A Dual Luminescent and Chromogenic Pt-NCN Complex for the Detection of GTP and CTP in Aqueous Media

Selective recognition of nucleotides by synthetic receptors in aqueous media is an important area in supramolecular analytical chemistry due to their key biochemical functions. However, selective receptors for GTP and CTP remain an ongoing challenge. Herein, a water-soluble [Pt(NCN)Cl] complex (NCN = 1,3-bis(benzimidazole)benzene derivative bearing two tetraethylene glycol chains), (4), was synthesized, characterized, and structurally described by single-crystal X-ray diffraction. Complex 4 was studied as receptor for the detection of nucleotides, nucleosides, and oxyanions in water at pH = 7.4, showing the greatest binding affinity for GTP (log K_1:1 = 6.85 ± 0.01) via a luminescence turn-off response, with a limit of detection (LOD) = 1.28 μM. Such GTP selectivity/affinity was ascribed to the formation of coordination bond Pt-N7 with a guanosine ring and hydrogen bonds between tetraethylene glycol chains and the triphosphate group. On the other hand, CTP induced a visual color change from colorless to green attributed to the formation of aggregates induced by Pt···Pt and π-π interactions. The logarithmic binding and oligomerization constants for CTP were determined to be 5.32 ± 0.03 and 4.55 ± 0.02, respectively, with a value of LOD = 2.29 μM. The chemosensing mechanisms were investigated by NMR spectroscopy, lifetime resolved fluorescence, Stern-Volmer quenching studies, electrospray mass spectrometry and DFT calculations.