Circular Dichroism of Cyclodextrin Complexes

Circular dichroism (CD) [1] is a spectroscopic technique that detects the differential absorption of circularly polarized light passing through a chiral substance. It is defined as the difference of the molar extinction coefficients for the left and right circularly polarized light Ae = — s. Consequently, nothing results other than an 

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Bose PK and Polavarapu PL (1999) Vibrational circular dichroism of cyclodextrin complexes. Journal of the American Chemical Society 121. 

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. 

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. Harata, H. Uedeira, The circular dichroism of the /3-cyclodextrin complex with naphthalene derivatives. Bull. Chem. Soc. Jpn., 1975, 48, 375-378. 

Nearly 22% of the publications are dedicated to studies of the CD-inclusion phenomena. These works are generally not directly practice-oriented, dealing with energetics and kinetics of inclusion, x-ray, FT-IR, liquid- and solid-phase NMR, EPR, circular dichroism, Raman spectroscopy, enhancement of luminescence and phosphorescence. thermal analysis, interaction of CDs. with specific guest types, enzyme modeling with CDs and CD derivatives, preparation, analysis of cyclodextrin complexes, etc. These methods, as well as the correlation between the complexation and various structural and external parameters, form the basis for all practical applications of CDs. 

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>. 

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. 

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 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. 

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. 

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. 

Suzuki M, Kajtar M, Szejtli J, Vikmon M, Fenyvesi E, Szente L. 1991. Inclusion compounds of cyclodextrins and azo dyes 9. Induced circular dichroism spectra of complexes of cyclomaltooligosaccharides and azobenzene derivatives. Carbohydr Res 214(1) 25 33. 

To obtain further information on the preferential inclusion of the aromatic residue of one of the two enantiomers electronic and c.d. spectra were recorded in the UV-vis region. The inclusion of several chromophores in the cyclodextrin cavity has been shown to produce induced circular dichroism (i.c.d.), due to the presence of many chiral centres. In several cases, it has been possible to correlate theoretically both the sign and the intensity of the observed i.c.d. and the orientation of the transition moment related to the cyclodextrin axis [S0-S2]. It is expected both that the differential inclusion of the aromatic residue of the amino acid in the CD cavity restricts the conformational mobility of the participating groups and that the different orientation of the transition vectors in the two diastereomeric complexes causes the opposite sign in c.d. activity. 

The interaction between cyclodextrin and ADP was examined by circular dichroism. In the presence of MgCla, an increase of g-cyclodextrin caused a decrease in the molar ellipticity at 258 and 210 nm. This suggested a complex formation between cyclodextrin and ADP with a magnesium ion involved in ATP formation. Moreover, the dependence of... 

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. 

Figure 3- The induced circular dichroism (top) and electronic (bottom) spectra of the 3-cyclodextrin complex with I (full line, 0.00000267 M dotted line, 0.0000302 M).

Circular Dichroism (CD) Spectroscopy New circular dichroism (CD) bands can be induced in the absorption bands of the achiral guest molecule when it is included within the asymmetric locus of the cyclodextrin cavity which consists of chiral glucose units [62]. Chiral guest molecules may also show changes in circular dichroism (CD) spectra upon the formation of inclusion complexes with cyclodextrin [63]. 

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