where the θ CD is the angle between the bilayer normal (i.e., the z-axis) and the carbondeuterium vector, with the deuterium atom position predicted based on the coordinates of acyl chain carbon atoms. The order parameters were calculated by averaging five 100 ns blocks, and the resulting block averages were subsequently used to derive the final average and standard deviation. The average angle between the tail vector (C20-C7, C35-C21) and the bilayer normal was determined using gmx gangle (see Figure for atom numbering).