| As the main constituents of dissolved organic nitrogen?DON?,detached amino acid in the water plays an important role in natural water DON.It mainly comes from reclaimed water disposed by sewage treatment plant,at the same time,the metabolic activity of microorganism in natural water and the protein synthesis after plankton death may bring a large number of detached amino acid.Amino acid also is absorpted and utilized by algae as important nutrient substance in the process of reproduction growth,causing water bloom,and threaten to the natural water quality greatly.The aromatic amino acid may occur photochemical reaction under the exposure of sunlight or ultraviolet ray,which can oxidize to degrade the components including amino acid and persistent organic pollutant by direct light degradation and indirect light degradation,so as to realize carbon-nitrogen cycle.The purpose of research of this paper is photochemical characteristics of detached aromatic amino acid in water,at the same time,the standard natural organic matter?HA?FA?is added as comparison.The methods of UV scanning spectrum,Fourier infrared spectrometry and Boehmn titration and so on are adapted to analyze molecular structure characteristics and absorption characteristics of the three aromatic amino acid?Tryptophan,Tyrosine and phenylalanine?,HA and FA.Then the three reactive oxygen of H2O2?1O2 and·OH are chosen as mark product of photochemical reaction after illumination radiation,to explore the photochemical characteristics of three aromatic amino acid.By the functional group titration,it was found that the two standard natural organic matter HA?FA contain high concentration of phenolic hydroxyl group as tyrosine.Meanwhile,as the phenolic hydroxyl group,the indole ring structure inside tryptophan can generate superoxide to provide electron for aromatic compounds and quinones under light radiation condition,while the superoxide is the important precursor to generate hydrogen peroxide.Therefore,the quantum yield of H2O2 of tryptophan and tyrosine are very high,they are 5.23×10-5 and2.24×10-5,respectively.The results of three-dimensional fluorescence spectroscopy showed that the components of tryptophan protein appeared in HA and FA,which provided a conjecture for explaining the source of luminescence of HA and FA.The tryptophan is very special among the three aromatic amino acid,with a higher generative capacity of 1O2 and H2O2 as well.The generating rate of singlet oxygen reaches to 7.36×10-8Ms-1,which is the highest among the three aromatic amino acid,and a little lower than HA and FA.While its apparent quantum yields even exceed HA and FA,reaching to 2.1×10-3?While in the process of generating H2O2 by photosensitivity,as the indole ring structure with electron-rich function exists inside ? molecular structure,H2O2of tryptophan is the highest among the three aromatic amino acid,reaching to 5.23×10-5?? H2O2 of phenylalanine is the lowest,while its?×OHis a little higher than Tyrosine,which indicating that the decomposition of H2O2 is not the main path to generate hydroxyl radical from PHE phenylalanine,it derived from other path.The negative correlation between efficiency of generating hydroxyl radical from the five sample solution and E2/E3 is better.Among the three detection reactive oxygen,the retention time of H2O2 reaches as long as 2 days;the oxidability of·OH is the strongest,it ranks only second to fluorine;However,it was show from the detection result of photosensitized reaction product,The steady-state levels of 1O2 is the highest.[1O2]SS is nearly a hundred times of[H2O2]SS.At the same time,[·OH]SS is only hundred percent to thousand percent of[1O2]SS.Therefore,the reactive oxygen generated by aromatic amino acid photosen sitized reaction is singlet oxygen mainly.The concentration of photosensitizer has a certain effect on the formation of 1O2.At low concentration,the rate of 1O2 formation increases with the increase of TOC concentration. |
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