Ultrasmall Ruthenium Nanoclusters Anchored on Thiol-Functionalized Metal–Organic Framework as a Catalyst for the Oxygen Evolution Reaction

The rational design of an efficient nanocatalyst is pivotal for catalyzing kinetically sluggish oxygen evolution reaction (OER). However, the uncontrolled nucleation and growth of nanostructures present significant challenges in the effectiveness and economic viability of implementing noble metal-based electrocatalysts. Functionalized metal–organic frameworks (MOFs) exhibit properties that can stabilize unstable nanoclusters in extremely small sizes by mitigating issues related to high surface energy and Ostwald’s ripening effect. In this study, we present the synthesis of ultrasmall Ruthenium nanoclusters stabilized through a thiol-functionalized Ni-MOF (RuNC/Ni-M-SH). The stabilization of ruthenium under reduced conditions on the MOF surface is facilitated by the lower electronegativity and increased orbital overlapping effect of sulfur, resulting in an average size of 1.5 nm. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy studies confirm a perturbed electronic structure, providing a fundamental understanding of electronic redistribution. With this favorable electronic structure, the catalytic OER activity of RuNC/Ni-M-SH surpasses that of the state-of-the-art RuO2, exhibiting a 3-fold increase in current density (242 mA cm–2) and a 82 mV reduced overpotential. Furthermore, in situ FTIR and Raman analyses were performed to analyze the catalytically active sites and intermediates. With 95% faradaic efficiency, the turnover frequency (TOF) and mass activity of RuNC/Ni-M-SH are several orders of magnitude higher than RuO2. Remarkably, unlike other Ru-based catalysts, RuNC/Ni-M-SH demonstrates exceptional high stability, as evidenced by over 24 h of chronoamperometry study. These attributes of RuNC/Ni-M-SH established it as an economically sustainable OER electrocatalyst

Designing Configurable Soft Microgelsomes as a Smart Biomimetic Protocell

Self-assembly is an intriguing aspect of primitive cells. The construction of a semipermeable compartment with a robust framework of soft material capable of housing an array of functional components for chemical changes is essential for the fabrication of synthetic protocells. Microgels, loosely cross-linked polymer networks, are suitable building blocks for protocell capsule generation due to their porous structure, tunable properties, and assembly at the emulsion interface. Here, we present an interfacial assembly of microgel-based microcompartments (microgelsomes, MGC) that are defined by a semipermeable, temperature-responsive elastic membrane formed by densely packed microgels in a monolayer. The water-dispersible microgelsomes can thermally shuttle between 10 and 95 °C while retaining their structural integrity. Importantly, the microgelsomes exhibited distinct properties of protocells, such as cargo encapsulation, semipermeable membrane, DNA amplification, and membrane-gated compartmentalized enzymatic cascade reaction. This versatile approach for the construction of biomimetic microcompartments augments the protocell library and paves the way for programmable synthetic cells

Bienzymatic Sequential Reaction on Microgel Particles and Their Cofactor Dependent Applications

We report, the preparation and characterization of bioconjugates, wherein enzymes pyruvate kinase (Pk) and l-lactic dehydrogenase (Ldh) were covalently bound to poly­(<i>N</i>-isopropylacrylamide)-poly­(ethylenimine) (PNIPAm-PEI) microgel support using glutaraldehyde (GA) as the cross-linker. The effects of different arrangements of enzymes on the microgels were investigated for the enzymatic behavior and to obtain maximum Pk-Ldh sequential reaction. The dual enzyme bioconjugates prepared by simultaneous addition of both the enzymes immobilized on the same microgel particles (PL), and PiLi, that is, dual enzyme bioconjugate obtained by combining single-enzyme bioconjugates (immobilized pyruvate kinase (Pi) and immobilized lactate dehydrogenase (Li)), were used to study the effect of the assembly of dual enzymes systems on the microgels. The kinetic parameters (<i>K</i>_m, <i>k</i>_cat), reaction parameters (temperature, pH), stability (thermal and storage), and cofactor dependent applications were studied for the dual enzymes conjugates. The kinetic results indicated an improved turn over number (<i>k</i>_cat) for PL, while the <i>k</i>_cat and catalytic efficiency was significantly decreased in case of PiLi. For cofactor dependent application, in which the ability of ADP monitoring and ATP synthesis by the conjugates were studied, the activity of PL was found to be nearly 2-fold better than that of PiLi. These results indicated that the influence of spacing between the enzymes is an important factor in optimization of multienzyme immobilization on the support