Back Cover: Bio-Inspired Bimetallic Cooperativity Through a Hydrogen Bonding Spacer in CO2 Reduction (Angew. Chem. Int. Ed. 8/2023)

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO₂ and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi-point hydrogen-bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO₂ reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi-identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X-ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO₂ capture, activation, and reduction.     

Inside Back Cover: Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical Nanographenes (Angew. Chem. Int. Ed. 7/2023)

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate ( 1 a , b ). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2 , or the expected dehydrogenation reaction leading solely to the helical nanographene 3 . The crystal structures of four of the new spiro compounds (syn 2 , syn 9 , anti 9 and syn 10 ) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission.     

Inside Back Cover: Retina-Inspired Organic Photonic Synapses for Selective Detection of SWIR Light (Angew. Chem. Int. Ed. 6/2023)

Photonic synapses with the dual function of optical signal detection and information processing can simulate human visual system. However, photonic synapses with selective detection of short-wavelength infrared (SWIR) light have never been reported, which can not only broaden the human vision region but also integrate neuromorphic computation and infrared optical communication. Here, organic photonic synapses based on a new donor-acceptor copolymer P1 are fabricated, which exhibit excellent synaptic characteristics with selective detection for SWIR and extremely low energy consumption (2.85 fJ). The working mechanism is rooted in energy level barriers and unbalanced charge transportation. Moreover, these photonic synapses demonstrate excellent performance in multi-signal logic editing, letter imaging and memory with noise reduction function. This contribution provides ideas of constructing selective-response synapses for artificial visual system and neuromorphic computing.     

Inside Back Cover: Prolinyl Nucleotides Drive Enzyme-Free Genetic Copying of RNA (Angew. Chem. Int. Ed. 41/2023)

Proline is one of the proteinogenic amino acids. It is found in all kingdoms of life. It also has remarkable activity as an organocatalyst and is of structural importance in many folded polypeptides. Here, we show that prolinyl nucleotides with a phosphoramidate linkage are active building blocks in enzyme- and ribozyme-free copying of RNA in the presence of monosubstituted imidazoles as organocatalysts. Both dinucleotides and mononucleotides are incorporated at the terminus of RNA primers in aqueous buffer, as instructed by the template sequence, in up to eight consecutive extension steps. Our results show that condensation products of amino acids and ribonucleotides can act like nucleoside triphosphates in media devoid of enzymes or ribozymes. Prolinyl nucleotides are metastable building blocks, readily activated by catalysts, helping to explain why the combination of α-amino acids and nucleic acids was selected in molecular evolution.     

Back Cover: Metal-Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical-Mediated Reactions (Angew. Chem. Int. Ed. 21/2023)

Visible-light copper photocatalysis has recently emerged as a viable technology for building sustainable synthetic processes. To broaden the applications of phosphine-ligated copper(I) complexes, we describe herein an effective metal-organic framework (MOF)-supported copper(I) photocatalyst for multiple iminyl radical-mediated reactions. Due to site isolation, the heterogenized copper photosensitizer has a significantly higher catalytic activity than its homogeneous counterpart. Using a hydroxamic acid linker to immobilize copper species on MOF supports affords the heterogeneous catalysts with high recyclability. The post-synthetic modification sequence on MOF surfaces allows for the preparation of previously unavailable monomeric copper species. Our findings highlight the potential of using MOF-based heterogeneous catalytic systems to address fundamental challenges in the development of synthetic methodologies and mechanistic investigations of transition-metal photoredox catalysis.     

Inside Back Cover: Rigid-Flexible Hybrid Porous Molecular Crystals with Guest-Induced Reversible Crystallinity (Angew. Chem. Int. Ed. 13/2023)

A weak CH/O hydrogen-bonded organic framework (HOF) with both rigidity and flexibility that could easily and reversibly switch from a non-crystalline to a crystalline phase was constructed. The specific solvent molecule acts as a “key” to control the crystallinity, while the highly rigid triangle macrocycle as the building block is the “lock”. The introduction and removal of the “key” could influence the local flexibility of the whole framework and lead to switchable crystallinity. Furthermore, the obtained HOF exhibits excellent separation efficiency for benzene and cyclohexane (94.4 %).     

Inside Cover: Mechanistic Understanding of Efficient Polyethylene Hydrocracking over Two-Dimensional Platinum-Anchored Tungsten Trioxide (Angew. Chem. Int. Ed. 40/2023)

Chemical upcycling of polyethylene (PE) can convert plastic waste into valuable resources. However, engineering a catalyst that allows PE decomposition at low temperatures with high activity remains a significant challenge. Herein, we anchored 0.2 wt.% platinum (Pt) on defective two-dimensional tungsten trioxide (2D WO₃) nanosheets and achieved hydrocracking of high-density polyethylene (HDPE) waste at 200–250 °C with a liquid fuel (C_5–18) formation rate up to 1456 g_products ⋅ g_{metal species}⁻¹ ⋅ h⁻¹. The reaction pathway over the bifunctional 2D Pt/WO₃ is elucidated by quasi-operando transmission infrared spectroscopy, where (I) well-dispersed Pt immobilized on 2D WO₃ nanosheets trigger the dissociation of hydrogen; (II) adsorption of PE and activation of C−C cleavage on WO₃ are through the formation of C=O/C=C intermediates; (III) intermediates are converted to alkane products by the dissociated H. Our study directly illustrates the synergistic role of bifunctional Pt/WO₃ catalyst in the hydrocracking of HDPE, paving the way for the development of high-performance catalysts with optimized chemical and morphological properties.