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Use of 13 C MAS NMR to Study Domain Structure and Dynamics of Polysaccharides in the Native Starch Granules

2003; American Chemical Society; Volume: 4; Issue: 5 Linguagem: Inglês

10.1021/bm0340772

1526-4602

Huiru Tang, B.P. Hills,

Polysaccharides Composition and Applications

To investigate the domain structure and dynamics of polysaccharides in the native starch granules, a variety of high resolution, solid-state 13C 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 amylopectin clusters. Under magic-angle spinning, proton relaxation-time measurements showed a single component for T1, two components for T1ρ, and three components for T2. PRISE experiments permitted the neat separation of the 13C resonances of polysaccharides in the crystalline lamellae from those in the amorphous lamellae and the amylose in the gaps between amylopectin clusters. It has been found that the long 1H T1ρ component (∼30 ms) is associated with polysaccharides in the crystalline lamellae in the form of double helices, whereas the short T1ρ component (2−4 ms) is associated with amylose in the gaps between amylopectin clusters. The short 1H T2 component (∼14 μs) is associated with polysaccharides in the crystalline lamellae; the intermediate component (300−400 μs) is associated with polysaccharides in the amorphous lamellae and amylose in the gaps between amylopectin clusters. The long T2 component is associated with both mobile starch protons and the residue water protons.