Design and synthesis of a carbohydrate-derived chemosensor for selective Ni(II) ion detection: A turn-off approach

Nickel, an essential transition metal, plays a vital role in biological systems and industries. However, exposure to nickel can cause severe health issues, such as asthma, dermatitis, pneumonitis, neurological disorders, and cancers of the nasal cavity and lungs. Due to nickel's toxicity and extensive industrial use, efficient sensors for detecting Ni²⁺ ions in environmental and biological contexts are essential. Carbohydrates, with their inherent water solubility and biocompatibility, are ideal for constructing chemosensors. Incorporating a pyridyl group enhances the selectivity and sensitivity of these sensors. We present a carbohydrate-derived colorimetric chemosensor 5-(2'-Pyridoylethene-1'-yl)-4-(2''-phenylethene-1''-yl)-2,3-O-isopropylidene-2,3-dihydrofuran-2,3-diol (7a) that exhibits a distinct colour change and significant fluorescence quenching upon binding with Ni²⁺ ions. The synthesis of receptor (7a) was validated by using ¹H, ¹³C NMR, HRMS, and single crystal X-ray analysis. Detection limit of receptor (7a) for Ni²⁺ was calculated to be 0.97 μM, which is below the standard (1.2 μM) set by the United States Environmental Protection Agency (EPA). The binding ratio of receptor (7a) to Ni²⁺ was determined to be 1:1 by using Job's plot. The binding constant of receptor (7a) and Ni²⁺ was calculated as 4.38 × 10⁴ M^-1 by using the Benesi-Hildebrand equation. This sensor demonstrates exceptional selectivity for Ni²⁺ ions over other metal cations. Receptor (7a) is stable and can be used to detect Ni²⁺ in the range of pH from 6 to 10. The sensor responded to Ni²⁺ ions selectively and a large number of coexisting ions showed almost no obvious interference with the detection. Our findings shed light on the potential of carbohydrate-derived chemosensors for nickel detection, paving the way for further exploration in this field. The binding mechanism of receptor (7a) to Ni²⁺ ions was proposed by Job's plot, UV-vis spectra and DFT (Density Functional Theory) calculations.