Katarzyna Dopierała

Surface properties of the derivatives of lysosomotropic substances against other quaternary ammonium salts

Equilibrium adsorption at the air/water interface of cationic surfactants belonging in the group of quaternary ammonium bromides was studied. Quaternary ammonium salts, derivatives of lysosomotropic substances with different alkyl chain numbers and hydrophobicities were investigated. Surface properties of considered compounds, were examined and presented against other quaternary ammonium bromides of different chemical structure and with different number of alkyl chains in the molecule. The Frumkin equation and reorientation model were used for a quantitative description of the process of their adsorption. It was found that considered biologically active derivatives reveal strong surface activity. Chemical structure-surface activity relationship was analyzed and referenced to biological activity. Symmetry of the molecules resulting from the number of alkyl chains is the factor determining the behavior of the surfactants at the air/water interface as well as in the bulk. Surfactants with asymmetrical structure show a strong tendency to reorientation, in opposite to tetraalkylammonium bromides and double chain surfactants. Furthermore, the role of ester bond was emphasized.

Dynamics of adsorption in micellar and non micellar solutions of derivatives of lysosomotropic substances

Dynamics of adsorption in micellar and non micellar solutions of derivatives of lysosomotropic substances was studied. The following compounds were considered in our research work: alkyl N,N-dimethyl-alaninates methobromides (DMALM-n), alkyl N,N-dimethylglycinates methobromides (DMGM-n), fatty acids N,N-dimethylaminoethylesters methobromides (DMM-n), fatty acids N,N-dimethylaminopropylesters methobromides (DMPM-n), fatty acids 1-dimethylamino-2-propyl methobromides (DMP(2)M-n), and derivatives of aminoesters with double alkyl chains (M(2)M-n). The examined compounds show interesting biological properties which can be useful, especially in medicine. The exact mechanism of interaction of such compounds with biological membrane is not fully known. However, it is supposed that the presence of micelles has an important role in biological systems. In this paper we show the results of dynamic surface tension measurements in solutions containing the investigated compounds at concentrations above and below cmc. Moreover, we analyzed the influence of the chemical structure of molecules on the diameters of the micelles formed in the solutions. It was found that adsorption dynamics for the studied compounds is strongly affected by the chemical structure of the considered derivatives, especially by the presence of the ester bond, linearity of the molecule, as well as its hydrophobicity. The obtained results show that the structure of the bromide M(2)M-n with two short hydrocarbon chains favors a faster and more efficient adsorption of the molecules at the air/water interface, compared with compounds having one long alkyl chain. Moreover, the double chained derivatives of the M(2)M-n type do not form typical spherical micelles but bilayer structures probably exist in these solutions. The micelles present in the solutions influence the dynamics of adsorption drastically. Moreover, the obtained results indicated that the compounds with especially high biological activity form rather small aggregates.

Interfacial behaviour of cubic silsesquioxane and silica nanoparticles in Langmuir and Langmuir–Blodgett films

In recent years fluorinated polyhedral oligomeric silsesquioxanes (POSS) have been established as useful for the fabrication of superhydrophobic surfaces, however little attention has been paid to their use for making ultrathin coatings by the Langmuir–Blodgett method. On the other hand, recently POSS compounds have been recognized as a new group of film-forming materials. In this study the interfacial behavior of fluorinated polyhedral oligomeric silsesquioxanes (POSS) mixed with silica nanoparticles was studied at the air/water interface. Surface pressure-area isotherms and Brewster angle microscopy revealed the formation of a mixed film. Incorporation of nanoparticles in a POSS monolayer caused formation or more condensed and rigid film as shown by analysis of compressibility and dilatational viscoelasticity. On the other hand POSS molecules act as an excellent dispersant which prevents silica nanoparticles from aggregation. Deposition of the Langmuir–Blodgett film composed of POSS and silica nanoparticles allowed a hydrophobic surface showing water contact angles reaching 135° to be obtained, which suggests possible application of our approach in the fabrication of ultrathin, water-repellent coatings.

Interaction of polyhedral oligomeric silsesquioxane containing epoxycyclohexyl groups with cholesterol at the air/water interface.

Binary mixtures of cholesterol and fully-condensed octakis[{2-(3,4-epoxycyclohexyl) etyl}dimethyl-silyloxy]octasilsesquioxane (OE-POSS) were characterized using Langmuir trough for obtaining surface pressure-area isotherms. The most characteristic feature of the mixed films is the presence of two collapse points on the isotherms. The first one is attributed to the collapse of less stable OE-POSS and it occurs at similar surface pressures for all compositions, while the second one corresponds to cholesterol collapse. Brewster angle microscopy observations confirmed the collapse behavior of the mixed film. Strong condensing effect was observed for the mean molecular areas dependence on cholesterol content in the film. Moreover, formation of microdomains of each component in the matrix of the other one was confirmed by BAM images. For the reasons of molecular structures and interactions a true mixed and homogenous film did not form in the systems considered. Phase separation was observed for all the compositions experimented. The lack of the interactions of OE-POSS with biomembrane components represented by cholesterol is beneficial for applications of OE-POSS in biomedical devices.

Preparation and characterisation of monolayers and Langmuir–Blodgett films of liquid crystal mixed with cubic silsesquioxanes

ABSTRACT Polyhedral oligomeric silesquioxanes (POSS) with eight polyether substituents were mixed with the liquid crystal (LC) 4-octyloxy-4′-cyanobiphenyl and spread at the air/water interface. The surface pressure-area and surface potential-area isotherms were recorded for different weight ratios of both components. The obtained results showed that POSS molecules had beneficial influence on LC monolayer improving its stability and rigidity. Moreover, it was found that some LC–POSS mixtures collapse reversibly and form multilayer films on the top of LC monolayer. On the other hand, interfacial dilatational and shear rheology indicated decrease of elasticity of the films after mixing. Brewster angle microscopy revealed multilayer structure of the condensed film and formation of net-like structures in the expanded film. These films were successfully transferred on solid substrates using the Langmuir–Blodgett technique. The scanning electron microscopy images confirmed the film deposition and formation of networks by POSS–LC mixtures. These findings may be useful in the fabrication of electronic devices based on LCs. Graphical Abstract

Morphology, compressibility and viscoelasticity of the mixed lipid monolayers in the presence of β-carotene

The aim of the present study was to investigate the interfacial behaviour of model biomembranes in the presence of β-carotene (βC). The Langmuir monolayer technique was used to form the mixed lipid film at the air/water interface. Using the surface pressure-area isotherms, the surface potential-area curves and the Brewster angle microscopy the nature of interactions between carotenoid and lipid components of the monolayers was investigated. The results were obtained for complex models of the lipid bilayer composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (CHOL). It was found that β-carotene affected the membrane stability, fluidity and rigidity, however this influence varied with the DPPC/CHOL ratio. The membrane permeability which is significant for biological functions was found to be affected by the presence of β-carotene in the membrane. The morphology of mixed films visualized by Brewster angle microscopy was similar for DPPC/CHOL and DPPC/CHOL/βC films indicating incorporation of carotenoid into the film. In contrary to previous reports for individual lipids, we did not observed the aggregation of βC in the mixed lipid monolayer. Moreover, from dilatational rheology experiment we concluded about the significant role of β-carotene in modulation of the elastic behaviour of the membrane, especially in physiologically significant surface pressure, i.e. at π = 30 mN/m.