Molecular cyclodextrin studies

CL Copper, JB Davis, RO Cole, MJ Sepaniak. Separations of derivatized amino acid enantiomers by cyclodextrin-modified capillary electrophoresis Mechanistic and molecular modeling studies. Electrophoresis 15 785-792,... 

Liu, Y. Li, L. and Chen, Y. (2002) Molecular Recognition Studies on Supramolecular Systems. Part 38. Inclusion Complexation of Organic Dyes by Organoselenium Bridged Bis-(/f-cyclodextrin)s with a Short linker,/. Incl. Phenom. 42, 151-155. 

Molecular model studies have shown that PMVE, PEVE, and PnPVE chains are capable to penetrate y -CD cavities. Model studies further indicate that the single cavity can accommodate three monomer units. The inclusion complex formation of polymers with cyclodextrins is entropically unfavorable. However, formation of the complexes is thought to be promoted by hydrogen bond formation between cyclodextrins. Therefore, the head - to - head and tail - to - tail arrangement, which results in a more effective formation of hydrogen bonds between cyclodextrins, is thought to be the most probable structure. This structure was proved by X-ray studies on a single crystal of the complex between y -CD and 1-propanol. 

Koehler, J. E., Saenger, W. and van Gunsteren, W. F. (1988). Conformational differences between alpha-cyclodextrin in aqueous solution and in crystalline form. A molecular dynamics study. J Mol Biol, 203, 241-250. 

Another popular host for molecular recognition studies in monolayers is thiol-derivatized cyclodextrin. Kaifer and coworkers have prepared monolayers from fi-cyclodextrin 19 in which all primary hydroxyls are replaced by SH groups. This compound can form up to seven gold-sulphur chemical bonds on the surface. These monolayers are incomplete to cover the gold surface completely, they were treated successively with ferrocene (to block the cyclodextrin cavities) and pentanethiol (to fill in the spaces between cavities). Cyclic voltammetry showed that the layers obtained bind ferrocene. Ferrocene trapped in the cyclodextrin cavities can be replaced by another known guest, electroinactive m-toluic acid444. 

Fig. 10. Depths of the cavities of modified /8-cyclodextrins (20) and (21) as well as the native one, estimated by molecular model studies. From Breslow, R. et al. (1980) J. Am. Chem. Soc. 102, 762, reprinted by permission.

Tong WQ, Lach JL, Chin TF, Guillory JK, Structural effects on the binding of amine drugs with the diphenylmethyl functionality to cyclodextrins. II. A molecular modeling study, Pharm. Res. 1991 8 1307-1312. 

M. Prabhakaran and S. C. Harvey, Biopolymers, 26, 1087 (1987). Asymmetric Oscillations in Cyclodextrin—A Molecular Dynamics Study. 

Liu. Y. Han, B.H. Qi, A.D. Chen, R.T. Molecular recognition study of a supramolecular system. 11. Chiial recognition of aliphatic amino acids by natural and modified a-cyclodextrins in acidic aqueous solution. Bioorg. Chem. 1997. 25 (3), 155-162. 

Liu, Y. You. C.-C. Wada, T. Inoue, Y. Molecular recognition studies on supramolecular systems. 22. Size, shape, and chiral recognition of aliphatic alcohols by organoselenium-modified cyclodextrins. J. Org. Chem. 1999. 64 (10). 3630-3634. 

Comprehensive reviews of the history, chemistry, and physical chemistry of rotaxanes and the related architecture, the catenanes, have been published [115-120], Joyce et al. [121] reported a molecular modeling study of cyclics of poly(dimethylsiloxane) to imderstand the energetics of the threading process of linear chains with particular reference to rotaxanes. Of relevance is also the exhaustive review by Wenz [122] on the role of cyclodextrins in the building of supramolecular structures. Cyclodextrins are cyclics of D-glucose, with a-1,4 linkages. The common ones are a,/3, y-cyclodextrins, with 6, 7, and 8 D-glucose units, respectively. 

R208 A. Moreira da SUva, Food Antioxidants Cyclodextrin Inclusion Compounds Molecular Spectroscopic Studies and Molecular ModeUing , in Macrocyclic Chemistry, eds. D. W. Fitzpatrich and H. J. Ulrich, Nova Science Pubhshers, Inc. Hauppauge, N. Y., 2010, p. 447. 

Several physical studies have been carried out on cyclodextrin derivatives. Thus the X-ray structure of per-(6-bromo-6-deoxy-2,3-di-0-methyl)P-cyclodextrin has been examined by single crystal X-ray diffraction analysis. The conformation deviates significantly from C symmetry. Likewise the X-ray structure of heptakis-2,3,6-tri-C>-methyl-P-cyclodextrin shows that one of the seven rings is inverted. Conformational analysis of an extensive set of per-O-substituted p-cyclodextrins reveals that several show conformational isomerism. The relevance of this to the use of cyclodextrins in molecular device design is examined. Related work undertook n.m.r. and molecular modeling studies on a-cyclodextrin in vriiich one of the units is in the 3,6-anhydro from. The work included the examination of two model disaccharide imits. ... 

Monoazide a- and p-cyclodextrins 77a-b were easily obtained from the corresponding monohydroxy cyclodextrins 63a-b. When submitted to DIBAL-H, the azide is reduced first. Aluminum derivatives complexed on the formed amide create steric hindrance, which directs the following de-O-benzylation toward the farthest position [74] (Scheme 9.36) as in the case of monohydroxy cyclodextrin 63a (Scheme 9.30 and Scheme 9.31). For a-cyclodextrin, the farthest position is 6D, which leads to the 6A-amino,6D-hydroxyl regioisomer 78a in 74% yield. For P-cyclodextrin, a molecular model study revealed that the farthest position is 6E, leading to the formation of the 6A-amino,6E-hydroxyl regioisomer 78b in 89% yield. It has to be noted that this pattern of differentiation is the same as for 6A-hydroxyl,6D-azido cyclodextrins 43a-b (Scheme 9.18). 

Four of the molecular mechanics studies of the inclusion compounds of cyclodextrins discussed in this section present, as necessary preliminary work, detailed pictures of calculated structures for cyclodextrins without guest molecules [6,11-13]. The resulting structures often show a high degree of (sometimes imposed) symmetry, and compare well with published X-ray structures of cyclodextrins (Figure 3). 

NMR and Molecular Modelling Studies on the Interaction of Fluconazole with p-Cyclodextrin... 

Dodziuk H, Ejchart A, Lukin O, Vysotsky MO. H and C NMR and molecular dynamics study of chiral recognition of camphor enantiomers by a-cyclodextrin. J. Org. Chem. 1999 64 1502 1507. 

Quantum Mechanics and Molecular Mechanics Studies of Host-Guest Stabilization and Reactivity in Cyclodextrin Nanocavities... 

The problem of molecular recognition has attracted biologically oriented chemists since Emil Fischer s lock-and-key theory l0). Within the last two decades, many model compounds have been developed micelle-forming detergents11, modified cyclodextrins 12), many kinds of crown-type compounds13) including podands, coronands, cryptands, and spherands. Very extensive studies using these compounds have, however, not been made from a point of view of whether or not shape similarity affects the discrimination. 

A prehminary study of the use of larch AGs in aqueous two-phase systems [394] revealed that this polysaccharide provides a low-cost alternative to fractionated dextrans for use in aqueous two-phase, two-polymer systems with polyethylene glycol (PEG). The narrow molecular-weight distribution (Mw/Mn of 1-2) and low viscosity at high concentration of AG can be exploited for reproducible separations of proteins under a variety of conditions. The AG/PEG systems were used with success for batch extractive bioconversions of cornstarch to cyclodextrin and glucose. 

Cyclodextrins can solubilize hydrophobic molecules in aqueous media through complex formation (5-8). A nonpolar species prefers the protective environment of the CDx cavity to the hulk aqueous solvent. In addition, cyclodextrins create a degree of structural rigidity and molecular organization for the included species. As a result of these characteristics, these macrocycles are used in studies of fluorescence and phosphorescence enhancement (9-11), stereoselective catalysis (.12,13), and reverse-phase chromatographic separations of structurally similar molecules (14,15). These same complexing abilities make cyclodextrins useful in solvent extraction. 

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