We report here the cloud point (CP) phenomenon in amphiphilic drug amitriptyline (AMT) solutions. We have investigated the influence of electrolytes on the micellar behavior of AMT by using CP and dye solubilization techniques. The CP was found to considerably decrease with increasing pH due to a reduction in electrical repulsion between AMT micelles. It increased on addition of electrolyte due to an increase in electrical repulsion resulting from an increase in the cationic AMT micelle size. The binding effect of anionic counterions was in the order: Br -> Cl -> F -. The effect of cations was insignificant compared to anions.
Cloud point (CP) measurements have been performed to investigate the influence of alcohols (C 2 -C 10 OH) on the micellar growth of amphiphilic drug amitriptyline (AMT) in the presence of salt and surfactant. In the case of shorter-chain alcohols (C 4 OH or C 5 OH), the CP increased with increasing alcohol concentration in the presence of a small amount of sodium phosphate because they partition very little in AMT micelles. On the other hand, it steeply decreased with increasing alcohol concentration in the case of longer-chain alcohols (C 8 OH or C 10 OH) due to their considerable partitioning in AMT micelles. The effect of hindering the micellar aggregation was enhanced as the alcohol chain length increased in the case of shorter-chain alcohols. The CP became less sensitive to addition of C 6 OH at higher sodium phosphate concentrations, resulting from incorporation of more C 6 OH molecules into the enlarged micelles. Addition of cationic surfactant cetylpyridinium chloride to the AMT micellar solutions increased the CP because cetylpyridinium cations affect electrostatic interactions with the cationic AMT headgroup, while addition of anionic surfactant, sodium dodecyl sulfate, decreased the CP because of penetration of dodecyl chains into the micelles, resulting in a micellar growth.
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