Four-photon microwave laser spectroscopy of molecules in the hydration layers of biopolymers and nanoparticles

Four-photon laser scattering spectra of bidistilled water and aqueous solutions of biopolymers (proteins and DNA), carbon nanotubes and hydrogen peroxide have been measured in the range ±10 cm^-1. The spectra show rotational resonances of H₂O₂, ortho-H₂O and para-H₂O molecules. The resonance contribution of the H₂O rotational spectrum to the four-photon scattering signal in the solutions of the biopolymers and hydrophobic nanoparticles is an order of magnitude larger in comparison with water, which points to free rotation of the water molecules near the surface of such particles. This effect is due to the formation of water depletion layers near hydrophobic nanoparticles, as predicted in earlier theoretical studies.