Implementation of High Resolution 43Ca Solid State NMR Spectroscopy: Toward the Elucidation of Calcium Sites in Biological Materials
Danielle Laurencin*†‡, Christel Gervais§, Alan Wong†, Cristina Coelho§, Francesco Mauri, Dominique Massiot#, Mark E. Smith† and Christian Bonhomme*§
Abstract
Calcium is one of the most abundant cations in living organisms. It is found in the mineral phase of bone and in proteins like calmodulin. However, its exact environment beyond the first coordination sphere is often unknown, thus hampering the understanding of many biological processes. Here, calcium benzoate trihydrate (Ca(C6H5COO)2·3H2O) was used as a model for the NMR analysis of calcium sites in biological materials, because of the similarity of its calcium coordination, to water and carboxylate ligands, to that in several calcium-proteins. First, calcium-43 magic angle spinning (MAS) and static NMR spectra of a 43Ca enriched sample were recorded at different magnetic fields, to investigate the electronic environment of calcium. Complex static lineshapes were obtained because of the presence of anisotropic NMR interactions of similar magnitude (chemical shift anisotropy and quadrupolar interaction), and the full interpretation of the spectra required simulations and gauge-including projector augmented wave (GIPAW) DFT calculations. An NMR investigation of the coordination environment of Ca2+ was carried out, using high resolution 13C−43Ca MAS NMR experiments such as TRAPDOR (transfer of population double resonance) and heteronuclear J-spin−echoes. It was shown that despite the weakness of 13C−43Ca interactions, it is possible to discriminate carbon atoms according to their calcium environment. Long-range calcium−carbon correlations were even evidenced by TRAPDOR, reaching distances >5.6 Å. This work demonstrates that by combining solid state NMR experiments, DFT calculations, and simulations, it will be possible to elucidate the electronic and coordination environment of calcium in many important and complex materials.
Thursday, October 22, 2009
J. Am. Chem. Soc., 2009, 131 (37), pp 13228–13229
13C−13C Correlation Spectroscopy of Membrane-Associated Influenza Virus Fusion Peptide Strongly Supports a Helix-Turn-Helix Motif and Two Turn Conformations
Yan Sun and David P. Weliky*
Abstract
The influenza virus fusion peptide (IFP) is the N-terminal domain of the viral hemagglutinin protein, binds to the endosomal membrane, and plays a critical role in fusion between the viral and endosomal membranes which is a primary step in infection. The IFP is also an important system for testing simulation methods for membrane-associated peptides. In detergent, the IFP forms helix-turn-helix and helix-turn-strand structures at pH 5.0 and 7.4, respectively, while simulations in membranes by different groups have yielded conflicting results with some reports of a continuous helix without a turn. In this study, 13C−13C NMR correlation spectra were obtained for the membrane-associated IFP and the 13C chemical shifts supported a helix-turn-helix motif at both pH 5.0 and 7.4 with an alternate turn conformation at pH 5.0 that was absent at pH 7.4. The alternate conformation was correlated with protonation of the side chain of Glu-11 in the turn and with greater fusion at pH 5.0. The structures are overall consistent with the hypothesis of “inverted V” membrane location of the IFP with insertion of the N-terminal region into the membrane and contact of the turn with the lipid/water interface. The positions of hydrophobic residues in the pH 5.0 structure may favor membrane insertion with resultant increased membrane perturbation and fusion rate. In addition to their functional relevance, these IFP structures are important reference data for simulations of the membrane-associated IFP which can in principle detect the full conformational distribution of the IFP.
Yan Sun and David P. Weliky*
Abstract
The influenza virus fusion peptide (IFP) is the N-terminal domain of the viral hemagglutinin protein, binds to the endosomal membrane, and plays a critical role in fusion between the viral and endosomal membranes which is a primary step in infection. The IFP is also an important system for testing simulation methods for membrane-associated peptides. In detergent, the IFP forms helix-turn-helix and helix-turn-strand structures at pH 5.0 and 7.4, respectively, while simulations in membranes by different groups have yielded conflicting results with some reports of a continuous helix without a turn. In this study, 13C−13C NMR correlation spectra were obtained for the membrane-associated IFP and the 13C chemical shifts supported a helix-turn-helix motif at both pH 5.0 and 7.4 with an alternate turn conformation at pH 5.0 that was absent at pH 7.4. The alternate conformation was correlated with protonation of the side chain of Glu-11 in the turn and with greater fusion at pH 5.0. The structures are overall consistent with the hypothesis of “inverted V” membrane location of the IFP with insertion of the N-terminal region into the membrane and contact of the turn with the lipid/water interface. The positions of hydrophobic residues in the pH 5.0 structure may favor membrane insertion with resultant increased membrane perturbation and fusion rate. In addition to their functional relevance, these IFP structures are important reference data for simulations of the membrane-associated IFP which can in principle detect the full conformational distribution of the IFP.
Thursday, October 15, 2009
Cryst. Growth Des., 2009, 9 (2), pp 921–937
Solid-State NMR Analysis of Organic Cocrystals and Complexes
Frederick G. Vogt*†, Jacalyn S. Clawson†, Mark Strohmeier†, Andrew J. Edwards‡, Tran N. Pham‡ and Simon A. Watson‡
Abstract
Solid-state NMR (SSNMR) is capable of providing detailed structural information about organic and pharmaceutical cocrystals and complexes. SSNMR nondestructively analyzes small amounts of powdered material and generally yields data with higher information content than vibrational spectroscopy and powder X-ray diffraction methods. These advantages can be utilized in the analysis of pharmaceutical cocrystals, which are often initially produced using solvent drop grinding techniques that do not lend themselves to single crystal growth for X-ray diffraction studies. In this work, several molecular complexes and cocrystals are examined to understand the capabilities of the SSNMR techniques, particularly their ability to prove or disprove molecular association and observe structural features such as hydrogen bonding. Dipolar correlation experiments between spin pairs such as 1H−1H, 1H−13C, and 19F−13C are applied to study hydrogen bonding, intermolecular contacts, and spin diffusion to link individual molecules together in a crystal structure and quickly prove molecular association. Analysis of the principal components of chemical shift tensors is also utilized where relevant, as these are more sensitive to structural effects than the isotropic chemical shift alone. In addition, 1H T1 relaxation measurements are also demonstrated as a means to prove phase separation of components. On the basis of these results, a general experimental approach to cocrystal analysis by SSNMR is suggested.
Frederick G. Vogt*†, Jacalyn S. Clawson†, Mark Strohmeier†, Andrew J. Edwards‡, Tran N. Pham‡ and Simon A. Watson‡
Abstract
Solid-state NMR (SSNMR) is capable of providing detailed structural information about organic and pharmaceutical cocrystals and complexes. SSNMR nondestructively analyzes small amounts of powdered material and generally yields data with higher information content than vibrational spectroscopy and powder X-ray diffraction methods. These advantages can be utilized in the analysis of pharmaceutical cocrystals, which are often initially produced using solvent drop grinding techniques that do not lend themselves to single crystal growth for X-ray diffraction studies. In this work, several molecular complexes and cocrystals are examined to understand the capabilities of the SSNMR techniques, particularly their ability to prove or disprove molecular association and observe structural features such as hydrogen bonding. Dipolar correlation experiments between spin pairs such as 1H−1H, 1H−13C, and 19F−13C are applied to study hydrogen bonding, intermolecular contacts, and spin diffusion to link individual molecules together in a crystal structure and quickly prove molecular association. Analysis of the principal components of chemical shift tensors is also utilized where relevant, as these are more sensitive to structural effects than the isotropic chemical shift alone. In addition, 1H T1 relaxation measurements are also demonstrated as a means to prove phase separation of components. On the basis of these results, a general experimental approach to cocrystal analysis by SSNMR is suggested.
J. Am. Chem. Soc., 2009, 131 (33), pp 11939–11948
Measurement of Methyl Axis Orientations in Invisible, Excited States of Proteins by Relaxation Dispersion NMR Spectroscopy
Andrew J. Baldwin, D. Flemming Hansen, Pramodh Vallurupalli and Lewis E. Kay*
Abstract
Few detailed studies of transiently populated conformations of biological molecules have emerged despite the fact that such states are often important to processes such as protein folding, enzyme catalysis, molecular recognition and binding. A major limitation has been the lack of experimental tools to study these often invisible, short-lived conformers. Recent advances in relaxation dispersion NMR spectroscopy are changing this paradigm with the potential to generate high resolution structural information which is necessary for a rigorous characterization of these states. In this study, we present an experimental method for establishing the relative orientations of methyl groups in invisible, excited states of proteins by measuring methyl 1H−13C residual dipolar couplings (RDCs). In our approach, four two-dimensional spectra are acquired at a pair of static magnetic fields. Each spectrum contains one of the four isolated multiplet components of a coupled methyl carbon, whose signal intensities, modulated by the pulsing frequency of a Carr−Purcell−Meiboom−Gill (CPMG) element, are sensitive to both chemical shift and RDC differences between exchanging states. In addition, data sets from a CPMG experiment which monitors the decay of in-phase methyl 13C magnetization are recorded, that are sensitive only to the differences in chemical shifts between the states. Using our methodology, RDC values obtained from an invisible state in an exchanging system are shown to be in good agreement with the corresponding values measured under conditions where the invisible state is stabilized to become the highly populated ground state. The approach allows the measurement of anisotropic restraints at methyl positions in excited states and complements previously developed experiments focusing on the protein backbone.
Andrew J. Baldwin, D. Flemming Hansen, Pramodh Vallurupalli and Lewis E. Kay*
Abstract
Few detailed studies of transiently populated conformations of biological molecules have emerged despite the fact that such states are often important to processes such as protein folding, enzyme catalysis, molecular recognition and binding. A major limitation has been the lack of experimental tools to study these often invisible, short-lived conformers. Recent advances in relaxation dispersion NMR spectroscopy are changing this paradigm with the potential to generate high resolution structural information which is necessary for a rigorous characterization of these states. In this study, we present an experimental method for establishing the relative orientations of methyl groups in invisible, excited states of proteins by measuring methyl 1H−13C residual dipolar couplings (RDCs). In our approach, four two-dimensional spectra are acquired at a pair of static magnetic fields. Each spectrum contains one of the four isolated multiplet components of a coupled methyl carbon, whose signal intensities, modulated by the pulsing frequency of a Carr−Purcell−Meiboom−Gill (CPMG) element, are sensitive to both chemical shift and RDC differences between exchanging states. In addition, data sets from a CPMG experiment which monitors the decay of in-phase methyl 13C magnetization are recorded, that are sensitive only to the differences in chemical shifts between the states. Using our methodology, RDC values obtained from an invisible state in an exchanging system are shown to be in good agreement with the corresponding values measured under conditions where the invisible state is stabilized to become the highly populated ground state. The approach allows the measurement of anisotropic restraints at methyl positions in excited states and complements previously developed experiments focusing on the protein backbone.
J. Am. Chem. Soc., 2009, 131 (33), pp 11861–11874
31P MAS Refocused INADEQUATE Spin−Echo (REINE) NMR Spectroscopy: Revealing J Coupling and Chemical Shift Two-Dimensional Correlations in Disordered Solids
Paul Guerry†, Mark E. Smith and Steven P. Brown*
Abstract
Two-dimensional (2D) variations in 2JP1,P1, 2JP1,P2, and 2JP2,P2 are obtained—using the REINE (REfocused INADEQUATE spin−Echo) pulse sequence presented by Cadars et al. (Phys. Chem. Chem. Phys. 2007, 9, 92−103)—from pixel-by-pixel fittings of the spin−echo modulation for the 2D correlation peaks due to linked phosphate tetrahedra (P1−P1, P1−P2, P2−P1, and P2−P2) in a 31P refocused INADEQUATE solid-state MAS NMR spectrum of a cadmium phosphate glass, 0.575CdO−0.425P2O5. In particular, separate variations for each 2D 31P REINE peak are obtained which reveal correlations between the J couplings and the 31P chemical shifts of the coupled nuclei that are much clearer than those evident in previously presented 2D z-filtered 31P spin−echo spectra. Notably, such correlations between the J couplings and the 31P chemical shifts are observed even though the conditional probability distributions extracted using the protocol of Cadars et al. (J. Am. Chem. Soc. 2005, 127, 4466−4476) indicate that there is no marked correlation between the 31P chemical shifts of neighboring phosphate tetrahedra. For 2D peaks at the P2 31P chemical shift in the direct dimension, there can be contributions from chains of three units (P1−P2−P1), chains of four units (P1−P2−P2−P1), or longer chains or rings (−P2−P2−P2−): for the representative glass considered here, best fits are obtained assuming a glass comprised predominantly of chains of four units. The following variations are found: 2JP1,P1 = 13.4 ± 0.3 to 14.8 ± 0.5 Hz, 2JP1,P2 = 15.0 ± 0.3 to 18.2 ± 0.3 Hz, and 2JP2,P2 = 5.9 ± 0.6 to 9.1 ± 0.9 Hz from the fits to the P1−P1, P1−P2, and P2−P2 peaks, respectively. The correlation of a particular J coupling with the 31P chemical shifts of the considered nucleus and the coupled nucleus is quantified by the coefficients CF2 and CF1 that correspond to the average pixel-by-pixel change in the J coupling with respect to the chemical shift of the observed (F2) and neighboring (F1) 31P nuclei, respectively.
Paul Guerry†, Mark E. Smith and Steven P. Brown*
Abstract
Two-dimensional (2D) variations in 2JP1,P1, 2JP1,P2, and 2JP2,P2 are obtained—using the REINE (REfocused INADEQUATE spin−Echo) pulse sequence presented by Cadars et al. (Phys. Chem. Chem. Phys. 2007, 9, 92−103)—from pixel-by-pixel fittings of the spin−echo modulation for the 2D correlation peaks due to linked phosphate tetrahedra (P1−P1, P1−P2, P2−P1, and P2−P2) in a 31P refocused INADEQUATE solid-state MAS NMR spectrum of a cadmium phosphate glass, 0.575CdO−0.425P2O5. In particular, separate variations for each 2D 31P REINE peak are obtained which reveal correlations between the J couplings and the 31P chemical shifts of the coupled nuclei that are much clearer than those evident in previously presented 2D z-filtered 31P spin−echo spectra. Notably, such correlations between the J couplings and the 31P chemical shifts are observed even though the conditional probability distributions extracted using the protocol of Cadars et al. (J. Am. Chem. Soc. 2005, 127, 4466−4476) indicate that there is no marked correlation between the 31P chemical shifts of neighboring phosphate tetrahedra. For 2D peaks at the P2 31P chemical shift in the direct dimension, there can be contributions from chains of three units (P1−P2−P1), chains of four units (P1−P2−P2−P1), or longer chains or rings (−P2−P2−P2−): for the representative glass considered here, best fits are obtained assuming a glass comprised predominantly of chains of four units. The following variations are found: 2JP1,P1 = 13.4 ± 0.3 to 14.8 ± 0.5 Hz, 2JP1,P2 = 15.0 ± 0.3 to 18.2 ± 0.3 Hz, and 2JP2,P2 = 5.9 ± 0.6 to 9.1 ± 0.9 Hz from the fits to the P1−P1, P1−P2, and P2−P2 peaks, respectively. The correlation of a particular J coupling with the 31P chemical shifts of the considered nucleus and the coupled nucleus is quantified by the coefficients CF2 and CF1 that correspond to the average pixel-by-pixel change in the J coupling with respect to the chemical shift of the observed (F2) and neighboring (F1) 31P nuclei, respectively.
J. Am. Chem. Soc., 2009, 131 (33), pp 11855–11860
Direct Interaction between Amphotericin B and Ergosterol in Lipid Bilayers As Revealed by 2H NMR Spectroscopy
Nobuaki Matsumori, Kazuaki Tahara, Hiroko Yamamoto, Atsushi Morooka, Mototsugu Doi, Tohru Oishi and Michio Murata
Abstract
Although amphotericin B (AmB) is thought to exert its antifungal activity by forming transmembrane ion-permeable self-assemblies together with ergosterol, no previous study has directly proven AmB−ergosterol interaction. To establish the interaction, we measured 2H NMR using deuterium-labeled sterols and AmB. The 2H NMR spectra of deuterated ergosterol in palmitoyloleoylphosphatidylcholine (POPC) bilayers showed that fast axial diffusion of erogosterol was almost completely inhibited by the coexistence of AmB. Conversely, cholesterol mobility in POPC membrane was essentially unchanged with or without AmB. These results unequivocally demonstrate that ergosterol has significant interaction with AmB in POPC bilayers. In addition, we examined the mobility of AmB using deuterium-labeled AmB, and found that, although AmB is almost immobilized in sterol-free and cholesterol-containing POPC membranes, a certain ratio of AmB molecules acquires mobility in the presence of ergosterol. The similar mobility of AmB and ergosterol in POPC bilayers confirmed the idea of the direct intermolecular interaction between ergosterol and AmB.
Nobuaki Matsumori, Kazuaki Tahara, Hiroko Yamamoto, Atsushi Morooka, Mototsugu Doi, Tohru Oishi and Michio Murata
Abstract
Although amphotericin B (AmB) is thought to exert its antifungal activity by forming transmembrane ion-permeable self-assemblies together with ergosterol, no previous study has directly proven AmB−ergosterol interaction. To establish the interaction, we measured 2H NMR using deuterium-labeled sterols and AmB. The 2H NMR spectra of deuterated ergosterol in palmitoyloleoylphosphatidylcholine (POPC) bilayers showed that fast axial diffusion of erogosterol was almost completely inhibited by the coexistence of AmB. Conversely, cholesterol mobility in POPC membrane was essentially unchanged with or without AmB. These results unequivocally demonstrate that ergosterol has significant interaction with AmB in POPC bilayers. In addition, we examined the mobility of AmB using deuterium-labeled AmB, and found that, although AmB is almost immobilized in sterol-free and cholesterol-containing POPC membranes, a certain ratio of AmB molecules acquires mobility in the presence of ergosterol. The similar mobility of AmB and ergosterol in POPC bilayers confirmed the idea of the direct intermolecular interaction between ergosterol and AmB.
J. Am. Chem. Soc., 2009, 131 (33), pp 11801–11810
Solid-State NMR Investigations of the Immobilization of a BF4− Salt of a Palladium(II) Complex on Silica
Jerzy W. Wiench, Christophe Michon, Arkady Ellern, Paul Hazendonk, Adriana Iuga, Robert J. Angelici and Marek Pruski
Abstract
The structure of the silica supported palladium(II) complex [Pd(dppp)(S2C-NEt2)]BF4 (abbreviated as [Pd(dppp)(dtc)]BF4, where dppp is Ph2P(CH2)3PPh2) and interactions between the [Pd(dppp)(dtc)]+ cation, the BF4− anion, and the silica surface are studied using solid-state NMR spectroscopy. The unsupported, crystalline form of [Pd(dppp)(dtc)]BF4 is also investigated, both by X-ray diffraction and NMR. The structures of the cation and anion are found to be essentially the same in both unsupported and supported complex. The [Pd(dppp)(dtc)]BF4 loading has been determined by quantitative measurements of 11B, 19F, and 31P intensities, whereas the arrangement of anions and cations on the surface of silica has been established by two-dimensional heteronuclear correlation experiments involving 1H, 11B, 13C, 19F, 29Si, and 31P nuclei. At low coverages, the [Pd(dppp)(dtc)]+ cations are located near the BF4− anions, which in turn are immobilized directly on the surface near the Q4 sites. At higher loadings, which in this study corresponded to 0.06−0.15 mmol/g, the complexes stack on top of each other, despite the fact that the directly adsorbed molecules take up less than 10% of the silica surface. The relevance of these findings to heterogeneous catalysis is discussed.
Jerzy W. Wiench, Christophe Michon, Arkady Ellern, Paul Hazendonk, Adriana Iuga, Robert J. Angelici and Marek Pruski
Abstract
The structure of the silica supported palladium(II) complex [Pd(dppp)(S2C-NEt2)]BF4 (abbreviated as [Pd(dppp)(dtc)]BF4, where dppp is Ph2P(CH2)3PPh2) and interactions between the [Pd(dppp)(dtc)]+ cation, the BF4− anion, and the silica surface are studied using solid-state NMR spectroscopy. The unsupported, crystalline form of [Pd(dppp)(dtc)]BF4 is also investigated, both by X-ray diffraction and NMR. The structures of the cation and anion are found to be essentially the same in both unsupported and supported complex. The [Pd(dppp)(dtc)]BF4 loading has been determined by quantitative measurements of 11B, 19F, and 31P intensities, whereas the arrangement of anions and cations on the surface of silica has been established by two-dimensional heteronuclear correlation experiments involving 1H, 11B, 13C, 19F, 29Si, and 31P nuclei. At low coverages, the [Pd(dppp)(dtc)]+ cations are located near the BF4− anions, which in turn are immobilized directly on the surface near the Q4 sites. At higher loadings, which in this study corresponded to 0.06−0.15 mmol/g, the complexes stack on top of each other, despite the fact that the directly adsorbed molecules take up less than 10% of the silica surface. The relevance of these findings to heterogeneous catalysis is discussed.
J. Am. Chem. Soc., 2009, 131 (33), pp 11762–11769
89Y and 13C NMR Cluster and Carbon Cage Studies of an Yttrium Metallofullerene Family, Y3N@C2n (n = 40−43)
Wujun Fu, Liaosa Xu, Hugo Azurmendi, Jiechao Ge, Tim Fuhrer, Tianming Zuo, Jonathan Reid, Chunying Shu, Kim Harich and Harry C. Dorn*
Abstract
The members of a new family of yttrium trimetallic nitride-templated (TNT) endohedral metallofullerenes (EMFs), Y3N@C2n (n = 40−43), have been synthesized and purified. On the basis of experimental and computational 13C NMR studies, we propose cage structures for Y3N@Ih-C80 (IPR allowed), Y3N@D5h-C80 (IPR allowed), Y3N@Cs-C82 (non-IPR), Y3N@Cs-C84 (non-IPR), and Y3N@D3-C86 (IPR allowed). A significant result is the limited number of isomers found for each carbon cage. For example, there are 24 isolated pentagon rule (IPR) and 51568 non-IPR structures possible for the C84 cage, but only one major isomer of Y3N@Cs-C84 was found. The current study confirms the unique role of the trimetallic nitride (M3N)6+ cluster template in the Krtschmer−Huffman electric-arc process for fullerene cage size and high symmetry isomer selectivity. This study reports the first 89Y NMR results for Y3N@Ih-C80, Y3N@Cs(51365)-C84, and Y3N@D3(19)-C86, which reveal a progression from isotropic to restricted (Y3N)6+ cluster motional processes. Even more surprising is the sensitivity of the 89Y NMR chemical shift parameter to subtle changes in the electronic environment at each yttrium nuclide in the (Y3N)6+ cluster (more than 200 ppm for these EMFs). This 89Y NMR study suggests that 89Y NMR will evolve as a powerful tool for cluster motional studies of EMFs.
Wujun Fu, Liaosa Xu, Hugo Azurmendi, Jiechao Ge, Tim Fuhrer, Tianming Zuo, Jonathan Reid, Chunying Shu, Kim Harich and Harry C. Dorn*
Abstract
The members of a new family of yttrium trimetallic nitride-templated (TNT) endohedral metallofullerenes (EMFs), Y3N@C2n (n = 40−43), have been synthesized and purified. On the basis of experimental and computational 13C NMR studies, we propose cage structures for Y3N@Ih-C80 (IPR allowed), Y3N@D5h-C80 (IPR allowed), Y3N@Cs-C82 (non-IPR), Y3N@Cs-C84 (non-IPR), and Y3N@D3-C86 (IPR allowed). A significant result is the limited number of isomers found for each carbon cage. For example, there are 24 isolated pentagon rule (IPR) and 51568 non-IPR structures possible for the C84 cage, but only one major isomer of Y3N@Cs-C84 was found. The current study confirms the unique role of the trimetallic nitride (M3N)6+ cluster template in the Krtschmer−Huffman electric-arc process for fullerene cage size and high symmetry isomer selectivity. This study reports the first 89Y NMR results for Y3N@Ih-C80, Y3N@Cs(51365)-C84, and Y3N@D3(19)-C86, which reveal a progression from isotropic to restricted (Y3N)6+ cluster motional processes. Even more surprising is the sensitivity of the 89Y NMR chemical shift parameter to subtle changes in the electronic environment at each yttrium nuclide in the (Y3N)6+ cluster (more than 200 ppm for these EMFs). This 89Y NMR study suggests that 89Y NMR will evolve as a powerful tool for cluster motional studies of EMFs.
Tuesday, October 13, 2009
J. Am. Chem. Soc., 2009, 131 (35), pp 12745–12754
Measurement of Methyl Group Motional Parameters of Invisible, Excited Protein States by NMR Spectroscopy
D. Flemming Hansen, Pramodh Vallurupalli and Lewis E. Kay*
Abstract
An understanding of many biological processes can only be achieved through studies of the structure (enthalpy) and motions (entropy) of the key molecules that are involved, including those that are formed only transiently and with low population. These transiently formed, low populated states are invisible to most biophysical techniques but in many cases they can be studied in detail using relaxation dispersion NMR spectroscopy. Relaxation dispersion methodology has recently been described for the measurement of protein backbone excited state chemical shifts as well as bond vector orientations, which form the basis for structural studies of these invisible conformers. It is of interest to extend such studies by quantifying motional parameters of the excited state, providing a more complete description of the energy landscape that drives the biochemical event in question. Herein we describe a relaxation dispersion method for measuring site-specific motional parameters of methyl containing residues in the excited state. The approach is applied to the invisible unfolded state of the G48M Fyn SH3 domain that is in exchange with the folded conformation. Not surprisingly, the degree of disorder is in general higher in the unfolded state than in the folded conformer, although there is some ordering of side-chains in the unfolded state toward the C-terminal region of the domain. The development of the present methodology provides the first step toward characterizing the motional properties of invisible conformers, complementing the structural information that is already available from relaxation dispersion studies.
D. Flemming Hansen, Pramodh Vallurupalli and Lewis E. Kay*
Abstract
An understanding of many biological processes can only be achieved through studies of the structure (enthalpy) and motions (entropy) of the key molecules that are involved, including those that are formed only transiently and with low population. These transiently formed, low populated states are invisible to most biophysical techniques but in many cases they can be studied in detail using relaxation dispersion NMR spectroscopy. Relaxation dispersion methodology has recently been described for the measurement of protein backbone excited state chemical shifts as well as bond vector orientations, which form the basis for structural studies of these invisible conformers. It is of interest to extend such studies by quantifying motional parameters of the excited state, providing a more complete description of the energy landscape that drives the biochemical event in question. Herein we describe a relaxation dispersion method for measuring site-specific motional parameters of methyl containing residues in the excited state. The approach is applied to the invisible unfolded state of the G48M Fyn SH3 domain that is in exchange with the folded conformation. Not surprisingly, the degree of disorder is in general higher in the unfolded state than in the folded conformer, although there is some ordering of side-chains in the unfolded state toward the C-terminal region of the domain. The development of the present methodology provides the first step toward characterizing the motional properties of invisible conformers, complementing the structural information that is already available from relaxation dispersion studies.
Cryst. Growth Des., 2009, 9 (9), pp 4051–4059
Solid-State NMR and X-ray Diffraction Study of Structure and Dynamics of Dihydrate and Anhydrous Form of Tyr-Ala-Phe
Katarzyna Trzeciak-Karlikowska, Anna Bujacz, Agata Jeziorna, Włodzimierz Ciesielski†, Grzegorz D. Bujacz, Jarosław Gajda†, Danuta Pentak and Marek J. Potrzebowski*
Tyr-d-Ala-Phe is a “message sequence” of naturally occurring opioid peptides, deltorphin I (Tyr-d-Ala-Phe-Asp-Val-Val-Gly-NH2), deltorphin II (Tyr-d-Ala-Phe-Glu-Val-Val-Gly-NH2), and dermorphin (Tyr-d-Ala-Phe-Gly-Tyr-Pro-Ser-NH2). Analogous heptapeptides containing l-alanine instead of d-alanine are not biologically active. In a previous paper (J. Phys. Chem. B 2004, 108 (14), 4535−4545), we reported X-ray and NMR data for Tyr-d-Ala-Phe. In the current report, we present structural studies of Tyr-Ala-Phe, a “false message sequence” of opioid peptides. It has been found that Tyr-Ala-Phe crystallizes in two forms, as anhydrate (Form I) and dihydrate (Form II). Crystal and molecular structure of both forms was established by means of low-temperature X-ray measurements. Form I is orthorhombic with space group P212121, while II is hexagonal with space group P65. Solid-state NMR was employed to study the structure and molecular dynamics of I and II. Analysis of cross-polarization buildup curves and 13C chemical shift tensor (CST) parameters obtained by a two-dimensional PASS experiment have revealed a dramatic difference in the molecular motion of both modifications. 13C T1 relaxation times have provided further evidence confirming distinct molecular dynamics. The attempt to understand the role of the stereochemistry of Ala residue in opioid peptide sequences in relation to intramolecular interactions and preorganization mechanisms is presented.
Katarzyna Trzeciak-Karlikowska, Anna Bujacz, Agata Jeziorna, Włodzimierz Ciesielski†, Grzegorz D. Bujacz, Jarosław Gajda†, Danuta Pentak and Marek J. Potrzebowski*
Tyr-d-Ala-Phe is a “message sequence” of naturally occurring opioid peptides, deltorphin I (Tyr-d-Ala-Phe-Asp-Val-Val-Gly-NH2), deltorphin II (Tyr-d-Ala-Phe-Glu-Val-Val-Gly-NH2), and dermorphin (Tyr-d-Ala-Phe-Gly-Tyr-Pro-Ser-NH2). Analogous heptapeptides containing l-alanine instead of d-alanine are not biologically active. In a previous paper (J. Phys. Chem. B 2004, 108 (14), 4535−4545), we reported X-ray and NMR data for Tyr-d-Ala-Phe. In the current report, we present structural studies of Tyr-Ala-Phe, a “false message sequence” of opioid peptides. It has been found that Tyr-Ala-Phe crystallizes in two forms, as anhydrate (Form I) and dihydrate (Form II). Crystal and molecular structure of both forms was established by means of low-temperature X-ray measurements. Form I is orthorhombic with space group P212121, while II is hexagonal with space group P65. Solid-state NMR was employed to study the structure and molecular dynamics of I and II. Analysis of cross-polarization buildup curves and 13C chemical shift tensor (CST) parameters obtained by a two-dimensional PASS experiment have revealed a dramatic difference in the molecular motion of both modifications. 13C T1 relaxation times have provided further evidence confirming distinct molecular dynamics. The attempt to understand the role of the stereochemistry of Ala residue in opioid peptide sequences in relation to intramolecular interactions and preorganization mechanisms is presented.
Monday, September 28, 2009
Science, v325
Some nice 27Al SSNMR spectra can be seen here:
Science, v325, page 1670
Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on -Al2O3
Ja Hun Kwak,1,* Jianzhi Hu,1 Donghai Mei,1 Cheol-Woo Yi,2 Do Heui Kim,1 Charles H. F. Peden,1,* Lawrence F. Allard,3 Janos Szanyi1,*
In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a -Al2O3 catalyst support material. The results obtained show that coordinatively unsaturated pentacoordinate Al3+ (Al3+penta) centers present on the (100) facets of the -Al2O3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al3+penta = 1), whereas two-dimensional Pt rafts form at higher coverages.
1 Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Post Office Box 999, MSIN K8-87, Richland, WA 99352, USA.2 Department of Chemistry and Institute of Basic Science, Sungshin Women’s University, Seoul 136-742, Repulic of Korea.3 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Science, v325, page 1670
Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on -Al2O3
Ja Hun Kwak,1,* Jianzhi Hu,1 Donghai Mei,1 Cheol-Woo Yi,2 Do Heui Kim,1 Charles H. F. Peden,1,* Lawrence F. Allard,3 Janos Szanyi1,*
In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a -Al2O3 catalyst support material. The results obtained show that coordinatively unsaturated pentacoordinate Al3+ (Al3+penta) centers present on the (100) facets of the -Al2O3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al3+penta = 1), whereas two-dimensional Pt rafts form at higher coverages.
1 Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Post Office Box 999, MSIN K8-87, Richland, WA 99352, USA.2 Department of Chemistry and Institute of Basic Science, Sungshin Women’s University, Seoul 136-742, Repulic of Korea.3 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Thursday, September 03, 2009
http://www.dailymail.co.uk/sciencetech/article-1209726/Single-molecule-million-times-smaller-grain-sand-pictured-time.html
Single molecule, one million times smaller than a grain of sand, pictured for first time
By Claire Bates
Last updated at 11:45 AM on 31st August 2009
Comments (330) Add to My Stories It may look like a piece of honeycomb, but this lattice-shaped image is the first ever close-up view of a single molecule.
Scientists from IBM used an atomic force microscope (AFM) to reveal the chemical bonds within a molecule.
'This is the first time that all the atoms in a molecule have been imaged,' lead researcher Leo Gross said.
The delicate inner structure of a pentacene molecule has been imaged with an atomic force microscope
The researchers focused on a single molecule of pentacene, which is commonly used in solar cells. The rectangular-shaped organic molecule is made up of 22 carbon atoms and 14 hydrogen atoms.
In the image above the hexagonal shapes of the five carbon rings are clear and even the positions of the hydrogen atoms around the carbon rings can be seen.
To give some perspective, the space between the carbon rings is only 0.14 nanometers across, which is roughly one million times smaller than the diameter of a grain of sand.
Textbook model: A computer-generated image of how we're used to seeing a molecule represented with balls and sticks
'If you think about how a doctor uses an X-ray to image bones and organs inside the human body, we are using the atomic force microscope to image the atomic structures that are the backbones of individual molecules,' said IBM researcher Gerhard Meyer.
A 3D view showing how a single carbon monoxide molecule was used to create the image using a 'tuning fork' effect
The team from IBM Research Zurich said the results could have a huge impact of the field of nanotechnology, which seeks to understand and control some of the smallest objects known to mankind.
The AFM uses a sharp metal tip that acts like a tuning fork to measure the tiny forces between the tip and the molecule. This requires great precision as the tip moves within a nanometer of the sample.
'Above the skeleton of the molecular backbone (of the pentacene) you get a different detuning than above the surface the molecule is lying on,' Mr Gross said.
This detuning is then measured and converted into an image.
To stop the tip from absorbing the pentacene molecule, the researchers replaced the metal with a single molecule of carbon monoxide. This was found to be more stable and created weaker electrostatic attractions with the pentacene, creating a higher resolution image.
Enlarge IBM researchers Nikolaj Moll, Reto Schlittler, Gerhard Meyer, Fabian Mohn and Leo Gross (l-r) stand behind an atomic force microscope Photo taken by Michael Lowry Image courtesy of IBM Research - Zurich
The experiment was also performed inside a high vacuum at the extremely cold temperature of -268C to avoid stray gas molecules or atomic vibrations from affecting the measurements.
'Eventually we want to investigate using molecules for molecular electronics,' Mr Gross said.
'We want to use molecules as wires
Read more: http://www.dailymail.co.uk/sciencetech/article-1209726/Single-molecule-million-times-smaller-grain-sand-pictured-time.html#ixzz0Q6QeWXOq
By Claire Bates
Last updated at 11:45 AM on 31st August 2009
Comments (330) Add to My Stories It may look like a piece of honeycomb, but this lattice-shaped image is the first ever close-up view of a single molecule.
Scientists from IBM used an atomic force microscope (AFM) to reveal the chemical bonds within a molecule.
'This is the first time that all the atoms in a molecule have been imaged,' lead researcher Leo Gross said.
The delicate inner structure of a pentacene molecule has been imaged with an atomic force microscope
The researchers focused on a single molecule of pentacene, which is commonly used in solar cells. The rectangular-shaped organic molecule is made up of 22 carbon atoms and 14 hydrogen atoms.
In the image above the hexagonal shapes of the five carbon rings are clear and even the positions of the hydrogen atoms around the carbon rings can be seen.
To give some perspective, the space between the carbon rings is only 0.14 nanometers across, which is roughly one million times smaller than the diameter of a grain of sand.
Textbook model: A computer-generated image of how we're used to seeing a molecule represented with balls and sticks
'If you think about how a doctor uses an X-ray to image bones and organs inside the human body, we are using the atomic force microscope to image the atomic structures that are the backbones of individual molecules,' said IBM researcher Gerhard Meyer.
A 3D view showing how a single carbon monoxide molecule was used to create the image using a 'tuning fork' effect
The team from IBM Research Zurich said the results could have a huge impact of the field of nanotechnology, which seeks to understand and control some of the smallest objects known to mankind.
The AFM uses a sharp metal tip that acts like a tuning fork to measure the tiny forces between the tip and the molecule. This requires great precision as the tip moves within a nanometer of the sample.
'Above the skeleton of the molecular backbone (of the pentacene) you get a different detuning than above the surface the molecule is lying on,' Mr Gross said.
This detuning is then measured and converted into an image.
To stop the tip from absorbing the pentacene molecule, the researchers replaced the metal with a single molecule of carbon monoxide. This was found to be more stable and created weaker electrostatic attractions with the pentacene, creating a higher resolution image.
Enlarge IBM researchers Nikolaj Moll, Reto Schlittler, Gerhard Meyer, Fabian Mohn and Leo Gross (l-r) stand behind an atomic force microscope Photo taken by Michael Lowry Image courtesy of IBM Research - Zurich
The experiment was also performed inside a high vacuum at the extremely cold temperature of -268C to avoid stray gas molecules or atomic vibrations from affecting the measurements.
'Eventually we want to investigate using molecules for molecular electronics,' Mr Gross said.
'We want to use molecules as wires
Read more: http://www.dailymail.co.uk/sciencetech/article-1209726/Single-molecule-million-times-smaller-grain-sand-pictured-time.html#ixzz0Q6QeWXOq
Tuesday, September 01, 2009
J. Am. Chem. Soc., 2009, 131 (31), pp 11062–11079
Searching for Microporous, Strongly Basic Catalysts: Experimental and Calculated 29Si NMR Spectra of Heavily Nitrogen-Doped Y Zeolites
Fulya Dogan†, Karl D. Hammond‡, Geoffrey A. Tompsett‡, Hua Huo†, W. Curtis Conner, Jr.‡, Scott M. Auerbach‡§ and Clare P. Grey*†
Nitrogen substituted zeolites with high crystallinity and microporosity are obtained by nitrogen substitution for oxygen in zeolite Y. The substitution reaction is performed under ammonia flow by varying the temperature and reaction time. We examine the effect of aluminum content and charge-compensating cation (H+/Na+/NH4+) on the degree of nitrogen substitution and on the preference for substitution of Si−O−Al vs Si−O−Si linkages in the FAU zeolite structure. Silicon-29 magic angle spinning (MAS) nuclear magnetic resonance (NMR) and 1H/29Si cross-polarization MAS NMR spectroscopy have been used to probe the different local environments of the nitrogen-substituted zeolites. Experimental data are compared to simulated NMR spectra obtained by constructing a compendium (>100) of zeolite clusters with and without nitrogen, and by performing quantum calculations of chemical shifts for the NMR-active nuclei in each cluster. The simulated NMR spectra, which assume peak intensities predicted by statistical analysis, agree remarkably well with the experimental data. The results show that high levels of nitrogen substitution can be achieved while maintaining porosity, particularly for NaY and low-aluminum HY materials, without significant loss in crystallinity. Experiments performed at lower temperatures (750−800 °C) show a preference for substitution at Si−OH−Al sites. No preference is seen for reactions performed at higher temperatures and longer reaction times (e.g., 850 °C and 48 h).
Fulya Dogan†, Karl D. Hammond‡, Geoffrey A. Tompsett‡, Hua Huo†, W. Curtis Conner, Jr.‡, Scott M. Auerbach‡§ and Clare P. Grey*†
Nitrogen substituted zeolites with high crystallinity and microporosity are obtained by nitrogen substitution for oxygen in zeolite Y. The substitution reaction is performed under ammonia flow by varying the temperature and reaction time. We examine the effect of aluminum content and charge-compensating cation (H+/Na+/NH4+) on the degree of nitrogen substitution and on the preference for substitution of Si−O−Al vs Si−O−Si linkages in the FAU zeolite structure. Silicon-29 magic angle spinning (MAS) nuclear magnetic resonance (NMR) and 1H/29Si cross-polarization MAS NMR spectroscopy have been used to probe the different local environments of the nitrogen-substituted zeolites. Experimental data are compared to simulated NMR spectra obtained by constructing a compendium (>100) of zeolite clusters with and without nitrogen, and by performing quantum calculations of chemical shifts for the NMR-active nuclei in each cluster. The simulated NMR spectra, which assume peak intensities predicted by statistical analysis, agree remarkably well with the experimental data. The results show that high levels of nitrogen substitution can be achieved while maintaining porosity, particularly for NaY and low-aluminum HY materials, without significant loss in crystallinity. Experiments performed at lower temperatures (750−800 °C) show a preference for substitution at Si−OH−Al sites. No preference is seen for reactions performed at higher temperatures and longer reaction times (e.g., 850 °C and 48 h).
J. Am. Chem. Soc., 2009, 131 (31), pp 10834–10835
Observation of NMR Signals from Proteins Introduced into Living Mammalian Cells by Reversible Membrane Permeabilization Using a Pore-Forming Toxin, Streptolysin O
Shinji Ogino†, Satoshi Kubo†, Ryo Umemoto†, Shuxian Huang†, Noritaka Nishida† and Ichio Shimada*†‡
We have developed a new in-cell NMR method that is applicable to any type of cell and does not require target protein modification or specialized equipment. The stable-isotope-labeled target protein, thymosin β4 (Tβ4), was delivered to 293F cells, which were permeabilized by a pore-forming toxin, streptolysin O, and resealed by Ca2+ after Tβ4 uptake. As a result, we successfully observed 1H−15N HSQC signals originating from the Tβ4, including those from the N-terminal acetylation, which had occurred inside the cell as a post-translational modification.
Shinji Ogino†, Satoshi Kubo†, Ryo Umemoto†, Shuxian Huang†, Noritaka Nishida† and Ichio Shimada*†‡
We have developed a new in-cell NMR method that is applicable to any type of cell and does not require target protein modification or specialized equipment. The stable-isotope-labeled target protein, thymosin β4 (Tβ4), was delivered to 293F cells, which were permeabilized by a pore-forming toxin, streptolysin O, and resealed by Ca2+ after Tβ4 uptake. As a result, we successfully observed 1H−15N HSQC signals originating from the Tβ4, including those from the N-terminal acetylation, which had occurred inside the cell as a post-translational modification.
J. Am. Chem. Soc., 2009, 131 (31), pp 10832–10833
Measuring the Signs of 1Hα Chemical Shift Differences Between Ground and Excited Protein States by Off-Resonance Spin-Lock R1ρ NMR Spectroscopy
Renate Auer†‡, Philipp Neudecker‡, D. Ranjith Muhandiram‡, Patrik Lundstrm‡§, D. Flemming Hansen‡, Robert Konrat† and Lewis E. Kay*‡
Analysis of Carr−Purcell−Meiboom−Gill (CPMG) relaxation dispersion NMR profiles provides the kinetics and thermodynamics of millisecond-time-scale exchange processes involving the interconversion of populated ground and invisible excited states. In addition, the absolute values of chemical shift differences between NMR probes in the exchanging states, |Δ|, are also extracted. Herein, we present a simple experiment for obtaining the sign of 1Hα Δ values by measuring off-resonance 1Hα decay rates, R1ρ, using weak proton spin-lock fields. A pair of R1ρ values is measured with a spin-lock field applied |Δω| downfield and upfield of the major-state peak. In many cases, these two relaxation rates differ substantially, with the larger one corresponding to the case where the spin-lock field coincides with the resonance frequency of the probe in the minor state. The utility of the methodology is demonstrated first on a system involving protein ligand exchange and subsequently on an SH3 domain exchanging between a folded state and its on-pathway folding intermediate. With this experiment, it thus becomes possible to determine 1Hα chemical shifts of the invisible excited state, which can be used as powerful restraints in defining the structural properties of these elusive conformers.
Renate Auer†‡, Philipp Neudecker‡, D. Ranjith Muhandiram‡, Patrik Lundstrm‡§, D. Flemming Hansen‡, Robert Konrat† and Lewis E. Kay*‡
Analysis of Carr−Purcell−Meiboom−Gill (CPMG) relaxation dispersion NMR profiles provides the kinetics and thermodynamics of millisecond-time-scale exchange processes involving the interconversion of populated ground and invisible excited states. In addition, the absolute values of chemical shift differences between NMR probes in the exchanging states, |Δ|, are also extracted. Herein, we present a simple experiment for obtaining the sign of 1Hα Δ values by measuring off-resonance 1Hα decay rates, R1ρ, using weak proton spin-lock fields. A pair of R1ρ values is measured with a spin-lock field applied |Δω| downfield and upfield of the major-state peak. In many cases, these two relaxation rates differ substantially, with the larger one corresponding to the case where the spin-lock field coincides with the resonance frequency of the probe in the minor state. The utility of the methodology is demonstrated first on a system involving protein ligand exchange and subsequently on an SH3 domain exchanging between a folded state and its on-pathway folding intermediate. With this experiment, it thus becomes possible to determine 1Hα chemical shifts of the invisible excited state, which can be used as powerful restraints in defining the structural properties of these elusive conformers.
J. Am. Chem. Soc., 2009, 131 (31), pp 10830–10831
High Resolution Heteronuclear Correlation NMR Spectroscopy of an Antimicrobial Peptide in Aligned Lipid Bilayers: Peptide−Water Interactions at the Water−Bilayer Interface
Riqiang Fu*†, Eric D. Gordon‡, Daniel J. Hibbard‡ and Myriam Cotten*§
High-resolution two-dimensional (2D) 1H−15N heteronuclear correlation (HETCOR) spectroscopy has been used to characterize the structure and dynamics of 15N-backbone labeled antimicrobial piscidin 1 (p1) oriented in “native-like” hydrated lipid bilayers. Piscidin belongs to a family of amphipatic cationic antimicrobial peptides, which are membrane-active and have broad spectrum antimicrobial activity on bacteria. When the 1H chemical shifts are encoded by the 1H−15N dipolar couplings, 2D dipolar-encoded HETCOR (i.e., de-HETCOR) solid-state NMR spectra yield high resolution 1H and 15N chemical shifts as well as 1H−15N heteronuclear dipolar couplings. Several advantages of HETCOR and de-HETCOR techniques that emerge from our investigations could facilitate the atomic-level investigations of structure−function relationships in membrane-active peptides and membrane-bound species. First, the de-HETCOR NMR spectrum of a ten-site 15N-labeled sample of p1 aligned in hydrated lipid bilayers can resolve resonances that are overlapped in the standard HETCOR spectrum. Second, the resolution in de-HETCOR spectra of p1 improves significantly at higher magnetic field due to an enhanced alignment that improves spectrum definition uniformly. Third, the HETCOR spectrum of 15N−K14 p1 oriented in hydrated lipid bilayers displays not only the expected crosscorrelation between the chemical shifts of bonded amide1H and 15N spins but also a cross peak between the 1H chemical shift from bulk water and the 15N chemical shift from the labeled amide nitrogen. This information provides new insights into the intermolecular interactions of an amphipathic antimicrobial peptide optimized to partition at the water-bilayer interface and may have implications at the biological level.
Riqiang Fu*†, Eric D. Gordon‡, Daniel J. Hibbard‡ and Myriam Cotten*§
High-resolution two-dimensional (2D) 1H−15N heteronuclear correlation (HETCOR) spectroscopy has been used to characterize the structure and dynamics of 15N-backbone labeled antimicrobial piscidin 1 (p1) oriented in “native-like” hydrated lipid bilayers. Piscidin belongs to a family of amphipatic cationic antimicrobial peptides, which are membrane-active and have broad spectrum antimicrobial activity on bacteria. When the 1H chemical shifts are encoded by the 1H−15N dipolar couplings, 2D dipolar-encoded HETCOR (i.e., de-HETCOR) solid-state NMR spectra yield high resolution 1H and 15N chemical shifts as well as 1H−15N heteronuclear dipolar couplings. Several advantages of HETCOR and de-HETCOR techniques that emerge from our investigations could facilitate the atomic-level investigations of structure−function relationships in membrane-active peptides and membrane-bound species. First, the de-HETCOR NMR spectrum of a ten-site 15N-labeled sample of p1 aligned in hydrated lipid bilayers can resolve resonances that are overlapped in the standard HETCOR spectrum. Second, the resolution in de-HETCOR spectra of p1 improves significantly at higher magnetic field due to an enhanced alignment that improves spectrum definition uniformly. Third, the HETCOR spectrum of 15N−K14 p1 oriented in hydrated lipid bilayers displays not only the expected crosscorrelation between the chemical shifts of bonded amide1H and 15N spins but also a cross peak between the 1H chemical shift from bulk water and the 15N chemical shift from the labeled amide nitrogen. This information provides new insights into the intermolecular interactions of an amphipathic antimicrobial peptide optimized to partition at the water-bilayer interface and may have implications at the biological level.
J. Am. Chem. Soc., 2009, 131 (31), pp 10816–10817
Transverse-Dephasing Optimized Homonuclear J-Decoupling in Solid-State NMR Spectroscopy of Uniformly 13C-Labeled Proteins
Sgolne Laage†, Anne Lesage†, Lyndon Emsley†, Ivano Bertini‡, Isabella C. Felli‡, Roberta Pierattelli‡ and Guido Pintacuda*†
A transverse-dephasing optimized S3E (spin-state selective excitation) method is implemented in solid-state NMR experiments of uniformly labeled protein samples, and it is shown to provide a simultaneous significant gain in both resolution (up to a factor of 2.2) and sensitivity (up to a factor of 1.4). This is illustrated with high-resolution NCO and NCA correlations of a microcrystalline sample of the oxidized form of the 153 residue human Cu(II)Zn(II) superoxide dismutase (SOD), a dimeric paramagnetic enzyme of 32 kDa. This method allows the resolution of 145 signals in the highly crowded carbonyl region in the NCO correlation spectrum.
Sgolne Laage†, Anne Lesage†, Lyndon Emsley†, Ivano Bertini‡, Isabella C. Felli‡, Roberta Pierattelli‡ and Guido Pintacuda*†
A transverse-dephasing optimized S3E (spin-state selective excitation) method is implemented in solid-state NMR experiments of uniformly labeled protein samples, and it is shown to provide a simultaneous significant gain in both resolution (up to a factor of 2.2) and sensitivity (up to a factor of 1.4). This is illustrated with high-resolution NCO and NCA correlations of a microcrystalline sample of the oxidized form of the 153 residue human Cu(II)Zn(II) superoxide dismutase (SOD), a dimeric paramagnetic enzyme of 32 kDa. This method allows the resolution of 145 signals in the highly crowded carbonyl region in the NCO correlation spectrum.
Friday, August 14, 2009
PCCP: Solid-State NMR themed issue
A great collection of papers, plus two "recent advances" articles on spin-1/2 and quadrupolar nuclei.
Guest Editors: Paul Hodgkinson, Durham, UK, and Stephen Wimperis, Glasgow, UK
Editorial
Solid-State NMR Spectroscopy
Phys. Chem. Chem. Phys., 2009, DOI: 10.1039/b914008p
Perspectives
Recent advances in solid-state NMR spectroscopy of spin
I = 1/2 nuclei
Anne Lesage, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907733m
Recent advances in solid-state NMR spectroscopy of
quadrupolar nuclei
Sharon E. Ashbrook, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b907183k
Papers
Solid-state 17O NMR as a sensitive probe of keto and gemdiol
forms of -keto acid derivatives
Jianfeng Zhu, Amanda J. Geris and Gang Wu, Phys. Chem.
Chem. Phys., 2009, DOI: 10.1039/b906438a
Anomalous resonances in 29Si and 27Al NMR spectra of
pyrope ([Mg,Fe]3Al2Si3O12) garnets: effects of paramagnetic
cations
Jonathan F. Stebbins and Kimberly E. Kelsey, Phys. Chem.
Chem. Phys., 2009, DOI: 10.1039/b904731j
New opportunities in acquisition and analysis of natural
abundance complex solid-state 33S MAS NMR spectra:
(CH3NH3)2WS4
Hans J. Jakobsen, Henrik Bildsøe, Jørgen Skibsted, Michael
Brorson, Bikshandarkoil R. Srinivasan, Christian Näther and
Wolfgang Bensch, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b904841n
An analytic expression for the double quantum 1H nuclear
magnetic resonance build-up and decay from a Gaussian
polymer chain with dynamics governed by a single
relaxation time
Michael E. Ries and Michael G. Brereton, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b905350f
Static solid-state 14N NMR and computational studies of
nitrogen EFG tensors in some crystalline amino acids
Luke A. O Dell and Robert W. Schurko, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906114b
Solid state deuteron relaxation time anisotropy measured
with multiple echo acquisition
Robert L. Vold, Gina L. Hoatson, Liliya Vugmeyster, Dmitry
Ostrovsky and Peter J. De Castro, Phys. Chem. Chem. Phys.,
2009, DOI: 10.1039/b907343d
Application of multinuclear magnetic resonance and gaugeincluding
projector-augmented-wave calculations to the
study of solid group 13 chlorides
Rebecca P. Chapman and David L. Bryce, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906627f
High-resolution 17O double-rotation NMR characterization of
ring and non-ring oxygen in vitreous B2O3
Alan Wong, Andy P. Howes, Ben Parkinson, Tiit Anupõld, Ago
Samoson, Diane Holland and Ray Dupree, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906501f
Probing chemical disorder in glasses using silicon-29 NMR
spectral editing
Julien Hiet, Michaël Deschamps, Nadia Pellerin, Franck Fayon and
Dominique Massiot, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b906399d
GIPAW (gauge including projected augmented wave) and local
dynamics in 13C and 29Si solid state NMR: the study case of
silsesquioxanes (RSiO1.5)8
Christel Gervais, Laure Bonhomme-Coury, Francesco Mauri,
Florence Babonneau and Christian Bonhomme, Phys. Chem.
Chem. Phys., 2009
DOI: 10.1039/b907450c
Determining relative proton–proton proximities from the buildup
of two-dimensional correlation peaks in 1H double-quantum
MAS NMR: insight from multi-spin density-matrix simulations
Jonathan P. Bradley, Carmen Tripon, Claudiu Filip and Steven P.
Brown, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b906400a
Manifestation of Landau level effects in optically-pumped NMR
of semi-insulating GaAs
Stacy Mui, Kannan Ramaswamy, Christopher J. Stanton, Scott A.
Crooker and Sophia E. Hayes, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907588g
Motional heterogeneity in single-site silica-supported species
revealed by deuteron NMR
Julia Gath, Gina L. Hoaston, Robert L. Vold, Romain Berthoud,
Christophe Copéret, Mary Grellier, Sylviane Sabo-Etienne, Anne
Lesage and Lyndon Emsley, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907665d
Magnesium silicate dissolution investigated by 29Si MAS, 1H–
29Si CPMAS, 25Mg QCPMG, and 1H–25Mg CP QCPMG NMR
Michael C. Davis, William J. Brouwer, David J. Wesolowski,
Lawrence M. Anovitz, Andrew S. Lipton and Karl T. Mueller, Phys.
Chem. Chem. Phys., 2009
DOI: 10.1039/b907494e
Intermediate motions and dipolar couplings as studied by Lee–
Goldburg cross-polarization NMR: Hartmann–Hahn matching
profiles
Marcio Fernando Cobo, Kate ina Mali áková, Detlef Reichert, Kay
Saalwächter and Eduardo Ribeiro deAzevedo, Phys. Chem.
Chem. Phys., 2009
DOI: 10.1039/b907674c
Measurements of relative chemical shift tensor orientations in
solid-state NMR: new slow magic angle spinning dipolar
recoupling experiments
Andrew P. S. Jurd and Jeremy J. Titman, Phys. Chem. Chem.
Phys., 2009
DOI: 10.1039/b906814g
Signal loss in 1D magic-angle spinning exchange NMR
(CODEX): radio-frequency limitations and intermediate
motions
Christiane Hackel, Cornelius Franz, Anja Achilles, Kay Saalwächter
and Detlef Reichert, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b906527j
Calculation of fluorine chemical shift tensors for the
interpretation of oriented 19F-NMR spectra of gramicidin A in
membranes
Ulrich Sternberg, Marco Klipfel, Stephan L. Grage, Raiker Witter
and Anne S. Ulrich, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b908236k
J-Based 3D sidechain correlation in solid-state proteins
Ye Tian, Lingling Chen, Dimitri Niks, J. Michael Kaiser, Jinfeng
Lai, Chad M. Rienstra, Michael F. Dunn and Leonard J. Mueller,
Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b911570f
Natural abundance 13C and 15N solid-state NMR analysis of
paramagnetic transition-metal cyanide coordination polymers
Pedro M. Aguiar, Michael J. Katz, Daniel B. Leznoff and Scott
Kroeker, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907747b
Guest Editors: Paul Hodgkinson, Durham, UK, and Stephen Wimperis, Glasgow, UK
Editorial
Solid-State NMR Spectroscopy
Phys. Chem. Chem. Phys., 2009, DOI: 10.1039/b914008p
Perspectives
Recent advances in solid-state NMR spectroscopy of spin
I = 1/2 nuclei
Anne Lesage, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907733m
Recent advances in solid-state NMR spectroscopy of
quadrupolar nuclei
Sharon E. Ashbrook, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b907183k
Papers
Solid-state 17O NMR as a sensitive probe of keto and gemdiol
forms of -keto acid derivatives
Jianfeng Zhu, Amanda J. Geris and Gang Wu, Phys. Chem.
Chem. Phys., 2009, DOI: 10.1039/b906438a
Anomalous resonances in 29Si and 27Al NMR spectra of
pyrope ([Mg,Fe]3Al2Si3O12) garnets: effects of paramagnetic
cations
Jonathan F. Stebbins and Kimberly E. Kelsey, Phys. Chem.
Chem. Phys., 2009, DOI: 10.1039/b904731j
New opportunities in acquisition and analysis of natural
abundance complex solid-state 33S MAS NMR spectra:
(CH3NH3)2WS4
Hans J. Jakobsen, Henrik Bildsøe, Jørgen Skibsted, Michael
Brorson, Bikshandarkoil R. Srinivasan, Christian Näther and
Wolfgang Bensch, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b904841n
An analytic expression for the double quantum 1H nuclear
magnetic resonance build-up and decay from a Gaussian
polymer chain with dynamics governed by a single
relaxation time
Michael E. Ries and Michael G. Brereton, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b905350f
Static solid-state 14N NMR and computational studies of
nitrogen EFG tensors in some crystalline amino acids
Luke A. O Dell and Robert W. Schurko, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906114b
Solid state deuteron relaxation time anisotropy measured
with multiple echo acquisition
Robert L. Vold, Gina L. Hoatson, Liliya Vugmeyster, Dmitry
Ostrovsky and Peter J. De Castro, Phys. Chem. Chem. Phys.,
2009, DOI: 10.1039/b907343d
Application of multinuclear magnetic resonance and gaugeincluding
projector-augmented-wave calculations to the
study of solid group 13 chlorides
Rebecca P. Chapman and David L. Bryce, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906627f
High-resolution 17O double-rotation NMR characterization of
ring and non-ring oxygen in vitreous B2O3
Alan Wong, Andy P. Howes, Ben Parkinson, Tiit Anupõld, Ago
Samoson, Diane Holland and Ray Dupree, Phys. Chem. Chem.
Phys., 2009, DOI: 10.1039/b906501f
Probing chemical disorder in glasses using silicon-29 NMR
spectral editing
Julien Hiet, Michaël Deschamps, Nadia Pellerin, Franck Fayon and
Dominique Massiot, Phys. Chem. Chem. Phys., 2009,
DOI: 10.1039/b906399d
GIPAW (gauge including projected augmented wave) and local
dynamics in 13C and 29Si solid state NMR: the study case of
silsesquioxanes (RSiO1.5)8
Christel Gervais, Laure Bonhomme-Coury, Francesco Mauri,
Florence Babonneau and Christian Bonhomme, Phys. Chem.
Chem. Phys., 2009
DOI: 10.1039/b907450c
Determining relative proton–proton proximities from the buildup
of two-dimensional correlation peaks in 1H double-quantum
MAS NMR: insight from multi-spin density-matrix simulations
Jonathan P. Bradley, Carmen Tripon, Claudiu Filip and Steven P.
Brown, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b906400a
Manifestation of Landau level effects in optically-pumped NMR
of semi-insulating GaAs
Stacy Mui, Kannan Ramaswamy, Christopher J. Stanton, Scott A.
Crooker and Sophia E. Hayes, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907588g
Motional heterogeneity in single-site silica-supported species
revealed by deuteron NMR
Julia Gath, Gina L. Hoaston, Robert L. Vold, Romain Berthoud,
Christophe Copéret, Mary Grellier, Sylviane Sabo-Etienne, Anne
Lesage and Lyndon Emsley, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907665d
Magnesium silicate dissolution investigated by 29Si MAS, 1H–
29Si CPMAS, 25Mg QCPMG, and 1H–25Mg CP QCPMG NMR
Michael C. Davis, William J. Brouwer, David J. Wesolowski,
Lawrence M. Anovitz, Andrew S. Lipton and Karl T. Mueller, Phys.
Chem. Chem. Phys., 2009
DOI: 10.1039/b907494e
Intermediate motions and dipolar couplings as studied by Lee–
Goldburg cross-polarization NMR: Hartmann–Hahn matching
profiles
Marcio Fernando Cobo, Kate ina Mali áková, Detlef Reichert, Kay
Saalwächter and Eduardo Ribeiro deAzevedo, Phys. Chem.
Chem. Phys., 2009
DOI: 10.1039/b907674c
Measurements of relative chemical shift tensor orientations in
solid-state NMR: new slow magic angle spinning dipolar
recoupling experiments
Andrew P. S. Jurd and Jeremy J. Titman, Phys. Chem. Chem.
Phys., 2009
DOI: 10.1039/b906814g
Signal loss in 1D magic-angle spinning exchange NMR
(CODEX): radio-frequency limitations and intermediate
motions
Christiane Hackel, Cornelius Franz, Anja Achilles, Kay Saalwächter
and Detlef Reichert, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b906527j
Calculation of fluorine chemical shift tensors for the
interpretation of oriented 19F-NMR spectra of gramicidin A in
membranes
Ulrich Sternberg, Marco Klipfel, Stephan L. Grage, Raiker Witter
and Anne S. Ulrich, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b908236k
J-Based 3D sidechain correlation in solid-state proteins
Ye Tian, Lingling Chen, Dimitri Niks, J. Michael Kaiser, Jinfeng
Lai, Chad M. Rienstra, Michael F. Dunn and Leonard J. Mueller,
Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b911570f
Natural abundance 13C and 15N solid-state NMR analysis of
paramagnetic transition-metal cyanide coordination polymers
Pedro M. Aguiar, Michael J. Katz, Daniel B. Leznoff and Scott
Kroeker, Phys. Chem. Chem. Phys., 2009
DOI: 10.1039/b907747b
Monday, July 27, 2009
Al's Literature Update
Symmetry-based dipolar recoupling by optimal control: Band-selective experiments for assignment of solid-state NMR spectra of proteins
J. Chem. Phys. 131, 025101 (2009); DOI:10.1063/1.3157737
Anders Bodholt Nielsen, Morten Bjerring, Jakob Toudahl Nielsen, and Niels Chr. Nielsen
Abstract:
We present design of novel low-power homonuclear dipolar recoupling experiments for magic-angle-spinning solid-state NMR studies of proteins. The pulse sequences are developed by combining principles of symmetry-based dipolar recoupling and optimal control-based pulse sequence design. The scaffold of the pulse sequences is formed by known CN-type recoupling sequences, while the intrinsic sequence elements are designed using optimal control. This procedure allows for the development of high-performance pulse sequences demanding significantly weaker rf fields than previous symmetry-based pulse sequences while compensating for rf inhomogeneity and providing excitation over relevant ranges of chemical shifts for biological applications. The new recoupling experiments, referred to as optimal control CN (OCCN), are demonstrated numerically and experimentally by two-dimensional (2D) 13C–13C and three-dimensional (3D) 15N–13C–13C chemical shift correlation experiments on uniformly 13C, 15N-labeled ubiquitin. Exploiting the double-quantum, band-selective dipolar recoupling properties of the OCCN experiments, we demonstrate significant sensitivity enhancement for 2D and 3D correlation spectra showing exclusively one- or two-bond correlations.
Effect of glass-forming biopreservatives on head group rotational dynamics in freeze-dried phospholipid bilayers: A 31P NMR study
J. Chem. Phys. 131, 025102 (2009); DOI:10.1063/1.3170927
P. Jain, S. Sen, and S. H. Risbud
Abstract:
31P NMR spectroscopy has been used to elucidate the role of glass-forming sugars in the preservation of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers. 31P wideline NMR spectra of freeze-dried pure DPPC, DPPC/trehalose, DPPC/glucose, and DPPC/hydroxyethyl starch (HES) mixtures collected in the temperature range of 25–80 °C have been simulated to obtain quantitative information about rotational dynamics and orientation of the lipid head groups in these media. In the case of pure DPPC, DPPC/glucose, and DPPC/HES, the gel-to-liquid crystalline phase transition of DPPC bilayer is characterized by a sudden increase in the rate of rotational diffusion of the PO4 head groups near 40 °C. The corresponding rotational jump frequency increases from a few kilohertz in the gel phase to at least several megahertz in the liquid crystalline phase. On the other hand, in the case of DPPC/trehalose mixture the temperature of this onset of rapid head group dynamics is increased by ~10 °C. Trehalose reduces the lipid head group motions most effectively in the temperature range of T50 °C relevant for biopreservation. Additionally, and possibly more importantly, trehalose is found to strongly restrict any change in the orientation of the diffusion axis of the PO4 head groups during the phase transformation. This unique ability of trehalose to maintain the dynamical and orientational rigidity of lipid head groups is likely to be responsible for its superior ability in biopreservation.
Structural and Dynamic Properties of BaInGeH: A Rare Solid-State Indium Hydride
Inorg. Chem., 2009, 48 (13), pp 5602–5604
Michael J. Evans, Verina F. Kranak, Francisco J. Garcia-Garcia, Gregory P. Holland, Luke L. Daemen, Thomas Proffen, Myeong H. Lee, Otto F. Sankey and Ulrich Hussermann
Abstract:
BaInGeH was synthesized by hydrogenating the intermetallic compound BaInGe. The crystal structure determination from the powder neutron diffraction data of BaInGeD [P3m1, Z = 1, a = 4.5354(3) Å, c = 5.2795(6) Å] reveals the presence of hydrogen in tetrahedral voids defined by three Ba atoms and one In atom.
Sodium Ion Mobility in NaxCoO2 (0.6 < x < 0.75) Cobaltites Studied by 23Na MAS NMR
Inorg. Chem., 2009, 48 (15), pp 7018–7025
Dany Carlier, Maxime Blangero, Michel Mntrier, Michal Pollet, Jean-Pierre Doumerc and Claude Delmas
Abstract:
Various P2 and P′3-NaxCoO2 phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature 23Na magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na+ ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the 23Na MAS NMR signal differs for the P2 and P′3 stackings and is interpreted by the differences of Na+ ion sites and of sodium diffusion pathways in the two structures.
Reactivity of NH4H2PO4 toward LaCl3 in LiCl-KCl Melt Flux. Step by Step Formation of Monazite-Like LaPO4.
Inorg. Chem., 2009, 48 (15), pp 7141–7150
Damien Hudry, Aydar Rakhmatullin, Catherine Bessada, Isabelle Bardez, Florence Bart, Stphane Jobic and Philippe Deniard
Abstract:
The synthesis of lanthanum phosphates in molten LiCl-KCL eutectic was chosen to address the preliminary treatment of chlorinated wastes containing fission products that are already present in a Li/Cl eutectic. The obtained monazite compound shows interesting properties to be considered as a good candidate to trap lanthanum for a long-time. The synthesis route based on LaCl3 reaction with NH4H2PO4 in a stoichiometric amount is a key point to obtain monazite as a pure phase. Hence, the salt composition is not modified during the synthesis reaction. The chemical reactivity of ammonium dihydrogenphosphate (NH4H2PO4, hereafter abbreviated ADP) toward lanthanum chloride (LaCl3) in molten LiCl-KCl eutectic is probed by NMR spectroscopy to follow the formation of LaPO4. Formally, a direct transformation of the two aforementioned precursors into LaPO4, NH4Cl and HCl can be discarded on the basis of the low thermal stability of ADP. To shed some light on the formation of LaPO4, in situ and ex situ NMR experiments were carried out on LiCl-KCl/LaCl3/ADP, as well as LiCl-KCl/ADP, KCl/ADP, and LiCl/ADP mixtures. First, the reactivity of the precursors in contact with the eutectic was studied from room temperature to 600 °C by means of 31P, 35Cl, and 139La high temperature NMR. Second, ex situ room temperature magic angle spinning (MAS) and RadioFrequency driven recoupling (RFDR) 31P solid-state NMR experiments were carried out on solid samples prepared in different conditions (i.e., temperature and atmosphere) and quenched at room temperature to identify frozen intermediate species in their metastable state. On the basis of this approach, we propose a model for the LaPO4 formation based on a multistep mechanism which highlights the strong reactivity of ADP toward the alkaline salts but without final change in the composition of the solvent.
J. Chem. Phys. 131, 025101 (2009); DOI:10.1063/1.3157737
Anders Bodholt Nielsen, Morten Bjerring, Jakob Toudahl Nielsen, and Niels Chr. Nielsen
Abstract:
We present design of novel low-power homonuclear dipolar recoupling experiments for magic-angle-spinning solid-state NMR studies of proteins. The pulse sequences are developed by combining principles of symmetry-based dipolar recoupling and optimal control-based pulse sequence design. The scaffold of the pulse sequences is formed by known CN-type recoupling sequences, while the intrinsic sequence elements are designed using optimal control. This procedure allows for the development of high-performance pulse sequences demanding significantly weaker rf fields than previous symmetry-based pulse sequences while compensating for rf inhomogeneity and providing excitation over relevant ranges of chemical shifts for biological applications. The new recoupling experiments, referred to as optimal control CN (OCCN), are demonstrated numerically and experimentally by two-dimensional (2D) 13C–13C and three-dimensional (3D) 15N–13C–13C chemical shift correlation experiments on uniformly 13C, 15N-labeled ubiquitin. Exploiting the double-quantum, band-selective dipolar recoupling properties of the OCCN experiments, we demonstrate significant sensitivity enhancement for 2D and 3D correlation spectra showing exclusively one- or two-bond correlations.
Effect of glass-forming biopreservatives on head group rotational dynamics in freeze-dried phospholipid bilayers: A 31P NMR study
J. Chem. Phys. 131, 025102 (2009); DOI:10.1063/1.3170927
P. Jain, S. Sen, and S. H. Risbud
Abstract:
31P NMR spectroscopy has been used to elucidate the role of glass-forming sugars in the preservation of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers. 31P wideline NMR spectra of freeze-dried pure DPPC, DPPC/trehalose, DPPC/glucose, and DPPC/hydroxyethyl starch (HES) mixtures collected in the temperature range of 25–80 °C have been simulated to obtain quantitative information about rotational dynamics and orientation of the lipid head groups in these media. In the case of pure DPPC, DPPC/glucose, and DPPC/HES, the gel-to-liquid crystalline phase transition of DPPC bilayer is characterized by a sudden increase in the rate of rotational diffusion of the PO4 head groups near 40 °C. The corresponding rotational jump frequency increases from a few kilohertz in the gel phase to at least several megahertz in the liquid crystalline phase. On the other hand, in the case of DPPC/trehalose mixture the temperature of this onset of rapid head group dynamics is increased by ~10 °C. Trehalose reduces the lipid head group motions most effectively in the temperature range of T50 °C relevant for biopreservation. Additionally, and possibly more importantly, trehalose is found to strongly restrict any change in the orientation of the diffusion axis of the PO4 head groups during the phase transformation. This unique ability of trehalose to maintain the dynamical and orientational rigidity of lipid head groups is likely to be responsible for its superior ability in biopreservation.
Structural and Dynamic Properties of BaInGeH: A Rare Solid-State Indium Hydride
Inorg. Chem., 2009, 48 (13), pp 5602–5604
Michael J. Evans, Verina F. Kranak, Francisco J. Garcia-Garcia, Gregory P. Holland, Luke L. Daemen, Thomas Proffen, Myeong H. Lee, Otto F. Sankey and Ulrich Hussermann
Abstract:
BaInGeH was synthesized by hydrogenating the intermetallic compound BaInGe. The crystal structure determination from the powder neutron diffraction data of BaInGeD [P3m1, Z = 1, a = 4.5354(3) Å, c = 5.2795(6) Å] reveals the presence of hydrogen in tetrahedral voids defined by three Ba atoms and one In atom.
Sodium Ion Mobility in NaxCoO2 (0.6 < x < 0.75) Cobaltites Studied by 23Na MAS NMR
Inorg. Chem., 2009, 48 (15), pp 7018–7025
Dany Carlier, Maxime Blangero, Michel Mntrier, Michal Pollet, Jean-Pierre Doumerc and Claude Delmas
Abstract:
Various P2 and P′3-NaxCoO2 phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature 23Na magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na+ ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the 23Na MAS NMR signal differs for the P2 and P′3 stackings and is interpreted by the differences of Na+ ion sites and of sodium diffusion pathways in the two structures.
Reactivity of NH4H2PO4 toward LaCl3 in LiCl-KCl Melt Flux. Step by Step Formation of Monazite-Like LaPO4.
Inorg. Chem., 2009, 48 (15), pp 7141–7150
Damien Hudry, Aydar Rakhmatullin, Catherine Bessada, Isabelle Bardez, Florence Bart, Stphane Jobic and Philippe Deniard
Abstract:
The synthesis of lanthanum phosphates in molten LiCl-KCL eutectic was chosen to address the preliminary treatment of chlorinated wastes containing fission products that are already present in a Li/Cl eutectic. The obtained monazite compound shows interesting properties to be considered as a good candidate to trap lanthanum for a long-time. The synthesis route based on LaCl3 reaction with NH4H2PO4 in a stoichiometric amount is a key point to obtain monazite as a pure phase. Hence, the salt composition is not modified during the synthesis reaction. The chemical reactivity of ammonium dihydrogenphosphate (NH4H2PO4, hereafter abbreviated ADP) toward lanthanum chloride (LaCl3) in molten LiCl-KCl eutectic is probed by NMR spectroscopy to follow the formation of LaPO4. Formally, a direct transformation of the two aforementioned precursors into LaPO4, NH4Cl and HCl can be discarded on the basis of the low thermal stability of ADP. To shed some light on the formation of LaPO4, in situ and ex situ NMR experiments were carried out on LiCl-KCl/LaCl3/ADP, as well as LiCl-KCl/ADP, KCl/ADP, and LiCl/ADP mixtures. First, the reactivity of the precursors in contact with the eutectic was studied from room temperature to 600 °C by means of 31P, 35Cl, and 139La high temperature NMR. Second, ex situ room temperature magic angle spinning (MAS) and RadioFrequency driven recoupling (RFDR) 31P solid-state NMR experiments were carried out on solid samples prepared in different conditions (i.e., temperature and atmosphere) and quenched at room temperature to identify frozen intermediate species in their metastable state. On the basis of this approach, we propose a model for the LaPO4 formation based on a multistep mechanism which highlights the strong reactivity of ADP toward the alkaline salts but without final change in the composition of the solvent.
Journal of Physical Chemistry C, vol. 113, Issues 25-30
29Si NMR Relaxation of Silicated Nanoparticles in Tetraethoxysilane−Tetrapropylammonium Hydroxide−Water System (TEOS−TPAOH−H2O)
Mohamed Haouas*†, David P. Petry†‡, Michael W. Anderson‡ and Francis Taulelle†
Institut Lavoisier de Versailles, Universit de Versailles-St. Quentin en Yvelines, Versailles, J. Phys. Chem. C, 2009, 113 (25), pp 10838–10841
DOI: 10.1021/jp903454f
Abstract: Silicon-29 longitudinal (T1) and transverse (T2) NMR relaxation times have been measured in the clear solution precursor of silicalite-1 of composition 25 TEOS−5 TPAOH−400 H2O. The nanoparticles as well as the silicate oligomers are giving rise to observable resonances. An unusually long T1 relaxation time of 126 s is observed for Q4 in nanoparticles. Proper care for acquisition is therefore required for quantifying the distribution of Qn of the nanoparticles, an essential measurement to follow the nanoparticles connectivity evolution.
Clathrate Hydrate Formation: Dependence on Aqueous Hydration Number
Steven F. Dec*
J. Phys. Chem. C, 2009, 113 (28), pp 12355–12361
DOI: 10.1021/jp9009977
Abstract: The formation of methane−ethane (C1−C2) clathrate hydrate was studied with high-resolution, solid-state 13C NMR and density functional theory techniques. The 13C NMR experiments yield a number of significant findings: (1) the hydration number of C2(aq) is 26, (2) the initial quantity of C2−51262 sI hydrate cages outnumber C1−512 cages at 274 K, (3) C1−C2 sII hydrate forms at a C1−C2 gas phase composition where only sI hydrate is thermodynamically stable, (4) the initial composition of C1−C2 sII hydrate at 268 K contains less than the original amount of C1, (5) a quasi-liquid water layer solvating both C1 and C2 exists at 268 K, (6) any C1(qll) and C2(qll) present at 253 K is too small to be detected, (7) the initial amounts of C1−C2 sI and sII hydrates formed at 253 K are much smaller than those formed at 268 and 274 K, and (8) C1(aq), C2(aq) and C1(qll), C2(qll) facilitate the formation of C1−C2 sI and sII clathrate hydrate at 268 and 274 K, respectively. On the basis of these experimental observations, a model is developed that states that the aqueous hydration number of the most water-soluble clathrate hydrate former controls the structure of the clathrate hydrate that forms during the initial stages of the clathrate hydrate formation reaction. For methane−ethane clathrate hydrate, this means that ethane in a water liquid phase or quasi-liquid layer eliminates or adds two water molecules to its hydration shell to form the ethane-filled 51262 or 51264 cage building blocks of structure I or structure II clathrate hydrate, respectively. Density functional theory computations on methane-filled 512, 51262, and 51264 and ethane-filled 51262, 51263, and 51264 clathrate hydrate cages yield the stabilization energy of the gas-filled cages and provide theoretical evidence consistent with the experimentally based clathrate hydrate formation model. The proposed model is found to explain the results of other clathrate hydrate formation reactions.
Hierarchical Meso-/Macroporous Aluminum Phosphonate Hybrid Materials as Multifunctional Adsorbents
Tian-Yi Ma, Xue-Jun Zhang and Zhong-Yong Yuan*
J. Phys. Chem. C, 2009, 113 (29), pp 12854–12862
DOI: 10.1021/jp903412m
Abstract: Inorganic−organic hybrid aluminum phosphonate (AlPPh) materials with hierarchical meso-/macroporous structure were synthesized by using two different kinds of organophosphonic acids: amino tri(methylene phosphonic acid) and bis(hexamethylenetriamine)-penta(methylenephosphonic acid). The preparation was accomplished both with and without the assistance of surfactant F127. All the samples possess a uniform macroporous (500−2000 nm) structure of mesoporous (4−5 nm) framework, which were characterized by SEM, TEM, N2 sorption, XRD, TGA-DSC, elemental analysis, MAS NMR, and FT-IR spectroscopy techniques. The as-prepared AlPPh materials were used as multifunctional adsorbents for the efficient removal of heavy metal ions (e.g., Cu2+) and the adsorption of proteins (e.g., lysozyme). The heavy metal ion adsorption results show that the AlPPh materials have a large adsorption capacity, comparable to those of previous reported Cu(II)-adsorbents made up of functionalized mesoporous silica. The isotherms for lysozyme adsorption are of type L (Langmuir isotherm), and different monolayer capacities were calculated using Langmuir equation. The differences between the metal ion and the lysozyme adsorption were mainly caused by the nature of inorganic ions and proteins and the interactions between the adsorbents and adsorbates. The synthesized AlPPh hybrid materials were confirmed to be useful multifunctional adsorbents for both metal ions and proteins.
Observation of Distinct Surface AlIV Sites and Phosphonate Binding Modes in γ-Alumina and Concrete by High-Field 27Al and 31P MAS NMR
George W. Wagner*† and Roderick A. Fry‡§
J. Phys. Chem. C, 2009, 113 (30), pp 13352–13357
DOI: 10.1021/jp902474z
Publication Date (Web): July 1, 2009
Abstract: High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.
Mohamed Haouas*†, David P. Petry†‡, Michael W. Anderson‡ and Francis Taulelle†
Institut Lavoisier de Versailles, Universit de Versailles-St. Quentin en Yvelines, Versailles, J. Phys. Chem. C, 2009, 113 (25), pp 10838–10841
DOI: 10.1021/jp903454f
Abstract: Silicon-29 longitudinal (T1) and transverse (T2) NMR relaxation times have been measured in the clear solution precursor of silicalite-1 of composition 25 TEOS−5 TPAOH−400 H2O. The nanoparticles as well as the silicate oligomers are giving rise to observable resonances. An unusually long T1 relaxation time of 126 s is observed for Q4 in nanoparticles. Proper care for acquisition is therefore required for quantifying the distribution of Qn of the nanoparticles, an essential measurement to follow the nanoparticles connectivity evolution.
Clathrate Hydrate Formation: Dependence on Aqueous Hydration Number
Steven F. Dec*
J. Phys. Chem. C, 2009, 113 (28), pp 12355–12361
DOI: 10.1021/jp9009977
Abstract: The formation of methane−ethane (C1−C2) clathrate hydrate was studied with high-resolution, solid-state 13C NMR and density functional theory techniques. The 13C NMR experiments yield a number of significant findings: (1) the hydration number of C2(aq) is 26, (2) the initial quantity of C2−51262 sI hydrate cages outnumber C1−512 cages at 274 K, (3) C1−C2 sII hydrate forms at a C1−C2 gas phase composition where only sI hydrate is thermodynamically stable, (4) the initial composition of C1−C2 sII hydrate at 268 K contains less than the original amount of C1, (5) a quasi-liquid water layer solvating both C1 and C2 exists at 268 K, (6) any C1(qll) and C2(qll) present at 253 K is too small to be detected, (7) the initial amounts of C1−C2 sI and sII hydrates formed at 253 K are much smaller than those formed at 268 and 274 K, and (8) C1(aq), C2(aq) and C1(qll), C2(qll) facilitate the formation of C1−C2 sI and sII clathrate hydrate at 268 and 274 K, respectively. On the basis of these experimental observations, a model is developed that states that the aqueous hydration number of the most water-soluble clathrate hydrate former controls the structure of the clathrate hydrate that forms during the initial stages of the clathrate hydrate formation reaction. For methane−ethane clathrate hydrate, this means that ethane in a water liquid phase or quasi-liquid layer eliminates or adds two water molecules to its hydration shell to form the ethane-filled 51262 or 51264 cage building blocks of structure I or structure II clathrate hydrate, respectively. Density functional theory computations on methane-filled 512, 51262, and 51264 and ethane-filled 51262, 51263, and 51264 clathrate hydrate cages yield the stabilization energy of the gas-filled cages and provide theoretical evidence consistent with the experimentally based clathrate hydrate formation model. The proposed model is found to explain the results of other clathrate hydrate formation reactions.
Hierarchical Meso-/Macroporous Aluminum Phosphonate Hybrid Materials as Multifunctional Adsorbents
Tian-Yi Ma, Xue-Jun Zhang and Zhong-Yong Yuan*
J. Phys. Chem. C, 2009, 113 (29), pp 12854–12862
DOI: 10.1021/jp903412m
Abstract: Inorganic−organic hybrid aluminum phosphonate (AlPPh) materials with hierarchical meso-/macroporous structure were synthesized by using two different kinds of organophosphonic acids: amino tri(methylene phosphonic acid) and bis(hexamethylenetriamine)-penta(methylenephosphonic acid). The preparation was accomplished both with and without the assistance of surfactant F127. All the samples possess a uniform macroporous (500−2000 nm) structure of mesoporous (4−5 nm) framework, which were characterized by SEM, TEM, N2 sorption, XRD, TGA-DSC, elemental analysis, MAS NMR, and FT-IR spectroscopy techniques. The as-prepared AlPPh materials were used as multifunctional adsorbents for the efficient removal of heavy metal ions (e.g., Cu2+) and the adsorption of proteins (e.g., lysozyme). The heavy metal ion adsorption results show that the AlPPh materials have a large adsorption capacity, comparable to those of previous reported Cu(II)-adsorbents made up of functionalized mesoporous silica. The isotherms for lysozyme adsorption are of type L (Langmuir isotherm), and different monolayer capacities were calculated using Langmuir equation. The differences between the metal ion and the lysozyme adsorption were mainly caused by the nature of inorganic ions and proteins and the interactions between the adsorbents and adsorbates. The synthesized AlPPh hybrid materials were confirmed to be useful multifunctional adsorbents for both metal ions and proteins.
Observation of Distinct Surface AlIV Sites and Phosphonate Binding Modes in γ-Alumina and Concrete by High-Field 27Al and 31P MAS NMR
George W. Wagner*† and Roderick A. Fry‡§
J. Phys. Chem. C, 2009, 113 (30), pp 13352–13357
DOI: 10.1021/jp902474z
Publication Date (Web): July 1, 2009
Abstract: High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.
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