Cation-sensitive compartmentalization in metallacarborane containing polymer nanoparticles

Alkaline cations (Li+, Na+ and K+) are introduced as agents suitable to control compartmentalization in metallacarborane-rich nanoparticles of double-hydrophilic block copolymer poly(ethylene oxide)-block-poly(2-alkyloxazoline), PEO-POX. Interaction of the metallacarborane (cobalt bis(dicarbollide) anion) with PEO-POX is based mainly on dihydrogen bonding between metallacarborane boron clusters and the polymer backbone resulting in compact nanoparticles. However, the cations are a crucial factor as to whether interaction with PEO or POX segments is preferred. Changes in the bulk concentration of alkaline cations can thus provoke changes in the inner structure of polymeric nanoparticles, which is accompanied by exchange of boron clusters and alkaline cations like Li+. Because of the biomedical importance of metallacarboranes, their conjugates and also lithium salts, the hybrid nanoparticles can act as stimuli-responsive systems for drug delivery.Peer reviewe

Nonclassical Hydrophobic Effect in Micellization: Molecular Arrangement of Non-Amphiphilic Structures

Micellization brought about by nonclassical hydrophobic effect invokes enthalpy as the driving force. Thus, the underlying molecular phenomena differ from the entropically dominated hydrophobic effect. In quest for a molecular-scale understanding, we report on the molecular arrangement of nonamphiphilic structures of an anionic boron cluster compound, COSAN. We synergistically combine experimental (NMR and calorimetry) and theoretical (molecular dynamics and quantum chemical calculations) approaches. The experimental data support the mechanism of closed association of COSAN, where the self-assembly is driven by the enthalpy contribution to the free energy. Molecular dynamics simulations in explicit solvent show that water molecules form a patchy network around COSAN molecules, giving rise to the strong hydrophobic self-association. In the second solvation shell, water forms a slightly hydrophilic “spot” close to the C-H segments of the cluster. The simulations further show a counterintuitive short-range [COSAN]−∙∙∙[COSAN]− attraction and Na+∙∙∙[COSAN]− repulsion. Quantum chemical calculations reveal a major role of solvation in stabilizing the contact pairs. Further, the calculations show the parallel/X-shape geometrical arrangements of COSAN dimers as the most preferred. Lastly, dihydrogen bonding are found to influence the structure of micelles. In summary, we provide a molecular view of nonclassical micellization that can be extended to other amphiphiles like boranes