FIGURE 5.

Osmotic stress forces curves are shown for DNA condensed by R₃AR₃, R₃SR₃, R₃IR₃, and R₃PR₃. Force curves are also shown for DNA arrays with R₆ and R₃A₂R₃ for comparison. The arrows indicate equilibrium spacings in the absence of applied osmotic pressure. The solid lines are fits of the data to Equation 3. The identity of the neutral amino acid makes little difference to measured forces. Osmotic pressure and free energy contributions from the repulsive and attractive components of the force calculated from the fitting parameters are given in Table 1. The DNA pellet bathing solutions contained various concentrations of PEG, 10 mm Tris-Cl (pH 7.5), and 100 μm peptide.