The interaction of methylcobalamin with tetracyanoplatinate(II), tetrathiocyanoplatinate(II) and tetrachloroplatinate(II)

Abstract

The interactions of methylcobalamin (CH 3-B 12) with Pt(CN) 4 2−, PtCl 4 2−, and Pt(SCN) 4 2− in aqueous solution were studied by UV-visible and 1H NMR spectroscopy. Together with earlier results on the mechanism of the Pt(IV)-dependent methyl-transfer reaction from CH 3-B 12 to Pt(II), these studies suggest at least three Pt binding sites on CH 3-B 12. One site, which is occupied by all three complexes (K 1 = 4 X 10 3 M −1 for Pt(CN) 4 2− and 3 X 10 3 M −1 for PtCl 4 2−), is located on the CoCH 3 side of the corrin macrocycle, and is involved in the methyl-transfer process in the presence of a Pt(IV) complex. An additional site for Pt(SCN) 4 2− is the N-3 of the benzimidazole group, resulting in dissociation of this group from the cobalt. An additional site for Pt(CN) 4 2− has a binding constant of 16 M 1̄ and 1H NMR changes indicate perturbation but not dissociation of the benzimidazole group. Only the first interaction is discerned for PtCl 4 2−.