Photocleavage of DNA by the p-nitrobenzoyl group covalently linked to proflavine.

We have synthesized two novel DNA photocleaving agents,3,6-diamino-10-[6-(4-nitrobenzoyloxy)hexyl]acridinium chloride and 3,6-diamino-10-[6-(4-nitrobenzamido)-hexyl]acridinium chloride, and studied their DNA binding mode and cleavage properties. These compounds contain the photoactive p-nitrobenzoyl group attached to proflavine via an amide or ester linker group and a polymethylene chain. Spectroscopic and viscometric studies have shown that the compounds bind DNA by an intercalative mode. The presence of covalently-bonded intercalator is essential for the UV (310 nm) induced DNA scission. Above a critical ratio, an increase in the relative concentration of compound to DNA did not induce further cleavage. The cleavage efficiency was dependent on the type of linker group. These results are discussed in regard to possible mechanisms for photoinduced DNA breakage.