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

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. background: Owing to important biological and environmental effects of metal ions, it has become obligatory to monitor these in our surroundings. Chemosensors are molecular probes which can detect the specific analytes in the presence of multiple analytes in various media. Thymol is a naturally occurring monoterpenoid phenol having good coordination sites which can be utilized for affording chemosensors via derivatization to compounds like mannich bases, esters, imine derivatives etc. These naturally occurring non-toxic compounds and their derivatives may emerge as eco-friendly materials for development of chemosensing probes . By realizing the importance of biocompatible phenol thymol in the field of sensors, it was anticipated that the chemosensors based on thymol moiety may emerge as non-toxic probes for the detection of metal ions. objective: To synthesize thymol based chemosensor for detection of metal ions. result: The absorption spectrum of TPC showed a band at 277 nm. The presence of Cu2+ and Pb2+ ions induced increase in the absorption intensity at 277 nm by 2-fold and 1.5- fold, respectively. Although, no alteration was observed in the UV-Visible spectra with the addition of other metal ions. 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 deduced LOD and LOQ for Cu2+ was 623.64 µM and 1889.85 µM, respectively. For Pb2+ ions, LOD and LOQ was calculated as 676.70 µM and 2050.60 µM, respectively. The binding stoichiometry was estimated as 1:1 by Job’s plot method of continuous variation for both TPC-Cu2+ and TPC-Pb2+ complex. TPC was found reusable up to two cycles. The toxicity study inferred that TPC was non-toxic against all tested PGPR species at all the tested concentrations.