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1

Electrical Properties and Relaxation Behavior of TOPO Monolayers Formed at the Air/Water Interface

Wydro P., Hąc-Wydro K.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 1

115-127

EN

The properties of the Langmuir monolayer formed by tri-n-octylphosphine oxide (TOPO) have been analyzed. The investigations were based both on traditional (surface potential measurements) and more advanced (the relative reflectivity using Brewster angle microscopy BAM) experimental techniques and, for better analysis, the semiempirical computation using HyperChem programme has been done. Moreover, detailed characteristics of the relaxation behaviour of TOPO monolayers have been performed. It has been found that with the increase of the surface pressure () the film thickness increases, and TOPO monolayer becomes denser; however its state does not change. Upon film compression, the reorientation of TOPO molecules occurs in this way that they become progressively more perpendicular to the surface until the collapse of the monolayer. The relaxation of TOPO monolayers formed both on water subphase as well as on NaCl solution of various concentrations were analyzed according to two-steps desorption mechanism. As it turned out, the stability of TOPO monolayer decreases with the surface pressure. At lower the loss of the monolayer material is controlled both by dissolution and diffusion mechanism, while at higher surface pressure the monolayer relaxation is controlled by two dissolution steps of different rates and the monolayer does not achieve a steady-state. Moreover, the monolayer stability increases with ionic strength.

2

Langmuir monolayers of selected monoacylglycerols

Szyszko A., Szeląg H., Pawalec M. K., Sosnowski T. R.

Inżynieria i Aparatura Chemiczna

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2006

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Nr 5s

135-136

EN

A study dealing with behaviour of pure C14-18 monoacyl-glycerols (MAG) Langmuir monolayers at the air-water interface is presented in the paper. It was observed the differences in monolayer properties depended on the hydrocarbon chain length of examined compounds, temperature and compression rate.

3

Comparative Studies of Film-Forming Properties of partially Fluorinated Tetracosanes

Broniatowski M., Miňones J., Sandez Macho I, Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 6

1047-1061

EN

Contrary to simple n-alkanes of moderate molecular weight, which are not capable of Langmuir monolayer formation, partially fluorinated hydrocarbons of the general formula: F(CF2)m(CH2)nH (abbreviated as FmHn) were found to form monomolecular layers at the air/water interface. The aim of this study was to characterize several semifluorinated alkanes (SFA) containing 24 carbon atoms in total (tetracosanes) differing in the m/n ratio, as Langmuir monolayers at the free water surface. The following compounds have been investigated: F4H20, F6H18, F8H16, F10H14 and F12H12. Surface pressure (pi) and electric surface potential deltaV) isotherms were recorded in addition to quantitative Brewster angle microscopy results. The negative sign of deltaV evidenced for the orientation of all the semifluorinated tetracosanes investigated here, regardless the length of the hydrogenated segment, with their perfluorinated parts directed towards the air. As inferred from apparent dipole moment values and relative reflectivity results, tetracosanes with shorter perfluorinated fragment (F4H20 and F6H18) were found to take vertical orientation at the air/water interface, while those with longer perfluorinated moiety (F8H16, F10H14 and F12H12) remain tilted even in the vicinity of the film collapse. The observed differences may result from a different conformation of the perfluorinated chain, i.e. more fluorinated tetracosanes (F10H14 and F12H12) have their perfluorinated parts sufficiently long to form a helix, while less fluorinated derivatives (F4H20 and F6H18) may possibly exist in all-trans configuration. In particular, the perfluorinated fragment in F8H16 is considered to have an intermediate character between these two structures.

4

Perfluoroalkyl-n-eicosanes at the Air-Water Interface-A Monolayer Study

Broniatowski M., Dynarowicz-Łątka P.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 7

973-985

EN

Perfluoroalkyl-n-eicosanes of the general formula F(CF2)m(CH2)20H, where m = 4,6, 8,10,12 were spread at the air/water as Langmuir monolayers and studied at different experimental conditions, such as spreading volume, subphase temperature and compression speed. The Langmuir monolayer experiments (-A isotherms) have been complemented with quantitative Brewster angle microscopy results, which enabled estimation of the film thickness at different stages of compression. Although the investigated molecules do not possess any polar group and are purely hydrophobic, they form stable monomolecular layers at the free water surface. The negative sign of the measured surface potential, Delta V, evidences for the orientation of the molecules with their perfluorinated parts exposed towards the air, independently of the length of the perfluorinated moiety. The relative intensity measurements allow one to conclude that the molecules with shorter perfluorinated part (F4H20, F6H20 and F8H20) are oriented almost vertically (in respect to the interface) in the vicinity of film collapse, while F10H20 and F12H20 are tilted to the water surface.

5

Interaction in mixed amphotericin B / sterols monolayers spread at the air / water interface

Dynarowicz-Łątka P., Seoane J. R., Trillo J. M., Mouzo O. C., Parada M. C.

Bulletin of the Polish Academy of Sciences. Chemistry

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1999

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Vol. 47, No.2

153-166

EN

Different methods for studying molecular interaction between film-forming components in Langmuir monolayers were applied and compared for the mixed systems of amphotericin B with four different sterols: cholesterol, ergosterol, stigmasterol and B-sitosterol. Among the sterols studied, ergosterol exhibits the strongest interaction with amphotericin B and B-sitosterol the weakest. Cholesterol and stigmasterol show interme-diate behaviour. As a consequence of the interactions, deviations from ideality are ob-served; negative at low and positive at high surface pressures. 1'he interactions are most pronounced for monolayers with the mole fraction of amphotericin Xa == 0.5 and 0.7 which lea.ds to the formation of an amphotericin B-sterol complexes of 2:1 stoichiometry. The obtained results support pharmacological assumption that amphotericin B has a greater affinity to ergosterol than to other sterols. Also the presence of amphotericin B-sterol com-plexes of 2: 1 stoichiometry, responsible for the formation of channels in cell membranes, has been confirmed.

6

Molecular interaction in Langmuir monolayers - statistical thermodynamics approach

Dynarowicz-Łątka P., Jawień W., Minones Trillo J., Vila Romeu N., Conde Mouzo O.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 2

195-206

EN

A regular solution theory for a two-dimensional system with three components of different molecular sizes, adapted from statistical thermodynamics, is used to derive equations describing parameters related to the molecular interactions in mixed Langmuir monolayers. The theory has been applied by examining interactions at the interface for the mixed system of 1-hexadecanol and 1,16-hexadecanediol spread at the water/air interface, basing on experimental data of surface pressure/area (/area (p/A) isotherms. The obtained results show that the attractive forces between film-forming molecules are much stronger than those between particular amphiphiles and water.