The miscibility of dodecyltrihydroxyethylammonium bromide with cationic, nonionic and anionic surfactants in mixed monolayers and micelles

Adsorption and Micellization Behavior of Mixtures of Amphiphilic Drugs with Small Amounts of Bile Salts

Bile acid salts are the most important biological surfactant-like molecules. These compounds play an active role in the cholesterol and lipid solubilization. They are also used as drug carriers. The salts give anionic amphiphilic moiety in aqueous solution and will interact strongly when mixed with cationic amphiphiles. With this aim we have investigated mixed systems of three bile acid salts (sodium cholate (NaC), sodium deoxycholate (NaDC) and sodium taurocholate (NaTC)) with two cationic drugs (adiphenine hydrochloride (ADP) and clomipramine hydrochloride (CLP)) by surface tension measurements. It was found that the two components mix nonideally, i.e., the cmc values of the mixtures decrease with the stoichiometric mole fraction (α1) of bile salts and are lower than cmc* values (cmc at ideal mixing condition). The interaction parameters, βm and βσ, come out to be negative and large in magnitude which is obvious from the fact that the two components are of opposite charge and would experience attractive interactions. The results suggest that the contribution of bile salts in the mixed micelles (X1m) is greater than both the α1 and X1id (the contribution in ideal mixing condition). These components also form mixed interface where the contribution of bile salts is more than α1 (i.e., X1σ > α1). The minimum area occupied by a monomer decreases with increase in the content of bile salts in the solution. This confirms that the opposite charges on the two components decrease the repulsion among the head groups. All the evaluated thermodynamic parameters (i.e., ΔG0m, ΔGex, ΔG°ads and Gmin) support the above explanations.

Interaction of hexadecylbetainate chloride with biological relevant lipids

The present work investigates the interaction of hexadecylbetainate chloride (C(16)BC), a glycine betaine-based ester with palmitoyl-oleoyl-phosphatidylcholine (POPC), sphingomyelin (SM), and cholesterol (CHOL), three biological relevant lipids present in the outer leaflet of the mammalian plasma membrane. The binding affinity and the mixing behavior between the lipids and C(16)BC are discussed based on experimental (isothermal titration calorimetry (ITC) and Langmuir film balance) and molecular modeling studies. The results show that the interaction between C(16)BC and each lipid is thermodynamically favorable and does not affect the integrity of the lipid vesicles. The primary adsorption of C(16)BC into the lipid film is mainly governed by a hydrophobic effect. Once C(16)BC is inserted in the lipid film, the polar component of the interaction energy between C(16)BC and the lipid becomes predominant. Presence of CHOL increases the affinity of C(16)BC for membrane. This result can be explained by the optimal matching between C(16)BC and CHOL within the film rather by a change of membrane fluidity due to the presence of CHOL. The interaction between C(16)BC and SM is also favorable and gives rise to highly stable monolayers probably due to hydrogen bonds between their hydrophilic groups. The interaction of C(16)BC with POPC is less favorable but does not destabilize the mixed monolayer from a thermodynamic point of view. Interestingly, for all the monolayers investigated, the exclusion surface pressures are above the presumed lateral pressure of the plasma membranes suggesting that C(16)BC would be able to penetrate into mammalian plasma membranes in vivo. These results may serve as a useful basis in understanding the interaction of C(16)BC with real membranes.