Stabilization of the inclusion complex

The results were simple and clear-cut Only the two terms ofa° and Emin were involved for the a-cyclodextrin systems, and the two terms of k and Emin, for (S-cyclodextrin systems. This means that the stabilities of the inclusion complexes are mainly governed by the electronic and steric interactions in a-cyclodextrin systems and by the hydro-phobic and steric interactions in (i-cyclodextrin systems, regardless of the position of the substituents in the phenols. These observations agree well with those by Harata23), who showed that there is no appreciable difference in thermodynamic parameters between cyclodextrin complexes of m- and p-di substituted benzenes and that the contribution of the enthalpy term to the complexation is more significant in a-cyclodextrin systems than in P-cyclodextrin systems, where the inhibitory effect... 

Macrocyclic tetraammonium compounds VIII and IX 611 form stable 1 1 inclusion complexes with anionic molecules in aqueous solutions 62). The anions are halides, carbonate, phosphate, AMP, ATP etc. The stability of the inclusion complexes hepends on electrostatic as well as hydrophobic interactions. Whereas the complexes of VIII are dominated by the electfostatic component, the hydrophobic interaction plays the main part in complexes of IX. 

Values of /c2, the maximal rate constant for disappearance of penicillin at pH 10.24 and 31.5°, and Ka, the cycloheptaamylose-penicillin dissociation constant are presented in Table VII. Two features of these data are noteworthy. In the first place, there is no correlation between the magnitude of the cycloheptaamylose induced rate accelerations and the strength of binding specificity is again manifested in a rate process rather than in the stability of the inclusion complex. Second, the selectivity of cycloheptaamylose toward the various penicillins is somewhat less than the selectivity of the cycloamyloses toward phenyl esters—rate accelerations differ by no more than fivefold throughout the series. As noted by Tutt and Schwartz (1971), selectivity can be correlated with the distance of the reactive center from the nonpolar side chain. Whereas the carbonyl carbon of phenyl acetates is only two atoms removed from the phenyl ring, the reactive center... 

The reaction of cyclohexaamylose with a series of p-carboxyphenyl esters is an example of a decelerating effect which may be clearly attributed to nonproductive binding. Rate effects imposed by cyclohexaamylose on the hydrolyses of three such esters are summarized in Table IX. As the hydrophobicity of the ester function is increased by alkyl substitution, the hydrolysis is inhibited the stability of the inclusion complex, on the other... 

Although the techniques just considered have been widely used for the development of practical uses of the cyclodextrins, the underlying forces responsible for the stability of the inclusion complexes, as well as the mechanism of their formation, are at present not completely understood. 

Decene was hydrocarboxylated with a [PdClaj/TPPTS catalyst in acidic aqueous solutions (pH adjusted to 1.8) in the presence of various chemically modified cyclodextrins (Scheme 10.11) [18]. As in most cases, the best results were obtained with DiOMe-P-CD. In an interesting series of reactions 1-decene was hydrocarboxylated in 50 50 mixtures with other compounds. Although all additives decreased somewhat the rate of 1-decene hydroformylation, the order of this inhibitory effect was 1,3,5-trimethylbenzene < cumene < undecanoic acid, which corresponds to the order of the increasing stability of the inclusion complexes of additives with p-CD, at least for 1,3,5-trimethylbenzene (60 M ) and cumene (1200 M ). These results clearly show the possible effect of competition of the various components in the reaction mixture for the cyclodextrin. 

As the aforementioned results indicate, it is difficult to predict the molecular structure of a suitable host for Cl-MIT, so it is necessary to employ a degree of trial and error. However, it becomes easier to design the host molecule if the crystal structure and stability of the inclusion complex are predictable. 

Mielcarek, J. Photochemical stability of the inclusion complexes of nicardipine with a-, y-cyclodextrin, methyl-P-cyclodextrin, and hydroxypropyl-P-cyclodextrin in the solid state and in solution. Pharmazie 1996, 51 (7), 477-479. 

The CD s form stable inclusion complexes in aqueous solution with guests containing hydrophobic residues that fit well inside the host cavity [13]. The stability of the inclusion complex is the result of hydrophobic interactions and is usually enthalpically driven. Typically, the equilibrium association constant (K) between... 

Mielcarek, J. (1995) Inclusion complexes of nifedipine and other 1,4-dihydropyridine derivatives with cyclodextrins. The IR and XRD-ray diffraction study on photochemical stability of the inclusion complexes formed by nimodipine, nisoldipine and nitrendipine with fi-cyclodextrin, Acta Pol. Pharm. Drug Res., 52, 465 470. 

Yuan, C, ZY Jin, XM Xu, HN Zhuang and WY Shen (2008). Preparation and stability of the inclusion complex of astaxanthin with hydroxypropyl-/3-cyclodextrin. Food Chemistry, 109, 264-268. 

Harada et al [4 have compared the stability of the inclusion complexes of/S-cdx-epichlorohydrin (Ep), jS-cdx and -cdx-acrylate and discussed the inclusion capability of cdx on a polymer chain. 

The azo complexons, 3-IDA-5-R-HAB (Fig. 1), which have a coordinating iminodiacetate group, show the conformational change in the acid dissociation and the complexation with metal ions.3 The stability of the inclusion complexes of the azo complexons with a-cyclodextrin (oMX)j ) depends on the complementary geometry between the diameter of hydrophobic cavity of a-cyclodextrin and the shape and the size of guest molecule. ... 

Most industrial uses of cyclodextrins are based on their ability to form supramolecular inclusion complexes with diverse guests [4]. They are used as solubilizers or drug transporters for pharmaceutical applications [5], as stabilizers and taste protectors in food and cosmetic industries [6], and as static phase in chromatography [7] for the separation of chiral entities. The required properties of cyclodextrin derivatives vary depending on the desired application, such as enantioselectivity for the separation of enantiomers or stability of the inclusion complex for encapsulation of drugs. Native cyclodextrins rarely match perfectly to the application so their modification is necessary to fine-tune their properties. In that context, efficient and selective methodologies have to be developed to access new derivatives that could be adapted to the desired application. Cyclodextrins are a particular class of complex carbohydrate derivatives, as they are easily produced... 

Ohashi and coworkers [12] have reported that MMP2 [20] calculations on the interactions of cyanine dyes with P- and y-cyclodextrin correctly reproduced the relative stability of the inclusion complexes, as well as predicting that in most cases a dye dimer would be preferentially bound within the cavity of the cyclodextrin. Electrostatic interactions between the dye molecules and the cyclodextrin played an important role, in addition to the VDW interactions, in stabilizing the complex. Menger and Sherrod [6,21], enroute to an exploration of the interactions of ferrocenylacrylate esters with P-cyclodextrin, have reported the calculated host-guest complexes between ferrocene and a-, p-, and y- cyclodextrin which are consistent with X-ray structures and spectroscopic data Ferrocene was found to bind in an equatorial manner with y-cyclodextrin, in an axial manner with P-cyclodextrin, and the predicted structure for the 2 1 complex between a-cyclodextrin and ferrocene was found to be precisely correct when the X-ray structure of the complex was published over one year later by Harada [22]. 

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