The rINEPT delays used were multiples of the MAS period and equal to: τ 1 = 1.2 ms and τ 2 = 2.0 ms. Rf-pulses were calibrated to give the following nutation frequencies: 45.00 kHz (R18 7 1 recoupling pulses), 71.43 kHz ( 13 C 90°and 180°pulses), 71.43 kHz ( 1 H INEPT and 90°), 35.71 kHz ( 1 H broadband decoupling pulses). For each t 1 point, 256 transients were collected over an acquisition time of 50 ms using a 5-s recycle delay. A total of 32 points in the indirect dimension were collected with increments of 18×2×11.11(1) µs. The R-PDLF spectra were processed as described previously and the absolute values of S CH calculated by dividing the measured dipolar splittings by the 1 H-13 C rigid dipolar constant of 22 kHz. The signs of S CH values were determined previously by two independent methods for egg yolk PC, which contains PC molecules with a distribution of distinct unsaturated and saturated acyl chains, and for DMPC: Both works found the α carbon to be the only segment having positive S CH .