Raman spectral analysis in the C-H stretching region of proteins and amino acids for investigation of hydrophobic interactions

Raman spectra of amino acids showed complexity in the C-H stretching region (2800-3100 cm(-1)) attributed to diversity of CH, CH2, and CH3 groups in the side chains, ionization state, and microenvironment. The involvement of specific amino acids in the C-H stretching region of selected proteins, namely, lysozyme, alpha-lactalbumin, beta-lactoglobulin, and their binary mixtures, was investigated by deconvolution using maximum likelihood techniques. The main protein band near 2940 cm(-1) was attributed not only to aromatic and aliphatic amino acids but also to many other amino acids. A band near 3065 cm(-1) was assigned to aromatic residues, whereas bands near 2880 and 2900 cm(-1) corresponded primarily to aliphatic amino acids. Heating at 90 degrees C increased relative intensity near 2940 cm(-1) and decreased relative intensity at 2895-2902 cm(-1) for lysozyme and its mixtures with alpha-lactalbumin or beta-lactoglobulin. Additional bands at 2812 or 2838 and 3003 cm(-1) were observed after heating or in 8 M deuterated urea, reflecting changes upon denaturation.