摘要
采用MP2/6-31+G(d)和B3LYP/6-31+G(d)理论方法研究了5-氟胞嘧啶水解脱氨基生成5-氟尿嘧啶的反应机理.确定了两条脱氨基反应途径:五步反应机理(途径A)和两步反应机理(途径B).并利用自洽反应场极化连续模型(CPCM模型)在气相优化结构的基础上研究了反应体系在水溶液中反应的溶剂化效应,结果表明溶剂水有利于降低两条反应途径速控步骤的能垒,但由于在气相和溶液中两条反应途径均涉及较高的能垒,因此5-氟胞嘧啶利用这两条途径进行脱氨基反应都是不可能的,从而强调了脱氨基酶的重要作用.该结论有助于更好地了解取代氟原子和水溶剂对这个重要反应的影响.
The mechanism for the hydrolytic deamination of 5-fluorocytosine （5 -FC） to yield 5-fluorouracil （5- FU） was examined at the MP2/6-31 ＋ G（d） and B3LYP/6-31 ＋ G（d） theory of levels. Two pathways for deamination reaction were characterized, a five-step mechanism （pathway A） and a two-step mechanism （pathway B）. In addition, the solvent effect of water on the two processes was assessed at the geometry optimization level by means of the conductor-like polarized continuum model （CPCM）, indicating that the water solvent contributed to decrease the free energy barriers of the two rate-determining steps of paths A and B. These results indicate that the deamination reaction of 5-fluorocytosine by either pathway is therefore improbable because of the high barriers that are involved in the gas phase and water solution, which emphasizes the important role of deaminases. Our results offer a greater fundamental understanding of the effects of the substituent F atom and solvent water on this important reaction.
出处
《西华师范大学学报（自然科学版）》
2010年第2期154-162,共9页
Journal of China West Normal University(Natural Sciences)
