Raman optical activity instrument for studies of biopolymer structure and dynamics

Abstract

The latest version of a multi-channel Raman optical activity (ROA) instrument implementing incident circular polarization (ICP) modulation within a in a backscattering geometry and optimized for measurements on biopolymers in aqueous solution is described. It is based on a fast single-stage, imaging (stigmatic) monochromator equipped with a high optical density holographic notch filter, a holographic transmission grating and a thinned back-illuminated thermoelectrically cooled charge-coupled device (CCD) detector with a high quantum efficiency. A large-aperture longitudinal electro-optic modulator (Pockels cell) is employed to switch between orthogonal circular polarization states in the incident laser radiation. A thick Lyot depolarizer is used for depolarization of the backscattered Raman radiation. This backscattering ICP CCD ROA design is currently realized with two prototype instruments dedicated to studies of the structure and dynamics of biopolymers in aqueous solution. Backscattered ICP ROA spectra of the following samples are presented as typical examples of the excellent performance characteristics: poly(L-glutamic acid) in α-helical and disordered conformations; bovine α-lactalbumin in native and acid molten globule states; human immunoglobulin; calf thymus DNA and both magnesium-bound and magnesium-free phenylalanine-specific transfer RNA; and filamentous bacterial viruses Pf1 and M13. Copyright © 1999 John Wiley & Sons, Ltd.