Cyclodextrins thermodynamic parameters

Table 1. Thermodynamic parameters for the association of cyclodextrin with alcohol in an aqueous solution at 25 °C...

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... 

Table 2 Thermodynamic parameters for the /1-cyclodextrin-catalysed decarboxylation of the 4-chlorophenylcyanoacetate anion."...

The most important property of cyclodextrins is in their ability to accommodate guest molecules within their cavity, which has a volume of 262 per molecule or 157 mL per mol of [3-CD (cavity diameter 6.0-6.5 A). In aqueous solution, this cavity is filled with molecules of water the displacement of which by a less polar guest leads to an overall decrease in free energy. Stability constants and thermodynamic parameters for complexation of a vast number of guest molecules can be found in ref. [3]. 

Part II starts with the possibilities of ACE for characterizing the relevant physicochemical properties of drugs such as lipophilicity/hydrophilicity as well as thermodynamic parameters such as enthalpy of solubilization. This part also characterizes interactions between pharmaceutical excipients such as amphiphilic substances (below CMC) and cyclodextrins, which are of interest for influencing the bioavailability of drugs from pharmaceutical formulations. The same holds for interactions of drugs with pharmaceutical vehicle systems such as micelles, microemulsions, and liposomes. 

SG Penn, ET Bergstrom, DM Goodall, JS Loran. Capillary electrophoresis with chiral selectors. Optimization of separation and determination of thermodynamic parameters for binding of ticonazole enantiomers to cyclodextrins. Anal Chem 66 2866-2873, 1994. 

Mourtzis, N. Cordoyiannis, G. Nounesis, G. and Yannakopoulou, K. (2003) Single and Double Threading of Congo Red into y-Cyclodextrin. Solution Structures and Thermodynamic Parameters of 1 1 and 2 2 Adducts, as Obtained from NMR Spectroscopy and Microcalorimetry, Supramol. Chem. 15, 639-649. 

A similar complexation study supported by thermodynamic parameters was performed by the same author for mono-(6-anilino-6-deoxy)- 3-cyclodextrin and mono-[ 6-( 1 -pyridinio)-6-deoxy]-P-cyclodextrin complexation with several amino acids in zwitterionic form [24]. The inclusion complexation was enthalpy driven for the former and entropy driven for the latter host. 

Determination of Thermodynamic Parameters for Stoichiometric 1 1 Complexation by Cyclodextrin... 

Table 1 Thermodynamic parameters for the complexation by cyclodextrins and transfer from watei to hydrocarbon media of heptane cyclohexane, and benzene at 298 K...

THERMODYNAMIC PARAMETERS FOR THE MOLECULAR INCLUSION REACTIONS OF SOME AZO COMPOUNDS WITH a-CYCLODEXTRIN... 

The association constants (K and K ) and the thermodynamic parameters (AH and AS) for the inclusion reactions with a-cyclodextrin (a-CD ) have been determined for various systems. However the kinetic studies " on the inclusion reactionsare relatively few as compared with the equilibrium studies. This is because the signal amplitude accompanying the inclusion process is very small. Therefore, the mechanism for the inclusion process by a-cyclodextrin and the transition state in the course of the inclusion process are not clear even now. 

Table 2. Thermodynamic Parameters for the Inclusion Reactions by a-Cyclodextrin... 

R. Chadha, P. Arora, S. Bhandari, and D. V.S. Jain, Effect of hydrophilic polymer on com-plexing efficiency of cyclodextrins towards efavirenz-characterization and thermodynamic parameters, 7. Incl. Phenom. Macrocycl. Chem., 72,275-287,2012. 

The keto-enol equilibrium constant of benzoylacetone in water is perturbed in the presence of -cyclodextrin, from a value of 0.62 to 5, and also in sodium dodec-yl sulfate micelles, in both cases by preferential binding of the enol tautomer. Thermodynamic parameters from temperature studies of the equilibrium give more information about the structures of the complexes for example, the enol penetrates further into the cavity of the cyclodextrin, as confirmed by H NMR spectroscopy. Nitrosation of benzoylacetone is slowed in the presence of the cyclodextrin, consistent with a protective effect arising from the strong binding to the enol. 

Sadlej-Sosnowska, N., Thermodynamic parameters of the formation of complexes between cyclodextrins and steroid hormones, J. Chromatogr., 728 89, 1996. 

The applications of quantitative structure-reactivity analysis to cyclodextrin com-plexation and cyclodextrin catalysis, mostly from our laboratories, as well as the experimental and theoretical backgrounds of these approaches, are reviewed. These approaches enable us to separate several intermolecular interactions, acting simultaneously, from one another in terms of physicochemical parameters, to evaluate the extent to which each interaction contributes, and to predict thermodynamic stabilities and/or kinetic rate constants experimentally undetermined. Conclusions obtained are mostly consistent with those deduced from experimental measurements. 

Water plays a crucial role in the inclusion process. Although cyclodextrin does form inclusion complexes in such nonaqueous solvents as dimethyl sulfoxide, the binding is very weak compared with that in water 13 Recently, it has been shown that the thermodynamic stabilities of some inclusion complexes in aqueous solutions decrease markedly with the addition of dimethyl sulfoxide to the solutions 14,15>. Kinetic parameters determined for inclusion reactions also revealed that the rate-determining step of the reactions is the breakdown of the water structure around a substrate molecule and/or within the cyclodextrin cavity 16,17). 

The transport protein which we have just described complexes an entire family of maltodextrins. The thermodynamic and kinetic parameters are shown in Table 14.1. It is remarkable that there are so few variations from maltose to cyclodextrins. The first three complexes in the table were obtained in the crystalline state. 

ABSTRACT. Molecular inclusion reactions of some azocompounds with a-cyclodextrin were studied in aqueous solution by means of a stopped-flow method. The forward rate constants for the inclusion reactions were found to be in the order of 10-10 mol dm s . The thermodynamic activation parameters were also determined firstly in a-cyclodextrin system. 

Also, from the measurements of diffusion coefficients of the ternary systems already studied (e.g., y -cyclodextrin plus caffeine [15], 2-hydroxypropyl-p-cyclodextrin plus caffeine [16], CuCl (1) plus caffeine [10], and KCl plus theophylline (THP) [18]), it is possible to give a contribution to the understanding of the stmcture of electrolyte solutions and their thermodynamic behavior. For example, by using Equations (22) and (23), and through the experimental tracer ternary diffusion coefficients of KCl dissolved in supporting THP solutions, D (c/c = 0) and tracer ternary diffusion coefficients of THP dissolved in supporting KCl solutions, D°2 (c /Cj = 0) [18], it will be possible to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP [18] and the respective association constant. 

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