Continuous gradient temperature Raman spectroscopy of six unsaturated fatty acids provides systematic three dimensional molecular structures

Authors: BROADHURST, CATHERINE - University Of Maryland; Schmidt, Walter; Nguyen, Julie; Qin, Jianwei - Tony Qin; Chao, Kuanglin - Kevin Chao; Kim, Moon

Submitted to: Journal of Biophysical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2018
Publication Date: 1/18/2018
Citation: Broadhurst, C.L., Schmidt, W.F., Nguyen, J.K., Qin, J., Chao, K., Kim, M.S. 2018. Continuous gradient temperature Raman spectroscopy of six unsaturated fatty acids provides systematic three dimensional molecular structures. Journal of Biophysical Chemistry. 9:1-14.

Interpretive Summary: Polyunsaturated fatty acids (PUFA) are essential for all mammals because they cannot be manufactured they must be provided in the diet. PUFA, lipids whose carbon chain have multiple double bonds, are converted to about 100 biochemicals that control inflammation, immunity, and brain and nervous system growth, maintenance and protection. Continuous gradient temperature Raman spectroscopy (GTRS) has proven to be a simple, rapid technique for determining the structures of polyunsaturated fats. We applied GTRS to six PUFA and report novel three dimensional structures. This benefits ARS and the public because billions of dollars of medical, veterinary and scientific research funds are spent each year trying to understand and control chronic inflammation, systemic infections and dementia. These improved structures will finally allow pharmaceutical researchers to fully understand the enzymatic reactions that convert PUFA to the active biochemicals, leading to new drugs and natural products.

Technical Abstract: Background: 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 cycloxygenase enzymes but not on the substrates. Objective: 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 docosahexanoic (22:6n-3) acids. Method: 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 exhibit such extreme functional differences. Results: 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. Conclusion: Recognizing that individual sites on the polyunsaturated fatty acid chain are nonequivalent infers that the high degree of specificity of lipoxygenase and cyclooxygenase enzymes should be considered more of a dual process involving intrinsic enzyme and intrinsic lipid carbon number specificity.