Large Centimeter-Sized Macroporous Ferritin Gels as
Versatile Nanoreactors
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Abstract
Organized
assemblies of bionanoparticles such as ferritin provides
templates that can be exploited for nanotechnological applications.
Organization of ferritin into well-defined three-dimensional assemblies
is challenging and has attracted considerable attention recently.
We have synthesized, for the first time, large (centimeter-sized)
self-standing macroporous scaffold monoliths from ferritin bionanoparticles,
using dynamic templating of surfactant H<sub>1</sub> domains. These
scaffolds comprise three-dimensionally connected strands of ferritin,
organized as a porous gel with porosity ∼55 μm. The iron
oxide inside the ferritin scaffold can be easily replaced with catalytically
active monodisperse zerovalent transition metal nanoparticles using
a very simple protocol. Since the ferritin is cross-linked in the
scaffold, it is significantly robust with enhanced thermal stability
and better tolerance toward several organic solvents in comparison
to the native ferritin bionanoparticle. In addition, the scaffold
macropores facilitate substrate and reagent transport and hence the
monoliths containing active Pd or iron oxide nanoparticles inside
apo-ferritin bionanoparticles were used as a recyclable heterogeneous
catalyst for the oxidation of 2,3,6-trimethyl phenol to 2,3,6-trimethyl-1,4-benzoquinone
(precursor for Vitamin E synthesis) and for Suzuki–Miyaura
cross-coupling reaction in both aqueous and organic solvents. The
protein shell around the nanoparticles protects them from agglomeration,
a phenomenon that otherwise plagues nanoparticles-based catalysis.
The presence of macropores allow the ferritin scaffold to act as catalytic
monolith for continuous flow reactions having rapid reaction rates,
while offering a low pressure drop. Finally, the Pd@apo-ferritin scaffold
was immobilized inside a steel cartridge and used for the continuous
flow hydrogenation of alkenes to their corresponding alkanes for 15
cycles without any loss of activity