DETERMINING BINDING CONSTANTS OF METAL-COMPLEXES TO DNA BY QUENCHING OF THE EMISSION OF PT2(POP)4(4-)(POP = P2O5H22-)

The quenching of the emission of the excited state of Pt2(pop)4(4-) (p op = P2O5H22-) by metal complexes that bind to DNA has been investigat ed. The quenching rate constant decreases by up to two orders of magni tude when excess DNA is added to the solution. This change in rate con stant can be used to determine the binding constant of the quencher to DNA. This has permitted the determination of binding constants for me tal complexes where the affinity is quite high (greater-than-or-equal- to 10(5) M-1) or quite low (less-than-or-equal-to 1000 M-1). Uniquely, the precision of the determination is not dependent on the effect of DNA binding on the absorption spectrum of the metal complex, allowing for the determination of binding constants for metal complexes that ex hibit small electronic changes upon binding. In addition, the method a pparently does not depend on the loading level of metal complexes boun d to DNA. This method has made possible the first study of the binding constant of a high-affinity (K > 10(5) M-1), octahedral metallointerc alator on buffer cation concentration. With use of polyelectrolyte the ory, it can now be shown that there is a significant thermodynamic con tribution to the binding affinity from forces other than electrostatic s.