Effect of inorganic salts on the clouding behavior of hydroxypropyl methyl cellulose in presence of amphiphilic drugs.

In this paper we report the effect of two cationic (imipramine hydrochloride (IMP) and promazine hydrochloride (PMZ)) and one anionic (sodium salt of ibuprofen (IBF)) drugs on the clouding behavior of a nonionic polymer hydroxypropyl methyl cellulose (HPMC). Though all the three drugs increase the cloud point (CP) of HPMC, the effect was found to be minimum in the case of IBF. Further, the effect of adding salts (NaF, NaCl, NaBr, NaNO(3), Na(2)SO(4), Na(3)PO(4), KCl, KBr, KNO(3)) in the presence of amphiphilic drugs (IMP and PMZ) on the CP of HPMC was seen. Almost linear decrease in the CP was observed with the [salt] at fixed concentrations of these drugs whereas in the absence of drugs the decrement in the CP was slight. The energetic parameters (ΔG(c)(0), ΔH(c)(0) and TΔS(c)(0)) were evaluated and it implies that the disruption of water structure becomes significantly prominent at lower concentrations of the drugs at fixed salt concentrations.

Studies on the mixed micelles of alkyltrimethylammonium bromides and butanediyl-1,4-bis(alkyldimethylammonium bromide) dimeric surfactants in the presence and absence of ethylene glycol at different temperatures.

Mixed micellization of two cationic dimeric surfactants butanediyl-1,4-bis(alkyldimethylammonium bromide) [C(m)H(2m+1)N(+)(CH(3))(2)-(CH(2))(4)-N(+)(CH(3))(2)C(m)H(2m+1),2Br(-)] with their monomeric counterparts alkyltrimethylammonium bromides [C(m)H(2m+1)N(+)(CH(3))(3)Br(-)](m=14 and 16) has been studied at different temperatures (298.15-323.15K) in presence and absence of ethylene glycol (EG) using conductivity data. Steady state fluorescence quenching (SSFQ) measurements were performed to estimate the average aggregation number (N(agg)) of the mixed micelles at 298.15K. The ideal cmc values, experimental and ideal micellar compositions, interaction parameters, activity coefficients of the components, etc. have been evaluated by considering theoretical models of Clint, Rubingh and Rodenas. The analysis reveals that the fraction of the monomeric surfactant in the mixed micelles is higher than the expected ideal micellar mole fraction, and in most of the cases mixed micelles of the studied components become more ideal in the presence of EG.

Effects of solvent media and temperature on the self-aggregation of cationic dimeric surfactant 14-6-14, 2Br- studied by conductometric and fluorescence techniques.

To explore how the solvent characteristics influence the self-aggregation of the cationic dimeric surfactant hexamethylene-1,6-bis(tetradecyldimethylammonium bromide) (14-6-14, 2Br(-)) and to obtain various energetic parameters, conductometric experiments were performed on the binary mixtures of three organic solvents--viz., 2-methoxyethanol (ME)-, acetonitrile (AN)-, and formamide (FA)- water (WR) at different temperatures ranging from 298.15 to 323.15 K. The steady state fluorescence measurements allowed us to calculate the average aggregation number (N(agg)) and the air-bulk phase surface tension helped us to correlate the solvent cohesive energy density with Gibbs energy of micellization (DeltaG(0)(m)). The results showed that, although micellization process becomes less favorable with the increase in volume % of the ME, AN and FA in the binary mixed media, the increment in the cmc below 20% (v/v) of the organic solvents is comparatively less showing the predominance of WR character in the bulk phase. Because of the decrease in Gibbs interfacial energy contribution (DeltaG(0)(interf)) to DeltaG(0)(m), the average aggregation number (N(agg)) decreased with the increase in the volume % of the organic solvent in the mixed media. As the enthalpy of micellization became more negative, the corresponding entropy change became less positive and enthalpy-entropy compensation phenomenon was observed for the micellization of 14-6-14, 2Br(-) in all the mixed media in the studied temperature range.

Conductometric studies of micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) in water and water-organic solvent mixed media.

The micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) has been investigated in water and water-organic solvent mixed media (organic solvents used: 1,4-dioxane (DO), dimethylformamide (DMF), ethylene glycol (EG)). The conductivity in water and in mixed media (water+organic solvent) as a function of surfactant concentration was measured at different temperatures and the data were used to find critical micelle concentration (cmc) and degree of counterion dissociation (alpha) of the micelle. From the study, it is observed that the micellization tendency of the surfactant decreases in the presence of organic solvents and the increase in the cmc values is comparatively less below 20% (v/v) of organic solvents showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values. The standard free energy of micellization was found to be negative in all the cases that became less negative with the increase in the cosolvent content.