Fig. 5.

Dipolar C-H order parameters of DMPC were extracted from dipolar splittings obtained from pure DMPC (A) and from a mixture of DMPC/C16 (20%) (B). The order parameters of C16 were obtained from a sample of DMPC-d₆₇/C16 (20%) in which the ¹³C-DMPC resonances show much reduced cross polarization intensities (C). The 1D spectra on the left and right are ¹³C spectra of DMPC and DMPC-d₆₇/C16 (20%), respectively. The order parameters are plotted along the lipid carbon positions (D). Resonance b in C16 corresponds to the main CH₂ signal, but the other resonances are not assigned and are therefore plotted as “smoothed” order parameter profile in order of increasing chemical shift. Both C16 and DMPC show a similar degree of chain order, which is higher than pure DMPC. All spectra were recorded at 325 K. At this temperature, both C16 and DMPC are within a fluid phase within the mixture as judged from ¹H-MAS NMR spectra (Fig. 6). Dipolar couplings were calculated by dividing the dipolar splittings by the FSLG scaling factor (0.577 for CH and 0.816 for CH₂). Order parameters were calculated from the ratio of the measured dipolar couplings to the rigid single bond ¹³C-¹H bond dipolar coupling (21.5 kHz [35]).