Dichroism CD Spectroscopy

There has been considerable recent interest in chiral CEPs in which polymer chains (or aggregates of polymer chains) adopt a one-handed helical arrangement. Circular dichroism (CD) spectroscopy provides a powerful tool to probe the chain conformation (and preferred hand) in such chiral polymers. This spectroscopic technique measures the difference in absorption of left- and right-hand circularly polarized light by a chiral sample as follows  

In situ spectroelectrochemical studies can also be carried out on chiral CEP films deposited on ITO-coated glass electrodes inserted in electrochemical cells constructed in quartz cuvettes, allowing detailed studies of the changes in the CEP structures upon redox switching between different oxidation states. 

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To obtain statistically significant comparisons of ordered and disordered sequences, much larger datasets were needed. To this end, disordered regions of proteins or wholly disordered proteins were identified by literature searches to find examples with structural characterizations that employed one or more of the following methods (1) X-ray crystallography, where absence of coordinates indicates a region of disorder (2) nuclear magnetic resonance (NMR), where several different features of the NMR spectra have been used to identify disorder and (3) circular dichroism (CD) spectroscopy, where whole-protein disorder is identified by a random coil-type CD spectrum. 

Structural characterization of the biomolecule-AMP lamellar nanocomposites using FTIR and circular dichroism (CD) spectroscopies showed no change in the... 

Analyses by native polyacrylamide gel electrophoresis and circular dichroism (CD) spectroscopy revealed that spontaneous coiled-coil associations between EGF-E5-His and EGF-K5-His promoted heterodimer (dEGF-His) formation. The CD spectroscopic analysis suggested that the E5 peptide in monomeric EGF-E5-His had a disordered structure. However, the ot-helical structure was induced in the E5 peptide when it associated with EGF-K5-His. These findings are shown schematically in Fig. 6. 

FAB and MALDI-TOF MS, and IR, UV/Vis, and circular dichroism (CD) spectroscopies, and microanalysis. The limited conformational flexibility of the bridging ligand is key to the facile one-pot self-assembly of chiral molecular polygons 19-24. 

The detection of ordered structures such as a-helix or p-structurcs, and quantitative measurements of their populations, are essential aspects of structural investigation in polypeptides. The most sensitive technique for such investigation is certainly circular dichroism (CD) spectroscopy, because the various structures are characterized by typical and standard CD spectra. 

The major isomer 34 is desilylated with TBAF, and oxidative cleavage of the diol with sodium periodate generates the corresponding aldehyde 35, the racemic form of which is a known intermediate in the total synthesis of racemic CP compounds. The conversion to the indoline derivative mt-31 therefore follows the strategy of the racemic route. Circular dichroism (CD) spectroscopy verified the identity of the synthetic mt-31 as the enantiomer of the naturally derived indoline (—)-31. Synthetic ent-31 was also processed to give ent-1 and ent-2. 

The system shown in Scheme 2 is based on the fact that irradiation at 250 and 300 nm yielded photostationary states of slightly different composition. Irradiation of enantiomerically pure (M)-cis-10 or (P)-trans-10 at 250 nm resulted in a photostationary state consisting of 68% (M)-cis-10 and 32% (P)-trans-10, whereas irradiation at 300 nm yielded 64% (M)-cis-10 and 36% (P)-trans-10. Thanks to the thermal stability of these pseudoenantiomers— no (P)-cis or (M)-trans-10 were detected after irradiation—the small difference in composition of the photostationary states could be detected by circular dichroism (CD) spectroscopy. In this case, the photoinduced 180° rotation around the olefin results in a change in the helicity of the tetrahy-drophenanthrene unit. Similar behavior was observed for the structurally related benzoannulated bithioxanthylidene [28]. 

Circular dichroism (CD) spectroscopy is a sensitive analytical tool for assessing protein structure. It can detect changes in both the secondary and tertiary structure of proteins, as well as provide information regarding prosthetic groups, bound ligands and co-factors. The origin of circular dichroism in proteins is described and various applications of CD spectroscopy to the study of protein structure, function, and folding is discussed. 

The advent of recombinant DNA technology has led to an increased interest in the structural characterization of proteins by spectroscopic methods. Few spectroscopic techniques can provide the amount of information regarding protein secondary and tertiary structure which can be obtained from circular dichroism (CD) spectroscopy. In this chapter we describe the capabilities of CD spectroscopy to provide details on the globular structure of proteins. In addition, we will provide an overview of quantitative secondary structure estimates via CD spectroscopy and of specialized CD methods for studying proteins in contact with membranes and other biomolecules. Certain aspects of protein CD spectroscopy have been previously reviewed [1-19]. 

The power of circular dichroism (CD) spectroscopy is unfortunately limited to the study of chiral molecules having accessible chromophores, and cannot be applied to the study of achiral compounds. However, a great many compounds of interest are not intrinsically dissymmetric, so the induction of chirality into such species is a fundamental requirement for the performance of CD studies. In the present work, investigations into the CD induced in achiral molecules by the action of chiral agents is reviewed. 

The chirality of tartrates 60 and 61 are confirmed by circular dichroism (CD) spectroscopy <20060L1701>. Multiple bands in the CD spectra of 60 and 61 are due to tartrate dianions inducing CD in the anthracene rings. This is the first reported case of induced circular dichroism (ICD) observed in a chiral macrocycle. 

In general, stopped-flow methods provide a reasonably inexpensive means of determining a large number of fairly fast reactions. Stopped-flow mixing is usually coupled with real-time optical observation using absorbance (UV through IR see. Vibrational Spectroscopy), fluorescence emission, or circular dichroism (CD) spectroscopy. In addition, the stopped-flow technique has been implemented in conjunction with many other biophysical techniques, such as EPR, NMR (see Nuclear Magnetic Resonance (NMR) Spectroscopy... 

Steady-State fluorescence and circular dichroism (cd) spectroscopies [157]. (l-Naphthyl)methyl and (2-naphthyl)methyl side chains interacted most considerably with j6-CD. Cd spectra indicated that P-CD included polymercarrying INp groups shallowly, but it included deep polymer-carrying 2Np groups to form inclusion complexes, in which the longer axis of the 2Np group is rather parallel to the rotation axis of P-CD. 

Circular dichroism (CD) spectroscopy has been used to study the cleaved (73), deflavo (74), and intact (19, 60) forms of flavocytochrome 62 from S. cerevisiae and the intact enzyme from H. anomala (73, 75). Magnetic circular dichroism (MCD) has been used to probe the holo-and deflavo-cleaved enzyme from S. cerevisiae (76), as well as the cytochrome 62 core (77). It was noted that bands in the CD and MCD spectra ascribed to the heme were affected by removal of the FMN group, providing direct evidence of an interaction between the two prosthetic groups (73). Circular dichroism experiments on the intact and cleaved forms of S. cerevisiae flavocytochrome 62 led Jacq and Lederer (19) to conclude that there were differences in the heme environment between these two forms of the enzyme. 

To determine the absolute configuration of optically active organic compounds, there are two nonempirical methods. One is the Bijvoet method in the X-ray crystallographic structure analysis, which is based on the anomalous dispersion effect of heavy atoms. - The X-ray Bijvoet method has been extensively applied to various chiral organic compounds since Bijvoet first succeeded in determination of the absolute stereochemistry of tartaric acid in 1951. The second method is a newer one based on the circular dichroism (CD) spectroscopy. Harada and Nakanishi have developed the CD dibenzoate chirality rule, a powerful method for determination of the absolute configuration of glycols, which was later generalized as the CD exciton chirality method. 8 The absolute stereochemistry of various natural products has been determined by application of this nonempirical method. 

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