A bio-compatible pyridine–pyrazole hydrazide based compartmental receptor for Al3+ sensing and its application in cell imaging

Abstract

For practical applications, the development of bio-compatible organic molecules as p-block ion chemosensors is critical. Herein, we report the single crystal (SC) of new pyridine–pyrazole derived Al³⁺ sensor H₂PPC [(Z)-N'-(2,3-dihydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] as well as its Cu-complex SC. The probe exhibits an “off–on” fluorescence response towards Al³⁺ ions, and this has been modulated with different solvents. For selective detection of Al³⁺ ions, a special coordination pocket in the structural backbone is advantageous. The chemosensor exhibits a submicromolar detection level (LOD = 4.78 μM) for Al³⁺. The density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of H₂PPC and [Al(HPP)₂]⁺ (1) reveal that a change of the structural conformation of probe H₂PPC upon complexation causes the pyrazole and pyridine units to create a specific cavity to tether Al³⁺, and consequently H₂PPC proves to be a promising molecule for Al³⁺ detection. Furthermore, the probe has been successfully used to evaluate Al³⁺ as a low-cost kit using filter paper strips, and the in situ Al³⁺ ion imaging in Vero cells as well as A549 cell lines shows the sensor's nuclear envelope penetrability, indicating that it has great potential for biological and environmental applications.