Acid-catalysed reduction of p-benzoquinone derivatives by an NADH analogue, 9,10-dihydro-10-methylacridine. The energetic comparison of one-electron vs. two-electron pathways

Abstract

The energetic comparison of one-electron vs. two-electron pathways has been made for the acid-catalysed reduction of a series of p-benzoquinone derivatives (Q) by an NADH analogue, 9,10-dihydro-l0-methylacridine (AcrH₂), in aqueous solutions (H₂O–EtOH; 5:1 v/v) at 298 K. The pH dependences of the second-order rate constants (log k_obs) as well as the primary kinetic isotope effects (k_H/k_D) for the acid-catalysed reduction of Q by AcrH₂ have been correlated well with the pH dependences of the one-electron reduction potentials of p-benzoquinone derivatives. On the other hand, no direct correlation of log k_obs or k_H/k_D with the corresponding two-electron reduction potentials has been observed. Mechanisms of the acid-catalysed hydride transfer reactions from AcrH₂ to Q have been discussed based on the energetic comparison of one-electron vs. two-electron pathways.