DIMERIZATION OF METALATED NUCLEOBASE PAIRS VIA HYDROGEN-BOND FORMATION - OPEN METALATED BASE QUARTETS OF MIXED ADENINE-N-3, GUANINE-N-7 COMPLEXES OF TRANS-(H3N)(2)PT-II WITH 2 DIFFERENT GUANINE-GUANINE PAIRINGSCHEMES

Reactions of trans-[Pt(NH3)(2)(tmade-N-3)X](n+) (tmade = N-6',N-6',N-9 -trimethyladenine, X = Cl, n = 1; X = H2O, n = 2) with other nucleobas es [9-ethylguanine (Hegua), 9-methyladenine (made) or l-methylcytosine (mcyt)] have been studied in solution (D2O) applying H-1 NMR spectros copy. Mixed nucleobase complex formation has been observed in all case s. The complex trans-[Pt(NH3)(2)(tmade-N-3)(Hegua-N-7)][ClO4](2) 1a an d its hemideprotonated form )(2)(tmade-N-3)(egua-N-7)}][ClO4](2)[NO3]. 1.6H(2)O 2 have been isolated in crystalline form and characterized by X-ray crystallography. In both cases mononuclear cations are associat ed via two (la) and three (2) hydrogen bonds between the guanine nucle obases. In la association is via N-3 and the amino group N-2, whereas in 2 a neutral Hegua and a deprotonated egua are joined via three hydr ogen bonds involving O-6 N-1 and N-2 sites.