Design and development of imidazo[4,5-f] [1,10] phenanthroline-Zn(ii) based fluorescent probes for specific recognition of ATP with tunable optical responses and probing the enzymatic hydrolysis of ATP by alkaline phosphatase

Abstract

The development of chemosensors for the selective detection of specific biologically important analytes continues to be of great attention in contemporary analytical chemistry. Among the several biologically important analytes, selective detection of adenosine 5′-triphosphate (ATP), is extremely crucial as this is considered as a primary energy source of all living organisms, and responsible for intracellular energy transfer that in turn controls several cellular functions. In this context, imidazo [4,5-f] [1,10] phenanthroline-based Zn(II) complexes, (P1)₂Zn, (P2)₂Zn, and (P3)₂Zn, with three different benzene analogue substitutions at the 2 position were prepared. These metal complexes selectively detect ATP over other phosphate-based biologically important anions (P₂O₇⁴⁻, HPO₄²⁻, H₂PO₄²⁻, and PO₄³⁻) and nucleotides (AMP, ADP, CTP, UTP, and GTP) with different optical responses in physiological conditions. DFT studies exhibited that this variation in the emission responses of these metal complexes in the presence of ATP is tuned by the electron-donating and withdrawing ability of the para positional functional group of phenyl ring substitution at the 2 position of the imidazole ring. Our results provide a new strategy to achieve tunable optical responses with a specific targeted analyte by simply changing the para positional functional group of the 2 substituted terminal phenyl ring of the imidazo [4,5-f] [1,10] phenanthroline-based system. Furthermore, this excellent selectivity towards ATP for these three Zn(II) based fluorescent probes helps to develop real-time turn-on fluorescence assays for estimating the enzymatic activity of alkaline phosphatase (ALP) under physiological conditions. Furthermore, our studies with human blood serum established the possibility of using our (Pn)₂Zn based sensing strategy for the quantitative estimation of ALP in biological fluids. These results evidently validate the possibility of using this sensing strategy using (Pn)₂Zn in clinical biology and diagnostic applications.