Quantitative Differences in Sulfur Poisoning Phenomena over Ruthenium and Palladium: An Attempt To Deconvolute Geometric and Electronic Poisoning Effects Using Model Catalysts

Intrinsic Effects of Sulfidation on the Reactivity of Zero-Valent Iron With Trichloroethene: A DFT Study

Sulfidation represents a promising approach to enhance the selectivity and longevity of zero-valent iron (ZVI) in water treatment, particularly for nanoscale ZVI (nZVI). While previous mechanistic studies have primarily concentrated on the impact of sulfidation on the (n)ZVI hydrophobicity, the fundamental effects of sulfidation on the (n)ZVI reactivity with target contaminants remain poorly understood. Herein, we employed density functional theory to elucidate reaction mechanisms of trichloroethene (TCE) dechlorination at various (n)ZVI surface models, ranging from pristine Fe0 to regularly sulfidated Fe surfaces. Our findings indicate that sulfidation intrinsically hinders the TCE dechlorination by (n)ZVI, which aligns with prior observations of sulfur poisoning in transition metal catalysts. We further demonstrate that the positive effects of sulfidation emerge when the surface of (n)ZVI undergoes corrosion. Notably, S sites exhibit higher reactivity compared to the sites typically present on the surface of (n)ZVI oxidized in water. Additionally, S sites protect nearby Fe sites against oxidation and make them more selective for direct electron transfer. Overall, our results reveal that the reactivity of sulfidated (n)ZVI is governed by an interplay of intrinsic inhibitory effects and corrosion protection. A deeper understanding of these phenomena may provide new insights into the selectivity of sulfidated (n)ZVI for specific contaminants.

Applying green chemistry principles to iron catalysis: mild and selective domino synthesis of pyrroles from nitroarenes

An efficient and general cascade synthesis of pyrroles from nitroarenes using an acid-tolerant homogeneous iron catalyst is presented. Initial (transfer) hydrogenation using the commercially available iron-Tetraphos catalyst is followed by acid catalysed Paal-Knorr condensation. Both formic acid and molecular hydrogen can be used as green reductants in this process. Particularly, under transfer hydrogenation conditions, the homogeneous catalyst shows remarkable reactivity at low temperatures, high functional group tolerance and excellent chemoselectivity transforming a wide variety of substrates. Compared to classical heterogeneous catalysts, this system presents complementing reactivity, showing none of the typical side reactions such as dehalogenation, debenzylation, arene or olefin hydrogenation. It thereby enhances the chemical toolbox in terms of orthogonal reactivity. The methodology was successfully applied to the late-stage modification of multi-functional drug(-like) molecules as well as to the one-pot synthesis of the bioactive agent BM-635.

Selective Hydrogenation of 5-Hydroxymethylfurfural to 1-Hydroxy-2,5-hexanedione by Biochar-Supported Ru Catalysts

The development of sustainable and efficient catalysts -namely Ru supported on activated biochars- is carried out for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 1-hydroxy-2,5-hexanedione (HHD). Activated biochars obtained from pyrolysis and steam-based physical activation of two different biomasses from animal (leather tannery waste; A_Lw ) and vegetal (hazelnut shells; A_HSw ) origins show completely different chemical, textural, and morphological properties. Compared to A_Lw , after impregnation with 0.5 wt % Ru, A_HSw , with inner micro-mesochannels and cavities and higher layer stacking disorder, leads to better trapping and anchoring of Ru nanoparticles on the catalyst and a suitable Ru single crystal dispersion. This leads to a highly active Ru/A_HSw catalyst in the proposed reaction, giving more than 80 % selectivity to HHD and full HMF conversion at 100 °C with 30 bar H₂ for 3 h. Ru/A_HSw also shows promising performance compared to a commercial Ru/C catalyst.

Selective Catalysis Remedies Polysulfide Shuttling in Lithium-Sulfur Batteries

The shuttling of soluble lithium polysulfides between the electrodes leads to serious capacity fading and excess use of electrolyte, which severely bottlenecks practical use of Li-S batteries. Here, selective catalysis is proposed as a fundamental remedy for the consecutive solid-liquid-solid sulfur redox reactions. The proof-of-concept Indium (In)-based catalyst targetedly decelerates the solid-liquid conversion, dissolution of elemental sulfur to polysulfides, while accelerates the liquid-solid conversion, deposition of polysulfides into insoluble Li₂ S, which basically reduces accumulation of polysulfides in electrolyte, finally inhibiting the shuttle effect. The selective catalysis is revealed, experimentally and theoretically, by changes of activation energies and kinetic currents, modified reaction pathway together with the probed dynamically changing catalyst (LiInS₂ catalyst), and gradual deactivation of the In-based catalyst. The In-based battery works steadily over 1000 cycles at 4.0 C and yields an initial areal capacity up to 9.4 mAh cm^-2 with a sulfur loading of ≈9.0 mg cm^-2 .

Hierarchical Hybrid Supports and Synthesis Strategies for Hydrodesulfurization of Recalcitrance Organosulfur Compounds

It is undisputed that there is a paradigm shift in the global trend of crude oil towards being more sour and heavier than usual light sources. Consequently, the hydrotreating activity becomes a bottleneck with high content of S, N, metals and other impurities than expected. On the other hand, the price of petroleum products lately witnessed instability and fell to the lowest average price (<USD 20) in recent times. In the same vein, the regulation to control the emission of toxic compounds in the atmosphere become stricter as promulgated by various policymakers. In this sense, robust hydrotreating catalysts with characteristics efficient catalytic activity, selectivity and stability are highly desirable. Recently, different approaches have been used to improve and cushion the unprecedented effect emanated from economic, social and environmental challenges posed by heavy and sour crude sources, price instability of the refined products and regulation to lower the sulfur to minimum level or zero parts per millions (ppm). Importantly, the role of support in catalysis cannot be over emphasized, whilst the surface area and porosity, mechanical and thermal stability, dispersion of active metals, acidity/basicity have been greatly improved, the increased activity, stability and selectivity has been observed significantly. In this review, hybrid supports based on aluminosilicates (zeolitic types) and other notable supports from recent literatures were explored and discussed for Ni(Co)Mo(W) supported catalysts for hydrodesulfurization (HDS) activity of heavy organosulfur molecules. The emphasis on the hybrid supports' varied characteristics for HDS of organosulfur molecules, where there are necessities for fast diffusion of reactants and products, better dispersion of MoS₂ crystallites, high surface area and pore volume, and increased acidity of the catalysts are greatly emphasized. Furthermore, the progress made so far on different HDS active phases viz. noble metals, metal phosphides, intermetallic silicides, carbides and iron-zinc are highlighted in this write-up, irrespective of the support composition in the supported catalysts formulations. The need for application of predictive tools, like machine learning (ML) in the design and development of HDS catalysts, and performance evaluation of HDS activity towards achieving better catalytic operation was briefly highlighted. Finally, the review will serve as a summary of scientific efforts in this regards and bridge a gap for the newcomers to investigate the topic in a better way through proper selection and efficient catalysts design.

Safe, Scalable, Inexpensive, and Mild Nickel-Catalyzed Migita-Like C-S Cross-Couplings in Recyclable Water

A new approach to C-S couplings is reported that relies on nickel catalysis under mild conditions, enabled by micellar catalysis in recyclable water as the reaction medium. The protocol tolerates a wide range of heteroaromatic halides and thiols, including alkyl and heteroaryl thiols, leading to a variety of thioethers in good isolated yields. The method is scalable, results in low residual metal in the products, and is applicable to syntheses of targets in the pharmaceutical area. The procedure also features an associated low E Factor, suggesting a far more attractive entry than is otherwise currently available, especially those based on unsustainable loadings of Pd catalysts.

Organoruthenium-catalyzed chemical protein synthesis to elucidate the functions of epigenetic modifications on heterochromatin factors

The application of organometallic compounds for protein science has received attention. Recently, total chemical protein synthesis using transition metal complexes has been developed to produce various proteins bearing site-specific posttranslational modifications (PTMs). However, in general, significant amounts of metal complexes were required to achieve chemical reactions of proteins bearing a large number of nucleophilic functional groups. Moreover, syntheses of medium-size proteins (>20 kDa) were plagued by time-consuming procedures due to cumbersome purification and isolation steps, which prevented access to variously decorated proteins. Here, we report a one-pot multiple peptide ligation strategy assisted by an air-tolerant organoruthenium catalyst that showed more than 50-fold activity over previous palladium complexes, leading to rapid and quantitative deprotection on a protein with a catalytic amount (20 mol%) of the metal complex even in the presence of excess thiol moieties. Utilizing the organoruthenium catalyst, heterochromatin factors above 20 kDa, such as linker histone H1.2 and heterochromatin protein 1α (HP1α), bearing site-specific PTMs including phosphorylation, ubiquitination, citrullination, and acetylation have been synthesized. The biochemical assays using synthetic proteins revealed that the citrullination at R53 in H1.2 resulted in the reduced electrostatic interaction with DNA and the reduced binding affinity to nucleosomes. Furthermore, we identified a key phosphorylation region in HP1α to control its DNA-binding ability. The ruthenium chemistry developed here will facilitate the preparation of a variety of biologically and medically significant proteins containing PTMs and non-natural amino acids.

Chemical protein synthesis assisted by an organoruthenium catalyst streamlined the production of heterochromatin factors bearing various patterns of epigenetic modifications, and their biological significance was elucidated.

Mannose-coated polydiacetylene (PDA)-based nanomicelles: synthesis, interaction with concanavalin A and application in the water solubilization and delivery of hydrophobic molecules

Carbohydrate-lectin interactions are involved in a number of relevant biological events including fertilization, immune response, cell adhesion, tumour cell metastasis, and pathogen infection. Lectins are also tissue specific, making carbohydrates not only promising drug candidates but also excellent low molecular weight ligands for active drug delivery system decorations. In order for these interactions to be effective multivalency is essential, as the interaction of a lectin with its cognate monovalent carbohydrate epitope usually takes place with low affinity. Unlike the covalent approach, supramolecular self-assembly of glyco-monomers mediated by non-covalent forces allows accessing multivalent systems with diverse topology, composition, and assembly dynamics in a single step. In order to fine-tune the size and sugar adaptability of spherical micelles at the nanoscale for an optimal glycoside cluster effect, herein we report the synthesis of mannose-coated static micelles from diacetylene-based mannopyranosyl glycolipids differing in the length of the poly(ethyleneglycol) (PEG) chains and the oxidation state of the anomeric sulfur atom. The reported shot-gun like synthetic approach for the synthesis of dilution-insensitive micelles is based on the ability of diacetylenic-based neoglycolipids to self-assemble into micelles in water and to undergo an easy photopolymerization by a simple irradiation at 254 nm. The affinity of the obtained 6 nanosystems was assessed by enzyme-linked lectin assay (ELLA) using the mannose-specific concanavalin A lectin as a model receptor. Relative binding potency enhancements, compared to methyl α-d-mannopyranoside used as control, from 20-, to 29- to 300-fold on a sugar molar basis were observed for micelles derived from sulfonyl-, sulfinyl- and thioglycoside monomers with a tatraethyleneglycol spacer, respectively, indicative of a significant cluster glycoside effect. Moreover, pMic1 micelles are able to solubilize and slowly liberate lipophilic clinically relevant drugs, and show the enhanced cytotoxic effect of docetaxel toward prostate cancer cells. These findings highlight the potential of mannose-coated photopolymerized micelles pMic1 as an efficient nanovector for active delivery of cytotoxic hydrophobic molecules.

Discovery, Synthesis, and Scale-up of Efficient Palladium Catalysts Useful for the Modification of Nucleosides and Heteroarenes

Nucleic acid derivatives are imperative biomolecules and are involved in life governing processes. The chemical modification of nucleic acid is a fascinating area for researchers due to the potential activity exhibited as antiviral and antitumor agents. In addition, these molecules are also of interest toward conducting useful biochemical, pharmaceutical, and mutagenic study. For accessing such synthetically useful structures and features, transition-metal catalyzed processes have been proven over the years to be an excellent tool for carrying out the various transformations with ease and under mild reaction conditions. Amidst various transition-metal catalyzed processes available for nucleoside modification, Pd-catalyzed cross-coupling reactions have proven to be perhaps the most efficient, successful, and broadly applicable reactions in both academia and industry. Pd-catalyzed C-C and C-heteroatom bond forming reactions have been widely used for the modification of the heterocyclic moiety in the nucleosides, although a single catalyst system that could address all the different requirements for nucleoside modifications isvery rare or non-existent. With this in mind, we present herein a review showcasing the recent developments and improvements from our research groups toward the development of Pd-catalyzed strategies including drug synthesis using a single efficient catalyst system for the modification of nucleosides and other heterocycles. The review also highlights the improvement in conditions or the yield of various bio-active nucleosides or commercial drugs possessing the nucleoside structural core. Scale ups wherever performed (up to 100 g) of molecules of commercial importance have also been disclosed.

Efficient Non-dissociative Activation of Dinitrogen to Ammonia over Lithium-Promoted Ruthenium Nanoparticles at Low Pressure

There is an exciting possibility to decentralize ammonia synthesis for fertilizer production or energy storage without carbon emission from H₂ obtained from renewables at small units operated at lower pressure. However, no suitable catalyst has yet been developed. Ru catalysts are known to be promoted by heavier alkali dopants. Instead of using heavy alkali metals, Li is herein shown to give the highest rate through surface polarisation despite its poorest electron donating ability. This exceptional promotion rate makes Ru-Li catalysts suitable for ammonia synthesis, which outclasses industrial Fe counterparts by at least 195 fold. Akin to enzyme catalysis, it is for the first time shown that Ru-Li catalysts hydrogenate end-on adsorbed N₂ stabilized by Li⁺ on Ru terrace sites to ammonia in a stepwise manner, in contrast to typical N₂ dissociation on stepped sites adopted by Ru-Cs counterparts, giving new insights in activating N₂ by metallic catalysts.

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X-ray Probes

Bimetallic nanocatalysts are key enablers of current chemical technologies, including car exhaust converters and fuel cells, and play a crucial role in industry to promote a wide range of chemical reactions. However, owing to significant characterization challenges, insights in the dynamic phenomena that shape and change the working state of the catalyst await further refinement. Herein, we discuss the atomic-scale processes leading to mono- and bimetallic nanoparticle formation and highlight the dynamics and kinetics of lifetime changes in bimetallic catalysts with showcase examples for Pt-based systems. We discuss how in situ and operando X-ray spectroscopy, scattering, and diffraction can be used as a complementary toolbox to interrogate the working principles of today's and tomorrow's bimetallic nanocatalysts.