Rotatory-Diffusion Broadening of Rayleigh Lines Scattered from Optically Anisotropic Macromolecules in Solution

Abstract

A technique for the spectroscopic detection of pure rotatory Brownian movement of anisotropic macromolecules in solution are developed in combination with a high‐resolution optical heterodyne spectrometer. The line broadening originating in the translational diffusion of the solute macromolecule, which is a dominant factor in intensity in the Rayleigh component, is suppressed by taking the forward scattering. Then, only the depolarized light whose amplitude is fully modulated by the rotation of solute molecules is filtered off by the polarizer and received by a photomultiplier tube. The time‐dependent component of the output from the phototube is analyzed by a wave analyzer to give a spectrum of the scattered light. From the spectral linewidth thus obtained, the rotatory diffusion coefficient of Tobacco Mosaic Virus in aqueous solution has been obtained and found to be 350 ± 20 sec⁻¹. On the other hand, the optically isotropic polystyrene latex sphere has shown no broadening in this system. From these results and from the evidence of sharpening of the linewidth with increasing solvent viscosity, it is concluded that the observed broadening originates in the amplitude modulation of the scattered light by the rotatory diffusion of TMV. This “depolarized light mixing” technique is quite general and able to cover a frequency range from 10¹ to 10⁷ Hz. And it is believed to be useful especially in the studies of rotatory diffusion and transconformation of anisotropic macromolecules, and in studies of chemical kinetics accompanying an anisotropic change of polarizabilities.