Monthly Archives: March 2024

Effect of carbon oxygen functionalization on the activity of Pd/C catalysts in hydrogenation reactions

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Effect of carbon oxygen functionalization on the activity of Pd/C catalysts in hydrogenation reactions

The effects of oxygen functionalities on GNP (Graphene Nanoplatelets) has been investigated, functionalizing GNP in liquid phase using different oxidants (HNO3, H2O2, KMnO4), with the aim to tune the amount and the type of oxygen functionalities. Pd NPs have been deposited on the different functionalized carbon supports to be tested in benzaldehyde hydrogenation/hydrogenolysis to benzyl alcohol and toluene as model reaction.


Abstract

This paper presents a study on the effects of oxygen functionalities on a mesoporous and graphitized carbon support (GNP, Graphene Nanoplatelets), on the catalytic activity of Pd/GNP catalysts in hydrogenation reactions. A functionalization method in liquid phase has been employed, using different oxidants (HNO3, H2O2, KMnO4), with the aim to tune the amount and the type of introduced oxygen functionalities. Preformed Pd nanoparticles have been used as Pd-precursor to limit differences in metal particle size and dispersion on differently functionalized carbon. The catalytic behaviour in benzaldehyde hydrogenation/hydrogenolysis to benzyl alcohol and toluene revealed that the introduction of oxygen functionalities has a generally detrimental effect. NMR relaxometry studies highlighted the weaker interaction between the carbonyl group and the functionalized Pd/GNP surface than the non–functionalized Pd/GNP demonstrating that the origin of the different catalytic activity lies on the first step of the reaction. O-functionalities also impacted on the Pd0/Pd2+ ratio at the surface which is an established parameter correlated to the reaction rate.

Development of an Enzyme Cascade System for the Synthesis of Enantiomerically Pure D‐Amino Acids Utilizing Ancestral L‐Amino Acid Oxidase

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Development of an Enzyme Cascade System for the Synthesis of Enantiomerically Pure D-Amino Acids Utilizing Ancestral L-Amino Acid Oxidase

D-Amino acids (D-AAs) are increasingly recognized as valuable precursors for the synthesis of fine chemicals, including pharmaceuticals and pesticides. This study reports the construction of an enzyme cascade system specifically designed for the synthesis of D-AAs from their corresponding racemates and L-isomers. Employing this system, we successfully synthesized seven enantiomerically pure D-AAs at a preparative scale.


Abstract

Enantiomerically pure D-amino acids hold significant potential as precursors for synthesizing various fine chemicals, including peptide-based drugs and other pharmaceuticals. This study focuses on establishing an enzymatic cascade system capable of converting various L-amino acids into their D-isomers. The system integrates four enzymes: ancestral L-amino acid oxidase (AncLAAO-N4), D-amino acid dehydrogenase (DAADH), D-glucose dehydrogenase (GDH), and catalase. AncLAAO-N4 initiates the process by converting L-amino acids to corresponding keto acids, which are then stereo-selectively aminated to D-amino acids by DAADH using NADPH and NH4Cl. Concurrently, any generated H2O2 is decomposed into O2 and H2O by catalase, while GDH regenerates NADPH from D-glucose. Optimization of reaction conditions and substrate concentrations enabled the successful synthesis of five D-amino acids, including a D-Phe derivative, three D-Trp derivatives, and D-phenylglycine, all with high enantiopurity (>99 % ee) at a preparative scale (>100 mg). This system demonstrates a versatile approach for producing a diverse array of D-amino acids.

Research Progress on the Assembly of Large DNA Fragments

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Research Progress on the Assembly of Large DNA Fragments

DNA assembly serves as the fundamental technology in the field of synthetic biology. This paper briefly reviews the recent advancements in the assembly of large DNA fragments. We spotlight on in vivo methods using E. coli, B. subtilis, and S. cerevisiae as hosts, and highlight the various applications that can be explored after the assembly of large DNA fragments.


Abstract

Synthetic biology, a newly and rapidly developing interdisciplinary field, has demonstrated increasing potential for extensive applications in the wide areas of biomedicine, biofuels, and novel materials. DNA assembly is a key enabling technology of synthetic biology and a central point for realizing fully synthetic artificial life. While the assembly of small DNA fragments has been successfully commercialized, the assembly of large DNA fragments remains a challenge due to their high molecular weight and susceptibility to breakage. This article provides an overview of the development and current state of DNA assembly technology, with a focus on recent advancements in the assembly of large DNA fragments in Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae. In particular, the methods and challenges associated with the assembly of large DNA fragment in different hosts are highlighted. The advancements in DNA assembly have the potential to facilitate the construction of customized genomes, giving us the ability to modify cellular functions and even create artificial life. It is also contributing to our ability to understand, predict, and manipulate living organisms.

Recent Advances in Non‐Standard Macrocyclic Peptide Ligand Discovery using mRNA Display

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Recent Advances in Non-Standard Macrocyclic Peptide Ligand Discovery using mRNA Display


Abstract

Advancements in platform technologies have facilitated the production of libraries consisting of macrocyclic peptides composed of natural and non-canonical amino acids for more drug-like characteristics. Identification of macrocyclic peptide ligands against targets of interest can be accomplished using mRNA display. Despite numerous successful in vitro selections for macrocyclic peptide ligands against extracellular targets, identifying macrocyclic peptide hits that can reach intracellular targets continue to be a challenge. Breakthroughs in defining the features of a macrocyclic peptide that promote cell permeability have recently been disclosed. Here, we review the successful selections of non-standard macrocyclic peptide ligands using mRNA display in the last five years and chemical optimization of a drug-like macrocyclic peptide ligand for targeting intracellular KRAS.

The Molecular Structures of Lithium Trichlate, Li[Cl3CSO3]⋅2H2O, and Lithium Tribrate, Li[Br3CSO3]⋅2H2O

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The Molecular Structures of Lithium Trichlate, Li[Cl3CSO3]⋅2H2O, and Lithium Tribrate, Li[Br3CSO3]⋅2H2O

The bigger siblings of the triflate anion, namely the trichlate [Cl3CSO3]− and the tribrate [Br3CSO3]− are synthesized as their lithium salts. The compounds display molecular structures with the anions, the lithium cations and water molecules arranged into dimers [Li2(X3CSO3)2(H2O)4] (X=Cl, Br). The figure shows both dimers, partly in an ORTEP style and partly as a Lewis formula.


Abstract

Lithium trichlate, Li[Cl3CSO3] ⋅ 2H2O (triclinic, , Z=2, a=630.29(3) pm, b=630.65(3) pm, c=1246.10(6) pm, α=100.657(2)°, β=97.813(2)°, γ=107.994(2)°) was obtained from the reaction of (H5O2)[Cl3CSO3] and LiOH in aqueous solution. Similarly, colourless single crystals of the tribrate Li[Br3CSO3] ⋅ 2H2O (triclinic, , Z=4, a=634.65(4) pm, b=636.83(4) pm, c=2496.8(2) pm, α=83.518°, β=86.081(5)°, γ=72.061(5)°) form in the reaction of aqueous Br3CSO3H and LiOH. The acid (H5O2)[Cl3CSO3] was obtained from the chlorination of CS2, followed by oxidation of the intermediate Cl3CSCl with H2O2. The bromo derivative Br3CSO3H has been prepared by bromination of phenylsulfonate with KOBr and subsequent ion exchange of the obtained potassium salt. Both lithium compounds exhibit molecular dimers according to {Li2(X3CSO3)2/1(H2O)2/1(H2O)2/2} with the Li+ ions in tetrahedral coordination of oxygen atoms. The difference in the crystal structures result from the variation of the orientation of the dimers with respect to each other. The experimental findings for the dimers are in good agreement with DFT calculations.

Modern Cyclopropanation via Non‐Traditional Building Blocks

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Small, strained carbocyclic systems have fascinated organic chemists from both a theoretical and synthetic standpoint. These systems often challenge conventional wisdom when it comes to molecular structure and tactics for chemical construction. The cyclopropyl motif is one such ring system that remains at the forefront of method development in the modern era. With the advent of an array of non-traditional building blocks, a range of new cyclopropanation processes using one- and two-electron strategies have been developed that not only overcome the synthetic shortcomings of classical approaches but also provide entry into a wide range of new classes of cyclopropanes. This review discusses recent advances in this area with an emphasis on their mechanistic underpinnings and potential applications. Additionally, a concise overview of the properties of and traditional approaches to cyclopropanes is provided.

Pd‐Catalyzed Highly Regioselective Hydroesterification of Terminal Alkyl Olefins with Formates

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Pd-Catalyzed Highly Regioselective Hydroesterification of Terminal Alkyl Olefins with Formates

A wide variety of linear aryl esters can be obtained in generally good yields and high regioselectivities from alkyl terminal olefins via hydroesterification with aryl formates. The reaction process is operationally simple and requires no handling of toxic CO or strong acid.


Comprehensive Summary

A Pd-catalyzed regioselective hydroesterification of alkyl terminal olefins with aryl formates is described. A wide variety of linear carboxylic esters bearing various functional groups can be obtained in good yields with high regioselectivities under mild reaction conditions by using 1,2-DTBPMB or (p-F-Ph)3P as ligand. The reaction process is operationally simple and requires no handling of toxic CO or strong acid. The resulting aryl esters can be readily converted to other carboxylic acid derivatives.

Surface Topological Glycosylation‐Mediated Mucoadhesion of Bacteria

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Surface Topological Glycosylation-Mediated Mucoadhesion of Bacteria†

Surface topological glycosylation enhances mucoadhesion of bacteria.


Comprehensive Summary

Sugar moieties present on bacterial surface serve as pivotal regulators of bacterial activity. Precisely adjusting the abundance and distribution of surface sugar moieties can offer an important approach to manipulating bacterial behavior, but has been proven to be difficult. Herein, surface topological glycosylation is reported to mediate the interaction of bacteria with mucous layer. Alkynes functionalized by sugar moieties with different branching are synthesized through iterative Michael addition and amide condensation reactions. By a copper-catalyzed azide-alkyne cycloaddition, the resulting compounds with different branching structures can be attached onto bacterial surface that is modified with azido groups. As a proof-of-concept study, a set of topologically glycosylated probiotics (TGPs) is prepared using linear, two-branched, and tetra-branched compounds, respectively. The interaction between mucin and TGPs was studied and the results demonstrate that, compared to unmodified bacteria, TGPs exhibit an enhanced adhesive capacity to mucin, which increases with the branching numbers. Similar binding trend is observed in ex vivo colonic mucus adhesion experiments and bacteria glycosylated with tetra-branched compounds display the highest binding efficiency. This work proposes a chemical method to tune the abundance and distribution of sugar moieties on bacteria, providing unique significant insights into the manipulation of bacterial behavior through surface modification.

Free‐Standing Multiscale Porous High Entropy NiFeCoZn Alloy as the Highly Active Bifunctional Electrocatalyst for Alkaline Water Splitting

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Free-Standing Multiscale Porous High Entropy NiFeCoZn Alloy as the Highly Active Bifunctional Electrocatalyst for Alkaline Water Splitting

The free-standing multiscale porous NiFeCoZn high-entropy-alloy is in-situ constructed on the surface of NiZn intermetallic and Ni heterojunction over nickel foam (NiFeCoZn/NiZn-Ni/NF) by one scalable electroplating-annealing-etching protocal. The as-made NiFeCoZn/NiZn-Ni/NF fulfills the outstanding electrocatalytic performances with the small overpotentials (η 500 = 184/348 mV), low Tafel slopes, as well as exceptional long-term catalytic durability for 400 h in alkaline solution toward both hydrogen evolution reaction and oxygen evolution reaction.


Comprehensive Summary

In the endeavor of searching for highly active and stable electrocatalysts toward overall water splitting, high-entropy-alloys have been the intense subjects owing to their advanced physicochemical property. The non-noble metal free-standing multiscale porous NiFeCoZn high-entropy-alloy is in situ constructed on the surface layer of NiZn intermetallic and Ni heterojunction over nickel foam (NiFeCoZn/NiZn-Ni/NF) by one scalable dealloying protocal to fulfill the outstanding bifunctional electrocatalytic performances toward overall water splitting. Because of the high-entropy effects and specific hierarchical porous architecture, the as-made NiFeCoZn/NiZn-Ni/ NF displays high intrinsic catalytic activities and durability toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. In particular, the in-situ construction of bimodal porous NiFeCoZn high-entropy-alloy results in the small overpotentials (η 1000 = 254/409 mV for HER and OER), low Tafel slopes, and exceptional long-term catalytic durability for 400 h. Expressively, the electrolyzer constructed with NiFeCoZn/NiZn-Ni/NF as both cathode and anode exhibits a low cell voltage of 1.72 V to deliver the current density of 500 mA·cm–2 for overall water splitting. This work not only provides a facile and scalable protocol for the preparation of self-supporting high-entropy-alloy nanocatalysts but also enlightens the engineering of high performance bifunctional electrocatalysts toward water splitting.