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Ethyl (S)-4-chloro-3-hydroxybutyrate ((S)-CHBE) is an important chiral intermediate in the synthesis of the cholesterol-lowering drug atorvastatin. Studying the use of SpyTag/SpyCatcher and SnoopTag/SnoopCatcher systems for the asymmetric reduction reaction and directed coupling coenzyme regeneration is practical for efficiently synthesizing (S)-CHBE. In this study, Spy and Snoop systems were used to construct a double-enzyme directed fixation system of carbonyl reductase (BsCR) and glucose dehydrogenase (BsGDH) for converting 4-chloroacetoacetate (COBE) to (S)-CHBE and achieving coenzyme regeneration. We discussed the enzymatic properties of the immobilized enzyme and the optimal catalytic conditions and reusability of the double-enzyme immobilization system. Compared to the free enzyme, the immobilized enzyme showed an improved optimal pH and temperature, maintaining higher relative activity across a wider range. The double-enzyme immobilization system was applied to catalyze the asymmetric reduction reaction of COBE, and the yield of (S)-CHBE reached 60.1% at 30 °C and pH 8.0. In addition, the double-enzyme immobilization system possessed better operational stability than the free enzyme, and maintained about 50% of the initial yield after six cycles. In summary, we show a simple and effective strategy for self-assembling SpyCatcher/SnoopCatcher and SpyTag/SnoopTag fusion proteins, which inspires building more cascade systems at the interface. It provides a new method for facilitating the rapid construction of in vitro immobilized multi-enzyme complexes from crude cell lysate. [ABSTRACT FROM AUTHOR]

Amino- and sulfhydryl- functionalized biomass carbon dots (BCDs) were prepared by one-pot reverse microemulsion for specific recognition of ferric ions (Fe3+) and L-cysteine (L-Cys). Green grapefruit peel was used as the carbon source while aminosilane and mercaptosilane were used as N- and S-supplier. Following the adsorption of Fe3+ on the surfaces of BCDs-NH2 and BCDs-SH, the fluorescence responses was quenched step by step, while adding L-Cys to the BCDs-NH2/Fe3+ system restored the fluorescence. The BCDs-NH2 and BCDs-SH system exhibited extremely low limits of detection for Fe3+ of 3.2 and 3.0 nM, respectively, within a wide linear ranges of 0.006–200 μM and 0.004–200 μM, respectively. The BCDs-NH2/Fe3+ systems were used as an optosensor for L-Cys in the concentration ranges of 0.08–30 and 30–1000 μM with a detection limit of 65 nM. Developed BCDs-NH2 and BCDs-SH were able to respond to Fe3+ in water samples with satisfactory recoveries of 100.1%-103.1% and 94.6%-108.5%, respectively, and the BCDs-NH2/Fe3+ system was also able to respond to BCDs-NH2/Fe3+ in actual lake water samples with recoveries from 87.3% to 98.8%. Meanwhile, The BCDs-NH2 exhibited good photoluminescence and stability, and the with a fluorescence quantum yield was as high as 25%. This work demonstrates the feasibility of using such materials to remove hazardous ions from water and employing the resulting complexes for optosensing in a sustainable manner. [ABSTRACT FROM AUTHOR]

This study designed a "turn-off–on" fluorescence analysis method based on carbon quantum dots (CQDs) to detect metal ions and amino acids in real sample systems. CQDs were derived from green pomelo peel via a one-step hydrothermal process. The co-doped CQDs with N and S atoms imparted excellent optical properties (quantum yield = 17.31%). The prepared CQDs could be used as fluorescent "turn-off" probes to detect Fe3+ with a limit of detection of 0.086 µM, a linear detection range of 0.1–160 µM, and recovery of 83.47–106.53% in water samples. The quenched CQD fluorescence could be turned on after adding L-cysteine (L-Cys), which allowed detection of L-Cys with a detection limit of 0.34 µM and linear range of 0.4–85 µM. Recovery of L-Cys in amino acid beverage was 87.08–122.74%. Visual paper-based testing strips and cellulose/CQDs composite hydrogels could be also used to detect Fe3+ and L-Cys. [ABSTRACT FROM AUTHOR]

Methane reforming with carbon dioxide (DRM) is one promising way to achieve carbon neutrality and convert methane to syngas for high-value chemical production. Catalyst development with better performance is the key to its potential large-scale industrial application due to its deactivation caused by carbon deposition and metal sintering. Hence, a Ni/CeO2 catalyst (Ni/CeO2-M) with higher CO2 conversion and better stability is prepared, supported on CeO2 precipitated via a novel microimpinging stream reactor. A series of ex-situ or in-situ characterizations, such as CO titration measurements, two-step transient surface reaction (two-step TSR), CO2 and CH4 temperature-programmed surface reaction (CO2-TPSR and CH4-TPSR), X-ray absorption fine structure (XAFS), and in-situ Raman spectroscopy study, were used to investigate its structure and mechanism. In contrast to Ni supported on commercial CeO2 (Ni/CeO2-C), the Ni/CeO2-M catalyst with stronger lattice oxygen mobility and higher oxygen storage capacity enhances its CO2 activation ability and carbon deposition. The Ni particle size of the Ni/CeO2-M catalyst decreased, and a higher oxidation state was obtained due to the strong metal–support interaction. Besides the reaction performance improvement of the Ni/CeO2-M catalyst, the novel microimpinging stream reactor could achieve catalyst continuous production with a high preparation efficiency. This work provides a novel method for the high-performance catalyst preparation for DRM reaction and its mechanism study gives a deep insight into high-performance catalyst development via bottom-up study. [ABSTRACT FROM AUTHOR]

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