Quantum-mechanical study of the interaction of alpha-cyclodextrin with methyl mercury chloride

The inclusion process involving alpha-cyclodextrin (alpha-CD) and methyl me rcury chloride (CH3HgCl) was investigated using the PM3 quantum-mechanical semi-empirical method. Fully unconstrained geometry optimizations were carr ied out for the free alpha-CD and the complexed forms with CH3HgCl. The inc lusion orientation with the methyl mercury chloride passing perpendicular t o the center of the cyclodextrin ring was found to be favored over the expe rimentally hinted parallel structure. It was also observed that the inclusi on takes place in a more favored way when solvation water molecules are exp licitly included, therefore stabilizing the complex in relation to the free species. The experimentally observed Raman shift for the Hg-Cl stretching mode after the complexation was used in conjunction with the respective PM3 calculated vibrational frequencies for the determination of the preferred structure for the inclusion complex. (C) 2000 Elsevier Science B.V. All rig hts reserved.