核酸碱基在磷酸盐水溶液中的新型光化学反应及机理研究

The photochemistry of nucleic acids has been being a hotspot research topic in life science, and nucleobases and phosphate, component parts of nucleic acids group are, play an important role in the photochemistry of nucleic acids. Under UV irradiation the photoreaction of pyrimidine bases in aqueous solution has disclosed three types of reactions, namely: (a) nucleophilic addition of water, ethanol, or hydrogen cyanide at the 5,6-double bond; (b) dimerization by addition at the same double bond; (c) ring cleavage. It has been reported that the presence of phosphates altered the course of the photolysis process of pyrimidine bases and derivatives under the irradiation of low pressure mercury lamp (LPML, 254 nm), but the role of phosphate in the mechanism was not clear. .In this research topic, it was found that the photolysis of nucleobases, nucleosides and nucleotides (NA) was sharply enhanced by phosphate undergoing MPML irradiation (continuous spectrum)--phosphate effect. Experiments show that photochemical reactions are a series of unreported reactions of nucleobases --photolytic replace reaction, and get new compound with phosphate groups. .The research on photolytic replace reaction of pyrimidine bases of nucleotides in phosphate aqueous solution：.（1）.The study on photochemical reaction of uracil in phosphate aqueous solution.the photoreaction of 1.5×10-4 mol/L uracil in 0.05 mol/L K2HPO4 by irradiation of medium pressure mercury lamp (MPML) and found the photoreactive enhancement of uracil by added phosphate, which produced a novel compound , as follows：. .The composition and structure of the compound have been identified by elemental analysis, EI-MS, UV, IR, 1H, 13C, 31P-NMR..（2）.The study on photochemical reaction of thymine in phosphate aqueous solution.the photochemical reaction of 1.5×10-4 mol/L thymine in 0.05 mol/L K2HPO4 by irradiation of MPML and found a novel compound , as follows ：. . .The composition and structure of the compound have been identified by elemental analysis, EI-MS, UV, IR, 1H, 13C, 31P-NMR..（3）.The study on photochemical reaction of 1,3- dimethyluracil (DMU) in phosphate aqueous solution.the photolysis of 1×10-4 mol/dm3 DMU in 0.05 mol/dm3 phosphate solution by irradiation of MPML results in formation of a novel compound , as follows：. .The composition and structure of the compound have been identified by elemental analysis, EI-MS, UV, IR, 1H, 13C, 31P-NMR..（4）.The study on photochemical reaction of adenine in phosphate aqueous solution.It was found that the photoreactive loss of adenine was sharply enhanced by phosphate undergoing MPML irradiation (continuous spectrum), and investigated the photoreaction of 5.0×10-5 mol/L adenine in 0.05 mol/L K2HPO4 aqueous solution, which forms tow photoproducts absorbing ultraviolet light. . .(5) The possible mechanism of photolytic replace reaction of pyrimidine bases of nucleotides in phosphate aqueous solution.The photoreactions of nucleobases are sharply enhanced by phosphate undergoing MPML irradiation (phosphate effect). Filter experiments demonstrated that the wavelengths (190-220 nm) in the spectrum of MPML are responsible for the phosphate-induced enhancement６. The possible mechanism of reaction is that HPO42- absorbs the energy of UV light (190-220 nm), and then forms phosphate anion radical HPO4-, which reacts with nucleobases to produce compounds with phosphate groups. For example, the possible mechanism of uacril in phosphate aqueous solution under the irradiation of MPML, as follows：HPO42- . H2O + hn ? [HPO42- . H2O]* ? HPO4-. + eaq-.H20 + hn ? H + OH.eaq- + O2 ? O2-.HO2. + H ? H2O2.OH + HPO42- ? HPO4-. + OH-.HPO4-. + H ? H2PO4-.

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