Dinuclear nickel(II) triple-stranded supramolecular cylinders: Syntheses, characterization and G-quadruplexes binding properties

Three dinuclear nickel triple-stranded supramolecular cylinders [Ni-2(L1)(3)][ClO4](4) (1), [Ni-2(L2)(3)][ClO4](4) (2) and [Ni-2(L3)(3)][ClO4](4)(3) with bis(pyridylimine) Schiff base containing triphenyl groups in the spacers as ligands were synthesized and characterized. The human telomeric G-quadruplexes binding properties of cylinders 1-3 were evaluated by means of UV-Vis spectroscopy, circular dichroism (CD) spectroscopy and fluorescence resonance energy transfer (FRET) melting assay. UV-Vis studies revealed that the supramolecular cylinders 1-3 could bind to G-quadruplex DNA with high binding constants (K-b values ranging from 0.11-2.2 x 10(6) M-1). FRET melting studies indicated that the cylinders 1-3 had much stronger stabilizing effect on G-quadruplex DNA (Delta T-m up to 24.5 degrees C) than the traditional cylinder Ni2L34+ just containing diphenylmethane spacers (Delta T-m = 10.6 degrees C). Meanwhile, cylinders 1-3 were found to have a modest degree of selectivity for the quadruplex DNA versus duplex DNA in competition FRET assays. Moreover, CD spectroscopy revealed that complex I could induce G-quadruplex formation in the absence of metal ions solution and convert antiparallel G-quadruplex into hybrid structure in Na+ solution. These results provided a new insight into the development of supramolecular cylinders as potential anticancer drugs targeting G-quadruplex DNA. (C) 2014 Elsevier B.V. All rights reserved.