Graphdiyne‐Based Multiscale Catalysts for Ammonia Synthesis

Posted on 22 September 2023 by

Graphdiyne catalysts for ammonia synthesis! This review highlights the unique structures and properties of graphdiyne, provides a comprehensive update in regard to the synthesis of graphdiyne-based multiscale catalysts and their applications in the synthesis of ammonia, and discusses the challenges and future perspectives relating to graphdiyne.

Abstract

Graphdiyne, a sp/sp²-cohybridized two-dimensional all- carbon material, has many unique and fascinating properties of alkyne-rich structures, large π conjugated system, uniform pores, specific unevenly-distributed surface charge, and incomplete charge transfer properties provide promising potential in practical applications including catalysis, energy conversion and storage, intelligent devices, life science, photoelectric, etc. These superior advantages have made graphdiyne one of the hottest research frontiers of chemistry and materials science and produced a series of original and innovative research results in the fundamental and applied research of carbon materials. In recent years, considerable advances have been made toward the development of graphdiyne-based multiscale catalysts for nitrogen fixation and ammonia synthesis at room temperatures and ambient pressures. This review aims to provide a comprehensive update in regard to the synthesis of graphdiyne-based multiscale catalysts and their applications in the synthesis of ammonia. The unique features of graphdiyne are highlighted throughout the review. Finally, it concludes with the discussion of challenges and future perspectives relating to graphdiyne.

Cu−NHC Complex for Chan‐Evans‐Lam Cross‐Coupling Reactions of N‐Heterocyclic Compounds and Arylboronic Acids

Posted on 22 September 2023 by

An efficient copper(II) N-heterocyclic carbene (NHC) complex catalyzing the Chan–Evans-Lam cross-coupling reaction of N-heterocyclic nucleophiles with arylboronic acid has been explored. This air-stable copper catalyst shows practical robustness that tolerates a diverse array of functional groups on both the N-nucleophile and arylboronic acid coupling partners in C−N bond forming reactions through the CEL reaction.

Abstract

An efficient copper(II) N-heterocyclic carbene (NHC) complex with an NCN coordination mode was optimized to catalyze the Chan–Evans-Lam (CEL) cross-coupling reaction of imidazole and other N-heterocyclic nucleophiles with arylboronic acid. This air-stable copper catalyst shows robust catalytic performance and tolerates a diverse array of functional groups on both the N-nucleophile and arylboronic acid coupling partners in C−N bond forming reactions with up to 95 % yield. Formation of the Cu−NHC complex in situ generated similar catalytic performance for CEL coupling. Alternative metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Ru²⁺, and Pd²⁺) were also screened in the presence of the NHC precursor as CEL catalysts.

One‐Photon and Two‐Photon Absorption Properties of Multi‐Branched Squaraine Dyes Comprised of Triphenylamine Cores and Ethynylene Linkers

Posted on 22 September 2023 by

The squaraine chromophores, which have single, two-branched, and three-branched structures with ethynyl-triphenylamine central units, exhibit efficient two-photon absorption (TPA) with a cross section that corresponds to the number of branches present, indicating an additive effect. Among these chromophores, the three-branched dye displays the highest TPA cross section, reaching a maximum value of 4.0×10³ GM.

Abstract

We developed multi-branched π-conjugated systems using squaraine dyes with triphenylamine cores connected by ethynylene linkers. We investigated the influence of interbranch coupling between squaraine branches on their one-photon (OPA) and two-photon absorption (TPA) properties. These dyes with triphenylamine components showed a red-shifted one-photon absorption (OPA) compared to the precursor squaraine dyes. Among branched dyes, the lack of apparent splitting or shift in the absorption maxima, even as the absorption intensity increased with the number of chromophores, implies the presence of limited exciton coupling between the squaraine branches. The present squaraine dyes with triphenylamine cores exhibited a moderate TPA compared to the precursor squaraine without the triphenylamine core, due to the extended π-conjugation. Notably, both the 3-branched and 2-branched dyes demonstrated additional enhancement in the TPA response, surpassing that of the monochromophoric counterpart. This resulted in achieving a substantial TPA cross section of up to 3905 GM at 830 nm.

[1,2,4]Triazolo[1,5‐c]pyrimidines as Tools to Investigate A3 Adenosine Receptors in Cancer Cell Lines

Posted on 22 September 2023 by

A new series of [1,2,4]triazolo[1,5-c]pyrimidines was investigated at position 2 to obtain potent and selective A₃ #adenosine receptor antagonists. #Docking studies were performed to rationalize these results, particularly with respect to selectivity. The best compound in the series was then tested on #cancer cell lines expressing the target receptor and showed an interesting proliferative effect.

Abstract

The A₃ adenosine receptor is an interesting target whose role in cancer is controversial. In this work, a structural investigation at the 2-position of the [1,2,4]triazolo[1,5-c]pyrimidine nucleus was performed, finding new potent and selective A₃ adenosine receptor antagonists such as the ethyl 2-(4-methoxyphenyl)-5-(methylamino)-[1,2,4]triazolo[1,5-c]pyrimidine-8-carboxylate (20, DZ123) that showed a K_i value of 0.47 nM and an exceptional selectivity profile over the other adenosine receptor subtypes. Computational studies were performed to rationalize the affinity and the selectivity profile of the tested compounds at the A₃ adenosine receptor and the A₁ and A_2A adenosine receptors. Compound 20 was tested on both A₃ adenosine receptor positive cell lines (CHO-A₃AR transfected, THP1 and HCT16) and on A₃ negative cancer cell lines, showing no effect in the latter and a pro-proliferative effect at a low concentration in the former. These interesting results pave the way to further investigation on both the mechanism involved and potential therapeutic applications.

Antibacterial Compound Isolation and Characterization from the Plant Cynotis axillaris Schult

Posted on 22 September 2023 by nKesar Singh, nR. N. Yadava, nRitu Yadavn

Abstract

A novel flavone glycoside was isolated from the methanolic extract of Cynotis axillaris Schult. Various analysis and characterization techniques were used to determine its structure and properties. The compound exhibited a melting point range of 231–232 °C and had a molecular formula of C₂₇H₃₀O₁₄. Several spectral characterization techniques were employed to establish the isolated compound's structure. These included UV-visible spectroscopy, FT-IR, LC-ESI-MS, and NMR spectroscopy. Based on these analyses, the structure of the isolated compound was determined to be 5,7,4’-trihydroxyflavone-8-α-L-rhamnopyranoside-4’-O-β-D-galactopyranosyl. This structure indicates that it is a flavone glycoside consisting of a flavone (5,7,4’-trihydroxyflavone) moiety attached to a sugar molecule (galactopyranosyl) at position 4’, which further bears a rhamnose group at position 8 of the flavone. In addition, to the structural characterization, the compound also demonstrated significant antibacterial efficacy against various bacterial pathogens, including Gram-positive bacteria such as Bacillus subtilis MTCC441 and Gram-negative bacteria such as Escherichia coli MTCC1098, Proteus vulgarize MTCC426, and Salmonella Typhimurium MTCC3224. The antimicrobial activity was evaluated by measuring the zone of inhibition in millimetres, which provides an indication of the compound's ability to inhibit bacterial growth. The study successfully identified and characterized a novel flavone glycoside from Cynotis axillaris Schult. and its antimicrobial activity.

Chloride‐Bridged Dimeric SalphenZr(IV) Cobaltate Catalyst Unleashes the Potential of Base‐Free Carbonylative Polymerization for Biodegradable PHAs

Posted on 22 September 2023 by nVinothkumar Ganesan, nSungho Yoonn

Poly(3-hydroxyalkanoates) (PHA), promising biodegradable polymers, are hindered by the lack of efficient catalytic systems for competitive commercialization. Addressing this, we introduce a chloro-bridged dimeric salphen zirconium cobaltate complex. Under mild conditions under base-free conditions, it achieves full monomer conversion, 92% PHA selectivity, and challenges the prevailing β-lactone pathway. Instead, direct epoxide and carbon monoxide co-polymerization emerges as a unique and efficient PHA synthesis mechanism

Comprehensive Summary

Poly(3-hydroxyalkanoates) (PHAs) are a promising class of biodegradable polymers, exhibiting properties comparable to traditional petroleum-based counterparts. Nonetheless, the widespread commercialization of PHAs is hindered by the absence of an efficient and economically viable catalytic system, impeding their competitiveness against non-biodegradable polymers. In an effort to address this challenge, we present a study on a newly developed chloro-bridged dimeric salphen zirconium cobaltate complex for the direct synthesis of PHAs via carbonylative polymerization of epoxides. The catalytic system demonstrates favorable activity under mild reaction conditions, enabling complete monomer conversion and an impressive 92% selectivity towards PHA formation. Through meticulous control experiments and mechanistic studies, we have gained crucial insights into the polymerization process. Remarkably, our findings challenge the prevailing notion of sequential ring-opening polymerization of in-situ generated β-lactones as the primary pathway. Instead, we demonstrate that the polymerization predominantly proceeds through direct co-polymerization of epoxide and carbon monoxide, unveiling a unique and efficient mechanism for PHA synthesis.

Liquid‐Liquid Phase Equilibrium of Glycerolysis Precursors: Experimental and Modeling Study

Posted on 22 September 2023 by nKapil Mamtani, nChristian L. da Silveira, nMohammed M. Farid, nKaveh Shahbazn

Glycerol and oleic acid are mutually immiscible components. Their rigorous reaction produces glycerol esters and water. Such mutual immiscibility of glycerol and free fatty acids limits glycerolysis, a reaction capable of upgrading waste-derived oils. The glycerol solubility in the fatty phase increases when glycerol esters are added to the immiscible mixture of glycerol and oleic acid.

Abstract

The mutual immiscibility of glycerol and free fatty acids limits glycerolysis, a reaction capable of upgrading waste-derived oils. In the present work, the liquid-liquid phase equilibrium data for the glycerol-water-oleic acid and glycerol-monoolein-oleic acid ternary systems were determined experimentally and compared with predictions of the UNIFAC-LLE and COSMO-SAC models. Monoolein was found to affect the glycerol solubility in oleic acid strongly. None of the models investigated adequately determined phase equilibria for the glycerol-monoolein-oleic acid system. COSMO-SAC predictions showed the best trend for glycerol solubility in the fatty phase. For the glycerol-water-oleic acid system, UNIFAC-LLE predictions were in good agreement with experimental data.

Divergent Total Syntheses of 2, 6‐Dioxabicyclo[3.3.1]nonan‐3‐one Styryllactones: (−)‐Goniopypyrone, (+)‐Goniochelienlactone and (+)‐7‐Acetylgoniochelienlactone

Posted on 22 September 2023 by

The stereoselective syntheses of three 2,6-dioxabicyclo[3.3.1]nonan-3-one styryllactones, goniopypyrone, goniochelienlactone and 7-acetylgoniochelienlactone, has been accomplished based on chiron approach. In particular, (+)-goniochelienlactone and (+)-7-acetylgoniochelienlactone, which are the first total syntheses so far, were achieved in 5 steps (longest linear sequence) with a 28.3 % overall yield and in 8 steps (longest linear sequence) with a 22.2 % overall yield, respectively. The feature of this work involved a sequential reaction of Bernet-Vasella-type reductive elimination and nucleophilic addition by a one-pot sequence, sequential crossing metathesis (CM)/intramolecular oxa-Michael addition, and one-pot tandem deprotection/lactonization.

Abstract

Stereoselective total syntheses of (+)-goniochelienlactone, (+)-7-acetylgoniochelienlactone and (−)-goniopypyrone were accomplished by divergent strategies starting from readily available chiral pool methyl α-D-mannopyranoside. The present work provided an efficient strategy for the stereoselective construction of highly functionalized dioxabicyclo[3.3.1]nonan-3-one ring system through a sequential Bernet-Vasella-type reductive elimination/nucleophilic addition and a sequential cross-metathesis/intramolecular oxa-Michael addition in a one-pot process.

Promoting Electrocatalytic CO2 Reduction to CO via Sulfur‐Doped Co‐N‐C Single‐Atom Catalyst

Posted on 22 September 2023 by nZhiming Wei, nYuhang Liu, nJie Ding, nQinye He, nQiao Zhang, nYueming Zhain

S doping can promote H₂O activation and adjust Co active site. As a result, Co₁-SNC catalyst exhibits a greatly enhanced CO₂RR to CO performance compared to Co₁-NC.

Comprehensive Summary

Electrocatalytic reduction of CO₂ to fuels and chemicals possesses huge potential to alleviate current environmental crisis. Heteroatom doping in metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) has been found to be capable to promote the electrocatalytic CO₂ reduction reaction (CO₂RR). However, the origin of the enhanced activity is still elusive. Here, we report that sulfur-doped cobalt-nitrogen-carbon single-atom catalyst (Co₁-SNC) exhibits superior CO₂RR performance compared to sulfur-free counterpart (Co₁-NC). On the basis of in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), kinetic isotope effect (KIE) and theoretical calculation, it is demonstrated that sulfur doping can promote water activation, elevate the d-band center of Co active site, and reduce the free energy of *COOH intermediate formation. This work deepens the understanding of the CO₂RR chemistry over heteroatom-doped SACs for designing efficient CO₂RR processes.

Asymmetric Hydrogenation of Tetrapyridine‐Type N‐Heteroarenes Using Phosphine‐Free Ruthenium Diamine Catalysts

Posted on 22 September 2023 by

The first asymmetric hydrogenation of tetrapyridine-type N-heteroarenes, catalyzed by phosphine-free chiral cationic ruthenium diamine complexes, was successfully developed. With this methodology, a broad range of enantiopure tetradentate pyridine-amine-type ligands were obtained in high yields (up to 93%) with excellent stereoselectivities (up to 92 : 8 dl/meso and >99% ee) under mild conditions. Furthermore, the resulting tetradentate nitrogen-donor ligands were successfully applied in the Cu-catalyzed asymmetric Friedel–Crafts alkylation of indoles.

Comprehensive Summary

Chiral ruthenium-catalyzed enantioselective hydrogenation of tetrapyridine-type N-heteroarenes was firstly developed. The partial reduction of adjacent tetraheteroaromatic substrates proceeded smoothly in the presence of phosphine-free chiral cationic ruthenium diamine complexes, affording unprecedented high reactivity, enantioselecitivity and diastereoselectivity (up to 93% yield, >99% ee and 92 : 8 dr). The potential application of chiral tetradentate pyridine-amine products as chiral ligands has been demonstrated in the Cu-catalyzed asymmetric Friedel–Crafts alkylation reaction between indoles and nitroalkenes.