Slow and Very Fast MAS Solid State NMR Study of Biopolymers

Abstract

SummaryIn the first part of article, the “NMR Crystallography” approach as tool to fine refinement of solid state structure of biopolymers is presented, employing the α polymorph of L‐polylactide (PLLA) as model. Slow Magic Angle Spinning (MAS) technique (with spinning rate of sample in range from 1.2 kHz to 8.0 kHz) was used to assign 13C isotropic chemical shifts and values of 13C δii principal elements of chemical shifts tensors (CST). Theoretical 13C shielding parameters σii were obtained employing GIPAW (Gauge Invariant Projector Augmented Wave) method and compared with experimental 13C δii elements. The computed and experimental 13C CP/MAS spectra for WAND (Wide Angle Neutron Diffraction) geometry of powdered α PLLA were evaluated. It was revealed that the computed model of α PLLA model better fit to experimental NMR spectra.In the second part of article the applications of the new NMR methodology, so called very fast MAS (VF MAS) with sample spinning over 60 kHz are presented. The power of this approach is shown employing the 13C and 15N labeled protein, ubiquitin. We revealed that Cross‐Polarization with Variable Contact (CPVC) time sequence under very‐fast MAS condition performed in two‐dimensional (2D) mode is very efficient method to measure accurately the CH and NH distances, and to analyze the dynamics of proteins with overlapped resonances in aliphatic and aromatic regions.