Synergistically Enhanced Oxidase-like Property of Core-Shell MOF Nanozymes by Decorating Au and Ag/AgCl Nanoparticles for l-Cysteine Colorimetric Sensing.

Monitoring l-cysteine (l-Cys) is of importance for human health and food safety. Herein, we designed a novel strategy for bimetallic Au and Ag/AgCl anchoring on Ni-doped ZIF-67 to form core-shell nanocubes (Ni-ZIF-67/AuAg/AgCl) using the galvanic replacement processes. The unique properties of ZIF-67 nanocubes were conducive to generating strong synergistic catalytic effects with Au and Ag/AgCl, particularly when Ni-ZIF-67/AuAg/AgCl composites were employed as oxidase mimics for catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The Ni-ZIF-67/AuAg/AgCl composites displayed strong affinity toward TMB, displaying a lower Michaelis constant Km value of 0.25 mM and a higher maximum initial rate Vmax of 9 × 10-8 M s-1. By virtue of the nanozyme, the colorimetric sensor was constructed for l-Cys detection with a relatively low detection limit of 0.051 µM. The superior catalytic performance of the as-prepared Ni-ZIF-67/AuAg/AgCl composites can be ascribed to the core-shell structure, large specific surface area, and strong synergistic catalytic effects, which are beneficial for exposing more active sites and enhancing the conductivity to further boost their catalytic activity.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis.

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Regioselective synthesis of 6-nitroindole derivatives from enaminones and nitroaromatic compounds via transition metal-free C-C and C-N bond formation.

Few methods are known for the synthesis of nitroindole derivatives. A simple and practical Cs2CO3-promoted method for the synthesis of 6-nitroindole derivatives from enaminones and nitroaromatic compounds has been developed. Two new C-C and C-N bonds were formed in a highly regioselective manner under transition metal-free conditions.

Metal-free [3 + 2 + 1] annulation of allylic alcohols, ketones, and ammonium acetate: radical-involving synthesis of 2,3-diarylpyridine derivatives.

A three-component [3 + 2 + 1] annulation strategy for the synthesis of biologically and pharmaceutically active 2,3-diarylpyridine derivatives by using a series of allylic alcohols, ketones, and ammonium acetate as substrates has been developed. The method proceeds efficiently under metal-free conditions, and the desired heterocycles could be obtained in a site-specific selectivity manner with good functional group tolerance.

Preparation of a γ-Fe2 O3 /Ag nanowire coaxial nanocable for high-performance lithium-ion batteries.

In this study, we report the design and synthesis of a silver nanowire-γ-Fe2 O3 coaxial nanocable architecture (Ag NWs@γ-Fe2 O3 nanocable) through mild oxidation of [Fe(CO)5 ] on the surface of silver nanowires followed by a calcination process. After optimization of the structural design, the Ag NWs@γ-Fe2 O3 nanocable could deliver superior lithium storage performance in terms of high reversible capacity, good rate performance, and excellent stability, such as a high reversible capacity of about 890 mA h g(-1) after 60 cycles at a current rate of 0.1 C (1.0 C=1005 mA g(-1) ). The reversible capacity remains as high as about 550 mA h g(-1) even at a high current rate of 2.0 C. This dramatic performance is mainly attributed to the smart coaxial design, which can not only alleviate the large volume change and prevent the aggregation of γ-Fe2 O3 nanoparticles, but also enables good conductivity and thus enhances fast charge transfer. The unique structural features of the Ag NWs@γ-Fe2 O3 nanocable represent a promising anode material in lithium-ion battery applications.

Enhanced oxidase mimic activity of raspberry-like N-doped Mn3O4 with oxygen vacancies for efficient colorimetric detection of gallic acid coupled with smartphone.

The content of gallic acid (GA) is positively correlated with the quality grade of tea. Here, we developed a colorimetric method based on raspberry-like N-doped Mn3O4 nanospheres (N-Mn3O4 NSs) with oxidase-like activity for GA assay. Modulating the electronic structure of Mn3O4 by N doping could promote the catalysis ability, and the produced oxygen vacancies (OVs) can provide high surface energy and abundant active sites. The N-Mn3O4 NSs presented low Michaelis-Menten constant (Km) of 0.142 mM and maximum initial velocity (Vmax) of 9.8 × 10-6 M s-1. The sensor exhibited excellent analytical performance towards GA detection, including low LOD (0.028 µM) and promising linear range (5 âˆ¼ 30 µM). It is attributed that OVs and O2- participated in TMB oxidation. Based on the reaction color changes, a visualized semi-quantitative GA detection could be realized via a smartphone-based system. It could be applied for evaluating GA quality in market-purchased black tea and green tea.

Chemo-, regio-, and stereoselective tetrafunctionalization of fluoroalkynes enables divergent synthesis of 5-7-membered azacycles.

Alkyne annulation has been widely used in organic synthesis for the construction of azacycles with unique structural and physicochemical properties. However, the analogous transformation of fluoroalkynes remains a challenge and has seen limited progress. Herein we report a 1,2,3,4-tetrafunctionalization of polyfluoroalkynes for the divergent construction of 5-7-membered (E)-1,2-difluorovinyl azacycles. The use of the fluorine atom as a detachable "activator" not only obviates the use of any transition metal catalysts and oxidizing reagents, but also ensures the [3-5 + 2]-annulation and defluorinative functionalization of fluoroalkynes with high chemo-, regio-, and stereoselectivities. This method exhibits a broad substrate scope, good functional group tolerance, and excellent scalability, providing a modular platform for accessing fluorinated skeletons of medicinal and biological interest. The late-stage modification of complex molecules, the multi-component 1,2-diamination of fluoroalkyne, and the synthesis of valuable organofluorides from the obtained products further highlight the real-world utility of this fluoroalkyne annulation technology.

Combining (CH2O)n and (NH4)2CO3 as a Formamidine Equivalent for "Four-in-One" Synthesis of Fluoroalkylated 2-H-Pyrimidines.

Multicomponent reactions hold the potential to maximize the synthetic efficiency in the preparation of diverse and complex molecular scaffolds. An unprecedented formal [3+1+1+1] annulation approach for the one-step synthesis of fluoroalkylated 2-H-pyrimidines commencing from perfluoroalkyl alkenes, paraformaldehyde, and ammonium carbonate is described. By harnessing readily accessible (CH2O)n and cheap (NH4)2CO3 as a formamidine surrogate, this method effectively replaces traditionally preformed amidines with a pyrimidine assembly. The multicomponent reaction proceeds in a step-economical, operationally simple, metal-free, and additive-free manner, featuring a broad substrate scope, excellent functional group compatibility, and scalability. The potential for the synthetic elaboration of the obtained 2-H-pyrimidine is further demonstrated in the alkylation and vinylation of its C2 position.

Polyoxometalate functionalizing CeO2 hollow nanospheres as enhanced oxidase mimics for ascorbic acid colorimetric sensing.

Phosphotungstic acid covered with CeO2 hollow nanospheres (CeO2@PTA HNSs) has been successfully prepared by a simple method, serving as highly efficient nanozymes for ascorbic acid (AA) colorimetric sensing. In virtue of the unique hollow nanostructures, oxide defects and synergic effects of CeO2 and PTA, the proposed CeO2@PTA HNSs present remarkable intrinsic oxidase-like activity and help capture electrons from 3,3',5,5'-tetramethylbenzidine (TMB). Due to the reducibility of AA, a promising colorimetric sensing platform based on CeO2@PTA HNSs has been constructed for quantitative analysis of AA. The present colorimetric detection exhibits a low limit of detection, good selectivity and stability, as well as reliability in orange juice and milk. This work provides a simple surface defect engineering to prepare high-performance oxidase mimics in the application of colorimetric biosensing.

Dual-mode sensing of hydrogen peroxide on self-assembled Ag nanoparticles anchored on polydopamine wrapping 2D Cu-MOFs.

In this study, we have fabricated a dual-signal sensor for H2O2 determination based on 2D Cu-MOFs decorated with Ag NPs. A novel polydopamine (PDA) reduction method was utilized to reduce [Ag(NH3)2]+ to highly dispersed Ag NPs in situ without other reductive agents, and Cu-MOF@PDA-Ag was obtained. For the electrochemical sensor, the Cu-MOF@PDA-Ag modified electrode exhibits outstanding electrocatalytic properties toward H2O2 reduction with a high sensitivity of 103.7 µA mM-1 cm-2, a wide linear range from 1 µM to 35 mM and a low detection limit of 2.3 µM (S/N = 3). Moreover, the proposed sensor shows good feasibility in an orange juice sample. For the colorimetric sensor, colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be oxidized by the Cu-MOF@PDA-Ag composite in the presence of H2O2. A Cu-MOF@PDA-Ag catalysis-based colorimetric platform is further established for the quantitative analysis of H2O2 ranging from 0 to 1 mM with a lower detection limit of 0.5 nM. Importantly, such a dual-signal method for the detection of H2O2 could potentially have wide practical applications.