Figure 2.

The dependence of osmolyte exclusion on the distance between HPC chains. The excess osmotic pressure as indicated in figure 1 normalized by the osmolyte contribution to the solution osmotic pressure is shown as a function of the interaxial spacing for several protein stabilizing solutes at two or three concentrations. Π_excess/Π₀ = 1 corresponds to complete exclusion, while Π_excess/Π₀ = 0 indicates no preferential inclusion or exclusion. The overlap of the different concentrations indicates an osmotic effect, i.e., that ΔN_w is constant at a fixed D_int over the concentration range examined. The exclusion curves for sorbitol, glycine betaine, and proline are virtually identical. Glycerol is excluded more weakly. TMAO has a somewhat different exponential decay length compared with the others. The solute concentrations examined are: 0.4 and 0.8 m glycine betaine; 0.4, 0.8, and 1.2 m glycerol; 0.25, .05, and 1 m sorbitol, 0.25, 0.5, and 1 m TMAO; and 0.25 and 0.5 m proline. Plain symbols are for the lowest solute concentration, followed by dotted and crossed symbols. The different concentrations for each osmolyte overlap within experimental error indicating an osmotic effect, i.e., Γ_w is constant at a fixed HPC interaxial spacing insensitive to osmolyte concentration.