Ground state vibrational spectra of cysteine and serine hydrochlorides: A theoretical prediction

Abstract

Transferability of scale factors from smaller constituents to a larger one is successfully attempted for two important amino acids cysteine and serine in acidic solution. The scale factors of glycine in acidic solution from our earlier study were used to scale the ab initio force fields of both the molecules. Scale factors of the side chain residues of both cysteine and serine are obtained by fitting the ab initio force fields of ethanethiol and ethanol to their respective experimental frequencies at the same level of theory. The present study is in support of our earlier observation that an isolated molecule ab initio model with a right choice of basis set can mimic the experimental spectra of amino acids at acidic pH. In both the cases the predictions of the frequencies and their normal mode descriptions are excellent. This further indicates that the scale factors of structurally related small organic molecules (ethanethiol and ethanol in the present case) can be used to mimic the right features of the amino acid side chain residues.