Deuterium quadrupole coupling in N-acetylglycine and librational dynamics in solid poly (.gamma.-benzyl-L-glutamate)

Abstract

To study the dynamics of peptide groups in solid proteins, we have accurately determined the principal components and molecular orientation of the electric field gradient tensor for the exchangeable deuterons in monoclinic N-acetylglycine by single-crystal deuterium nuclear magnetic resonance. These results are compared with the principal components of the amide deuterons in solid poly(gamma-benzyl-L-glutamate) measured in powder samples over a wide temperature range (140-400 K). The comparison indicates that in the solid polypeptide the N-D bonds undergo a small-amplitude torsional reorientation (libration) perpendicular to the peptide plane. To estimate dynamic rates, longitudinal relaxation times (T1 values) are reported for N-acetylglycine and poly(gamma-benzyl-L-glutamate). T1 values for the carboxyl and amide deuterons in N-acetylglycine are approximately 100 s, whereas for the amide deuterons in the polypeptide T1 approximately 1 s, also indicating that the N-D bonds are not stationary in the polypeptide. We determine from the reduced quadrupole coupling tensor the mean-square amplitude for the libration and show that it increases linearly with temperature. A simple qualitative theory for the relaxation times is presented on the basis of the assumption that the N-D reorientation is described either as a diffusion process in a square well or as a damped Langevin oscillator with a harmonic restoring force. The conclusion is that the short relaxation times of the polypeptide amide deuterons result from substantial frictional effects on reorientation that increase with temperature.

Deuterium Quadrupole-Coupling and Chemical-Shielding Tensors in the Model Dipeptide Glycylglycine Monohydrochloride Monohydrate

“…This is not surprising in view of the data of Ref. ( 12 ) , where for NAG there is no that component, i.e., observable variation of h over this temperature range, and e 2 qQ / h changes by only 5%. n zz Å n zz 0 0 Ecos j cos z…”

“…The other molecules biologically important peptide group. These are N-acetylvaare related by inversion through the (010) plane and, in line (11) and N-acetylglycine (12). Both molecules considgeneral, give rise to separate peaks.…”

“…Although deuteron electric field gradient (EFG) four molecules per unit cell. The second molecule is related tensors have been determined for many chemically represento the first through an inversion center, which makes it indistative species (6)(7)(8)(9)(10)(11)(12), there are only two models for the tinguishable by magnetic resonance. The other molecules biologically important peptide group.…”

Changes in protein structure and dynamics as a function of hydration from 1H second moments

“…The resulting structural reorganization may facilitate local motion of some groups because of changes in the effective free volume in the folded structure. Of course, it is well known that such motions as N-H small librations [12] or methyl rotations [13,14] are present at 298 K whether the protein is dry or hydrated; however, it is clear from earlier work that solvation of side chains permits side chain motions that lengthen the transverse decay significantly [15]. The present analysis of the transverse decay isolates the fast component, which then corresponds to the majority of the protein protons that do not experience significant dynamical averaging.…”

Applications of solid state NMR to cardiolipin and elastin.

“…Third, the stretch-induced decrease in polymer correlation times so obtained were interpreted as the reciprocal oscillator frequency of an undamped, harmonic oscillator. Undamped harmonic motions are far too high in frequency to cause spin relaxation and are a poor model for large amplitude reorientational motions about chemical bonds [147] which are better described as diffusive or jump-like [148]. Finally, interpreting a decrease in correlation times, i.e., an increase in dynamical rates, as an increase in entropy is not necessarily valid since entropy is an equilibrium property and depends only on the equilibrium distribution of orientations and not on the rates at which different orientations or configurations are sampled.…”