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

Publication at Faculty of Science |


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 (NM R 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.