The easy synthesis of new N-substituted 5-oxindoline-rhodanines and their sensing ability: the recognition of acetate ions in aqueous solution

Abstract

Recently, there has been increasing interest in developing innovative synthetic strategies for the decoration of rhodanine-cores. In addition, detection of anions from an aqueous organic solvent medium has attracted lots of interest as it is commonly observed in most environmental and biological systems. For this purpose, new N-substituted 5-oxindoline-rhodanine derivatives containing important aromatic groups were synthesized via an easy and effective synthetic approach, and their anion sensing properties were evaluated by colorimetric and fluorometric detection and ¹H-NMR spectroscopy. The study revealed that the specific ion affinity for AcO⁻ ions in aqua systems and the multi-ion affinity for AcO⁻, BnO⁻, CN⁻, and F⁻ in organic solvents resulted in drastic color and spectral changes. According to the data obtained, while the peak intensity increased at 386 nm, the peak intensity decreased at 253 nm in the absorption spectrum of 5-OxI-Rh and an increase in the fluorescence intensity of 5-OxI-Rh was observed in the presence of AcO⁻ ions. The binding ratio of 5-OxI-Rh to AcO⁻ was found to be 1 : 1 according to Job's plot experiments. The binding constants were calculated using the Benesi–Hildebrand equation and found to be 6.51 × 10³ M⁻¹ for AcO⁻. Based on these concentration dependent fluorescence and absorbance changes, the LOD and LOQ values were also calculated and found to be 6.4 μM and 19.3 μM for AcO⁻, respectively. Overall, the results suggest that 5-OxI-Rh is a good selective candidate turn on sensor that can be used for AcO⁻ detection in industrial wastewaters.