FIGURE 5.

The interdependence of SpdCl₃ and 1,4 diaminobutane·2HCl (DABCl₂ or putrescineCl₂) concentrations at the hexagonal-to-cholesteric transition. We use the divalent diamine DAB²⁺ to estimate SpdCl²⁺ binding. The total Cl⁻ concentration from SpdCl₃, DABCl₂, and TrisCl is held constant at 12 mM (•) or 32 mM (▪) to neglect changes in Cl⁻ binding that might accompany the transition. The ratio [DAB²⁺]/[Spd³⁺]^2/3 at the transition point is the same for these two Cl⁻ concentrations, as expected for a simple binding competition. At 12 mM total Cl⁻, the transition point occurs at ∼0.3 mM SpdCl₃ and 1.55 mM DABCl₂; at 32 mM total Cl⁻, [SpdCl₃] ∼3.2 mM and [DABCl₂] ∼7.2 mM. All samples also contain 10 mM TrisCl (pH 7.5) and were equilibrated at 20°C.