Directed evolution of Escherichia coli surface-displayed Vitreoscilla hemoglobin as an artificial metalloenzyme for the synthesis of 5-imino-1,2,4-thiadiazoles

Artificial metalloenzymes (ArMs) are constructed by anchoring organometallic catalysts to an evolvable protein scaffold. They present the advantages of both components and exhibit considerable potential for the in vivo catalysis of new-to-nature reactions. Herein, Escherichia coli surface-displayed Vitreoscilla hemoglobin (VHbSD-Co) that anchored the cobalt porphyrin cofactor instead of the original heme cofactor was used as an artificial thiourea oxidase (ATOase) to synthesize 5-imino-1,2,4-thiadiazoles. After two rounds of directed evolution using combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy, the evolved six-site mutation VHbSD-Co (6SM-VHbSD-Co) exhibited significant improvement in catalytic activity, with a broad substrate scope (31 examples) and high yields with whole cells. This study shows the potential of using VHb ArMs in new-to-nature reactions and demonstrates the applicability of E. coli surface-displayed methods to enhance catalytic properties through the substitution of porphyrin cofactors in hemoproteins in vivo.

Acridine-Functionalized Covalent Organic Frameworks (COFs) as Photocatalysts for Metallaphotocatalytic C-N Cross-Coupling

Covalent organic frameworks (COFs) are structurally tuneable, porous and crystalline polymers constructed through the covalent attachment of small organic building blocks as elementary units. Using the myriad of such building blocks, a broad spectrum of functionalities has been applied for COF syntheses for broad applications, including heterogeneous catalysis. Herein, we report the synthesis of a new family of porous and crystalline COFs using a novel acridine linker and benzene‐1,3,5‐tricarbaldehyde derivatives bearing a variable number of hydroxy groups. With the broad absorption in the visible light region, the COFs were applied as photocatalysts in metallaphotocatalytic C−N cross‐coupling. The fully β‐ketoenamine linked COF showed the highest activity, due to the increased charge separation upon irradiation. The COF showed good to excellent yields for several aryl bromides, good recyclability and even catalyzed the organic transformation in presence of green light as energy source.

Progress in Development of Photocatalytic Processes for Synthesis of Fuels and Organic Compounds under Outdoor Solar Light

With photovoltaics becoming a mature, commercially feasible technology, society is willing to allocate resources for developing and deploying new technologies based on using solar light. Analysis of projects supported by the European Commission in the past decade indicates exponential growth of funding to photocatalytic (PC) and photoelectrocatalytic (PEC) technologies that aim either at technology readiness levels (TRLs) TRL 1-3 or TRL > 3, with more than 75 Mio€ allocated from the year 2019 onward. This review provides a summary of PC and PEC processes for the synthesis of bulk commodities such as solvents and fuels, as well as chemicals for niche applications. An overview of photoreactors for photocatalysis on a larger scale is provided. The review rounds off with the summary of reactions performed at lab scale under natural outdoor solar light to illustrate conceptual opportunities offered by solar-driven chemistry beyond the reduction of CO₂ and water splitting. The authors offer their vision of the impact of this area of research on society and the economy.

α-Functionalization of ketones promoted by sunlight and heterogeneous catalysis in the aqueous phase

Herein, a protocol that combines heterogeneous catalysis and solar photocatalysis for the regioselective α-substitution of asymmetric ketones with quinoxalinones has been reported. The result indicates that the reaction is more likely to occur on the α-carbon. This strategy provides a green and efficient way for the α-functionalization of ketones. A singlet oxygen involved mechanism is suggested for the transformation.

Metal-Free Photocatalysis: Two-Dimensional Nanomaterial Connection toward Advanced Organic Synthesis

Two-dimensional (2D) nanostructures are a frontier in materials chemistry as a result of their extraordinary properties. Metal-free 2D nanomaterials possess extra appeal due to their improved cost-effectiveness and lower toxicity with respect to many inorganic structures. The outstanding electronic characteristics of some metal-free 2D semiconductors have projected them into the world of organic synthesis, where they can function as high-performance photocatalysts to drive the sustainable synthesis of high-value organic molecules. Recent reports on this topic have inspired a stream of research and opened up a theme that we believe will become one of the most dominant trends in the forthcoming years.

An ultrastable olefin-linked covalent organic framework for photocatalytic decarboxylative alkylations under highly acidic conditions

An ultrastable olefin-linked covalent organic framework 2D-COF-2 offers an alternative heterogeneous photocatalyst for photocatalytic decarboxylative alkylations, exhibiting impressive effciency, sustainabilty and promising industrial potential.

Metal–Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) Applied to Photocatalytic Organic Transformations

Among the different alternatives for catalysis using metal–organic frameworks (MOFs) or covalent organic frameworks (COFs), photocatalysis has remarkably evolved during the last decade. Photocatalytic reticular materials allowed recyclability and easy separation of catalyst from the product, also reaching the activity and selectivity commonly observed for molecular systems. Recently, photocatalytic MOFs and COFs have been applied to synthetic applications in order to obtain organic molecules of different complexity. However, although a good number of works have been devoted to this issue, an updated comprehensive revision on this field is still needed. The aim of this review was to fill this gap covering the following three general aspects: (1) common strategies on the design of reticular photocatalytic materials, (2) a comprehensive discussion of the photocatalytic organic reactions achieved by the use of COFs and MOFs, and (3) some critical considerations highlighting directions that should be considered in order to make advances in the study of photocatalytic COFs and MOFs.