Showing papers on "Solid-state nuclear magnetic resonance published in 1982"
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01 Jan 1982425 citations
393 citations
TL;DR: In this paper, an asymmetric double minimum potential with an energy difference ΔG = 1.0 kJ/mol and an activation energy of Ea = 4.8 kj/mol between the two tautomeric forms is found.
Abstract: Direct evidence for dynamic intramolecular double proton exchange in carboxylic acid dimers in the solid is obtained from NMR measurements. For the p‐toluic acid dimer, an asymmetric double minimum potential with an energy difference ΔG = 1.0 kJ/mol and an activation energy of Ea = 4.8 kJ/mol between the two tautomeric forms is found. The equilibrium position of the carboxylic proton pair at low temperature is derived from the corresponding dipolar coupling tensor. The importance of double proton tunneling at low temperature is discussed.
204 citations
201 citations
TL;DR: In this article, the sign, magnitude, and asymmetry parameters of the 14N quadrupole coupling tensor were determined from 13C NMR data using single crystal studies or molecular symmetry.
Abstract: The dipolar coupling between 14N and 13C is not suppressed by magic angle sample spinning because the relatively large 14N quadrupole interaction shifts the axis of quantization of the 14N spins away from the direction of the applied field. The resulting 13C resonance line shapes are influenced by the sign, magnitude, and asymmetry parameter of the 14N quadrupole coupling tensor; the internuclear distance; the magnitude of the applied magnetic field; and the orientation of the internuclear vector in the principal axis system of the electric field gradient. It is demonstrated that one or more of these parameters can be determined from the 13C NMR data if the others are known by virtue of single crystal studies or molecular symmetry.
194 citations
TL;DR: In this article, it was shown that sets of dipolar rotational sidebands, corresponding to individual chemical shift sidebands exhibit some unusual features, in particular, in the slow spinning regime, the dipolar sideband patterns are asymmetric and in some instances, individual sidebands are inverted.
Abstract: Magic angle sample spinning is combined with two‐dimensional NMR methods to obtain high resolution chemical shift‐dipolar spectra. Because both interactions are inhomogeneous, the 2D spectrum consists of a set of rotational sidebands spaced at the spinning frequency in each dimension. Projection of these sidebands onto the chemical shift or dipolar axis yields either the chemical shift or the dipolar spectrum fully separated from the other interaction. The projections may be used to extract the principal values of either the chemical shift or dipolar tensor, and from the latter, internuclear distances may be calculated. In addition, it is shown that sets of dipolar sidebands, corresponding to individual chemical shift sidebands, exhibit some unusual features. In particular, in the slow spinning regime, the dipolar rotational sideband patterns are asymmetric and in some instances, individual sidebands are inverted. The physical origin of this effect is discussed, and experimental results and computer simulations are in excellent agreement. Finally, it is shown that the intensity distribution of the sidebands permits a determination of the relative orientation of the shift and dipolar tensors.
168 citations
145 citations
TL;DR: In this article, high-resolution 31P solid-state NMR spectra of triphenylphosphine copper(I) complexes, obtained by combining proton dipolar decoupling, proton-phosphorus cross polarization and magic-angle sample spinning, often reveal asymmetric quartets rather than single resonance lines.
128 citations
124 citations
119 citations
TL;DR: In this article, a rotational sideband pattern for each magnetically inequivalent spin was proposed to project the dipolar information onto a single rotational pattern for a single spin pair.
Abstract: Two‐dimensional magic angle NMR methods produce high resolution dipolar‐chemical shift spectra of polycrystalline solids which permit determination of the mutual orientation and principle values of the two coupling tensors. This technique is applied to the amide 15N–1H spin pair in the dipeptide GlyGly ⋅ HCl ⋅ H2O, and we find the nearly axially symmetric 15N shift tensor is tilted 25° away from the NH bond. In many situations, however, only the magnitude of the heteronuclear dipolar coupling is required, and simplification of the spectrum would be desirable. An experiment that projects the dipolar information onto a single rotational sideband pattern for each magnetically inequivalent spin is proposed. The approach involves scaling the isotropic chemical shifts with a multiple‐pulse train, together with rotationally synchronized sampling. The method is demonstrated with spectra of the above mentioned dipeptide.
TL;DR: By applying magic angle spinning to proton magnetic resonance of zeolites, two different lines were separated as mentioned in this paper, showing that the signals must be due to hydroxyl groups of different acidity.
TL;DR: Topical magnetic resonance (TMR) is a method of obtaining high-resolution NMR spectra from a selected, localized place within a larger object, by modifying the main magnetic field, Bo, using only static magnetic field gradients.
Abstract: Topical magnetic resonance (TMR) is a method of obtaining high-resolution NMR spectra from a selected, localized place within a larger object, by modifying the main magnetic field, Bo, using only static magnetic field gradients. TMR is described together with the scope of metabolic information that can be obtained non-invasively from animals and human beings.
TL;DR: In this paper, the authors demonstrated that well-resolved 14 N- 195 Pt couplings can be observed in the NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature.
TL;DR: Spin-spin coupling constants between H alpha protons and HN and H beta protons correlated well with values predicted from the crystal structure by means of the Karplus relationship, which indicates that for the residues studied here the torsion angles phi and chi 1 describe accurately, generally well within 20 degrees, those for the average solution state.
Abstract: Resonances of H alpha, H beta, and HN (amide) protons have been assigned in the NMR spectrum for ten residues in a region of beta-sheet structure of lysozyme. The assignments were achieved primarily by interpretation of nuclear Overhauser effects in conjunction with spin decoupling. The HN hydrogens involved in main-chain hydrogen bonding were found to exchange slowly with D2O solvent, although one of the most slowly exchanging HN hydrogens is not classified as being involved in a hydrogen bond in the crystal structure. Spin-spin coupling constants between H alpha protons and HN and H beta protons correlated well with values predicted from the crystal structure by means of the Karplus relationship. For no residues are the coupling constant discrepancies greater than 2.5 HZ. This indicates that for the residues studied here the torsion angles phi and chi 1 defined in the crystal structure describe accurately, generally well within 20 degrees, those for the average solution state.
TL;DR: The carboxyl-containing sialic acids in gangliosides have glycosidic linkage resonance shifts only approximately 30% as large as those found for neutral hexopyranosides; thus, care must be used in interpreting the 13C spectra of charge oligosaccharides.
Abstract: Complete 13C nuclear magnetic resonance assignments are presented for gangliosides in the series GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. The gangliosides studied are related by the sequential addition of single saccharide residues. The structural relationships among these molecules were confirmed and subsequently utilized to provide the basis for a detailed investigation of 13C NMR oligomer-monomer shielding differences accompanying increasing oligosaccharide complexity. This gradual increase in complexity was reflected in the 13C NMR spectra and proved to be of significant value in the assignment task, resulting in the reassignment of four GM1 resonances from our previous work [Sillerud, L. O., Prestegard, J. H., Yu, R. K., Schafer, D. E., & Konigsberg, W. H. (1978) Biochemistry 17, 2619--2628]. The carboxyl-containing sialic acids in gangliosides have glycosidic linkage resonance shifts only approximately 30% as large as those found for neutral hexopyranosides; thus, care must be used in interpreting the 13C spectra of charge oligosaccharides. Secondary structural effects are also found to produce shifts in the resonances of the sialic acid adjacent to the GalNAc residue of GM2 and the more complex gangliosides, leading to inequivalence of the sialic acids in GD1a, GD1b, and GT1b.
TL;DR: The 1 7 0 NMR chemical shifts of the carbonyl oxygens have been determined for benzohydroxamic acid (1) and its derivatives in dioxane, benzene, and methanol and as functions of pH in the last solvent as mentioned in this paper.
Abstract: The 1 7 0 NMR chemical shifts of the carbonyl oxygens have been determined for benzohydroxamic acid (1) and its N-methyl (2), 0-methyl (3), and N,O-dimethyl (4) derivatives in dioxane, benzene, and methanol and as functions of pH in the last solvent. The observed chemical shift values (33C-350 ppm downfield in dioxane from external HzO) are in the range characteristic of benzamides, supporting the amide structure A. Upfield shifts of ca. 31 and 57 ppm were observed for the N-methyl(2 and 4) and NH compounds (1 and 3), respectively, in methanol solutions. Stronger hydrogen bonding with the solvent molecules in the NH compounds was suggested. From the 170 chemical shift titration curves of these compounds, the pK, values were obtained as 10.1, 9.8, and 10.8 for 1-3, respectively. On deprotonation, the carbonyl oxygen of 1 suffers an upfield shift of 72 ppm which corresponds better with that of 3 (83 ppm), namely, NH deprotonation. A smaller but significant upfield shift for 2 indicated unexpectedly large charge delocalization on OH dissociation. The pH dependence of 13C chemical shifts due to the carbonyl and aromatic ring carbons in methanol was less conspicuous. The NH compounds 1 and 3 behaved similarly to each other, supporting the conclusions obtained from 170 NMR. The NH deprotonation in 1 and dipole stabilization of the terminal 0 anion were supported by the ab initio MO theoretical calculations.
TL;DR: The polypeptide backbone of the protein has no large amplitude motions rapid compared to 10 4 Hz, which is reconciled with a model where an otherwise rigid backbone undergoes small amplitude, rapid motions.
TL;DR: The NMR data for the labeled collagens show that the intermolecular interactions that occur in collagen fibrils take place in fluid-like domains at the molecular surfaces.
Abstract: Publisher Summary This chapter describes the nuclear magnetic resonance (NMR) studies of molecular motion within collagen fibrils Solid state NMR methods, when used in conjunction with samples that contain 13 C- or 2 H-enriched amino acid residues, provide information about the rate and angular range of molecular motion at specific sites in collagen From the experiments carried out in chapter, it is found that the amplitudes of side-chain reorientations within collagen fibrils are large and that the rates of these motions are greater than 10 3 sec -1 The relaxation times and Overhauser enhancements values measured for the 13 C labeled side chains show that some of the side-chain motions have rates that exceed l0 9 sec –1 Taken together, the NMR data for the labeled collagens show that the intermolecular interactions that occur in collagen fibrils take place in fluid-like domains at the molecular surfaces It is anticipated that the quantitative understanding of these interactions will be further refined by studies of the temperature dependence of 2 H lineshapes
TL;DR: Using perturbation theory, it was demonstrated that the second order quadrupole broadening of the central line of the NMR spectra of half integer spins is reduced by rapid sample spinning at the magic angle down to about 1/36 of the original value.
Abstract: Using perturbation theory it is demonstrated that the second order quadrupole broadening of the central line of the NMR spectra of half integer spins is reduced by rapid sample spinning at the magic angle down to about 1/36 of the original value The centre of gravity of the central line remains unchanged Thus, the method of rapid sample spinning at the magic angle in the NMR of nuclei with strong quadrupole couplings can be used to get directly the spatial average of the chemical shift tensor This situation is demonstrated experimentally in the case of high-field 27 Al- and 23 Na-NMR of various materials