Physiologically relevant concentrations of NaCl and KCl increase DNA photocleavage by an N-substituted 9-aminomethylanthracene dye.

This paper describes the synthesis of a new 9-aminomethylanthracene dye N-substituted with a pyridinylpolyamine side chain (4). The effects of NaCl and KCl on anthracene/DNA interactions were then studied, with the goal of simulating the conditions of high ionic strength that a DNA photosensitizer might encounter in the cell nucleus (∼150 mM of NaCl and 260 mM of KCl). As exemplified by methylene blue (5), the expected effect of increasing ionic strength is to decrease DNA binding and photocleavage yields. In contrast, the addition of 150 mM of NaCl in combination with 260 mM of KCl to photocleavage reactions containing micromolar concentrations of 4 triggers the conversion of supercoiled, nicked, and linear forms of pUC19 plasmid into a highly degraded band of DNA fragments (350 nm hν, pH 7.0). Circular dichroism spectra point to a correlation between salt-induced unwinding of the DNA helix and the increase in DNA photocleavage yields. The results of circular dichroism, UV–vis absorption, fluorescence em...