Raman optical activity instrument for studies of biopolymer structure and dynamics

The latest version of a multi-channel Raman optical activity (ROA) instrume nt implementing incident circular polarization (ICP) modulation within a ba ckscattering geometry and optimized for measurements on biopolymers in aque ous solution is described. It is based on a fast single-stage, imaging (sti gmatic) monochromator equipped with a high optical density holographic notc h 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 polarizati on states in the incident laser radiation. A thick Lyot depolarizer is used for depolarization of the backscattered Raman radiation. This backscatteri ng ICP CCD ROA design is currently realized with two prototype instruments dedicated to studies of the structure and dynamics of biopolymers in aqueou s solution, Backscattered ICP ROA spectra of the following samples are pres ented as typical examples of the excellent performance characteristics: pol y(L-glutamic acid) in alpha-helical and disordered conformations; bovine al pha-lactalbumin in native and acid molten globule states; human immunoglobu lin; calf thymus DNA and both magnesium-bound and magnesium-free phenylalan ine-specific transfer RNA; and filamentous bacterial viruses Pf1 and M13. C opyright (C) 1999 John Whey & Sons, Ltd.