Electronic circular dichroism applications

Polavarapu PL, Petrovic AG, Zhang P. Kramers-Kronig transformation of experimental electronic circular dichroism application to the analysis of optical rotatory dispersion in dimethyl-L-tartrate. Chirality 2006 18(9) 723-732. 

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). 

The primary motivation for the development and application of vibrational optical activity lies in the enhanced stereochemical sensitivity that it provides in relation to its two parent spectroscopies, electronic optical activity and ordinary vibrational spectroscopy. Over the past 25 years, optical rotatory dispersion and more recently electronic circular dichroism have provided useful stereochemical information regarding the structure of chiral molecules and polymers in solution however, the detail provided by these spectra has been limited by the broad and diffuse nature of the spectral bands and the difficulty of accurately modeling the spectra theoretically. 

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... 

Vibrational optical activity (VOA) is a relatively new area of natural optical activity. It consists of the measurement of optical activity in the spectral regions associated with vibrational transitions in chiral molecules. There are two basic manifestations of VOA. The first is simply the extension of electronic circular dichroism (CD) into the infrared region where fundamental one-photon vibrational transitions are located. This form of VOA is referred to as vibrational circular dichroism (VCD). It was first measured as a property of individual molecules in 1974 [1], and was independently confirmed in 1975 [2]. Within the past twelve years, VCD has been reviewed on a number of occasions from a variety of perspectives [3-15], and two more reviews are currently in press [16,17], The second form of VOA has no direct analog in classical forms of optical activity. Optical activity in Raman scattering, known simply as Raman optical activity (ROA), was measured successfully for the first time in 1973 [18], and confirmed independently in 1975 [19], ROA has been described in detail and reviewed several times in the past decade from several points of view [20-24], and two additional reviews [25,26], one with a view toward biological applications [25] and the other from a theoretical perspective [26], are currently in press. In addition, two articles of a pedagogical nature are in press that have been written for a general audience, one on infrared CD [27] and the other on ROA [28],... 

Berova N, Bari LD, Pescitelli G (2007) Application of electronic circular dichroism in configurational and conformational analysis of organic compounds. Chem Soc Rev 36 914-931... 

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. 

Figure 1 Various types of CD measuranents and their applicability. The conventional CD can be called BCD (electronic circular dichroism) to distinguish it from otha types of CDs such as VUV-CD (vacuum-ultraviolet CD), NIR-CD (near-infrared CD), and VCD (vibrational CD). This list represents one of the typical classifications, although there is no clear boundary between each type of CDs. At the bottom, the wavelength coverage of normal CD/VCD spectrometers is shown (black lines). The coverage may be wida for some instruments or can be extended by an optional apparatus (gray lines).

A large part of the QM/MM applications to photoinduced processes are focused on the calculations of stationary properties, namely transition energies and dipoles, absorption/emission and electronic circular dichroism spectra, etc. 

There have been numerous applications of continuum models to equilibria and reactions in solution surveys of these and extensive listings are provided by Cramer and Truhlar.16 Other studies have focused upon the effects of solvents upon solute molecular properties, such as electronic and vibrational spectra,16 dipole moments, nuclear quadrupole and spin-spin coupling constants and circular dichroism.12... 

Notice that each step in the overall sequence changes the electronic or steric characteristics of the complex in a way that facilitates the next step.246 This is an important principle that is applicable throughout enzymology For an enzyme to be an efficient catalyst each step must lead to a change that sets the stage for the next. These consecutive steps often require proton transfers, and each such transfer will influence the subsequent step in the sequence. Some steps also require alterations in the conformation of substrate, coenzyme, and enzyme. One of these is the transimination sequence (Eqs. 14-26,14-39). On the basis of the observed loss of circular dichroism in the external aldimine, Ivanov and Karpeisky suggested that a... 

To end this section, it is worthwhile mentioning the recent TDDFT study by Autschbach et al [107] on the electronic and circular dichroism (CD) spectra of several chiral Werner complexes, since it represents the first application of TDDFT to the computation of the circular dichroism (CD) spectra of transition metal complexes. The absorption and CD spectra of the... 

This paper summarizes briefly the physicochemistry and enzymology of plant copper oxidases with particular emphasis on polyphenol oxidase and laccase. A brief comparative discussion of other naturally occurring copper proteins and artificial copper proteins is appropriate when discussing the physicochemistry of the copper site itself. In the case of the copper proteins listed in Table I, we know a great deal more about the copper site than about the physicochemistry of the rest of the protein molecule. This is primarily a result of the availability of sophisticated spectroscopic techniques such as optical spectroscopy (both absorption and circular dichroism) and electron spin resonance which are applicable to the electronic transitions of the copper ion. On the other hand, protein chemistry has progressed more slowly. Many of the proteins are large and complex multisubunit enzymes, difficult to purify, and often unstable. There are several excellent reviews on this group of proteins (59, 60, 61, 62). 

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