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 of the 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 downfield shift depends on the platinum ligands and their configuration. We show 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 the 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 NMe2 group to a cis-guanine, forcing it into an orientation approximately perpendicular to the coordination plane. In this position, the H8 proton apparently experiences a downfield shift arising from the paramagnetic anisotropy of the platinum(II) atom.