engleski

A Combined Ab Initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of HOMO of the former. It is also shown beyond any doubt that the spin-density in neutral and cationic radical of 2 is almost exclusively placed on the s-3p AO of sulphur. In contrast, the spin-density of radicals of 1 is distributed over their pi-network.

nucleic acid bases; thymine; 2-thiothymine; spin-density; ionization potentials

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