Binding of dimethyl 2,3-naphthalenedicarboxylate with alpha-, beta- and gamma-cyclodextrins in aqueous solution

Influence of the macroring size on the self-association thermodynamics of cyclodextrins with a double-linked naphthalene at the secondary face

The conformational properties and aggregation behavior of two selectively modified cyclomaltooligosaccharides (cyclodextrins, CDs) containing a double-linked 1,8-dimethylnaphthalene cap-like moiety at the secondary face, namely, 2(I),3(I)-O-(1,8-dimetylnaphthalene-α,α'-diyl)-per-O-Me-α- and -γ-cyclodextrins (NmαCD and NmγCD, respectively), in water and in organic solvents were investigated. Both CD derivatives self-associated in water to form dimer species, but the characteristics of the dimerization process and of the resulting dimer strongly depended on the size of the macrocycle. Dimerization constants, thermodynamic parameters upon association, and information about the preferred conformations of the monomer and dimer CD structures were obtained by using NMR, UV-vis, steady-state and time-resolved fluorescence, and circular dichroism experimental techniques, as well as molecular mechanics (MM) and molecular dynamics (MD) simulations. The complexation of 1,8-di(methoxymethyl)naphathalene (oNy) and the heteroassociation of both NmCDs with their permethylated CD partners (mCDs), lacking the aromatic cap, were examined. In addition, the influence of the size of the chromophore moiety on the thermodynamics of self-association was also assessed by comparison of the results obtained for the new naphthalene derivatives with those of the 2(I),3(I)-O-(1,2-xylylene)-modified CD analogues (XmCDs).

Fluorimetric investigation of supramolecular system by modified β-cyclodextrin and its analytical application

The supramolecular interaction of MAH-β-cyclodextrin (MAH-β-CD, a modified β-cyclodextrin carrying seven vinyl carboxylic acid groups) and meferamic acid (MF) has been studied by spectrofluorimetry. The results showed that MAH-β-CD reacted with MF to form a host-guest complex (MAH-β-CD-MF) with stoichiometry (1:1) and the inclusion constant (K=7.15×10(2) L/mol) was ascertained by the typical double reciprocal plots. From the phase-solubility diagram, an increase in the water solubility of the drug was observed and the apparent stability constant (K(1:1)) was calculated to be 8.62×10(2) L/mol. Furthermore, the thermodynamic parameters (ΔG°, ΔH° and ΔS°) of MAH-β-CD-MF were obtained and the inclusion mechanism was also preliminarily discussed. In order to further confirm the experimental results, investigation on the molecular modeling was performed. On the basis of the significant enhancement of the fluorescence intensity of MF, a spectrofluorimetric method for MF determination in bulk aqueous solution in the presence of MAH-β-CD was developed. The linear range was 2.00×10(-8)-9.00×10(-5) mol/L and the detection limit was 3.36×10(-9) mol/L. The proposed method was successfully applied to determine MF in tablets, serum and urine with the satisfactory result.

Thermodynamics of the dimer formation of 2(I),3(I)-O-(o-xylylene)-per-O-Me-gamma-cyclodextrin: fluorescence, molecular mechanics and molecular dynamics

The thermodynamics of the dimer formation of 2(I),3(I)-O-(o-xylylene)-per-O-Me-gamma-cyclodextrin (XmgammaCD) in aqueous solution was studied by fluorescence techniques, Molecular Mechanics and Molecular Dynamics. Lifetime averages <tau>, obtained from fluorescence decay profiles upon excitation of the xylylene appended group, were used as the property sensitive to the association process. The dimerization equilibrium constants (K(D)) were obtained from non-linear regression analysis of the plots of <tau> against [XmgammaCD] at several temperatures and they were compared with the values obtained for the counterparts Xmalpha- and XmbetaCDs. The van't Hoff plot allows us to obtain the DeltaH and DeltaS showing that the dimerization process was also entropically disfavoured. Molecular Mechanics as well as Molecular Dynamics calculations in the presence of water were also employed to study the conformational behaviour of isolated XmgammaCDs, the possible structure of the dimers formed and the driving forces involved in such association processes. Results indicate that those conformations where Xy moiety does not block the cavity entrance are favoured. Dimers are preferably formed by head-to-head CD approaching. However, the formation of stable head-to-tail is not dismissed.

Complexation of morin with three kinds of cyclodextrin. A thermodynamic and reactivity study

Properties of inclusion complexes between morin (M) and beta-cyclodextrin (betaCD), 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) and Heptakis (2,6-O-di methyl) beta-cyclodextrin (DMbetaCD) such as aqueous solubility and the association constants of this complex have been determined. The water solubility of morin was increased by inclusion with cyclodextrins. The phase-solubility diagrams drawn from UV spectral measurements are of the A(L)-type. Also ORAC(FL) studies were done. An increase in the antioxidant reactivity is observed when morin form inclusion complex with the three cyclodextrin studied. Finally, thermodynamics studies of cyclodextrin complexes indicated that for DMbetaCD the inclusion is primarily enthalpy-driven process meanwhile betaCD and HPbetaCD are entropy-driven processes. This is corroborated by the different inclusion geometries obtained by 2D-NMR.