Zn complex can catalyze superoxide dismutation
Zinc is a trace metal important to keep us healthy. Although per se it is not redox active, zinc is involved in antioxidant protection, which mechanisms are versatile and still intriguing. In an international joint venture with a group of Christian Goldsmith, from Auburn University in USA, we have explained how zinc activates organic molecules containing a quinol functional group towards defense against superoxide, a reactive oxygen species associated with a number of disease states.
Quinol functional groups can be found in polyphenols, which are natural products present for example in tea, wine, coffee and chocolate. The quinol ligand alone is not capable to catalytically decompose superoxide, whereas upon binding to zinc the obtained complex exhibits activity of superoxide dismutation (SOD) enzyme. An essential role of zinc lies in deprotonation of the quinol under physiological pH and consequently the modulation of its redox potential, as well as in binding of superoxide and thus bringing redox reaction partners in close proximity, a critical event common for catalytic processes within enzymatic pockets. The redox cycling of quinol to para-quinone, through quinoxyl radical, is additionally supported by physiologically relevant phosphate buffer that is involved in proton coupled electron transfer (PCET) mechanism that favors overall catalysis.
A unique feature of this finding is the demonstration that, different from all metal complexes used as SOD mimetics till now, which contain redox active metals, such as manganese, iron, copper or nickel, redox inactive zinc can trigger antioxidative properties of organic molecules that are physiologically available. Even more, zinc is less toxic than above mentioned redox active metals, which offers a new strategy for safe pharmaceutical intervention to protect against oxidative damage with wide physiological consequences. Obtained results offer new directions for a potential application of zinc in a combination with quinol-, or more general, phenol-containing molecules of food ingredients and/or dietary supplements for a benefit of our health.