title: Influence of salt purity on Na+ and palmitic acid interactions.
abstract: The influence of salt purity on the interactions between Na(+) ions and the carboxylate (COO(-)) head group of palmitic acid (PA) monolayers is studied in the COO(-) and OH stretching regions using broad-band vibrational sum frequency generation (VSFG) spectroscopy. Ultrapure (UP) and ACS grade NaCl salts are used for aqueous solution preparation after proper pretreatment. The time evolution of VSFG spectra of PA monolayers on solutions made from these two grades of salts is different, which reveals that the salt purity has a significant impact on the interactions between Na(+) ions and the COO(-) group of PA. The trace metal impurities in ACS grade salt, which are more abundant than those in UP grade salt, are responsible for this difference due to their stronger affinity for the carboxylate group relative to Na(+) and further affects the interfacial water structure. These results suggest that the alkali salt grade even after pretreatment is critical in the studies of alkali cation-carboxylate interactions and comparison of relative binding affinities of different cations.
authors.affiliation: Department of Chemistry & Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Zishuai
authors.initials: Z
authors.lastname: Huang
authors.forename: Wei
authors.initials: W
authors.lastname: Hua
authors.forename: Dominique
authors.initials: D
authors.lastname: Verreault
authors.forename: Heather C
authors.initials: HC
authors.lastname: Allen
mesh_terms: D000388:Air; D002264:Carboxylic Acids / Q000737:chemistry; D006878:Hydroxides / Q000737:chemistry; D019308:Palmitic Acid / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D002264:Carboxylic Acids; D006878:Hydroxides; D014867:Water; D019308:Palmitic Acid; D012965:Sodium Chloride; C031356:hydroxide ion