NANOSECOND OPTICAL-ROTATORY DISPERSION SPECTROSCOPY - APPLICATION TO PHOTOLYZED HEMOGLOBIN-CO KINETICS

A standard technique for static optical rotatory dispersion (ORD) meas urements is adapted to the measurement of ORD changes on a nanosecond (ns) time scale, giving approximately a million-fold improvement in ti me-resolution over conventional instrumentation. The technique describ ed here is similar in principle to a technique recently developed for ns time-resolved circular dichroism (TRCD) spectroscopy, although the time-resolved optical rotatory dispersion (TRORD) technique requires f ewer optical components. As with static ORD, TRORD measurements may be interpreted by empirical comparisons or may be transformed, via the K ramers-Kronig relations, to more easily interpreted TRCD spectra. TROR D can offer experimental advantages over TRCD in studying kinetic proc esses effecting changes in the chiral structures of biological molecul es. In particular, the wider dispersion of ORD bands compared with the corresponding CD bands means that ORD information may often be obtain ed outside of absorption bands, a signal-to-noise advantage for multic hannel measurements. Demonstration of the technique by its application to ns TRORD and the transform-calculated TRCD of carboxy-hemoglobin ( Hb-CO) after laser photolysis is presented.