Primary kinetic isotope effects on acid-catalysed reduction of p-benzoquinone derivatives by an acid-stable NADH analogue

The primary kinetic deuterium isotope effects on the reduction of a series of p-benzoquinone derivatives (Q) by an acid-stable NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2) in an aqueous solution (H2O–EtOH; 5 : 1 v/v) as well as in acetonitrile have been determined in the absence and presence of various concentrations of perchloric acid at 298 K. Origins of observed variation of the primary kinetic isotope effects depending on the acid concentration and p-benzoquinone derivatives are ascribed to the hydrogen-atom transfer from AcrH+˙2 to QH˙ following the acid-catalysed electron-transfer from AcrH2 to Q, based on the dependence of the primary kinetic isotope effects on the energetics of transfer of hydride ion, proton, and hydrogen atom.