Aldolases are powerful C−C bond-forming enzymes with high stereoselectivity and broad substrate scope in biocatalysis, but their ability to stereoselectively construct tertiary alcohols has not been fully explored. Herein, we demonstrate that vicinal diones and α-keto esters are electrophiles that can be accepted by both natural and computationally designed aldolases via various catalytic mechanisms. This method allows for the efficient asymmetric synthesis of small molecules with tertiary alcohols, including noncanonical amino acids. This study presents the first types of generic nonnatural substrates of aldolases and reveals new opportunities for the use of aldolases in the synthesis of versatile chiral synthons.

Catalytic hydrogenation of carbon dioxide (CO2) for the preparation of higher carboxylic acids is attractive and promising. Herein, we demonstrate a general strategy for producing higher carboxylic acids via reaction of CO2 and H2 with light (C2~C4) oxygenates such as ketones, alcohols, polyols, ethers and epoxides. In a green solvent consisting of ionic liquid (1-ethyl-3-methylimidazolium iodide) and water, the reaction can be efficiently accelerated by RhI3 catalyst and I2 promoter at 170 °C. Very high or remarkable yields of higher carboxylic acids were synthesized via C-C bond formation between the intermediates generated from the oxygenates and CO2. Detailed study indicated that the catalyst and the solvent had excellent synergistic effect for promoting the reaction. The strategy can effectively convert the bulk and inexpensive feedstocks to value-added carboxylic acids, and therefore is promising for commercial application.

Electron donor acceptor (EDA) complexes formed between arylating agents and nucleophilic substrates or additives, undergo photoexcitation to produce aryl radicals. Two main modes of reactivity for such complexes exist: mediation, where EDA complex is formed between two reagents, or catalysis, in which the electron donor additive is used as an organocatalyst.

Abstract

Visible-light-activated organic reactions unlock novel avenues for complex molecular transformations, impossible under standard “thermal” conditions, which makes them powerful tools in the arsenal of synthetic chemistry. However, transition metal-based or organic photoredox catalysts are often used to ensure productive absorption of visible light, which might be not desirable to medicinal chemistry and industry due to toxicity, low sustainability, and high cost of most photocatalysts. A more environmentally and economically benign approach is based on the formation of transient electron donor-acceptor (EDA) complexes between two reagents or a reagent and an additive, that readily absorb visible light, acting as internal photosensitizers. Within the EDA complex-based arylation strategies, chemical transformations are mediated by noncovalent interaction between two molecules, namely between electron-poor aryl halides or their synthetic equivalents and electron-rich nucleophilic reagents or additives. Moreover, besides stoichiometric EDA complexes between two molecules, EDA complex based organocatalysis can be achieved in certain cases through regeneration of the donor molecules in the course of the reaction. Photoexcitation of the EDA complexes induces a single electron transfer (SET) process to generate aryl radical species for the arylation step. This Review will focus on the state-of-the-art EDA complex-based arylation strategies utilizing aryl halides, aryldiazonium, diaryliodonium, arylsulfonium and arylphosphonium salts as reactants, published mainly in the last five years.

Carbon quantum dots (CQDs), or fluorescent carbon nanoparticles, have attracted a lot of attention due to their many uses in chemical sensing, biomedical imaging, nanotechnology, photovoltaics, LEDs, and hydrogen production. This review's main goal is to provide a detailed analysis and highlight the revolutionary potential of CQDs in advancing hydrogen-generating technology.

Abstract

Fluorescent carbon nanoparticles, also known as carbon quantum dots (CQDs), have piqued the interest of researchers due to their numerous uses in chemical sensing, biomedical imaging, nanotechnology, photovoltaics, LEDs, and hydrogen generation. Aside from their optical brilliance, CQDs have benefits like low toxicity, environmental friendliness, cost-effectiveness, and ease of manufacture, with adjustable properties via surface passivation and functionalization. This review article goes over CQDs in-depth, addressing synthesis advances, benefits, limits, various synthesis processes, and prospective hydrogen generation applications. While CQDs have photocatalytic properties, they confront a few challenges, including low quantum yields, spectrum limitations, photostability limitations, limited catalytic activity, scaling difficulties, and environmental issues. Thorough research is required to use CQDs in sustainable hydrogen generation. Despite obstacles, CQD research remains appealing, with transformational promise for a cleaner and more sustainable energy future through controlled synthesis approaches displaying CQDs’ many uses.

Multiple enzymes catalyze the formation of pyrroloindoles from indoles, usually coupled with a functional group transfer in the 3-position. In this work, two high-throughput complementary absorbance-based assays were developed for the monitoring of substrate depletion (indole) and product formation (pyrroloindole). The assays were used successfully for enzymatic activity determination, but can be also used for the quantification of natural products.

Abstract

Indoles and pyrroloindoles are structural motifs present in many biologically active natural products. Multiple classes of enzymes catalyze the transformation of indoles into pyrroloindoles via group transfer followed by intramolecular cyclization, such as peroxydases, methyltransferases, and prenyltransferases. Due to the selective introduction of a stereogenic center, these enzymes receive increasing attention as catalytic tools for the production of pharmacologically relevant compounds. Two new colorimetric assays are described in this work, which allow for the quantification of such enzymatic reactions from the perspective of the substrate and the product. For the substrates, the indole assay is based on a modified version of the Ehrlich test, with the use of light as a driving force for color formation. The pyrroloindole assay uses cerium sulfate as a reagent for the colorimetric quantification of the enzymatic products. The assays are complementary and both were successfully utilized for enzymatic activity determination of a C3-indole methyltransferase. They can facilitate high-throughput screening of mutant libraries, offering support for the engineering of such enzymes, but can also be used as stand-alone methods for the detection and quantification of natural products.

Metal-zeolite bifunctional catalysts, incorporating a judicious combination of metal and acid functionalities within confined spaces, have been widely acknowledged as highly efficient catalysts for the hydrodeoxygenation of lignin-derived phenolics to hydrocarbons. Elucidating the distinct roles and synergistic effects of these active components offers valuable insights for the rational design of advanced catalysts for the hydrodeoxygenation process.

Abstract

The hydrodeoxygenation (HDO) reaction provides a promising catalytic strategy to remove oxygen in biomass-derived bio-oil to produce renewable transportation fuels and value-added chemicals. The development of highly efficient and stable HDO catalysts plays an essential role in biomass valorization. Metal-zeolite bifunctional catalysts have been well-developed as the effective HDO catalysts in upgrading lignin-derived phenolics due to their excellent activity, selectivity, and thermal and hydrothermal stability. However, clarifying the roles of the active sites and their synergistic effect, and establishing effective structure-performance relationships in the HDO process still face challenges. In this review, we first survey the conventional catalysts applied in the HDO of bio-oil, followed by thoroughly discussing the roles of metal centers, acid sites, supports, and their impacts on the HDO process of phenolic model compounds or bio-oil. Finally, a discussion on the stability and deactivation of metal-zeolite catalysts, especially in the aqueous-phase HDO reaction, is provided. This critical review offers new insights into the development of state-of-the-art metal-zeolite bifunctional catalysts with well-defined porosity and metal-acid properties for viable biomass valorization.

A facile hydrogenation of glucose to sorbitol has been reported with Ni-HAP catalyst using water as a solvent. The excellent yield of sorbitol, 97 % in 1 h is possible due to the high surface area and high acid-base strength of the Ni-HAP-4 catalyst.

Abstract

A series of nickel hydroxyapatite catalysts were synthesized by the co-precipitation method followed by calcination and reduction. These catalysts were employed for the aqueous phase hydrogenation of glucose to sorbitol. The Ni-HAP catalyst with comparatively high surface area and acid-base strength gave high sorbitol selectivity in 1 h. Ni-HAP-4 catalyst with moderate Ni (3.5 wt. %) content having smaller and highly dispersed nickel particles gives an excellent yield of sorbitol, 97 % in 1 h. The Ni-HAP-4 catalyst works well with other polar protic solvents. Different characterization techniques like XRD, TEM, SEM-EDS, BET, NH₃-TPD, and CO₂-TPD were employed to analyze the Ni-HAP-4 catalyst.

Recent developments in the liquid–phase selective hydrogenation of α,β-unsaturated aldehydes, with metal oxides derived from perovskite or spinel as supports or catalyst precursors, were summarized. Spatial isolation of A-site ions with B-site ions makes these ions highly dispersed and enhances the intimate contact with the active components supported on them, leading to electron transfer or synergistic effect to promote the catalytic ability.

Abstract

Mixed metal oxides with perovskite ABO₃ or spinel AB₂O₄ structure can provide uniformly and highly dispersed metal oxides, which can be adopted as catalyst supports, as catalysts directly or as catalysts after reduction. When they are used as catalyst supports, the spatial isolation of A-site ions with B-site ions not only makes these ions highly dispersed, but also enhances the intimate contact with the active components supported on them, leading to electron transfer or synergistic effect to promote the catalytic ability. After reduction, highly dispersed A/B nanoparticles supported on BO_x/AO_x can be achieved for the relevant applications. Herein, recent developments in the liquid–phase selective hydrogenation of α,β-unsaturated aldehydes, with metal oxides derived from perovskite or spinel as supports or catalyst precursors, were summarized.

The study examines Co₃Mo₃N catalysts on two MgO substrates, revealing MgO preparation‘s impact on surface basicity. Remarkably, Co₃Mo₃N on single-crystalline MgO exhibits a superior rate of 162.0 mmol g⁻¹ _metal h⁻¹, surpassing commercial MgO support (41.2 mmol g⁻¹ _metal h⁻¹) and unsupported Co₃Mo₃N (15.0 mmol g⁻¹ _metal h⁻¹).

Abstract

Co₃Mo₃N has been reported to have activity for the synthesis of ammonia surpassing that of industrial Fe catalysts under certain conditions. However, so far the research has largely focused on unsupported Co₃Mo₃N. We report a comprehensive study on the catalytic activity of Co₃Mo₃N when supported on two distinct MgO substrates. Our findings reveal that the method of MgO preparation plays a crucial role in influencing surface basicity. Remarkably, Co₃Mo₃N supported on single-crystalline MgO demonstrates significantly enhanced catalytic activity, achieving a 162.0 mmol g⁻¹ _metal h⁻¹ rate. This surpasses the performance on commercial MgO support (41.2 mmol g⁻¹ _metal h⁻¹) and unsupported Co₃Mo₃N (15.0 mmol g⁻¹ _metal h⁻¹). While kinetic analyses show no substantial differences between the two supported catalysts, spectroscopic studies employing CO₂ and N₂ temperature-programmed desorption (TPD) reveal a richer array of basic sites and adsorption/desorption phenomena on the single-crystalline MgO support. These catalysts exhibit exceptional stability. The drastically reduced Co/Mo loading amounts in comparison to the bulk form, make the commercialization of Co₃Mo₃N catalysts more practical.

Sulfonated carbons and commercial Amberlyst 15 and 45 served as model catalysts to explore the impact of the ratio between stronger and weaker acid sites (NS/NW) on 5-hydroxymethylfurfural (HMF) and furfural production from fructose and xylose. Catalysts with varying structural and surface properties, and consequently different NS/NW ratios, were prepared from diverse templated mesoporous carbons and distinct sulfonation methods. HMF or furfural yields exhibited an exponential correlation with the NS/NW ratio. However, the catalytic activity per site (TON) displayed a volcano-like plot, reaching a maximum between NS/NW = 2 – 4. Consequently, our findings suggest the involvement of both strong (sulfonic acid) and weak acid (surface carboxylic acid, alcohol, and phenol groups) sites in monosaccharide dehydration mechanisms. These insights may guide the development of novel catalysts.