A computational investigation of cytosine and 5-methyl cytosine reactivity by means of ionization potentials and one specific methylation pathway

摘要

Results from DFT/omega B97X-D/6-311+G**/C-PCM calculations show that the aqueous vertical IP of 5-methylcytosine is lower than that of cytosine by 0.25 eV. Using the HSAB concept, the HOMO-LUMO gap for 5-methylcytosine is smaller than that of cytosine, making it soft and opt to form covalent bonds and more reactive. Carcinogenic methane diazonium ion can methylate cytosine at the N3 site and mutate it via an S(N)2 mechanism and the activation energy is approximately 5.05 kcal/mol in water.