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

• Three dinuclear nickel triple-stranded supramolecular cylinders were synthesized.
• The cylinders could bind to G-quadruplexes with high binding constants.
• 1 could convert G-quadruplexes from antiparallel to hybrid structure in Na+ solution.

Three dinuclear nickel triple-stranded supramolecular cylinders [Ni2(L1)3][ClO4]4 (1), [Ni2(L2)3][ClO4]4 (2) and [Ni2(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 (Kb values ranging from 0.11–2.2 × 106 M−1). FRET melting studies indicated that the cylinders 1–3 had much stronger stabilizing effect on G-quadruplex DNA (ΔTm up to 24.5 °C) than the traditional cylinder Ni2L34+ just containing diphenylmethane spacers (ΔTm = 10.6 °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 1 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.

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