A unifying Tm diagram for phosphatidylethanolamines with sn-1 C20 saturated and sn-2 C18 unsaturated acyl chains.

We have determined calorimetrically the phase transition temperature (Tm) values of five sn-1 saturated/sn-2 unsaturated phosphatidylethanolamines (PE) in which the sn-1 acyl chain has 20 carbons and the sn-2 acyl chain has 18 carbons with different number and position of the cis double bond. When these Tm values are combined with the five published Tm values of related unsaturated PE, a unifying Tm diagram is generated for the first time. Moreover, as the molecular mechanics simulated structures of these lipids are taken into consideration, this unifying Tm diagram provides insight into how variations in the number and position of the cis double bond in the lipid's sn-2 acyl chain can influence the phase transition behavior of the lipid bilayer.