Thiadiazole Functionalized Salicylaldehyde-Schiff Base as a pH-responsive and chemo-reversible “Turn-Off” fluorescent probe for selective cu (II) detection: Logic Gate Behaviour and Molecular Docking Studies

Abstract

A novel thiadiazole functionalized schiff base chemoreceptor (E)-2,4-dichloro-6-(((5-mercapto-1,3,4thiadiazol-2-yl)imino)methyl)phenol (SB-1) has been synthesized and characterized spectroscopically by using various techniques. Its photophysical behaviour was scanned towards a variety of metal ions in mixed aqueous media. The chemosensor (SB-1) displayed excellent selectivity towards Cu 2+ ion through uorescent diminishment (turn-off phenomenon). Colorimetric analyses showed a rapid colour change from yellow to dark red under visible light upon addition of Cu 2+ ions. Interestingly, the original yellow colour reappeared back instantly after the addition of EDTA 2anions, thus con rming the reversible nature of SB-1. Competitive experiments validated no interference from the other co-existing metal ions in the recognition process of SB-1 towards Cu 2+ ion. Job's plot con rmed 1:1 binding stoichiometry between SB-1 and Cu 2+ ion with the binding constant value of 3.87×10 4 M -1 . The limit of detection was determined to be 1.01×10 -7 M suggesting good sensitivity of SB-1 towards Cu 2+ ions. Furthermore, pH-dependent UV-Vis spectral behaviour of SB-1 con rmed that it could act as an effective optical pH-sensor for highly acidic environment as well. Portable nature of probe SB-1 was explored by fabricating "easy-to-use" paper test strips, which allow robust and rapid detection of Cu 2+ ions. Based on the multi-responsive properties of SB-1, a 'NOR' logic gate was constructed by applying Cu 2+ and EDTA 2as chemical inputs (ln1: Cu 2+ , ln2: EDTA 2-) while emission intensity observed at 560 nm was considered as output signal (O1). DFT optimized geometries con rmed that chemosensor SB-1 exists in Azo form (Enol form) in its ground state. Molecular docking of the SB-1 and its copper complex, into the binding site of TRK protein tyrosine kinase (PDB: 1t46) was also carried out to explore their biological activity and their potential use as TRK inhibitors.

One-step synthesis of a pH switched pyrene-based fluorescent probe for ratiometric detection of HS− in real water samples

“…43 In 2023, a benzo-hemicyanine based pH sensitive uorescent probe for monitoring bone resorption was reported by Y. Meng et al 44 However, these previously described probes have certain drawbacks, such as they can only detect pH between 4.0 and 7.4, must be synthesised using many steps, have less Stokes shi and are not reversible for specic reactive sulphur species. [45][46][47][48][49] Keeping this in mind, herein we constructed and synthesized a pH-switched pyrene-based uorescent probe for selective HS − sensing by a reversible reaction within 5 s. In the neutral conditions, probe Pyr remained colourless in visible light and displayed bright blue emission under a UV lamp. However, under an acidic environment (pH 2.0), absorption and emission spectra were red shied, accompanied by a signicant Stokes shi (113 nm).…”