The Lorentzian function fits the intensity profiles [I(/)] very well for all /. For calculation of the average lipid acyl chain distance a (Eq. 2) and the correlation length n only intensity traces at small / were used in order to minimize the q z component. Depending on the angle of beam incidence the sample horizon was partially shadowing the intensity profiles at / \ 8°for some of the samples. Therefore, the Lorentzian fits for / = 8° (Fig. 5a) were used for the calculations of a and n (Fig. 5b) . In addition to the acyl chain distance a and the correlation length n, the extension of the cc peak in D/ gives information about the tilt homogeneity of the acyl chains (Fig. 4a, inset) . Quantitative fits of the profiles along this dimension, as performed for pure lipids (Weinhausen 2010), were not applicable for the present data for reasons of the signal-tonoise ratio.