Four-photon microwave laser spectroscopy of aqueous solutions of biopolymers

The four-photon laser radiation scattering spectra are obtained in the submillimetre range (75 – 95 cm^-1) for deionised water, aqueous solutions of DNA and α-chymotrypsin protein. Narrow resonances are recorded whose frequencies coincide (within the resolution power of a spectrometer) with rotational frequencies in the ground electronic state and vibrational state of ortho and para isomers of H₂O molecule in a gas phase and with the frequencies of the lines of H₂O₂ and OH^- molecules. It is shown that the resonance contribution of the rotational lines of ortho isomers of H₂O to the signal of four-photon scattering of native solutions of biopolymers increases by a factor of at least 8 compared to their contribution to the scattering signal in water, and becomes considerably larger than the contribution from the paraisomer lines. Denaturation of DNA after heating and cooling of the solution leads to the disappearance of such selectivity.