乙腈-水和乙二醇-水均相溶液中光诱导杜醌激发三重态与色氨酸、酪氨酸的氢原子转移反应

本文用激光闪光光解技术研究了光诱导生物醌杜醌激发三重态(³DQ^*)和色氨酸(Trp)与酪氨酸(Tyr)在乙腈-水(MeCN-H₂O)及乙二醇-水(EG-H₂O)均相溶液中的光化学反应，分析了反应的机理，并基于Stern-Volmer方法测量了反应速率常数. 光解DQ体系可以生成³DQ^*，³DQ^*与Trp、Tyr发生的氢原子转移反应占主导地位. 对于DQ/Trp/MeCN-H₂O和DQ/Trp/EG-H₂O溶液，³DQ^*与Trp反应生成杜醌中性自由基DQH^·、以碳为中心的色氨酸中性自由基Trp^·/NH和以氮为中心的色氨酸中性自由基Trp/N^·. 对于DQ/Tyr/MeCN-H₂O和DQ/Tyr/EG-H₂O溶液，³DQ^*与Tyr反应生成DQH^·和酪氨酸中性自由基Tyr/O^·. ³DQ^*与Trp、Tyr的氢原子转移反应速率常数都在10⁹ L·mol^-1·s^-1量级，反应近似受扩散控制. MeCN/H₂O均相溶液中³DQ^*与Trp、Tyr的反应速率常数要明显高于EG/H₂O均相溶液中的反应速率常数，这与Stokes-Einstein方程定性一致.

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 reac-tions 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 radi-cal 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.