Circular dichrograph

Circular Dichrograph. An instrument similar to a specliopolaiimeter. Instead of a change in angle of optical rotation versus wavelength, the instrument records the difference in dichroic absorption versus wavelength,... 

A circular dichrograph alternately sends left- and right-handed circularly polarized light (LCPL and RCPL) through a sample. If this sample differentially absorbs these two forms of... 

Acknowledgements. We would like to express our gratitude to Dr. L. Sawyer from the Department of Biochemist, The University of Edinburgh Medical School for the tridimensional coordinates of p-lactoglobulin structure, to Dr. F. Toma from Service de Biochimie, CEA de Saclay for allowing us to use die circular dichrograph and to Dr. B. Ribadeau Dumas from INRA in Jouy-en-Josas for his stimulating discussions and critical comments. 

The i.c.d. and absorption spectra were measured at room temperature using a Jasco J-500C circular dichrograph with a J-DP 501N data-processor.and a Hitachi 200-20 recording spectrophotometer. Stoppered silica cells of 5 0 and 10.0 cm path lengths were used. The concentration of 3-c.d. was adjusted to 0.01 M throughout the i.c.d. measurement. The l.d. in stretched polyethylene sheet was measured at ca. 

Absorbance measurements were made by using a Cary IE UV-visible spectrometer (Varian, France), while circular dichroism spectra were recorded with a Jobin-Yvon Mark V dichrograph, both at 20°C, after dilution in water. 

The dichrograph gives a direct measure of Ae. A circular dichroism (CD) spectrum often resembles an absorption spectrum, the peaks coming at the same positions as the peaks in the absorption spectrum of the same sample. However, the CD can be either positive or negative and may be positive for one transition and negative for another (Fig. 23-8). It is most convenient to plot Ae directly as a function of wavelength or wave number. However, much of the literature makes use of the molar ellipticity (Eq. 23-8) ... 

Circular dichroism is measured using a dichrograph, which modulates a monochromatic beam of light between left-handed and right-handed circular polarization. A difference between and k produces an intensity modulation that can be amplified and displayed. A separate measurement of Ct nd r would be much more exacting because the differences between Sicl and rc7 are usually very small. (The optical densities differ by I0 -10 units.)... 

Methods. Absorption spectra were measured on Specord UV/VIS spectrophotometer (Zeiss, Jena). Circular dichroism (CD) spectra were recorded on Mark III Dichrographe (ISA Jobin Yvon). Quantum chemical calculations were performed with the programme POLY (Skala (1981)), using the porphyrine atom coordinates from Maggiora et al.(1978). 

Yet another method used for studying optically active compounds is circular dichroism (CD). CD curves that are obtained with the help of a dichrograph, represent wavelength dependence on differential absorption of the circularly (levorotatory and dextrorotatory) polarized light. 

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