Insights into the cobalt(II)-catalyzed decomposition of peroxide

Generation of a specific aptamer for accurate detection of sarafloxacin based on fluorescent/colorimetric/SERS triple-readout sensor

Sarafloxacin (SAR), one of the most widely used fluoroquinolone antibiotics, is a serious threat to aquatic environments and human health due to its illegal abuse. Herein, we first screened an aptamer (SAR-1) that specifically binds to SAR using capture-SELEX technology. Based on molecular docking technology, SAR-1 was gradually truncated, and a short SAR-1a with better affinity and specificity was obtained. The optimal SAR-1a was further combined with a Pt nanoparticle (Pt NP)- decorated bimetallic Fe/Co-MOF to fabricate a multimode sensing platform for SAR determination. The Fe/Co-MOF@Pt NPs exhibited excellent peroxidase-like activity, which catalyzed the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), thereby enabling visual detection of SAR. Meanwhile, the generated oxTMB can also produce SERS responses and be used for the SERS detection of SAR. Moreover, the inherent fluorescence property of Fe/Co-MOF@Pt NPs enabled fluorescence detection of SAR. The designed triple-readout aptasensor showed good sensitivity for SAR detection with limits of detection of 0.125 ng/mL (fluorescent mode) and 0.05 ng/mL (colorimetric and SERS mode). The aptamer-based triple-mode sensing platform provided mutual verification of detection results in different output modes, effectively improving the assay accuracy and providing a promising tool for highly sensitive, selective, and accurate determination of SAR in daily life.

Organo-photocatalytic C-H bond oxidation: an operationally simple and scalable method to prepare ketones with ambient air

Oxidative C-H functionalization with O₂ is a sustainable strategy to convert feedstock-like chemicals into valuable products. Nevertheless, eco-friendly O₂-utilizing chemical processes, which are scalable yet operationally simple, are challenging to develop. Here, we report our efforts, via organo-photocatalysis, in devising such protocols for catalytic C-H bond oxidation of alcohols and alkylbenzenes to ketones using ambient air as the oxidant. The protocols employed tetrabutylammonium anthraquinone-2-sulfonate as the organic photocatalyst which is readily available from a scalable ion exchange of inexpensive salts and is easy to separate from neutral organic products. Cobalt(ii) acetylacetonate was found to be greatly instrumental to oxidation of alcohols and therefore was included as an additive in evaluating the alcohol scope. The protocols employed a nontoxic solvent, could accommodate a variety of functional groups, and were readily scaled to 500 mmol scale in a simple batch setting using round-bottom flasks and ambient air. A preliminary mechanistic study of C-H bond oxidation of alcohols supported the validity of one possible mechanistic pathway, nested in a more complex network of potential pathways, in which the anthraquinone form - the oxidized form - of the photocatalyst activates alcohols and the anthrahydroquinone form - the relevant reduced form of the photocatalyst - activates O₂. A detailed mechanism, which reflected such a pathway and was consistent with previously accepted mechanisms, was proposed to account for formation of ketones from aerobic C-H bond oxidation of both alcohols and alkylbenzenes.

Enantioselective Radical-Type 1,2-Alkoxy-Phosphinoylation to Styrenes Catalyzed by Chiral Vanadyl Complexes

A series of vanadyl complexes bearing 3-t-butyl-5-bromo, 3-aryl-5-bromo, 3,5-dihalo-, and benzo-fused N-salicylidene-tert-leucinates was examined as catalysts for 1,2-alkoxy-phosphinoylation of 4-, 3-, 3,4-, and 3,5-substituted styrene derivatives (including Me/t-Bu, Ph, OR, Cl/Br, OAc, NO₂ , C(O)Me, CO₂ Me, CN, and benzo-fused) with HP(O)Ph₂ in the presence of t-BuOOH (TBHP) in a given alcohol or cosolvent with MeOH. The best scenario involved the use of 5 mol % 3-(2,5-dimethylphenyl)-5-Br (i.e., 3-DMP-5-Br) catalyst at 0 °C in MeOH. The desired catalytic cross coupling reactions proceeded smoothly with enantioselectivities of up to 95 % ee of (R)-configuration as confirmed by X-ray crystallographic analysis of several recrystallized products. The origin of enantiocontrol and homolytic substitution of the benzylic intermediates by vanadyl-bound methoxide and radical type catalytic mechanism were proposed.

Bimetallic Metal-Organic Framework Fe/Co-MIL-88(NH2) Exhibiting High Peroxidase-like Activity and Its Application in Detection of Extracellular Vesicles

Metal-organic frameworks (MOFs) have many attractive features, including tunable composition, rigid structure, controllable pore size, and large specific surface area, and thus are highly applicable in molecular analysis. Depending on the MOF structure, a high number of unsaturated metal sites can be exposed to catalyze chemical reactions. In the present work, we report that using both Co(II) and Fe(III) to prepare the MIL-88(NH₂) MOF, we can produce the bimetallic MOF that can catalyze the conversion of 3,3',5,5″-tetramethylbenzidine (TMB) to a color product through a reaction with H₂O₂ at a higher reaction rate than the monometallic Fe-MIL-88(NH₂). The Michaelis constants (K_m) of the catalytic reaction for TMB and H₂O₂ are 3-5 times smaller, and the catalytic constants (k_cat) are 5-10 times higher than those of the horseradish peroxidase (HRP), supporting ultrahigh peroxidase-like activity. These values are also much more superior to those of the HRP-mimicking MOFs reported previously. Interestingly, the bimetallic MOF can be coupled with glucose oxidase (GOx) to trigger the cascade enzymatic reaction for highly sensitive detection of extracellular vesicles (EVs), a family of important biomarkers. Through conjugation to the aptamer that recognizes the marker protein on EV surface, the MOF can help isolate the EVs from biological matrices, which are subsequently labeled by GOx via antibody recognition. The cascade enzymatic reaction between MOF and GOx enables the detection of EVs at a concentration as low as 7.8 × 10⁴ particles/mL. The assay can be applied to monitor EV secretion by cultured cells and also can successfully detect the different EV quantities in the sera samples collected from cancer patients and healthy controls. Overall, we prove that the bimetallic Fe/Co-MIL-88(NH₂) MOF, with its high peroxidase activity and high biocompatibility, is a valuable tool deployable in clinical assays to facilitate disease diagnosis and prognosis.

Efficient and reusable catalysis of benzylic C-H oxidation over layered [Co5(OH)6]4+ derivatives

Aerobic oxidation of benzylic C(sp³)-H bonds in a green and heterogeneous manner is a major target in organic catalysis. Herein, we report the synthesis of 3D coordination polymers containing [Co₅(OH)₆]⁴⁺ layers, affording reusable and efficient oxidation of ethylbenezene and tetralin by using O₂ as the oxidant. Moreover, the cleavage of Co^II-carboxylate bonding renders atomically thin cobaltate nanosheets and enhanced catalytic performance. This is one of the top catalytic performances for Co^II-catalyzed benzylic C(sp³)-H oxidation (∼0.02 mol% Co and 76% conversion for nanosheets), ascribed to the exposed, accessible and coordinatively unsaturated Co^II species.

Fluorine-Retentive Strategies for the Functionalization of gem-Difluoroalkenes

gem-Difluoroalkenes are readily available fluorinated building blocks, and the fluorine-induced electronic perturbations of the alkenes enables a wide array of selective functionalization reactions. However, many reactions of gem-difluoroalkenes result in a net C─F functionalization to generate monofluorovinyl products or addition of F to generate trifluoromethyl-containing products. In contrast, fluorine-retentive strategies for the functionalization of gem-difluoroalkenes remain less generally developed, and is now becoming a rapidly developing area. This review will present the development of fluorine-retentive strategies including electrophilic, nucleophilic, radical, and transition metal catalytic strategies with an emphasis on key physical organic and mechanistic aspects that enable reactivities.

Promoting Atomically Dispersed MnN4 Sites via Sulfur Doping for Oxygen Reduction: Unveiling Intrinsic Activity and Degradation in Fuel Cells

Carbon supported and nitrogen coordinated single Mn site (Mn-N-C) catalysts are the most desirable platinum group metal (PGM)-free cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) due to their insignificant Fenton reactions (vs. Fe), earth abundances (vs. Co), and encouraging activity and stability. However, current Mn-N-C catalysts suffer from high overpotential due to low intrinsic activity and less dense MnN₄ sites. Herein, we present a sulfur-doped Mn-N-C catalyst (Mn-N-C-S) synthesized through an effective adsorption-pyrolysis process. Using electron microscopy and X-ray absorption spectroscopy (XAS) techniques, we verify the uniform dispersion of MnN₄ sites and confirm the effect of S doping on the Mn-N coordination. The Mn-N-C-S catalyst exhibits a favorable oxygen reduction reaction (ORR) activity in acidic media relative to the S-free Mn-N-C catalyst. The corresponding membrane electrode assembly (MEA) generates enhanced performance with a peak power density of 500 mW cm^-2 under a realistic H₂/air environment. The constant voltage tests of fuel cells confirm the much-enhanced stability of the Mn-N-C-S catalyst compared to the Fe-N-C and Fe-N-C-S catalysts. The electron microscopy and Fourier transform XAS analyses provide insights into catalyst degradation associated with Mn oxidation and agglomeration. The theoretical calculation elucidates that the promoted ORR activity is mainly attributed to the spatial effect stemmed from the repulsive interaction between the ORR intermediates and adjacent S dopants.

Generative Algorithm for Molecular Graphs Uncovers Products of Oil Oxidation

The autoxidation of triglyceride (or triacylglycerol, TAG) is a poorly understood complex system. It is known from mass spectrometry measurements that, although initiated by a single molecule, this system involves an abundance of intermediate species and a complex network of reactions. For this reason, the attribution of the mass peaks to exact molecular structures is difficult without additional information about the system. We provide such information using a graph theory-based algorithm. Our algorithm performs an automatic discovery of the chemical reaction network that is responsible for the complexity of the mass spectra in drying oils. This knowledge is then applied to match experimentally measured mass spectra with computationally predicted molecular graphs. We demonstrate this methodology on the autoxidation of triolein as measured by electrospray ionization-mass spectrometry (ESI-MS). Our protocol can be readily applied to investigate other oils and their mixtures.

On the Mechanism of Cross-Dehydrogenative Couplings between N-aryl Glycinates and Indoles: A Computational Study

Despite the widespread use of cross-dehydrogenative couplings in modern organic synthesis, mechanistic studies are still rare in the literature and those applied to α-amino carbonyl compounds remain virtually unexplored. Herein, the mechanism of Co-catalyzed cross-dehydrogenative couplings of N-aryl glycinates with indoles is described. Density functional theory studies supported the formation of an imine-type intermediate as the more plausible transient electrophilic species. Likewise, key information regarding the role of the N-aryl group and free NH motif within the reaction outcome has been gained, which may set the stage for further developments in this field of expertise.

Cobalt-Catalyzed Selective Unsymmetrical Dioxidation of gem-Difluoroalkenes

gem-Difluoroalkenes represent valuable synthetic handles for organofluorine chemistry; however, most reactions of this substructure proceed through reactive intermediates prone to eliminate a fluorine atom and generate monofluorinated products. Taking advantage of the distinct reactivity of gem-difluoroalkenes, we present a cobalt-catalyzed regioselective unsymmetrical dioxygenation of gem-difluoroalkenes using phenols and molecular oxygen, which retains both fluorine atoms and provides β-phenoxy-β,β-difluorobenzyl alcohols. Mechanistic studies suggest that the reaction operates through a radical chain process initiated by Co(II)/O₂/phenol and quenched by the Co-based catalyst. This mechanism enables the retention of both fluorine atoms, which contrasts most transition-metal-catalyzed reactions of gem-difluoroalkenes that typically involve defluorination.

Co(II/III) Complexes with Benzoxazole and Benzothiazole Ligands as Efficient Heterogenous Photocatalysts for Organic Dyes Degradation

The problem of pollution in the current world is growing, however people’s awareness of environmental protection and ecology is also increasing. The aim of the study is to present three new Schiff base compounds with Co(II/III) ions and to assess their photocatalytic activity. The study was supported by cyclic voltammetry technique. In due course the complex 2 revealed as the most effective in AR18 degradation, even more than commercially available TiO2. The search for new photocatalysts able to decompose harmful organic dyes into environmentally friendly basic substances is becoming a new trend in the area of chemistry development.

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol^-1 above the hydroperoxide substrate and around 15 kJ mol^-1 below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O-O bond homolysis is coupled with a C-H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule-induced radical formation (MIRF) process is significantly lower than that of the unimolecular O-O bond cleavage. The same type of reaction is also possible in the self-reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co-products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen-bonding interactions.

Wettability Control of Co-SiO2@Ti-Si Core-Shell Catalyst to Enhance the Oxidation Activity with the In Situ Generated Hydroperoxide

With the aim of utilizing O₂ as an oxidant, cascade reaction strategy was usually employed by first transforming O₂ into the in situ generated hydroperoxide and then oxidized the substrate. To combine the two steps more efficiently to get a higher reaction rate, a series of core-shell catalysts with core and shell having different wettabilities were designed. The catalysts were characterized by transmission electron microscopy, UV-vis spectroscopy, Fourier transform infrared, sessile water contact angle, among other methods. These catalysts were applied in the research of the diphenyl sulfide oxidation by the in situ generated hydroperoxide derived from ethylbenzene oxidation. Through control experiments, the hydrophobic modification in the shell and core will influence different steps of the overall cascade reaction. Further insight into the reaction illustrated that the overall reaction rate was not simply an adduct of the promotion effects from the two steps, which was mainly attributed to the inhibition effect for the co-oxidation of ethylbenzene with diphenyl sulfide. Through the guidance of the relationship, a rationally designed core-shell catalyst with appropriate modifying organic groups showed an enhanced performance of the overall cascade reaction. The rational design of the catalysts would provide a reference for other cascade reactions.

Investigating homogeneous Co/Br−/H2O2 catalysed oxidation of lignin model compounds in acetic acid

The catalytic oxidation of lignin model compounds by Co/Br⁻/H₂O₂ is investigated; substituting Br⁻ for N-hydroxyphthalimide improved substrate conversion and product yield.

A copper-catalyzed radical coupling/fragmentation reaction: efficient access to β-oxophosphine oxides

The development of a novel copper-catalyzed three-component radical coupling/fragmentation cascade reaction to generate diverse β-oxophosphine oxides is reported.

Selective assembly of N1- and N2-alkylated 1,2,3-triazoles via copper-catalyzed decarboxylative cycloaddition of alkynyl carboxylic acids with ethers and azidotrimethylsilane

An efficient and regiocontrolled method for the synthesis of various N1- and N2 alkylated 1,2,3-triazoles via copper-catalyzed decarboxylative cycloaddition of alkynyl carboxylic acids with ethers and azidotrimethylsilane.

Modeling the Evolution of Crosslinked and Extractable Material in an Oil-Based Paint Model System

The construction of mechanistic models for the autoxidation of fatty acid or ester substrates found in oil paint binders is a challenging undertaking due to the complexity of the large crosslinked species that form, and the small molecules that volatilize. Building models that capture this product diversity are made possible by automating the process of network generation. This work presents a microkinetic model for the autoxidation of ethyl linoleate catalyzed by cobalt(II) 2-ethyl hexanoate. The mechanism size was controlled by using a rate-based criterion to include the most kinetically relevant reactions from among the millions of possible reactions generated. The resulting model was solved and compared to experimental metrics. Quantities such as hexanal production and the consumption of unsaturated moieties were in good agreement with experiment. Finally, the model was used to explore the effect of the catalyst concentration and temperature on key measurables.

Enhanced catalytic activity of MnCo-MOF-74 for highly selective aerobic oxidation of substituted toluene

Novel MnCo-MOF-74 catalysts were prepared and used for highly selective aerobic oxidation of substituted toluene under mild conditions.

Surface organometallic chemistry in heterogeneous catalysis

Surface organometallic chemistry has been reviewed with a special focus on environmentally relevant transformations (C–H activation, CO₂conversion, oxidation).

Expedient stereospecific Co-catalyzed tandem C–N and C–O bond formation of N-methylanilines with styrene oxides

The Co(ii)-catalyzed stereospecific sequential C–N and C–O bond formation of styrene oxides with N-methylanilines has been developed. Optically active epoxides can be coupled with high enantiomeric purity.

Influence of the lanthanide(iii) ion in {[Cu3Ln2(oda)6(H2O)6]·nH2O}n (LnIII: La, Gd, Yb) catalysts on the heterogeneous oxidation of olefins

{[Cu₃Ln₂(oda)₆(H₂O)₆]·nH₂O}_n (Ln^III: La, Gd, Yb; odaH₂: oxydiacetic acid) are reported as reusable heterogeneous catalysts in the oxidation of olefins.

Cobalt salt-catalyzed carbocyclization reactions of α-bromo-N-phenylacetamide derivatives

A Co(ii)-catalyzed carbocyclization reaction for the synthesis of 4-substituted quinolin-2-(1H)-ones is described.

Hybrid compounds assembled from copper-triazole complexes and phosphomolybdic acid as advanced catalysts for the oxidation of olefins with oxygen

Hybrid compounds of [CuI4(3atrz)₄][PMoVI11Mo^VO₄₀] (1) and [CuI6(3atrz)₆][PMo₁₂O₄₀]₂ (2) are active catalysts for olefin oxidation.

Cobalt(ii)-catalyzed oxidative esterification of aldehydes: a cooperative effect between cobalt and iodide ions

Efficient cobalt(ii) catalyzed oxidative alkoxylation of aldehydes leading to the corresponding esters is presented. Mechanism studies provide fresh insights into the cobalt mediated decomposition of TBHP in the presence of the iodide ion.