Investigation of C-O tautomerism in a derivative of Flucytosine: A DFT study
Subject Areas :Keywords: transition state, tautomerism, Flourocytosine, Density function theory, tunneling effect,
Abstract :
In this research investigation of tautomerism and transition states of 6-Hydroxy 5-Flourocytosine from 1,3 proton transfer between oxygen and carbon atoms in the gas phase and in solution and in a micro hydrated environment with 1-3 water molecules was performed by quantum calculations at the DFT/B3LYP/6-31++G(d,p) level of theory. For this purpose, the optimized geometries of various tautomers of the desired molecule were obtained. Also by using frequency calculations at the same level thermodynamic properties of different tautomeric equilibriums such as ΔE, ΔH, ΔG and Keq were obtained. Then transition states of various tautomeric interconversion of 6-Hydroxy 5-Flourocytosine and it’s kinetic and thermodynamic amounts were calculated by QST2 and QST3 methods. And also the tunneling effects on rates of reaction were investigated. The results show in both gas phase and solution, rate constants of tautomeric reactions have high sensitivity on tunneling effects and rate of tautomeric interconversion increase by about five or more. Also transition state calculations show in absence of water assisted molecules the tautomeric interconversion reacctions have high barrier energy and so are very slow, in other word they can not be done
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