A split beam method for measuring time-resolved circular dichroism.
An improvement to the Lewis-Kliger method for measuring transient CD on the nanosecond time scale is described. The method uses a single-probe beam that is split into two different beams of plane polarized light entering the sample and a retarder from opposite directions in different succession. Rochon polarizers were used as high-quality polarizing beam splitters to select the slow axis component of the emerging elliptical polarized light beams. The intensities of the light beams are detd. by an imaging spectrograph coupled to an intensified charge coupled device detector. The split beam method reduces the need for very precise calibration of the central strain plate acting as a retarder and controlling the ellipticity of the probe light. The necessary calcns. are simple and can be shown to be equiv. to the formulas derived by Lewis and Kliger. The static CD spectrum of vitamin B12 is presented and compared to a spectrum obtained with a com. instrument and std. technique. The time resoln. of the instrument is demonstrated by observation of photobleaching of C monoxy myoglobin from horse heart muscle.
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