Monthly Archives: March 2024

On the Existence of Pnictogen Bonding Interactions in As(III) S‐Adenosylmethionine Methyltransferase Enzymes

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On the Existence of Pnictogen Bonding Interactions in As(III) S-Adenosylmethionine Methyltransferase Enzymes

This study advances our understanding of As(III) interactions in biological systems, revealing the important role of pnictogen bonding in As(III) S-adenosylmethionine methyltransferases. The noncovalent As⋅⋅⋅O pnictogen bonds have been analyzed energetically and characterized studied using a variety of computational tools.


Abstract

As(III) S-adenosylmethionine methyltransferases, pivotal enzymes in arsenic metabolism, facilitate the methylation of arsenic up to three times. This process predominantly yields trivalent mono- and dimethylarsenite, with trimethylarsine forming in smaller amounts. While this enzyme acts as a detoxifier in microbial systems by altering As(III), in humans, it paradoxically generates more toxic and potentially carcinogenic methylated arsenic species. The strong affinity of As(III) for cysteine residues, forming As(III)-thiolate bonds, is exploited in medical treatments, notably in arsenic trioxide (Trisenox®), an FDA-approved drug for leukemia. The effectiveness of this drug is partly due to its interaction with cysteine residues, leading to the breakdown of key oncogenic fusion proteins. In this study, we extend the understanding of As(III)′s binding mechanisms, showing that, in addition to As(III)−S covalent bonds, noncovalent O⋅⋅⋅As pnictogen bonding plays a vital role. This interaction significantly contributes to the structural stability of the As(III) complexes. Our crystallographic analysis using the PDB database of As(III) S-adenosylmethionine methyltransferases, augmented by comprehensive theoretical studies including molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) analysis, emphasizes the critical role of pnictogen bonding in these systems. We also undertake a detailed evaluation of the energy characteristics of these pnictogen bonds using various theoretical models. To our knowledge, this is the first time pnictogen bonds in As(III) derivatives have been reported in biological systems, marking a significant advancement in our understanding of arsenic‘s molecular interactions.

Synthesis and in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes activity of aldehyde and Schiff base substituted cobalt (II), copper (II), and zinc (II) phthalocyanines

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Synthesis and in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes activity of aldehyde and Schiff base substituted cobalt (II), copper (II), and zinc (II) phthalocyanines

Synthesis and characterization of 4-(5-(diethylamino)-2-formylphenoxy)phthalonitrile, aldehyde-, and Schiff base-substituted peripheral tetra-substituted Co(II), Cu(II), and Zn(II) phthalocyanine compounds. In vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes activity of aldehyde- and Schiff base-substituted cobalt (II), copper (II), and zinc (II) phthalocyanines


In this work, a series of aldehyde-substituted phthalocyanine compounds (1, 3, and 5) were prepared by the cyclotetramerization of the 4-(5-(diethylamino)-2-formylphenoxy) phthalonitrile (a) and the corresponding metal salts. Schiff base-substituted phthalocyanines (2, 4, and 6) were derived from an aldehyde-substituted phthalocyanine (1, 3, and 5) via the reaction of aldehyde-substituted phthalocyanines with an amine reagent. The compounds that were obtained were characterized using FT-IR, 1H {13C} NMR, UV–Vis, and MS spectra (a and 1–6). The inhibitory qualities of synthesized aldehyde and Schiff base-substituted complexes against the enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) were assessed. The majority of phthalocyanines exhibited strong enzyme-inhibiting properties. Out of the six produced phthalocyanines, 3 and 4 displayed the most intriguing profiles as submicromolar selective AChE inhibitors (IC50 = 0.060 μM), whereas 1 demonstrated the most potent BChE inhibitor (IC50 = 0.024 μM). The aggregation studies of CoPcs, CuPcs, and ZnPcs (1–6) were also carried out in this work.

Electrocatalytic Applications of Carbon Dots and Their Composites

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Carbon dots (CDs) have attracted much attention in the field of electrocatalysis due to their many advantages. These reactions are of great significance for energy conversion and storage, as well as environmental remediation. In this review, we summarize the latest achievements in the electrochemical applications of CDs and their composites, with a focus on environmentally relevant electrocatalysis. We present some representative examples of CDs-based electrocatalysts for different reactions and analyze the catalytic mechanisms and the factors that affect the electrocatalytic performance. Furthermore, we conclude with some challenging issues and future perspectives of this emerging material. This review aims to help readers better understand the application of CDs in the field of electrocatalysis, reveal the reasons that affect electrocatalytic performance, and guide further constructing more efficient, stable, and green electrocatalysts.

Modifications of Protein‐Bound Substrates by Trans‐Acting Enzymes in Natural Products Biosynthesis

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Modifications of Protein-Bound Substrates by Trans-Acting Enzymes in Natural Products Biosynthesis

In polyketide biosynthesis, modifications commonly occur after the completion of the polyketide backbone assembly and the mature products are released from the acyl-carrier protein (ACP). However, exceptions to this rule are widespread, and some are modified on-line by discrete enzymes. This review article highlights more recently reported trans-acting proteins that catalyze modifications of ACP-bound substrates in natural product biosynthesis.


Abstract

Enzymatic modifications of small molecules are a common phenomenon in natural product biosynthesis, leading to the production of diverse bioactive compounds. In polyketide biosynthesis, modifications commonly take place after the completion of the polyketide backbone assembly by the polyketide synthases and the mature products are released from the acyl-carrier protein (ACP). However, exceptions to this rule appear to be widespread, as on-line hydroxylation, methyl transfer, and cyclization during polyketide assembly process are common, particularly in trans-AT PKS systems. Many of these modifications are catalyzed by specific domains within the modular PKS systems. However, several of the on-line modifications are catalyzed by stand-alone proteins. Those include the on-line Baeyer-Villiger oxidation, α-hydroxylation, halogenation, epoxidation, and methyl esterification during polyketide assembly, dehydrogenation of ACP-bound short fatty acids by acyl-CoA dehydrogenase-like enzymes, and glycosylation of ACP-bound intermediates by discrete glycosyltransferase enzymes. This review article highlights some of these trans-acting proteins that catalyze enzymatic modifications of ACP-bound small molecules in natural product biosynthesis.

Molybdenum Catalyzed Acceptorless Dehydrogenation of Alcohols for the Synthesis of Quinolines

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Molybdenum Catalyzed Acceptorless Dehydrogenation of Alcohols for the Synthesis of Quinolines

Molybdenum triazolylidene complexes displayed excellent catalytic activity in the synthesis of a wide variety of quinolines through acceptorless dehydrogenative coupling reactions.


Abstract

The first molybdenum triazolylidene complexes catalyzing the atom-economical synthesis of quinolines through acceptorless dehydrogenative coupling of alcohols is reported. A new family of Mo(0) complexes bearing chelating bis-1,2,3-triazolylidene, pyridyl-1,2,3-triazolylidene, and bis-triazole ligands have been prepared and applied as catalysts for the synthesis of quinolines. Interestingly, Mo complexes bearing bis-1,2,3-triazolylidene ligands with alkyl groups (Et, n-Bu) displayed superior catalytic activities than those containing aryl substituents on the triazolylidene rings. Control experiments corroborated that the catalytic reaction involves the dehydrogenation pathway.

Achieving 78.2 % Faraday Efficiency for Electrochemical Ammonia Production Via Covalent Modification of CNTs with B4C

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Achieving 78.2 % Faraday Efficiency for Electrochemical Ammonia Production Via Covalent Modification of CNTs with B4C

carbon nanotubes (CNTs) have been demonstrated to have far-reaching applications in modifying electrodes, and electrocatalysts due to their high surface area and high mobility for charge carriers. Present study shows a catalyst constructed from covalent modification of CNTs with B4C for electrochemical nitrogen reduction. The formation of new C−B−O covalent bonds was verified by a series of characterizations.


Abstract

Electrochemical reduction of N2 to NH3 provides an alternative to the Haber-Bosch process for sustainable NH3 production driven by renewable electricity. Here, we reported carbon nanotubes (CNTs) covalently modified with boron carbide (B4C) as a nonmetallic catalyst for efficient electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The structure of the catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), elemental mapping, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The catalyst held a superior selectivity for NRR with high Faraday efficiency of 78.2 % accompanying with NH3 yield rate of 14.0 μg mg−1 cat. h−1 under the condition of 0.1 M Na2SO4 and −0.6 V vs. RHE. Electrochemical experiments including cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves were performed to explain the best electrochemical properties of B4C/CNTs among the samples. This work demonstrates that the strategy of covalent modification plays an important role to improve the selectivity of electrochemical NRR catalyst, thus allowing the reactions to proceed more efficiently.

First Insight into the Catalytic Activity of Stereolithographically 3D‐printed Tannin‐based Carbon Architectures

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The remediation of polluted water is a major concern for public health and the environment. Catalytic removal of model organic and inorganic pollutants in water using carbon catalysts has shown promising results. In the present work, stereolithographically 3D-printed bio-based carbon monoliths with different textural and surface chemistry properties were used as catalysts for oxalic acid oxidation and catalyst supports for bromate reduction in continuous systems. A significant synergistic effect between ozone or dihydrogen and carbon catalyst was evidenced by mineralization of 14-25 % of oxalic acid or reduction of 15-45 % of bromates in the steady state, respectively. The best results were achieved with samples with the highest mesoporous surface area or, in the case of lower surface area, with samples having the strongest basic character. As materials with great potential, optimizing the textural properties of architected carbon monoliths will enable them to compete with other macro-structured carbon catalysts.

Zinc Doping Induces Enhanced Thermoelectric Performance of Solvothermal SnTe

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Zinc Doping Induces Enhanced Thermoelectric Performance of Solvothermal SnTe

We report a microwave-assisted wet chemical method for doping Zn into SnTe thermoelectric materials to in-situ induce rich ZnTe nanoprecipitates, nanopores, a large number of grain boundaries and other multi-dimensional defects. While ensuring competitive electrical transport performance, the introduced multi-dimensional defects induced phonon scattering across the entire scale, reducing the lattice thermal conductivity of SnTe to the amorphous limit and enhancing its thermoelectric performance.


Abstract

The creation of hierarchical nanostructures can effectively strengthen phonon scattering to reduce lattice thermal conductivity for improving thermoelectric properties in inorganic solids. Here, we use Zn doping to induce a remarkable reduction in the lattice thermal conductivity in SnTe, approaching the theoretical minimum limit. Microstructure analysis reveals that ZnTe nanoprecipitates can embed within SnTe grains beyond the solubility limit of Zn in the Zn alloyed SnTe. These nanoprecipitates result in a substantial decrease of the lattice thermal conductivity in SnTe, leading to an ultralow lattice thermal conductivity of 0.50 W m−1 K−1 at 773 K and a peak ZT of ~0.48 at 773 K, marking an approximately 45 % enhancement compared to pristine SnTe. This study underscores the effectiveness of incorporating ZnTe nanoprecipitates in boosting the thermoelectric performance of SnTe-based materials.