Showing papers on "Solid-state nuclear magnetic resonance published in 2005"
TL;DR: Main isotropic chemical shifts report on conformation, enabling a detailed comparison of the microcrystalline state with the conformation of single crystals and the protein in solution; the consistency of backbone conformation is the best among proteins studied so far.
Abstract: Magic-angle spinning solid-state NMR (SSNMR) studies of the β1 immunoglobulin binding domain of protein G (GB1) are presented. Chemical shift correlation spectra at 11.7 T (500 MHz 1H frequency) were employed to identify signals specific to each amino acid residue type and to establish backbone connectivities. High sensitivity and resolution facilitated the detection and assignment of every 15N and 13C site, including the N-terminal (M1) 15NH3, the C-terminal (E56) 13C‘, and side-chain resonances from residues exhibiting fast-limit conformational exchange near room temperature. The assigned spectra lend novel insight into the structure and dynamics of microcrystalline GB1. Secondary isotropic chemical shifts report on conformation, enabling a detailed comparison of the microcrystalline state with the conformation of single crystals and the protein in solution; the consistency of backbone conformation in these three preparations is the best among proteins studied so far. Signal intensities and line widths ...
314 citations
TL;DR: It is shown that molecular structure and dynamics of a uniformly labeled membrane protein can be studied under magic-angle-spinning conditions and NMR data are consistent with an alpha-helical trans-membrane segment and a cytoplasmic domain that exhibits a high degree of structural disorder.
Abstract: It is shown that molecular structure and dynamics of a uniformly labeled membrane protein can be studied under magic-angle-spinning conditions. For this purpose, dipolar recoupling experiments are combined with novel through-bond correlation schemes that probe mobile protein segments. These NMR schemes are demonstrated on a uniformly [13C,15N] variant of the 52-residue polypeptide phospholamban. When reconstituted in lipid bilayers, the NMR data are consistent with an alpha-helical trans-membrane segment and a cytoplasmic domain that exhibits a high degree of structural disorder.
293 citations
TL;DR: In this paper, solid-state 1H and 13C NMR spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake.
269 citations
TL;DR: The study shows that the surfactant (CTAB) was almost completely removed by acid extraction, and the residual molecules assumed prone positions along the pores, with the tailgroup being most mobile.
Abstract: A systematic study of the surface of MCM-41-type mesoporous silica nanoparticles prepared under low surfactant concentration was carried out using high-resolution solid-state nuclear magnetic resonance spectroscopy. The structures and concentrations of various species present during dehydration and rehydration of mesoporous silicas between −25 and 500 °C were detailed by employing one-dimensional and two-dimensional 1H, 13C, and 29Si NMR, including 1H signal intensity measurements, 1H−1H homonuclear correlation experiments (double quantum, exchange, and RFDR), and 1H−29Si heteronuclear correlation NMR. These experiments employed high MAS rates of up to 45 kHz. The study shows that the surfactant (CTAB) was almost completely removed by acid extraction. The residual molecules assumed prone positions along the pores, with the tailgroup being most mobile. The weakly adsorbed water was hydrogen bonded to the silanol groups, all of which were involved in such bonds under ambient humidity. Specific structures in...
226 citations
TL;DR: The structure determination strategies for solid samples described herein are likely to be generally applicable to many proteins that cannot be studied by X-ray crystallography or solution NMR spectroscopy.
Abstract: High-resolution solid-state NMR spectroscopy has become a promising method for the determination of three-dimensional protein structures for systems which are difficult to crystallize or exhibit low solubility. Here we describe the structure determination of microcrystalline ubiquitin using 2D 13C−13C correlation spectroscopy under magic angle spinning conditions. High-resolution 13C spectra have been acquired from hydrated microcrystals of site-directed 13C-enriched ubiquitin. Interresidue carbon−carbon distance constraints defining the global protein structure have been evaluated from ‘dipolar-assisted rotational resonance' experiments recorded at various mixing times. Additional constraints on the backbone torsion angles have been derived from chemical shift analysis. Using both distance and dihedral angle constraints, the structure of microcrystalline ubiquitin has been refined to a root-mean-square deviation of about 1 A. The structure determination strategies for solid samples described herein are l...
210 citations
TL;DR: A clear correlation between a large chemical shift change and both a short H...O distance and a CHO bond angle greater than 130 degrees is observed, thus showing that directionality is important in C-H...O hydrogen bonding.
Abstract: Two-dimensional 1H−13C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental 1H chemical shifts of the CH and CH2 protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudopotential approach. Further calculations show that the calculated change in the 1H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C−H···O weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short H···O distance (<2.7 A) and a CHO bond angle greater than 130° is observed, thus showing that directionality is important in C−H···O hydrogen bonding.
179 citations
TL;DR: Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected.
Abstract: C-13, N-14, N-15, O-17, and Cl-35 NMR parameters, including chemical shift tensors and quadrupolar tensors for N-14, O-17, and Cl-35, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The C-13 shift tensors and N-14 electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static O-17 NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the O-17 NMR shielding parameters and the Cl-35 quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of C-13 and N-15 are relatively insensitive to small differences in the experimental structure, the O-17 shift is markedly affected.
166 citations
TL;DR: The investigation of 1H-1H spin-diffusion build-up curves using a rate matrix analysis approach shows that high-resolution magic angle spinning NMR of protons, applied to powdered organic compounds, provides a method to probe crystalline arrangements.
Abstract: The investigation of 1H−1H spin-diffusion build-up curves using a rate matrix analysis approach shows that high-resolution magic angle spinning NMR of protons, applied to powdered organic compounds, provides a method to probe crystalline arrangements. The comparison between experimental 1H data and simulation is shown to depend strongly on the parameters of the crystal structure, for example on the unit cell parameters or the orientation of the molecule in the unit cell, and those parameters are experimentally determined for a model organic compound.
156 citations
154 citations
TL;DR: A method for structure determination of zeolite crystal structures that combines powder XRD and nuclear magnetic resonance (NMR) spectroscopy in which the crucial step of structure solution is achieved using solid-state (29)Si double-quantum dipolar recoupling NMR, which probes the distance-dependent dipolar interactions between naturally abundant nuclei in the zeolites framework.
Abstract: Since zeolites are notoriously difficult to prepare as large single crystals, structure determination usually relies on powder X-ray diffraction (XRD). However, structure solution (i.e., deriving an initial structural model) directly from powder XRD data is often very difficult due to the diffraction phase problem and the high degree of overlap between the individual reflections, particularly for materials with the structural complexity of most zeolites. Here, we report a method for structure determination of zeolite crystal structures that combines powder XRD and nuclear magnetic resonance (NMR) spectroscopy in which the crucial step of structure solution is achieved using solid-state 29Si double-quantum dipolar recoupling NMR, which probes the distance-dependent dipolar interactions between naturally abundant 29Si nuclei in the zeolite framework. For two purely siliceous zeolite blind test samples, we demonstrate that the NMR data can be combined with the unit cell parameters and space group to solve st...
146 citations
TL;DR: Shielding parameters for all three nuclei have been calculated using Density Functional Theory (DFT) together with the Gauge Including Projector Augmented Wave (GIPAW) method which takes full allowance for the repetition inherent in crystalline structures.
Abstract: The 1H, 13C and 19F magic-angle spinning NMR spectra have been recorded for Form 1 of flurbiprofen. In the case of 19F, spinning sideband analysis has produced data for the components of the shielding tensor. The chemical shift of the hydrogen-bonded proton was found to be 14.0 ppm. Shielding parameters for all three nuclei have been calculated using Density Functional Theory (DFT) together with the Gauge Including Projector Augmented Wave (GIPAW) method which takes full allowance for the repetition inherent in crystalline structures. Such computations were made for the reported geometry, for a structure with all the atomic positions relaxed using DFT, and with only the hydrogen positions relaxed. The relationships of the computed shifts to those observed are discussed. In general, the correlations are good.
TL;DR: It is shown that a well-defined amplitude modulation of one of the two radio-frequency fields in the FSLG-CP sequence results in highly efficient heteronuclear dipolar recoupling.
Abstract: This paper presents a theoretical, numerical, and experimental study of phase- and frequency-switched Lee–Goldburg cross-polarization (FSLG–CP) under magic-angle spinning conditions. It is shown that a well-defined amplitude modulation of one of the two radio-frequency (rf) fields in the FSLG–CP sequence results in highly efficient heteronuclear dipolar recoupling. The recoupled dipolar interaction is γ-encoded and, under ideal conditions, the effective spin Hamiltonian is equivalent to that in continuous-wave Lee–Goldburg CP. In practice, however, FSLG–CP is less susceptible to rf field mismatch and inhomogeneity, and provides better suppression of 1H spin diffusion. The performance of FSLG–CP is experimentally demonstrated on liquid-crystalline samples exhibiting motionally averaged dipolar couplings.
TL;DR: A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid organic solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological solids.
Abstract: A refocused INEPT through-bond coherence transfer technique is demonstrated for NMR of rigid organic solids and is shown to provide a valuable building block for the development of NMR correlation experiments in biological solids. The use of efficient proton homonuclear dipolar decoupling in combination with a direct spectral optimization procedure provides minimization of the transverse dephasing of coherences and leads to very efficient through-bond 1H−13C INEPT transfer for crystalline organic compounds. Application of this technique to 2D heteronuclear correlation spectroscopy leads to up to a factor of 3 increase in sensitivity for a carbon-13 enriched sample in comparison to standard through-bond experiments and provides excellent selectivity for one-bond transfer. The method is demonstrated on a microcrystalline sample of the protein Crh (2 × 10.4 kDa).
TL;DR: This study presents the first direct NMR experimental evidence that there are two types of isolated protons with different acid strengths in the anhydrous Keggin HPW.
Abstract: Solid-state C-13 NMR experiments and quantum chemical Density Functional Theory (DFT) calculations of acetone adsorption were used to study the location of protons in anhydrous 12-tungstophosphoric acid (HPW), the mobility of the isolated and hydrated acidic protons, and the acid strength heterogeneity of the anhydrous hydroxyl groups. This study presents the first direct NMR experimental evidence that there are two types of isolated protons with different acid strengths in the anhydrous Keggin HPW. Rotational Echo DOuble Resonance (REDOR) NMR experiments combined with quantum chemical DFT calculations demonstrated that acidic protons in anhydrous HPW are localized on both bridging (O-c) and terminal (O-d) atoms of the Keggin unit. The CP/MAS NMR experiments revealed that the isolated acidic protons are immobile, but hydrated acidic protons are highly mobile at room temperature. The isotropic chemical shift of the adsorbed acetone suggested that the acid strength of the H(H2O)(n)(+) species in partially hydrated HPW is comparable to that of a zeolite, while the acidity of an isolated proton is much stronger than that of a zeolite. Isolated protons on the bridging oxygen atoms of anhydrous HPW are nearly superacidic.
TL;DR: The solid-state NMR spectra of the amyloid form of the HET-s prion protein show the resonances for 43 residues with high resolution, whereas 29 residues give no observable NMR signals, suggesting that the protein structure consists of both highly ordered and strongly disordered domains.
Abstract: Partly present, partly absent: The solid-state NMR spectra (figure, right side) of the amyloid form of the HET-s prion protein (EM image at left) show the resonances for 43 residues with high resolution, whereas 29 residues give no observable NMR signals. A possible explanation could be that the protein structure consists of both highly ordered and strongly disordered domains.
TL;DR: A variety of NMR methods applied to different types of surfactant aggregates, predominantly micelles, are reviewed in this article, where the treatment attempts to be short but pedagogical instead of being comprehensive or chronological.
TL;DR: Measurements of rhodopsin containing 13C-labeled histidine show that a strong hydrogen bond between the side-chain of Glu122 and the backbone carbonyl of His211 is disrupted in metarhodopin II, and the implications for the activation mechanism of r Rhodopsin are discussed.
TL;DR: (31)P solid-state NMR spectroscopy has been used to investigate the macroscopic phase behavior of phospholipid bilayers in the presence of increasing amounts of magainin antibiotic peptides, resulting in spectra characterized by the coexistence of isotropic signals and line shapes typical for phosphate bilayers.
TL;DR: It is found that the phase formed by DOPC with 30% cholesterol is analogous to the liquid-ordered (lo) phase, and this technique can, in principle, be applied to natural lipids and biomembranes.
Abstract: Most biological phospholipids contain at least one unsaturated alkyl chain. However, few order parameters of unsaturated lipids have been determined because of the difficulty associated with isotopic labeling of a double bond. Dipolar recoupling on axis with scaling and shape preservation (DROSS) is a solid-state nuclear magnetic resonance technique optimized for measuring 1H–13C dipolar couplings and order parameters in lipid membranes in the fluid phase. It has been used to determine the order profile of 1,2-dimyristoyl-sn-glycero-3-phosphocholine hydrated membranes. Here, we show an application for the measurement of local order parameters in multilamellar vesicles containing unsaturated lipids. Taking advantage of the very good 13C chemical shift dispersion, one can easily follow the segmental order along the acyl chains and, particularly, around the double bonds where we have been able to determine the previously misassigned order parameters of each acyl chain of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). We have followed the variation of such order profiles with temperature, unsaturation content and cholesterol addition. We have found that the phase formed by DOPC with 30% cholesterol is analogous to the liquid-ordered (lo) phase. Because these experiments do not require isotopic enrichment, this technique can, in principle, be applied to natural lipids and biomembranes.
TL;DR: In this article, a crosslinking reaction of starch-enriched flour using epichlorohydrin as a cross-linking agent in the presence of NH 4 OH was investigated by elemental analysis, electrophoretic mobility and NMR spectroscopy.
TL;DR: Local and medium range order in the glass system 50Ag2O-50[(B2O3)x-(P2O5)(1-x)], suggesting that anionic BO4/2- groups are stabilized by the interaction with the phosphate groups, and some net charge transfer from the borate to the phosphate network former species.
TL;DR: The approach is particularly powerful in combination with magic-angle sample spinning, producing site-resolved dipolar coupling information, and new applications to oxide-based network glasses are presented, permitting network connectivities and spatial cation distributions to be elucidated.
Abstract: Modern solid state nuclear magnetic resonance presents new powerful opportunities for the elucidation of medium range order in glasses in the sub-nanometer region. In contrast to standard chemical shift spectroscopy, the strategy presented here is based on the precise measurement and quantitative analysis of internuclear magnetic dipole-dipole interactions, which can be related to distance information in a straightforward manner. The review discusses the most commonly employed experimental techniques, producing dipolar coupling information in both homo- and heteronuclear spin systems. The approach is particularly powerful in combination with magic-angle sample spinning, producing site-resolved dipolar coupling information. We present new applications to oxide-based network glasses, permitting network connectivities and spatial cation distributions to be elucidated.
TL;DR: Solid‐state NMR methods tailored to the construction of 3D molecular structure are discussed and a comparative analysis of 13C′, 13Cα, and 13Cβ resonance frequencies suggests that 13C chemical‐shift variations are most likely to occur in protein regions that exhibit an enhanced degree of molecular mobility.
Abstract: Understanding of the effects of intermolecular interactions, molecular dynamics, and sample preparation on high-resolution magic-angle spinning NMR data is currently limited. Using the example of a uniformly [13C,15N]-labeled sample of ubiquitin, we discuss solid-state NMR methods tailored to the construction of 3D molecular structure and study the influence of solid-phase protein preparation on solid-state NMR spectra. A comparative analysis of 13C', 13Calpha, and 13Cbeta resonance frequencies suggests that 13C chemical-shift variations are most likely to occur in protein regions that exhibit an enhanced degree of molecular mobility. Our results can be refined by additional solid-state NMR techniques and serve as a reference for ongoing efforts to characterize the structure and dynamics of (membrane) proteins, protein complexes, and other biomolecules by high-resolution solid-state NMR.
TL;DR: In this paper, structural investigations of membrane proteins at high resolu-tion have proven to be difficult, primarily because well-ordered3D crystals do not form easily and many of them cannot be besolubilised in a manner suitable for solution NMR.
Abstract: Structural investigations of membrane proteins at high resolu-tion have proven to be difficult, primarily because well-ordered3D crystals do not form easily and many of them cannot besolubilised in a manner suitable for solution NMR. Over thepast few years, solid-state NMR has developed into a comple-mentary method for structural research.
TL;DR: It was theoretically and experimentally confirmed that the absolute sensitivity of 1H VFMAS for small paramagnetic complexes such as Cu(dl-alanine)2 can be an order of magnitude higher than that of equimolar diamagnetic ligands because of short 1H T1 of the paramagnetic systems and improved sensitivity under V FMAS.
Abstract: High-resolution NMR spectroscopy for paramagnetic complexes in solids has been rarely performed because of its limited sensitivity and resolution due to large paramagnetic shifts and associated technical difficulties. The present study demonstrates that magic angle spinning (MAS) at speeds exceeding 20 kHz provides unusually high sensitivity and excellent resolution in 1H solid-state NMR (SSNMR) for paramagnetic systems. Spinning-speed dependence of 1H MAS spectra showed that very fast MAS (VFMAS) at 24−28 kHz enhanced sensitivity by a factor of 12−18, compared with the sensitivity of 1H SSNMR spectra under moderate MAS at 10 kHz, for Cu(dl-alanine)2·H2O and Mn(acac)3, for which the spectral ranges due to 1H paramagnetic shifts reach 200 and 1000 ppm, respectively. It was theoretically and experimentally confirmed that the absolute sensitivity of 1H VFMAS for small paramagnetic complexes such as Cu(dl-alanine)2 can be an order of magnitude higher than that of equimolar diamagnetic ligands because of short...
TL;DR: NMR spectroscopy was mostly applied to the bone mineral and confirmed that the structure resembles that of calcium carbonatoapatite of type B, and apatite in bone was found to be deficient in structural hydroxyl groups.
Abstract: Solid-state NMR studies on bone, bone mineral standards and collagen are reviewed. NMR spectroscopy was mostly applied to the bone mineral and confirmed that the structure resembles that of calcium carbonatoapatite of type B. Apatite in bone was found to be deficient in structural hydroxyl groups. Concentration and distribution of hydrogenphosphate and carbonate ions, and of water in apatite crystals (interior vs surface and crystal defects vs structural positions) were closely investigated. The NMR characterization of the organic matrix still remains a challenge for future research.
TL;DR: First-order homonuclear decoupling efficiency parameters are defined which provide the line-narrowing characteristics of the various pulse sequences when applied to fast rotating samples, and these parameters are used to compare theLine- narrowing efficiencies of the multiple-pulse schemes.
Abstract: We describe radiofrequency (RF) pulse schemes in solid-state NMR applied to samples rotating at the magic angle (MAS) to obtain high-resolution 1H spectra. Without combined RF schemes and MAS, 1H spectra are normally severely broadened by the strong homonuclear proton-proton dipolar couplings. This review gives an outline of a representative class of multiple-pulse sequences, designed to work with and without MAS, and commonly used for high-resolution proton spectroscopy in solid-state NMR. We give a theoretical treatment of these sequences based on Floquet theory, both single-mode and bimodal. Using this approach, we define first-order homonuclear decoupling efficiency parameters which provide the line-narrowing characteristics of the various pulse sequences when applied to fast rotating samples. These parameters are used to compare the line-narrowing efficiencies of the multiple-pulse schemes.