RESUMO
This work highlighted the counterion association of diphenhydramine hydrochloride (DPC) and chlorpheniramine maleate (CPM) with anionic sodium tetradecyl sulfate (STS) by conductivity, fluorescence, and UV spectrophotometer measurements. The presence of drugs and the formation of premicellar aggregates of STS were highlighted. The modified Corrin-Harkins CH approaches assessed the STS counterion binding values B = 0.300 for DPC and 0.379 for CPM in the aqueous media at 25 °C. The counterion binding constant (ßc) and Gibb's free energy of micellization (ΔGmic°) were increased and became more negative, suggesting that the drug-surfactant interaction was controlled by electrostatic interaction. Furthermore, the spectral study evaluated that the three isosbestic points for CPM and one isosbestic point for DPC in the STS micelles were observed, which confirmed that CPM was more binding than DPC with the STS micelles. The differential absorbance spectra study was applied to UV spectra to determine the binding constants (Kb) of 2.232 and 2.837 and partition coefficients (Kx) of 286.64 and 3209.21 for DPC and CPM in the presence of STS micelles. The findings demonstrated that the CPM molecules have been associated with the Palisade layer of the STS micelles, and the DPC molecules were bound to the Stern layer of the STS micelles. Finally, we came to the conclusion that ionic drugs could improve the micellization capabilities of surfactants, which might be useful for choosing the best excipients for pharmaceutical applications.
RESUMO
The poor water solubility of rebamipide was enhanced by the mixed micelles of transglycosylated stevia (Stevia-G) and trimethylammonium chloride with varying carbon chain length (C nTAC, n = 14, 16, and 18). Fluorometry, isothermal titration calorimetry (ITC) and dynamic light scattering techniques examined the aggregation properties of Stevia-G and C nTAC. Synergism was found between Stevia-G and C nTAC using the approaches of Clint and Rubingh. The negative interaction parameter (average ßm = -4.17, -5.47, and -7.07) and excess free energy (average ΔG°ex = -2.47, -3.06, and -3.88 kJ mol-1) increased with increasing chain length of C nTAC. The negative B1 values by the Maeda approach suggested that chain-chain interactions contribute to the formation of a mixed micelle. The solubilization of rebamipide in the mixed micelle was evaluated in the term of the molar solubilization ratio (MSR) and partition coefficient ( Km). The Km from the Stevia-G/C16TAC system was highest at a low mole fraction of C nTAC (0.2-0.6). In conclusion, the solubilization of rebamipide was more favorable between Stevia-G and C16TAC, although the stability of the mixed micelle was enhanced by an increase in hydrophobicity of the longer chain lengths used in C nTAC.