Figure 6.

The exclusion of nonpolar alcohols from spermidine³⁺ condensed DNA and of salts and polar solutes from HPC mirrors the forces between macromolecules. Interaxial spacings have been adjusted for macromolecular diameters to give surface separations. The excess osmotic pressure due to exclusion is calculated from the dependence of the interhelical spacing between macromolecules on the salt or solute concentration; Π₀ is the maximal osmotic pressure that could be applied by the salt or solute if completely excluded from the macromolecular phase. For each curve, several different concentrations of salt or solute were used. The overlap indicates that the excess number of water molecules at a fixed spacing is constant, independent of solute concentration. The exponential decay lengths vary between 3.5 and 4.3 Å. Data taken from [31,48,51].