A zinc-based
metal organic framework, Zn-MOF-74, which has a unique
one-dimensional (1D) channel and nanoscale aperture size, was rapidly
obtained in 10 min using a de novo mild water-based
system at room temperature, which is an example of green and sustainable
chemistry. First, catalase (CAT) enzyme was encapsulated into Zn-MOF-74
(denoted as CAT@Zn-MOF-74), and comparative assays of biocatalysis,
size-selective protection, and framework-confined effects were investigated.
Electron microscopy and powder X-ray diffraction were used for characterization,
while electrophoresis and confocal microscopy confirmed the immobilization
of CAT molecules inside the single hexagonal MOF crystals at loading
of ∼15 wt %. Furthermore, the CAT@Zn-MOF-74 hybrid was exposed
to a denaturing reagent (urea) and proteolytic conditions (proteinase
K) to evaluate its efficacy. The encapsulated CAT maintained its catalytic
activity in the decomposition of hydrogen peroxide (H2O2), even when exposed to 0.05 M urea and proteinase K, yielding
an apparent observed rate constant (kobs) of 6.0 × 10–2 and 6.6 × 10–2 s–1, respectively. In contrast, free CAT exhibited
sharply decreased activity under these conditions. Additionally, the
bioactivity of CAT@Zn-MOF-74 for H2O2 decomposition
was over three times better than that of the biocomposites based on
zeolitic imidazolate framework 90 (ZIF-90) owing to the nanometer-scaled
apertures, 1D channel, and less confinement effects in Zn-MOF-74 crystallites.
To demonstrate the general applicability of this strategy, another
enzyme, α-chymotrypsin (CHT), was also encapsulated in Zn-MOF-74
(denoted as CHT@Zn-MOF-74) for action against a substrate larger than
H2O2. In particular, CHT@Zn-MOF-74 demonstrated
a biological function in the hydrolysis of l-phenylalanine p-nitroanilide (HPNA), the activity of ZIF-90-encapsulated
CHT was undetectable due to aperture size limitations. Thus, we not
only present a rapid eco-friendly approach for Zn-MOF-74 synthesis
but also demonstrate the broader feasibility of enzyme encapsulation
in MOFs, which may help to meet the increasing demand for their industrial
applications.