Asymmetrical complexes [Pt(N,N-dmen)(dGuo)L]((2)+) (N,N-dmen = N,N-dimethylethylenediamine; L = H2O, Cl-, dGuo): H8 nuclei experience an orientation-dependent deshielding effect attributable to the paramagnetic anisotropy ofthe platinum atom

N7 coordination of deoxyguanosine (dGuo) to platinum(II) is known to shift the NMR signal of the guanine H8 proton downfield. The amplitude of this do wnfield shift depends on the platinum ligands and their configuration. We s how here that the guanine H8 chemical shift variation upon coordination of dGuo to [Pt(N,N-dmen)(H2O)(2)](2+) (N,N-dmen = N,N-dimethylethylenediamine) or to [PtCl(N,N-dmen)(H2O)] is 0.2-0.3 ppm larger when dGuo binds cis to t he NMe2 group than when it coordinates the site cis to the NH2 group. This difference can be explained by sterical restrictions imposed by the bulky N Me2 group to a cis-guanine, forcing it into an orientation approximately pe rpendicular to the coordination plane. In this position, the H8 proton appa rently experiences a downfield shift arising from the paramagnetic anisotro py of the platinum(II) atom. (C) 2000 Elsevier Science S.A. All rights rese rved.