Effects of β-Sitosteryl Sulfate on the Phase Behavior and Hydration Properties of Distearoylphosphatidylcholine: a Comparison with Dipalmitoylphosphatidylcholine

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We have studied the phase behavior of distearoylphosphatidylcholine (DSPC) in the presence of sodium β-sitosteryl sulfate (PSO₄). PSO₄ was found to induce sterol-rich and sterol-poor domains in the DSPC membrane. These two domains constitute a fluid, liquid ordered (L_o) phase and a gel (L_β) phase. PSO₄ was less miscible in DSPC than in a dipalmitoylphosphatidylcholine (DPPC) membrane, as evidenced by its tendency to separate from the bilayer at a concentration of 50 mol%. This lack of miscibility was attributed to the greater van der Waals forces between the PC hydrocarbon chains. In addition to affecting the phase behavior, PSO₄ also enhanced the hydration of the membrane. Despite its weaker interaction with DSPC compared to DPPC, its tendency to fluidize this phospholipid and enhance its hydration can be useful in formulating cosmetics and pharmaceutical products.