title: Influence of a Neighboring Charged Group on Hydrophobic Hydration Shell Structure.
abstract: Raman multivariate curve resolution (Raman-MCR), as well as quantum and classical calculations, are used to probe water structural changes in the hydration shells of carboxylic acids and tetraalkyl ammonium ions with various aliphatic chain lengths. The results reveal that water molecules in the hydration shell around the hydrophobic chains undergo a temperature and chain length dependent structural transformation resembling that previously observed in aqueous solutions of n-alcohols. Deprotonation of the carboxylic acid headgroup (at pH ∼ 7) is found to suppress the onset of the hydration-shell structural transformation around the nearest aliphatic methylene group. Tetraalkyl ammonium cations are found to more strongly suppress the water structural transformation, perhaps reflecting the greater intramolecular charge delocalization and suppression of dangling OH defects in water's tetrahedral H-bond network. The observed coupling between ionic and hydrophobic groups, as well as the associated charge asymmetry, may influence the hydrophobicity of proteins and other materials.
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Joel G
authors.initials: JG
authors.lastname: Davis
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Samual R
authors.initials: SR
authors.lastname: Zukowski
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Blake M
authors.initials: BM
authors.lastname: Rankin
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
authors.forename: Dor
authors.initials: D
authors.lastname: Ben-Amotz
mesh_terms: D000438:Alcohols / Q000737:chemistry; D064751:Ammonium Compounds / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007477:Ions / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D009584:Nitrogen / Q000737:chemistry; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D000438:Alcohols; D064751:Ammonium Compounds; D002264:Carboxylic Acids; D007477:Ions; D014867:Water; D002244:Carbon; D009584:Nitrogen