Induced circular dichroism absorption

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 first silver clusters made using DNA as template were reported by Dickson et al. in 2004 [32], The paper describes the time-dependent formation of silver clusters in a 12-base (5 -AGGTCGCCGCCC-3 ). The clusters have intense absorption in the region 400-550 nm (Fig. 2b) and emission at around 630 nm. The latter band could be decomposed as the emission bands of two distinct excitations at 540 and 580 nm, indicating the existence of two different emitters. As the clusters do not have inherent chirality, the induced circular dichroism associated with the silver cluster electronic transitions is evidence that the clusters are bound to DNA (Fig. 2c). 

Fig. 2 (a) Schematic of the formation of silver clusters using DNA oligonucleotide as scaffold. After complexation of DNA with silver cations, the mixture is reduced with NaBtL, and the fluorescent cluster is formed, (b) Absorption spectra of silver clusters acquired every 30 min using [5 -AGGTCGCCGCCC-3 ] = 10 uM. [Ag+] = 60 uM. and [BfLj-] = 60 pM. The foremost spectrum was acquired 9 min after adding the BH4, and it has at 426 nm. The inset spectrum shows the last spectmm in the series (692 min), with peaks at 424 and 520 nm. (c) Induced circular dichroism spectra. The cell path length was 5 cm. The spectra were collected 2 min (A, dashed-dotted line), 20 min (B, dotted line), 40 min (C,fine dashed line), 60 min (D, coarse dotted line), and 150 min (E, solid line) after adding the BH [32]... 

The absolute configuration of chiral nonracemic compounds can be established by forming a complex which can bind to the axial position of [Rh2(02CCF3)4] and thus induce circular dichroism within its electronic absorption bands. This method works well for chiral secondary alcohols and monoolefins. For these compounds tentative rules were proposed, which correlate the configuration of the starting materials with the sign of certain Cotton effects of their complexes178. 

The hetero-dimerization behavior of dye-modified -cyclodextrins with native CDs was investigated by means of absorption and induced circular dichroism spectroscopy in aqueous solution [43], Three types of azo dye-modified /i-CDs show different association behavior, depending on the positional difference and the electronic character of substituent connected to the CD unit in the dye moiety. p-Methyl Red-modified fi-CD (1), which has a 4-(dimethylamino)azobenzene moiety connected to the CD unit at the 4 position by an amido linkage, forms an intramolecular self-complex, inserting the dye moiety in its / -CD cavity (Figure 13). 1 also associates with native a-CD by inserting the dye residue into the a-CD cavity. The association constants for such hetero-dimerization are 198 M"1 at pH 1.00 and 305 M 1 at pH 6.59, which are larger than the association constants of 1 for / -CD (43 M 1 at pH 1.00). 

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. 

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). 

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. 

D. Krois, U. H. Brinker, Induced circular dichroism and UV-vis absorption spectroscopy of cyclodextrin inclusion complexes structural elucidation of supramolecular aziadamantane (spiro[adamantane-2,3 -diazirine]), /. Am. Chem. Soc., 1998, 120, 11627-11632. 

ABSTRACT. The induced circular dichroism (i.c.d.) and absorption spectra of the B-cyclodextrin (3-c.d.) complex with cyclohuta[l,2-i> 3, -Hdiquinoxaline (I) have been measured. The linear dichroism (l.d.) spectra of I in stretched polyethylene sheet have been also measured. 

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. 

The use of CD as a probe of liquid crystalline properties has been rather limited. A helicoidal structure will induce circular dichroism at an absorption band of a nonchi-ral chromophore, and the magnitude of the induced CD absorption depends on the pitch of the helix, the sign of the CD changing if pitch inversion occurs. This technique has been used to investigate phase transitions between ferrielectric, ferroelectric and anti-ferroelectric smectic C states of MHPOBC... 

Liquid crystal induced circular dichroism (LCICD) examines the differential absorption of circularly polarized radiation by an achiral solute oriented in a cholesteric liquid crystal. The circular dichroism results from an induced Cotton effect in the achiral solute due to the macroscopic chirality of its ordering in the helical solvent matrix. The effect has been shown theoretically to arise... 

Induced circular dichroism (ICD) is the CD observed in an optically inactive (achiral) chromophore due to its interaction with an optically active (chiral) moiety. Early applications exploited ICD just as evidence for such an interaction. For example, the ICD in the absorption band of an achiral drug may be used to prove its binding to a (chiral) protein or nucleic acid. More recent use of ICD includes the structural information that theoretical analysis of the inducing mechanism can provide. ICD has been an important complement to linear dichroism (LD) for the assessment of binding geometries in drug-nucleic acid systems. 

Electronic transitions of the carbazole chromophores afford a highly sensitive probe for studies of carbazole-containing polymers in respect of their absorption and emission characteristics as well as of either inherent or induced circular dichroism. They have been conveniently employed to describe microstructural characteristics of carbazole-containing polymers, including homopolymers of carbazolated a-aminoacids and of vinylated carbazoles with chiral substituents. Data obtained are entirely consistent with interpretation of polymer structures derived from related UV absorption, excimer fluorescence emission and NMR studies and are especially valuable as a completely new indication of copolymer sequence distributions. 

The discovery of the fluorescence variation of pyrene-modified y-CD 1 upon addition of guests prompted the use of fluorophore-modified CD as chemosensors [9,10]. The pyrene-modified y-CD forms an association dimer in aqueous solution and exhibits excimer emission around 470 nm. The addition of a guest into the solution of the pyrene-modified y-CD causes a remarkable decrease in the excimer emission and an increase in the monomer emission around 378 and 397 nm. The guest-induced circular dichroism and absorption variations of 1 substantiated that this fluorescence variation occurs associated with the conversion from the association dimer to a 1 1 host-guest complex (Fig. 1). Since the... 

The UV-Vis absorption, NMR, ICD (induced circular dichroism), fluorescent spectra and cyclic voltammetry are the methods used to monitor the co-con-formational changes for switchable rotaxanes. Unlike other spectral signals, a fluorescence signal is highly sensitive so even a single-molecular fluorescence can be detected, and furthermore, a fluorescence output can be easily and remotely detected. 

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 ... 

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