•The solubility data allow us to obtain the information on the interactions that occur in the process of solvation.•For the seven pure n-alcohols analyzed, as the amount of carbon atoms increases, ...the Ibu's solubility decreases.•The analysis of solution processes in binary aqueous systems shows a non-ideal behavior and an influence of solvent–solvent interactions.•The process of solution in water and in water-rich cosolvent mixtures studied is driven by the entropic term.
The solubility of Ibu in fifteen pure solvents and in eight aqueous–organic cosolvent mixtures was determined. The results obtained indicate that Hildebrand's solubility parameter of pure solvent, which accounts for the cohesive forces of the solvent, has a greater influence on the solubility of Ibu. In all the cosolvent mixtures analyzed, the solute was preferentially solvated by the organic cosolvent. For aqueous binary mixtures formed by ethanol, ethylene glycol and propylene glycol, the enthalpy, entropic and Gibbs free energy changes involved with the solvation process were determined. In the three systems analyzed, it can be seen that the energy of formation of the cavity decreases as the polarity of the solvent decreases by increasing the amount of organic cosolvent, which, in this case, favors solute–solvent interactions. However, it was noted that there is a significant interaction between water and the organic cosolvent, which has a marked influence on the solvation process.
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 > β-cyclodextrin (β-CD). The first two inhibitors presented a non-competitive mechanism while the inhibition by β-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 β-CD was obtained in solution and solid state. The stoichiometry of the paeonol:β-CD complex was 1:1 and its ΔG° of formation was −26 kJ/mol. The complexation of paeonol by β-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:β-CD inclusion complex allows employing this compound as PPO inhibitor in aqueous solutions.
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The solubilization and solvatochromic behavior of piroxicam (PRX) were analyzed using UV-vis spectroscopy in neat (protic and aprotic) and binary solvent mixtures. The effects of solvent ...dipolarity/polarizability and solvent–solute hydrogen bonding interactions on the absorption maxima were evaluated by means of the linear solvation energy relationship concept of Kamlet and Taft. This analysis indicated that both interactions play an important role in the position of the absorption maxima in neat solvents. While, the PRX solubility depends on the solute–solvent specific interactions, polarizability and the cohesive forces of the solvent, manifested mainly by means of the Hildebrand’s solubility parameter. Preferential solvation (PS) was studied in 10 binary mixtures. A non-ideal behavior of the wavenumber curve as the function of analytical mole fraction of co-solvent was detected. Index of preferential solvation, as well as the influence of solvent parameters were calculated. The process of dissolution was analyzed in aqueous binary mixtures of ethanol, ethylene glycol and propylene glycol. They were not spontaneous in all proportions, but when water concentration decreases in the mixtures, the process becomes more spontaneous.
Polyphenoloxidase was extracted from September peach (∧SEPPO) and Summerset peach (∧SUPPO) and its physicochemical characteristics were analyzed. The optimum pH was 6.5 for ∧SEPPO and 5.5 for ∧SUPPO. ...The optimum temperature was 35℃ for ∧SEPPO and 39.4℃ for ∧SUPPO. Activation energy (Ea) from thermal activation was 41.5 kJ/mol for ∧SEPPO and 37.5 kJ/mol for ∧SUPPO. Heating at 60℃ by 5 min, ∧SUPPO was denatured whereas ∧SEPPO retained 2.6% of activity. Activation enthalpy (ΔH∨No.) and activation entropy (ΔS∨No.) for ∧SEPPO heat-inactivation were 69.9 J/mol and -83.5 kJ/molㆍK for SUPPO, Delta H∨No. was 91.8 J/mol while ΔS∨No. was -21.0 kJ/molㆍK. Substrate specificity (V∧max/K∧M) was 4-methylcatechol greater than catechol greater than pyrogallol for ∧SEPPO and 4-mehtylcatechol greater than pyrogallol greater than catechol for ∧SUPPO. For both enzymes, the order of inhibition effectiveness using reductor agents was metabisulphite greater than ascorbic acid. Benzaldehyde, 4-hydroxybenzaldehyde, and DL-dopa were competitive inhibitors, and their K∧I values were 38.86, 8.43, and 2.08 mM, respectively.
The experimental solubility of Nap in fifteen pure solvents and in eight aqueous–organic cosolvent mixtures was determined. The results obtained indicate that the π⁎ parameter which describes the ...polarity/polarizability of the solvent, and the Hildebrand's solubility parameter, which accounts for the cohesive forces of the solvent, have a greater influence on the solubility of Nap. This drug has a lower solubility (T=300.0±0.3K) in water (3.02 10−4M) and a greater solubility in DMS (1.56M) and DMF (1.48M). In all the cosolvent mixtures analyzed, the solute was preferentially solvated by the organic cosolvent. For the aqueous binary mixtures formed by ethanol, ethylene glycol and propylene glycol, the apparent enthalpy, entropic and Gibbs free energy changes involved with the solvation process were determined. In the three systems analyzed, it can be seen that the process is always entropically favorable and endothermic or unfavorable; hence, solute–solute and/or solvent–solvent interactions predominate. The solution process is driven by the enthalpy term. The contributions of enthalpy and therefore entropy do not change when modifying the composition of the mixture of cosolvents.
•The solubility data allows us to obtain good information on the interactions.•The polarity/polarizability of the solvent have influence on the solubility of Nap.•In all the mixtures, the solute was preferentially solvated by the organic cosolvent.
The characterization of the inclusion complex between 2-hydroxybenzophenone (2OHBP) and β-cyclodextrin (βCD) 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.
The stoichiometry and apparent stability constants (β) of the complexes formed between Ni2+ and four different hydroxyflavones (3-hydroxyflavone, 5-hydroxyflavone, chrysin, and galangin) were ...determined in methanolic solutions. A multivariate curve resolution methodology was applied to estimate the β values using UV–vis spectroscopic data. All the complexes exhibit 1:2 metal:ligand stoichiometry. The highest and lowest β values were obtained for the galangin and 5-hydroxyflavone complexes, respectively. The formation of the complexes was confirmed by Fourier transform infrared spectroscopy. Time-dependent density functional theory and natural transition orbital analysis were performed to describe the spectroscopic features of the studied compounds, and quantum theory of atoms in molecules was applied to evaluate different intermolecular interactions. Good correlations were obtained between the calculated UV–vis absorption spectra using the M06 functional and the experimental ones. The main absorption band of these Ni2+ complexes have an important metal-to-ligand charge transfer mixed with an intraligand charge transfer (ILCT). Two possible chelation sites were considered for the interaction of Ni2+ with galangin. The combination of spectroscopic and quantum chemistry calculations results indicate the existence of an equilibrium between the two carbonyl-hydroxyl sites of galangin in the Ni2+ complex formation.
A thermodynamic study of the inclusion process between 2-chlorobenzophenone (2ClBP) and cyclomaltoheptaose (β-cyclodextrin, β-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 (Kc) is 3846M−1 at 30°C. Temperature dependence of Kc 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 β-CD was added. The apparent formation constants in MeOH–H2O (KF) were dependent of the proportion of the mobile phase employed (50:50, 55:45, 60:40 and 65:35, v/v). The KF 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.
Polyphenoloxidase was extracted from September peach ($_{SE}PPO$) and Summerset peach ($_{SU}PPO$) and its physicochemical characteristics were analyzed. The optimum pH was 6.5 for $_{SE}PPO$ and 5.5 ...for $_{SU}PPO$. The optimum temperature was $35^{\circ}C$ for $_{SE}PPO$ and $39.4^{\circ}C$ for $_{SU}PPO$. Activation energy (Ea) from thermal activation was 41.5 kJ/mol for $_{SE}PPO$ and 37.5 kJ/mol for $_{SU}PPO$. Heating at $60^{\circ}C$ by 5 min, $_{SU}PPO$ was denatured whereas $_{SE}PPO$ retained 2.6% of activity. Activation enthalpy (${\Delta}H^#$) and activation entropy (${\Delta}S^#$) for $_{SE}PPO$ heat-inactivation were 69.9 J/mol and $-83.5\;kJ/mol{\cdot}K$ for $_{SU}PPO$, ${\Delta}H^#$ was 91.8 J/mol while ${\Delta}S^#$ was $-21.0\;kJ/mol{\cdot}K$. Substrate specificity ($V_{max}/K_M$) was 4-methylcatechol>catechol>pyrogallol for $_{SE}PPO$ and 4-mehtylcatechol>pyrogallol> catechol for $_{SU}PPO$. For both enzymes, the order of inhibition effectiveness using reductor agents was metabisulphite>ascorbic acid. Benzaldehyde, 4-hydroxybenzaldehyde, and DL-dopa were competitive inhibitors, and their $K_I$ values were 38.86, 8.43, and 2.08 mM, respectively.
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.
