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

0498554 - ÚOCHB 2019 RIV DE eng J - Journal Article
Uchman, M. - Abrikosov, A. I. - Lepšík, Martin - Lund, M. - Matějíček, P.
Nonclassical Hydrophobic Effect in Micellization: Molecular Arrangement of Non-Amphiphilic Structures.
Advanced Theory and Simulations. Roč. 1, č. 1 (2018), č. článku 1700002. E-ISSN 2513-0390
R&D Projects: GA ČR(CZ) GBP208/12/G016
Institutional support: RVO:61388963
Keywords : metallacarboranes * molecular dynamics simulations * nonclassical hydrophobic effect * quantum mechanics * self-assembly
OECD category: Physical chemistry
https://onlinelibrary.wiley.com/doi/full/10.1002/adts.201700002

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](-)center dot center dot center dot[COSAN] attraction and Na+center dot center dot center dot[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.
Permanent Link: http://hdl.handle.net/11104/0291123