STUDY OF ELECTRONIC STRUCTURE OF CYTOSINE

Experimental studies of excitation thymine, guanine, cytosine, uracil, which are the basis biological structure DNA and RNA, contribute to study mechanisms their destruction under influence low-energy β-radiation ultraviolet radiation. Crystal chemical analysis cytosine molecule showed that it exists in two crystalline forms crystallize orthorhombic syngony, but different space groups (form Cyt (I) – Pccn (56) (II) P212121 (19)). The crystal (I)) is formed by repeating fragments consisting parallel chains, each three molecules. Parallel chains connected hydrogen bonds between N atoms amino group one heterocyclic ring another N–H¼N (1,897 Å). individual perpendicular other (along x-axis y-axis) O carbonyl N–H¼O (2.158 Linear molecules (II)) located along y-axis single adjacent (2,127 Chains from (2.153 Å) (1.898 Ab initio quantum calculations electronic using Quantum Espresso (QE) software package based on density functional theory (DFT) characterized a direct conductivity type, band gap Eg=3.52 eV, cell energy Ecrys= –571.81 Ry, per atom E/at= –142.95 Fermi EFermi=2.67 eV. optical (Eg) electron transitions 2p(O 2p) → C 2p(N 2p).