Ground state vibrational spectra of cysteine and serine zwitterion: a theoretical prediction

Transferability of scale factors from smaller constituents to a larger one is successfully attempted for two important amino acids cysteine (Cys) and serine (Ser) in zwitterionic form. A complete set of scale factors are generated for alanine (Ala) by fitting the ab initio (HF/6-31++G*) solvated model force field to the experimental frrequencies of five different isotopomers. These scale factors are then used to scale the ab initio force field of both the molecules. Scale factors of the side chain residues of both cysteine and serine are obtained by fitting the ab initio solvated model force field of ethanethiol and ethanol to their respective experimental frequencies at the same level of theory. In both the cases the predicted frequencies and their normal mode descriptions are excellent compared to the size and complexity of the molecules. (C) 1998 Elsevier Science B.V.