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摘要
The association behavior of tetrakis(N,N',N '',N'"-tetramethyl tetra-2,3-pyridino)porphyrazine copper(II) ([Cu(II) 2,3-tmtppa](4+)) was investigated in aqueous solutions at 25 degrees C and various ionic strengths using optical absorption and resonance light scattering (RLS) spectroscopies. The results show that [Cu(II) 2,3-tmtppa](4+) does not have any affinity for aggregation due to increasing of salt concentration and exists as monomers even in homogeneous aqueous solutions of high ionic strengths (more than 1 M NaCl). Interaction of [Cu(II) 2,3-tmtppa](4+) with calf thymus DNA has also been studied in 1 mM aqueous phosphate buffer of pH 7.0, by optical absorption and RLS spectroscopies, and thermal denaturation experiments. The appearance of hypochromicity of less than 10% and bathochromicity shift of Delta lambda <= 2 nm in UV-vis spectra of [Cu(II) 2,3-tmtppa](4+), increasing of thermal melting point of DNA, and no change in RLS spectra of porphyrazine due to interaction with DNA, represent the minor outside groove binding mode without any stack aggregate formation. The thermodynamic of the binding of [Cu(II) 2,3-tmtppa](4+)-DNA also has been studied. The binding constant (K) was obtained by analysis of the optical absorption spectra of the complex at various DNA concentrations using SQUAD software. The value of K was estimated to be 2.34 x 10(5) +/- 0.06 M(-1) at 25 degrees C. The thermodynamic parameters were calculated by van't Hoff equation. The enthalpy and entropy changes were 41.83 +/- 3.28 kJ/mol and 242.08 +/- 9.88 J/mol. K at 25 degrees C, respectively. The results indicate that the process is entropy-driven and suggest that hydrophobic interactions are the main driving forces for the complex formation. Increasing of the ionic strength due to addition of NaCl destabilized porphyrazine-DNA complexes, indicating the competition of Na(+) ions with porphyrazine complexes for occupation of minor groove binding sites.
- 出版日期2010-4
