Amylose-vanillin complexation assessed by a joint experimental and theoretical analysis

A joint experimental and theoretical study has been carried out on the amylose-vanillin complex, demonstrating its formation by X-ray diffraction as well as UV/visible and circular dichroism spectroscopic techniques. Theoretical simulations substantiate these experimental data and the variations of properties upon complexation by evidencing the stability of the inclusion of vanillin in the helical cavity as well as by explaining the related changes of the linear (chiro-)optical properties. In particular, the circular dichroism (CD) signature of the vanillin inclusion complex results from a geometrical distortion induced by the complexation with the surrounding amylose helix. The use of the ONIOM technique mixing B3LYP and PM6 levels of approximation to include the interactions between different layers (together with the IEFPCM model to describe the solvent) appears to be a satisfactory methodology to simulate both the UV and CD spectra for these compounds.