Fluorescence-Based Chemosensor Developed for Analyzing Chromium Ions

In a recent study led by scientists from CSIR – Central Leather Research Institute in Tamil Nadu, India, a new fluorescence-based chemosensor was developed for selectively detecting trivalent chromium (Cr³⁺) ions in different samples. The scientists published their findings in Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (1).

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Chromium is a mineral that occurs naturally in places like soil, rocks, plants, animals, volcanic dust, and gases. Drinking water systems can be highly contaminated by chromium, since large amounts of chromium compounds can be released into water bodies by industrial processes, such as leather tanning, smelting, and electroplating. Chromium is also used as a corrosion inhibitor in water pipes, which increases the risk of contamination.

While it can be dangerous to be exposed to chromium in water, trivalent chromium (Cr³⁺) is essential to human survival and wellness. Chromium can form a compound in the body that enhances the effects of insulin and help lower glucose levels. Other studies show chromium has potential benefits in fighting polycystic ovary syndrome (PCOS), which is linked to insulin resistance (2). Chromium deficiency can increase the risk of diabetes and cardiovascular diseases in human beings, and trivalent chromium is important for metabolizing lipids and proteins. However, if the concentration exceeds 50–200 µg per day, then it can cause cross-linkage of proteins or DNA, resulting in potentially cancerous mutations. Further, under oxidizing conditions, trivalent chromium can potentially convert into more fatal hexavalent chromium. As such, environmental chromium detection is necessary. The maximum permissible level of chromium in drinking water is 0.05 µg mL⁻¹ and the total chromium has a maximum contamination limit of 0.1 µg mL⁻¹. The concentration window between its toxicity and essentiality is low, meaning that an efficient, practical, focused, sensitive, and rapid detection for Cr³⁺ analysis in biological and environmental samples is needed.

In this study, a simple single step one pot multicomponent reaction was performed to synthesize N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2-a]pyridine-3-amine (TBFIPA). With this, the scientists utilized the synthesized compound alongside a library of cations to study its ability for selectively and sensitively detecting specific metal ions. With Cr³⁺ and other chromium ions, selective detection with TBFIPA was found from the significant hypsochromic shift (335 nm → 285 nm) in the UV–Visible spectra. This sensing mechanism was then confirmed by 1H nuclear magnetic resonance (NMR) titrations and electrospray ionization–mass spectrometry (ESI–MS) spectroscopic techniques. From there, theoreticaldensity functional theory (DFT) calculations were made to corroborate the experimental studies, while selective Cr³⁺ detection was demonstrated using fluorescence imaging of onion epidermal cells.

All the experimental confirmation for complex formation was corroborated with theoretical DFT studies optimized using a RB3LYP/6-31G(d) basis set. TBFIPA’s selectivity and sensitivity towards Cr³⁺ ions were found suitable for the scientists to design user-friendly silica-based portable test kit. The results obtained for biological, environmental, and industrial samples showed solid evidence for TBFIPA in estimating chromium ions in real samples. Though there is more research to do, this system can help regulate chromium content and ensure that peoples’ intake is in the proper amounts.

References

(1) Divya, D.; Ramanjaneyulu, M.; Nandhagopal, M.; Srinivasan, V.; Thennarasu, S. A Fluorescent Chemosensor for Selective Detection of Chromium (III) Ions in Environmentally and Biologically Relevant Samples. Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 2024, 316, 124286. DOI: 10.1016/j.saa.2024.124286

(2) Sheikh, Z. Chromium. WebMD LLC 2023. https://www.webmd.com/diet/supplement-guide-chromium (accessed 2024-5-23)