Interaction of .DELTA.- and .LAMBDA.-[Ru(phen)2DPPZ]2+ with DNA: A Calorimetric and Equilibrium Binding Study

作者：Ihtshamul Haq, Per Lincoln, Dongchul Suh, Bengt Nordén, Babur Z. Chowdhry, Jonathan Brad Chaires · 发表于：Journal of the American Chemical Society · 年份：1995 · DOI：10.1021/ja00122a008 · 被引用次数：490 · 研究领域：Metal complexes synthesis and properties、DNA and Nucleic Acid Chemistry、Ferrocene Chemistry and Applications

Fluorescence and absorption spectroscopy, isothermal titration calorimetry, and viscosity measurements have been used to characterize the interaction of Delta and Lambda [Ru(phen)(2)DPPZ](2+) with calf thymus DNA. The method of continuous variations revealed two distinct binding stoichiometries for both Delta- and Lambda-DPPZ, corresponding to 0.7 and 3 mol of base pair/mol of ligand. Binding isotherms were obtained for the two enantiomers, both of which show strong binding to DNA, with K = 3.2 x 10(6) M(-1) bp and 1.7 x 10(6) M(-1) bp for the Delta and Lambda isomers, respectively, at 25 degrees C in solutions containing 50 mM NaCl. Titration calorimetry gave Delta H values of +0.3 kcal mol(-1) for Delta-DPPZ and +2.9 kcal mol(-1) for Lambda-DPPZ for their interaction with DNA. These small positive enthalpies, which were confirmed using thermal difference spectroscopy, indicated that the binding of these compounds to DNA is entropically driven. An enthalpy of +2.5 kcal mol(-1) was obtained for the binding of the parent compound, tris(phenanthroline)-Ru(II), to DNA. Titration of all three compounds into buffer gave a nonnegligible heat of dilution. The salt dependence of the binding constant was examined for both isomers. The slope SK = (delta logK/delta log[Na+]) was found to be 1.9 and 2.1 for the Delta and Lambda isomers, respectively. By using polyelectrolyte theory to interpret the observed salt dependence of the equilibrium constant, it can be shown that there is a sign...