Microemulsion-Assisted Synthesis of Ni(II)-Grafted Cellulose Metallogel: Structural Insights into a High-Performance...

The rapid rise of bacterial resistance presents a major global health challenge, requiring innovative therapeutic strategies against multidrug-resistant pathogens. We report a crystalline dinuclear Ni(II) Schiff base complex (NC), synthesized from an N,N,O,O-donor ligand (H₂L) and subsequently grafted onto microcrystalline cellulose to produce a porous metallogel (CNG). The material was fabricated in a CTAB/octan-2-ol/n-hexane/water microemulsion (W₀ = 38). XRD, HR-TEM, Raman, and XPS confirmed the formation of a 3D nanostructure, while DFT analyses verified repeated d-glucose attachment at active NC sites. CNG shows strong mechanical stability, shear-thinning behavior, and no sol-gel transition between 20 and 50 °C. BET measurements indicate a type II isotherm and a surface area of 240 m²/g. The β-lactamase activities of NC and CNG were evaluated using nitrocefin. CNG displays significantly enhanced hydrolytic activity over NC in 95:5 MeOH/H₂O, with pronounced pH dependence, with minimal conversion at pH 6.0 and ∼99% at pH 7.8. Water-content studies show that gel-entrapped water molecules act as internal nucleophiles, while excess water disrupts the framework and decreases activity. The hydrolysis mechanism involves Ni(II)-assisted coordination of nitrocefin via its carboxylate group, followed by nucleophilic attack of a gel-entrapped water molecule. Guanidine strongly inhibits hydrolysis, highlighting the first report of Ni(II)-anchored cellulose metallogel as a promising next-generation β-lactamase inhibitor.