Optical Kerr effect induced by picosecond light pulses in tRNA solutions

Abstract

The optical Kerr effect (OKE) of tRNA solutions induced by picosecond light pulses of a YAG-Nd 3+ laser, λ = 1060 nm, was investigated. A weak He-Ne laser light beam, λ = 632.8 nm, served as the measuring beam. The experimentally determined molecular Kerr constants B mol NL, and previously obtained values of the molecular total Kerr constants B mol TOT, allowed for the calculation of the molecular orientational-redistributional components B mol OR+RE of the OKE constants. The mean third-order optical polarizabilities c ai were also determined. The B mol NL, B mol OR + RE and c ai parameters estimated for tRNA macromolecules in water and in two different buffer solutions with and without magnesium ions are discussed in the light of data obtained by other methods. For different tRNA structures, different values of the optical Kerr constants and third-order optical polarizabilities were observed. It was found that the linear optical parameters, i.e., optical polarizability a and anisotropy δ a , obtained in the present studies, are much smaller in comparison with corresponding values obtained from the static light-scattering measurements. The relative nonlinear optical Kerr constants in pure water and salt buffers were measured, and are found to be opposite in sign. The relative values of the optical Kerr constants of both buffer solvents obtained in our picosecond measurements are smaller by a factor of two than those obtained in nanosecond studies.