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The effects of tetrakis(1-methylpyridinium-4-yl)porphyrinatomercury(II) [Hg(TMPyP)]⁴⁺ (6) along with [Pb(TMPyP)]⁴⁺ (7), [Cd(TMPyP)]⁴⁺ (8), and [H₂(TMPyP)]⁴⁺ (1) (free base porphyrin) on DNA cleavage by Haemophilus aegyptius (HaeIII) have been studied using gel electrophoresis, UV-vis absorption spectroscopy, and circular dichroism (CD) spectroscopy. The gel electrophoresis results indicate that in the absence of 6, HaeIII restriction enzyme could not cleave plasmid DNA at a low concentration of 0.2 units μl^-1 after 1 h incubation at 37 °C. However, DNA cleavage occurred in the presence of 6 at the concentrations of 1.0 × 10^-6 and 1.0 × 10^-7M and 0.2 units μl^-1 of HaeIII under the same conditions. In addition, acceleration of DNA cleavage occurred at a higher concentration of HaeIII (0.4 units μl^-1) in the presence of a wider concentration range of 6 from 1.0 × 10^-5 to 1.0 × 10^-7M. 8, 7, and 1 could not enhance DNA cleavage in the presence of HaeIII (0.2 units μl^-1). However, when the concentration of HaeIII was increased to 0.4 units μl^-1, only 8 inhibited DNA cleavage by HaeIII at higher concentrations (1.0 × 10^-5-10^-6M) whereas 6, 7, and 1 did not. The UV-vis and CD spectroscopic results indicate that these porphyrins interact differently with DNA based on their binding modes. 6 enhanced DNA cleavage due to the synergistic effect of the Hg²⁺ ions and the free base porphyrin 1 that dissociated from the mercury(II) porphyrin complex upon binding to DNA which resulted in the enhanced transformation of the DNA conformation from the original B-form to a Z-like conformation, while 8 inhibited HaeIII activity at higher concentrations and 7 and 1 neither enhanced nor inhibited DNA cleavage. A mechanism for this phenomenon is suggested.

5,10,15,20-tetrakis(4-amidinophenyl)porphyrin (Por 1), its Zn complex (Por 2) and its conjugate with a tetraphenylporphyrin to form a bisporphyrin (Por 3) were prepared. The monomeric Por 1 and Por 2 showed both intercalative and external binding with DNA whereas only external DNA binding was seen in the bisporphyrin, Por 3 by circular dichroism and UV-vis. The DNA photocleavage activities of these porphyrins followed the order: Por 1 ~ Por 2 > Por 3, which did not correlate with their measured ¹O₂ production rates. It suggests 4-amidinophenylporphyrins are promising new photodynamic therapeutic agents.

In this paper, three $\beta$,${\beta }^{\prime }$-conjugated cationic porphyrin compounds were designed and synthesized. The structure of the intermediates and desired porphyrins were confirmed by UV, IR, ¹H NMR, MS and elemental analysis. The interaction modes between these porphyrins and ct-DNA were studied by UV-vis spectroscopy and fluorescence emission spectroscopy. The results showed that PCP 1 had an external binding mode with DNA at low DNA concentration and could intercalate DNA with the increase of concentration. PCP 2 interacted with DNA through an external binding mode, and PCP 3 could insert into DNA. The binding constants ($K)$ between PCP1$\sim$PCP3 and ct-DNA were calculated to be 8.41 × 10⁴, 7.33 × 10⁴ and 4.14 × 10⁴ M${}^{-1}$, respectively. The singlet oxygen (¹O${}_2)$ generation of PCP1$\sim$PCP3 was determined by the 1,3-diphenylisobenzofuran (DPBF) method using tetrapyridylporphyrin (H₂TMPyP) as a reference. The ¹O₂ generation rate of PCP1$\sim$PCP3 followed the order of PCP2 >PCP1>H₂TMPyP >PCP3. Subsequently, the photocleavage effect of porphyrins on pBR322 plasmid DNA was studied by gel electrophoresis. At 10.0 $\mu$M, PCP1 and PCP2 could cleave DNA completely. At 2.0 $\mu$M, the cleavage rate of DNA by PCP3 was 57.5%, which was significantly higher than that of H₂TMPyP (38.8%). These results verified that the amount of cationic ions in the porphyrin structure could affect the binding modes of porphyrins with DNA and their cleavage ability of DNA.