title: Phase behaviour of oleanolic acid/stearyl stearate binary mixtures in bulk and at the air-water interface.
abstract: The solid-liquid phase behaviour of oleanolic acid (OLA)/stearyl stearate (SS) was investigated by differential scanning calorimetry and polarizing optical microscopy. A eutectic type diagram, with the eutectic composition close to pure SS was obtained. Complementary studies by NMR, X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy were performed. A mutual influence was detected in mixtures: the low melting form of SS is favoured at low OLA molar fractions (X(OLA)) and spherulitic structures appear at high X(OLA) and high temperature. Additionally, H-bonding between OLA carbonyl groups increases in the presence of SS. The study of OLA/SS by the Langmuir method and Brewster angle microscopy revealed the organization at the air-water interface: OLA interacts with water in the first layer, while SS is completely segregated to the upper layer for X(OLA)>0.3, and it distributes in the first and upper layers for X(OLA)<0.3.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal.
authors.forename: Ana C T
authors.initials: AC
authors.lastname: Teixeira
authors.forename: Ana R
authors.initials: AR
authors.lastname: Garcia
authors.forename: Laura M
authors.initials: LM
authors.lastname: Ilharco
authors.forename: Amélia M P S
authors.initials: AM
authors.lastname: Gonçalves da Silva
authors.forename: Anabela C
authors.initials: AC
authors.lastname: Fernandes
mesh_terms: D000388:Air; D002152:Calorimetry, Differential Scanning; D006358:Hot Temperature; D009828:Oleanolic Acid / Q000737:chemistry*; D044367:Phase Transition; D017550:Spectroscopy, Fourier Transform Infrared; D013228:Stearates / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D014885:Waxes / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D013228:Stearates; D014885:Waxes; D014867:Water; C530758:stearyl stearate; D009828:Oleanolic Acid