UV absorbance and melting studies were carried out on an Agilent 8453 spectrophotometer equipped with a programmable temperature-control unit (Agilent 89090A). Melting temperatures (T m ) were taken as the temperature of half-dissociation of the quadruplex and were obtained from the maximum of the first derivative dA/dT plots at 295 nm. The heat-treated DNA solutions at several concentrations were introduced into a quartz cuvette and overlaid with a thin layer of silicone oil to prevent evaporation. The optical path length was 1 cm. Absorbance and temperature were recorded every 2uC.