Interfacial Properties of Lecithin Microemulsions in the Presence of Lipase. A Membrane Spin-Probe Study

Abstract

The interfacial properties of lecithin layers in isooctane and in water-in-oil microemulsions were studied by electron paramagnetic resonance spectroscopy. The mobility of the spin probes 5- and 12-doxyl stearic acid (12-DSA) were monitored in both binary and tertiary lecithin systems. In the binary systems the two probes showed important differences caused by the relative positioning of the nitroxide group within the hydrophobic chains of lecithin. The concentration of lecithin also affected the mobility of the probe. In the lecithin microemulsions the presence of water and alcohol restored the probe mobility to some extent. Depending on the water content, the curvature of the lecithin layer was modified in a “hedgehog” way, i.e., when the size of the reverse micelles increased, the spacing among the hydrophobic lecithin tails decreased. The effect of the nature and concentration of the alcohol on the structure of the lecithin interface was also examined. The observed differences were mainly caused by the different partitioning of the alcohols among the various microdomains of the microemulsions. When an enzyme such as lipase was solubilized in the water core of the lecithin reverse micelles, the mobility of the 12-DSA was modified as a function of time. This was caused by the catalytic esterification of the fatty acid probe with propanol, a reaction that could be followed directly by monitoring the electron paramagnetic resonance spectra.

Virgin olive oil: Free radical production studied with spin‐trapping electron paramagnetic resonance spectroscopy

“…This three-line spectrum was characterized by wide line widths and is reminiscent of that of an immobilized amphiphilic nitroxide free radical 5-doxyl-stearic acid (5-DSA) with anisotropic motion (Fig. 5B) (17). Apparently, the high viscosity of olive oil, as well as the hydrophobic interactions between the lipid chains of the trapped radicals (or the alkyl chains of 5-DSA) and the oil phase resulted in the anisotropic interaction between the free electron and the nitrogen nuclei and produced excessive line broadening in the spectrum.…”

Spectroscopic and catalytic studies of lipases in ternary hexane–1-propanol–water surfactantless microemulsion systems

“…This was done by placing 10 l of a 7.8 × 10 −3 M 184 ethanol solution in the tube and by further evaporating the 185 ethanol [19,20].…”

“…(3) is applicable in the fast 200 motion region, i.e. for rotational correlation times in the range 201 of 10 −11 < τ R < 3 × 10 −9 s [19].…”

Phase Inversion and Interfacial Layer Microstructure in Emulsions Stabilized by Glycosurfactant Mixtures

“…By using purposely tailored molecular probes, the EPR technique has proved to provide detailed information on the structure and dynamics of micelles [ 27 ], polymer–surfactant aggregates [ 28 ] and vesicles [ 29 ]. It has also been used to analyze the properties of surfactants layers adsorbed at the solid/liquid and liquid/liquid interfaces, as in emulsions, microemulsions [ 30 , 31 , 32 , 33 , 34 , 35 ], nanoemulsions [ 7 ] and reversed micelles [ 36 , 37 ]. Specifically, in the present study we characterize by EPR the Span80/Tween80 layer interposing between water and oil domains by using two amphiphilic spin-labeled fatty acids, 5- and 16-doxyl stearic acids (abbreviated as 5- and 16-DSA, respectively).…”