NMR local range investigations in amorphous starchy substrates: II-Dynamical heterogeneity probed by 1H/ 13C magnetization transfer and 2D WISE solid state NMR

Abstract

In the preceding paper, we have investigated the structural heterogeneous character of a series of amorphous samples prepared from various starchy substrates (native potato starch, amylopectin and amylose) following different techniques of preparation (casting, freeze drying and solvent exchange). Spectral decompositions of the C1 resonances of the 13C CP-MAS (Cross Polarization and Magic Angle Spinning) spectra under 1H decoupling have shown the existence of five main types of α(1-4) linkages. In this part, 2D solid state NMR WISE experiments and the 13C/ 1H magnetization transfer in CP as a local probe for both structures and dynamics were used. The 13C CP magnetization curves versus contact time of each C1 component in each recorded spectrum were fitted with an analytic function taking into account two 1H reservoirs. Interpretation of the characteristic times derived from fitting yields some improvements on the knowledge of the heterogeneity of the samples and on the water molecules distribution.