Density functional theory study of the hydrogen bonding interaction of 1:1 complexes of formamide with cysteine

The hydrogen bonding of 1:1 complexes formed between formamide and cysteine molecules has been completely studied in the present paper using density functional theory (DFT), second-order Moller-Plesset Perturbation (MP2) method and the Hartree-Fock (HF) method at varied basis set levels from 6-31g to 6-31+g(d). Nine reasonable geometries on the potential energy hypersurface of formamide and cysteine system are considered with the global minimum, eight of them are cyclic double-hydrogen bonded structures and only one is single-hydrogen bonded structure. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported.