P. Peretti

Low-frequency raman spectrum of benzophenone at 300 and 30°K

Abstract The Raman spectrum of a single crystal of benzophenone has been recorded from 25 to 130 cm −1 and an assignment has been made. A comparison with far-infrared data suggests that librational motions occur at the following frequencies: 126−116 cm −1 , 104−97 cm −1 and 61−54 cm −1 at 300°K. The shift of these frequencies with temperature is also given.

Lasalocid and biomimetic membranes: insertion in Langmuir films of lipids

The interfacial properties at the water surface of dipalmitoylphosphatidylcholine (DPPC) in monomolecular films containing various concentrations of lasalocid sodium salt (LAS) have been studied in the range from r = 0.005 to 0.1 (r = molar ratio LAS:DPPC). The data from which the results have been expressed were obtained from the following compression isotherms at constant temperature (22 degrees C): of mixed films, of pure DPPC and of pure LAS. The incorporation of LAS resulted in pressure and concentration dependent molecular area increase, between 0 and 16 mN m-1. The observed effect has been expressed as the area SA* occupied by each antibiotic molecule in the mixed films. The variations of SA* have been discussed at two levels of constant surface pressure, at 8 mN m-1 which is situated in the phase transition region of the DPPC isotherm and at 4 mN m-1 in the liquid expanded state. In both cases, the SA* values decreased as r increased. They have been related to the molar areas SA of LAS, obtained from the compression isotherm of the pure antibiotic and expressed as SA*/SA. This ratio was considerably greater than unity in the phase transition region within the studied concentration range and close to unity in the liquid expanded state. Using the method of Goodrich, the excess free energy of mixing GXS has been calculated. The values were positive above r = 0.01 and they increased with increasing concentrations. The results indicate non miscibility and strong repulsion between the two kinds of molecules in the mixed films. Two different mechanisms of insertion have been suggested.

Molecular Orientation in a Semi-Fluorinated Alkane Monolayer Spread at the Air-Water Interface

Abstract We show that a stable monolayer of F(CF2)8 (CH2)2-S-(CH2)16H molecules can be obtained at the air water interface. The molecular orientation within the monolayer has been determined at the air-water interface by means of surface pressure isotherms, surface charge as a function of the molecular area measurements and fluorescence microscopy. We propose a theoretical model to explain the experimental results. For molecular areas larger than 60 A2(π=0 mN/m), half of the molecules extend their perfluorinated chains up and their hydrocarbonated chains down. At molecular areas about 30 A2, the monolayer exhibits a condensed-like phase for which all the molecules extend their perfluorinated chains up. The transition between these two phases is first order. Eventually, we deduce a value about 4 for the dielectric constant of the monolayer.

Lasalocid and Monensin: Aggregation at the Lipid-Water Interface in Mixed Films

Abstract Insertion properties of the antibiotics Lasalocid and Monensin sodium salts (LAS-Na and MON-Na) in Langmuir monolayers of two different lipid molecules, dipalmitoylphosphatidylcholine (DPPC) and octadecanol (C180H), have been investigated. Results from compression isotherms of the films on pure water and on a biologically buffered subphase have been compared. Values of the molecular areas of mixed films of antibiotic/lipid and of the molecular areas of the pure lipids, at a given surface pressure, have been used to calculate the aggregation number k of the solute molecules in a concentration range of ρ (moles of antibiotic/moles of lipid) from 0.005 to 0.1. The k number in the film of DPPC increases when ρ increases, it is enhanced on the buffered subphase compared to the subphase of water and it is more important for MON-Na than for LAS-Na. There is hardly any evidence ofaggregation in the films of C180H. The two lipid systems both have in common that the mixed films with LAS-Na on the buffered ...

Line intensities and interpretation of low frequency Raman spectra of benzophenone h10, and benzophenone d10, at T = 6K

Abstract The low frequency Raman spectrum of a single crystal of benzophenone h 10 , is given at a lower temperature ( T = 6°K) than the one used ( T = 30°K) in our previous work. Assignments of librational modes have been made by calculating the intensity of the rotational oscillators lines of molecules in a unit cell (oriented gas model). The position of torsional modes of the molecule in the low frequency special range is also reported. The Raman spectrum of benzophenone d 10 is given and compared with the former.

Drugs in biomimetic models: a monolayer study of two antibiotics

Abstract We have recently shown that the usual ionic cavity formation in lipid bilayers from the antibiotics lasalocid and monensin is also likely to take place in monolayers. The present study of Langmuir films of the pure antibiotic ionophores indicates that such formation might occur from two ring complexes at the interface.

Monolayers as Membrane Models. A Study of Antibiotic Action on Lipids

Abstract Langmuir films of the lipids dipalmitoylphosphatidylcholine, docosanoic acid and octadecanol, in presence of two antibiotic ionophores, monensin sodium salt and lasalocid sodium salt have been studied. An important area increase as a consequence of antibiotic addition has been observed in the π-A isotherms of the phospholipid. The effect has been considered as a result of ionic cavity formation accompanied by rearrangements in the lipid hydrocarbon chains. A smaller area increase of monolayers from the single chain lipids has been observed only when monensin sodium salt was added. Monolayer studies of monensin sodium salt allowed molecular area estimations of the pure antibiotic in the film.

Experimental study of triplet exciton diffusion in diphenyl and benzophenone crystals

Abstract Biphenyl crystals to which have been added to 10−2 mole/mole of benzophenone and a various concentration of naphthalene, excited by radiation absorbed only by benzophenone molecules give naphthalene phosphorescence. This emission is interpreted as a consequence of energy migration from benzophenone molecules to the naphthalene molecules through the triplet exciton band of biphenyl. From the study, at 120 K, of the intensity of the naphthalene phosphorescence dependence on concentrations, a coefficient of diffusion of triplet excitons of biphenyl is measured (D ≈ 10−6 cm2 s−1). Analogous kinetics applied to binary mixed crystals, naphthalene-benzophenone, give a coefficient of diffusion of triplet excitions for benzophenone (D ≈ 10−7 cm2 s−1).

Langmuir films of pure antibiotic ionophores and of mixtures with phospholipid at different temperatures

Abstract New results are presented concerning insertion of two antibiotic ionophores Lasalocid and Monensin as sodium salts (LAS-Na, MON-Na) in biomimetic membranes. Langmuir films of Dipalmitoylphosphatidylcholine (DPPC) have been used as model systems. Evolution of the compression isotherms has been investigated below the gel - liquid crystal phase transition, between the ambiant and temperatures approching physiological conditions, not only for the pure antibiotics but also for the antibiotic - lipid mixtures, the molecular ratio ρ antibi-otic/lipid equal to 0.1. In the mixed films with LAS-Na, the antibiotic molecule is well maintained by the film also when raising the temperature, whereas MON-Na is expelled above the low pressure region. The results are discussed and compared with effects produced in model systems of bilayers submitted to similar temperature variations.

Dynamic Behavior of Pyramidic Liquid Crystal Film at the Air-Water Interface

Abstract Molecular organization of the different phases of a pyramidic liquid crystal film spread at the air-water interface has been investigated using Langmuir balance and current displacement techniques simultaneously. The mesogenic compound exhibits a main transition from an expanded phase to a metastable condensed phase. The results are in agreement with previous polarized and fluorescence light microscopy measurements and grazing incidence X-ray reflectometry. The study shows that the molecules are oriented edge-on in the condensed phase and side-on in the liquid expanded phase. The value of the dipole moment of the pyramidic molecules is given in the liquid expanded phase. Two kinds of displacement current curves were obtained depending on the kinetic of compression.