Fig. 4.

DNA CD meltings, S1 digestion, and fluorescence changes in the presence of SWNTs. (A) CD melting profiles of the G/C duplex under different conditions: at pH 7.0 in the absence (line 1) or presence (line 2) of 10 μg·ml⁻¹ SWNTs and at pH 5.5 in the absence (line 3) or presence (line 4) of 10 μg·ml⁻¹ SWNTs in cacodylic buffer (0.1 mM cacodylic acid/sodium cacodylate/100 mM NaCl). DNA concentration was 9.2 μg/ml for i-motif and 9.5 μg/ml for G-quadruplex in base. Normalized CD changes at 260 nm were plotted against temperature. (B) Image of fluorescent nondenaturating PAGE after S1 digestion. Lane 1, untreated 5′-fluorescein-labeled 21-mer sequence; lane 2, S1 treated at pH 5.5; lanes 3–5, S1 treated the complexes of 5′-fluorescein-labeled DNA and SWNT-COOH (0.75, 1.75, and 5 μg·ml⁻¹). For details see Materials and Methods. (C) Plot of fluorescence intensity at 370 nm of 2-Ap individually labeled i-motif vs. concentration of SWNTs. The DNA sequence was shown in Materials and Methods. DNA concentration was fixed at 4 μM in base titrated by SWNTs in pH 5.5 cacodylic buffer at 15°C. Open squares, T(2-Ap)A loop near 5′ end in the major groove; open circles, loop in the narrow groove; open triangles, loop near 3′ end in the major groove. Fluorescence emission spectra were recorded from 320 nm to 500 nm with an excitation wavelength at 305 nm.