Potentiometric and spectroscopic evidence for co-ordination of dimethyltin(IV) to phosphate groups of DNA fragments and related ligands

Abstract

The co-ordination of dimethyltin(IV) to 5′-GMP, 5′-ATP and 5′-d(CGCGCG)₂ and to their sugar constituents (D-ribose and 2-deoxy-D-ribose) was investigated in aqueous solution by means of potentiometric titration and ¹H and ³¹P NMR spectroscopic methods. The results showed that in acidic media the phosphate groups can provide suitable sites for metal ion co-ordination, while the hydroxy groups of the sugars or the sugar moieties of the two nucleotides play a role in this process at higher pH. The base moieties of 5′-GMP and 5′-ATP were not co-ordinated to dimethyltin(IV). The stability constants of the complexes formed in the above systems were determined by pH-metric titration. The data revealed a stronger co-ordination ability of the triphosphate as compared with that of the monophosphate. The comparison of the stability constants of the D-ribose and 2-deoxy-D-ribose complexes showed that more stable species were formed when neighbouring alcoholic hydroxy groups were available for co-ordination. The observed chemical shift changes of the ³¹P NMR resonances, as compared with those measured for the metal-free systems, demonstrated that the phosphate groups of the DNA fragment 5′-d(CGCGCG)₂ chains act as binding sites for dimethyltin(IV) between pH 4.5 and 7. The 1- and 2-D ¹H NMR spectra indicated that the base and sugar moieties do not participate in the co-ordination process under these conditions.