TITLE:
Gradient Temperature Raman Spectroscopy of Fatty Acids with One to Six Double Bonds Identifies Specific Carbons and Provides Systematic Three Dimensional Structures
AUTHORS:
C. Leigh Broadhurst, Walter F. Schmidt, Julie K. Nguyen, Jianwei Qin, Kuanglin Chao, Moon S. Kim
KEYWORDS:
Gradient Temperature Raman Spectroscopy, Raman Spectroscopy, Arachidonic Acid, Docosapentaenoic Acid, Docosahexaenoic Acid, Alpha-Linolenic Acid, N-3DPA, DHA, GTRS
JOURNAL NAME:
Journal of Biophysical Chemistry,
Vol.9 No.1,
January
18,
2018
ABSTRACT: Specialized pro-resolving mediators provide promising
targets for new drugs and natural products. Much work has been accomplished on the
structure/ function of the lipoxygenase and cyclooxygenase enzymes but not on the
substrates. A better visualization of three-dimensional lipid structures will allow
increased refinement of the interactions that produce the pro-resolving mediators,
and lead to improvements in synthetic pathways. We present systematic analysis of
oleic (18:1n-9), linoleic (18:2n-6), alpha-linolenic (18:3n-3), arachidonic (20:4n-6), docosapentaenoic (22:5n-3), and docosahexaenoic (22:6n-3) acids. Continuous
gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients
utilized in differential scanning calorimetry to Raman spectroscopy. GTRS can identify
and differentiate specific carbon chain sites, finally allowing Raman analysis to
explain why the long-chain polyunsaturated fatty acids (LC-PUFA) exhibit such extreme
functional differences despite minimal changes in chemical structure. Detailed vibrational
analysis of the important frequency ranges 1450
- 1200 cm-1 (includes CH2 bending and twisting) and
1750 - 1425 cm-1 (includes C=C stretching and C-C stretching plus H-C
in-plane rocking) shows for the first time that each molecule has its own characteristic
set of modes with only some redundancy/commonality. The number and frequency of
modes correlates with three-dimensional molecular structure, not the degree of unsaturation.
The high degree of specificity of lipoxygenase and cyclooxygenase enzymes should
be reconsidered in light of the fact that individual sites on the polyunsaturated
fatty acid chain are nonequivalent, and each
LC-PUFA molecule has an individual, specific three dimensional structure
incorporating torsion.