title: Dynamic molecular behavior of semi-fluorinated oleic, elaidic and stearic acids in the liquid state.
abstract: Ordinary fatty acids such as oleic, elaidic and stearic acids exist as their hydrogen-bonded dimers in their liquids and in non-polar solvents. Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy have revealed that semi-fluorinated (SF) acids containing a perfluorooctyl group (C₈F₁₇) as a terminal segment exist also as hydrogen-bonded dimers, which are the units of inter- and intramolecular movements in their liquids and CCl₄. The dynamic molecular properties, such as self-diffusion coefficients and intramolecular movements of SF-oleic, SF-elaidic, and SF-stearic acids were compared with those of corresponding ordinary fatty acids (H-acids). From the high equilibrium spreading pressures (ESPs) for SF-acids compared with those for their corresponding H-acids, it was expected that the inter-acyl chain interaction is weaker for the SF-acid than for the H-acid: the SF-fatty acids should have higher molecular mobility than the corresponding ordinary H-acids in the liquid state. However, the self-diffusion coefficients obtained for SF-acids were smaller than those for the corresponding H-acids; the apparent activation energies for the self-diffusion process (translational movement) of SF-acids were larger than those for the corresponding H-acids. Namely, the motion of SF-acid molecules in a liquid phase is rather restricted compared with H-acid in spite of lower inter-acyl chain interaction of SF-acid. This unexpected result suggests that the molecular motion of SF-acid in a liquid phase is not directly governed by inter-acyl interaction, but may be interpreted as a reptation movement of an acid molecule, which is related to intramolecular movement. In fact, low intramolecular movements for SF-acid were confirmed by ¹³C-NMR T₁ measurements.
authors.affiliation: Department of Chemistry, School of Science, Kitasato University, Sagamihara, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Haruna
authors.initials: H
authors.lastname: Matsuda
authors.forename: Yasutoshi
authors.initials: Y
authors.lastname: Kasahara
authors.forename: Makio
authors.initials: M
authors.lastname: Iwahashi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takagi
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Baba
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kanamori
mesh_terms: D004058:Diffusion; D019281:Dimerization; D054879:Halogenation; D006860:Hydrogen Bonding; D019301:Oleic Acid / Q000737:chemistry*; D009829:Oleic Acids; D044367:Phase Transition; D012399:Rotation; D013055:Spectrophotometry, Infrared; D013229:Stearic Acids / Q000737:chemistry*; D044366:Transition Temperature
chemical_list: D009829:Oleic Acids; D013229:Stearic Acids; D019301:Oleic Acid; C011459:elaidic acid