In vitro and in vivo inhibition of Hass avocado polyphenol oxidase enzymatic browning by paeonol, ß-cyclodextrin, and paeonol:ß-cyclodextrin inclusion complex.

Polyphenol oxidase (PPO) was extracted from Hass avocados and its physicochemical properties were analyzed. The optimum pH and temperature of the enzyme were pH 7.5 and 20°C. This PPO showed a high thermal stability, since 26% of the initial activity was retained by the enzyme after heating at 60°C for 40 min. Inhibition studies were performed using different chemical reagents, and the order in the inhibition efficiency was paeonol > 4-hydroxybenzaldehyde > ß-cyclodextrin (ß-CD). The first two inhibitors presented a non-competitive mechanism while the inhibition by ß-CD results from a mixed type mechanism. Since the aqueous solubility of paeonol (a natural compound) is very low, the inclusion complex between this drug and ß-CD was obtained in solution and solid state. The stoichiometry of the paeonol:ß-CD complex was 1:1 and its ΔG° of formation was -26 kJ/mol. The complexation of paeonol by ß-CD not only enhances the aqueous solubility and thermal stability of the drug, but also improves the in vitro inhibition efficiency against PPO. Colorimetric analysis on avocados pulp (in vivo) showed that the inclusion complex does not increase the inhibitory effect of paeonol, remaining practically unchanged. However, the formulation of paeonol:ß-CD inclusion complex allows employing this compound as PPO inhibitor in aqueous solutions.

Physicochemical characterization of 2-hydroxybenzophenone with ß-cyclodextrin in solution and solid state.

The characterization of the inclusion complex between 2-hydroxybenzophenone (2OHBP) and ß-cyclodextrin (ßCD) in the solid state was performed using Fourier transform infrared spectroscopy (FTIR), powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The apparent formation constant of the complex was determined by phase solubility diagrams and liquid chromatography (HPLC) at different temperatures. The formation of the inclusion complex induced slight shifts in the FTIR spectrum while by PXRD a new crystalline phase was observed. TEM studies revealed that the complex forms aggregates of nanometric size. The inclusion complex showed a higher solubility in the tested dissolution media than free 2OHBP. Moreover, the freeze-dried solid complex exhibits a higher thermal stability than the solid free drug. The thermodynamic analysis allowed us to conclude that the encapsulation process is endothermic in water and exothermic in methanol-water.

Inclusion complex of 2-chlorobenzophenone with cyclomaltoheptaose (ß-cyclodextrin): temperature, solvent effects and molecular modeling.

A thermodynamic study of the inclusion process between 2-chlorobenzophenone (2ClBP) and cyclomaltoheptaose (ß-cyclodextrin, ß-CD) was performed using UV-vis spectroscopy, reversed-phase liquid chromatography (RP-HPLC), and molecular modeling (PM6). Spectrophotometric measurements in aqueous solutions were performed at different temperatures. The stoichiometry of the complex is 1:1 and its apparent formation constant (K(c)) is 3846M(-1) at 30°C. Temperature dependence of K(c) values revealed that both enthalpy (ΔH°=-10.58kJ/mol) and entropy changes (ΔS°=33.76J/Kmol) are favorable for the inclusion process in an aqueous medium. Encapsulation was also investigated using RP-HPLC (C18 column) with different mobile-phase compositions, to which ß-CD was added. The apparent formation constants in MeOH-H(2)O (K(F)) were dependent of the proportion of the mobile phase employed (50:50, 55:45, 60:40 and 65:35, v/v). The K(F) values were 419M(-1) (50% MeOH) and 166M(-1) (65% MeOH) at 30°C. The thermodynamic parameters of the complex in an aqueous MeOH medium indicated that this process is largely driven by enthalpy change (ΔH°=-27.25kJ/mol and ΔS°=-45.12J/Kmol). The results of the study carried out with the PM6 semiempirical method showed that the energetically most favorable structure for the formation of the complex is the 'head up' orientation.

Encapsulation of methyl and ethyl salicylates by beta-cyclodextrin HPLC, UV-vis and molecular modeling studies.

The complexation of methyl salicylate (MS) and ethyl salicylate (ES), non-steroidal analgesic, anti-inflammatory and antirrheumatic drugs with beta-cyclodextrin (betaCD) has been studied from thermodynamic and structural points of view. The complexation with betaCD has been investigated using reversed-phase liquid chromatography. Retention behavior has been analyzed on a reverse-phase column Luna 18(2) 5 microm. The mobile-phase was methanol:water in different ratios (55:45 to 70:30) in which betaCD (1-9 mM) was incorporated as a mobile-phase additive. The decrease in retention times with increasing concentrations of betaCD enables the determination of the apparent stability constant of the complexes. Values at 30 degrees C with 55% methanol were K(MS:betaCD): 15.84 M(-1) and K(ES:betaCD): 12.73 M(-1) for MS and ES, respectively. The apparent stability constants decrease as the polarity of the solvent decreases. The low solubility of MS and ES in aqueous solution has been improved by complexation with betaCD (1-9 mM). The stability constants of the complexes obtained from the phase-solubility diagrams using a UV-vis spectrophotometric method were K(MS:betaCD): 229 M(-1) and K(ES:betaCD): 166 M(-1). In addition, semi-empirical quantum mechanics calculations using AM1 and PM3 methods in vacuum were performed. The energetically favorable inclusion structures were identified and the most favorable orientation for the inclusion process was found to be the head-down orientation for both complexes. Enthalpy for encapsulation processes was found to be favorable (DeltaH degrees <0), while entropy (DeltaS degrees <0) and Gibbs free energy were unfavorable (DeltaG degrees >0). By means of HPLC and UV-vis measurements and quantum mechanics calculations, it was found that MS and ES form a 1:1 inclusion complex with betaCD. The theoretical results are in agreement with the experimental parameters associated with the encapsulation process.