Induced circular dichroism, ICD

Photochemically Triggered Induced Circular Dichroism in Liposomes When an optically inactive chromophore is subject to the effect of optically active environment, optical activity may be induced at the absorption wavelength of the optically inactive chromophore. This phenomenon of induced circular dichroism(ICD) is often observed in polypeptides bearing various achiral chromophores on the side chain( ). The strong chiral environment caused by the peptide helix structure is responsible for this. Distance from, and orientation to, the chiral field decide the degree of ICD appearing on the achiral chromophore. 

The observed induced circular dichroism (ICD) is classified as follows ... 

In enzymology, binding constants of substrates or inhibitors of enzymes are estimated by registering the changes of CD the magnitudes induced at the wavelengths of the added molecules. This induced circular dichroism (ICD) depends on the binding mode and the chemical quantity of the bound molecules. This chemical measure is essential... 

In a study of chiral dipeptide [2]rotaxanes it was found that the presence of an intrinsically achiral benzylic amide macrocycle near to the chiral center could induce an asymmetric response in the aromatic ring absorption bands [62], This induced circular dichroism (ICD) effect was stronger in apolar solvents (Fig. 9), where intercomponent interactions are maximized, showing a direct relationship to the tightness with which the macrocycle binds the chiral thread. Computer simulations showed that chirality is transmitted from the amino acid asymmetric center on the thread via the achiral macrocycle to the aromatic rings of the achiral C-terminal stopper. 

The induced circular dichroism (ICD) spectra of the (/ -CDr) complexes of pyrido[2,3-6]pyrazines have been measured. The polarization analysis and spectral assignments were made by comparing the theoretical results calculated using the CNDO/S-CI approximation with the observed ICD spectra <82JA7059>. 

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. 

The induced circular dichroism (ICD) spectra of five /3-cyclodextrin derivatives containing a benzisoselenazol-3(27T)-one moiety show two positive Cotton effects at ca. 232-246 and 259-264 nm. This indicates that the benzisoselenazolone moiety lies outside the chiral cavity of /3-cyclodextrin, and both of the transition moments may be perpendicular to the axis of the /3-cyclodextrin cavity. In contrast, the ICD spectra of other /3-cyclodextrin derivatives display one negative Cotton effect at 229 nm and a positive Cotton effect at 248 nm. It can be inferred that the benzisoselenazolone moiety is located inside the chiral cavity of /3-cyclodextrin <2002HCA9>. 

Several physical methods have been employed to ascertain the existence and nature of ICs infrared (IR) absorption spectroscopy nuclear magnetic resonance (NMR) spectroscopy,14 including JH nuclear Overhauser effect (NOE) difference spectroscopy, H 2-D rotating-frame Overhauser effect spectroscopy (2-D ROESY),15 and solid-state 13C cross-polarization/magic angle spinning (CP/MAS) spectroscopy 16 induced circular dichroism (ICD) absorption spectroscopy 17 powder and singlecrystal X-ray diffraction 18 and fast atom bombardment mass spectrometry (FAB MS). 

Most applications of ECD spectroscopy in supramolecular chemistry, which can be counted to hundreds, involve proofs of existence and determination of properties (chirality) of potentially chiral supramolecular structures. The convergence of the ECD amplitude is taken as a criterion of pure enantiomers. The loss of structure upon the change of physico-chemical properties can be followed by the decrease of CD signal. Another concept uses chromophores [24] for testing the three dimensional structure of supramolecular systems. If the isolated chromophore is not chiral and induced circular dichroism (ICD) is observed in the system, we can sometimes deduce the structure of the chromophoric environment (see section 8.4.2). Ab initio calculations open another possibility to employ ECD into supramolecular chemistry (Section 8.1.3). 

On the other hand, it was reported that either several reactions could not be reproduced or no asymmetric effect was found Negative results in several works were explained by the large steps of the helix in the structure of cholesteric liquid crystals (300-400 nm) and by the absence of chirodiastaltic interaetion with the small molecules of the substrates. In the case of large molecules of complicated stereostmctures it was possible to wait for the appearance of such interactions as revealed by the appearance of induced circular dichroism (ICD) in the absorption bands of chromophors of components and products of the reaction. 

Induced circular dichroism (ICD), 9-16 Infrared active vibrations Theory, 22-5 Inherent one-dimensional (ID) nature, 16-2 Inherently nonhomogeneous character, 16-2 Inhomogeneous disorder model, 15-8, 15-10-15-14 comparison with experimental results... 

Cationic zinc porphyrins are well-known DNA interca-lators. Interestingly, however, they are not effective for Z-DNA since binding destabilizes the left-handed helix and causes it to revert to the B state. However, the simple modification of coordinating water in an axial position of a Zn porphyrin prevents intercalation, thereby obviating the reversion to the B-form. This was a feature that was exploited by Purrello and coworkers. They found that at a micromolar concentration of porphyrin, an intense bisig-nate induced circular dichroism (ICD) signal was seen in the case of Z-DNA only a small ICD signal was seen in the case of B-DNA. 

Nagasaki and Kimura have used polymers of poly(lysine) with boronic acids appended to the amine residue as saccharide receptors [158-160]. On saccharide com-plexation these polymers are converted from neutral sp boron into anionic sp hybridized boron. The anionic polymer thus formed interacts with added cyanine dye. Saccharide binding can then be read-out by changes in the absorption and induced circular dichroism (ICD) spectra of the cyanine dye molecule. 

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