A Theoretical Study Of The Interactions Between Formaldehyde And DNA Base

The interactions of cytosine, thymine, adenine with formaldehyde systems were investigated with DFT and ab initio methods at 6-311G(d, p) basis sets levels respectively. According to the calculation results of all these complexes, we have taken the systematically analysis to interaction about the principle and mechanism.We performed DFT caculation on the formaldehyde-cytosine system. The results indicate that all the isomers were formed withσ–p type interactions between cytosine and formaldehyde. The optimization geometries and vibrational frequencies of formaldehyde , thymine and two complexes acquired between cytosine and formaldehyde have been calculated. The NBO and AIM methods are used to analysis interaction as well. Conformers (A) and (B) are cyclic structures with C-H···O and C-H···N hydrogen bonds on a common plane. The corrected complex interaction energies of cyclic structures (A) and (B) at MP2/6-311G(d, p) levels are -36.51 and -29.93kJ/mol, respectively. The stable order is (A)> (B).Essentially, the interaction of thymine and formaldehyde is formed with the charge transfer. According to the AIM and NBO analysises, hydrogen bond between thymine and formaldehyde plays an important role in stabilizing the complex. Conformer (A) has the most stability in this work.We have also studied the interaction of adenine with formaldehyde 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 formaldehyde-cytosine system was more stable than the formaldehyde-thymine system or the formaldehyde-adenine 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.