Four-photon laser spectroscopy of water and aqueous solution of protein in the subterahertz frequency range

For the first time, resonances with frequencies of 1.2, 1.6, 2.0, and 2.3 cm(-1) and a width of about 0.2 cm(-1) are detected in a frequency range of 3.5 cm(-1) in water and aqueous solution of the protein alpha-chymotrypsin using the spectroscopy of four-photon scattering in the Rayleigh wing. The line with a frequency of 2.3 cm(-1) is assigned to the rotational transition 3(2,1)-4(1,4) of the fundamental vibrational state. In the presence of the protein, the spectrum is modified and new bands emerge at frequencies of 0.74, 2.8, and 3.2 cm(-1). The spectral changes are interpreted, first, as a manifestation of the low-frequency vibrations of large molecular fragments in aqueous solution of the protein and, second, as a consequence of the induced structurization of water in the vicinity of the protein molecule. It is demonstrated that, based on the spectra obtained, one can estimate the fractal dimensions D of the liquids under study. It is found that the fractal dimensions are 1.91 +/- 0.01 and 1.97 +/- 0.201 for distilled water and the solution of the protein, respectively. The variation in the fractal dimension in the presence of the protein points to the rearrangement of the H-bond network of water.