Measurement of oriented circular dichroism

Abstract

The determination of circular dichroism (CD) of an oriented system requires meticulous consideration of the optics of sample and instrumentation unless the system is uniaxial and the light propagating parallel to the optical axis. A main error is due to the combination of a generally unavoidable stray birefringence of the modulator, or other instrumental elements preceding the sample, and a linear dichroism of the sample. A way of analysing and correcting for this effect is presented. The fact that the LD is usually several orders of magnitude greater than the CD in many cases obstructs a sufficiently accurate determination of the apparent CD correction. It was thus found impossible, with two different modern commercial CD spectrometers, to obtain even the sign of the difference between the isotropic CD and the perpendicular element of the CD tensor of DNA.