Facile Preparation Method for Inclusion Complexes between Amylose and Polytetrahydrofurans

Several methods were used to investigate the possibility of preparing inclusion complexes between amylose and polytetrahydrofurans (PTHF) via direct mixing. Potato amylose (Mv ~ 200 kg/mol) and synthetic amylose (Mn 42 kg/mol) were complexed with PTHF having different molecular weights (Mn between 650 and 2900 g/mol) to study the effect of the length of the host and the guest molecules on the complexation. The resulted products were studied by differential scanning calorimetry (DSC) that showed a characteristic melting peak in the range of 120−140 °C. Emulsification of both amylose and polytetrahydrofuran improved the complexation. The largest amount of complexes was obtained with shorter PTHF chains, which also resulted in less amylose retrogradation. Furthermore, PTHF chains with similar molecular weight but different end groups were used. Amine terminated PTHF formed a higher amount of complexes compared to the hydroxyl terminated PTHF. However, no amylose complexes were formed using benzoyl terminated PTHF with low molecular weight. This is due to the bulky group of benzoyl, which indicates that the mechanism of the complexation between amylose and PTHF occurs via insertion rather than wrapping. In addition, X-ray diffraction (XRD) analysis showed that the included PTHFs induced the formation of the so-called V-amylose with six glucose residues per helix turn. Some additional diffraction peaks indicate that the induced V6-amylose is probably an intermediate or the mixtures between V6I- and V6II-amylose.