The synthesis of several pentaammineruthenium(I1 and 111)-guanine complexes is reported, in which the metal is believed to be bound to Ni. The Ru(II1) compounds exhibit a broad low energy guanine-to-metal chargetransfer absorption, while the Ru(1I) complexes show a metal-to-ligand charge transfer in the ultraviolet. The effect of Ru(I1 and 111) on the acidity of the protons at N1 and Ng is investigated. Electrochemical potentials are reported for the complexes over a broad pH range. At low pH the Ru(II1) nucleoside complexes undergo acidcatalyzed hydrolysis of the sugar-purine bond at a much slower rate than do the corresponding free nucleosides. he interaction of metal ions with nucleotides has T been the subject of considerable investigation for the past several years. Areas of interest include: the effect of metal ions on the stability of nucleic acids, 2, synthesis of heavy-atom derivatives as aids in determining the structure of RNA by X-ray crystallogr a ~ h y , ~ the participation of metal ions in the biological function of nucleic acids,5 the use of heavy metal derivatives of nucleosides as cytological stains,6 and the sequencing of nucleic acids by electron microscopy with the aid of a metal ion complex binding selectively to sites along the polynucleotide chain.7~8 (1) R. M. Izatt, J. J. Christensen, and J. H. Rytting, Chem. Rev., 71, (2) G. L. Eichhorn, eral., Adaan. Chem. Ser., No. 100,135 (1971). (3) G. L. Eichhorn, E. Tarien, and J. Butzow, Biochemistry, 10,2014 (4) S. H. Kim, G. J. Quigley, F. L. Suddath, A. McPherson, D. ( 5 ) W. Szer and S. Ochoa, J . Mol. Biol., 8 , 823 (1964). (6) R. J. Barrnett, J. Roy. Microsc. SOC., 83, 143 (1964). (7) M. Beer and I. Moudrianakis, Proc. Nut. Acad. Sci. U. S., 48, (8) D. Gibson, M. Beer, and R. Barrnett, Biochemistry, 10, 3699 439 (1971).