Electronic circular dichroisms ECD , spectra

Determination of protein secondary structure has long been a major application of optical spectroscopic studies of biopolymers (Fasman, 1996 Havel, 1996 Mantsch and Chapman, 1996). These efforts have primarily sought to determine the average fractional amount of overall secondary structure, typically represented as helix and sheet contributions, which comprise the extended, coherent structural elements in well-structured proteins. In some cases further interpretations in terms of turns and specific helix and sheet segment types have developed. Only more limited applications of optical spectra to determination of tertiary structure have appeared, and these normally have used fluorescence or near-UV electronic circular dichroism (ECD) of aromatic residues to sense a change in the fold (Haas, 1995 Woody and Dunker, 1996). 

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. 

One-Photon Processes OPA, OPE, BCD One-photon absorption (OPA), electronic circular dichroism (ECD) and one-photon emission (OPE) spectra can be generally written in the form... 

In this chapter, the characterization of natural products by circular dichroism (CD) spectroscopy in the UV/Vis region, called electronic CD (ECD), as well as a brief explanation of optical rotation (OR) [ct] values, which are fundamental constants for chiral compounds, is reviewed. ECD is a very sensitive diagnostic tool for determining not only AC and conformation, but also for monitoring intermolecular interactions where chiral systems are involved.2 3 There will be no discussion of vibrational CD (VCD) even though this method has made significant advances in the last decade in combination with theoretical ab initio calculations of VCD spectra.4-6... 

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