A Computational Study On The Mechanism For The Interaction Of Cytosine With Some Small Molecules

The interactions of cytosine,furan and BX₃ (X=H, F, Cl) systems were investigated with DFT and ab initio methods at 6-311++G (d, p) and Lanl2dz basis sets levels respectively. The mechanism of the interaction of different systems were analyzed and compared. According to the calculation results of all these complexes, we have taken the systematically analysis to weak interaction about the principle and mechanism.We performed DFT caculation on the cytosine-BX₃ (X=F, Cl, Br, I) system. Different conformers corresponding to the minimum points at the molecular energy hypersurface were found. The results indicate that all the isomers were formed withσ–p type interactions between cytosine and BX₃, in which pyridine-type nitrogen or carbonyl oxygen or nitrogen atom of amino group offers its lone pair electron to the empty p orbital of boron atom and the concomitances of charge transference from cytosine to BX₃ were occurred. Cytosine–BF₃ complex was more stable than the others. The stability is in proper order: cytosine -BF₃> cytosine -BCl₃> cytosine -BBr₃> cytosine -I₃.Essentially, the interaction of cytosine and furan is formed with the charge transfer. According to the AIM and NBO analysises, hydrogen bonds between cytosine and furan fragments have been formed all the conformers obtained in this work. The dihydrogen system B is the stability, the O of furan offers lone pair electron to the acceptor orbital of C16 - H21 and the concomitances of charge transference from furan to cytosine were occurred.We have also studied the interaction of furan homologues with BX₃ (X=H, F, Cl) system. They are all formed stable conformers through the electron transfer. Accordening to the binding energy and NBO analysis, we can get the conclution that the furan-BX₃ (X=H, F, Cl) system was more stable than the thiofuran- BX₃ (X=H, F, Cl) system.Comparing all these interaction systems, it can be seen that the charge transferring interaction between donor and acceptor plays an important role in stabilizing the complex. The results of the natural bond orbital (NBO) analyses also show that donor to acceptor interactions make mainly contribution to the stabilities of complexes.