Continuous gradient temperature Raman spectroscopy of 1-stearoyl-2-docosahexonyl, 1-stearoyl- 2-arachidonoyl, and 1,2-steroyl phosphocholines

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

Submitted to: Chemistry and Physics of Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2021
Publication Date: 7/9/2021
Citation: Broadhurst, C., Schmidt, W.F., Qin, J., Chao, K., Kim, M.S. 2021. Continuous gradient temperature Raman spectroscopy of 1-stearoyl-2-docosahexonyl, 1-stearoyl- 2-arachidonoyl, and 1,2-steroyl phosphocholines. Chemistry and Physics of Lipids. https://doi.org/10.1016/j.chemphyslip.2021.105116.
DOI: https://doi.org/10.1016/j.chemphyslip.2021.105116

Interpretive Summary: Proteins, carbohydrates and fats are the biological LEGO blocks out of which physical structures in every living thing is made (and are also building blocks of what we eat). Cells are surrounded by very specialize membranes critical to among other things keeping essential nutrients in and excess water out and some membranes containing the specific lipid docosahexaenoic acid (DHA) are crucial for sight: babies with insufficient DHA in their diet will be permanently blind. DHA is a major component in the fat within membrane structures in human brain cells as well. The scientific question is where does DHA concentrate and what are the other structures that keep it from being lost and diluted when surrounded by many, many other non-essential lipids. Our lab developed a technique which uses a laser shined on its surface to capture a scattered spectral fingerprint that identifies when DHA presence. Complicating this detection is its signature fingerprint actually “morphs” with changing temperature and, we discovered, with the amount/number of close in space water molecules present. This shape shifting is like LEGO block made of soft plastic, not hard plastic. This on the one hand makes identifying what the starting material looks like much more difficult, AND at the same time, once proven and documented, the specific characteristic shape shifting property ascertained itself becomes a fingerprint. Just as plastics to be recycled are classified into different types, fish oil containing essential fatty acids are also chemically different and different fish oil component have different commercial uses. The fish oil industry globally in 2019 was a $2 billion market. The benefits to ARS are that chemically distinct fish oil components properly characterized adds value to this market and to the potential generation of a new fish oil markets/products.

Technical Abstract: Mixed chain phospholipids containing a saturated fatty acid at sn1 and a polyunsaturated fatty acid in sn2 are the most common in biological membranes. Particularly important are mixed lipids containing palmitic or stearic acid and arachidonic or docosahexaenoic acid since these molecules are prevalent in neural, retinal and organ tissues. Gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements and phase transitions. Herein we utilize GTRS for 1-18:0, 2-20:4n-6 (ASPC), 1-18:0 2-22:6n-3 (DSPC) and 1-18:0, 2-18:0 (SSPC) from -80 to 50°C temperatures. 20 Mb three-dimensional data arrays with 0.2°C increments and first/second derivatives allowed detailed vibrational mode assignment and analysis. Samples were analyzed neat and with molecular hydration. Previously reported phase transitions for hydrated ASPC and DSPC and numerous spectral differences resulting from hydration and the double bond structure were clearly observed. Molecular models showed that the addition of minimal water molecules results in significant structural differences compared to the neat molecules; DSPC is strikingly compact with water when viewed from the hydrophilic end. This precise Raman data cannot be observed in typically utilized fully hydrated vesicle samples, however the improved GTRS will allow for more precise analysis in fully hydrated vesicles because the underlying modes in the unavoidably broadened spectra can be identified.