Complexation of transition-metal ions, SnII, PbII and AlIII with nucleobase-substituted polyethers and dissociation of adduct ions studied by fast atom bombardment mass spectrometry

Abstract

Metal-ion-complexed dinucleotide analogues were studied by FAB mass spectrometry using tri- and bi-valent transition-metal ions (Cr to Zn), Sn ^II , Pb ^II and Al ^III . Pairs of thymine nucleobases linked by (CH ₂ ) ₂ - [O(CH ₂ ) ₂ ] _n O(CH ₂ ) ₂ chains (n = 1 1, 2 2, 3 3 or 4 4) and of adenine nucleobases (n = 1 5 or 4 6) co-ordinate to metal ions and form significant [M + M - H] ⁺ and [M + MCl] ⁺ ions. In addition, many transition-metal ions also give [M + M ₂ X - 2H] (X = Cl or NO ₃ ) ions but Cr ^III produces [M + CrCl ₂ ] ⁺ ions. The effect of the spacer chain length is reflected in the ease of formation of [M + M - H] ⁺ and [M + MX] ⁺ ions. Fragmentation of [M + MX] ⁺ and [M + M ₂ X - 2H] ions give [M + M - H] ⁺ ions, suggesting that metal chelation through the nucleobase is more favoured than through the polyether. Complexes of compounds 1–6 with Al ^III –glycerol give abundant [M + 117] ⁺ complex ions (117 = Al + glycerol - 2H). The intensities of these ions decrease with increasing number of ethylene oxide units from 1–4. The same trend is also observed in 5 and 6. Bimetallic ions with an unipositive charge are also produced from 1–4. Dissociation of adduct ions labelled with deuterium confirms the substitution of amide protons with aluminium(III) in the elimination of glycerol.