DNA-binding and photocleavage properties of cationic porphyrin–anthraquinone hybrids with different lengths of links

Four cationic porphyrin–anthraquinone (Por–AQ) hybrids differing in lengths of flexible alkyl linkage, 5-[4-(1-N-anthraquinonon-yl)-l-oxophenyl]-10,15,20-tris(N-methylpyridinium-4-yl)porphyrin triiodide, (l = acetyl, pentanoyl, octanoyl, undecanoyl, designed as [AQATMPyP]I3, [AQPTMPyP]I3, [AQOTMPyP]I3 and [AQUTMPyP]I3, respectively, see Fig. 1), were synthesized and their interactions with DNA were investigated. The results of spectroscopic, denaturation and viscosity measurements suggest that [AQATMPyP]I3 binds to DNA through non-intercalative mode while the other three hybrids with longer links bind via bis-intercalative mode. Ethidium bromide (EB) competition experiment was carried out to determine the binding constants (Kb) of these compounds for CT DNA, and [AQPTMPyP]I3 shows the largest Kb among these hybrids. The photocleavage mechanism and wavelength-dependent cleaving abilities of these hybrids to pBR322 plasmid DNA were also comparably investigated.