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.

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.

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.

Na2S·9H2O Enabled Defluorodisulfuration and Hydrodefluorination of Perfluorobutyl Tetralones: Synthesis of Trifluoromethyl 1,2-Dithioles.

An unprecedented defluorocyclization of perfluorobutyl tetralones with Na2S·9H2O was developed for the synthesis of trifluoromethyl 1,2-dithioles, which provided chemists novel access to biologically and pharmaceutically relevant organofluorides. Successive C(sp3)-F bond functionalization at the perfluoroalkyl chain is vital for the formation of four C-H/C-S/S-S bonds and a five-membered S-heterocycle assembly. Cheap, weakly toxic, and odorless inorganic sulfide Na2S·9H2O acts as both a disulfurating precursor and a hydrodefluorinating reagent in this tandem multi-bond-interconverting reaction.

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.

Defect Surface Engineering of Hollow NiCo2S4 Nanoprisms towards Performance-Enhanced Non-Enzymatic Glucose Oxidation.

Transition metal sulfides have been explored as electrode materials for non-enzymatic detection. In this work, we investigated the effects of phosphorus doping on the electrochemical performances of NiCo2S4 electrodes (P-NiCo2S4) towards glucose oxidation. The fabricated non-enzymatic biosensor displayed better sensing performances than pristine NiCo2S4, with a good sensitivity of 250 µA mM-1 cm-2, a low detection limit (LOD) of 0.46 µM (S/N = 3), a wide linear range of 0.001 to 5.2 mM, and high selectivity. Moreover, P-NiCo2S4 demonstrated its feasibility for glucose determination for practical sample testing. This is due to the fact that the synergetic effects between Ni and Co species, and the partial substitution of S vacancies with P can help to increase electronic conductivity, enrich binary electroactive sites, and facilitate surface electroactivity. Thus, it is found that the incorporation of dopants into NiCo2S4 is an effective strategy to improve the electrochemical activity of host materials.

Prism-like bimetallic (Ni-Co) alkaline carboxylate-based non-enzymatic sensor capable of exceptionally high catalytic activity towards glucose.

In this study, we fabricated a novel non-enzymatic glucose sensor based on prism-like bimetallic alkaline carboxylate (CoNi-MIM). The morphology and structure of CoNi-MIM were carefully investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical glucose oxidation of the synthesized sensor was then explored by cyclic voltammetry (CV) and chronoamperometry in alkaline medium. It was found that CoNi-MIM is the optimal choice with a remarkably high sensitivity of 5024.4 µA mM-1 cm-2, low detection limit of 56.1 nM (S/N = 3), linear response of up to 14.3 mM and excellent selectivity compared to Co-MIM, CoFe-MIM and CoMn-MIM. Furthermore, the as-fabricated sensor demonstrated appreciable practicality for the determination of glucose in real samples. These results indicate that CoNi-MIM holds a good application prospect in non-enzymatic glucose sensing.

Fabrication of Ag nanoparticles coupled with ferrous disulfide biocatalyst as a peroxidase mimic for sensitive electrochemical and colorimetric dual-mode biosensing of H2O2.

Ag nanoparticles (Ag NPs) with high electrocatalytic activity are of great significance for electrochemical sensors. Nanostructures as scaffold can solve aggregation problem of Ag NPs so that to ensure the stability. In this work, Ag NPs immobilized on FeS2 nanoprisms (Ag/FeS2) were prepared via an in-situ photocatalytic reduction approach. The enlarged electrode effective surface area, enhanced electron transfer and the synergic impact between Ag NPs and FeS2 lead to an enhanced catalytic activity. The electrochemical detection method exhibited great performance of low detection limit (0.6 µM), wide linear range and high sensitivity (244.4 µA mM-1 cm-2) for H2O2. Moreover, Ag/FeS2 as a peroxidase mimic can catalyze oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue product (oxTMB) by H2O2, which achieved effective detection of H2O2 with a 3.0 µM detection limit. A promising way was successfully eatablished to perform the quantitation of H2O2 in serum and beverage.

Facile construction of an Ag/MoSe2 composite based non-enzymatic amperometric sensor for hydrogen peroxide.

We report an electrochemical non-enzymatic method for hydrogen peroxide (H2O2) detection based on Ag nanoparticle-decorated MoSe2 (Ag/MoSe2-500) hybrid nanostructures. These hybrid nanocomposites are easily prepared by in situ reduction of Ag+ on the surface of MoSe2. Benefiting from the strong synergy of Ag nanoparticles and MoSe2 nanosheets in enhancing electrical conductivity, the Ag/MoSe2-500 hybrid nanostructures perform excellent sensing activity for H2O2 electrocatalytic reduction with a wide linear range of 0.02-15.2 mM, a high sensitivity of 400.0 µA mM-1 cm-2 and a low detection limit of 0.39 µM (S/N = 3). Furthermore, the sensor displays satisfactory reproducibility and stability and is applicable for practical quantitative analysis of H2O2 in milk and orange juice samples. In a word, Ag/MoSe2-500 nanocomposites are promising candidates for non-enzymatic H2O2 sensing in the fields of biology and food science.

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.

Efficient improvement in non-enzymatic glucose detection induced by the hollow prism-like NiCo2S4 electrocatalyst.

Hollow prism-like NiCo2S4 materials (NiCo2S4 HNPs) were successfully fabricated by a two-step method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) confirmed the morphology and structure of the as-prepared NiCo2S4 nanoprisms. A non-enzymatic sensor based on NiCo2S4 HNPs was constructed with outstanding electrochemical activity towards glucose oxidation in alkaline medium. The sensor showed a rapid response time (∼0.1 s), a high sensitivity of 82.9 µA mM-1 cm-2, a wide linear range (0.005-20.2 mM) and a detection limit of 0.8 µM (S/N = 3) with a good selectivity and reproducibility. Additionally, the proposed electrode also confirmed the feasibility in practical blood serum. These results indicate that NiCo2S4/ITO has great potential in the development of non-enzymatic glucose sensor applications.

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.

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.

Vitamin B1-catalyzed aerobic oxidative esterification of aromatic aldehydes with alcohols.

A straightforward aerobic oxidative esterification of aryl aldehydes with alcohols has been developed for the synthesis of substituted esters by employing vitamin B1 as a cost-effective, metal-free, and eco-friendly NHC catalyst. Air is used as a green terminal oxidant. The reaction is a useful addition to the existing NHC-catalytic oxidative esterification.

Self-template formation of porous Co3O4 hollow nanoprisms for non-enzymatic glucose sensing in human serum.

A novel type of porous Co3O4 hollow nanoprism (HNP) was successfully prepared using tetragonal cobalt acetate hydroxide [Co5(OH)2(OAc)8·2H2O] as precursor by a facile solvothermal process and a subsequent calcination treatment. The morphology and structure of the Co3O4 HNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and N2 adsorption-desorption measurements. An enzyme-free glucose sensor was constructed based on the Co3O4 HNPs, and the electrochemical performance was tested by cyclic voltammetry (CV) and chronoamperometry. The as-prepared sensor exhibited a good electrocatalytic activity for glucose oxidation at the applied potential of 0.6 V in alkaline solution, with a high sensitivity of 19.83 µA mM-1 cm-2 and a high upper limit of 30 mM, which provide the potential for direct determination of blood glucose without any dilution pretreatment. The Co3O4 HNPs had a porous and tubular structure with a large amount of accessible active sites, which enhanced the mass diffusion and accelerated the electron transfer. Moreover, the sensor also demonstrated a desirable stability, selectivity and reproducibility, and could verify the non-enzymatic analysis of glucose in real samples.

Combining Fluoroalkylation and Defluorination to Enable Formal [3 + 2 + 1] Heteroannulation by Using Visible-Light Photoredox Organocatalysis.

A metal-free, visible-light photoredox-catalyzed three-component [3 + 2 + 1] heteroannulation for accessing modular fluoroalkylated pyrimidines from readily available silyl enol ether, amidine, and fluoroalkyl halide is developed. This protocol distinguishes itself by broad functional group tolerance in a regioselective manner, which provides a complement to the existing methods for the construction of pharmaceutically and biologically active organofluorine compounds.

Copper-catalyzed three-component cyclization of amidines, styrenes, and fluoroalkyl halides for the synthesis of modular fluoroalkylated pyrimidines.

An efficient copper-catalyzed three-component cyclization for the construction of highly functionalized pyrimidine derivatives from readily available amidines, styrenes and fluoroalkyl halides is developed. This protocol distinguishes itself by the formation of three new C-C/C-N bonds and a new six-membered ring through a radical addition/oxidation/cyclization sequence in a one-pot manner.

Formation of porous nitrogen-doped carbon-coating MnO nanospheres for advanced reversible lithium storage.

Herein, we have developed a facile and effective approach for synthesizing a novel kind of porous nitrogen-doped carbon-coated MnO nanosphere. The porous Mn2O3 nanospheres are initially obtained by the calcination treatment of a coordination self-assembled aggregation precursor (referred to as Mn(OAc)2-C-8). Then, MnO@N-doped carbon composites (MnO@NCs) are obtained by the calcination of the Mn2O3 nanospheres coated with polydopamine (Mn2O3@PDA). The MnO@NCs are evaluated as an anode for lithium ion batteries (LIBs), which exhibit high specific capacity, stable cycling performance (1096.6 mA h g-1 after 100 cycles at 100 mA g-1) and high coulombic efficiency (about 99% over 100 cycles). The unique structure design and synergistic effect not only settle the challenges of low conductivity and poor cycling stability of transition metal oxides but also resolve the imperfection of inferior specific capacity of traditional graphite materials. Importantly, it may provide a commendable conception for developing new-fashioned anode materials to improve the lithium storage capability and electrochemical performance.

One-pot synthesis of PtRu nanodendrites as efficient catalysts for methanol oxidation reaction.

Bimetallic Pt-based nanodendrites are of particular interest in various catalytic applications due to their high surface areas and low densities. Herein, we provide a facile method for one-pot synthesis of PtRu nanodendrites via the co-reduction of Pt and Ru precursors in oleylamine by H2. The as-fabricated PtRu nanodendrites exhibit superior catalytic activity and durability compared with PtRu nanocrystals (NCs), synthesized under the same reaction conditions, and the commercial Pt/C catalyst towards the methanol oxidation reaction (MOR).

Rapid and large-scale synthesis of bare Co3O4 porous nanostructures from an oleate precursor as superior Li-ion anodes with long-cycle lives.

In this study, we describe a rapid and environmentally friendly synthesis of bare Co3O4 nanocrystals derived from Co(ii) oleate complexes by calcination treatment. When directly used as anode materials for lithium-ion batteries (LIBs), the as-prepared nanocrystals could deliver a high reversible capacity of 980 mA h g(-1) after 250 cycles at a current density of 100 mA g(-1) and excellent cycling performance, which may be beneficial to promote the further development of the next generation of lithium ion batteries. The synthetic route can offer great advantages for the flash preparation of other metal oxide nanocrystals for energy storage application.