Substances for Efficient Recognition of Explosives and Mercury Obtained

14:37, August 21, 2023

The technology is simple to use, cost effective and environmentally friendly [photo report]

Russian scientists have synthesized two new fluorophores that can be used to effectively detect the presence of mercury and explosives in water. The article about the research and its results was published in the journal Molecules.

The scientists used polyethylene glycol, a widely used material, as the starting material. It is used, for example, as a base for ointments and as an ingredient in detergents. The choice of polyethylene glycol is dictated by the fact that it is also a typical component of many complexing molecules, including those used to trap metal cations and nitro explosives.

The researchers also modified polyethylene glycol with acetylene fragments. This made it possible to carry out the synthesis of fluorophores via the so-called click reaction of azide-alkyne cycloaddition.

Click reactions are designed to produce chemical products quickly, efficiently, and reliably by combining different elements and modules. In this case, the maximum number of reagent atoms is involved in the formation of the final product. In other words, the atomic efficiency is close to one hundred percent, and the number of by-products that need to be recycled is close to zero. Thus, click reactions are not only productive and economical, but also environmentally friendly and in line with the principles of "green chemistry".

Within the framework of the conducted research, the click-response was developed and realized by Mohammed Samir Mohammed, a graduate student of the Ural Federal University and a citizen of Iraq. The work was carried out under the supervision of Igor Kovalev, head of the research group for the creation of sensor materials, leading researcher of the Laboratory of Advanced Materials, Green Methods and Biotechnologies of the Ural Federal University, and UrFU professor Grigory Zyryanov.

"We used copper sulfate in the presence of ascorbic acid as the simplest catalyst for the click reaction. It is known that the addition of univalent copper causes the reaction to accelerate and proceed easily, at room temperature the atomic efficiency reaches 100 percent. As a result, only one product is formed," says Igor Kovalev.

Structurally, the fluorophores obtained resemble bolas (boleadoras). Bolas are a throwing device of South American shepherds and hunters, consisting of a rope with weights at both ends, used to catch animals. In the structure of fluorophores, polyethylene glycol serves as a bridge between molecules of heterocyclic compounds triazole and oxadiazole, which are characterized by bright emission in the visible range.

"In the course of our research, we have verified that our fluorophores actively emit absorbed light energy with quantum yields approaching the limit. In the presence of explosives, such as 2,4-dinitrotoluene and 2,4,6-trinitrotoluene (TNT), the luminescence of the fluorophores is quenched, with the bola structure contributing to the doubling of the intensity of their response to explosives. The point is that under certain external conditions, such a structure can fold in half, its ends, in this case triazole and oxadiazole molecules, come closer together, and the penetrating explosive molecule between them simultaneously extinguishes both fragments, the efficiency of fluorescence quenching doubles," explains Igor Kovalev.

According to him, due to the bola structure and the presence of polyethylene glycol in it, the synthesized fluorophores even recognize pentaerythritol tetranitrate (PETN) - a powerful explosive used in plastic explosives. PETN has low volatility, does not vaporize well, and is therefore difficult to detect.

"To solve this problem, we used PETN in the form of a solution. In this state, it successfully interacted with our fluorophores, causing them to quench," says Igor Kovalev.

In addition, both polyethylene glycol and triazole with oxadiazole interact well with mercury. Experiments have shown that even at low concentrations and in the presence of other metals - copper, cobalt, cadmium, tin, zinc, nickel and manganese - it causes a sharp quenching of synthesized fluorophores. Therefore, they can be used as highly sensitive selective chemosensors for this extremely toxic and dangerous natural pollutant.

Employees of the Postovsky Institute of Organic Synthesis of the Ural Branch of the Russian Academy of Sciences, the Ural State Medical University, Saint Petersburg State University, and the People's Friendship University of Russia (RUDN University) took part in the research. The research was financially supported by the Ministry of Science and Higher Education of the Russian Federation (Project No. 075-15-2022-1118).

Reference

Detection of explosives and toxic substances using chemosensors is one of the most convenient methods for their recognition. Notable advantages of fluorescence technologies are their simplicity, mobility, cost-effectiveness, efficiency, possibility of precise structural adjustment of the chemosensor to increase its selectivity and improve its response to detected substances.

Aleksandr Zadorozhny

The news article was translated by UrFU International Marketing Office. 
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