Circular dichroism, induce

The circular dichroism induced in achiral compounds upon complexation with a chiral material can be used to characterize the nature of the interaction responsible for the association. Studies of this type may be conveniently classified as being the optical activity induced upon dissolution of a solute in a chiral solvent, through association of the species of interest with a co-dissolved chiral solute, or through association of the solute with chiral polymers. 

Fig. 23 TDDFT sector maps calculated at the B3LYP/aug-cc-pVDZ level of theory for the circular dichroism induced in the carbonyl centered n-to-n transition of formaldehyde. The scan was performed 1.3 A above the chromophore plane using point charges of —O.le and +0.3e, respectively...

The methods were straightforward to use for chiral molecules generally, as discussed in sec 6, [116], and for particular applications such as circular dichroism induced by a chiral neighbour [138]. 

Induced circular dichroism. Induced circular dichroism is observable for electronic transitions of an achiral molecule when, for example, it is associated in the form of a coordination complex with a chiral molecule. In the example given by Stang of a tetranuclear platinum complex where two achiral fragments are linked by two S,S)-tartrate anions (2.36) (Figure 2.59), a Cotton effect is observed for the transitions of the achiral anthracene unit. 

Wu, Y, Seo, T., Maeda, S., Sasaki, T., Irie, S., and Sakurai, K. (2005). Circular dichroism induced by the helical conformations of acylated chitosan derivatives bearing cinnamate chromophores, /. Polym. Sci. Polym. Phys., 43,1354-1364. 

The determination of the absolute configuration of a chiral substance is a very important part of the characterization of that molecule. That is also true for chiral solvents. Circular dichroisms induced in the UV spectra of metal complexes solvated by a chiral solvent can be used for the determination of the absolute configuration of the solvent [Br 80]. This method is attractive in that the experiments are easy to carry out. 

See also Biochemical Applications of Raman Spectroscopy Biomacromolecular Applications of Circular Dichroism and ORD Carbohydrates Studied by NMR Circularly Polarized Luminescence and Fluorescence Detected Circular Dichroism Induced Circular Dichroism Magnetic Circular Dichroism, Theory Nucleic Acids and Nucleotides Studied Using Mass Spectrometry Organometallics Studied Using Mass Spectrometry Polymer Applications of IR and Raman Spectroscopy Proteins Studied Using NMR Spectroscopy Vibrational CD Spectrometers Vibrational CD, Theory. 

Incorporation of chiral units into polymers generates optically active polymers.27 Two types of optically active polymers could be obtained according to where the chiral units reside optically active polymers with chirality derived from chiral side chains and optically active polymers with chirality derived from tire chiral main chain. The circular dichroism (CD) measurement of 32, an optically active polymer with chiral side chains, showed that the chiral substituents have induced main-chain chirality. The induced main-chain chirality disappeared at higher temperature and appeared upon cooling. This type of chiral conjugated polymer is potentially useful in reversing optical recording28 ... 

Hatano, M. Induced Circular Dichroism in Biopolymer-Dye System. Vol. 77, pp. 1-121. 

Ever since Pasteur s work with enantiomers of sodium ammonium tartrate, the interaction of polarized light has provided a powerful, physical probe of molecular chirality [18]. What we may consider to be conventional circular dichroism (CD) arises from the different absorption of left- and right-circularly polarized light by target molecules of a specific handedness [19, 20]. However, absorption measurements made with randomly oriented samples provide a dichroism difference signal that is typically rather small. The chirally induced asymmetry or dichroism can be expressed as a Kuhn g-factor [21] defined as ... 

Fig. 29. Equilbrium unfolding of C40A/C82A/P27A (pseudo-wild-type) barstar monitored by A R, mean residue circular dichroism. Conditions for near-UV CD were 50 /xM protein in 50 mM Tris-HCl buffer, pH 8, 0.1 M KC1, path length 1 cm. (A) Urea-induced unfolding at 25°C at urea concentrations as indicated. (B) Cold-induced unfolding in...

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. 

The influence of adsorption on the structure of a -chymotrypsin is shown in Fig. 10, where the circular dichroism (CD) spectrum of the protein in solution is compared with that of the protein adsorbed on Teflon and silica. Because of absorbance in the far UV by the aromatic styrene, it is impossible to obtain reliable CD spectra of proteins adsorbed on PS and PS- (EO)8. The CD spectrum of a protein reflects its composition of secondary structural elements (a -helices, / -sheets). The spectrum of dissolved a-chymotrypsin is indicative of a low content of or-helices and a high content of //-sheets. After adsorption at the silica surface, the CD spectrum is shifted, but the shift is much more pronounced when the protein was adsorbed at the Teflon surface. The shifts are in opposite directions for the hydrophobic and hydrophilic surfaces, respectively. The spectrum of the protein on the hydrophilic surface of silica indicates a decrease in ordered secondary structure, i.e., the polypeptide chain in the protein has an increased random structure and, hence, a larger conformational entropy. Adsorption on the hydrophobic Teflon surface induces the formation of ordered structural elements, notably an increase in the content of O -helices (cfi, the discussion in Sect. 3.1.4). 

The enzymatic activities of O -chymotrypsin in solution and adsorbed at the different surfaces are presented in Fig. 11, where the specific enzymatic activity (defined as activity per unit mass of protein) is plotted as a function of temperature. The enzyme loses activity due to adsorption. On the hydrophobic Teflon and PS surfaces, the activity is completely gone, whereas on the hydrophilic silica surface, or-chymotrypsin has retained most of its biological function. These differences are in agreement with the adsorption isotherms and the circular dichroism spectra. The influence of the hydrophobicity of the sorbent surface on the affinity of the protein for the sorbent surface, as judged from the rising parts of the adsorption isotherms (Fig. 8), suggests that the proteins are more perturbed and, hence, less biologically active when adsorbed at hydrophobic surfaces. Also, the CD spectra indicate that adsorption-induced structural perturbations are more severe at hydrophobic surfaces. 

Figure 14 shows the circular dichroism spectra for the LB films of p-CDNH C12-H25 including Naph-SOsNa molecules under the initial surface pressure of 30 mN/m. Different induced circular dichro-isms are clearly observed at1 Bbband of naphthalene, depending on the substituted position the negative and positive Cotton effects occur for 1 - and 2-Naph-SOaNa included in the cavity of the CD... 

Fig. 4. Time-induced conformational change of spider silk protein (spidroin) in solution. Solutions of silk proteins at 1% w/v in distilled water were monitored using circular dichroism. The graph shows a change in secondary structure with time. The silk proteins underwent a kinetically driven transition from a partially unfolded structure to a -sheet-rich structure (from Dicko et al., 2004c). ( ) after 0 days, (O) after 1 day, and (A) after 2 days. The conformational change appeared faster at 20°C compared to 5°C, suggesting a hydrophobically driven mechanism. (Copyright 2004 American Chemical Society.)...

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