Résumé
Metalla-bis-dicarbollides, such as COSAN [Co(C2B9H11)2]-, are inorganic and ionic complexes composed of a central metal cation, sandwiched between two dicarbollide cages, which confers a global negative charge delocalized over the entire nanometric molecular architecture (Fig. 1, left as a theta shape anion).[1] Despite lacking a classical amphiphilic structure, COSAN distinguished for its surfactant properties such as surface activity and self-assembly properties.[2] COSAN forms indeed monolayer vesicles at low concentrations in water (<10 mM). Then, increasing concentrations, the vesicles undergo a Coulomb explosion into small aggregates [3] and finally self-assemble in lyotropic lamellar phase,[4] at much higher concentration (<150 mM). It is well known that surfactant micelles, through their aggregation mechanism controlled by the hydrophobic effect, solubilize hydrophobic organic compounds.[5a-b] In this present work, we studied the solubilization of hydrophobic organic compounds of various types (medium chain aliphatic and aromatic alcohols, terpenes) and of different hydrophobicity (logP) in water by COSAN and its derivatives. On the contrary to classical surfactants, the solubilization efficiency of COSAN anion under monomeric (or vesicle) state is stronger below the critical micellar concentration. This work aims to decipher this new solubilization mechanism of hydrophobic organic compounds by COSAN at the supramolecular level using scattering techniques (SAXS,DLS). The solubility limit of the systems was also investigated to define phase diagrams. Remarkably, we observed a correlation between the hydrophobicity (logP) of an alcohol and its ability to interact with COSAN based on solubility measurements in water. Moreover, the amount of solubilized hydrophobic compound increases with the increasing COSAN concentration regardless of its aggregation form, which is not the case for classical surfactants such as SDS. This work aims at the better understanding of COSAN-hydrophobic organic compounds interactions that are essential for the biological and medical applications of COSAN.[6]