Searching study for the suitable ferrocenylnaphthalene diimide derivative in the electrochemical telomerase assay

Interaction of ferrocenylnaphthalene diimide 1 with the tetraplex oligonucleotide, AGGG(TTAGGG)3, which is a part of human telomere sequence, was studied in 0.1 M AcONa-AcOH (pH 5.5) containing 0.1 M NaCl coupled with 22-meric single and double stranded oligonucleotides using spectrophotometric titration experiment to search for the more suitable tetraplex DNA-binding ligand to achieve the electrochemical telomerase assay. CD spectra and polyacrylamide gel electrophoresis revealed that this tetraplex oligonucleotide kept to the single conformational structure of basket type G-quadruplex under these conditions. Scatchard analysis showed that 1 can bind to the tetraplex oligonucleotide with the binding constant of 10(5) M(-1) order, which was the highest value among the other oligonucleotides. Binding number of 1 for these oligonucleotides were ca. 2, 11, and 3 for tetraplex, double stranded, and single stranded oligonucleotides, respectively. These values were reasonable when considering with the binding mode of 1 as a threading intercalator.