Figure 4.

(a) Transient absorption spectra recorded after a nanosecond single 308 nm XeCl laser pulse excitation of samples containing 50 µM G-quadruplex 1, 25 mM Na₂S₂O₈ (or K₂S₂O₈) and 35 mM Na₂SO₄ (or K₂SO₄) in air-equilibrated 20 mM phosphate buffer solutions, pH 7.0. (b) The transient kinetic traces at 510 nm are attributed to the decay of G(−H)^• radicals in G-quadruplex solutions containing Na⁺ (blue) and K⁺ cations (red) and B-form DNA duplex containing Na⁺ (black).