tis-Dichlorodiammineplatinum(II) (I) is an effective antitumor agent in animals and man. The trans isomer II is ineffective. Since the cis configuration has the two neighboring leaving chloride groups, I may act as a bifunctional agent and II as a monofunctional agent. The interaction of I and II with purines, substituted purines, pyrimidines, and substituted pyrimidines in 0.1 M NaC104 at 37°, using uv spectrophotometry, is reported. It is possible to distinguish bidentate from monodentate binding, and to suggest the locations of the site of attack on nucleic acid components. The cis isomer forms a bidentate chelate with either 6-NH2 + N-7 or 6-NH2 + N-l of adenosine, and 4-NH2 + N-3 of cytidine. The trans isomer interacts monofunctionally at N-7,N-l of adenosine and N-3 of cytidine. Both isomers bind monofunctionally to N-7 of guanosine and inosine. No evidence of binding of either isomer to uridine or thymidine is detected. We conclude that there is no monofunctional attack at the NH2 group of cytidine, adenosine, or guanosine. The cis isomer binds bifunctionally at either N-l + 6-NH2 or N-7 + 6-NH2 groups. This suggests that the amino groups of adenosine and cytidine will be occupied when they are sterically well disposed for bidentate chelation. Such sites are available in the organized structure of DNA.

No abstract

No abstract

Using data on the equilibrium constants for hydrolysis of CH3Hg+ and for its binding to uridine and cytidine, solutions in the 10-100 mMrange have been prepared for which a particular complex should predominate. Raman spectra and particularly Raman difference spectra have been used to determine the perturbations of the cation and of the nucleoside ligand vibrations upon metal binding. The difference technique, applied here for the first time, is particularly effective for observing small spectral changes. Spectra have been obtained for the complex with polyuridilic acid to show that the perturbations are very similar with polynucleotides. A procedure for determining heavy metal binding sites on polynucleotides with two or more base moieties in aqueous solution is outlined. The methylmercury(II) ion binds to uridine (Urd) with displacement of a proton and coordination to N(3). Binding to cytidine also occurs at N(3), although, at pH 7, coordination to Urd is favored. The behavior of CH3-Recently the usefulness of Raman spectroscopy in

Literature values of equilibrium constants for binding CH3Hgn to guanosine and adenosine have been used to construct models describing the species distribution as a function of pH in these systems. Raman difference spectra have been determined for H20 and D20 solutions of CH3Hgu and Guo-5'-p as well as CH3Hgn + Ado-5'-P and Ado to determine the perturbations of both cation and nucleotide vibrations upon metalation at different sites. At approximately neutral pH, Guo-5'-P mercuriates at N(n with displacement of a proton giving a spectrum rather like that of [GuoH-i-5'-P]~. This behavior is very similar to that observed for mercuriation of Urd at N(3). At low pH, ( > is blocked and mercuriation occurs at a second site. The perturbations of the spectrum are similar to those caused by protonation at N(7), and the same site is suggested for mercuriation. Mercuriation of Ado-5'-P at pH 3.5 gives a complex with a spectrum similar to that of [AdoD-5'-P]+. Consequently, mercuriation is assigned at N(u. This is not in agreement with recent calculations which suggest hard acids should bind preferentially to N(p and soft acids to N(7). This coordination also causes a very large and unusual hyperchromic effect on the (Hg-C) stretching band. There is no involvement of the phosphate group in coordination with either Guo-5'-P or Ado-5'-P. When l-MeAdoH+ reacts with CH3Hgn at pH 3.5, only small spectral perturbations result. The vibrations associated primarily with CH3Hgn suggest that coordination is to a weakly basic site, i.e., coordination appears to occur at the N(7) position. Applications of Raman difference spectroscopy in the determination of structures for metal-nucleotide and -nucleoside complexes in dilute aqueous solutions are discussed.In a previous paper,2 34567we reported on the Raman spectral changes which occur upon coordination of the methylmercury(II) cation to Cyd, Urd, and poly(U)8 in moderately dilute aqueous solution. This involved the first use of Raman difference spectroscopy (RDS) to study the behavior of biological molecules in aqueous solution. It was shown that CH3Hg+ binds strongly to uridine and by inference to thymidine with transfer of a proton as has generally been assumed in discussions of the reversible reaction of mercury(II) compounds with This interpretation had been brought into question, because earlier Raman studies had shown no interaction between HgCl2 and Ura, Urd, 1-MeUra, and l,3-Me2Urd in aqueous solution,7 and the crystal structure of HgCl2-2Ura8 showed that mercury(II) coordinated to the C(4)=0 of the nonionized Ura. Lord and Thomas7 did find evidence for reaction of HgCl2 with Cyd but were unable to obtain spectra for solutions containing Ado or Guo derivatives.The present work has two principal objectives. The first is to obtain information on the binding of a heavy metal ion to purine nucleotides because of the current interest in mutagenic and cytotoxic effects of heavy metals, particularly platinum, arising by interaction with nuclear DNA.910 The methylmercury(II) cation