Problems of CD spectrometers (V): Can we measure CD and LD simultaneously? Comments on differential polarization microscopy (CD and linear dichroism)

Abstract

AbstractAn interesting paper on circular dichroism (CD) and linear dichroism (LD) microscopy by Livolant, Mickols, and Maestre [(1988) Biopolymers 27, 1761–1969] has attracted our attention. They reported that they have succeeded in deconvoluting mathematically true CD and LD from signals obtained for their samples of strong and incompatible anisotropies. If this is true, then their method of mathematical deconvolution will open new possibilities in polarization‐modulation spectroscopy. However, after carefully reading through their paper, we found the following obscure points in their results: (1) the hardware of their spectrometer; (2) the sensitivity matrix; (3) the method for separation of CD and LD by using two standards; (4) average CD curves; and (5) circular intensity differential scattering (CIDS) and linear intensity differential scattering (LIDS) in the wavelength range from 300 to 330 nm. Making use of the Mueller matrix analysis, we present our comments on the above subjects together with our data. In conclusion, we maintain that it is difficult to accept their claim of having a general and useful approach to separating true CD and LD from signals observed in macroscopically anisotropic samples.