Interactions of organotins with biological systems

The bonding and structure in the environments of tin atoms in organotin-biological molecules has been investigated by 119Sn Mossbauer spectroscopy, mainly through the rationalization of the nuclear quadrupole splitting parameter by pointcharge model approaches. Organotin moieties R2SnIV and R3SnIV (R = Me, nBu, Ph) generally assume trigonal-bipyramidal type configurations in membranes of human erythrocytes, when incubated with whole erythrocytes and erythrocyte ghosts at the level of micromolar (μmol dm−3) organotin per mg of membrane protein. Corresponding structures are assumed by Me2SnIV and Me3SnIV in the cytoplasm. Ethanolic Me2SnCl2 yielded distorted trans-octahedral species when reacted with ghost cells. These configurations may in principle originate through coordination of the metal by donor nitrogen or oxygen atoms from the cell constituents, such as protein side chains and related component molecules, carbohydrate fragments, and phospholipids, according to data from various model systems. Hydrolyzed species, such as bis(chlorodiorganotin) oxides and triorganotin hydroxides, could also occur for the n-butyltin and phenyltin species. The moieties Me2SnIV and Alk3SnIV (Alk = Me, Et, nBu), present as the hydrolysis products Me2Sn(OH)2 and Alk3SnOH at physiological pH in the aqueous phase (eventually coordinated by donor atoms from buffers), react with thiol groups of model molecules, as well as of feline and rat hemoglobin, forming tetrahedral or trigonalbipyramidal tin sites characterized by covalent SnS bonds (C2SnS, C2SnS2 and C3SnS skeletons); tin atoms are eventually further coordinated by nitrogen donors from amino acid fragments or from buffers, as well as by hydroxyl oxygen.