New 2-thiazol-5-yl-benzimidazoles: synthesis and determining of their potential as chemosensor reagents for polyvalent metal ions

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Thiabendazole and its analogues are widely used and reasonably well studied in terms of their biological activity, while their potential as chemosensory compounds with optical detection and sensitivity to metal ions remains unexplored. On the other hand, the introduction of a thiazole ring into the heteroaromatic system of benzimidazole significantly expands the directions of practical application of benzimidazole derivatives. Thus, one of the important structural features of the benzimidazole-thiazole system is the presence of a chelate cavity. It is a potential center of complexation with metal ions, which, with their bright fluorescence, create additional opportunities for their use as luminescent probes and chemosensors. Considering the affinity of the sulfur atom for polyvalent heavy metals, sensors based on these compounds can be used in medically and environmentally oriented analysis of toxic metal compounds. In this publication, we focus on the synthesis of various 2- and 4-substituted 2-thiazol-5-yl-benzimidazoles, as well as the determination of their spectral-fluorescence properties. Therefore, we started from 2,4-dihalogen 5-formyl thiazoles, the methods of synthesis of which are well known. Their modification in 2nd position we have described in previous works. To obtain the target products, the Weidenhagen method was chosen, which consists in the reaction of o-phenylenediamine with an aromatic or aliphatic aldehyde under oxidation conditions. For creating such conditions copper acetate was used. The possibility of coordination of metal ions by the obtained compounds was established using electronic absorption and fluorescence spectroscopy. It was found that these compounds selectively form complexes with Cd2+ and Mg2+ ions. Our qualitative studies allow us to make conclusion that the benzimidazole-thiazole fragment is a promising coordination site for metal ions, which can be used in the design of fluorescent probes for the determination of Cd2+ and Mg2+ ions.