of a supported nanoparticle on an ultrathin oxide film (211 references).
Some interesting Chem. Soc. Rev. articles that might be of interest to the group
(no NMR here, but some interesting topics)
Critical Review
Chem. Soc. Rev., 2009, 38, 185 - 196, DOI: 10.1039/b802262n
Photosynthetic energy conversion: natural and artificial
James Barber
Photosystem II (PSII) is the water splitting enzyme of photosynthesis. Its appearance during evolution dramatically changed the chemical composition of our planet and set in motion an unprecedented explosion in biological activity. Powered by sunlight, PSII supplies biology with the hydrogen needed to convert carbon dioxide into organic molecules. The questions now are can we continue to exploit this photosynthetic process through increased use of biomass as an energy source and, more importantly, can we address the energy/CO2 problem by developing new photochemical technologies which mimic the natural system? (Critical review, 82 references)
--
Tutorial Review
Chem. Soc. Rev., 2009, 38, 25 - 35, DOI: 10.1039/b800582f
Biology and technology for photochemical fuel production
Michael Hambourger, Gary F. Moore, David M. Kramer, Devens Gust, Ana L. Moore and Thomas A. Moore
Sunlight is the ultimate energy source for the vast majority of life on Earth, and organisms have evolved elegant machinery for energy capture and utilization. Solar energy, whether converted to wind, rain, biomass or fossil fuels, is also the primary energy source for human-engineered energy transduction systems. This tutorial review draws parallels between biological and technological energy systems. Aspects of biology that might be advantageously incorporated into emerging technologies are highlighted, as well as ways in which technology might improve upon the principles found in biological systems. Emphasis is placed upon artificial photosynthesis, as well as the use of protonmotive force in biology.
--
Tutorial Review
Chem. Soc. Rev., 2009, 38, 73 - 82, DOI: 10.1039/b718842k
New approaches to hydrogen storage
Jason Graetz
The emergence of a Hydrogen Economy will require the development of new media capable of safely storing hydrogen in a compact and light weight package. Metal hydrides and complex hydrides, where hydrogen is chemically bonded to the metal atoms in the bulk, offer some hope of overcoming the challenges associated with hydrogen storage. The objective is to find a material with a high volumetric and gravimetric hydrogen density that can also meet the unique demands of a low temperature automotive fuel cell. Currently, there is considerable effort to develop new materials with tunable thermodynamic and kinetic properties. This tutorial review provides an overview of the different types of metal hydrides and complex hydrides being investigated for on-board (reversible) and off-board (non-reversible) hydrogen storage along with a few new approaches to improving the hydrogenation–dehydrogenation properties.
--
Tutorial Review
Chem. Soc. Rev., 2008, 37, 2383 - 2392, DOI: 10.1039/b710347f
Current state for the development of metallopharmaceutics and anti-diabetic metal complexes
Hiromu Sakurai, Yutaka Yoshikawa and Hiroyuki Yasui
This tutorial review introduces the current state of metallopharmaceutics development by focusing on the topics of anti-diabetic vanadium and zinc complexes. Over thousands of years, people have produced many types of inorganic compounds, and the modern concept of chemotherapy was achieved by Ehrlich, who used an arsenic-containing compound to treat syphilis. Since then, many metallopharmaceutics have been developed worldwide. This review will be helpful to researchers who are interested in the current states of not only metallopharmaceutics but also anti-diabetic metal complexes.
--
Critical Review
Chem. Soc. Rev., 2008, 37, 2274 - 2309, DOI: 10.1039/b719149a
In-silico investigations in heterogeneous catalysis—combustion and synthesis of small alkanes
Oliver R. Inderwildi and Stephen J. Jenkins
In this critical review, we cover first-principles density functional calculations relevant to alkane oxidation and synthesis over transition metal catalysts. For oxidation, we focus upon Pt, Rh, Pd and Ni surfaces, while for synthesis we consider Co, Ru, Fe and Ni. Throughout, we emphasise the insight to be gained by thinking of each kind of reaction as the inverse of the other, with the directionality determined simply by the choice of metal catalyst and the reaction conditions. We highlight particularly the role of low-coordination sites (steps, kinks, etc.) and the emerging consensus over the importance of the formyl intermediate in facilitating the rate-determining step (249 references).
--
Editorial
Chem. Soc. Rev., 2008, 37, 2153 - 2154, DOI: 10.1039/b814437k
Chemistry at surfaces
Hans-Peter Steinrück, Jörg Libuda and Sir David A. King
--
Tutorial Review
Chem. Soc. Rev., 2008, 37, 2204 - 2211, DOI: 10.1039/b719206c
Automotive catalysis studied by surface science
Michael Bowker
In this tutorial review I discuss the significant impact that surface science has had on our understanding of the catalytic phenomena associated with automobile exhaust depollution catalysis. For oxidation reactions it has generally been found that reactions are self-poisoned at low temperatures by the presence of strongly adsorbed reactants (such as molecular CO and NO), and that the rapid acceleration in rate at elevated temperatures (often called light-off) is due to the desorption of such adsorbates, which then frees up sites for dissociation and hence for oxidation reactions. In some circumstances such autocatalytic phenomena can then manifest themselves as oscillatory reactions which can vary in rate in both space and time. For NO reduction, the efficiency of depollution (by production of molecular nitrogen) is strongly affected by the nature of the metal used. Rh is extremely effective because it can dissociate NO much more readily than metals such as Pd and Pt, enabling oxygen removal (by reaction with CO to CO2) even at room temperature. Rh is also very selective in producing predominantly N2, rather than N2O. NOx storage and reduction (NSR) is an important recent development for removal of NOx under the highly oxidising conditions of a lean-burn engine exhaust, and the strategy involves storing NOx on BaO under oxidising conditions followed by the creation of reducing conditions to de-store and reduce it to nitrogen. By the use of STM it has been shown that this storage process is extremely facile, occurring fast even under UHV conditions, and that the storage occurs on BaO in the vicinity of Pt, with most of the oxide being converted to nitrate.
--
Critical Review
Chem. Soc. Rev., 2008, 37, 2224 - 2242, DOI: 10.1039/b718768h
Oxide ultra-thin films on metals: new materials for the design of supported metal catalysts
Hans-Joachim Freund and Gianfranco Pacchioni
Ultrathin oxide films on metals offer new opportunities for the design of supported nanoclusters with potential use in catalysis. This requires a characterization at the atomistic level of the structure and composition of the thin film, of its morphology and defect structure. A proper selection of metal/oxide interface, film thickness, lattice mismatch, etc. makes it possible to prepare collections of supported metal particles with novel properties. This critical review describes some illustrative examples, emphasizes the role of the interplay between theory and experiment, and relates some recent findings related to the possibility to control the charge state of a supported nanoparticle on an ultrathin oxide film (211 references).
CMR: Concepts in NMR (Wiley) - up to Jan. 10, 2009
Concepts in NMR (Wiley) - up to Jan. 10, 2009
Concepts in Magnetic Resonance Part A
Volume 34A Issue 1, Pages 60 - 61
Published Online: 9 Jan 2009
2nd edition of Spin Dyanmics is now out, review is available on the CMR website!
Spin dynamics: Basics of nuclear magnetic resonance, 2nd edition.
William S. Price
Nanoscale Organisation and Dynamics Group, College of Health and Science, University of Western Sidney, Penrith South, Australia
--
Concepts in Magnetic Resonance Part A
Volume 32A Issue 6, Pages 417 - 435
Published Online: 17 Nov 2008
Nonuniform sampling: Bandwidth and aliasing
from Concepts in Magnetic Resonance Part A by G. Larry Bretthorst
For spectroscopic measurements, there are good reasons why one might consider using nonuniformly nonsimultaneously sampled complex data. The primary one is that the effective bandwidth, the largest spectral window free of aliases, can be much wider than with uniformly sampled data. In this article, we discuss nonuniformly nonsimultaneously sampled data, describe how these data are traditionally analyzed, analyze them using probability theory, and show how probability theory generalizes the discrete Fourier transform: first for uniformly sampled data, then for nonuniformly sampled data, and finally for nonuniformly nonsimultaneously sampled data. These generalizations demonstrate that aliases are not so much removed by nonuniform nonsimultaneous sampling as they are moved to much higher frequencies. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 417-435, 2008.
--
Concepts in Magnetic Resonance Part A
Volume 32A Issue 5, Pages 329 - 340
Published Online: 3 Sep 2008
Is quantum mechanics necessary for understanding magnetic resonance?
from Concepts in Magnetic Resonance Part A by Lars G. Hanson
Educational material introducing magnetic resonance (MR) typically contains sections on the underlying principles. Unfortunately the explanations given are often unnecessarily complicated or even wrong. MR is often presented as a phenomenon that necessitates a quantum mechanical explanation whereas it really is a classical effect, i.e. a consequence of the common sense expressed in classical mechanics. This insight is not new, but there have been few attempts to challenge common misleading explanations, so authors and educators are inadvertently keeping myths alive. As a result, new students' first encounters with MR are often obscured by explanations that make the subject difficult to understand. Typical problems are addressed and alternative intuitive explanations are provided. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 329-340, 2008.
Concepts in Magnetic Resonance Part A
Volume 34A Issue 1, Pages 60 - 61
Published Online: 9 Jan 2009
2nd edition of Spin Dyanmics is now out, review is available on the CMR website!
Spin dynamics: Basics of nuclear magnetic resonance, 2nd edition.
William S. Price
Nanoscale Organisation and Dynamics Group, College of Health and Science, University of Western Sidney, Penrith South, Australia
--
Concepts in Magnetic Resonance Part A
Volume 32A Issue 6, Pages 417 - 435
Published Online: 17 Nov 2008
Nonuniform sampling: Bandwidth and aliasing
from Concepts in Magnetic Resonance Part A by G. Larry Bretthorst
For spectroscopic measurements, there are good reasons why one might consider using nonuniformly nonsimultaneously sampled complex data. The primary one is that the effective bandwidth, the largest spectral window free of aliases, can be much wider than with uniformly sampled data. In this article, we discuss nonuniformly nonsimultaneously sampled data, describe how these data are traditionally analyzed, analyze them using probability theory, and show how probability theory generalizes the discrete Fourier transform: first for uniformly sampled data, then for nonuniformly sampled data, and finally for nonuniformly nonsimultaneously sampled data. These generalizations demonstrate that aliases are not so much removed by nonuniform nonsimultaneous sampling as they are moved to much higher frequencies. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 417-435, 2008.
--
Concepts in Magnetic Resonance Part A
Volume 32A Issue 5, Pages 329 - 340
Published Online: 3 Sep 2008
Is quantum mechanics necessary for understanding magnetic resonance?
from Concepts in Magnetic Resonance Part A by Lars G. Hanson
Educational material introducing magnetic resonance (MR) typically contains sections on the underlying principles. Unfortunately the explanations given are often unnecessarily complicated or even wrong. MR is often presented as a phenomenon that necessitates a quantum mechanical explanation whereas it really is a classical effect, i.e. a consequence of the common sense expressed in classical mechanics. This insight is not new, but there have been few attempts to challenge common misleading explanations, so authors and educators are inadvertently keeping myths alive. As a result, new students' first encounters with MR are often obscured by explanations that make the subject difficult to understand. Typical problems are addressed and alternative intuitive explanations are provided. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 329-340, 2008.
Chem. Soc. Rev.: The Science of Champagne Bubbles
Just an article for fun...nice follow up to the previous Chem. Soc. Rev. article on wine.
Critical Review
Chem. Soc. Rev., 2008, 37, 2490 - 2511, DOI: 10.1039/b717798b
Recent advances in the science of champagne bubbles
Gérard Liger-Belair, Guillaume Polidori and Philippe Jeandet
The so-called effervescence process, which enlivens champagne and sparkling wines tasting, is the result of the fine interplay between CO2-dissolved gas molecules, tiny air pockets trapped within microscopic particles during the pouring process, and some liquid properties. This critical review summarizes recent advances obtained during the past decade concerning the physicochemical processes behind the nucleation, rise, and burst of bubbles found in glasses poured with champagne and sparkling wines. Those phenomena observed in close-up through high-speed photography are often visually appealing. Let
s hope that your enjoyment of champagne will be enhanced after reading this fully illustrated review dedicated to the deep beauties of nature often hidden behind many everyday phenomena (51 references).
Tuesday, January 20, 2009
Marcel's Update
J. Mater. Chem., 2008, 18, 4266 - 4273, DOI: 10.1039/b807778a
Detection of surface layers using 7Li MAS NMR
Nicolas Dupré, Jean-Frédéric Martin, Dominique Guyomard, Atsuo Yamada and Ryoji Kanno
Magic angle spinning solid state NMR is generally used to characterize bulk materials. We show here that it is also a promising tool to detect and characterize the diamagnetic surface layer on a paramagnetic material, which is a novel development. We apply this technique to the very hot topic of positive electrode/electrolyte characterization in the field of lithium rechargeable batteries. We report a 7Li MAS NMR study of physisorbed surface layers on LiNi1/2Mn1/2O2, a positive electrode material for lithium ion batteries. 7Li MAS NMR signals arising from surface layers formed by mixing the material with lithium carbonate or from contact of the material with ambient atmosphere, as well as with electrolyte are collected and analyzed. The progressive broadening of the line shape of the MAS NMR spectra reflects the increasing intimacy of the surface layer or secondary phase with the bulk material and therefore gives extremely useful complementary structural information on the surface not available using XPS or IR. We show that relaxation time measurements can be used as a probe of surface layers, allowing for discrimination of interphases from different origins. We propose a detailed analysis of the relaxation curves with a stretched exponential model allowing the description of the distribution of environments inside the surface layer. Our work indicates that MAS NMR can provide useful information for fine surface characterization of materials.
Detection of surface layers using 7Li MAS NMR
Nicolas Dupré, Jean-Frédéric Martin, Dominique Guyomard, Atsuo Yamada and Ryoji Kanno
Magic angle spinning solid state NMR is generally used to characterize bulk materials. We show here that it is also a promising tool to detect and characterize the diamagnetic surface layer on a paramagnetic material, which is a novel development. We apply this technique to the very hot topic of positive electrode/electrolyte characterization in the field of lithium rechargeable batteries. We report a 7Li MAS NMR study of physisorbed surface layers on LiNi1/2Mn1/2O2, a positive electrode material for lithium ion batteries. 7Li MAS NMR signals arising from surface layers formed by mixing the material with lithium carbonate or from contact of the material with ambient atmosphere, as well as with electrolyte are collected and analyzed. The progressive broadening of the line shape of the MAS NMR spectra reflects the increasing intimacy of the surface layer or secondary phase with the bulk material and therefore gives extremely useful complementary structural information on the surface not available using XPS or IR. We show that relaxation time measurements can be used as a probe of surface layers, allowing for discrimination of interphases from different origins. We propose a detailed analysis of the relaxation curves with a stretched exponential model allowing the description of the distribution of environments inside the surface layer. Our work indicates that MAS NMR can provide useful information for fine surface characterization of materials.
Monday, January 19, 2009
C&E News: MRI On The Nanoscale
from C&E News: http://pubs.acs.org/isubscribe/journals/cen/87/i03/html/8703scic1.html
"January 19, 2009
Volume 87, Number 03
p. 56
Science & Technology Concentrates
MRI On The Nanoscale
IBM scientists report the first nanometer-scale magnetic resonance imaging of a biological sample.
Celia Arnaud
IBM
An artist's rendering (left) shows the magnetic microscope tip (blue) interacting with virus particles (rods) on the end of a cantilever (yellow). The virus particles can also be viewed on the end of the cantilever in an SEM micrograph (right).
Scientists at IBM’s Almaden Research Center, in San Jose, Calif., report the first nanometer-scale magnetic resonance imaging of a biological sample. At such length scales, MRI could be used to image the three-dimensional structure of individual macromolecules and complexes, they note. Conventional MRI microscopy is limited to the micrometer scale. The IBM team, led by Dan Rugar, manager of nanoscale studies, improved the spatial resolution by combining magnetic resonance force microscopy (MRFM) with 3-D image reconstruction (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0812068106). MRFM is based on the mechanical measurement of ultrasmall magnetic forces between the nuclear spins in a sample and a nearby magnetic tip, which is scanned in three dimensions over the sample. The best spatial resolution previously achieved was 90 nm in 19F MRFM of inorganic samples. The IBM researchers extended the technology to biological samples and obtained 1H MRI images of tobacco mosaic virus particles with 4-nm resolution. Such a technique “would be complementary to other techniques, such as cryo-electron microscopy, and could develop into a powerful tool for structural biology,” the researchers write."
"January 19, 2009
Volume 87, Number 03
p. 56
Science & Technology Concentrates
MRI On The Nanoscale
IBM scientists report the first nanometer-scale magnetic resonance imaging of a biological sample.
Celia Arnaud
IBM
An artist's rendering (left) shows the magnetic microscope tip (blue) interacting with virus particles (rods) on the end of a cantilever (yellow). The virus particles can also be viewed on the end of the cantilever in an SEM micrograph (right).
Scientists at IBM’s Almaden Research Center, in San Jose, Calif., report the first nanometer-scale magnetic resonance imaging of a biological sample. At such length scales, MRI could be used to image the three-dimensional structure of individual macromolecules and complexes, they note. Conventional MRI microscopy is limited to the micrometer scale. The IBM team, led by Dan Rugar, manager of nanoscale studies, improved the spatial resolution by combining magnetic resonance force microscopy (MRFM) with 3-D image reconstruction (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0812068106). MRFM is based on the mechanical measurement of ultrasmall magnetic forces between the nuclear spins in a sample and a nearby magnetic tip, which is scanned in three dimensions over the sample. The best spatial resolution previously achieved was 90 nm in 19F MRFM of inorganic samples. The IBM researchers extended the technology to biological samples and obtained 1H MRI images of tobacco mosaic virus particles with 4-nm resolution. Such a technique “would be complementary to other techniques, such as cryo-electron microscopy, and could develop into a powerful tool for structural biology,” the researchers write."
Sunday, January 18, 2009
J Phys Chem C, vol 113, issues 2 and 3
Calculating the Concentration of SiOHAl Species in Ferrierites by 29Si and 27Al NMR Spectroscopy
Tamás I. Korányi*†‡ and János B.Nagy‡
J. Phys. Chem. C, 2009, 113 (3), pp 907–913
Abstract:Two NH4-ferrierites (NH4-FER) and their calcined H-FER forms with Si/Al ratios of 10 and 27.5 were characterized by 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The 27Al and 29Si NMR spectral resolutions of two NH4-FER samples with Si/Al = 8.4 and 30.0 were taken from the literature. The quantitative contributions of the Al sites, defect-free Si(nAl), and silanol groups to the different periodical building units (PerBUs) of the FER zeolite framework were calculated from the various Si/Al ratios and relative 27Al and 29Si NMR signal intensities. Two possible PerBU models and a dealumination route were suggested by the FER structure, and the distribution of PerBUs followed the composition of the framework with appropriate precision in the studied composition range (Si/Al = 8.4−30.0). The independently measured [Fourier transform infrared (FTIR) spectroscopy, NH3 temperature-programmed desorption (TPD)] extraframework aluminum (EFAl) concentrations and those measured by 27Al NMR spectroscopy were in a good agreement. The concentration of strong Brønsted acidic SiOHAl groups calculated with the SiOHAl PerBU model revealed that one-quarter to one-third of all OH groups were present in these SiOHAl sites in the ferrierites with Si/Al = 10 and one-half of them were in these sites in the NH4-FER sample with Si/Al = 27.5. The former zeolites were dealuminated at a higher degree than the latter. Tetrahedral aluminum species occupied the SiOHAl sites, and both deformed and octahedral Al species were present in the EFAl positions.
Tamás I. Korányi*†‡ and János B.Nagy‡
J. Phys. Chem. C, 2009, 113 (3), pp 907–913
Abstract:Two NH4-ferrierites (NH4-FER) and their calcined H-FER forms with Si/Al ratios of 10 and 27.5 were characterized by 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The 27Al and 29Si NMR spectral resolutions of two NH4-FER samples with Si/Al = 8.4 and 30.0 were taken from the literature. The quantitative contributions of the Al sites, defect-free Si(nAl), and silanol groups to the different periodical building units (PerBUs) of the FER zeolite framework were calculated from the various Si/Al ratios and relative 27Al and 29Si NMR signal intensities. Two possible PerBU models and a dealumination route were suggested by the FER structure, and the distribution of PerBUs followed the composition of the framework with appropriate precision in the studied composition range (Si/Al = 8.4−30.0). The independently measured [Fourier transform infrared (FTIR) spectroscopy, NH3 temperature-programmed desorption (TPD)] extraframework aluminum (EFAl) concentrations and those measured by 27Al NMR spectroscopy were in a good agreement. The concentration of strong Brønsted acidic SiOHAl groups calculated with the SiOHAl PerBU model revealed that one-quarter to one-third of all OH groups were present in these SiOHAl sites in the ferrierites with Si/Al = 10 and one-half of them were in these sites in the NH4-FER sample with Si/Al = 27.5. The former zeolites were dealuminated at a higher degree than the latter. Tetrahedral aluminum species occupied the SiOHAl sites, and both deformed and octahedral Al species were present in the EFAl positions.
J Phys Chem B, vol 113, issues 2 and 3
Network Dynamics and Species Exchange Processes in Aluminophosphate Glasses: An in situ High Temperature Magic Angle Spinning NMR View
Sebastian Wegner†, Leo van Wüllen*† and Gregory Tricot†‡
J. Phys. Chem. B, 2009, 113 (2), pp 416–425
Abstract: In this contribution, we present an in situ high temperature 27Al and 31P magic angle spinning (MAS) NMR study of binary and ternary phosphate glasses at temperatures above the glass transition temperature TG. For binary phosphate glasses, xK2O−(1 − x)P2O5 and ternary aluminophosphate glasses 30K2O−xAl2O3−(70 − x)P2O5 with 7 < x < 15 dynamic exchange processes between the various phosphate species (and aluminate species) present in the glasses could be identified in the temperature range between TG and the maximum achievable temperature Tmax of our high temperature MAS NMR setup, TG < T < Tmax. This observation indicates rapid P−O−P and P−O−Al bond formation and bond breaking in the (alumino)phosphate glasses. From a modeling of the temperature dependence of these exchange processes, the activation energy EA for the corresponding process could be determined. These local bond breaking and making processes are ultimately linked to the macroscopic viscous flow and may indeed form the basic microscopic local step of viscous flow.
Sebastian Wegner†, Leo van Wüllen*† and Gregory Tricot†‡
J. Phys. Chem. B, 2009, 113 (2), pp 416–425
Abstract: In this contribution, we present an in situ high temperature 27Al and 31P magic angle spinning (MAS) NMR study of binary and ternary phosphate glasses at temperatures above the glass transition temperature TG. For binary phosphate glasses, xK2O−(1 − x)P2O5 and ternary aluminophosphate glasses 30K2O−xAl2O3−(70 − x)P2O5 with 7 < x < 15 dynamic exchange processes between the various phosphate species (and aluminate species) present in the glasses could be identified in the temperature range between TG and the maximum achievable temperature Tmax of our high temperature MAS NMR setup, TG < T < Tmax. This observation indicates rapid P−O−P and P−O−Al bond formation and bond breaking in the (alumino)phosphate glasses. From a modeling of the temperature dependence of these exchange processes, the activation energy EA for the corresponding process could be determined. These local bond breaking and making processes are ultimately linked to the macroscopic viscous flow and may indeed form the basic microscopic local step of viscous flow.
Tuesday, January 13, 2009
J Phys Chem C, v113, issue 1
Study of Aluminoborane Compound AlB4H11 for Hydrogen Storage
Ji-Cheng Zhao*†, Douglas A. Knight‡, Gilbert M. Brown‡, Chul Kim§, Son-Jong Hwang§, Joseph W. Reiter∥, Robert C. Bowman, Jr.∥, Jason A. Zan∥ and James G. Kulleck∥
J. Phys. Chem. C, 2009, 113 (1), pp 2–11
Aluminoborane compounds AlB4H11, AlB5H12, and AlB6H13 were reported by Himpsl and Bond in 1981, but they have eluded the attention of the worldwide hydrogen storage research community for more than a quarter of a century. These aluminoborane compounds have very attractive properties for hydrogen storage: high hydrogen capacity (i.e., 13.5, 12.9, and 12.4 wt % H, respectively) and attractive hydrogen desorption temperature (i.e., AlB4H11 decomposes at ∼125 °C). We have synthesized AlB4H11 and studied its thermal desorption behavior using temperature-programmed desorption with mass spectrometry, gas volumetric (Sieverts) measurement, infrared (IR) spectroscopy, and solid state nuclear magnetic resonance (NMR). Rehydrogenation of hydrogen-desorbed products was performed and encouraging evidence of at least partial reversibility for hydrogenation at relatively mild conditions is observed. Our chemical analysis indicates that the formula for the compound is closer to AlB4H12 than AlB4H11.
Solid-State 17O NMR Spectroscopy of Hydrous Magnesium Silicates: Evidence for Proton Dynamics
John M. Griffin†, Stephen Wimperis*‡, Andrew J. Berry§, Chris J. Pickard∥ and Sharon E. Ashbrook*†
J. Phys. Chem. C, 2009, 113 (1), pp 465–471
Abstract: First-principles calculations of 17O quadrupolar and chemical shift NMR parameters were performed using CASTEP, a density functional theory (DFT) code, to try and interpret high-resolution 17O NMR spectra of the humite group minerals hydroxyl-chondrodite (2Mg2SiO4·Mg(OH)2) and hydroxyl-clinohumite (4Mg2SiO4·Mg(OH)2), which are models for the incorporation of water within the Earth’s upper mantle. The structures of these humite minerals contain two possible crystallographically inequivalent H sites with 50% occupancy. Isotropic 17O multiple-quantum magic angle spinning (MQMAS) spectra were therefore simulated using the calculated 17O NMR parameters and assuming either a static or dynamic model for the positional disorder of the H atoms. Only the dynamic disorder model provided simulated spectra that agree with experimental 17O MQMAS spectra of hydroxyl-chondrodite and hydroxyl-clinohumite. Previously published 17O satellite-transition magic angle spinning (STMAS) spectra of these minerals showed significant dynamic line-broadenings in the isotropic frequency dimension. We were able to reproduce these line-broadenings with at least qualitative accuracy using a combination of the same dynamic model for the positional H disorder, calculated values for the change in 17O quadrupolar NMR parameters upon H exchange, and a simple analytical model for dynamic line-broadening in MAS NMR experiments. Overall, this study shows that a combination of state-of-the-art NMR methodology and first-principles calculations of NMR parameters is able to provide information on dynamic processes in solids with atomic-scale resolution that is unobtainable by any other method.
Ji-Cheng Zhao*†, Douglas A. Knight‡, Gilbert M. Brown‡, Chul Kim§, Son-Jong Hwang§, Joseph W. Reiter∥, Robert C. Bowman, Jr.∥, Jason A. Zan∥ and James G. Kulleck∥
J. Phys. Chem. C, 2009, 113 (1), pp 2–11
Aluminoborane compounds AlB4H11, AlB5H12, and AlB6H13 were reported by Himpsl and Bond in 1981, but they have eluded the attention of the worldwide hydrogen storage research community for more than a quarter of a century. These aluminoborane compounds have very attractive properties for hydrogen storage: high hydrogen capacity (i.e., 13.5, 12.9, and 12.4 wt % H, respectively) and attractive hydrogen desorption temperature (i.e., AlB4H11 decomposes at ∼125 °C). We have synthesized AlB4H11 and studied its thermal desorption behavior using temperature-programmed desorption with mass spectrometry, gas volumetric (Sieverts) measurement, infrared (IR) spectroscopy, and solid state nuclear magnetic resonance (NMR). Rehydrogenation of hydrogen-desorbed products was performed and encouraging evidence of at least partial reversibility for hydrogenation at relatively mild conditions is observed. Our chemical analysis indicates that the formula for the compound is closer to AlB4H12 than AlB4H11.
Solid-State 17O NMR Spectroscopy of Hydrous Magnesium Silicates: Evidence for Proton Dynamics
John M. Griffin†, Stephen Wimperis*‡, Andrew J. Berry§, Chris J. Pickard∥ and Sharon E. Ashbrook*†
J. Phys. Chem. C, 2009, 113 (1), pp 465–471
Abstract: First-principles calculations of 17O quadrupolar and chemical shift NMR parameters were performed using CASTEP, a density functional theory (DFT) code, to try and interpret high-resolution 17O NMR spectra of the humite group minerals hydroxyl-chondrodite (2Mg2SiO4·Mg(OH)2) and hydroxyl-clinohumite (4Mg2SiO4·Mg(OH)2), which are models for the incorporation of water within the Earth’s upper mantle. The structures of these humite minerals contain two possible crystallographically inequivalent H sites with 50% occupancy. Isotropic 17O multiple-quantum magic angle spinning (MQMAS) spectra were therefore simulated using the calculated 17O NMR parameters and assuming either a static or dynamic model for the positional disorder of the H atoms. Only the dynamic disorder model provided simulated spectra that agree with experimental 17O MQMAS spectra of hydroxyl-chondrodite and hydroxyl-clinohumite. Previously published 17O satellite-transition magic angle spinning (STMAS) spectra of these minerals showed significant dynamic line-broadenings in the isotropic frequency dimension. We were able to reproduce these line-broadenings with at least qualitative accuracy using a combination of the same dynamic model for the positional H disorder, calculated values for the change in 17O quadrupolar NMR parameters upon H exchange, and a simple analytical model for dynamic line-broadening in MAS NMR experiments. Overall, this study shows that a combination of state-of-the-art NMR methodology and first-principles calculations of NMR parameters is able to provide information on dynamic processes in solids with atomic-scale resolution that is unobtainable by any other method.
Thursday, January 08, 2009
Chemical Physics, Volume 355, Issue 1, 7 January 2009, Pages 67-72
Relationship between calculated NMR data and intermolecular hydrogen bond properties in X-pyridineHF
Ali Ebrahimi, Mostafa Habibia, Hamid Reza Masoodia and Ali Reza Gholipoura
Abstract
The effect of different substituents in para and metapositions on the NMR data of X-pyridineHF complex has been studied at B3LYP/6-311++G(d,p) level of theory. The relationship between NMR data and electron donation of substituents has been investigated. The results of topological properties of electron charge density calculated using atoms in molecules (AIM) analysis can be used to predict some NMR data. The magnetism-based indices, nucleus independent chemical shift NICS(1) and its z component NICS(1)ZZ, were used to investigate the ring aromaticity changes on complexation. A linear correlation between Hammett coefficients and some NMR data could be found with a good correlation coefficient.
Ali Ebrahimi, Mostafa Habibia, Hamid Reza Masoodia and Ali Reza Gholipoura
Abstract
The effect of different substituents in para and metapositions on the NMR data of X-pyridineHF complex has been studied at B3LYP/6-311++G(d,p) level of theory. The relationship between NMR data and electron donation of substituents has been investigated. The results of topological properties of electron charge density calculated using atoms in molecules (AIM) analysis can be used to predict some NMR data. The magnetism-based indices, nucleus independent chemical shift NICS(1) and its z component NICS(1)ZZ, were used to investigate the ring aromaticity changes on complexation. A linear correlation between Hammett coefficients and some NMR data could be found with a good correlation coefficient.
J. Am. Chem. Soc., 2009, 131 (1), pp 170–176
Structural Rearrangements of Membrane Proteins Probed by Water-Edited Solid-State NMR Spectroscopy
Christian Ader, Robert Schneider, Karsten Seidel‡, Manuel Etzkorn, Stefan Becker‡ and Marc Baldus
Abstract
We show that water-edited solid-state NMR spectroscopy allows for probing global protein conformation and residue-specific solvent accessibility in a lipid bilayer environment. The transfer dynamics can be well described by a general time constant, irrespective of protein topology and lipid environment. This approach was used to follow structural changes in response to protein function in the chimeric potassium channel KcsA-Kv1.3. Data obtained as a function of pH link earlier biochemical data to changes in protein structure in a functional bilayer setting.
Christian Ader, Robert Schneider, Karsten Seidel‡, Manuel Etzkorn, Stefan Becker‡ and Marc Baldus
Abstract
We show that water-edited solid-state NMR spectroscopy allows for probing global protein conformation and residue-specific solvent accessibility in a lipid bilayer environment. The transfer dynamics can be well described by a general time constant, irrespective of protein topology and lipid environment. This approach was used to follow structural changes in response to protein function in the chimeric potassium channel KcsA-Kv1.3. Data obtained as a function of pH link earlier biochemical data to changes in protein structure in a functional bilayer setting.
J. Am. Chem. Soc., 2009, 131 (1), pp 118–128
Observation of a Low-Temperature, Dynamically Driven Structural Transition in a Polypeptide by Solid-State NMR Spectroscopy
Vikram S. Bajaj†, Patrick C.A. van der Wel‡ and Robert G. Griffin*
Abstract
At reduced temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200 and 230 K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. Here, we use low-temperature solid-state NMR to examine site-specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, we employ magic angle spinning NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide, N-f-MLF-OH, lattice at temperatures as low as 90 K. This transition is characterized by the appearance of an extra set of lines in 1D 15N spectra as well as additional cross peaks in 2D 13C−13C and 13C−15N spectra. Interestingly, the gradual, temperature-dependent appearance of the new spectral component is not accompanied by the line broadening typical of dynamic transitions. A direct comparison between the spectra of N-f-MLF-OH and the analog N-f-MLF-OMe, which does not display this transition, indicates a correlation of the structural transition to the temperature dependent motion of the aromatic phenylalanine side chain. Several quantitative solid state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition.
Vikram S. Bajaj†, Patrick C.A. van der Wel‡ and Robert G. Griffin*
Abstract
At reduced temperatures, proteins and other biomolecules are generally found to exhibit dynamic as well as structural transitions. This includes a so-called protein glass transition that is universally observed in systems cooled between 200 and 230 K, and which is generally attributed to interactions between hydrating solvent molecules and protein side chains. However, there is also experimental and theoretical evidence for a low-temperature transition in the intrinsic dynamics of the protein itself, absent any solvent. Here, we use low-temperature solid-state NMR to examine site-specific fluctuations in atomic structure and dynamics in the absence of solvents. In particular, we employ magic angle spinning NMR to examine a structural phase transition associated with dynamic processes in a solvent-free polypeptide, N-f-MLF-OH, lattice at temperatures as low as 90 K. This transition is characterized by the appearance of an extra set of lines in 1D 15N spectra as well as additional cross peaks in 2D 13C−13C and 13C−15N spectra. Interestingly, the gradual, temperature-dependent appearance of the new spectral component is not accompanied by the line broadening typical of dynamic transitions. A direct comparison between the spectra of N-f-MLF-OH and the analog N-f-MLF-OMe, which does not display this transition, indicates a correlation of the structural transition to the temperature dependent motion of the aromatic phenylalanine side chain. Several quantitative solid state NMR experiments were employed to provide site-specific measurements of structural and motional features of the observed transition.
J. Am. Chem. Soc., 2009, 131 (1), pp 2–3
High-Resolution Double-Quantum Deuterium Magic Angle Spinning Solid-State NMR Spectroscopy of Perdeuterated Proteins
Vipin Agarwal†, Katja Faelber†, Peter Schmieder† and Bernd Reif*‡
Abstract
We show in this manuscript that 2H,13C correlation spectra in uniformly 2H,13C isotopically enriched peptides and proteins can be recorded in MAS solid-state NMR with site specific resolution. A resolved deuterium dimension is obtained by evolving 2H double-quantum coherences. Experimental 2H line widths are obtained that are as small as 16 Hz (0.17 ppm at 600 MHz) in the double-quantum dimension. The unprecedented resolution in the deuterium dimension obtained for proteins opens new perspectives for correlation experiments and, in particular, for the characterization of dynamics of proteins in the solid-state.
Vipin Agarwal†, Katja Faelber†, Peter Schmieder† and Bernd Reif*‡
Abstract
We show in this manuscript that 2H,13C correlation spectra in uniformly 2H,13C isotopically enriched peptides and proteins can be recorded in MAS solid-state NMR with site specific resolution. A resolved deuterium dimension is obtained by evolving 2H double-quantum coherences. Experimental 2H line widths are obtained that are as small as 16 Hz (0.17 ppm at 600 MHz) in the double-quantum dimension. The unprecedented resolution in the deuterium dimension obtained for proteins opens new perspectives for correlation experiments and, in particular, for the characterization of dynamics of proteins in the solid-state.
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