An Alternative Approach to Quantify Partition Processes in Confined Environments: The Electrochemical Behavior of PRODAN in Unilamellar Vesicles

Abstract

The main objective of this work is the investigation of the electroactive molecular probe: 6 - propionyl - 2- dimethyl amino naphthalene (PRODAN) behavior in large unilamellar vesicles (LUV) formed with the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) by using cyclic voltammetry (CV) techniques. The CV studies in pure water confirm our previous spectroscopic results that PRODAN self-aggregates due to its low water solubility. Moreover, the electrochemical results also reveal that the PRODAN aggregate species is non electroactive in the electrochemical potential region studied. In DOPC LUV media, the redox behavior of PRODAN shows how the LUV bilayer interacts with PRODAN aggregated species to form PRODAN monomer species. Moreover, the PRODAN electrochemical response allow us to propose a model to explain the electrochemical experimental results and, in conjunction with our measurements, to calculate the PRODAN partition constant (Kp) value between the water and the LUV bilayer pseudophases which coincides with the one obtained through an independent technique. Moreover, our electrochemical model allows us to calculate the diffusion coefficient (D) for the DOPC LUV which coincides with the D value obtained through dynamic light scattering (DLS). Thus, our data clearly show that the electrochemical measurements could be a powerful alternative approach to investigate the behavior of non-ionic electroactive molecules embed in a confined environment such as the LUV bilayer. Moreover, we believe that this approach can be used to investigate the behavior of non-optical molecular drugs embedded in bilayer media.