Interaction of metformin hydrochloride with ionic surfactants in aqueous and NaCl solution: Effect of temperatures and compositions

Effect of antidiabetic drug metformin hydrochloride on micellization behavior of cetylpyridinium bromide in aqueous solution

Herein, the interaction of an antidiabetic drug, metformin hydrochloride (MHCl), and a cationic surfactant, cetylpyridinium bromide (CPB) is investigated in an aqueous medium. The critical micellar concentration (CMC) of CPB is estimated through conductivity experiments and found to be reduced on adding MHCl and further decreased in the presence of NaCl. The reduced CMC is attributed to the solubilization of MHCl by CPB through micellization and the micellization is found to be thermodynamically spontaneous that experiences an augmentation in the presence of NaCl. This is identified from the negative value of standard free energy (Δ G0m). The higher negative value of Δ G0m (-55.41 kJ mol-1) for CPB + MHCl + NaCl than CPB (-37.89 kJ mol-1) and CPB + MHCl (-34.08 kJ mol-1) is suggestive of the above phenomenon. The positive values of Δ S0m in all three cases confirm that the micellization is entropy driven. The binding of MHCl on CPB is quantified by estimating binding constant using the Benesi-Hildebrand (B-H) plot through UV-visible spectral methods. The binding constant values were calculated to be 2.70 M-1 for CPB + MHCl + NaCl compared to 1.258 M-1 for CPB + MHCl predicting a favoring of micellization in the presence of NaCl which is higher than that in the presence of co-solvents. The molecular interaction of MHCl and CPB is justified using FT-IR and NMR techniques. The surface properties of drug surfactant interactions are assessed using SEM techniques. The point of interaction between the drug and surfactant is visualized through the molecular docking approach. The results suggest that CPB would be an effective solubilizer for developing MHCl drug formulations.Communicated by Ramaswamy H. Sarma.

Impact of salts on the phase separation and thermodynamic properties of mixed nonionic surfactants in absence/attendance of polyvinyl alcohol

Mixed surfactant systems are used in different applied fields like pharmaceutical formulation rather than single surfactant. Therefore, the determination of the clouding nature of the triton X-100 (TX-100) + Tween 80 (TW-80) mixture was carried out in H2O and polyvinyl alcohol (PVA). In the occurrence of PVA, the cloud point (CP) values of TX-100 initially enhance with enhancing the concentration of PVA and tend to decrease after a certain concentration. For different ratios of TX-100 and TW-80 mixture having the same concentration of both solutions, CP values increase through the decreasing ratios of TX-100 with/without PVA. In the presence of polymer, at higher ratios of TX-100 than TW-80, the CP values are higher in magnitudes in comparison to the aqueous medium but at lower ratios of TX-100, the value of CP are lower in magnitudes in comparison to the aqueous system. The CP values of the TX-100 + TW-80 mixture in the salt system are lower in magnitudes than the aqueous medium in both the absence/presence of PVA. However, a reduction of CP values was obtained to a large extent for Na2SO4 over NaCl in the case of lower volume ratios of TX-100. Various thermodynamic variables (standard free energy ( Δ G c o ${\Delta}{G}_{c}^{o}$ ), standard enthalpy ( Δ H c o ${\Delta}{H}_{c}^{o}$ ), standard entropy ( Δ S c o ${\Delta}{S}_{c}^{o}$ ) change, thermodynamic parameters of transfer (free energy of transfer ( Δ G c , t o ${\Delta}{G}_{c,t}^{o}$ ), and transfer of enthalpies ( Δ H c , t o ${\Delta}{H}_{c,t}^{o}$ )) of phase transition) were also determined.