Can aluminum, a non-redox metal, alter the thermodynamics of key biological redox processes? The DPPH-QH2 radical scavenging reaction as a test case

Abstract

The increased bioavailability of aluminum has led to a concern about its toxicity on living systems. Among the most important toxic effects, it has been proven that aluminum increases oxidative stress in biological systems, a controversial fact, however, due to its non-redox nature. In the present work, we characterize in detail how aluminum can alter redox equilibriums by analyzing its effects on the thermodynamics of the redox scavenging reaction between DPPH^., a radical compound often used as a reactive oxygen species model, and hydroquinones, a potent natural antioxidant. For the first time, theoretical and experimental redox potentials within aluminum biochemistry are directly compared. Our results fully agree with experimental reduction and oxidation potentials, unequivocally revealing how aluminum alters the spontaneity of the reaction by stabilizing the reduction of DPPH⋅ to DPPH^- and promoting a proton transfer to the diazine moiety, leading to the production of a DPPH-H species. The capability of aluminum to modify redox potentials shown here confirms previous experimental findings on the role of aluminum to interfere with free radical scavenging reactions, affecting the natural redox processes of living organisms.

Keywords: Aluminum; Metal; Oxidative stress; Reactive oxygen species.