Electronic circular dichroism ECD

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). 

As a continuation of the interest in the electronic circular dichroism (ECD) of the chiral nitrosamines, the ECD of the /V-nitroso derivatives of chiral 4-, 5- and 6-membered cyclic... 

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. 

Electronic Circular Dichroism In contrast to most organic compounds in which CD measurements are limited to the ultraviolet region, most metal complexes possess d-d absorption bands in the more accessible visible and near-infrared regions, allowing for relatively easier application of electronic circular dichroism (ECD) measurements. In fact, the first observation by Cotton of optical rotation measurements through an absorption band and interpretation in terms of differential absorption of the circularly polarized beam was performed on solutions of L-tartrate chromium(III) and copper(II) complexes.100... 

Recenfly fhe ah initio calculation mefhod of vibrational circular dichroism (VCD), optical rotatory dispersion (ORD), and electronic circular dichroism (ECD) has been developed as fhe third nonempirical method [3, 4]. The method is applicable to compounds having no chromophore, and so should be widely used in future. 

The circular dichroic phenomenon commonly exists throughout all spectral regions (Figure 1). Although the conventional CD, which targets the UV-vis region, is sometimes referred to as electronic circular dichroism (ECD) to differentiate it from VCD (Section 7), here we... 

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... 

The first contribution to the induced electric dipole moment in O Eq. 11.74 from the time dependence of the magnetic field, w G, gives rise to two different observable properties. In the dispersive region, this property determines the optical rotatory power, or just optical rotation (OR) for short, and in the absorptive region it determines the rotational strength observed in electronic circular dichroism (ECD). 

Similar to other chiroptical spectroscopy methods, electronic circular dichroism (ECD) also originates from the difrerential interaction of a chiral nonracemic molecule with left- and right-CPL however, contrary to OR and ORD discussed in the previous section, ECD does not result from different refraction indices for each circular component but from different absorption rates. ECD can be defined as ... 

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