Synthesis of valuable (Z)-1,2-dialkyl alkenes via cis-semihydrogenation of alkynes is often plagued by side reactions such as alkene isomerization and over-reduction. Here we report a catalyst-state induced color-change (CatSICC) strategy for precise detection of reaction endpoint of transfer hydrogenation (TH), enabling highly efficient and cis-selective semihydrogenation of dialkyl alkynes with EtOH as H-donor. A series of NHC carbene-containing pincer iridium complexes (PCCNHC)IrHX (X = Br or I) have been prepared and applied to the TH reaction. Monitoring the TH process reveals a vibrant color-change of the solution from purple to yellow-orange as a result of transition of the catalyst-state from (PCCNHC)Ir(alkyne) to (PCCNHC)IrHMe(CO), signifying the complete conversion of alkyne substrate. Quenching the reaction timely according to the color-change allows access to (Z)-1,2-dialkyl alkenes with very high efficiency, exquisite precision, and broad functional group tolerance. The reliability and practicability of this protocol is demonstrated by cis-semihydrogenation of complex polyfunctionalized bioactive molecules. Mechanistic studies establish that the propensity of (PCCNHC)Ir to undergo facile EtOH decarbonylation to form isomerization-inactive species (PCCNHC)IrHMe(CO) only when the semihydrogenation reaction is completed is important to stereo- and chemoselectivity control.

Background: Ammonia (NH3) serves as a promising medium for hydrogen storage and transportation, addressing the challenges associated with these processes. However, the ammonia decomposition reaction urgently requires catalysts with high activity and stability. Methods: Here, we present a synergistic strategy for the preparation of a highly dispersed Ru/Al2O3 catalyst using an atmosphere-induced method. Under an oxidizing atmosphere (Ru/Al2O3-O), the particle size of RuO2 exceeds 10 nm. Conversely, by oxygen vacancies anchoring in a reducing atmosphere, highly dispersed and structurally stable Ru catalysts with particle sizes lower 2 nm can be prepared. HRTEM, XPS, TPR and XRD have been employed to elucidate the morphology and electronic structure of the Ru metal. Significant Findings: This research investigated the impact of atmosphere-induced effects on the particle size and ammonia decomposition activity of Ru/gamma-Al2O3 catalysts. A reducing atmosphere induced the formation of oxygen vacancies in the alumina support, leading to highly dispersed Ru/gamma-Al2O3 catalysts. The interaction between Ru species and oxygen vacancies led to Ru particles of catalyst smaller than 2 nm and a stable structure. The removal of Cl ions from the Ru-based catalyst positively influenced the enhancement of ammonia decomposition activity. XPS and TPD results indicated that the introduction of the alkali metal potassium increased the electron density of Ru species, facilitating the ammonia decomposition reaction process. The K-Ru/gamma-Al2O3-RW catalyst achieved a conversion rate of 97 % at 450 degrees C at a flow rate of 18,000 mL/g(cat)/h. Stability tests showed that the K-Ru/gamma-Al2O3-RW catalyst did not deactivate after undergoing a 700-hour lifetime test. This work provides an effective method for synthesizing Ru-based catalysts to enhance ammonia decomposition for hydrogen production.

Different from the reported work focusing on the construction of single P- or C-stereocenter via hydrophosphinylation of unsaturated carbon bonds, the highly diastereo- and enantioselective hydrophosphinylation reaction of allenes, conjugated enynes and 1,3-dienes is achieved via a designed Pd/Co dual catalysis and newly modified masked phosphinylating reagent. A series of allyl motifs bearing both a tertiary C- and P-stereocenter are prepared in generally good yields, >20 : 1 dr, >20 : 1 rr and 99 % ee. The unprecedented diastereo- and enantioselective hydrophosphinylation of 1,3-enynes is established to generate skeletons containing both a P-stereocenter and a nonadjacent chiral axis. The first stereodivergent hydrophosphinylation reaction is also developed to achieve all four P-containing stereoisomers. The present protocol features the use of only 3-minutes reaction time and 0.1 % catalyst, and with the observation of up to 730 TON. A set of mechanistic studies reveal the necessity and roles of two metal catalysts and corroborate the designed synergistic process.

Cyclodipeptide synthases (CDPSs) catalyze the synthesis of diverse cyclodipeptides (CDPs) by utilizing two aminoacyl-tRNA (aa-tRNA) substrates in a sequential ping-pong reaction mechanism. Numerous CDPSs have been characterized to provide precursors for diketopiperazines (DKPs) with diverse structural characteristics and biological activities. BcmA, belonging to the XYP subfamily, is a cyclo(l-Ile-l-Leu)-synthesizing CDPS involved in the biosynthesis of the antibiotic bicyclomycin. The structural basis and determinants influencing BcmA enzyme activity and substrate selectivity are not well understood. Here, we report the crystal structure of SsBcmA from Streptomyces sapporonensis. Through structural comparison and systematic site-directed mutagenesis, we highlight the significance of key residues located in the aminoacyl-binding pocket for enzyme activity and substrate specificity. In particular, the nonconserved residues D161 and K165 in pocket P2 are essential for the activity of SsBcmA without significant alteration of the substrate specificity, while the conserved residues F158 as well as F210 and S211 in P2 are responsible for determining substrate selectivity. These findings facilitate the understanding of how CDPSs selectively accept hydrophobic substrates and provide additional clues for the engineering of these enzymes for synthetic biology applications.

Acridine scaffolds are present in biological and pharmaceutical molecules. However, achieving asymmetric functionalization of acridines remains challenging without an efficient and highly stereoselective approach. Here we demonstrate a facile electrooxidative asymmetric dehydrogenative coupling reaction of 9,10-dihydroacridines with aldehydes. This method offers a sustainable and effective route to various chiral alpha-alkylation of 9,10-dihydroacridines in high yields with excellent enantioselectivities facilitated by readily available aminocatalyst. Detailed mechanistic studies and cyclic voltammetric analyses reveal that this asymmetric electrochemical reaction proceeds through redox-mediated oxidation, followed by a nucleophilic attack with concurrently generated enamine. We anticipate that our research will open avenues for promising exploration in organocatalyzed electrochemical enantioselective transformations.

In this work, we report a visible light-induced energy transfer process related photochemical protocol of cumulative diene containing compounds for the construction of benzocyclohexene skeletons or the corresponding aromatized structures through an energy transfer process, 1,5-hydrogen atom transfer and a 6 pi electrocyclization or demethoxylation in the presence of different photocatalysts such as [Ir(dF(Me)ppy)(2)(dtbbpy)]PF6 or thioxanthone. This newly developed photochemical strategy is characterized by mild conditions, broad substrate applicability, good functional group tolerance and good yields. The mechanistic paradigm was clarified by deuterium labeling, kinetic, photophysical and electrochemical analyses, control experiments and density functional theory (DFT) calculations. The transformation of the obtained product to the drug-like molecules such as Sertraline and the luminescent conjugated aromatic compounds has also been disclosed.

Catalytic regio-, diastereo- and enantioselective reductive coupling of 1,3-dienes and aldehydes through regio- and enantioselective oxidative cyclization followed by regio- and diastereoselective protonation promoted by a chiral phosphine-cobalt complex is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis that enable selective transformation of the more substituted alkene in 1,3-dienes, affording a broad scope of bishomoallylic alcohols without the need of pre-formation of stoichiometric amounts of sensitive organometallic reagents in up to 98 % yield, >98 : 2 regioselectivity, >98 : 2 dr and 98 : 2 er. Application of this method to construction of axial stereogenicity and deuterated stereogenic center provided a wide range of multifunctional chiral building blocks that are otherwise difficult to access. DFT calculations revealed the origin of regio- and stereoselectivity as well as a unique oxidative cyclization mechanism for cobalt catalysis.

Photo catalysis has comprehensively become a powerful tool in organic synthesis, and organic molecules are thriving as catalyst. The thioxanthone-TfOH complex (9-HTXTF) as photoredox catalyst with high oxidative capacity can be applied in single electron reduction of alkene affording alkene radical anion as a key intermediate. To transform this intermediate from radical anion to radical cation, a well-designed strategy is proposed with N-arylacrylamides as substrate. Based on its single electron transfer (SET) with 9-HTXTF*, N-radical cation is generated and then transformed to alkene radical cation by intramolecular conjugated system. By using this photoredox catalysis strategy, we developed a 9-HTXTF-catalyzed photochemical cyclization of alkenes, which further expands the applications of this catalyst. The entire cyclization is metal-free and without sacrificing agents, which conforms to atom economy and environmental friendliness.

Over 200 genetic mutations in copper-zinc superoxide dismutase (SOD1) have been linked to amyotrophic lateral sclerosis (ALS). Among these, two ALS-causing mutants, histidine-46 -> arginine (H46R) and glycine-85 -> arginine (G85R), exhibit a decreased capacity to bind metal ions. Here, we report two cryo-electron microscopy structures of amyloid fibrils formed by H46R and G85R. These mutations lead to the formation of amyloid fibrils with unique structures distinct from those of the native fibril. The core of these fibrils features a serpentine arrangement with seven or eight beta strands, secured by a hydrophobic cavity and a salt bridge between arginine-85 and aspartic acid-101 in the G85R fibril. We demonstrate that these mutant fibrils are notably more toxic and capable of promoting the aggregation of wild-type SOD1 more effectively, causing mitochondrial impairment and activating ferroptosis in cell cultures, compared to wild-type SOD1 fibrils. Our study provides insights into the structural mechanisms by which SOD1 mutants aggregate and induce cytotoxicity in ALS.