title: Hydrophobic and hydrophilic associations of a methanol pair in aqueous solution.
abstract: The association dynamics of a methanol pair in aqueous solution were theoretically studied with QM/EFP-MD and quantum mechanical methods. Stable contact pairs and solvent separated configurations (SS) were found from simulations with a free energy barrier of 2 kcal/mol, revealing the strong tendency of methanol association. The stable contact pairs were further identified as the hydrophobic (CP(A)) and hydrophilic (CP(B)) species, with the CP(A) having a larger population. Although the free energy difference between the CP(A) and CP(B) is negligible with virtually no associated free energy barrier, the slow isomerization dynamics of intermolecular rotations ensures their individual identity. Further mechanistic analysis revealed that only the CP(A) has a direct path to the SS, showing that hydrophobic attraction initiates the association process. A subsequent intermolecular hydrophilic attraction isomerizes CP(A) and CP(B). Therefore, our results show that both the hydrophobic and hydrophilic attractions between methanol molecules play important roles in the association dynamics. The former operates on the longer intermolecular distance, while the latter is effective in contact pairs.
authors.affiliation: Department of Chemistry and Green-Nano Materials Research Center, College of Natural Sciences, Kyungpook National University, Taegu 702-701, South Korea.
authors.forename: Manik Kumer
authors.initials: MK
authors.lastname: Ghosh
authors.forename: Nizam
authors.initials: N
authors.lastname: Uddin
authors.forename: Cheol Ho
authors.initials: CH
authors.lastname: Choi
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D000432:Methanol / Q000737:chemistry*; D011789:Quantum Theory; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D000432:Methanol