Figure 4.

(A) CD spectral changes during thermal melting for TBA^(5,8)NB2·CS^(5,8)G7T (blue lines: from 15 to 70 °C at a 5 °C interval, gray line: 75 °C) and CD spectrum of TBA·CS^5C (red line). (B) Representative thermal CD (280 nm, blue squares for TBA^(5,8)NB2·CS^(5,8)G7T) and UV (260 nm, blue circles for TBA^(5,8)NB2·CS^(5,8)G7T, red circles for TBA·CS^(5,8)G7T) melting curves. (C) CD spectra of the TBA^(5,8)NB2·CS^(5,8)G7T duplex before (blue line) and after (red line) addition of Na₂S₂O₄. CD spectrum of a solution containing TBA and CS^(5,8)G7T (pink dotted line) and the theoretical sum of the CD spectra of TBA and CS^(5,8)G7T (purple dashed line) are also shown. The experimental temperature was set at 30 °C. (D) IP RP HPLC chromatograms of (a) TBA^(5,8)NB2·CS^(5,8)G7T duplex after addition of Na₂S₂O₄, (b) TBA^(5,8)NB2·CS^(5,8)G7T duplex before addition of Na₂S₂O₄, (c) CS^(5,8)G7T, (d) TBA^(5,8)NB2, and (e) TBA (detection at 260 nm). Conditions: TBA^(5,8)NB2·CS^(5,8)G7T (10 μM), Na₂S₂O₄/TBA^(5,8)NB2·CS^(5,8)G7T = 1050 ([Na₂S₂O₄] = 10.5 mM), 100 mM HEPES (pH 7.0) buffer with 0.1 mM EDTA and 105 mM KCl, and 0.1 cm cell length. (E) Schematic representations showing reduction-triggered dissociation of double-stranded helix to simultaneously form the G-quadruplex with the release of a nearly complementary strand.