Spectroscopic, thermodynamic and molecular docking studies on the interaction of two water-soluble asymmetric cationic porphyrins with calf thymus DNA

Abstract

The water-soluble cationic porphyrin, 5-(1-dodecyl pyridinium-4-yl)-10,15,20-tris(1-methylpyridinium-4-yl)-21H,23H-porphyrin tetrachloride (MDTMPyP), and its Cu(II) complex (CuMDTMPyP) have been prepared and characterized by 1H NMR, UV–visible spectroscopy and elemental analyses. The binding properties of the porphyrins with calf thymus DNA (CT-DNA) have been investigated by electrochemical, spectroscopic and molecular docking methods. These observations were further confirmed by monitoring DNA viscosity and also circular dichroism studies in the Soret region. The absorption spectrum changes of both porphyrins in Soret band region showed that they could intercalate in DNA structure. The obtained results showed that MDTMPyP has a higher affinity to CT-DNA than CuMDTMPyP. The porphyrin solutions were titrated with DNA and the UV–visible titration spectra were analyzed with multivariate curve resolution-alternating least squares (MCR-ALS) technique to obtain spectrum of porphyrin–DNA complex, and concentration profiles of free and DNA-bonded porphyrin. Then the binding constant was calculated by the combination of MCR-ALS and McGhee–von Hippel equation. Also, the thermodynamic parameters of the DNA binding process were acquired from the van’t Hoff equation at various temperatures. The positive and large values of the entropy, and enthalpy revealed that the interaction is endothermic, and the entropically driven process. Two water soluble cationic asymmetric porphyrins have been synthesized and structurally characterized with various techniques. Their binding properties with CT-DNA have been explored by electrochemical and spectroscopic methods. The DNA binding studies offered that these porphyrins can intercalate into CT-DNA.