Dichrograph

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 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... 

The separation was confirmed using simultaneous detection by a CD detector, namely a Jasco, J-600 dichrograph equipped with a micro HPLC cell attachment with a volume of 8pl, and a UV detector operating at 254 nm. In this case, the values of the anisotropy factors are constant but reversed in sign for the two enantiomers. When baseline resolution is obtained, (ee) is 100% for each enantiomer, and the point at which the fractions should be collected becomes obvious. 

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.)... 

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. 

Commercial instruments have been modified to make possible the simultaneous recording of linear absorption and CD data and to facilitate work on turbid preparations (Kfivacic et ai, 1971). Also, a prototype spectrophotometer for simultaneous measurement of ORD, CD, and linear absorbance has been described (Amato and Ewing, 1974). A Roussel-Jouan Dichrograph was modified to permit the direct reading of A and A /2 (Snatzke and Lohr, 1968). The sensitivity of a commercial CD instrument was improved by a factor of 10-12 by the use of a time-averaging system (Myer and MacDonald, 1967 Horwitz et al, 1968). Fourier transform spectrometry was applied to CD (Stewart, 1971). The fundamental aspects of its application were described, but no information was given about the performance. 

UV and visible spectra were measured with a Specord-M kO Carl Zeiss JENA usin a 0.2 cm cell CD spectra were measured with a Roussel-Jou ii Dichrographe N III (Jobin-Yvon) using a 0.5 cm cell 2x10" % host molecule and 2xlO M guest molecule were dissolved in 0,1 M phosphate buffer at pH 6.0 ... 

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. 

The anisotropic absorption of plane polarized light (parallel and perpendicular to the optic axis of the sample) can be recorded by inserting and rotating a plane polarizer in a "normal" spectro-photometer(3) (static method) or by converting, in a dichrograph. 

O. Lee and M. Diem, Anal. Instrum., 20, 23 (1992). Infrared CD in the 6-Micrometer Spectral Region Design of a Dispersive Infrared Dichrograph. 

The UV spectra were recorded with Specord M40 spectrophotometer. The CD measurements were carried out on a Jasco J-500 dichrograph in a quartz cells. The scanning tunneling microscopy (STM) were performed with a home-made high-stable STM under atmospheric conditions with a Pt/Ir tips... 

CD spectra were recorded with a dichrograph DC 111 Jobin Yvon (France), by use of a 1 mm quartz cell at room temperature (20 °C). The CD has been tested in the region of characteristic electronic absorption bands for amide groups between 190 and 250 nm. 

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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