Thymol-based Dual Chemosensor for Optical Detection of Cu2+ and Pb2+ ions and Evaluation of its Toxicity Against Plant Growth Promoting Rhizobacteria

Abstract

Abstract: Thymol is a naturally occurring monoterpenoid phenol, and its derivatives may emerge as eco-friendly materials for the development of chemosensing probes. To prepare a non-toxic chemosensing probe based on thymol moiety for the detection of metal ions. : A chemosensor (TPC) based on thymol was afforded by the reaction of thymol and piperidine in methanol. The structure elucidation of TPC was carried out with UV-Vis, 1H-NMR, 13C-NMR, and FT-IR analysis. The chemosensing properties of the synthesized probe were determined with UVvisible spectroscopy, and further, it was exploited for the determination of the concentration of Cu2+ and Pb2+ ions in spiked tap water samples. The toxicity studies of the chemosensing probe were conducted against the plant growth-promoting rhizobacteria (PGPR), i.e., Rhizobium sp., Pseudomonas sp., and Azospirillum sp. The absorption spectrum of TPC showed a band at 277 nm. The presence of Cu2+ and Pb2+ ions induced an increase in the absorption intensity at 277 nm by 2-fold and 1.5-fold, respectively. The binding constant for both TPC-Cu2+ and TPC-Pb2+ was calculated as 1.55 × 105 M-1 and 1.47 × 105 M-1, respectively. The respective limit of detection (LOD) and limit of quantification (LOQ) for Cu2+ were 623.64 × 10-6 mol L-1 and 1889.85 × 10-6 mol L-1. For Pb2+ ions, LOD and LOQ were calculated as 676.70 × 10-6 mol L-1 and 2050.60 × 10-6 mol L-1, respectively. In spiked tap water samples, percent recovery was observed in the range of 80.1 to 81.0 % and 80.1 to 81.9 % for Cu2+ and Pb2+ ions, respectively. Toxicity studies of the synthesized probe inferred that TPC was non-toxic against the tested PGPR at all the tested concentrations. In this work, we have synthesized a thymolbased chemosensor, which has been evaluated as a non-toxic sensor for Pb2+ and Cu2+ ions.