Figure 4

(a) Osmotic pressure vs. intercolumnar (interaxial) spacings (d_int) for all structures that are shown in Figs 1 and 2: Duplex (triangle), Poly(AT*T)-triplex (square), GMP-quadruplex (circle), 22-mer HT-quadruplex (filled circle), TG₄T-quadruplex (inverted triangle). Horizontal lines show the Φ_dc → Φ_oc transitions. The lines are drawn approximately between the two d_int values determined from the centers of the coexisting two peaks in the phase-coexistence region (see Fig. 3). Poly(AT*T)-triplex measurements are performed under [MgCl] = 5 mM and [KCl] = 0.3 M. The measurements with other DNA structures are at [KCl] = 0.3 M in the absence of any other ions. The effect of temperature is shown only for GMP-quadruplex (where black and red symbols show the measurements at 20 and 40 °C, respectively, when the osmotic pressures are corrected for temperature). The slight temperature dependence of the transition pressure for the GMP-quadruplex is discussed in the text. For other structures data at T = 20 °C are shown only. (b) Osmotic pressure vs. surface-to-surface separation (d_ss) for duplex, Poly(AT*T)-triplex, and GMP-quadruplex DNA. Here, d_ss = d_int − 2a, where a is the molecular (or columnar) radius ≈10 Å, 10.4 Å, 12.5 Å for duplex²⁶, Poly(AT*T)-triplex³², and GMP-quadruplex¹³, respectively.