Fluorescent sensing of Al³⁺ by benzophenone based Schiff base chemosensor and live cell imaging applications: Impact of keto-enol tautomerism

Developing simple probes to sense Al³⁺ in vivo and in vitro in real time is highly desirable as Al³⁺ imbalance has been linked to a variety of diseases in human being. Here, we introduce a new, highly selective and sensitive Schiff base chemosensor, H₂bpet, based on benzophenone that can detect Al³⁺ in a 0.01% ethanol in 50 mM HEPES buffer medium by fluorimetric sensing. The structure of the probe, H₂bpet involves existence of keto−–enol tautomerism. Single crystal X-ray diffraction study reveals prevalence of keto form of H₂bpet in the solid state. The binding properties of H₂bpet with Al³⁺ was thoroughly investigated by fluorescence spectroscopy and ESI–MS analyses. The binding of Al³⁺ to the probe H₂bpet, induces distinct ¹H and ¹³C NMR shifts in favour of H₂bpet (keto form):Al³⁺ aggregate. The sensing mechanism of H₂bpet toward Al³⁺ and composition of H₂bpet:Al³⁺ aggregate was proposed and established by DFT/TDDFT calculations. Its application in fluorescent imaging in HepG2 cells was also tested. This report demonstrates an advancement in detection of Al³⁺ with the introduction of a new benzophenone containing Schiff base chemosensor.