Influence of alkylation of the amino group on the reactions of adenine with the methylmercury(II) cation

Abstract

Reaction of the CH3Hg+ cation with 6-dimethylamino- and 6-diethylaminopurine (HL) yielded compounds of the types [(CH3Hg)L], [(CH3Hg)2L]X (X = NO3, ClO4), and [(CH3Hg)2(HL)](NO3)2. Metal binding to N(9) in [(CH3Hg)L] was deduced from the nmr spectra. The coordination sites in the other types of compounds were determined from X-ray diffraction studies on two complexes of 6-dimethylaminopurine. Crystals of [(CH3Hg)2L]ClO4 are monoclinic, space group P21/c, a = 9.319(3) Å, b = 9.581(8) Å, c = 19.624(8) Å, β = 118.23(3)°, and Z = 4. The structure was refined on 1521 nonzero MoKα reflections to R = 0.040. [(CH3Hg)2(HL)](NO3)2•H2O belongs to the same space group, a = 11.012(3) Å, b = 23.669(7) Å, c = 6.748(4) Å, β = 95.25(4)°, Z = 4, 1781 MoKα reflections, R = 0.053. In both complexes, the CH3Hg+ groups are bound to the N(9) and N(3) sites of the purine ring. In the [(CH3Hg)2L]+ cation, the lone pair of N(7) is free, whereas it is occupied by a proton in [(CH3Hg)2(HL)]2+. The 1H and 13C nmr spectra show that the solid state structures are retained in DMSO solutions. The 2J(199Hg—1H) coupling constants suggest that protonation on N(7) produces for N(9) and N(3) average decreases of basicity corresponding to ~3 pK units.