Circular dichroism spectrometers

Figure 6. Block diagram of a circular dichroism spectrometer.

Measurements. The absorption, circular dichroism (CD), and ESR spectra were recorded with a Hitachi 323 spectrophotometer, a JASCO MOE-1 magnetic circular dichroism spectrometer, and a JEOL JES-FE3X ESR spectrometer, respectively. The measurements of the spectra were carried out at 15°-20°C except for the ESR spectra, which were recorded at 77 K. The resonance Raman spectra were recorded at 10°C with 488.0-nm excitation (Ar+ laser) on a JEOL JRS-400D-002 spectrophotometer. The concentration of copper was determined to be 4.9mM by atomic absorption measured by a Nippon Jarrell-Ash AA-1 spectrometer. 

Bonmarin M, Helbing J (2008) A picosecond time-resolved vibrational circular dichroism spectrometer. Optics Lett 33 2086-2088... 

Takakuwa, T. Kurosu, Y. Sakayanagi, N. Kaneuchi, F. Takeuchi, N. Wada, A. Senda, M. Direct combination of a high performance liquid chromatograph and a circular dichroism spectrometer for separation and structural analysis of proteins. J. Liq. Chromatogr. 1987,10, 2759-2769. 

A reflective circular polarizer is used to construct the terahertz circular dichroism spectrometer (Error Reference source not found.). The... 

To calibrate and test the terahertz circular dichroism spectrometer, we successfully measured magnetic terahertz circular dichroism in a semiconductor. A Helmholtz coil was fabricated that produced an axial magnetic field, homogeneous in the transverse direction. A doped,... 

Figure 6. Frequency dependent magnetic circular dichroism in InAs measured by our terahertz circular dichroism spectrometer.

Apparatus. The spectrum and intensity of fluorescence were measured with a RF-540 spectrofluorometer (Shimadzu, Japan). An UV-260 (Shimadzu, Japan) spectrophotometer was employed in all absorption spectra recordings. The circular dichroism spectrometer JASCO J-810 (Hitachi. Japan) was used for measurement... 

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. 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

Circular dichroism (CD) spectra of proteins CD spectrometers, 226-227 cell selection, preparation, and handling, 227-229... 

My own introduction to this field came during the course of my graduate studies when my mentor decided that I needed to learn the Jones calculus for treating optical phenomena. The department also possessed a Cary 60 spectrometer system, and in the time between my final oral exam and the beginning of my postdoctoral work I investigated the induction of circular dichroism in several metal complexes of acetylacetone by various chiral agents. Little did I know at the time that this particular work would subconsciously prepare me for the writing of one of the chapters in this book. 

X-Band ESR spectra were obtained at 77 and 293 K with a JES-FE-3X spectrometer. The g-values were determined relative to Li-TCNQ(g = 2.0026) and the magnetic fields were calibrated by the splitting of Mn(II) in MgO(AH3 4 = 86.9 G). Magnetic circular dichroism (MCD) measurements, using a 11.7-kG magnet, were carried out on a Jasco J-20 spectro-polarimeter and are expressed in terms of molecular ellipticity, [0] = 2.303 (4500/7r) ( - r), with units of (deg cm2)/d mol. 

As a first step towards the measurement of single molecule effects, Schrader and Korte (1972) reported the measurement of the infrared rotatory dispersion of carvone in liquid crystalline solution. They used a modified commercial spectrometer. They observed a huge effect which is not the result of the carvone itself but of the liquid crystal in which a helical arrangement (cholesteric state) is induced by the chiral solute (Sec. 4.6.4). In this case the liquid crystal acts as a kind of molecular amplifier which allows the absolute configuration of tiny amounts of solutes to be determined reliably. At about the same time Dudley et al., (1972) measured the infrared circular dichroism of (-)-menthol in a liquid crystal. Their equipment consisted of a normal infrared spectrometer supplemented by a Fresnel rhomb made from sodium chloride. 

In the years to follow the key to the measurement of vibrational circular dichroism was the development of photoelastic modulators suitable for work in the infrared spectral region. The first successful measurements of circular dichroism originating from vibrational transitions in the infrared were done by Hsu and Holzwarth (1973) on thin slices of monocrystalline a-NiS04 6 H2O and a-ZnSe04 6 H2O. For this measurements the authors used a normal dispersive IR spectrometer supplemented by a linear polarizer and a photoelastic modulator made from Germanium. 

In addition, some other aspects should also be addressed so that CE can be used as a routine method in this field. The most important points related to this include the development of new and better chiral selectors, detector devices, and addition of a cooling device in the CE apparatus. In addition, chiral capillaries should be developed and the CE device should be hyphenated with mass spectrometer, polarimetric, and circular dichroism detectors, which may result in good reproducibihty and improved limits of detection. The advancement of CE as a chiral analysis technique has not yet been fiilly explored and research in this direction is currently underway. In summary, there is much to be developed for the advancement of CE for the analysis of chiral pollutants. It is hoped that CE will be recognized as the technique of choice for chiral analysis of the environmental pollutants. 

Sensitive Optical Detectors. More sensitive optical techniques that have been used with CE include fluorescence, refractive index, chemiluminescence, Raman spectrophotometry, and circular dichroism. The most sensitive optical detection method used in CE is laser-induced fluorescence (LIE), which is capable of detection limits in the 10 to 10" mol (or better) range. This detection mode is easily accomplished with analytes that are either easily labeled with a fluorescent substrate (e.g., intercalators for double-stranded DNA) or are naturally fluorescent (e.g., proteins or peptides containing tryptophan). CE systems have also been interfaced with mass spectrometers, and electrochemical detection methods have been developed, although such detectors must be isolated electrically from the electrophoretic voltages. 

Circular dichroism (CD) of free amino acids and peptides and their derivatives provides valuable information on conformational behaviour and can define absolute configurations. The UV fluorescence behaviour of particular derivatives can also highlight positions of groups in molecules, in relation to the positions of other groups, providing decisive structural information. Although fluorescence spectrometry can be carried out in most research laboratories, CD spectrometers are less widely available. 

Circular dichroism has been well understood and estabhshed in the ultra-violet, visible, near- and mid-infrared frequency range as an integral part of contemporary biophysics with numerous, excellent, turnkey instruments commercially available. However, there have been no documented measurements of terahertz circular dichroism. We have developed a simple physical model of circular dichroism in the terahertz frequency range, and build upon our broad band absorption spectrometer to explore the terahertz circular dichroism signatures of prototypical proteins in aqueous solutiom... 

Spectral Determinations. The circular dichroism spectra were obtained on a Cary 60 modified as reported previously (20J. The spectra were obtained with aqueous solutions. The 1 1 v/v CD30D/ CD2C12 XH NMR spectra were obtained with a Perkin Elmer R-12 spectrometer. The ultraviolet/visible electronic spectra in water or chloroform were obtained with a Cary 14 spectrophotometer with matched one cm Supracil cells. 

More esoteric experimental procedures which can be applied to complex molecules include, for example, picosecond time-resolved circular dichroism. A spectrometer for this purpose has been described and used to observe carbon monoxide elimination from excited carbon raonoxymyoglobulin.Fluorescence detected CD has also been used to observe riboflavin in capillary electrophoresis. 

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