Vibrational spectroscopic study on polymorphism and order-disorder phase transition in oleic acid

Abstract

Infrared and Raman spectra of three crystal modifications, a, ß, and 7, of oleic acid were investigated. The spectral data of the 7 (low-melting) phase were analyzed on the basis of crystal structure determined by Abrahamsson and Ryderstedt-Nahringbauer. The reversible solid-state phase transition between y and a was followed by the infrared and Raman spectra, and it was concluded that the phase transition was of an order (7)-disorder (a) type accompanied by a conformational disordering in the methyl-sided alkyl segment. Therefore, the y -» a transition was recognized as a new type of interface melting process occurring in layer-formed organic long-chain compounds. The extent of conformational disorder in alkyl chains was compared among various types of disordered crystalline phase. From the spectral feature of phase ß, it was supposed that the subcell structure of this phase differed from the already-known Ox and Tr (or O') type.

Prilling of fatty acids as a continuous process for the development of controlled release multiparticulate dosage forms

“…68 and 75 °C, corresponding to the melting point of the C polymorph), it indicates that only the polymorph C was present in the formulations [32]. These findings were in agreement with Kobayashi (1988), who stated that only the thermostable C-form could be formed from a melt [31]. In contrast, Corvis et al (2011) reported recrystallization of stearic acid in the Eform from a ibuprofen/stearic acid melt.…”

“…showed an onset melting temperature at 120.7 °C, while stearic acid and behenic acid started melting at 68.2 °C and 74.7 °C, respectively, indicating the crystalline state of these compounds. Even-numbered saturated fatty acids can crystallize in at least four polymorphs, named A, B, C and E. As form C is thermodynamically stable at high temperature, all other polymorphs irreversibly transform into form C upon heating [31]. However, as no solid-solid transformations were detected prior to the melting endotherms of stearic and behenic acid (i.e.…”

Surface-Enhanced Raman Scattering from Oleate-Stabilized Silver Colloids at a Liquid/Liquid Interface

“…Some representative peaks were assigned to the vibrations associated with the alkyl chains and the ethylene group. [20][21][22] The most prominent vibrations are the methylene rock at 888 cm -1 , the ν(C-C) modes at 924, 1064, 1095 and 1121 cm -1 , the methylene twist at 1294 cm -1 , the methylene scissor at 1437 cm -1 and ν(C=C) at 1655 cm -1 . Raman bands associated with the carboxylate group, νs(COO -) at ∼1405 cm -1 and νas(COO -) at 1597 cm -1 , are much weaker than those of the alkyl chains.…”

“…Table 1 gives the assignment of the TIR-SERS spectrum along with the Raman shifts of toluene (liquid) and sodium oleate (solid). The assignment was based on previous Raman data of oleic acid, its salt [20][21][22] and toluene. Although no SERS data on oleate ion has been reported, the SERS spectra on carboxylic acids 23 and olefines 24 could be used for the assignment.…”

Prilling as manufacturing technique for multiparticulate lipid/PEG fixed-dose combinations

“…Even-numbered saturated fatty acids can crystallize in at least four polymorphs, named A, B, C and E. As form C is thermodynamically stable at high temperature, all other polymorphs irreversibly transform into form C upon heating [31]. However, as no solid-solid transformations were detected prior to the melting endotherms of stearic and behenic acid (i.e.…”