Graphene–Encapsulated Si@C with Dual Carbon Layer Structure as High‐Performance Anode Materials for Lithium–Ion Batteries

Posted on 29 February 2024 by

Herein, dual carbon layer composites of graphene–encapsulated Si@C particles are prepared as silicon–based anode materials by anchoring Si@C particles in the rGO network through a simple electrostatic self-assembly method. The optimal Si@C@rGO-2 composite delivers 1038.5 mAh g⁻¹ at 0.2 A g⁻¹ after 200 cycles and 743.9 mAh g⁻¹ at 1 A g⁻¹ after 300 cycles, respectively.

Abstract

Silicon–based materials are among the highly promising anode candidates for Li–ion batteries owing to their excellent theoretical energy density. However, the huge volume variation makes the application of silicon anode in lithium–ion batteries be full of challenge. Herein, high–performance Si@C@rGO composites anode for lithium–ion batteries are successfully prepared by graphene oxide (GO) uniformly encapsulating resorcinol–formaldehyde resin (RF) coated silicon nanoparticles. The RF-derived carbon layer can prevent the silicon from direct contact with the electrolyte. Furthermore, the continuous conductive graphene network not only improves the overall electrical conductivity of the composite material, but also can be reversibly deformed with the volume change of silicon during the charging and discharging process, thus greatly improving the structural stability of the anode. The optimal Si@C@rGO-2 composite provides a high specific capacity of 743.9 mAh g⁻⁻¹ after 300 cycles at a current density of 1 A g⁻¹. Meanwhile, the material also exhibits good rate performance, showing a good reversible capacity of 719.5 mAh g⁻¹ even at a high current density of 2 A g⁻¹. In addition, this simple and low-cost strategy of Si@C@rGO anode can provide a design reference for the further development of anode materials in lithium–ion batteries.

The Biological Activities of Polyether Ionophore Antibiotic Routiennocin is Independent of Absolute Stereochemistry

Posted on 29 February 2024 by

A convergent synthesis was used to access both enantiomers of the polyether antibiotic routiennocin, and a diastereomeric variant, to probe the biological consequences of altering the naturally configured stereochemistry. Testing these compounds against a broad panel of bacteria and mammalian cells revealed independence of absolute stereochemistry in all tested cells.

Abstract

Carboxylic polyether ionophores (CPIs) are among the most prevalent agricultural antibiotics (notably in the US) and these compounds have been in use for decades. The potential to reposition CPIs beyond veterinary use, e. g. through chemical modifications to enhance their selectivity window, is an exciting challenge and opportunity, considering their general resilience towards resistance development. Given the very large societal impact of these somewhat controversial compounds, it is surprising that many aspects of their mechanisms and activities in cells remain unclear. Here, we report comparative biological activities of the CPI routiennocin and two stereoisomers, including its enantiomer. We used an efficient convergent synthesis strategy to access the compounds and conducted a broad survey of antibacterial activities against planktonic cells and biofilms as well as the compounds’ effects on mammalian cells, the latter assessed both via standard cell viability assays and broad morphological profiling. Interestingly, similar bioactivity of the enantiomeric pair was observed across all assays, strongly suggesting that chiral interactions do not play a decisive role in the mode of action. Overall, our findings are consistent with a mechanistic model involving highly dynamic behaviour of CPIs in biological membranes.

Fus‐SMO: Kinetics, Biochemical Characterisation and In Silico Modelling of a Chimeric Styrene Monooxygenase Demonstrating Quantitative Coupling Efficiency

Posted on 29 February 2024 by nTanja Knaus, nPeter Macheroux, nFrancesco G. Muttin

Fus-SMO, a chimera of StyA and StyB in styrene monooxygenase, has a trimeric structure with one bound flavin. In silico modelling indicated a well-distanced arrangement due to the flexible linker. Pre-steady-state kinetics highlighted the intricacies of FAD_ox reduction and aerobic FADH₂ oxidation. NADH consumption vs. styrene epoxidation revealed quantitative coupling efficiency. These findings advance our understanding of FADH₂ transfer mechanisms in SMO and underscore protein fusion‘s role in enhancing biocatalysis.

Abstract

The styrene monooxygenase, a two-component enzymatic system for styrene epoxidation, was characterised through the study of Fus-SMO – a chimera resulting from the fusion of StyA and StyB using a flexible linker. Notably, it remains debated whether the transfer of FADH₂ from StyB to StyA occurs through diffusion, channeling, or a combination of both. Fus-SMO was identified as a trimer with one bound FAD molecule. In silico modelling revealed a well-distanced arrangement (45–50 Å) facilitated by the flexible linker‘s loopy structure. Pre-steady-state kinetics elucidated the FAD_ox reduction intricacies (k_red=110 s⁻¹ for bound FAD_ox), identifying free FAD_ox binding as the rate-determining step. The aerobic oxidation of FADH₂ (k_ox=90 s⁻¹) and subsequent decomposition to FAD_ox and H₂O₂ demonstrated StyA′s protective effect on the bound hydroperoxoflavin (k_dec=0.2 s⁻¹) compared to free cofactor (k_dec=1.8 s⁻¹). At varied styrene concentrations, k_ox for FADH₂ ranged from 80 to 120 s⁻¹. Studies on NADH consumption vs. styrene epoxidation revealed Fus-SMO′s ability to achieve quantitative coupling efficiency in solution, surpassing natural two-component SMOs. The results suggest that Fus-SMO exhibits enhanced FADH₂ channelling between subunits. This work contributes to comprehending FADH₂ transfer mechanisms in SMO and illustrates how protein fusion can elevate catalytic efficiency for biocatalytic applications.

Human 2′‐Deoxynucleoside 5′‐Phosphate N‐Hydrolase 1: The Catalytic Roles of Tyr24 and Asp80

Posted on 29 February 2024 by

The human enzyme 2′-deoxynucleoside 5′-phosphate N-hydrolase 1 (HsDNPH1) is a promising target for inhibition towards anticancer drug development. Crystal structures, site-directed mutagenesis, and kinetic analysis, including pH-rate profiles and solvent deuterium isotope effects, help quantify contributions from conserved residues Tyr24 and Asp80 to HsDNPH1-catalysed hydrolysis of 5-hydroxymethyl-2′-deoxyuridine 5′-phosphate. These include nucleophile and substrate positioning and general-acid catalysis.

Abstract

The human enzyme 2′-deoxynucleoside 5′-phosphate N-hydrolase 1 (HsDNPH1) catalyses the hydrolysis of 5-hydroxymethyl-2′-deoxyuridine 5′-phosphate to generate 5-hydroxymethyluracil and 2-deoxyribose-5-phosphate via a covalent 5-phospho-2-deoxyribosylated enzyme intermediate. HsDNPH1 is a promising target for inhibitor development towards anticancer drugs. Here, site-directed mutagenesis of conserved active-site residues, followed by HPLC analysis of the reaction and steady-state kinetics are employed to reveal the importance of each of these residues in catalysis, and the reaction pH-dependence is perturbed by each mutation. Solvent deuterium isotope effects indicate no rate-limiting proton transfers. Crystal structures of D80N-HsDNPH1 in unliganded and substrate-bound states, and of unliganded D80A- and Y24F-HsDNPH1 offer atomic level insights into substrate binding and catalysis. The results reveal a network of hydrogen bonds involving the substrate and the E104-Y24-D80 catalytic triad and are consistent with a proposed mechanism whereby D80 is important for substrate positioning, for helping modulate E104 nucleophilicity, and as the general acid in the first half-reaction. Y24 positions E104 for catalysis and prevents a catalytically disruptive close contact between E104 and D80.

Zn(II)‐Stabilized Azo‐Anion Radical Catalyzed Sustainable C−C Bond Formation: Regioselective Alkylation of Fluorene, Oxindole, and Indoles

Posted on 29 February 2024 by

Taking advantage of the ligand-centered redox events, a well-defined air-stable Zn(II)-catalyst (1 a), bearing a tridentate redox noninnocent arylazo pincer, is used for synthesizing a wide variety of alkylated ketones, 9H-fluorenes, oxindoles, and indoles in moderate to good isolated yields (up to 91 %) using a broad range of alcohols as the alkylating agent.

Abstract

Herein we report a sustainable approach for the alkylation of ketones, 9H-fluorene, oxindole, and indole using alcohols as the alkylating agent catalyzed by a well-defined air-stable zinc catalyst (1 a) of a tridentate redox non-innocent arylazo ligand, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L^a ). 2–3 mol % of 1 a efficiently produces substituted α-alkylated ketones, 9-alkylated fluorenes, C3-alkylated oxindoles, and C3-alkylated indoles in moderate to good isolated yields. In aerial condition, the formation of bis(indolyl)methane (BIMs) derivatives were observed when indoles were subjected to alkylation by primary alcohols. A few drug molecules containing BIMs were prepared in good isolated yields. The catalyst 1 a exhibited good chemoselectivity during the functionalization of fluorene and indole with oleyl alcohol and β-citronellol. A few control experiments, including deuterium labeling experiments, performed to unveil the reaction mechanism indicate that the one-electron reduced azo-anion radical species [1 a]-formed in situ, acts as the active catalyst. All the redox events occur at the redox-active aryl-azo ligand, which acts as the reservoir of hydrogen and electrons throughout the catalytic cycle, keeping the Zn(II)-center as a template.

Investigating the Catalytic Efficiency of Supported NHC‐Ag(I) Complexes in the Borono‐Minisci Reaction

Posted on 29 February 2024 by

In this paper we report the preparation, characterization, and evaluation of N-heterocyclic carbenes (NHC)-Ag(I) complexes as catalysts for the borono-Minisci reaction, a powerful and practical approach for the decoration of N-heterocycles. While it represents an unprecedented method, kinetic and cyclic voltammetric analyses evidenced how the complex structure influence the Ag(I)/Ag(II) redox potential and, in turn, the reaction efficiency and scope.

Abstract

A series of supported N-heterocyclic carbene silver complexes (NHC-Ag(I)) were prepared and characterized as catalysts for the borono-Minisci reaction. After characterization, the synthesized catalysts were evaluated in batch mode to determine the reaction performance and kinetics. Interestingly, cyclic voltammetric analysis showed that the structure of both the complex and the ligand significantly influences the Ag(I)/Ag(II) redox potential and, in turn, the catalytic efficiency. Among the tested catalysts, the Si-supported NHC-Ag(I) 6 afforded the desired products in good to excellent yields in only 15 min, providing a complementary tactic to standard homogeneous approaches.

Concepts behind the Redox Photocatalysis with Quantum Dots

Posted on 29 February 2024 by nMarcelo Navarro, nJadielson Costa, nFelipe L. N. Sousan

Quantum dots are the investigative focus of many research groups due to the quantum confinement effect observed. Thus, the photocatalysis has emerging as an important research branch applied to organic synthesis. In this article, the properties and concepts of these semiconductor nanocrystals are related and discussed for a better understanding and guidance to catalysis applications.

Abstract

In this conceptual review, we present the optical and electronic characteristics of quantum dots for the designing of organic synthesis experiments through the photocatalysis. We discuss the control parameters associated to the charge recombination processes on the semiconductor interface. The positioning of bands and control of intragap states, such as charge donors and acceptors, can define the performance of faradaic processes. Electrochemical strategies, such as voltammetry, can be used as a powerful tool for the determining of the electronic band edges with good precision.

Effect of DNA Origami Nanostructures on Bacterial Growth

Posted on 29 February 2024 by

Bacteria can use DNA origami nanostructures as a nutrient source, leading to increased population growth. This process depends not only on the competence signal and uptake mechanisms of each species, but also on DNA origami shape and superstructure. It should thus be considered in the design and development of antimicrobial DNA origami nanostructures.

Abstract

DNA origami nanostructures are a powerful tool in biomedicine and can be used to combat drug-resistant bacterial infections. However, the effect of unmodified DNA origami nanostructures on bacteria is yet to be elucidated. With the aim to obtain a better understanding of this phenomenon, the effect of three DNA origami shapes, i.e., DNA origami triangles, six-helix bundles (6HBs), and 24-helix bundles (24HBs), on the growth of Gram-negative Escherichia coli and Gram-positive Bacillus subtilis is investigated. The results reveal that while triangles and 24HBs can be used as a source of nutrients by E. coli and thereby promote population growth, their effect is much smaller than that of genomic single- and double-stranded DNA. However, no effect on E. coli population growth is observed for the 6HBs. On the other hand, B. subtilis does not show any significant changes in population growth when cultured with the different DNA origami shapes or genomic DNA. The detailed effect of DNA origami nanostructures on bacterial growth thus depends on the competence signals and uptake mechanism of each bacterial species, as well as the DNA origami shape. This should be considered in the development of antimicrobial DNA origami nanostructures.

Expanding the Application of Alcohol Dehydrogenases in Pharmaceutical Chemistry: A Focus on Piperidone Synthesis

Posted on 29 February 2024 by

Our study presents the “substrate analogue functional screening” screening method for identifying an alcohol dehydrogenase and the phenylalanine/alanine-scanning and iterative saturation mutation technique was applied to improve its catalytic activity for the enzymatic synthesis of piperidones.

Abstract

Alcohol dehydrogenases (ADHs) have garnered recognition for their potential in the synthesis of pivotal pharmaceutical compounds. However, their utilization in the context of piperidone synthesis remains an area ripe for exploration. In this study, we examine the performance of an alcohol dehydrogenase derived from Corynebacterium glutamicum (CgADH) using a substrate analogue functional screening (SAFS) method to elucidate its substrate specificity. To improve the catalytic activity of CgADH, a phenylalanine/alanine-scanning and iterative saturation mutation (PAS-ISM) method was used. The most active variant, I151F/I195A, exhibited a remarkable 10.6-fold increase in catalytic activity compared to the wild-type. Structural analysis revealed that the introduction of residues 151F and 195A led to a remodeling of the substrate-binding pocket, enabling additional p-π hydrophobic interactions with the substrate, ultimately promoting a more favorable substrate binding pose. This study introduces the SAFS screening method, which enables the identification of enzymes with no sequence homology to known enzymes. Furthermore, the application of PAS-ISM presents an efficient approach for the engineering of alcohol dehydrogenases. These findings open up promising avenues to expand the utility of ADHs in the synthesis of piperidone, thereby advancing the field of pharmaceutical chemistry.

Insights on DHAP Aldolases ability to convert Dioxygen or a Ketone as Electrophile: use of a Strain Depleted in Triose Phosphate Isomerase

Posted on 29 February 2024 by

Rhamnulose-1-phosphate aldolase (RhuA) was the first DHAP-aldolase discovered to have an electrophilic promiscuity as astonishing as converting ketones or dioxygen from air, to give access respectively to the highly sought-after chiral tertiary alcohol motif or to hydroxypyruvaldehyde phosphate. This study reveals the behaviour of the other DHAP-aldolases in this area: fuculose-1-phosphate- (FucA), fructose-1,6-bisphosphate- (FruA) and tagatose-1,6-bisphosphate (TagA) aldolases.

Abstract

Rhamnulose-1-phosphate aldolases (RhuA) were the first dihydroxyacetone phosphate (DHAP) aldolases to be demonstrated to efficiently accept a ketone as the electrophile, providing the highly sought-after chiral tertiary alcohol motif. It has also been found that this enzyme family can use dioxygen as an electrophile, forcing to work under inert atmosphere conditions when the target electrophile is poorly reactive. However, these features have not been explored in all DHAP-aldolase families. Here, we present a study of E. coli K12 fuculose-1-phosphate- (FucA_K12), fructose-1,6-bisphosphate- (FruA_K12) and tagatose-1,6-bisphosphate (TagA_K12) aldolases. For the latter two enzymes, this was made possible by the development of a triose phosphate isomerase (TPI)-deleted E coli strain, which prevents DHAP isomerization into d-glyceraldehyde 3-phosphate (G3P), its natural electrophile. Like RhuA, TagA_K12 was found to be able to oxidize DHAP into hydroxypyruvaldehyde phosphate under dioxygen, leading to the corresponding diulose. On the other hand, FucA_K12 was revealed to be capable of converting ketone electrophiles with greater stereoselectivity than RhuA, and without the requirement of an inert atmosphere, since it was unable to oxidize DHAP. Finally, FruA_K12 proved unable either to oxidize DHAP and or to accept ketones as electrophiles.