Ferritin is an iron-storage protein consisting of subunits that self-assemble to form a cage of 12nm diameter and an interior cavity in which iron atoms can be localized. The external protein shell possesses both hydrophilic and hydrophobic characteristics that facilitate the uptake of iron as well as passage of other metal ions. For this reason, the iron atoms can be extracted from the cage making ferritin applicable for catalysis. The empty apoferritin can then be remineralized in vitro with a selected zero-valent metal nanoparticles, sulfides, and inorganic oxides.
Researchers led by professor David Diaz Diaz at the University of Regensburg in Germany demonstrated that iron oxide core within the ferritin scaffold can be replaced easily with catalytic active monodisperse gold nanoparticles implementing a defined protocol that avoids the complicated purification protocol normally involved in the fabrication of ferritin-encapsulated gold nanoparticles. Their research work is now published in ChemPlusChem.
The researchers first prepared macroporous ferritin hydrogel by adding an aqueous dispersion of N,N’-dimethyl-1,3-propanediamine ferritin to a surfactant and homogenized in water. They then added poly(ethylene glycol) diglycidyl ether and allowed the mixture to cool. The scaffold was allowed to cross-link and finally washed to remove the surfactant. They obtained a freestanding macro porous ferritin hydrogel. Apoferritin scaffold was then synthesized through demineralization of the resulting ferritin hydrogel.
Afterward the team incubated the resulting apoferritin hydrogel with sodium chloride solution and added chloroauric acid for about 2 h. The scaffold was then washed with water under sonication to eliminate absorbed gold nanoparticles.
The hydrogel was prepared through dynamic templating of the surfactant domains and later subjected to demineralization and remineralization processes to replace the localized iron oxide with gold nanoparticles. The authors proved the catalytic process of the gold/apoferritin hydrogels in the nitroaldol and nitroreduction reactions.
A synergistic effect was found between residues of gold nanoparticles and the protein, for the nitroaldol model reaction performed in water in the presence of tetra-n-butylammonium bromide as the phase-transfer catalyst. The researchers observed that the reduction of 4-nitroaniline and 4-nitrophenol catalyzed by the gold/apo-ferritin scaffold proceeded at a higher rate as compared to when well-known gold and silver based catalysts are used.
The study offered a proof of concept for the catalytic potential of gold/apo-ferritin hydrogel scaffolds. The synthesized hydrogels appear to be versatile nanoreactors and will facilitate development of improved antimicrobial products, optoelectronics, and catalysts and peroxidase mimics. Future research from the same group will focus on the substrate scope, possibility to undertake tandem reactions, catalyst reusability, and activity towards other reactions.
“understanding the intrinsic role of proteins in promoting the formation of chemical bonds may help to find missing links in natural evolution and the mechanisms of action of biological systems. In addition, the successful development of protein-based catalysts that are biocompatible and robust and can be mass-produced, can be very important for designing “green catalysts” Said Professor David Diaz Diaz.
Sushma Kumari Marleen Haring, Sayam Sen Gupta and David Diaz Diaz. Catalytic Macroporous Biohydrogels Made of Ferritin Encapsulated Gold Nanoparticles ChemPlusChem, volume (2017), 82, pages 225 – 232.Go To ChemPlusChem