Selective Detection of Copper Ions and Biological Activities of Isoniazid Schiff Bases

Abstract Following mechanical milling, the condensation reaction of the corresponding heterocyclic aldehydes with Isoniazid yields the Schiff base (E)‐N′‐((1H‐pyrrol‐2‐yl) methylene)isonicotinohydrazide (S1) and (E)‐N′‐(Thiophen‐2‐ylmethylene)isonicotinohydrazide (S2) supported heterocyclic derivatives. The structures of the Schiff bases, S1 and S2 were confirmed by 1 H NMR, 13 C NMR and IR spectroscopy. Copper ions (Cu 2+ ) were trapped by S1 in DMSO to form the yellow‐coloured complex Cu‐(E)‐N′‐((1H‐pyrrol‐2‐yl)methylene) isonicotinohydrazide (Cu 2+ +S1) with high sensitivity and selectivity. But the same ligand S1 could not be able to capture other metal ions tested for this work (namely, Co 2+ , Ni 2+ , Zn 2+ , Mn 2+ , Hg 2+ , Cd 2+ , Pb 2+ , Fe 2+ , and Fe 3+ ) in DMSO. UV‐visible spectroscopic results confirmed the complex formation (Cu 2+ +S1) with copper ions, but not with the other ions. Analysis of non‐covalent interactions (NCI) of ligand S1 with Ni 2+ , Cu 2+ and Zn 2+ in DMSO were investigated by density functional theory (DFT). NCI analysis of S1 by Cu 2+ ions in DMSO was in good agreement with the experimental results. S2 did not react with any metal ions used in this study to form a complex in DMSO and the same was confirmed by UV‐Visible spectra. Reasonably good antibacterial activity was observed with S1, S2, Cu 2+ +S1 compared to amoxicillin against Gram‐negative bacteria ( K. pneumoniae , E. coli ), Gram‐positive bacteria ( S. aureus , S. pneumoniae ), and fungal strain ( C. albicans ).