Efficient fluorescent recognition of ATP/GTP by a water-soluble bisquinolinium pyridine-2,6-dicarboxamide compound. Crystal structures, spectroscopic studies and interaction mode with DNA

Abstract

The new dicationic pyridine-2,6-dicarboxamide-based compound 1 bearing two N-alkylquinolinium units was synthesized, structurally determined by single-crystal X-ray diffraction, and studied in-depth as a fluorescent receptor for nucleotides and inorganic phosphorylated anions in pure water. The addition of nucleotides to 1 at pH = 7.0 quenches its blue emission with a selective affinity towards adenosine 5′-triphosphate (ATP) and guanosine 5′-tripohosphate (GTP) over other nucleotides such CTP, UTP, ADP, AMP, dicarboxylates and inorganic anions. On the basis of the spectroscopic tools (¹H, ³¹P NMR, UV-vis, fluorescence), MS measurements and DFT calculations, receptor 1 binds ATP with high affinity (log K = 5.04) through the simultaneous formation of strong hydrogen bonds and π–π interactions between the adenosine fragment and quinolinium ring with binding energy calculated in 8.7 kcal mol⁻¹. High affinity for ATP/GTP is attributed to the high acidity of amides and preorganized rigid structure of 1. Receptor 1 is an order of magnitude more selective for ATP than GTP. An efficient photoinduced electron transfer quenching mechanism with simultaneous receptor–ATP complexation in both the excited and ground states is proposed. Additionally, multiple spectroscopic studies and molecular dynamics simulations showed that 1 can intercalate into DNA base pairs.