Metallacarboranes (MCs) are molecular cages made of boron and carbon atoms, among which the COSAN anion [Co(C2B9H11)2]- is the most studied. COSAN is a nanometer sized anion composed of two nido-carborane clusters sandwiching a cobalt(III) ion. Although COSAN has no amphiphilic structure, it was shown to have surfactant properties: surface activity, foaming and formation of vesicles, micelles or lyotropic lamellar phase while increasing concentration. These properties result from the formation of intermolecular di-hydrogen bonds (C-H and B-H) and the hydrophobic effect in equilibrium with electrostatic repulsions (Fig 1a, b). [1] Lately MCs have attracted much attention due to their potential applications in biology.[2] MCs possess the ability to cross efficiently biological membranes [3-a] and to accumulate in living cells stopping proliferation and growth.[3-b] It is therefore essential to understand the molecular mechanisms and interactions of COSAN and its derivatives with membranes and cellular components. For this purpose, we investigate the interactions of COSAN with glucose moieties such as the octyl-glucopyranoside surfactant (C8G1) and with glycolipids such as MGDGsat and DGDGsat.Adsorption and co-micellisation between COSAN and C8G1 were observed and investigated at the molecular (UV-visible, NMR) and supramolecular scales (SLS/DLS, SAXS). We observed the formation of C8G1 decorated micelles at low COSAN content and mixed COSAN-C8G1 aggregates at low C8G1 content (Fig1 c, d). The strong COSAN-C8G1 interactions affect strongly both C8G1 and COSAN CMCs as confirmed by surface tension measurements. The COSAN-glycolipids interactions at the water/monolayer(/air) interface and analyzed through Langmuir isotherms and GIXRD/GIXOS (grazing incidence x-ray diffraction / off-specular scattering). Such non-purely electrostatic interactions between COSAN and neutral surfactants or glycolipids are a new example of the superchaotropic effect, generally observed with nanometric ions.[4] References [1] (a) P. Bauduin et al., Angew. Chem. Int., 50 2011, 5298-53000. (b) P. Bauduin et al., Angew. Chem. Int., 52 2013, 12114-12118. [2] P. Cigler et al, PNAS, 102 (43) 2005, 15394-15399. [3] (a) C. Vinas et al, Chem. Commun., 50(51) 2014, 6677-6806. (b) A J. Harwood et al, Scientific Reports, 5(7804) 2015, 7804. [4] B. Naskar et al., J. Phys. Chem. 119 2015, 20985-20992.