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Abstract We synthesized a class of ligands that feature single (L1) and dual amine-bis(triazole) chelates (L2 with a 1,3-phenylene linker and L3 with a 1,5-naphthalene linker). Our findings which were derived from UV–Vis titrations, crystal structure analysis of relevant copper complexes, and DFT calculations indicate the formation of both mononuclear CuBr(L1) and dinuclear (μ-Ln)(CuBr)2 (Ln = L2 and L3) complexes. The catalytic activities of CuBr/Ln, in combination with TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) co-catalyst and NMI (N-methylimidazole) for aerobic alcohol oxidation, reveal the following activity trend: CuBr/L3 > CuBr/L2 > CuBr/L1. Furthermore, electrochemical data from in-situ generated CuBr complexes suggest that the higher catalytic performance of CuBr/L3 is attributed to the presence of less stable mixed-valence and more reducible Cu(I)-L3-Cu(II) species compared to Cu(I)-L2-Cu(II). This difference is a result of weaker σ interactions between Cu–Namine, larger bridging π systems, and a longer Cu···Cu distance in the presence of L3. Additionally, the catalyst system, CuBr/L3/TEMPO/NMI, efficiently promotes the aerobic oxidation of benzyl alcohol to benzaldehyde at room temperature in CH3CN with a high turnover frequency (TOF) of 38 h−1 at 1 h.

[Display omitted] • The constituents of the fungus Beauveria asiatica BCC 16812 were investigated. • Six new compounds 1 – 6 and two synthetically known compounds 7 and 8 were isolated. • Compounds 9 ‒ 11 exhibited antimalarial, antimicrobial, and cytotoxic activities. • 3 S ,9ʹ S configurations of 6 were deduced by application of modified Mosher's method. • The 4 R ,9 R configurations of compound 6 were addressed by ECD calculation. Six new compounds 1 – 6 and two new naturally occurring compounds 7 and 8 , together with nine known compounds 9 – 14 , beauverioride I, dipicolinic acid, and 6-(methoxycarbonyl) picolinic acid were isolated from a wasp-pathogenic fungus Beauveria asiatica , strain BCC 16812. Their structures were determined by extensive spectroscopic analyses. The absolute configurations of compound 6 were established by the application of modified Mosher's method and ECD calculation. Compounds 9 – 11 exhibited antimalarial (IC 50 0.47–1.79 u g/mL), antimicrobial (MIC 3.13–50.0 u g/mL), and cytotoxic (IC 50 0.26–1.23 u g/mL) activities, while compounds 1 , 2 , 8 , and 14 showed only cytotoxicity against Vero cell lines, with IC 50 values range 12.96–47.03 u g/mL. [ABSTRACT FROM AUTHOR]

Three previously undescribed highly modified lanostane triterpenoids, ganopyrone A, ganocolossusin I, and ganodermalactone Y, were isolated from the artificially cultivated fruiting bodies of the basidiomycete Ganoderma colossus TBRC-BCC 17711. Ganopyrone A possesses an unprecedented polycyclic carbon skeleton with an α-pyrone ring and C-18/C-23 bond. It showed antimalarial activity against Plasmodium falciparum K1 (multidrug-resistant strain) with an IC 50 value of 7.8 μM (positive control: dihydroartemisinin, IC 50 1.4 nM), while its cytotoxicity (Vero cells) was much weaker (IC 50 103 μM)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Alkyl aluminium plays a primary role in activating Ti within Ziegler-Natta (ZN) catalysts for propylene polymerization. We performed density functional calculations to explore the additional roles of AlEt 3 and AlEt 2 Cl, in conjunction with diisobutyl phthalate (DIBP) internal donor and dicyclopentyl dimethoxysilane (DCPDMS) external donor, to enhance the stereoselectivity of propene insertion. Based on our calculated adsorption energies on the (MgCl 2 ) 13 /TiCl 2 i Bu cluster model for the ZN catalyst, the presence of DIBP on the cluster essentially facilitated AlEt 2 Cl adsorption while AlEt 2 Cl also promoted the adsorption of DIBP. The reaction between AlEt 3 and DIBP on the cluster led to the extraction of DIBP, creating an available site for DCPDMS adsorption. While the stereoselectivity, represented by the difference in the activation energies between 1,2- re and 1,2- si insertions of propene, was negligible on the cluster containing only DIBP, it became significant on the clusters containing both AlEt 2 Cl and DIBP (and DCPDMS). AlEt 2 Cl plays a pivotal role in imposing steric effects near the Ti active site, thereby increasing stereoselectivity. Our findings suggest the importance of including AlEt 2 Cl alongside DIBP (and DCPDMS) in the ZN cluster model to investigate stereoselective propene insertion. Considering AlEt 2 Cl adsorption and AlEt 3 reaction with internal donors is essential in developing Ziegler-Natta catalysts.

A colorimetric and fluorescent sensor, selective for Cu 2+ ions, was synthesized in two steps using a rhodamine-based compound attached to the semicarbazide-picolylamine moiety (RBP). Spectroscopic measurements, including UV-Vis absorption and fluorescence emission, were conducted in the semi-aqueous medium containing acetonitrile/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, denoted as MeCN/HEPES buffer (2:8, v/v, pH 7.0). The sensor exhibited high selectivity towards Cu 2+ ions compared to other cations and demonstrated remarkable sensitivity towards Cu 2+ ions, with a limit of detection at the nanomolar level. The calculated transitions indicated a 1:1 stoichiometric binding of RBP to Cu 2+ ions based on a 4-coordination mode involving additional chelation in the semi-aqueous medium. The sensing mechanism for the detection of Cu 2+ ions was investigated using high-resolution mass spectroscopy. The sensor could be employed as a real-time chemosensor for monitoring Cu 2+ ions. Furthermore, the sensor has the potential for utilization in the detection of Cu 2+ ions in actual water samples with the high precision and accuracy, as indicated by the small relative standard derivation values. The 50 th percentile cytotoxicity concentration of RBP was found to be 22.92 μM. Additionally, the fluorescence bioimaging capability of RBP was demonstrated for the detection of Cu 2+ ions in human hepatocellular carcinoma (HepG2) cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The hydrogen evolution reaction is an important process for energy storage. The six-coordinate cobalt complex [Co III (L 1- )(LH)] 2+ (LH = N -(4-amino-6-(pyridin-2-yl)-1,3,5-triazin-2-yl)benzamidine) was found to catalyze photocatalytic hydrogen evolution. In this work, we performed density functional calculations to obtain the reduction potentials and the proton-transfer free energy of possible intermediates to determine the preferred pathways for proton reduction. The mechanism involves the metal-based reduction of Co(III) to Co(II) before the protonation at the amidinate N on the pyridinyl-substituted diaminotriazine benzamidinate ligand L 1- to form [Co II (LH)(LH)] 2+ . Essentially, the subsequent electron transfer is not metal-based reduction, but rather ligand-based reduction to form [Co II (LH)(LH˙ 1- )] 1+ . Through a proton-coupled electron transfer process, the cobalt hydride [Co II H(LH)(LH 2 ˙)] 1+ is formed as the key intermediate for hydrogen evolution. As the cobalt hydride complex is coordinatively saturated, a structural change is required when the hydride on Co is coupled with the proton on pyridine. Notably, the redox-active nature of the ligand results in the low acidity of the protonated pyridine moiety of LH 2 ˙, which impedes its function as a proton relay. Our findings suggest that separating the proton relay fragment from the electron reservoir fragment of the redox-active ligand is preferred for fully utilizing both features in catalytic H 2 evolution.

A series of metal-free imidazole-benzimidazole catalysts (ImBenz-H, ImBenz-NO 2 , ImBenz-OCH 3 ) for oxygen reduction reaction (ORR) were prepared. We demonstrate that the electrocatalytic O 2 reduction by ImBenz-NO 2 with the electron-withdrawing group showed high selectivity toward H 2 O with the number of electrons transferred (n=3.7) in a neutral aqueous solution. The highest ORR selectivity toward H 2 O 2 was achieved using ImBenz-H (n=2.4) in an alkaline solution. Electrochemical studies of reaction kinetics disclosed that the highest turnover frequencies were obtained from ImBenz-H in both neutral and alkaline aqueous solutions. The results prove that the ORR selectivity is tunable by modulating the substituent of the ImBenz catalysts. Furthermore, DFT calculations suggested that the ORR mechanism of ImBenz-H involves the electron transfer from imidazole-benzimidazole to O 2 resulting in the formation of H 2 O 2 which supports the redox active properties of the catalysts ImBenz., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Five undescribed polyketide metabolites, oudemansins E (1), M (2), P (3), and Q (4), and 9-methoxystrobilurin I (5), were isolated from cultures of basidiomycete Favolaschia minutissima TBRC-BCC 19434. A γ-lactone derivative (6) of noroudemansin A (8), which was previously reported as a semisynthetic compound, was also isolated. The absolute configuration of the isoprene-derived moiety of the known cometabolite 9-methoxystrobilurin E (9) was determined to be 2' R ,6' S by comparison of the experimental and calculated ECD data, which was correlated to the new derivative 1. These compounds exhibited antimalarial activity against Plasmodium falciparum K1 (multidrug-resistant strain). A putative minor natural product, namely 9-methoxystrobilurin P (13), was prepared by semisynthesis, which exhibited significant antimalarial activity (IC 50 0.086 μM).

Base-catalyzed diastereodivergent thia-Michael addition of thiols to chiral β-trifluoromethyl-α,β-unsaturated N -acylated oxazolidin-2-ones is reported. By tuning the base-catalyst ( i -Pr 2 NEt, DABCO, or P 2 - t -Bu), a range of chiral thia-Michael adducts was synthesized in good yields with high diastereoselectivities. A plausible mechanism was proposed on the basis of the experimental results. This work is complementary to the existing methods offering advantages, e.g. , switchable diastereoselectivity using a readily synthesized chiral starting material, a cheap and readily available base catalyst, and a simple and practical operation, enabling synthetic application in organic synthesis.

New chemosensors, L1-L3, based on the coumarin Schiff base scaffold with substituent modifications, have been designed and synthesized. The chemosensors L1-L3 exhibited the absorbance and fluorescence spectral changes that can discriminate Co 2+ , Ni 2+ , and Cu 2+ ions. Sensor L1 demonstrated the ability to respond to Co 2+ , Ni 2+ , and Cu 2+ ions. Remarkably, the slight modification of substituent on L2 has been observed to cause selective binding to Ni 2+ and Cu 2+ ions while L3 can specifically detect Cu 2+ ions. The in-situ formation of metal and ligand complexes was determined by Job's plot analysis. The limit of detection and the sensing ability of all probes are estimated to be within the range of safe drinking water. Incorporation of the sensing compounds into a paper-based detection system using a laminated paper-based analytical device (LPAD) was demonstrated and found to be consistent to those obtained from the batchwise solution measurements., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Heptagon-embedded polycyclic aromatic dicarboximides were developed as new push-pull fluorescent dyes through palladium-catalysed [4+3] annulation followed by nucleophilic substitution. The introduction of a seven-membered ring in these push-pull systems can efficiently modulate the optical properties leading to an enhancement of the fluorescence quantum yields up to 0.93 with color tunable emission covering the visible-NIR spectrum.

A series of neutral tetradentate halogen bonding (XB) macrocycles, comprising of two bis-iodotriazole XB donors were synthesised in 60-70% yields via a stepwise CuAAC-mediated cyclisation strategy. Extensive 1 H NMR anion titration experiments reveal halide binding affinities are critically dependent on the substitution pattern of the xylyl spacer unit. The meta -substituted macrocycle remarkably displays cooperative tetradentate XB-halide anion recognition in highly competitive 40% aqueous-organic D 2 O/acetone-d 6 (40 : 60, v/v) solvent mixtures. Integration of para -xylyl and naphthyl spacer units generates extended macrocyclic cavities, capable of selective oxalate recognition. Furthermore, preliminary fluorescence exeperiments reveal dicarboxylate specific sensing can be achieved through monitoring of the naphthylene centred emission.

A novel three-coordinated tin(II) chloride [Ph 2 P(N t Bu) 2 ]SnCl (1) supported by an N , N '-di- tert -butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph 2 P(N t Bu) 2 ]Li with SnCl 2 ·(dioxane) in toluene. The molecular structure of 1 was established by X-ray diffraction analysis. Tin(II) chloride 1 can act as an efficient precatalyst for the hydroboration of a wide variety of aldehydes, ketones, and imines at -10 °C. DFT calculations propose that hydroboration involves hydride transfer from the corresponding tin(II) hydride intermediate [Ph 2 P(N t Bu) 2 ]SnH (10) to the carbonyl substrates via four-membered transition states (TS-12), affording three-coordinated tin(II) alkoxide intermediates [Ph 2 P(N t Bu) 2 ]SnOR (13), followed by the stepwise reaction of 13 with HBpin (pin = pinacolate) to release the boronate esters and regenerate the tin(II) hydride 10. The stoichiometric reaction of the in site-generated 10 with benzophenone 2a at -10 °C led to the formation of 13. Moreover, 13 also stoichiometrically reacted with HBpin at -10 °C, forming the corresponding boronate ester 3a and 10 based on the 1 H NMR spectrum of the reaction mixture.

Understanding CO 2 addition and H 2 activation by geminal P/Z (Z = B, Al) frustrated Lewis pairs (FLPs) is crucial for the development of transition metal-free catalysts for hydrogenation of unsaturated compounds and CO 2 conversion. The distortion-interaction energy decomposition and natural bond orbital were used to gain insights into the reactivity of CO 2 addition and H 2 activation. Remarkably, the orbital interactions in the reactions of CO 2 and H 2 with geminal P/B FLPs are stronger than those in the reactions with more reactive geminal P/Al FLPs, which contain a stronger Lewis acid. The fact that geminal P/B FLPs react with a higher energy barrier than geminal P/Al FLPs is actually due to the unfavorable core repulsion contribution to the interaction energy and the higher distortion energy found for the geminal P/B FLPs. In addition, we revealed that although the interaction energy is higher for H 2 activation, the distortion energy is significantly lower for CO 2 addition. Thus, geminal P/Z FLPs are more reactive toward CO 2 than toward H 2 . Overall, the reactivity and thermodynamic stability for the reactions of geminal P/Z FLPs with CO 2 and H 2 are not affected by the type of bridging carbon (sp 3 -C or sp 2 -C) but mainly influenced by the substituents on P and Z (B or Al). An insight into the thermodynamic stability of the H 2 activation product is gained by quantifying the hydride affinity, the proton affinity, and the stability of the zwitterionic product relative to the prototypical Lewis acid-base pair, P t Bu 3 /B(C 6 F 5 ) 3 .

The hydroheteroarylation of allylbenzene with pyridine as catalyzed by Ni/AlMe 3 and a N-heterocyclic carbene ligand has recently been established. Density functional calculations revealed that the common stepwise pathway, which involves the C-H oxidative addition of pyridine-AlMe 3 before the migratory insertion of allylbenzene, is unlikely as the migratory insertion needs to overcome a prohibitively high energy barrier. In contrast, the ligand-to-ligand hydrogen transfer pathway is more favorable in which the hydrogen is transferred directly from the para -position of pyridine-AlMe 3 to C2 of allylbenzene. Our distortion-interaction analysis and natural bond orbital analysis indicate that the interaction energy is strongly correlated with the extent of the charge transfer from the alkene (hydrogen acceptor) to the pyridine-AlMe 3 (hydrogen donor), which dictates the selectivity of the H-transfer to the C2 position of allylbenzene. Then, the subsequent C-C reductive elimination of the regioselective linear product is facilitated by the steric hindrance of the IPr ligand. Understanding these key factors affecting the product regioselectivity is important to the development of catalysts for hydroheteroarylation of alkenes.

A series of heteroditopic receptors containing halogen bond (XB) and unprecedented chalcogen bond (ChB) donors integrated into a 3,5-bis-triazole pyridine structure covalently linked to benzo-15-crown-5 ether motifs exhibit remarkable cooperative recognition of halide anions. Multi-nuclear 1 H, 13 C, 125 Te and 19 F NMR, ion pair binding investigations reveal sodium cation-benzo-crown ether binding dramatically enhances the recognition of bromide and iodide halide anions, with the chalcogen bonding heteroditopic receptor notably displaying the largest enhancement of halide binding strength of over two hundred-fold, in comparison to the halogen bonding and hydrogen bonding heteroditopic receptor analogues. DFT calculations suggest crown ether sodium cation complexation induces a polarisation of the sigma hole of ChB and XB heteroditopic receptor donors as a significant contribution to the origin of the unique cooperativity exhibited by these systems., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

MCR (mobile colistin resistance) enzymes catalyse phosphoethanolamine (PEA) addition to bacterial lipid A, threatening the "last-resort" antibiotic colistin. Molecular dynamics and density functional theory simulations indicate that monozinc MCR supports PEA transfer to the Thr285 acceptor, positioning MCR as a mono- rather than multinuclear member of the alkaline phosphatase superfamily.

Phenol derivatives have been increasingly used as alternatives for aryl halides in cross-coupling reactions due to their lower toxicity and easier availability. Nickel complexes have been developed as efficient catalysts for aryl C-O bond activation of phenol derivatives. Herein, we performed a density functional study to investigate the aryl C-O bond oxidative addition of phenol derivatives on Ni-SIPr. For phenyl sulfonates and phenyl esters, the pathway via a five-centered transition state involving the interaction from sulfonyl/carbonyl O to Ni is preferred over that via a three-centered transition state. While the five-centered transition state with the interaction from sulfamoyl N to Ni is favored over the interaction from sulfamoyl O to Ni for phenyl sulfamate, the interaction from carbamoyl O to Ni is more favored for phenyl carbamate. For aryl ethers, the Lewis acid AlMe 3 facilitates aryl C-O bond activation by forming a Lewis acid/base adduct with 2-methoxynaphthalene (NaphOMe) resulting in a lower free energy barrier than that in the absence of AlMe 3 . While the free energy barriers for the aryl C-O bond oxidative addition of a NaphOMe/AlMe 2 R (R = Me, Ph, OMe, and H) adduct via the "classical" three-centered transition state are all similar, the corresponding free energy barriers via the five-centered transition state, involving the interaction from the R group of AlMe 2 R to Ni, can be lower and depend on the R group. Not only is the aryl C-O bond weakened, but the nucleophilicity of Ni is enhanced in the latter pathway. In fact, these key interactions are analogous to those via the five-centered transition states of phenyl sulfonate/sulfamate and phenyl ester/carbamate. Our results revealed that the pathway involving an additional electron donating interaction to Ni via the five-centered transition state facilitates the aryl C-O bond oxidative addition of phenol derivatives. Through this pathway, the appropriate use of organoaluminum can improve the efficiency of Ni catalysts for cross-coupling reactions of inert aryl ethers.

Understanding the reaction mechanism underlying the functionalization of C-H bonds by an enzymatic process is one of the most challenging issues in catalysis. Here, combined approaches using density functional theory (DFT) analysis and transient kinetics were employed to investigate the reaction mechanism of C-H bond oxidation in d-glucose, catalyzed by the enzyme pyranose 2-oxidase (P2O). Unlike the mechanisms that have been conventionally proposed, our findings show that the first step of the C-H bond oxidation reaction is a hydride transfer from the C2 position of d-glucose to N5 of the flavin to generate a protonated ketone sugar intermediate. The proton is then transferred from the protonated ketone intermediate to a conserved residue, His548. The results show for the first time how specific interactions around the sugar binding site promote the hydride transfer and formation of the protonated ketone intermediate. The DFT results are also consistent with experimental results including the enthalpy of activation obtained from Eyring plots, as well as the results of kinetic isotope effect and site-directed mutagenesis studies. The mechanistic model obtained from this work may also be relevant to other reactions of various flavoenzyme oxidases that are generally used as biocatalysts in biotechnology applications., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The mechanism of HCO2H dehydrogenation catalyzed by [IrCp*(H2O)(bpymO4H4)]2+ (bpymO4H4 = 2,2',6,6'-tetrahydroxy-4,4'-bipyrimidine) was investigated using density functional theory. The relative free energy profiles at various protonation states corrected to pH 3.5 and pH 7.6 suggested that Na+ together with the ortho-oxyanion of bipyrimidine facilitates the Ir-HCO2 formation, subsequent hydride transfer, and H2 formation. HCO2H was found to be a more effective proton shuttle than H2O for H2 formation. Under experimental conditions, the highest catalytic reactivity was found at pH 3.5-4.0, where both HCO2Na and HCO2H were present. At lower pH and low formate concentration, HCO2H dehydrogenation tends to proceed via a Na+ independent pathway, involving a higher energy barrier. At higher pH, although Na+ can mediate hydride transfer and H2 formation, the low amount of HCO2H results in H2O as the proton shuttle, which involves a higher energy barrier than that for HCO2H proton shuttle. In other words, the catalytic activity of HCO2H dehydrogenation by the proton-responsive Ir complexes at different pH values is influenced by the protonation state, involvement of Na+, and the availability of HCO2H as a proton shuttle. For the hydrogenation of CO2 at pH 8.3, the rate determining step is the heterolytic cleavage of H2 mediated by Na+via a HCO3- proton shuttle. Our results demonstrate the importance of alkali metal ions in the design of catalysts for efficient, reversible, CO2 conversion.

Enzymes that are capable of detoxifying halogenated phenols (HPs) and nitrophenols (NPs) are valuable for bioremediation and waste biorefining. HadA monooxygenase was found to perform dual functions of oxidative dehalogenation (hydroxylation plus halide elimination) and denitration (hydroxylation plus nitro elimination). Rate constants associated with individual steps of HadA reactions with phenol, halogenated phenols and nitrophenols were measured using combined transient kinetic approaches of stopped-flow absorbance/fluorescence and rapid-quench flow techniques. Density functional theory was used to calculate the thermodynamic and electronic parameters associated with hydroxylation and group elimination steps. These parameters were correlated with the rate constants of hydroxylation, group elimination, and overall product formation to identify factors controlling individual steps. The results indicated that the hydroxylation rate constant is higher when the p K a of the phenolic group is lower, i.e. it is more easily deprotonated, but not higher when the energy gap between the E of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the p LUMO of the C4a-hydroperoxy-FAD intermediate and the E HOMO of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the p K a value of the substrate, indicating that the overall reaction is controlled by substrate deprotonation. This step also likely has the highest energy barrier and thus controls the overall process of oxidative dehalogenation and denitration by HadA. This report is the first to identify a key mechanistic factor controlling the enzymatic processes of oxidative dehalogenation and denitration.