H-Atom Transfer Reaction Of Photoinduced Excited Triplet Duroquinone With Tryptophan And Tyrosine In Acetonitrile-Water And Ethylene Glycol-Water Homogeneous Solutions

Laser flash photolysis was used to investigate the photoinduced reactions of excited triplet bioquinone molecule duroquinone (DQ) with tryptophan (Trp) and tyrosine (Tyr) in acetonitrile-water (MeCN-H2O) and ethylene glycol-water (EG-H2O) solutions. The reaction mechanisms were analyzed and the reaction rate constants were measured based on Stern-Volmer equation. The H-atom transfer reaction from Trp (Tyr) to (3)DQ* is dominant after the formation of (3)DQ* during the laser photolysis. For DQ and Trp in MeCN-H2O and EG-H2O solutions, (3)DQ* captures H-atom from Trp to generate duroquinone neutral radical DQH(center dot), carbon-centered tryptophan neutral radical Trp(center dot)/NH and nitrogen-centered tryptophan neutral radical Trp/N-center dot. For DQ and Tyr in MeCN-H2O and EG-H2O solutions, (3)DQ* captures H-atom from Tyr to generate duroquinone neutral radical DQH(center dot) and tyrosine neutral radical Tyr/O-center dot. The H-atom transfer reaction rate constant of (3)DQ* with Trp (Tyr) is on the level of 109 L center dot mol(-1)center dot s(-1), nearly controlled by diffusion. The reaction rate constant of (3)DQ* with Trp (Tyr) in MeCN/H2O solution is larger than that in EG/H2O solution, which agrees with Stokes-Einstein relationship qualitatively.