Recent progress in chemosensors based on pyrazole derivatives

Abstract

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016-2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

Fig. 1. Schematic representation of a colorimetric/fluorescent chemosensor.

Fig. 2. General structure of (a) pyrazole, (b) pyrazoline and (c) some fused-pyrazoles.

Fig. 3. Pyrazole-based probe for Cu²⁺ chemosensing. Three derivatives of (a) NH-pyrazole, (b) bis-pyrazole 2 and (c) pyrazoline 3 are shown.

Fig. 4. Probes for Cu²⁺ sensing based on fused pyrazoles (a) 4 and (b) 5. (c) Structural relationship between the pyrazole-based probe for Cu²⁺ sensing.

Fig. 5. (a) Pyrazoles and (b and c) pyrazolines in Zn²⁺ sensing.

Fig. 6. (a) Probe for Zn²⁺ sensing based on pyrazoline 4 and (b) structural requirements for improved Zn²⁺ ion sensing.

Fig. 7. Pyrazole-based probe for Hg²⁺ chemosensing. Three derivatives of (a) N-arylpyrazole 10, (b) N-phenylpyrazole 11 and (c) NH-pyrazole 12 are shown.

Fig. 8. Probes for Hg²⁺ sensing based on pyrazoles (a) 13 and (b) 14. (c) Structural relationship between the pyrazole-based probe for Hg²⁺ sensing.

Fig. 9. Pyrazole-based probe for Al³⁺ chemosensing. Three derivatives of (a) trialkylpyrazole 15, (b) 3-(3-pyridyl)pyrazole 16 and (c) N-(2-pyridyl)pyrazole 17 are shown.

Fig. 10. Probes for Al³⁺ sensing based on pyrazoles (a) 18 and (b) 19. (c) Structural similarity between compounds 15–19.

Fig. 11. (a) Fluorescent image of HeLa cells treated with probe 19 (5.0 μM) in the absence of Al³⁺; (b) microscope image of HeLa cells treated with probe 2a (5.0 μM) in the absence of Al³⁺; (c) merged image of frames (a) and (b); (d) microscope image of HeLa cells treated with Al³⁺ (5.0 μM) and probe 19 (5.0 μM); (e) fluorescence image of HeLa cells treated with Al³⁺ (50.0 μM) and probe 19 (5.0 μM); (f) merged image of frames (d) and (e). Reprinted with permission from ref. 112 of RSC.

Fig. 12. Probes for Fe³⁺, Cr³⁺ and Ag⁺ based on pyrazoles (a) 20, (b) 21 and (c) 22.

Fig. 13. Probes for F⁻ ions based on the pyrazole derivatives (a) 23, (b) 24, (c) 25, and (d) 26.

Fig. 14. Pyrazole-based probe for CN⁻ chemosensing. Three derivatives of (a) N-methylpyrazole 27, (b) 4-dicyanovinylpyrazole 28 and (c) N-(2-pyridyl)pyrazole 29 are shown.

Fig. 15. Probes for CN⁻ ions based on the fused pyrazoles (a) 30, (b) 31 and (c) 32–34.

Fig. 16. Probes for picric acid based on pyrazoles (a) 35 and (b) 36.

Fig. 17. Probes for tryptamine based on pyrazoles (a) 37 and (b) 38.

Fig. 18. TryptA fluorescence imaging analysis in 4 days old zebrafish embryos fed with different concentrations of TryptA (a) bright field images of pre-treated TryptA (50 μM), (b) fluorescence merged images of pre-treated TryptA (c) 10 μM of TryptA (d) 25 μM of TryptA (e) 50 μM of TryptA for 2 h followed by incubation with 37 (50 μM) for 1 h. Reprinted with permission from ref. 163. Centre National de la Recherche Scientifique (CNRS) and RSC.

Alexis Tigreros

Jaime Portilla