The Effect of \textit{Trans} Unsaturation on Molecular Organization in a Phospholipid Membrane

The ingestion of \textit{trans} fatty acids (TFA) formed during the partial hydrogenation of vegetable oils has been linked to a detrimental impact on health by an, as yet, unknown mechanism. We synthesized deuterated analogs of 1-elaidoyl-2-stearoylphosphatidylcholine ($t$18:1-18:0PC) that contains a single ``unnatural'' \textit{trans} double bond and 1-oleoyl-2-stearoylphosphatidylcholine ($c$18:1-18:0PC) that contains a single ``natural'' \textit{cis} double bond. Solid state $^{2}$H NMR spectra for model membranes prepared from these phospholipids reveal a higher chain melting temperature for the \textit{trans} isomer, indicating tighter molecular packing in the gel state. In the liquid crystalline, however, the difference between the \textit{trans} and \textit{cis }isomers is subtle. Order as probed by the perdeuterated [$^{2}$H$_{31}$]18:0 \textit{sn}-2 chain, and corroborated by molecular dynamics (MD) simulation, coincides within $<$5{\%}.