| Interaction of porphyrins and metalloporphyrins withDNA has a considerable interest due to their medicalapplications. Their special properties: high opticalabsorption, relatively high quantum yields of triplet stateand fluorescence,or paramagnetism of some metal complexes,provide the use of porphyrin in medicine, as active compoundsin radiological and magnetic resonance imaging of cancerdetection and as photosensitizers in photodynamictherapy (PDT) of cancer .Porphyrin demonstrates thephotodynamic activity against psoriasis atheromatous plaque,viral and bacterial infections including HIV as well.Cationic porphyrins are considered as double functionalcompounds that strongly bind to DNA and photodynamically modify the target site of a DNA molecule by amechanism similar to that of anti-cancer antibiotics suchas bleomycin and daunomycin based on the DNA cleavage.The interaction of cationic porphyrins with syntheticand natural DNA has been widely studied using visibleabsorption spectroscopy and circular dichroism(CD),fluorescence,Raman,NMR, ESR , viscometry footprinting,kinetic methods and X-ray crystallography.The complexation of porphyrin(meso-Tetrakis[3-methoxy-4-(N-carbazyl)n-buxyloxyphenyl]porphyrin,4C4-TPP) with calf thymus-DNA(ctDNA) was investigated. Toidentify binding mode and ionic strength effects, UV-vis,fluorescence and circular dichroism spectra at variousR(=[DNA]/[Porphyrin] were analyzed. A model is presented inwhich 4C4-TPP outside binds ctDNA with self-stacking butpositively charged rings of porphyrin intercalated. Theconstant of 4C4-TPP binding to ctDNA is 2.44×105L?mol-1。As the ionic strength increased, 4C4-TPP with ctDNA existedin transition between monomer·DNA and aggregate·DNA. |
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