Study of the temperature effect on IR spectra of crystalline amino acids, dipeptides, and polyamino acids. IV. L-cysteine and DL-cysteine

Abstract

A study of the IR spectra of L- and DL-cysteine is carried out in a range of frequencies from 4000 cm−1 to 600 cm−1 and temperatures from 333 K to 83 K. Changes in the spectra of L- and DL-cysteine (NH 3 + CH(CH2SH)-COO−) on cooling are analyzed in comparison with the spectra of L- and DL-serine (NH 3 + CH(CH2OH)-COO−) and three polymorphs of glycine (NH 3 + CH2-COO−) previously studied under temperature variation. Changes in the IR spectra at variable temperatures are correlated with previously obtained diffraction data on anisotropic compression of the structure and changes in the geometric parameters of hydrogen bonds. Special attention is paid to temperature regions in which anomalies were detected by vibrational spectroscopy, X-ray diffraction, and calorimetry.