Biomolecular dynamics and electron spin resonance spectra of copper complexes of antitumour agents in solution. Part 2.—Rifamycins

Abstract

Rifamycin SV has been characterized as a powerful inhibitor of RNA synthesis by certain prokaryotic RNA polymerases. It has been proposed that the antitumour activity of Rifamycin SV is due to its ability to chelate metal ions in solution, thus decreasing their availability to act as coenzymes for RNA polymerase. In this report, a two-step approach based on free-radical generation and metal complexation in solution was followed by e.s.r. spectroscopy. The e.s.r. measurements and u.v.-visible titration show by pH cycling that complexation is pH-dependent. In addition, the stability of these complexes in minimal essential media (MEM) was investigated.