Metal ion biomolecule interactions. VI: Synthesis and spectroscopic properties of methylmercury(II) complexes of xanthosine

The interaction of MeHg(II) with xanthosine (Xanth H₂, 1) in aqueous medium has been found to lead to several methylmercurated complexes depending on the reactant stoichiometries and the pH. The N-bound complexes [(MeHg)(Xanth H)] (2), [(MeHg)₂Xanth] (3), [(MeHg)₃(Xanth)]NO₃ (4), [(MeHg)(Xanth H₂)]NO₃ (5), and the N- and C-bound complex [(MeHg)₄(Xanth)]NO₃ (6) have thus been prepared. The complexes were characterized by means of ¹H and ¹³C nuclear magnetic resonance and infrared as well as elemental analysis. Formation of the carbon-bound methylmercurated species 6 is in accord with our previous results obtained with inosine and imidazole derivatives, thus substantiating our proposal that activation through electrophilic coordination at N₇ is a requirement for C₈-H abstraction. Correlations are drawn between ²J(¹H-¹¹⁹Hg) values and pK_a as well as ¹³C chemical shifts.