Structural Characterization of Biocompatible Reverse Micelles Using Small-Angle X-ray Scattering, 31 P Nuclear Magnetic Resonance, and Fluorescence Spectroscopy

ODELLA, EMMANUEL; FALCONE, R. DARÍO; CEOLÍN, MARCELO; SILBER, JUANA J.; CORREA, N. MARIANO

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Año: 2018 vol. 122 p. 4366 - 4375

1520-6106

The most critical problem regarding the use ofreverse micelles (RMs) in several fields is the toxicity of theirpartial components. In this sense, many efforts have been madeto characterize nontoxic RM formulations on the basis ofbiological amphiphiles and/or different oils. In this contribution,the microstructure of biocompatible mixed RMs formulated bysodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri-noctylphosphineoxide (TOPO) surfactants dispersed in thef riendly solvent methyl laurate was studied by using SAXS and31P NMR and by following the solvatochromic behavior of themolecular probe 4-aminophthalimide (4-AP). The resultsindicated the presence of RM aggregates upon TOPOincorporation with a droplet size reduction and an increase inthe interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edgeexcitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the externalnonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogenbond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionicsurfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches,i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of theinterfacial fluidity of RMs, a parameter that is difficult to measure directly.