Dimerization of metallated nucleobase pairs via hydrogen-bond formation: open metallated base quartets of mixed adenine-N 3, guanine-N 7 complexes of trans-(H3N)2PtII with two different guanine–guanine pairing schemes

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 nucleobases [9-ethylguanine (Hegua), 9-methyladenine (made) or 1-methylcytosine (mcyt)] have been studied in solution (D2O) applying 1H NMR spectroscopy. Mixed nucleobase complex formation has been observed in all cases. The complex trans-[Pt(NH3)2(tmade-N 3)(Hegua-N 7)][ClO4]2 1a and its hemideprotonated form trans-[{Pt(NH3)2(tmade-N 3)(Hegua-N 7)}·{Pt(NH3)2(tmade-N 3)(egua-N 7)}][ClO4]2[NO3]·1.6H2O 2 have been isolated in crystalline form and characterized by X-ray crystallography. In both cases mononuclear cations are associated via two (1a) and three (2) hydrogen bonds between the guanine nucleobases. In 1a association is via N3 and the amino group N2, whereas in 2 a neutral Hegua and a deprotonated egua are joined via three hydrogen bonds involving O6, N1 and N2 sites.

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