The Effect of Coinage Transition Metal (Cu, Ag, Au) Substitutions on Two-electron Redox Potential of Quinones

Quinones are a class of compounds which have widespread importance in chemistry, biology and medicine. Because of their appropriate performance in electron transferring rate, quinones are among the most applicable mediators in biosensors. Recently, the effects of different non-metal substitutions on redox potential of quinone have been investigated to design suitable mediators for different electrochemical measurements. In the present study, the effect of coinage transition metal (TM) substitutions (Cu, Ag, Au) alone or together with other functional group substitutions such as -OH, -Cl, -CH3, -NO2 and -CO2H on lowering or raising the redox potential of quinone was investigated. The range of calculated redox potential was from 0.193 to 1.056 volts in comparison with unsubstituted benzoquinone which is 0.7 volts. We found that coinage TMs, similar to electron donating groups (EDGs), cause lowering effect on redox potential of quinones. Our findings reveal that the copper and hydroxyl groups have the most decreasing effect on redox potential. Calculations were performed through density functional theory with B3LYP xc-functional and mixed basis set 6-31+G** + LANL2DZ.