Showing papers on "Solid-state nuclear magnetic resonance published in 1999"
311 citations
TL;DR: In this paper, a rotor-synchronized double-quantum magic-angle spinning (MAS) method was used to identify three distinct aromatic resonances in the singlequantum 1H NMR spectrum of hexa-perihexabenzocoronene (HBC).
Abstract: 1H NMR methods employing very fast magic-angle spinning (MAS) are applied to the investigation of both the structure and dynamics of an alkyl-substituted hexa-peri-hexabenzocoronene (HBC), which is known to form a columnar mesophase with a very high one-dimensional charge carrier mobility. For the crystalline phase, three distinct aromatic resonances are identified in the single-quantum MAS spectrum. The observation of these distinct aromatic resonances is explained in terms of the differing degrees to which the aromatic protons experience the ring current of adjacent layers. Using the rotor-synchronized double-quantum MAS method, definite proton−proton proximities are identified, which are shown to be in agreement with the known crystal structure of unsubstituted HBC. In the liquid-crystalline phase, axial motion of the HBC disks leads to the averaging of the three sites into a single resonance. Furthermore, the reduction of the dipolar coupling caused by this motion is quantitatively investigated by an ...
179 citations
TL;DR: An approach to efficiently determine the backbone conformation of solid proteins that utilizes selective and extensive (13)C labeling in conjunction with two-dimensional magic-angle-spinning NMR and this isotope-edited NMR approach is expected to facilitate the structure determination of proteins in the solid state.
142 citations
128 citations
TL;DR: The comprehensive structure determination of isotopically labeled proteins by solid-state NMR requires sequence-specific assignment of 13C and 15 N spectra, and cross-referencing these spectra and exploiting the selective and extensive 13 C labeling approach assigned 25% of the amino acids in ubiquitin sequence- specifically and 47% ofThe residues to the amino acid types.
Abstract: The comprehensive structure determination of isotopically labeled proteins by solid-state NMR requires sequence-specific assignment of 13C and 15 N spectra. We describe several 2D and 3D MAS correlation techniques for resonance assignment and apply them, at 7.0 Tesla, to 13C and 15N labeled ubiquitin to examine the extent of resonance assignments in the solid state. Both interresidue and intraresidue assignments of the 13C and 15N resonances are addressed. The interresidue assignment was carried out by an N(CO)CA technique, which yields Ni-Cαi−1 connectivities in protein backbones via two steps of dipolar-mediated coherence transfer. The intraresidue connectivities were obtained from a new 3D NCACB technique, which utilizes the well resolved Cβ chemical shift to distinguish the different amino acids. Additional amino acid type assignment was provided by a 13C spin diffusion experiment, which exhibits 13C spin pairs as off-diagonal intensities in the 2D spectrum. To better resolve carbons with similar chemical shifts, we also performed a dipolar-mediated INADEQUATE experiment. By cross-referencing these spectra and exploiting the selective and extensive 13 C labeling approach, we assigned 25% of the amino acids in ubiquitin sequence-specifically and 47% of the residues to the amino acid types. The sensitivity and resolution of these experiments are evaluated, especially in the context of the selective and extensive 13C labeling approach.
127 citations
TL;DR: In this article, a general treatment of nuclear magnetic resonance (NMR) spectra under magic-angle spinning (MAS) conditions is provided that is applicable both to homogeneously and inhomogeneously broadened lines.
Abstract: A general treatment of nuclear magnetic resonance (NMR) spectra under magic-angle spinning (MAS) conditions is provided that is applicable both to homogeneously and inhomogeneously broadened lines. It is based on a combination of Floquet theory and perturbation theory, and allows the factorization of the spin system response into three factors that describe different aspects of the resulting MAS spectrum. The first factor directly reflects the Floquet theorem and describes the appearance of sidebands. The other two terms give the integral intensities of the resulting sidebands and their line shapes and depend on the specific features of the considered interaction. The analytical form of these two factors is derived for multi-spin dipolar interactions under fast MAS. The leading term in the expansion of the integral intensities involves products of only two spin operators whereas the linewidths, which are found to be different for the different sideband orders, are determined predominantly by three-spin te...
125 citations
TL;DR: In this article, the authors have synthesized and studied via solid-state NMR, Mossbauer spectroscopy, single-crystal X-ray diffraction, and density functional theory the following Fe−O2 analogue metalloporphyrins:
Abstract: We have synthesized and studied via solid-state NMR, Mossbauer spectroscopy, single-crystal X-ray diffraction, and density functional theory the following Fe−O2 analogue metalloporphyrins: Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(1-methylimidazole); Fe(5,10,15,20-tetraphenylporphyrinate) (nitrosobenzene)(pyridine); Fe(5,10,15,20-tetraphenylporphyrinate)(4-nitroso-N,N-dimethylaniline)(pyridine); Fe(2,3,7,8,12,13,17,18-octaethylporphyrinate) (nitrosobenzene)(1-methylimidazole) and Co(2,3,7,8,12,13,17,18-octaethylporphyrinate)(NO). Our results show that the porphyrin rings of the two tetraphenylporphyrins containing pyridine are ruffled while the other three compounds are planar: reasons for this are discussed. The solid-state NMR and Mossbauer spectroscopic results are well reproduced by the DFT calculations, which then enable the testing of various models of Fe−O2 bonding in metalloporphyrins and metalloproteins. We find no evidence for two binding sites in oxypicket fence porphyrin, chara...
118 citations
TL;DR: In this article, the structure and acidity properties of HZSM-5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid state NMR with a system capable of in situ sample pretreatment.
Abstract: Variations in the structure and acidity properties of HZSM‐5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid‐state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of 27Al MAS NMR, 29Si MAS, CP/MAS NMR and 1H MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the 27Al, 29Si MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM‐5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of 1H MAS NMR obtained using Fluorinert® FC‐43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Bronsted acid sites on the external surface of the nano‐structured zeolite appears to be distinctly higher than that of the microsized zeolite.
104 citations
TL;DR: The experimental parameters critical for the implementation of multidimensional solid-state NMR experiments that incorporate heteronuclear spin exchange at the magic angle are discussed.
100 citations
TL;DR: Peat char samples produced by heat treatments under an inert atmosphere of nitrogen were characterized through 13C solid-state NMR, allowing the achievement of a detailed picture of the mechanism of mechanism.
Abstract: Peat char samples produced by heat treatments under an inert atmosphere of nitrogen were characterized through 13C solid-state NMR, allowing the achievement of a detailed picture of the mechanism o...
100 citations
TL;DR: In this paper, the residual dipolar couplings in elastomer system were measured using the spin response to two-dimensional pulse sequences used to record multiple-quantum (MQ) NMR coherences.
Abstract: The measurements of residual dipolar couplings in elastomer system is desirable, because they reflect the hindrance to molecular motions by the cross-linking, topological constraints and the external factors like mechanical stress. Dipolar-encoded longitudinal magnetization nuclear magnetic resonance (NMR) decay curves, double-quantum and triple-quantum NMR buildup intensities for measuring the residual dipolar couplings, and the associated dynamic order parameters are introduced. It is shown that in the short excitation time regime the effective dipolar network is simplified. In the limit of this model based on localized dipolar couplings, the spin response to two-dimensional pulse sequences used to record multiple-quantum (MQ) NMR coherences was evaluated for longitudinal magnetization, double-, and triple-quantum coherences of methylene, and methyl protons in synthetic 1,4-cis-polyisoprene. The dynamic order parameters can be evaluated from this NMR response using a classical scale-invariant polymer mo...
TL;DR: It has been clearly demonstrated that structural constraints can be assembled into uniquely defined three-dimensional structures at high resolution in solid-state NMR.
Abstract: ▪ Abstract Solid-state nuclear magnetic resonance (NMR) is rapidly emerging as a successful and important technique for protein and peptide structural elucidation from samples in anisotropic environments. Because of the diversity of nuclei and nuclear spin interactions that can be observed, and because of the broad range of sample conditions that can be studied by solid-state NMR, the potential for gaining structural constraints is great. Structural constraints in the form of orientational, distance, and torsional constraints can be obtained on proteins in crystalline, liquid-crystalline, or amorphous preparations. Great progress in the past few years has been made in developing techniques for obtaining these constraints, and now it has also been clearly demonstrated that these constraints can be assembled into uniquely defined three-dimensional structures at high resolution. Although much progress toward the development of solid-state NMR as a routine structural tool has been documented, the future is ev...
TL;DR: In this paper, the acquisition of distortion-free solid-state nuclear magnetic resonance (NMR) powder line shapes from half-integer spin systems possessing large quadrupole couplings is exemplified on cobaltophthalocyanine complexes.
Abstract: The acquisition of distortion-free solid-state nuclear magnetic resonance (NMR) powder line shapes from half-integer spin systems possessing large quadrupole couplings is exemplified on cobaltophthalocyanine complexes. The acquisition of ideal-like static line shapes even for megahertz-wide central transition patterns is discussed, with the aid of spin−echo sequences incorporating short and very weak radio frequency (rf) pulses. Under these conditions most of the crystallites within the bandwidth of interest are excited with essentially orientation-independent pulse angles, while the acquisition of several experiments with varying carrier frequency offsets alleviates the limited bandwidth of the excitation given by the rf pulse lengths. After this approach was tuned with the aid of quantum mechanical calculations and model compounds, it was applied to the study of diamagnetic metal centers in hexacoordinated Co(III)phthalocyanines. Solid-state 59Co NMR spectra were acquired as a function of the external m...
TL;DR: A mechanism of action in which CecA binds to and covers the membrane surface, thereby causing a general destabilization and leakiness of the lipid bilayer membrane is supported by a proposed mechanism of membrane lysis and bacterial killing via an ion channel activity of CecA.
TL;DR: Investigations of the structure and topology of membrane channels, peptide antibiotics, signal sequences as well as model systems that allow one to dissect the interaction contributions in phospholipid membranes will be presented in greater detail.
Abstract: Solid-state nmr spectroscopy provides a robust method for investigating polypeptides that have been prepared by chemical synthesis and that are immobilized by strong interactions with solid surfaces or large macroscopic complexes. Solid-state nmr spectroscopy has been widely used to investigate membrane polypeptides or peptide aggregates such as amyloid fibrils. Whereas magic angle spinning solid-state nmr spectroscopy allows one to measure distances and dihedral angles with high accuracy, static membrane samples that are aligned with respect to the magnetic field direction allow one to determine the secondary structure of bound polypeptides and their orientation with respect to the bilayer normal. Peptide dynamics and the effect of polypeptides on the macroscopic phase preference of phospholipid membranes have been investigated in nonoriented samples. Investigations of the structure and topology of membrane channels, peptide antibiotics, signal sequences as well as model systems that allow one to dissect the interaction contributions in phospholipid membranes will be presented in greater detail. © 1999 John Wiley & Sons, Inc. Biopoly 51: 174–190, 1999
TL;DR: In this paper, the local structural environment of lead atoms in lead silicate glasses has been studied by two complementary spectroscopic techniques: Pb-LIII edge X-ray absorption fine structure (XAFS) and 207Pb solid state nuclear magnetic resonance (NMR) XAFS results have been obtained with two kinds of experimental devices: a synchrotron radiation source and a laboratory spectrometer.
Abstract: The local structural environment of lead (Pb) atoms in lead silicate glasses has been studied by two complementary spectroscopic techniques: Pb-LIII edge X-ray absorption fine structure (XAFS) and 207Pb solid state nuclear magnetic resonance (NMR) XAFS results have been obtained with two kinds of experimental devices: a synchrotron radiation source and a laboratory spectrometer The weak photon flux is then compensated by a higher stability of the source and a longer acquisition time The experiments were carried out on selected compositions of lead silicate glasses in which we observed PbO3 and PbO4 pyramidal units with short Pb–O bond lengths typical of a covalent bonding state
TL;DR: A technique for obtaining dipolar-mediated INADEQUATE NMR spectra with a large spectral window in the double-quantum dimension is presented by incrementing the evolution period in synchrony with the phase of the radiofrequency pulses in the C7 sequence.
Book•
18 Mar 1999
TL;DR: In this paper, the authors describe recent advances in solid-state NMR methods as applied to modern inorganic materials such as metal oxides, catalysts, zeolites, glasses, ceramics, semiconductors, ion conductors, superconductors, and composites.
Abstract: This book describes recent advances in solid-state NMR methods as applied to modern inorganic materials such as metal oxides, catalysts, zeolites, glasses, ceramics, semiconductors, ion conductors, superconductors, and composites.
TL;DR: The solid–state NMR measurements suggest that the Gly–Pro–Gly–Arg (GPGR) motif adopts an antibody–dependent conformation in the bound state and may be conformationally heterogeneous in unbound, full–length gp120.
Abstract: Solid–state NMR evidence for an antibody–dependent conformation of the V3 loop of HIV–1 gp120
TL;DR: The structure of the membrane anchor domain of the HIV-1-specific accessory protein Vpu has been investigated in solution and in lipid bilayers by homonuclear two-dimensional and solid-state nuclear magnetic resonance spectroscopy and the line widths and chemical shift data of three selectively 15N-labeled peptides are consistent with a transmembrane alignment of a helical polypeptide.
Abstract: The structure of the membrane anchor domain (VpuMA) of the HIV-1-specific accessory protein Vpu has been investigated in solution and in lipid bilayers by homonuclear two-dimensional and solid-state nuclear magnetic resonance spectroscopy, respectively. Simulated annealing calculations, using the nuclear Overhauser enhancement data for the soluble synthetic peptide Vpu1-39 (positions Met-1−Asp-39) in an aqueous 2,2,2-trifluoroethanol (TFE) solution, afford a compact well-defined U-shaped structure comprised of an initial turn (residues 1−6) followed by a linker (7−9) and a short helix on the N-terminal side (10−16) and a further longer helix on the C-terminal side (22−36). The side chains of the two aromatic residues (Trp-22 and Tyr-29) in the longer helix are directed toward the center of the molecule around which the hydrophobic core of the folded VpuMA is positioned. As the observed solution structure is inconsistent with the formation of ion-conductive membrane pores defined previously for VpuMA in pl...
TL;DR: This correlation shows that the EFG at 71Ga sites are generally three times greater than those at equivalent 27Al sites, and proposes a correlation between gallium and aluminum electric field gradients (EFG).
TL;DR: Solid-state deuterium magic angle spinning NMR spectra of perdeuterated adamantane bound to the active site of microcrystalline cytochrome P450cam (CP450cam) in its resting state provide direct support for previous proposals that substrates are conformationally mobile on the time scale of enzymatic turnover.
Abstract: We report solid-state deuterium magic angle spinning NMR spectra of perdeuterated adamantane bound to the active site of microcrystalline cytochrome P450cam (CP450cam) in its resting state. CP450cam contains a high-spin ferric (Fe3+) heme in the resting state; the isotropic shift was displaced from the diamagnetic value and varied with temperature consistent with Curie-law dependence. A nondeuterated competitive tighter binding ligand, camphor, was used to displace the adamantane-bound species. This addition resulted in the disappearance of the hyperfine-shifted signal associated with a perdeuterated adamantane bound to CP450cam, while signals presumably associated with adamantane bound to other cavities persisted. We simulated the deuterium spinning side-band intensities for the enzyme-bound species using dipolar hyperfine coupling as the only anisotropic interaction; the deuterium quadrupolar interaction was apparently averaged due to a fast high-symmetry motion. These data provide direct support for pr...
TL;DR: The monovalent cation selective channel formed by a dimer of the polypeptide gramicidin A has a single-stranded, right-handed helical motif with 6.5 residues per turn forming a 4-A diameter pore, and the high-resolution structure has led to precise models for cation binding, cation selectivity, and cation conductance efficiency.
Abstract: The monovalent cation selective channel formed by a dimer of the polypeptide gramicidin A has a single-stranded, right-handed helical motif with 6.5 residues per turn forming a 4-A diameter pore. The structure has been refined to high resolution against 120 orientational constraints obtained from samples in a liquid-crystalline phase lipid bilayer. These structural constraints from solid-state NMR reflect the orientation of spin interaction tensors with respect to a unique molecular axis. Because these tensors are fixed in the molecular frame and because the samples are uniformly aligned with respect to the magnetic field of the NMR spectrometer, each constraint restricts the orientation of internuclear vectors with respect to the laboratory frame of reference. The structural motif of this channel has been validated, and the high-resolution structure has led to precise models for cation binding, cation selectivity, and cation conductance efficiency. The structure is consistent with the electrophysiological data and numerous biophysical studies. Contrary to a recent claim [Burkhart, B. M., Li, N., Langs, D. A., Pangborn, W. A. & Duax, W. L. (1998) Proc. Natl. Acad. Sci. USA 95, 12950-12955], the solid-state NMR constraints for gramicidin A in a lipid bilayer are not consistent with an x-ray crystallographic structure for gramicidin having a double-stranded, right-handed helix with 7.2 residues per turn.
TL;DR: In this paper, the regioselective hydrogen/deuterium exchange taking place between isobutane and acidic OH groups of strong solid acids has been investigated both byin-situsolid state 1H MAS NMR with perdeuteroisobutanes and H-ZSM5 and by liquid 1H and 2H NMR on various D2O-exchanged solid acids.
TL;DR: In this article, the 13C and 1H NMR measurements on the same samples were used to resolve the seven different forms of unprotonated and protonated CHx carbon, as well as the ratio between bound and unbound hydrogen.
Abstract: Various hydrogenated amorphous carbon films have been analyzed by 13C and 1H nuclear magnetic resonance (NMR) spectroscopies. The films have been deposited from acetylene or cyclohexane by dc plasma enhanced chemical vapor deposition, at various dc biases and gas pressures. The total hydrogen content has been measured by forward recoil elastic scattering (FRES). 13C NMR investigations have been performed in various configurations: high power decoupled to determine the sp2:sp3 carbon ratio, cross polarized at magic angle contact spinning with different contact times to provide information on carbon atoms directly bound to hydrogen, and with dipolar dephasing to study the quaternary carbon atoms. By performing the 13C and 1H NMR measurements on the same samples, it was possible to resolve for the first time the seven different forms of unprotonated and protonated CHx carbon, for both sp2(x=0,1,2) and sp3(x=0,1,2,3) carbon hybridizations, as well as the ratio between bound and unbound hydrogen. The results are discussed and compared with previously published FRES and Fourier transform infrared (FTIR) data. It is shown that NMR and FTIR combined with FRES do not agree systematically on the ratio of bound/unbound hydrogen.
TL;DR: In this article, a combination of Solid State NMR (SSNMR) dipolar recoupling and double quantum CSA−CSA correlation experiments are used to determine the Ramachandran angles φ and ι in a crystalline tripeptide (AGG) and a 14 amino acid peptide designed to be helical.
Abstract: A combination of Solid State NMR (SSNMR) dipolar recoupling and double quantum CSA−CSA correlation experiments are used to determine the Ramachandran angles φ and ι in a crystalline tripeptide (AGG) and a 14 amino acid peptide designed to be helical. The advantage of the SSNMR approach described herein is the ability to measure both φ and ψ to high resolution using a single noncrystalline, doubly carbonyl labeled peptide. It is also shown that DRAWS and DQDRAWS data are insensitive to 14N−13C and 15N−13C dipolar couplings making corrections for these effects unnecessary. Extremes in secondary structure (e.g., α-helix vs β-sheet) can be discerned by simple inspection of DQDRAWS spectra. Subtleties in secondary structure (α-helix vs 310-helix) can be distinguished by simulation of the DQDRAWS spectrum.
TL;DR: In this article, 27Al, 31P and 7Li NMR measurements have been performed on lithium conducting ceramics based on the LiTi2(PO4)3 structure with Al, V and Nb metal ions substituted for either Ti or P within the NASICON structure.
TL;DR: In this article, high-order multiple quantum (MQ) coherences among 13C nuclear spins in singly-13C-labeled organic solids are demonstrated experimentally using a time-reversible multiple pulse excitation sequence modified specifically for experiments on systems with weak homonuclear dipole-dipole couplings and strong inhomogeneous interactions.
Abstract: Excitation and detection of high-order multiple quantum (MQ) coherences among 13C nuclear spins in singly-13C-labeled organic solids is demonstrated experimentally. MQ signals involving at least ten quanta of spin angular momentum are observed in nuclear magnetic resonance (NMR) measurements on polycrystalline L-methionine-methyl-13C and L-alanine-1-13C, using a time-reversible multiple pulse excitation sequence modified specifically for experiments on systems with weak homonuclear dipole–dipole couplings and strong inhomogeneous interactions such as anisotropic chemical shifts. The feasibility of high-order MQ excitation and detection in 13C-labeled organic solids promises to expand significantly the range of applications of MQ NMR as a structural tool, to include such systems as 13C-labeled synthetic polymers and biopolymers.
TL;DR: The adsorption of CH(D)Cl3 and CHF3 on a series of alkali-exchanged Y-zeolites was studied by 1H- and 23Na-NMR and by FTIR spectroscopy as mentioned in this paper.
Abstract: The adsorption of CH(D)Cl3 and CHF3 on a series of alkali-exchanged Y-zeolites was studied by 1H- and 23Na-NMR and by FTIR spectroscopy. Several adsorption structures were detected which involve H-bonding C–H(D)···OZ between the acidic C–H(D) group and basic OZ-framework atoms and between the exchangeable cations and halogen atoms of the probe molecules. 1H-NMR demonstrated rapid exchange between several adsorption species and IR spectroscopy permitted detection of at least two different species, namely purely H-bonded species I and species II and/or III involving cation–halogen interactions. It is inferred that these species can undergo facile interconversion and that such processes may be involved in the rapid exchange as detected by NMR. Based on 23Na-NMR results it is concluded that adsorption of CHCl3 on NaY modifies the negative charge distribution in the zeolite framework. The adsorption-induced C–H(D)-stretching frequency shift of trichloromethane is considered to be a measure of the base strength of the framework OZ-atoms.