Cooperative Self-Assembly Process Involving Giant Toroidal Polyoxometalate as a Membrane Building Block in Nanoscale Vesicles

Abstract

The self-assembly of organic amphiphilic species into various aggregates such as spherical or elongated micelles and cylinders up to the formation of lyotropic hexagonal or lamellar phases results from cooperative processes orchestrated by the hydrophobic effect, while those involving ionic inorganic polynuclear entities and nonionic organic components are still intriguing. Herein, we report on the supramolecular behavior of giant toroidal molybdenum blue-type polyoxometalate, namely, the {Mo 154 } species in the presence of n-octyl-β-glucoside (C8G1), widely used as a surfactant in biochemistry. Structural investigations were carried out using a set of complementary multiscale methods including single-crystal X-ray diffraction analysis supported by molecular modeling, small-angle X-ray scattering and cryo-TEM observations. In addition, liquid NMR, viscosimetry, surface tension measurement, and isothermal titration calorimetry provided further information to decipher the complex aggregation pathway. Elucidation of the assembly process reveals a rich scenario where the presence of the large {Mo 154 } anion disrupts the selfassembly of the C8G1, well-known to produce micelles, and induces striking successive phase transitions from fluid-to-gel and from gel-to-fluid. Herein, intimate organic−inorganic primary interactions arising from the superchaotropic nature of the {Mo 154 } lead to versatile nanoscopic hybrid C8G1−{Mo 154 } aggregates including crystalline discrete assemblies, smectic lamellar liquid crystals, and large uni-or multilamellar vesicles where the large torus {Mo 154 } acts a trans-membrane component.

Superchaotropic polyoxometalates as membrane carriers

“…New low-charge density and superchaotropic POMs can be engineered and studied through computational modelling. As outlined, the sulphate/dithionatecontaining POMs, including low-charged organically modified POMs, show high promise for these applications [32]. The utility of these new POMs can be further extended to answer challenges in the construction of intelligent membranes [33] and ionic liquids [34,35], and, more generally, the design of new hybrid assemblies [32].…”