Résumé
Metalla-carboranes (MCs), complexes of a metal ion by two cages composed of boron, hydrogen and carbon, and polyoxometalates (POMs), soluble metal oxides can be referred to as Nanoions (NIs) with specific properties in aqueous solution. NIs are ionic species or ionic clusters of nanometre size, typically five to ten times larger than conventional ions, such as chlorides, bromides... The low charge density of NIs and their high polarizability give them a property that is called super-chaotropy.[1] In the field of ions in solution, the term chaotropy, or salting-in, comes from ion classifications made since the late nineteenth century according to the property of their salts to increase protein solubilisation. In contrast, kosmotropic ions, or salting-out, produce the opposite effect. During the 20th century, it became apparent that these ion series had a general character with non-specific effects (no coordination) for numerous physicochemical and biological phenomena, ranging from the solubilisation of hydrophobic compounds, the evolution of the surface tension of water and to the irritability of nerve cells. The super-chaotropic property of NIs is characterised by an exaltation of the "salting in" aspect by their strong propensity to adsorb at neutral hydrated interfaces with as driving energy, an entropic mechanism of dehydration origin, of both NIs and interfaces. Thus metalla-carboranes (MCs)[2] and polyoxometalates (POMs) are recognized as examples of super-chaotropic nano-anions. Despite their notable structural differences, MCs and POMs share numerous application properties in catalysis, in separation science or in biology, which suggests a common origin to these physico-chemical effects in connection with super-chaotropy. In this contribution, we will focus on the superchaotropic behaviour of MCs. We will show different examples of strong interactions between these NIs and various non-ionic and soluble structures such as surfactant micelles, phospholipid bilayers with a strong impact on self-aggregation in solution. This behaviour allows to imagine various new applications in aqueous solution chemistry.