A systematic study on hydrogen bonding interaction between formamide and cytosine

A systematic computational study was carried out to characterize the hydrogen bonding of complexes formed between formamide and cytosine by DFT calculations. The computations were performed mainly with the B3LYP/6-311++G(d,p) level. Seven stable cyclic structures are found on the potential energy surface. in which four structures have two normal hydrogen bonds and the others have only one normal hydrogen bond with a very weak hydrogen bond that can be neglected. in the four structures with two normal hydrogen bonds, two have seven-membered rings, and the others have an eight-membered ring. The eight-membered ring is preferred to the seven-membered one by analyzing the hydrogen bond lengths and the interaction energies. The infrared spectrum frequencies, vibrational frequency shifts and charge number are also reported. (C) 2009 Elsevier B.V. All rights reserved.