Metal ion-directed cooperative DNA binding of small molecules

Compound (1), which consists of an oxine and a pyridinium group, was synthesized as a metal-responsive DNA binding ligand. Two 1s coordinate to a Cu(II) to form a stable dimer (12-Cu), even in the presence of DNA. The binding of 1 with sonicated calf thymus DNA was enhanced by ca. 103 times after forming the dimer; the binding constants were estimated to be 3.2 × 104 M−1 and 2.4 × 107 M−1 in the absence and the presence, respectively, of a half mole of Cu(II). The enormous acceleration of the binding is partly attributed to the generation of a dicationic charge by the formation of the dimer. High cooperativity between dimers could be also responsible; dimers would gather along the duplex as a template to form 1D spiral aggregates.