Pyrenebutylamidopropylimidazole as a multi-analyte sensor for 3,5-dinitrosalicylic acid and Hg²⁺ ions

Pyrenebutylamidopropylimidazole 1 was synthesized as a sensor for 3,5-dinitrosalicylic acid (3,5-DNSA) and 5-nitrosalicylic acid (5-NSA), among other aromatic carboxylic acids, and Hg²⁺ among different metal ions in PBS-EtOH (5:95; pH=7.4) solutions. The sensing ability of probe 1 was examined using fluorescence and ¹H NMR spectroscopy. The presence of 3,5-DNSA and 5-NSA resulted in 97% and 50% quenching, respectively, of the emission intensity at λ_max=379 nm of probe 1, whereas the presence of Hg²⁺ resulted in the selective development of an excimer band at 476 nm with simultaneous quenching of the monomer emission. Probe 1 had good association constants with 3,5-DNSA (K_a=4.38×10⁴ M^-1) and 5-NSA (K_a=2.37×10⁴ M^-1) in a 1:1 stoichiometry in PBS-EtOH (5:95; pH=7.4) solution, whereas the presence of Hg²⁺ led to the formation of a 1:2 complex between Hg²⁺ and probe 1 with a high association constant (K_a=9.76×10⁴ M^-1). These results were further supported by energy-minimization density functional theory calculations.