Tuning catalysis of boronic acids in microgels by in situ reversible structural variations.

The catalysis of boronic acids immobilized in polymer microgels can be modulated by bubbling with N2/CO2 gas, and in some cases by adding glucose, making their catalytic activity comparable or even superior to that of the corresponding free boronic acid monomers homogeneously dispersed in solutions and, more importantly, making these boronic-acid-containing polymer microgels able to catalyze alternate reactions that may extend the usefulness. This enhanced catalytic function of these boronic-acid-containing microgels as organoboron acid catalysts is plausibly achieved via in situ reversibly structural variations. Kinetic studies have been carried out on the model boronic-acid-catalyzed aza-Michael addition, aldol, amidation, and [4 + 2] cycloaddition reactions in order to better understand the catalytic process.

One-pot HTST synthesis of responsive fluorescent ZnO@apo-enzyme composite microgels for intracellular glucometry.

Responsive fluorescent microgels, that can selectively, reversibly, and rapidly convert the fluctuation in intracellular glucose level into fluorescence signal, have the potential use for intracellular glucometry to promote the understanding of physiology. Herein, we report one-pot synthesis of such a responsive fluorescent composite microgels, which is made of a representative apo-enzyme, apo-glucose oxidase (apo-GOx), interpenetrated in a composite gel network that is comprised of ZnO quantum dots covalently bonded onto crosslinked poly(ethylene glycol) dimethacrylate. The key of this one-pot synthesis is applying a high-temperature short-time heating (HTST) method, so that the naturally dynamic profile of apo-GOx can be maintained and harnessed on the composite microgels to allow the highly selective response to glucose over a glucose concentration range of 0-20 mM. While the composite microgels can undergo volume phase transitions and convert both an increase and a decrease in glucose concentration into fluorescence signal shortly (<1 s), the changes in average hydrodynamic diameter and fluorescence of the composite microgels can be fully reversible even after twenty cycles of adding/removing glucose, indicating a reversible and rapid time response to the glucose concentration variations. With the composite microgels as biosensors, the fluorescence of the composite microgels embedded in the model cancer cells B16F10 can be modulated in response to intracellular glucose level variations, which are derived from a change in glucose concentration in the culture medium by an external supply, or that can be triggered by biochemical reactions (with the ß-galactosidase catalysed hydrolysis of lactose as a model reaction for achieving increased glucose levels, and the GOx catalysed oxidation of glucose for achieving decreased glucose levels).

Observation of Unusual Thermoresponsive Volume Phase Transition Behavior of Cubic Poly(N-isopropylacrylamide) Microgels.

Here, we report the observation of an unusual thermoresponsive volume phase transition behavior of cubic poly(N-isopropylacrylamide) (PNIPAM) microgels. Cubic PNIPAM microgels with a mean edge size of 125 ± 41 nm were synthesized via electrochemical-initiated radical polymerization with a photovoltaic cell as power supply. In turbidity and laser light scattering studies on dilute aqueous dispersions of these cubic microgels, both the light attenuation and hydrodynamic radius variations with temperature reveal an additional transition at about 25.0 °C, besides the widely reported volume phase transition at the PNIPAM LCST that is typically found for (quasi-)spherical microgels. This unusual thermoresponsive volume phase transition behavior of the cubic microgels can be elucidated by using a core-corona model, with the contribution from each part varying at different temperatures. The finding is also checked by thermal analysis.

The preparation of Ni/Mo-based ternary electrocatalysts by the self-propagating initiated nitridation reaction and their application for efficient hydrogen production.

In the hydrogen evolution reaction (HER), multi-component electrocatalysts with a synergistic effect may possess enhanced catalytic activity and broadened applicability in both acidic and alkaline media. Herein, we developed a novel strategy via the self-propagating initiated nitridation reaction for the synthesis of Mo2C, MoNi4, and Ni2Mo3N nanocrystals as active components assembled in a multiscale porous honeycomb-like carbon (Ni/MoCat@HCC). This strategy can be realized by simply calcining (NH4)6Mo7O24 and Ni(NO3)2 precursor hybrids under a H2/Ar atmosphere at a fairly low temperature of 600 °C. It relies on the in situ thermal decomposition of (NH4)6Mo7O24 and the subsequent nitridation reaction with released NH3, thus avoiding the continuous purging of NH3 in the conventional method. The rich reaction intermediates during the calcination of bimetallic precursors also offer other catalytically active components that are controllable by varying the calcining procedure. Benefiting from the multiscale porous structure, ultrafine size of catalyst particles, and strong synergistic effect of several catalytically active components, the as-prepared Ni/MoCat@HCC exhibits extraordinary HER electrocatalytic activity with low onset overpotentials, small Tafel slopes, and excellent cycling stability in both acidic and alkaline media, outperforming most current noble-metal-free electrocatalysts. This study paves a novel way for synthesizing multi-component electrocatalysts with enhanced catalysis performance.