Modulating the G‐Quadruplex and Duplex DNA Binding by Controlling the Charge of Fluorescent Molecules

Two fluorescent and non‐toxic spirobifluorene molecules bearing either positive (Spiro‐NMe3) or negative (Spiro‐SO3) charged moieties attached to the same aromatic structure have been investigated as binders for DNA. The novel Spiro‐NMe3 containing four alkylammonium substituents interacts with G‐quadruplex (G4) DNA structures and shows preference for G4s over duplex by means of FRET melting and fluorescence experiments. The interaction is governed by the charged substituents of the ligands as deduced from the lower binding of the sulfonate analogue (Spiro‐SO3). On the contrary, Spiro‐SO3 exhibits higher binding affinity to duplex DNA structure than to G4. Both molecules show a moderate quenching of the fluorescence upon DNA binding. The confocal microscopy evaluation shows the internalization of both molecules in HeLa cells and their lysosomal accumulation.