Structure–activity relationship disturbed by a solvolytic process: Study on the [Cu(II)-4-nitropyridine N-oxide derivative] system

The chelate complex [CuCl2(L)] where L = 2-methylamino-3-methyl-4-nitropyridine-N-oxide has been obtained and characterized, both physicochemically (by the X-ray structure analysis of the complex and the ligand, FTIR, EPR and electronic spectroscopy, and thermal analysis) and cytotoxically (MCF-7, A549, SW707, P388, Balb3T3). In solution, atypically for chelate complexes, it undergoes rapid solvolysis forming various 6- (or 5) and 4-coordinate species, depending upon the solvent. Such rapid decomposition may indicate a catalytic effect of the copper operating in the system. However, the cytotoxic activity in solution for the new copper chelate complex appeared to be a surprisingly low. Thus, before drawing any conclusions on the structure–activity relationship, one must carefully check the chemical identity of the compound(s) in both phases.

Graphical abstractThis paper contains the structural and spectroscopic characterization of 2-methylamino-3-methyl-4-nitropyridine N-oxide (L) and its Cu(II) mononuclear complex: [CuCl2(L)] (1). It presents an example where changing phase impacts a dramatic effect on the structure and consequently on the biological activity of the species.Figure optionsDownload full-size imageDownload as PowerPoint slide