Cyclodextrins circular dichroism

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

Fourier transform infrared spectroscopy has been used to monitor the Fe(lll)-and Fe(n)-mediated activation of artemisinin 9a <2001JME3150>. Circular dichroism studies on artemisinin 9a and epiartemisinin and their /3-cyclodextrin complexes have been reported <2004HCA2368>. 

C5-C6 ligands, in mononuclear Ru and Os compounds, overview, 6, 551-628 CDs, see Cyclodextrins CD studies, see Circular dichroism studies CE, see Capillary electrophoresis... 

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). 

Inclusion properties of molecular nanotubes composed of crosslinked a-cyclodextrin was investigated [47], Induced circular dichroism was used to probe the formation and dissociation of complexes between the nanotubes and azobenzene modified polyethylene glycol), either with or without a hydrophobic alkyl chain. The inclusion complex between the nanotubes and polymers formed at room temperature, and the polymers dissociated from the nanotubes with increasing temperature. 

Mayer, B. Zhang, X. Nau, W.M. and Marconi, G. (2001) Co-conformational Variability of Cyclodextrin Complexes Studied by Induced Circular Dichroism of Azoalkanes, J. Am. Chem. Soc. 123, 5240-5248. 

The magnetic circular dichroism spectrum of thioxanthone and the circular dichroism spectrum of its inclusion complex with cyclodextrin have been measured and interpreted with the aid of PPP and CNDO/S calculations. The first jtJt state exhibits intramolecular charge transfer characteristics <1994JPC10432>. 

The shuttling process was confirmed by H NMR and NOE experiments, and significantly also resulted in changes in the circular dichroism spectrum, suggesting that the change in position also affected the influence of the chirality of the cyclodextrin upon the aromatic regions of the thread. 

The rotaxane 57 has been obtained by initial formation of the 4,4 -diaminostil-bene inclusion complex of 3-cyclodextrin followed by reaction with the appropriate bulky blocking moieties. For this system, the UV-Vis and induced circular dichroism (CD) spectra confirmed that the central aromatic chromophore of the linear component was embedded in the cyclodextrin cavity. 

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>. 

Li, S. Purdy, W.C. Circular dichroism, ultraviolet, and proton nuclear magnetic resonance spectroscopic studies of the chiral recognition mechanism of P-cyclodextrin. Anal. Chem. 1992, 64 (13), 1405-1412. 

Patonay, G. Warner, I.M. Investigation of induced circular dichroism of benzo(a)pyrene cyclodextrin complexes. J. Inclusion Phenom. Mol. Recognit. Chem. 1991, 11 (4), 313-322. 

K. Ikeda, K. Uekama, M. Otagiri and M. Hatano. Circular dichroism study on inclusion complexes of / -cyclodextrin with antiinflammatory fana-mates. /. Pharm. Sci., 63, 1168-9 (1974)... 

Fig. 16A-D. Mechanical switching in rotaxanes. A Rotaxanes may exist in isomeric states by the movement of the ring component between dissymmetric sites on the string component. B A redox- or pH-switchable [2]rotaxane. While the cyclophane complexes the native benzidine site (spectrum, curve a), the reduced or protonated benzidine repels the cyclophane, causing it to move to the dioxybiphenylene site (spectrum, curve b). C An azobenzene-based switchable [2]rotaxane. The cyclodextrin ring complexes the azobenzene site in the trans-state, but it is repelled from the ds-azobenzene. The state of the system is measurable by circular dichroism (plot). D A pH-switchable rotaxane. When the amine on the string component is protonated, it complexes the crown ether ring by hydrogen-bonding interactions (40a). When the amine is deprotonated, however, the ring component moves to the bipyridinium unit, where it is complexed by n donor-acceptor interactions (40b). The plots in B and C are adapted from [67] and [69], respectively, with permission...

In catalysis the excess of a phosphine ligand is often necessary because it preserves the active species in the medium [2a]. However, it retards to some extent the co-ordination of the alkene to the metal center. Recent studies, performed by Monflier and coworkers, have shown that the water-soluble TPPTS ligand could reduce the rate of the reaction by another effect. Indeed, TPPTS can be included partially in the cyclodextrin hydrophobic cavity [53,54] NMR measurements, observation by UV-visible spectroscopy and circular dichroism, as well as scanning tunneling microscopy are consistent with a 1 1 inclusion complex in which the phosphorus atom would be incorporated into the torus of the /S-CD. NMR investigations carried out on (m-sulfonatophenyl)diphenylphosphine have shown that a phenyl group is incorporated [55]. Thus, the phosphorus ligand could modify the association constant of the alkene with the cyclodextrin so that the mass transfer between the two phases could be decreased. 

Further methods like circular dichroism, electron spin resonance, polarography, calorimetry, diffusion across semipermeable membranes and surface strain measurements were only used in the case of the cyclodextrins as yet they are described in more detail in the monographs cited above... 

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