How Nano‐Ions Act Like Ionic Surfactants

Abstract

Recently, nanometric ions were shown to adsorb to hydrated neutral surfaces and to bind to the cavities of macrocyclic molecules with an unexpectedly strong affinity arising from a solvent‐mediated effect named superchaotropicity. We show here that nano‐ions at low concentrations (μm range), similarly to anionic surfactants, induce the spontaneous transformation of a swollen lyotropic lamellar phase of non‐ionic surfactant into a vesicle phase. This transition occurs when the neutral lamellae acquire charges, either by adsorption of the nano‐ions onto, or by anchoring of the ionic surfactant into the lamellae. In contrast to ionic surfactants, nano‐ions strongly dehydrate the neutral surfactant assemblies. As a conclusion, these purely inorganic nanometric ions act as alternatives to the widely used organic ionic surfactants.

Highlights on the Binding of Cobalta‐Bis‐(Dicarbollide) with Glucose Units

“…The strong binding of nanometric sized ions at non‐ionic micellar surfaces [34b] or in the cavity of macrocycles [34a] has been previously explained to originate from a water‐mediated effect named the chaotropic effect or superchaotropicity regarding its reinforced effect compared with classical chaotropic ions such as SCN − or I − . In the present work, the superchaotropic behavior of COSAN is shown by its spontaneous adsorption on the surface of C8G1 micelles, comparably to POMs [34b, 36, 40] . Therefore, at high C8G1 concentrations, the superchaotropic effect is predominant over the hydrophobic effect observed between C8G1 and COSAN at low concentrations. At high COSAN content (above the CAC), the addition of COSAN disrupts continuously the C8G1 micelles, that is, with the COSAN penetrating in the micellar surface.…”

“…COSAN differs here from POMs owing to the surfactant properties of COSAN, that is, mainly surface activity and micelle formation. Indeed, at high POM content, POMs neither penetrate nor disrupt C8G1 micelles [34b, 40] …”

Preparing (Metalla)carboranes for Nanomedicine

“…Several explanations have been proposed since the early 2000s, trying to include these compounds in pre-existing categories of self-assembling substances, [8,10,[30][31][32][33][34] or, more recently, to propose new terms and new classifications, more appropriate to the peculiar nature of the clusters, for example, (super)chaotropic ions or nanoions. [9,[35][36][37][38][39] In contrast, only a few reports exist which suggest that also non-ionic icosahedral (metalla)carboranes show a tendency to aggregate into nano-and micro-entities in aqueous solutions. [40][41][42][43][44][45][46] However, investigations which translate the physicochemical self-assembling behaviour to the biological concept of colloidal drug aggregates are missing, except our most recent work.…”

“…A plethora of very sophisticated physicochemical and theoretical studies exist on the aggregation behaviour of ABCCs in water. Several explanations have been proposed since the early 2000s, trying to include these compounds in pre‐existing categories of self‐assembling substances, [8,10,30–34] or, more recently, to propose new terms and new classifications, more appropriate to the peculiar nature of the clusters, for example, (super)chaotropic ions or nano‐ions [9,35–39] . In contrast, only a few reports exist which suggest that also non‐ionic icosahedral (metalla)carboranes show a tendency to aggregate into nano‐ and micro‐entities in aqueous solutions [40–46] .…”

“Host in Host” Supramolecular Core–Shell Type Systems Based on Giant Ring‐Shaped Polyoxometalates

“…The pioneering works of Hofmeister in the end of the 19 th century allowed discriminating two distinct behaviours of solvated ions regarding their effect on co‐solutes, namely the salting‐in for chaotropes and the salting‐out for kosmotropes, characterized, respectively by a loosely and strongly bound hydration shell [10, 11] . Recent observations unveiling the remarkable supramolecular behaviour of low‐charge density inorganic polynuclear ions expanded the Hofmeister series toward super‐chaotropic species including polyoxometalates (abbreviated POMs) or boron clusters [12–15] . POM compounds correspond to a wide structural class of discrete metal‐oxo anionic species [16, 17] that encompasses unique electronic properties finding applications in many areas such as catalysis, biology or materials science [18, 19] .…”