Structure and dynamics of the branched polysaccharide scleroglucan in dilute solutions studied by 1D and 2D NMR spectroscopy

Variable temperature and magnetic field dependent C-13 NMR relaxation measu rements (T-1 and NOE) were carried out for the branched polysaccharide scle roglucan in DMSO-d(6) dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using the bimodal time-correlation functions developed by Dejean, Laupretre, and Monnerie (DLM), which offere d the best quantitative description of the segmental motion of the carbohyd rate chains. Simple internal rotations of the free hydroxymethyl groups of the backbone rings about the exocyclic C-5-C-6 bonds superimposed on segmen tal motion have been described as a diffusion process of restricted amplitu de. Multiple internal rotations involving the exocyclic hydroxymethyl group of the ring at the branched point and that of the side chain ring, as well as the side chain ring itself were described by employing a composite TCF for side chain motions superimposed on polymer segmental motions. These tim e-correlation functions and their Fourier transform pairs, the spectral den sities, offered the best interpretation of the relaxation data of the exocy clic free hydroxymethyl groups, and the pendent D-glucorynosyl ring. Finally, the H-1- and C-13 NMR spectra of the neutral scleroglucan in DMSO- d(6) were analyzed by employing a series of 2D NMR experiments. The 500 MHz H-1 NMR spectrum of scleroglucan at 283 K show severe peak overlaps, which do not allow the complete assignment of all signals in the carbon spectrum . (C) 2001 Elsevier Science Ltd. All rights reserved.