Stochastic Modelling of 13C NMR Spin Relaxation Experiments in Oligosaccharides

Abstract

A framework for the stochastic description of relaxation processes in flexible macromolecules including dissipative effects has been recently introduced, starting from an atomistic view, describing the joint relaxation of internal coordinates and global degrees of freedom, and depending on parameters recoverable from classic force fields (energetics) and medium modelling at the continuum level (friction tensors). The new approach provides a rational context for the interpretation of magnetic resonance relaxation experiments. In its simplest formulation, the semi-flexible Brownian (SFB) model has been until now shown to reproduce correctly correlation functions and spectral densities related to orientational properties obtained by direct molecular dynamics simulations of peptides. Here, for the first time, we applied directly the SFB approach to the practical evaluation of high-quality 13C nuclear magnetic resonance relaxation parameters, T1 and T2, and the heteronuclear NOE of several oligosaccharides, which were previously interpreted on the basis of refined ad hoc modelling. The calculated NMR relaxation parameters were in agreement with the experimental data, showing that this general approach can be applied to diverse classes of molecular systems, with the minimal usage of adjustable parameters.

The roto-conformational diffusion tensor as a tool to interpret molecular flexibility

“…[26][27][28][29][30], and R eff was set to the optimal value providing the lowest sum of squared percentage deviations for T 1 , T 2 and NOE over the entire ensemble of experimental data available for each system, as estimated in ref. 31. For DMF and GB3, temperature and viscosity were arbitrarily chosen, and a value of R eff = 2.0 Å was used.…”