Use of ~(13)C MAS NMR to study domain structure and dynamics of polysaccharides in the native starch granules

摘要

To investigate the domain structure and dynamic of polysaccharides in the native strach granules,a variety of high resolution,solid-state ~(13)C NMR techniques have been applied to all three (A-,B-,and C-) types of starch with different water content.Both single-pulse-excitation magic-angle-spinning (SPEMAS) and cross-polarization-magic-angle-spinning (CPMAS) methods have been employed together with the PRISE (proton relaxation induced spectral-editing) techniques to distinguish polysaccharide fractions in different domains and having distinct dynamics.It has been found that,for all three types of dry starch granules,there are two sets of NMR signals corresponding to two distinct ordered polysaccharides.Hydration leads to substantial mobilization of the polysaccharides in the amorphous regions,but no fundamental changes in the rigidity of the polysaccharides in the crystalline (double) helices.Full hydration also leads to limited mobility changes to the polysaccharides in the amorphous lamellae (branching zone) within the amylopectin clusters and in the gaps between the arrays of the amylopectinc lusters.Under magic-angle spinning,proton relaxation-time measurements showed a single component for T_1,two components for T_(1rho),and three components for T_2.PRISE experiments permitted the neat separation of the ~(13)C resonances of polysaccharides in the crystalline lamellae from those in the amorphous lamellae and the amylose in the gaps between amylopecin clusters.It has been found that the long ~1H T_(1rho) component (approx30ms) is associated wtih polysaccharides in the crystalline lamellae in the form of double helices,whereas the short T_(1rho) component (2-4 ms) is associated with amylose in the gaps between amylopecin clusters.The short ~1H T_2 component (approx14 mus) is associated with polysaccharides in the crystalline lamellae;the intermediate component (300-400 mus) is associated with polysaccharides in the amorphous lamellae and amylose in the gaps between amylopectin clusters.The long T_2 component is associated with both mobile starch protons and the residue water protons.