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The dipeptide complex [Pd(gly-~-hisN")Cl]~l.5H,O 1 (gly-L-hisN" = monoanion of glycylhistidine, deprotonated at the amide N ) has been prepared and structurally characterized. Co-ordination of Pd is through the terminal amino group of the glycyl entity, N(n) of the imidazole ring of the histidine, and the deprotonated amide nitrogen. Reactions of 1 with the model nucleobases 1 -methyluracil (Hmura), 1methylcytosine (mcyt), 9-methyladenine (made), 9-ethylguanine (Hegua) and 6-methoxy-9-methylguanine (momgua) have been studied in solution by 'H N M R spectroscopy. The mcyt complex, [Pd(gly-L-hisNa,O) (mcyt)].3.5H2O (gly-L-hisN*,O = dianion of glycylhistidine, deprotonated at the amide N and the carboxylic acid group) has been structurally characterized. Nucleobase co-ordination is via N3. Proton N M R spectra of complexes of 1 with all model bases are indicative of rotamer formation and, with the purine bases, of linkage isomerism (N7, N' and simultaneously with N7/N1). In weakly acidic, neutral or slightly alkaline media or with an excess of 1, Hegua and, most likely, also made form complexes of Pd,(nucleobase) stoichiometry with Pd binding through N' and N7 and the third Pd linked to one of these Pd(gly-L-his) entities. As a consequence, the resonances of some of the aromatic protons of the histidine imidazole ring are shifted upfield by as much as 1 ppm. Complex stability constants have been determined by means of 'H N M R spectroscopy for a number of 1 :1 complexes of 1 with model nucleobases.

With [Pt(Hamet)Cl 3 ] Ϫ a 6 ppm splitting of the 195 Pt resonance due to diastereomers has been detected at higher field strength.

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