Copper-Ligand Interactions and Physiological Free Radical Processes. pH-Dependent Influence of Cu2+Ions on Fe2+-Driven OH-Generation

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Abstract
Prior to comparative studies on the reactivity of various copper complexes with respect to OH. radicals, the influence of free Cu2+ ions on the superoxide-independent generation of OH. radicals through Fenton assays and water gamma radiolysis has been tested in the present work. Cu2+ ions have been shown to behave in a distinct manner towards each of these two production systems. As was logically expected from the noninvolvement of copper in OH. radical production through gamma radiolysis, no influence of Cu2+ ions has been observed on the amount of radicals detected in that case. In contrast, Cu2+ ions do influence OH. radical generation through iron-driven Fenton reactions, but differently depending on copper concentration. When present in high concentrations, Cu2+ ions significantly contribute to OH. radical production, which confirms previous observations on the reactivity of these in the presence of hydrogen peroxide. At lower levels corresponding to copper/iron ratios below unity on the contrary, Cu2+ ions behave as inhibitors of the OH. production in a pH-dependent manner over the 1-6 range investigated: the lower the pH, the greater the inhibition. The possible origin of this previously unreported inhibitory effect is discussed.

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