Measured force profiles between control (*a*) and diseased (PC-enriched) (*b*) lipid bilayers with no MBP in 0.15 M NaNO_{3} solutions at *t* = 25°C (cf. ). The right-hand axes give the corresponding energy per unit area between two flat surfaces as given by the Derjaguin approximation (), *E* = *F*/2π*R*. ○, □, and ▵, approach; •, ▪, and ▴, separation. Three to four separately measured approach and separation runs are shown in each case. The lines are theoretical expressions based on the DLVO theory (), where the repulsive electrostatic and attractive van der Waals forces are given by *F*/*R* = 64πεε_{0}κ(*kT*/*e*)^{2}tanh^{2}(*e*ψ_{0}/4*kT*)*e*^{–κD} – *A*/6*D*^{2}, where κ^{–1} = 0.8 nm is the expected Debye length in 0.15 M NaNO_{3} solution at 25°C(*T* = 298 K); ψ_{0} =–32 and –30 mV, respectively, as calculated for the surface potentials of healthy (*a*) and diseased (*b*) bilayers consisting of 5.7% and 5.3% negatively charged lipid (); and *A* = 3 × 10^{–21} J is the calculated nonretarded but screened Hamaker constant (). Inserting these values into the above equation yields the curves in *a* and *b*, where we have computed the repulsive electrostatic forces on the assumption that the negative charges are located 0.5 nm farther out from the compressed surfaces, which defines *D* = 0, because the negative charges are located at the extreme ends of the flexible PS^{–} and CerS^{–} head groups.

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