H-atom transfer reaction of photoinduced excited triplet duroquinone with tryptophan and tyrosine in acetonitrile-water and ethylene glycol-water homogeneous solutions

Abstract

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 3DQ* is dominant after the formation of 3DQ* during the laser photolysis. For DQ and Trp in MeCN-H2O and EG-H2O solutions, 3DQ* captures H-atom from Trp to generate duroquinone neutral radical DQH•, carbon-centered tryptophan neutral radical Trp•/NH and nitrogen-centered tryptophan neutral radical Trp/N•. For DQ and Tyr in MeCN-H2O and EG-H2O solutions, 3DQ* captures H-atom from Tyr to generate duroquinone neutral radical DQH• and tyrosine neutral radical Tyr/O•. The H-atom transfer reaction rate constant of 3DQ* with Trp (Tyr) is on the level of 109 L·mol−1·s−1, nearly controlled by diffusion. The reaction rate constant of 3DQ* with Trp (Tyr) in MeCN/H2O solution is larger than that in EG/H2O solution, which agrees with Stokes-Einstein relationship qualitatively.

Photosensitive damage of dipeptides: mechanism and influence of structure

“…A new positive absorption band appeared at 500 nm, which is the characteristic absorption of the Trp neutral radical (Trp/N˙). 28 The intensity of the dynamic curve at 610 nm declined rapidly (0.44 μs) as shown in Fig. 2b.…”

“…26 In recent years, our group has been investigating the dynamic processes and reaction mechanisms of polycyclic and biological quinone molecules with vitamin C, vitamin E, and amino acids. 12,27–29 The photosensitive reaction processes involving excited triplet states of quinones or ketones and free monomer amino acids are well understood after decades of investigation. However, reports on the photosensitive damaging reactions of peptides or dipeptides with multiple reaction sites are not common due to their complexity.…”