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 K1:1 = 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.