Synthesis of an unprecedented H-stitched binuclear crystal structure based on selective fluorescence recognition of Zn2+ in newly synthesized Schiff base ligand with DFT and imaging application in living cells

Abstract

A zinc coordinated rare binuclear complex was synthesised and characterized by elemental analysis and single-crystal X-ray diffraction. Two mononuclear units formed by two Schiff base ligands 2-((2-(pyrimidin-2-yl)hydrazono)methyl)phenol (PHP) coordinated with zinc ion are bonded together through a hydrogen atom to form the binuclear complex. Only a single H atom significantly linked the two giant mononuclear units to form this rare complex structure. Hydrogen bonding interactions and C–H⋯π interactions in the crystallographic binuclear complex result in a giant supramolecular assembly. In the solution, the PHP bound Zn²⁺ complex was investigated by several experimental procedures including UV-Vis absorption, steady state as well as time resolved fluorescence, proton NMR spectra and theoretical calculations to explain the response. NMR spectra clearly clarified the binding location and role of functional groups using the direct and neighbouring protons. Density functional theory explained the step by step formation of the H stitched binuclear complex from ligand PHP to validate the experimental outcomes. PHP selectively recognises Zn²⁺ by fluorescence “turn-on” owing to the formation of the complex in the solution. During the fluorescence study, the sensitivity was estimated from the slope of the calibration curve, and the detection limit was calculated (0.49 µM) using the 3Sigma method. The ligand is also active to detect in vitro Zn²⁺ ion in PC-3 i.e., human prostate carcinoma cells, by Confocal microscope. Therefore, the proposed PHP sensor offers a cost effective compound that can be considered as a viable alternative for Zn²⁺ ion detection and future trials for biophysical applications.