Interaction of toxic metals (Cd(II), Hg(II), Ni(II) AND Pb(II)) with 6-mercaptopurine in methanol−sodium perchlorate medium

Mercaptopurines exhibit a high activity against certain types of tumour [1]. HMP (1,7-dihydro-6H-purine-6-thione) is a purine derivative, containing double−bonded sulfur atom as a side group in the 6 position of the pyrimidinic ring, used for maintenance therapy of acute human leukemias. A spectrofluorimetric method for toxic metals detection (Hg, Cd, Ag and Pb) based in the reaction with HMP to form highly fluorescent complexes is described [2]. Interaction between Cd(II), Hg(II), Ni(II) e Pb(II) and HMP has been examined by potentiometric, UV-VIS spectrophotometric and spectrofluorimetric techniques. HMP is sparingly soluble in water (about 3×10−5 M) but soluble in methanol-water solutions. For this reason potentiometric studies have been conducted in methanol-0.1 M sodium perchlorate medium, by hydrogenionic concentration measurements with glass electrode. Spectrophotometric Job's method has shown the composition of the complexes to be 1:1 and 1:2. Solution 1H−NMR measurement and solid state FT−IR spectra indicate the coordination involves C(6)=S and N(7). According to the Circular Dichroism and spectrofluorimetric studies DNA−binding affinity of toxic metal is reduced by HMP coordination.