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Benzimidazole Conjugate of 1,1′-Thiobis(2-naphthol) as Switch-On Fluorescence Receptor for Ag+ and the Complex as Secondary Recognition Ensemble toward Cys, Asp, and Glu in Aqueous Methanolic Solution: Synthesis, Characterization, Ion and Amino Acid Recognition, Computational Studies, and Microscopy Features

Dessingou, Jayaraman, Mitra, Atanu, Tabbasum, Khatija, Baghel, Garima Singh, Rao, Chebrolu P.
Journal of organic chemistry 2012 v.77 no.1 pp. 371-378
2-naphthol, alkaline earth metals, amino acids, atomic force microscopy, benzimidazole, chemical reactions, electrospray ionization mass spectrometry, fluorescence, metal ions, methanol, moieties, nuclear magnetic resonance spectroscopy, organic chemistry, silver, transmission electron microscopy, ultraviolet-visible spectroscopy
A new 1,1′-thiobis(2-naphthoxy)-based receptor molecule (L) containing a benzimidazole moiety has been synthesized and characterized by ¹H NMR, ESI-MS, and elemental analysis. The selectivity of L has been explored in aqueous methanol, resulting in selective (7.5 ± 0.5)-fold switch-on fluorescence response toward Ag⁺ among 14 different transition, alkali, and alkaline earth metal ions studied. The complexation of Ag⁺ by L has been addressed by ESI-MS, ¹H NMR, and UV–vis spectra. Microstructural features of L and its Ag⁺ complex have been measured by AFM and TEM. The morphological features of L alone and L in the presence of Ag⁺ differ dramatically both in shape and size, and the ion induces the formation of chains owing to its coordinating ability toward benzimidazole. Further, the in situ [Ag⁺–L] complex was titrated against 20 naturally occurring amino acids and found that this complex acts as a secondary recognition ensemble toward Cys, Asp, and Glu by switch-off fluorescence.