Alpha-cyclodextrin

The nonylphenyl-polyethyleneoxide nonionic tensides (Hoechst FRG) contain 5, 9 and 30 ethyleneoxide groups per molecule on average (abbreviated to T5, T9 and T30 respectively). The cyclodextrins alpha-(aCD), beta-(/JCD) and gamma-cyclo-dextrin (yCD) are produced by Chinoin (Hungary). Oipalmitoyl-phosphatidyl-choline (DPPC) was used as purchased from the Sigma Chemical Co. 

Cyclodextrins (Alpha, Beta, and Gamma). Most of the earlier chiral phases have limited thermal stability. By chemically bonding a chiral stationary phase to a polysiloxane, the upper temperature limit can be extended. Chirasil-Val is perhaps the most famous stationary phase in this category. However, recent work has employed cyclodextrins as the key chiral recognition component in stationary... 

Cyclodextrins (alpha, beta, and gamma) were shown to be potential stabilizers for O/W/O emulsions (Yu et al., 1999,2003). The advantages of the cyclodextrins are their ability to complex with certain oil components at the oil/water interface, resulting in no need for additional surfactant. It appears that the stabilizer efficacy depends on the nature of the oil and the type of the cyclodextrin (alpha > beta > gamma). The presence of any active matter in the inner phase (e.g., benzophenone) destabilized the emulsion. The reason is the interfacial interaction between the components present at the interface allows a possible competition between the lipophilic entrapped molecules and the oil fatty acid residues to enter the cyclodextrin cavity. These formulations prepared with a-cyclodextrin may serve to entrap high-molecular weight-active molecules, since they are not able to enter the small cavity of the a-cyclodextrin molecules and thus cannot destabilize the interface. 

Inclusion compounds of the Cg aromatic compounds with tris((9-phenylenedioxy)cyclotriphosphazene have been used to separate the individual isomers (43—47). The Schardinger dextrins, such as alpha-cyclodextrin, beta-dextrin, and gamma-dextrin are used for clathration alpha-dextrin is particularly useful for recovering PX from a Cg aromatic mixture (48,49). PyromeUitic dianhydride (50) and beryllium oxybenzoate (51) also form complexes, and procedures for separations were developed. 

Monflier et al. (1997) have suggested Pd catalysed hydrocarboxylation of higher alpha olefins in which chemically modified P-cyclodextrin (especially dimethyl P-cyclodextrin) is u.sed in water in preference to a co-solvent like methanol, acetone, acetic acid, acetonitrile, etc. Here, quantitative recycling of the aqueous phase is possible due to easy phase separation without emulsions. A similar strategy has been adopted by Monflier et al. (1998) for biphasic hydrogenations for water-in.soluble aldehydes like undecenal using a water-soluble Ru/triphenylphosphine trisulphonate complex with a. suitably modified p-cyclodextrin. 

Panja S, Chakravorti S (2002) Photophysics of 4-(N, N-dimethylamino)cinnamaldehyde/ alpha-cyclodextrin inclusion complex. Spectrochim Acta A Mol Biomol Spectrosc 58(1) 113-122... 

A. Kitajima, T. Teranishi, and M. Miyake, Detection of nitric oxide on carbon electrode modified with ionic polymers and alpha-cyclodextrin. Electrochemistry 69, 16-20 (2001). 

Convergence properties of free energy calculations Alpha-cyclodextrin complexes as a case study. J. Am. Chem. Soc. 116 6293 (1994). 

Arima, H., F. Kihara, F. Hirayama, and K. Uekama. 2001. Enhancement of gene expression by polyamidoamine dendrimer conjugates with alpha-, beta-, and gamma-cyclodextrins. Bioconjug Chem 12(4) 476-84. 

Zhu, X., Lin, B., Jakob, A., Wuerthner, S., Koppenhoefer, B. Separation of drugs by capillary electrophoresis, part 10. Permethyl-alpha-cyclodextrin as chiral solvating agent. Electrophoresis 1999, 20,1878-1889. 

Since the time of Schardinger, one of the most important reasons for studying the cyclodextrins was for the information they might yield on the structure of starch and of the well known blue iodine-starch complex. In fact, the similarity between the iodine-starch reaction and the iodine-alpha cyclodextrin reaction was first noted by Schardinger in 1911, in his final paper on the cyclodextrins. 

G1c -6 + alpha cyclodextrin G1c -7 + beta cyclodextrin G1c -8 + gamma cyclodextrin... 

The first direct evidence for molecular inclusion came from X-ray crystallography. Hybl and coworkers determined the structure of the alpha cyclodextrin-potassium acetate complex by using three-dimensional X-ray diffraction data. They found that, in the solid state, the acetate anions are included by the alpha cyclodextrin. In the process, they also found that every D-glucosyl residue of the alpha cyclodextrin is in the C conformation. 

Yamamoto and coworkers used two-dimensional, nuclear Over-hauser effect experiments (NOESY) to determine the proximity of particular protons situated on an included p-nitrophenolate ion to particular protons of a host alpha cyclodextrin molecule. The experiments showed cross-peaks connecting the H-3 resonance of alpha cyclodextrin to both meta and ortho proton resonances of the p-nitrophenolate ion, whereas H-5 of the alpha cyclodextrin gave a cross-peak only with the resonance of the meta proton thereof. As a consequence, it was unequivocally confirmed that the p-nitrophenolate ion is, in solution, preferentially included with its nitro group oriented to the narrow end of the alpha cyclodextrin... 

Values of AH° and AS° for complex-formation between alpha and beta cyclodextrin and a variety of guest molecules are shown in Tables II and III. If AH° is plotted against AS°, a linear relationship is observed, in which AH° and AS° are compensating (see Figs. 4 and 5). The slope of the graph is called the compensation temperature or isoequilibrium... 

Fig. 4.—Enthalpy-Entropy Compensation for Alpha Cyclodextrin Inclusion-Complexes. [The guest identification numbers are as given in Table II.]...

The results just discussed suggest that it is only alpha cyclodextrin that shows a conformational change on complex-formation, due to the rotation of one of its D-glucosyl units. Whether this conformational change contributes to the stability of the complex, as proposed by Saenger, is, however, debatable. Bergeron and Meeley " showed that methylation of the... 

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