The thickness of cholesterol sulfate-containing membranes depends upon hydration.

The ordering of 30 mol % cholesterol (CH) or cholesterol sulfate (CS) on chain deuterated dimyristoylphosphatidylcholine (DMPC) was investigated by 2H-NMR for different hydrations. It is found that: (i) hydration has merely no influence on chain order (chain length) for DMPC-cholesterol systems, (ii) in CS-containing mixtures chain order (length) is greater at low hydration (DMPC-to-water molar ratio, Ri, of 11.3) than in excess water (Ri approximately 500) and (iii) at low hydration the ordering is about the same for CS or CH-containing systems whereas it is not at high hydration. DMPC-CS bilayer thickness is therefore very sensitive to hydration.