Cocatalysts play a key role in enhancing activity of photoelectrodes while the study of their interaction remains a challenge. Here, we decoupled the relationship between oxygen evolution reaction (OER) performance and photoelectrochemical (PEC) water oxidation performance by modifying an identical BiVO4 with different cobalt-based OER catalysts including Co, CoO, Co3O4, and Co4N. The electrochemical OER activities of these cobalt specimens were quite similar. Their anodic photocurrent density followed an order of: Co4N > Co > Co3O4 > CoO after loading on the BiVO4 electrode. The kinetics process and energy band diagram were analyzed, revealing that the interface between different cobalt specimens and BiVO4 electrode influenced the charge recombination and transfer. Accordingly, we propose a corresponding structural model, which shows that the cocatalysts consist of inner part for interface modulation and the outer layer for catalysis. The present work reveals the vital role of contact interface between cocatalysts and semiconductors, and more attention should be paid when selecting the cocatalysts

Taking advantage of the ligand-centered redox events, a well-defined air-stable Zn(II)-catalyst (1 a), bearing a tridentate redox noninnocent arylazo pincer, is used for synthesizing a wide variety of alkylated ketones, 9H-fluorenes, oxindoles, and indoles in moderate to good isolated yields (up to 91 %) using a broad range of alcohols as the alkylating agent.

Abstract

Herein we report a sustainable approach for the alkylation of ketones, 9H-fluorene, oxindole, and indole using alcohols as the alkylating agent catalyzed by a well-defined air-stable zinc catalyst (1 a) of a tridentate redox non-innocent arylazo ligand, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L^a ). 2–3 mol % of 1 a efficiently produces substituted α-alkylated ketones, 9-alkylated fluorenes, C3-alkylated oxindoles, and C3-alkylated indoles in moderate to good isolated yields. In aerial condition, the formation of bis(indolyl)methane (BIMs) derivatives were observed when indoles were subjected to alkylation by primary alcohols. A few drug molecules containing BIMs were prepared in good isolated yields. The catalyst 1 a exhibited good chemoselectivity during the functionalization of fluorene and indole with oleyl alcohol and β-citronellol. A few control experiments, including deuterium labeling experiments, performed to unveil the reaction mechanism indicate that the one-electron reduced azo-anion radical species [1 a]-formed in situ, acts as the active catalyst. All the redox events occur at the redox-active aryl-azo ligand, which acts as the reservoir of hydrogen and electrons throughout the catalytic cycle, keeping the Zn(II)-center as a template.

In this paper we report the preparation, characterization, and evaluation of N-heterocyclic carbenes (NHC)-Ag(I) complexes as catalysts for the borono-Minisci reaction, a powerful and practical approach for the decoration of N-heterocycles. While it represents an unprecedented method, kinetic and cyclic voltammetric analyses evidenced how the complex structure influence the Ag(I)/Ag(II) redox potential and, in turn, the reaction efficiency and scope.

Abstract

A series of supported N-heterocyclic carbene silver complexes (NHC-Ag(I)) were prepared and characterized as catalysts for the borono-Minisci reaction. After characterization, the synthesized catalysts were evaluated in batch mode to determine the reaction performance and kinetics. Interestingly, cyclic voltammetric analysis showed that the structure of both the complex and the ligand significantly influences the Ag(I)/Ag(II) redox potential and, in turn, the catalytic efficiency. Among the tested catalysts, the Si-supported NHC-Ag(I) 6 afforded the desired products in good to excellent yields in only 15 min, providing a complementary tactic to standard homogeneous approaches.

Quantum dots are the investigative focus of many research groups due to the quantum confinement effect observed. Thus, the photocatalysis has emerging as an important research branch applied to organic synthesis. In this article, the properties and concepts of these semiconductor nanocrystals are related and discussed for a better understanding and guidance to catalysis applications.

Abstract

In this conceptual review, we present the optical and electronic characteristics of quantum dots for the designing of organic synthesis experiments through the photocatalysis. We discuss the control parameters associated to the charge recombination processes on the semiconductor interface. The positioning of bands and control of intragap states, such as charge donors and acceptors, can define the performance of faradaic processes. Electrochemical strategies, such as voltammetry, can be used as a powerful tool for the determining of the electronic band edges with good precision.

Our study presents the “substrate analogue functional screening” screening method for identifying an alcohol dehydrogenase and the phenylalanine/alanine-scanning and iterative saturation mutation technique was applied to improve its catalytic activity for the enzymatic synthesis of piperidones.

Abstract

Alcohol dehydrogenases (ADHs) have garnered recognition for their potential in the synthesis of pivotal pharmaceutical compounds. However, their utilization in the context of piperidone synthesis remains an area ripe for exploration. In this study, we examine the performance of an alcohol dehydrogenase derived from Corynebacterium glutamicum (CgADH) using a substrate analogue functional screening (SAFS) method to elucidate its substrate specificity. To improve the catalytic activity of CgADH, a phenylalanine/alanine-scanning and iterative saturation mutation (PAS-ISM) method was used. The most active variant, I151F/I195A, exhibited a remarkable 10.6-fold increase in catalytic activity compared to the wild-type. Structural analysis revealed that the introduction of residues 151F and 195A led to a remodeling of the substrate-binding pocket, enabling additional p-π hydrophobic interactions with the substrate, ultimately promoting a more favorable substrate binding pose. This study introduces the SAFS screening method, which enables the identification of enzymes with no sequence homology to known enzymes. Furthermore, the application of PAS-ISM presents an efficient approach for the engineering of alcohol dehydrogenases. These findings open up promising avenues to expand the utility of ADHs in the synthesis of piperidone, thereby advancing the field of pharmaceutical chemistry.

Rhamnulose-1-phosphate aldolase (RhuA) was the first DHAP-aldolase discovered to have an electrophilic promiscuity as astonishing as converting ketones or dioxygen from air, to give access respectively to the highly sought-after chiral tertiary alcohol motif or to hydroxypyruvaldehyde phosphate. This study reveals the behaviour of the other DHAP-aldolases in this area: fuculose-1-phosphate- (FucA), fructose-1,6-bisphosphate- (FruA) and tagatose-1,6-bisphosphate (TagA) aldolases.

Abstract

Rhamnulose-1-phosphate aldolases (RhuA) were the first dihydroxyacetone phosphate (DHAP) aldolases to be demonstrated to efficiently accept a ketone as the electrophile, providing the highly sought-after chiral tertiary alcohol motif. It has also been found that this enzyme family can use dioxygen as an electrophile, forcing to work under inert atmosphere conditions when the target electrophile is poorly reactive. However, these features have not been explored in all DHAP-aldolase families. Here, we present a study of E. coli K12 fuculose-1-phosphate- (FucA_K12), fructose-1,6-bisphosphate- (FruA_K12) and tagatose-1,6-bisphosphate (TagA_K12) aldolases. For the latter two enzymes, this was made possible by the development of a triose phosphate isomerase (TPI)-deleted E coli strain, which prevents DHAP isomerization into d-glyceraldehyde 3-phosphate (G3P), its natural electrophile. Like RhuA, TagA_K12 was found to be able to oxidize DHAP into hydroxypyruvaldehyde phosphate under dioxygen, leading to the corresponding diulose. On the other hand, FucA_K12 was revealed to be capable of converting ketone electrophiles with greater stereoselectivity than RhuA, and without the requirement of an inert atmosphere, since it was unable to oxidize DHAP. Finally, FruA_K12 proved unable either to oxidize DHAP and or to accept ketones as electrophiles.

Thermocatalytic decomposition of methane provides opportunities for hydrogen (H2) production with no emission of carbon dioxide. However, high-value carbon products need to be produced for economic deployment of thermocatalytic decomposition and to achieve a minimum H2 selling price below the U.S, Department of Energy target of $1/kg H2. In this review, we re-evaluate data on catalyst development reported in the literature and propose fundamental correlations between catalyst characteristics, catalytic stability, and properties of carbon co-products. In the first part of the review, growth mechanisms for carbon nanotubes using state-of-the-art chemical vapor deposition are reviewed to catalog the effects of catalyst characteristics, the influence of carbon sources, interactions between metal particles and supports, and metal particle sizes on carbon growth. In the second part, representative developments in mono-, bi-, and tri-metallic nickel catalysts are highlighted. We present kinetic analysis of reactions catalyzed by mono-metallic nickel catalysts, which generates a correlation between metal particle size and catalyst stability.

Cyclodipeptides (CDPs) build an important class of secondary metabolites with a plethora of pharmacological impact such as antibiotic, cytotoxic, antifungal properties or even as anti-Alzheimer drug candidates. The core structure of 2,5-diketopiperazines, a subclass of CDPs, is composed of two ‘head-to-tail’ connected α-amino acids. Their chemical diversity is broadened by tailoring enzymes as members of their biosynthetic gene clusters, such as CDP-dimerizing P450s. Recently, a new class of P450 enzymes, termed GymBx, was identified in the biosynthetic pathway of guatyromycines. These enzymes catalyse both an intramolecular C-C bond formation within cyclo-l-Tyr-l-Tyr (cYY) and a nucleobase transfer reaction, which is unique for CDP-modifying P450 enzymes. In this study, we report the structures of two members, GymB1 and GymB5, in their unbound states, as well as GymB5 in complex with hypoxanthine and cYY. Structural data of the ternary complex shed light into CDP binding and nucleobase transfer reaction, identified key residues for substrate recognition and modified the enzymatic bifunctionality. By mutagenesis we established a GymB5 variant that strictly switched the chemoselectivity of the reaction towards an intermolecular coupling enzyme. This data set a solid basis for future protein engineering of P450 enzymes to synthesize new CDP-nucleobase adducts.

The discerning transformation of unsaturated compounds has arisen as an imperative approach in chemical synthesis, facilitating the creation of functional organic molecules. For several decades, there has been a great deal of research and development focused on the catalytic incorporation of silanes into multiple bonds. The organosilicon derivatives that are obtained exhibit mild toxicity, convenient handling, and notable stability, thereby presenting a diverse array of potential applications. The investigation of Earth-abundant alternatives has become a significant area of research focus due to the expensive nature, limited selectivity, and numerous side reactions associated with precious metal catalysts. The exploration of ligand skeleton construction, selectivity, and mechanism research reveals the superior potential of cobalt catalysts compared to iron and nickel catalysts.

Abstract

The selective conversion of unsaturated compounds has emerged as a crucial method in chemical synthesis, enabling the synthesis of functional organic molecules. In recent decades, transition metal-catalyzed hydrosilylation has emerged as a highly successful exemplar of industrialization within the realm of organic chemistry for the production of organosilanes, which have a pivotal role in organic chemistry and materials science. Precious metal complexes are typically employed as catalysts in most industrial hydrosilylation processes. The exploration of Earth-abundant alternatives has emerged as a focal point of considerable research attention due to the high cost, poor selectivity, and many side reactions reported for precious metal catalysts. Ligand skeleton construction, selectivity, and mechanism research are areas where cobalt catalysts have more potential than iron and nickel. This review discusses the recent advances in cobalt-catalyzed hydrosilylation across carbon-carbon, carbon-oxygen, and carbon-nitrogen multiple bonds from 2019 to 2023.

Bifunctional homogeneous and recyclable heterogeneous single-component catalysts for the cycloaddition of CO₂ to epoxides were obtained through a simple method based on the ring-opening of opportunely functionalized epoxides and applied for the synthesis of cyclic carbonates under atmospheric CO₂ pressure.

Abstract

The design of molecular scaffolds bearing multiple functional groups for the activation and ring-opening of epoxides is a crucial challenge for the synthesis of efficient homogeneous and heterogeneous catalysts that are used for the cycloaddition reaction of CO₂ to epoxides. Traditional approaches to prepare such multifunctional catalysts often imply multistep synthetic procedures and expensive building blocks. In this work we show that bifunctional catalysts for the cycloaddition of CO₂ to epoxides bearing a Lewis acid metal and a quaternary ammonium halide group can be prepared in just two steps starting from an opportunely designed epoxide precursor by using inexpensive substrates. Such a readily accessible catalyst was applied for the cycloaddition of CO₂ to a series of epoxides under atmospheric conditions generally leading to quantitative substrate conversion and high carbonate selectivities. Importantly, we also show that the epoxide-driven concept developed for the preparation of the molecular catalyst, could be applied to prepare recyclable heterogeneous systems for the target cycloaddition reaction.