Cyclo dextrin

Cyclo dextrin Molecular weight Solubihty in water, g/100 mL r 1 Diameter of cavity, nm Diameter of outer periphery, nm... 

Ozoe et al.76 have determined the Kd values for complexes of ot- and fl-cyclo-dextrin with a variety of 4-substituted bicyclic phosphates (4-substituted 2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane 1-oxides, 1), which are highly toxic convulsants. 

Upon formulating these relationships, phenols with branched alkyl substituents were not included in the data of a-cyclodextrin systems, though they were included in (3-cyclodextrin systems. In all the above equations, the n term was statistically significant at the 99.5 % level of confidence, indicating that the hydrophobic interaction plays a decisive role in the complexation of cyclodextrin with phenols. The Ibrnch term was statistically significant at the 99.5% level of confidence for (3-cyclo-dextrin complexes with m- and p-substituted phenols. The stability of the complexes increases with an increasing number of branches in substituents. This was ascribed to the attractive van der Waals interaction due to the close fitness of the branched substituents to the (3-cyclodextrin cavity. The steric effect of substituents was also observed for a-cyclodextrin complexes with p-substituted phenols (Eq. 22). In this case, the B parameter was used in place of Ibmch, since no phenol with a branched... 

Only the hydrophobic and steric terms were involved in these equations. There are a few differences between these equations and the corresponding equations for cyclo-dextrin-substituted phenol systems. However, it is not necessarily required that the mechanism for complexation between cyclodextrin and phenyl acetates be the same as that for cyclodextrin-phenol systems. The kinetically determined Kj values are concerned only with productive forms of inclusion complexes. The productive forms may be similar in structure to the tetrahedral intermediates of the reactions. To attain such geometry, the penetration of substituents of phenyl acetates into the cyclodextrin cavity must be shallow, compared with the cases of the corresponding phenol systems, so that the hydrogen bonding between the substituents of phenyl acetates and the C-6 hydroxyl groups of cyclodextrin may be impossible. 

Attempts to stabilize anthocyanins by complex inclusion with a- and P-cyclo-dextrins failed on the contrary, a discoloration of anthocyanin solutions was observed.Thermodynamic and kinetic investigations demonstrated that inclusion and copigmentation had opposite effects. In the anthocyanins, the cw-chalcone colorless structure is the best species adapted to inclusion into the P-dextrin cavity, shifting the equilibrium toward colorless forms. "... 

Figure 3.1 Simplified mechanism of an IPTC process mediated by cyclo-dextrins. 

The synthesis of [Ircp Cl(bpy-cd)]Cl, where bpy-cd is a /3-cyclo-dextrin attached at the 6 position to a bpy ligand, is detailed.138 The complexes [Ircp (diimine)X]+, X = C1, H, diimine = bpy, phen, are active catalysts for the light-driven water-gas-shift reaction.139 The hydride complexes luminesce at 77 K and room temperature, whereas the chloride complexes do not.140 The three-legged piano-stool arrangement of the ligands in [Ircp (bpy)Cl]+ and [Ircp (4,4 -COOFl-bpy)Cl]+ is confirmed by X-ray crystallography.141,142 Further mechanistic studies on the catalytic cycle shown in reaction Scheme 11 indicate that Cl- is substituted by CO and the rate-determining step involves loss of C02 and H+ to leave the Ir1 species, which readily binds Fl+ to yield the lrIH hydride species.143... 

I. Baussanne, J. M. Benito, C. Ortiz Mellet, J. M. Garcia Fernandez, and J. Defaye, Synthesis and comparative lectin-binding affinity of mannosyl-coated /i-cyclo-dextrin-dendrimer constructs, Chem. Commun. (2000) 1489-1490. 

Konig WA (1992) Gas chromatographic enantiomer separation with modified cyclo-dextrins. Hiithig, Heidelberg... 

Calculations based on simple molecular models and the charge density of the layers suggest that sulfopropylated-//-cyclodextrin and carboxyethylated-/3-cyclodextrin are arranged in the interlayer galleries with their conical axis parallel to the layers with a packing structure which is similar to that in crystalline cyclo dextrin complexes, where the molecules are arranged in a brickwork pattern [202]. 

While nature uses coenzyme-dependent enzymes to influence the inherent reactivity of the coenzyme, in principle, any chemical microenvironment could modulate the chemical properties of coenzymes to achieve novel functional properties. In some cases even simple changes in solvent, pH, and ionic strength can alter the coenzyme reactivity. Early attempts to present coenzymes with a more complex chemical environment focused on incorporating coenzymes into small molecule scaffolds or synthetic host molecules such as cyclophanes and cyclo-dextrins [1,2]. While some notable successes have been reported, these strategies have been less successful for constructing more complex coenzyme microenvironments and have suffered from difficulties in readily manipulating the structure of the coenzyme microenvironment. 

Another common theme that authors use to establish importance involves environmental impacts. For example, an environmental slant is used in the first sentence of the cyclodextrin article (P3, exercise 6.7), where the study of cyclo-dextrins is justified based on their role in soil remediation. The importance of work that benefits air or water quality and/or promotes green chemistry can also be stressed. Work is also viewed as important if it has cross-disciplinary applications. For example, in the Introduction section of the tetrazole article, the authors stress the importance of tetrazoles in coordination chemistry, medicinal chemistry, and in various materials science applications and point out their role as useful intermediates in the preparation of substituted tetrazoles ... 

K Otsuka, S Honda, J Kato, S Terabe, K Kimata, N Tanaka. Effects of compositions of dimethy 1-/3-cyclodextrins on enantiomer separations by cyclo-dextrin-modified capillary zone electrophoresis. J Pharm Biomed Anal 17 1177-1190, 1998. 

M Chiari, M Cretich, G Crini, L Janus, M Morcellet. AI ly I anune-/3-cyclo-dextrin copolymer. A novel chiral selector for capillary electrophoresis. J Chromatogr A 894 95-103, 2000. 

J Li, KC Waldron. Estimation of the pH-independent binding constants of alanylphenylalanine and leucylphenylalanine stereoisomers with /3-cyclo-dextrin in the presence of urea. Electrophoresis 20 171-179, 1999. 

YY Rawjee, G Vigh. A peak resolution model for the capillary electrophoretic separation of the enantiomers of weak acids with hydroxypropyl-beta-cyclo-dextrin-containing background electrolytes. Anal Chem 66 619-627, 1994. 

G Galavema, MC Paganuzzi, R Corradini, A Dossena, R Marcelli. Enantiomeric separation of hydroxy acids and carboxylic acids by diamino-/3-cyclo-dextrin (AB, AC, AD) in capillary electrophoresis. Electrophoresis 22 3171— 3177, 2001. 

At around the same time, Breslow and co-workers described bifunctional cyclo-dextrin-based catalysts that were capable of hydrolysis of a bound phosphate ester [88]. In later studies, an AD isomer (Scheme 4.9) of a P-cyclodextrin bisimidazole catalyst turned out to be the fastest catalyst for enolization of p-tert-butylacetophe-none (Scheme 4.9) [89]. Here, the extra binding is provided by the P-cyclodextrin... 

Neben optisch aktiven Basen bzw. Anunonium-Ionen vermogen nach Cramer und Dietsche (75, 76) auch EinschluBkatalysatoren die Cyan-hydrin-Bildung asymmetrisch zu lenken. In Gegenwart von a-Cyclo-dextrin wurden aus o- und p-Chlorbenzaldehyd und HCN schwach rechtsdrehende Cyanhydrine erhalten. 

Molecular cavities are of topical research interest because of their ability to enclose and bind guest molecules. They may serve as models for the study of binding sites between, e.g. drugs, odorant/taste substances, antigens, etc. and receptors. Cyclo-dextrins, as prime examples of host cavities, have found many useful applications. This is due to the guest molecules being bound within the cavity which changes properties such as solubility, volatility and reactivity. 

Capillary gas chromatography (GC) using modified cyclodextrins as chiral stationary phases is the preferred method for the separation of volatile enantiomers. Fused-silica capillary columns coated with several alkyl or aryl a-cyclo-dextrin, -cyclodextrin and y-cyclodextrin derivatives are suitable to separate most of the volatile chiral compounds. Multidimensional GC (MDGC)-mass spectrometry (MS) allows the separation of essential oil components on an achiral normal phase column and through heart-cutting techniques, the separated components are led to a chiral column for enantiomeric separation. The mass detector ensures the correct identification of the separated components [73]. Preparative chiral GC is suitable for the isolation of enantiomers [5, 73]. 

A real breakthrough in this field occurred when enantio-cGC became more and more available. In particular, since 1988 selectively modified cyclodextrins have been synthesised, serving as chiral stationary phases in enantio-cGC, reported by Schurig and Novotny [I], Konig et al. [2, 3], Armstrong et al. [4], Dietrich et al. [5,6 ], Saturin et al. [7], and Bicchi et al. [8]. 6-O-silylated modified /I-cyclo dextrin and y-cyclodextrin derivatives of well-defined structure and purity were synthesised and have proved to be chiral stationary phases of unique selectivity and versatility and, therefore, are successfully used in simultaneous enantio-cGC analysis [5,6]. Further derivatives were recently reported by Taka-hisa and Engel [9, 10], dealing with 2,3-di-0-methoxymethyl-6-0-tert-butyldi-methylsilyl modified cyclodextrins as chiral stationary phases in enantio-cGG. 

Takahisa E, Engel K-H (2005) 2,3-Di-0-methoxymethyl-6-0-tert-butyldimethysilyl-)6-cyclo-dextrin, a useful stationary phase for gas chromatographic separation of enantiomers. J Chromatogr A 1076 148... 

Cyclo- dextrin Guest Chemical composition" Space group Ref. 

The guest molecules having a benzene ring are included by a-cyclo-dextrin at the very similar position (depth) of the cavity, independent of the different inclusion mode for para- and meta-substituted benzene, e.g., as seen in Fig. 6. 

Fig. 4. Schematic representation of water molecules in cyclodextrin cavities (a) a-cyclo-dextrin (Form I) (b) /i-cyclodextrin.

Another beautiful example of multiple recognition by the use of multi-functionalized cyclodextrin is symmetrical triamino-O-permethyl-a-cyclo-dextrin (16), which is designed for the specific recognition for the phosphate group (Fig. 23) (55). As is expected, 16 shows a higher affinity toward benzyl phosphate (Kass = 3.2 x 104) than does the corresponding monoammonium derivative (Kaas = 3.3 x 101). 

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