Abstract
Interactions of cationic tetrakis (N, N′, N″, N‴- tetramethyltetra-3, 4-pyridinoporphyrazinatozinc (II) (Zn (tmtppa)) with synthetic polynucleotides, poly (G-C) and poly (A-T), and calf thymus DNA have been characterized in 7.5 mM phosphate buffer of pH 7.2 by UV-Vis absorption and fluorescence spectroscopy. The appearance of hypochromicity more than 30% in UV-Vis spectra of porphyrazine due to interaction of both poly (G-C) and poly (A-T) indicates interaction similar to that of porphyrazine with DNA.The binding constants were determined from the changes in the Q-band maximum of the porphyrazine spectra at various poly (G-C) and DNA concentrations. The values of K were 2.5 × 106M−1, 2.5 × 106M−1and 2.5 × 105M−1for poly (G-C), poly (A-T) and DNA, respectively, at 25°C. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated using the van't Hoff equation at various temperatures. The enthalpy and entropy changes were determined to be 41.14 kJ mol−1and 260.50 J mol−1·K−1for poly (G-C) and 53.59 kJ mol−1and 285.46 J mol−1·K−1for DNA at 25°C. The positive and large values of the entropy and enthalpy suggest that both hydrophobic and electrostatic interactions may play an important role in the stabilization of the complex formation. The binding of polynucleotides to porphyrazine quenches fluorescence emission of ethidium bromide (EB), and the quenching process obeys linear Stern-Volmer relationship. The results reviled groove-binding mode of porphyrazine for both AT- and GC-rich polynucleotides of DNA.
Highlights
The interaction of small molecules with DNA continues to be an extremely important area of research, from both fundamental and practical points of view, as the molecular recognition of DNA is of fundamental importance to life
We report the binding characteristics of porphyrazine tetrakis (N, N, N, N ́tetramethyltetra-3, 4-pyridinoporphyrazinatozinc (II) (Zn) (Scheme 1) with polynucleotides such as poly (G-C) and poly (A-T) and DNA on the basis of the binding mode, the binding affinity and thermody
High hypochromism (H ≥30%) in Q-band was observed, which represents the existence of non-covalent interaction and external groove binding between poly (G-C), poly (A-T), DNA and porphyrazine complex [22, 23]
Summary
The interaction of small molecules with DNA continues to be an extremely important area of research, from both fundamental and practical points of view, as the molecular recognition of DNA is of fundamental importance to life. Fyzolahjani / Study on interaction of cationic porphyrazine and small molecule is one of the important ways to find anti-tumor drugs [6, 7]. Most of these ligands have the common feature of extended planar aromatic electrondeficient chromophore with cationic substituents. Phthalocyanines differ from porphyrins by having nitrogen atoms link the individual pyrrol units They have been extensively studied as DNA binders. Porphyrazines absorb more strongly at longer wavelengths, a critical feature in biological and medical applications [11, 12] These compounds are synthesized from dicyanopyridine or pyridinedicarboxylic acid.
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