Circular Dichroism Using Synchrotron Radiation

Abstract

Since 1960 circular dichroism (CD) has been one of the spectroscopic tools at the disposal of scientists studying the conformation of biological molecules (Grosjean and Legrand, 1960). Most of the spectrometers that measure CD have relied on conventional laboratory sources of broad-spectrum UV and visible light, particularly the high-pressure xenon arc. Around 1970, the frontiers of CD spectroscopy were extended into the vacuum UV by spectrometers with hydrogen-discharge sources (Feinleib and Bovey, 1968; Schnepp et al., 1970; Johnson, 1971), and into the infrared by spectrometers based on blackbody sources (Osborne et al., 1973; Chabay and Holzwarth, 1975). Synchrotron sources, which offer superior performance, particularly for wavelengths less than roughly 190 nm, were first used to record CD in the vacuum UV about 1980 (Snyder and Rowe, 1980; Sutherland et al., 1980). Regardless of the light source employed, these vacuum-UV CD spectrometers are inherently limited to wavelengths greater than 105 nm, the transmission limit of lithium fluoride (Sampson, 1967), although ~ 130 nm has been the practical limit. We are, however, on the threshold of a new era in which synchrotron radiation will make it possible to extend measurements of CD into the extreme UV and x-ray regions (λ ≤ ~100 nm), a capability that may prove important in the analysis of the conformation of biomolecules.