In general, lowering the RH promotes the gel phase character of the lipid membranes causing a reduced fluidity and increased inter-bilayer potentials (Ho et al. 1995; Long and Hruska 1970) . Upon reducing the water content of the system, the fraction of gauche bonds within the lipid acyl chains is diminished and leads to lipid chain stretching. As a consequence, the lipid chain alignment and ordering (Cevc and Marsh 1985) as well as a lateral compression or packing (Bryant et al. 2001; Chen and Hung 1996) are enhanced. Such behavior was confirmed by the results obtained from measurements for samples 5-9. In line with the literature, a lowering of the acyl chain distance of about Da max = 0.097 ± 0.006 Å and an increase in the correlation length of Dn max = 0.8 ± 0.2 Å were observed when comparing the results for RH = 94% to RH = 25% and to RH = 60%, respectively. The revealed effect that at low water content with RHs between 40 and 25%, the correlation length n seems to reach saturation and even slightly decreases for sample 9, can be associated with the steric demands exerted by the peptide and cholesterol inclusions (Fig. 5b) . Steric demands of the relatively rigid peptide helices become more critical in the more condensed phases than in the fluid phase (Marčelja 1974) . This condition of so-called intermediate fluidity (Oldfield and Chapman 1972) describes the fact that the interaction between inclusions such as cholesterol or peptides cannot be as strong as interactions among ordered all-trans lipid chains (Marčelja 1974 ). We did not observe the phenomenon of an interchain hydration at high RH that is concomitant with an increased lipid chain-chain distance and results from defect structures caused by inserted peptides (Ho et al. 1995) .