First derivatives of the UV melting profiles of ST duplex DNA (A), hTel quadruplex DNA (B), poly(rA)•poly(rU) duplex RNA (C), and AurA quadruplex RNA (D) in the absence (red) and presence of either HXDV (blue) or 19 (green). The UV melting profiles of the quadruplexes were acquired at 295 nm, while those of the duplexes were acquired at 260 nm. In all experiments, the solution conditions were 10 mM potassium phosphate (pH 7.5) and sufficient KCl (132 mM) to bring the total K+ concentration to 150 mM.