Phase behaviour of oleanolic acid, pure and mixed with stearic acid: Interactions and crystallinity

• Published in: Chemistry and physics of lipids 2010-09, Vol.163 (7), p.655-666
• Main Authors: Teixeira, Ana C.T., Garcia, Ana R., Ilharco, Laura M., Gonçalves da Silva, Amélia M.P.S., Fernandes, Anabela C.
• Format: Article
• Language: English
• Subjects: Calorimetry, Differential Scanning; Crystallization; Cuticular membrane; Dimerization; DRIFT analysis; DSC; Hydrogen Bonding; Magnetic Resonance Spectroscopy; Oleanolic acid; Oleanolic Acid - chemistry; Phase diagram; Phase Transition; Spectroscopy, Fourier Transform Infrared; Stearic acid; Stearic Acids - chemistry; X-Ray Diffraction
• ISSN: 0009-3084; 1873-2941
• DOI: 10.1016/j.chemphyslip.2010.06.001

The phase behaviour of pure oleanolic acid (OLA) and in mixtures with stearic acid (SA) was characterized by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and nuclear magnetic resonance (NMR). The crystalline OLA as received (OLA ar) becomes amorphous after being dissolved in chloroform and vacuum-dried at 50 °C (OLA 50). Upon heating, both forms transform to the needle shape crystalline form (OLA 220). Dimerization through H-bonding between COOH groups was detected both in OLA ar and OLA 220. Dimers are stronger in OLA 220, where H-bonding also involves the alcohol groups and plays a role in the crystalline organization. A eutectic type phase diagram was established for mixtures, with the eutectic composition close to pure SA. Mixtures rich in SA are miscible in the liquid and in the amorphous solid states, where the presence of SA–OLA co-dimers, formed through H-bonding between carboxyl groups, was detected. Miscibility and SA crystallinity decrease drastically with the OLA content.