The effect of ionic liquids C n mimBr (n ) 4, 6, 8) on the properties of cationic Gemini surfactant trimethylene-1,3-bis(dodecyl ammonium bromide) (Gemini 12-3-12) aqueous solution was investigated. The critical micelle concentration (cmc) of Gemini 12-3-12 solutions containing different amounts of ionic liquids were obtained by measurement of surface tension. The composition of mixed micelle and the interaction parameter between ionic liquids and Gemini 12-3-12 were calculated by Rubingh regular solution model; the effective area of Gemini 12-3-12 molecule at air/water interface was calculated by Gibbs adsorption isotherm. The results show that the addition of ionic liquid has important effect on the properties of surfactant aqueous solution. The cmc of surfactant solution and the effective area of surfactant molecules at the air/water interface vary parabolically with the addition of ionic liquids owing to the two extra opposite effects of ionic liquids in surfactant aqueous solutions besides counterion effect, participation of micelles formation, and the effect on the properties of solvent. The effect of ionic liquids on surfactant solution can be regarded as the comprehensive effects of inorganic salt, cosurfactant, and cosolvent on surfactant solution.

Interactions between bovine serum albumin (BSA) and cationic gemini surfactant alkanediyl-alpha,omega-bis(dimethyldodecyl-ammonium bromide) (12-n-12, n=3, 4, 6) in aqueous solution have been investigated by measuring fluorescence, UV-vis transmittance, dynamic lighting scattering, and circular dichroism. Compared to a traditional surfactant dodecyltrimethylammonium bromide (DTAB), 12-n-12 interacts with BSA more strongly. With increasing concentration, 12-n-12 first binds specifically onto BSA leading to the unfolding and aggregation of BSA, and the decrease in alpha-helix content; and then forms micelle-like complexes along the unfolded BSA chains. A gemini surfactant with a longer spacer has a larger effect on BSA unfolding due to a stronger hydrophobic interaction.

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.

Pulmonary administration is widely used for the treatment of lung diseases. The interaction between drug molecules and pulmonary surfactants affects the efficacy of the drug directly. The location and distribution of drug molecules in a model pulmonary surfactant monolayer under different surface pressures can provide vivid information on the interaction between drug molecules and pulmonary surfactants during the pulmonary administration. Ketoprofen is a nonsteroidal anti-inflammatory drug for pulmonary administration. The effect of ketoprofen molecules on the lipid monolayer containing 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-glycerol (DPPG) is studied by surface pressure (π)−area (A) isotherms and compressibility modulus (C s −1 )−surface pressure (π) isotherms. The location and distribution of ketoprofen molecules in a lipid monolayer under different surface pressures are explored by surface tension, density profile, radial distribution function (RDF), and the potential of mean force (PMF) simulated by molecular dynamics (MD) simulation. The introduction of ketoprofen molecules affects the properties of DPPC/DPPG monolayers and the location and distribution of ketoprofen molecules in monolayers with various surface pressures. The existence of ketoprofen molecules hinders the formation of liquid-condensed (LC) films and decreases the compressibility of DPPC/DPPG monolayers. The location and distribution of ketoprofen molecules in the lipid monolayer are affected by cation−π interaction between the choline group of lipids and the benzene ring of ketoprofen, the steric hindrance of the lipid head groups, and the hydrophobicity of ketoprofen molecule itself, comprehensively. The contact state of lipid head group with water is determined by surface pressure, which affects the interaction between drug molecules and lipids and further dominates the location and distribution of ketoprofen in the lipid monolayer. This work confirms that ketoprofen molecules can affect the property and the inner structure of DPPC/DPPG monolayers during breathing. Furthermore, the results obtained using a mixed monolayer containing two major pulmonary surfactants DPPC/DPPG and ketoprofen molecules will be helpful for the in-depth understanding of the mechanism of inhaled administration therapy.