Characterization of biosurfactants' micelles formation using flu-orescence measurements: sodium taurocholate as case of study

Abstract

Background and purpose:The evaluation of micellization parameters of surfactants that aggregate gradually, such as bile salts, is not trivial. In this work,different probes and data treatment models are tested to set up ananalytical method based on fluorescence measurements to determinethe critical micelle concentration (CMC) and micellization range (C) of biosurfactants. Sodium taurocholate (NaTc)is used as example.Experimental approach: The fluorescence intensity of five fluorophores has been monitored upon the addition of a concentrated NaTcsolution in two different media: wateranda biorelevant buffer(maleic buffer pH 6.5, I = 120 mM). Four differentdata treatment methodshave been tested.Key results;The micellization processcan be evaluated satisfactorily using fluorescent probes such as propranolol and tetracaine, and also monitoring directly the intrinsic fluorescence of NaTc. However, the results obtained with nonpolar probes(pyrene andnaphthalene)aremore complex to evaluate due to the presence of confluent processes.Although the four models testedfor the data treatmentare commonly used for this purpose, Carpena’s method is the most appropriate as it provides the most accurate CMC and ΔCvalues. The micellization process isfaster in a biorelevant buffer than in water.Conclusion:The study of the micellization of bile salts is not an evident process. After the selection of adequate probes and data treatment methods, the CMC values for NaTC in water and maleic buffer reveal that the biorelevant conditions favour micellization, which in turn may allow faster solubilization of ingested compounds.