title: Effects of ions on the solubility transition and the phase-separation of N-isopropylacrylamide in water.
abstract: The effects of NaCl, NaOH, and HCl on the solubility transition and the phase-separation of N-isopropylacrylamide (NIPA) were investigated for the purpose of clarifying the physicochemical mechanism of salting-out and salting-in phenomena. The discrete change in the solubility of NIPA in the salt-free water at the solubility transition (reported in J. Phys. Chem. B 2010, 114, 14995-15002) decreased with the addition of HCl and disappeared in the HCl solutions at concentrations higher than 2 M, while it increased with additions of NaOH and NaCl. A difference in NIPA concentration between the phase-separated solutions decreases with the addition of HCl and increases with additions of NaOH and NaCl. Partition coefficients of HCl in the phase-separated NIPA-rich solutions are higher than those in the NIPA poor solutions, while partition coefficients of NaCl and NaOH between the NIPA-rich and -poor solutions have trends opposite to those of HCl. The present results clearly indicate that the HCl favors the dehydrated NIPA and stabilizes the H(2)O-poor state of the NIPA molecule more than NaCl.
authors.affiliation: Department of Chemistry, Faculty of Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan. shigeo-ssk@chem.kyushu-univ.jp
authors.forename: Shigeo
authors.initials: S
authors.lastname: Sasaki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okabe
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D006851:Hydrochloric Acid / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D044367:Phase Transition; D012965:Sodium Chloride / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry*
chemical_list: D000178:Acrylamides; D007477:Ions; D014867:Water; D012965:Sodium Chloride; D012972:Sodium Hydroxide; C067295:N-isopropylacrylamide; D006851:Hydrochloric Acid