Electrocatalytic investigations of a tri-iron cluster towards hydrogen evolution and relevance to [FeFe]-hydrogenase

Electrochemical investigations of a tri-iron cluster, [Fe₃(μ₃-S)₂(CO)₉] (designated as Fe₃CO thereafter), which possesses a core of [Fe^IIFe^IFe^I], is described. In 0.5 M [NBu₄]BF₄/dichloromethane, the cluster exhibits a fairly reversible redox process at −1.03 V and irreversible reduction wave at ca. −1.75 V. The latter is attributed to the reductions of both the decomposed product of the monoanion, [Fe₃CO]⁻, and the isomer of this anion. This cluster catalyses proton reduction with the presence of acid HBF₄·Et₂O in dichloromethane. Possible mechanisms were proposed to elucidate its electrochemistry and electrocatalytic behaviours on proton reduction. Digital simulations were performed to verify the proposed mechanisms and kinetic parameters were generated at our best estimation in the simulations. The simulated cyclic voltammograms fit well with the experimentally observed ones, which largely supports the proposed mechanisms.     

A CMP-based [FeFe]-hydrogenase dual-functional biomimetic system for photocatalytic hydrogen evolution coupled with degradation of tetracycline

A novel bio-inspired conjugated microporous polymer (CMP) had been designed, synthesized and characterized. The mimics of [FeFe]-hydrogenase active sites were covalently attached to the CMP skeleton, which facilitates charge transfer between the light-harvesting moiety and active sites, and exhibited high performance in visible-light photocatalytic hydrogen evolution (2120 μmol·h⁻¹·g⁻¹) in an aqueous solution. The flower-like morphology, covalently linked framework and the “single active-site” effect derived from the porous skeleton were deemed to go a long way toward boosting the properties above. Interestingly, when the electron sacrifice agent (triethanolamine) was replaced by tetracycline, the CMP-based photocatalyst maintained the capability of photocatalytic hydrogen production (370 μmol·h⁻¹·g⁻¹) and realized efficient photodegradation of tetracycline simultaneously. This work provides a heuristic green dual-function strategy for constructing a sustainable and efficient photocatalytic system for hydrogen evolution with concurrent antibiotic residue degradation.     

Mg(II)-Catalyzed [4+2] Annulation for the Synthesis of 2-Arylquinoline Motifs: Applications and DFT Studies

Mg-catalyzed [4+2] cycloaddition reactions between 2-aminobenzaldehydes and ynones offered an array of 2-arylquinoline motifs merged with a CF₃-acyl group. Furthermore, with Mg-catalyzed [4+2] annulation as the key step, DDD107498, DDD102542, and Hit analogues were assembled. Finally, a computational study of the reaction mechanism was conducted.     

Application of a Synthetic Ferredoxin-Inspired [4Fe4S]-Peptide Maquette as the Redox Partner for an [FeFe]-Hydrogenase

‘Bacterial-type’ ferredoxins host a cubane [4Fe4S]^2+/+ cluster that enables these proteins to mediate electron transfer and facilitate a broad range of biological processes. Peptide maquettes based on the conserved cluster-forming motif have previously been reported and used to model the ferredoxins. Herein we explore the integration of a [4Fe4S]-peptide maquette into a H₂-powered electron transport chain. While routinely formed under anaerobic conditions, we illustrate by electron paramagnetic resonance (EPR) analysis that these maquettes can be reconstituted under aerobic conditions by using photoactivated NADH to reduce the cluster at 240 K. Attempts to tune the redox properties of the iron-sulfur cluster by introducing an Fe-coordinating selenocysteine residue were also explored. To demonstrate the integration of these artificial metalloproteins into a semi-synthetic electron transport chain, we utilize a ferredoxin-inspired [4Fe4S]-peptide maquette as the redox partner in the hydrogenase-mediated oxidation of H₂.     

Kinetics and the difference for extraction of praseodymium and neodymium from nitrate aqueous solution by[A336] [NO3] using the single drop technique

The kinetics and the difference for Pr(Ⅲ) and Nd(Ⅲ) extraction from nitrate aqueous solution using trialkylmethylammonium nitrate([A336][NO_3]) as extractant were investigated by the single drop technique.The dependence of the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) on the concentrations of free Pr(Ⅲ) and Nd(Ⅲ)ions, the concentrations of Na NO_3 and H~+in aqueous solutions, and the concentrations of [A336][NO_3] in kerosene solutions were discussed and the corresponding extraction rate equations for Pr(Ⅲ) and Nd(Ⅲ) were obtained. These equations demonstrated that the reaction rate constant of Pr(Ⅲ) with [A336][NO_3] was double than that of Nd(Ⅲ). The effect of the addition of diethylenetriaminepentaacetic acid(DTPA) on the difference in the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] was also investigated. It was revealed that the difference in the complex formation rates of Pr(Ⅲ) and Nd(Ⅲ) with DTPA made a significant impact on the difference in the extraction rates of Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3]. The ratio of extraction rates of Pr(Ⅲ) to Nd(Ⅲ) with[A336][NO_3] was in proportion to the ratio of complex formation rates of Pr(Ⅲ) to Nd(Ⅲ) with DTPA. The extraction rate difference for Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3] increased due to a higher complex formation rate constant of DTPA with the free and un-complexed Nd(Ⅲ) ions in the aqueous nitrate solution than that with Pr(Ⅲ) ions. Therefore, the addition of DTPA in the aqueous nitrate solution is an effective method to intensify the separation of Pr(Ⅲ) and Nd(Ⅲ) in kinetics. The study on the extraction mechanism indicated that both the extraction of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] were diffusion controlled, and the reactions obeyed SN2 mechanism. The present work highlights a possible approach to strengthen the kinetic separation of Pr(Ⅲ) and Nd(Ⅲ).     

[(C_2H_5)_4N]_2｛Fe_4S_4[S_2CN(C_2H_5)_2]_4｝的晶体和分子结构

本文报导含类立方烷型簇核Ｆｅ４ｓ４的金硫配位化合物［（Ｃ２Ｈ５）４Ｎ］２｛Ｆｅ４Ｓ４［Ｓ２ＣＮ（Ｃ２Ｈ５）２］４｝的合成、晶体和分子结构测定的结果。     

On the role of conserved proline residues in the structure and function of Clostridium pasteurianum 2[4Fe-4S] ferredoxin

The widespread occurrence of Pro residues adjacent to Cys ligandsin the sequences of [4Fe-4S] electron transfer proteins hasnot yet found a functional basis. The two such Pro of Clostridiumpasteurianum 2[4Fe-4S] ferredoxin have been probed by site-directedmutagenesis. Any one of them, but not both simultaneously, canbe substituted without impairing the proper folding of the protein.The reduction potentials of the ferredoxin variants fall ina narrow range of <20 mV above the potential of the nativeprotein. The biological activities with C.pasteurianum hydrogenaseand pyruvate-ferredoxin oxidoreductase do not change significantly,except when Lys replaces Pro. In these cases, the data suggestthat the two clusters of 2[4Fe-4S] ferredoxin may not alwaysbe equivalent in the interaction with the redox partners. Destabilizationof the structure has been observed as the consequence of theProl9 or Pro48 substitutions. Using 2-D NMR, this effect hasbeen associated with perturbations of both the hydrogen bondnetwork and one amino acid side chain around the [4Fe-4S] clusters.Thus, the conserved Pro found in the binding motif of [4Fe-4S]clusters in proteins strongly stabilizes the active site butdoes not play an essential role in the mechanism of electrontransfer.     

Harnessing the Power of the De Mayo Reaction: Unveiling a Photochemical and Photocatalytic Masked [2+2] Methodology for Organic Synthesis

In 1962, Paul J. de Mayo initially described the photochemical reaction involving 1,3-diketones and double bonds, resulting in the formation of 1,5-diketones. Since then, this reaction has been extensively utilized for the synthesis of a wide range of fascinating natural products. Over time, this synthetic methodology has been applied to various carbonyl systems, including locked enol-tautomers of diketones, β-keto esters, and β-enaminones. Additionally, it has found application in other unsaturated systems such as allenes and alkynes. In this review article, we provide a comprehensive overview of the classical de Mayo reaction, highlighting its scope and potential. Furthermore, we focus on recent advances achieved through photocatalytic conditions. Special emphasis is placed on the regioselectivity of the process and the underlying reaction mechanism, particularly within the context of photocatalysis.     

A Metal‐Organic Framework Brønsted Acid Catalyst: Synthesis,Characterization and Application to the Generation of Quinone Methides for [4+2] Cycloadditions

A Brønsted acid‐derived metal‐organic framework (MOF) has been developed to serve as an efficient heterogeneous catalyst for a [4+2] cycloaddition. Aromatic sulfonyl groups were successfully installed using commercially available anhydridic reagents during post‐synthetic modifications. The MIL‐101‐NH‐RSO₃H MOF catalyst was fully characterized by SEM, PXRD, FTIR, TGA and N₂ adsorption/desorption isotherm. Furthermore, a novel [4+2] cycloaddition of substituted 2‐vinyl‐substituted phenol was evaluated. The MIL‐101‐NH‐RSO₃H catalyst showed superior catalytic capabilities when compared to a few other strong homogeneous Brønsted acid catalysts. The MIL‐101‐NH‐RSO₃H catalyst is compatible with a variety of substituted substrates and it can be recycled five times without loss of yield or selectivity.

     

Gold‐Catalyzed 5‐ and 6‐exo‐dig Selective Cyclizations of Alkynyl Silyl Enol Ethers: Efficient Method for [3+2] and [4+2] Annulations onto α,β‐Enones

An efficient method for the annulation of five‐ and six‐membered rings onto α,β‐enones is described via gold‐catalyzed 5‐ and 6‐exo‐dig selective cyclizations of alkynyl silyl enol ethers.     

Allosteric Coextraction of Sodium and Metal Ions with Calix[4]Arene Derivatives 3. Effect of Propyl Groups on Size-Discrimination for the Second Coextracted Ion

A calix[4]arene derivative containing two propyl groups and two acetic acids at each distal position has been synthesized and investigated for alkali metal extraction in individual and competitive systems. In an individual system, lithium ion simultaneously loads on a single molecule of the extraction reagent up to 200%, while sodium and potassium ions load up to 150% and 100%, respectively. In a competitive system, sodium as the first ion and lithium as the second among three ions each load up to 100%. The peak shift of the extraction reagent by using ¹H-NMR spectroscopy was investigated to elucidate the extraction mechanism of alkali metals in individual and competitive systems. The complex structures and extraction reactions for three ions are proposed from the results obtained. Size discrimination is observed not only for extraction of the first ion, but also the second ion as facilitated by an allosteric effect. Coordinatively-inert propyl groups provide a narrow coordination space for the discrimination of the second coextracted ion.     

MgO-CeO2 nanocomposite: efficient catalyst for the preparation of 2-aminothiophenes and thieno[2,3-d]pyrimidin-4(3H)-one derivatives

MgO-CeO₂ nanocomposite was prepared by a co-precipitation method and characterized by X-ray diffraction (XRD), FE-SEM, and particle size distribution analysis. The XRD pattern shows the cubic phase of cerium oxide as the dominate phase. FE-SEM images show the homogeneity distribution of magnesium and cerium oxides in the sample. The mean particle size of nanocomposite determined by the dynamic light scattering technique is 66?nm. The catalytic activity of MgO-CeO₂ nanocomposite was examined on the synthesis of 2-aminothiophenes and thieno[2,3-d]pyrimidin-4(3H)-one derivatives. In all cases, products were obtained in good to excellent yields.     

Silica-modified magnetite Fe3O4 nanoparticles grafted with sulfamic acid functional groups: an efficient heterogeneous catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-one and tetrahydrobenzo[b]pyran derivatives

Silica-modified magnetite-polyoxometalates functionalized with sulfamic acid groups as hybrid nanoparticles were prepared by sulfonation of diamine-functionalized propyl group grafted on the magnetic silica-coated Fe₃O₄ nanoparticles. This heterogeneous nanocatalyst was explored to present high catalytic performance for the synthesis of 3,4-dihydropyrimidinones and tetrahydrobenzo[b]pyrans under mild reaction conditions. The properties of this nanocatalyst were characterized by FT- infrared, energy-dispersive X-ray spectrum, scanning electron microscope, X-ray diffraction, X-ray fluorescence and elemental analysis. Easy separation of the nanocatalyst by using an external magnet, recyclability, non-toxicity, versatility and high stability of the catalyst combined with low reaction times and excellent yields make the present protocol very useful and attractive for the synthesis of the titled products.