Solid state NMR and X-ray studies on amylose complexes with small organic molecules

Crystalline complexes of amylose with lauric acid, n-butanol, n-pentanol, dimethyl sulfoxide and thymol were examined by C-13 CP/MAS NMR and X-ray diffraction methods. The complexes displayed the single helix V-amylose structure and were heat stable at least up to 90degreesC. In addition, the X-ray diffraction pattern of the amylose-n-butanol complex was similar to that of the amylose-n-pentanol complex which is interpreted to mean that the guest agents are not present in crystallographic register. It is suggested that the guests are in a matrix, of crystal surfaces, dislocations and chain folds, such that only the amylose chains contribute to the observed crystalline diffraction patterns. After humidification, the NMR spectra showed partial transformation to the double helix B-polymorph for all complexes except that formed with lauric acid. The transformation is dependent on the alkyl chain length of guest agents. Once the double helix polymorph was formed, it was permanent unless the sample was redissolved.