Tantalum-doped nanorod catalyst doubles as anti-allergy drug discovery platform

Chemists at the University of Kashan have unveiled a multifunctional nanomaterial that works equally hard as a green synthetic catalyst and as a springboard for next-generation anti-allergy drug design. In a study published in the Journal of the Saudi Chemical Society, the research team fabricated tantalum-doped nickel oxide nanorods embedded within zeolitic imidazolate framework-8 (ZIF-8), producing a hybrid nanocomposite that drove the eco-friendly synthesis of quinoline-3-carbonitrile derivatives at exceptional yields. When the researchers then subjected those same quinoline products to detailed computational screening, every derivative showed the ability to suppress histamine activation and bind strongly to the histamine H1 receptor, the molecular gateway through which allergic symptoms are triggered. The dual identity of the material, at once an industrial workhorse for chemical manufacturing and a source of pharmaceutically promising molecules, illustrates how advanced nanostructure engineering can bridge the traditionally separate worlds of catalysis and drug discovery.

The synthesis strategy combined two complementary fabrication routes. First, the team prepared tantalum-doped nickel oxide nanoparticles through a solvothermal procedure: nickel nitrate hexahydrate was dissolved in ethylene glycol, treated with aqueous ammonia to raise the pH to roughly 10 or 11, and mixed with a small quantity of tantalum pentachloride as the doping agent. The mixture was sealed in a Teflon-lined autoclave and held at 140 degrees Celsius for 12 hours, after which the solid product was washed, dried, and calcined at 550 degrees Celsius. Pure ZIF-8 was then grown from zinc nitrate and 2-methylimidazole in water at ambient temperature. To build the final hybrid, pre-sonicated Ta-doped NiO nanoparticles were mixed with the zinc and linker solutions in an ultrasound bath, and the resulting suspension underwent hydrothermal treatment at 110 degrees Celsius for 24 hours. The product emerged as a light beige solid in which the oxide nanorods were integrated into the porous framework.

A battery of structural and morphological techniques confirmed that the hybrid was real, crystalline, and well-formed. X-ray diffraction showed that the doped nickel oxide phase matched the reference pattern for cubic NiO with sharp, high-intensity peaks indicating high crystallinity and no impurity phases; applying the Scherrer equation gave an average crystallite size of 29.39 nanometers. The ZIF-8 scaffold displayed its characteristic strong reflection near 7.42 degrees in two-theta. Notably, when the two components were combined, the NiO reflections shifted slightly toward lower angles while the ZIF-8 peaks stayed put. According to Bragg’s law, that shift signals a modest expansion of the interplanar spacing within the oxide lattice, which the authors attribute to interfacial strain at the heterojunction boundaries, arising from lattice mismatch and potential coordination between the NiO surface and the nitrogen-donor sites of the imidazole linkers. The preserved ZIF-8 pattern confirmed the framework survived the integration intact.

Microscopy and spectroscopy reinforced the picture. Energy-dispersive X-ray spectroscopy mapping verified the expected elements in each material, with oxygen, nickel, and tantalum uniformly distributed in the doped oxide, carbon, oxygen, nickel, and zinc in pure ZIF-8, and carbon, nitrogen, oxygen, nickel, and tantalum spread across the final composite. Field-emission scanning electron microscopy revealed that the pure Ta-doped NiO particles formed nanorods roughly 266 nanometers long, while pure ZIF-8 crystallized as cubic particles averaging about 215 nanometers. In the hybrid, the in-situ incorporation of the oxide nanorods reshaped the final morphology into nanorods averaging 218 nanometers in length. Transmission electron microscopy confirmed that these rods formed homogeneously, with high uniformity and no agglomeration. Infrared spectroscopy picked up the expected Ni-O and Ni-O-Ta vibrations in the oxide, the imidazole ring and Zn-N stretch signatures of ZIF-8, and all of these features in the final composite, sealing the case for successful hybridization.

Porosity measurements told a subtler story. Nitrogen adsorption and desorption isotherms classified pure ZIF-8 as type IV with an H1-type hysteresis loop, while the composite showed type III behavior with an H3-type loop. The Brunauer-Emmett-Teller surface area of the hybrid came in at 183.73 square meters per gram, far below the 1187.71 square meters per gram of pure ZIF-8, and the total pore volumes and pore size distributions differed markedly as well. Hybridization, in other words, costs the framework much of its iconic surface area. Yet the catalytic performance did not suffer, because the Ta-doped NiO nanostructures brought their own active sites to the partnership, and a synergic interaction between those sites and the organic starting materials more than compensated for the loss of internal surface.

The model reaction chosen to test the catalyst was a three-component condensation of 4-bromoaniline, 4-nitrobenzaldehyde, and methyl 2-cyanoacetate to form a substituted quinoline-3-carbonitrile. After screening solvents, catalyst doses, and reaction conditions, the team settled on 14 milligrams of the Ta-doped NiO/ZIF-8 composite in ethanol under probe-ultrasound irradiation at 60 watts, which delivered a 97 percent yield. Ethanol beat water, chloroform, and acetonitrile on the combined grounds of yield, environmental friendliness, and accessibility. Raising the catalyst dose from 6 to 14 milligrams steadily improved the yield, but pushing beyond 14 milligrams brought no further gain. Under conventional reflux the reaction was slower and less productive, and without any catalyst the reaction essentially failed. The ultrasound advantage stems from acoustic cavitation: microscopic bubbles form, grow, and implode in the liquid, releasing bursts of mechanical and thermal energy directly into the reaction mixture without the need for bulk heating, which accelerates the reaction dramatically compared with conventional heating, where energy must diffuse through vessel walls and solvent.

The substrate scope proved impressively broad. Various substituted benzaldehydes bearing both electron-withdrawing and electron-donating groups, positioned at the para, meta, and ortho sites of the aryl ring, coupled with different anilines to give the desired quinoline-3-carbonitriles in consistently high yields, with electron-withdrawing substituents particularly effective, consistent with the electrophilic and nucleophilic interactions in the proposed mechanism. The authors propose that the carbonyl group is first activated by the catalyst’s active centers through interaction with the lone-pair electrons of the carbonyl oxygen, enabling a Knoevenagel condensation to form the first intermediate. The aniline nitrogen then attacks, the catalyst facilitates intramolecular cyclization and water removal, and a final aromatization step delivers the quinoline product. Unsaturated Zn-N centers on the ZIF-8 surface, together with defects and the doped oxide sites, provide the electrophilic character that drives the cascade.

Practical considerations for real-world use were also addressed. The catalyst was recovered after each run by washing with dry acetone, drying overnight at 60 degrees Celsius, and reused across six consecutive cycles with no major loss in performance. X-ray diffraction, infrared spectra, and electron microscopy of the recuperated material were essentially indistinguishable from the fresh sample, demonstrating robust structural and morphological stability. A hot filtration test, in which the catalyst was removed after only 45 seconds of stirring and the filtrate allowed to continue reacting, produced less than 10 percent yield, confirming that the reaction proceeds through genuine heterogeneous surface catalysis rather than leached species, a crucial credential for any catalyst aspiring to industrial relevance.

The second act of the study turned to medicine. Molecular docking simulations placed all 17 synthesized quinoline derivatives into the binding pocket of the histamine H1 receptor, the G protein-coupled receptor that mediates inflammation, smooth muscle contraction, and the classic symptoms of allergy. Every derivative blocked histamine activation, with interaction analysis revealing two key binding motifs: a hydrogen bond between the ligand’s nitrogen and the tyrosine 108 residue, at distances of 1.8 to 2.1 angstroms, and pi-pi stacking interactions with tyrosine 431 and phenylalanine 432, at 3.4 to 3.8 angstroms, the same aromatic contacts that stabilize known antihistamines and enable competitive displacement of histamine itself. Pharmacokinetic predictions using Lipinski’s Rule of Five and QikProp modeling showed excellent drug-likeness across the series: molecular weights under 500 grams per mole, logP values below 5, acceptable hydrogen bond donor and acceptor counts, and predicted human oral absorption of 88 to 100 percent, comfortably exceeding the 80 percent threshold for oral drug candidates. Most compounds also showed favorable Caco-2 intestinal permeability, although predicted transdermal absorption was poor, pointing to oral rather than topical delivery. The study, supported by the University of Kashan’s Department of Organic Chemistry, thus offers a rare double contribution: a green, reusable, ultrasound-driven catalytic platform for building biologically active quinolines, and a computationally validated set of anti-allergy leads poised for further preclinical development.

Subject of Research: Ta-doped NiO/ZIF-8 nanorod composites used as green nanocatalysts for quinoline-3-carbonitrile synthesis and as a platform for anti-allergy drug design targeting the histamine H1 receptor

Article Title: Nanomaterial-driven innovation: integrating catalytic quinoline synthesis and anti-allergy drug design using Ta-doped NiO/ZIF-8 nanorod composites

Article References: Mireei, N. S., Babaei, P., Kharazm, A. M., Ghasemi-Ghahsareh, A., Ebrahimi, S. M., & Rashki, S. (2026). Nanomaterial-driven innovation: integrating catalytic quinoline synthesis and anti-allergy drug design using Ta-doped NiO/ZIF-8 nanorod composites. Journal of Saudi Chemical Society, 30(5), Article 70. https://doi.org/10.1007/s44442-026-00125-2

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00125-2

Keywords: Ta-doped NiO/ZIF-8 nanocomposites, Green chemistry catalysis, Ultrasound irradiation, Quinoline-3-carbonitrile derivatives, Molecular docking, Histamine H1 receptor (HRH1), Heterogeneous catalysis, Solvothermal synthesis, Drug-likeness, ADMET, ZIF-8, Nanorods