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Continuous Gradient Temperature Raman Spectroscopy of Oleic and Linoleic Acids from −100 to 50 °C.
- Source :
- Lipids; Nov2016, Vol. 51 Issue 11, p1289-1302, 14p
- Publication Year :
- 2016
-
Abstract
- We analyzed the unsaturated fatty acids oleic (OA, 18:1n-9) and linoleic (LA, 18:2n-3), and a 3:1 LA:OA mixture from −100 to 50 °C with continuous gradient temperature Raman spectroscopy (GTRS). The 20 Mb three-dimensional data arrays with 0.2 °C increments and first/second derivatives allowed rapid, complete assignment of solid, liquid, and transition state vibrational modes. For OA, large spectral and line width changes occurred in the solid state γ to α transition near −4 °C, and the melt (13 °C) over a range of only 1 °C. For LA, major intensity reductions from 200 to 1750 cm and some peak shifts marked one solid state phase transition at −50 °C. A second solid state transition (−33 °C) had minor spectral changes. Large spectral and line width changes occurred at the melt transition (−7 °C) over a narrow temperature range. For both molecules, melting initiates at the diene structure, then progresses towards the ends. In the 3:1 LA:OA mixture, some less intense and lower frequencies present in the individual lipids are weaker or absent. For example, modes assignable to C8 rocking, C9H-C10H wagging, C10H-C11H wagging, and CH3 rocking are present in OA but absent in LA:OA. Our data quantify the concept of lipid premelting and identify the flexible structures within OA and LA, which have characteristic vibrational modes beginning at cryogenic temperatures. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00244201
- Volume :
- 51
- Issue :
- 11
- Database :
- Complementary Index
- Journal :
- Lipids
- Publication Type :
- Academic Journal
- Accession number :
- 118989310
- Full Text :
- https://doi.org/10.1007/s11745-016-4194-1