2. Structural studies of microemulsions, using spectroscopic techniques

Certain molecular organizates such as microemulsions can be considered as model biomembranes. The programme aimed at characterizing certain structural aspects of these systems, by means of techniques such as Electron Paramagnetic Resonance, Fluorescence Spectroscopy (static and dynamic) Small Angle X-ray Scattering etc.

The recent studies concerned the investigation of structural characteristics of ternary systems formed with hexane - 1-propanol - water that were used for the catalytic studies of lipases. We applied the technique of fluorescence energy transfer between the tryptophan residues of the enzymes (donor molecules) and an adequate acceptor molecule such as cis-parinaric acid. This technique is suitable for nanodispersed systems allowing the determination of the distances between the hydrophilic donor and the lipophilic acceptor, clarifying thus, the structure of the confined aqueous phase. The results were combined with Electron Paramagnetic Resonance experiments in the same systems using spin probes. More specifically we used the spin probe 5-DSA a stearic acid analogue with a stable single electron. The analysis of the obtained spectra allowed the determination of the micropolarity of the spin probe environment and consequently the interface between the dispersed aqueous phase and the external organic solvent.

Time evolution of 5-DSA EPR spectra, in presence of lipase. The enzymatically catalyzed esterification of the probe can be directly followed by EPR