Modeling of the Alcohol Dehydrogenase Active Site: Two Different Modes of Alcohol Binding in Crystals of Zinc and Cadmium Tri-tert-butoxysilanethiolates Evidenced by X-ray Diffraction and Solid-State Vibrational Spectroscopy

Two different modes of binding methanol and ethanol were found in crystals of heteroleptic zinc and cadmium complexes with MS2NO2 and MS2NO kernels and with a general formula M(RS)(2)(im) (M = Zn, Cd; RS = tri-tert-butoxysilanethiolate; im = im = imidazole, 2-methylimidazole, 2-ethylimidazole). Alcohol molecules are either trapped in the crystal lattice by NH center dot center dot center dot O and OH center dot center dot center dot S hydrogen bonds or directly coordinated to the metal centre. The complexes were studied by X-ray diffraction, solid state FTIR and H-1, C-13, Si-29, and Cd-113 NMR spectroscopy both in solution and the solid state. The zinc complexes containing coordinated methanol and ethanol are considered as structural mimics of the active site of alcohol dehydrogenase and support intermittent five-coordination of the zinc ion in the active site of alcohol dehydrogenase. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)