Laser Photolysis Study on Photo-Oxidation Reactions of Aromatic Amino Acids with Triplet 2-Methylanthraquinone
CAO Xi-yan1,2, FU Hai-ying2*, ZHU Li1, 3*, WU Guo-zhong2
1. School of Chemistry and Chemical Engineering of Hunan University of Science and Technology, Xiangtan 411201, China 2. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China 3. Beijing Union University，Beijing 100191, China
Abstract：The transient photo-sensitive oxidation between 2-methylanthraquinone (MAQ) and aromatic amino acids (namely tryptophan, tyrosine and phenylalanine) in acetonitrile/water (1∶1, V/V) solution was investigated by laser photolysis techniques with the excitation wavelength of 355 nm. The triplet state absorption of 2-methylanthraquinone was attributed to 390, 450 and 590 nm and the anion radical absorption of MAQ was due to 390 and 490 nm identified by the electron transfer reactions from 4-diazabicyclo [2.2.2] octane (DABCO) or diphenylamine (DPA) to 3MAQ*. With the decay of 3MAQ*, the MAQ·- at 490 nm appeared, which indicated that the electron transfer reactions between 3MAQ* and amino acids occurred. Moreover, the rate constants were deduced to be 3.0×109，1.1×109 and1.8×108 L·mol-1·s-1 for TrpH, TyrOH and PHE, respectively. On the other hand, the free energy changes (ΔG) of the reactions showed that the proposed electron transfer steps are thermodynamically feasible.
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