Improving the affinity of naphthalene diimide ligand to telomeric DNA by incorporating Zn2+ ions into its dipicolylamine groups

N,N′-bis[3-[3-(2,2′-dipicolyl)methylaminopropyl]-methylaminopropyl]naphthalene-1,4,5,8-tetracarboxylic acid diimide, 1, and its complex with zinc ions, 2, were investigated against telomeric sequences, [TAGGG(TTAGGG)3] and [AGGG(TTAGGG)3], which reveal different G-quadruplex structures depending on the conditions. Spectrophotometric, SPR, and CD techniques revealed that both ligands showed large binding constants to hybrid-type G-quadruplexes formed in the presence of K+ ions. Moreover, 2 revealed higher affinity to investigated oligonucleotides suggesting that complex of naphthalene diimide derivative with Zn2+, comparing to 1, provided additional electrostatic or coordination interactions between positively charged zinc ions and condensed negative charged phosphate anions from G4 DNA.