Catalysis

The noble metal nanocatalysts on high surface area magnetic material supports have huge technological importance in the field of catalysis. The green synthesis of magnetic-noble metal hybrid material has another technological importance. In this study, we report a novel, efficient, and sustainable synthesis methodology for Au nanoparticles (NPs) deposited hierarchical magnetic maghemite (γ-Fe2O3) tubes. In this methodology, the green tea extract was used as a reducing agent for both iron oxide and Au NPs synthesis...

Accurate predictions of spin-state ordering, reaction energetics and barrier heights are critical for the computational discovery of open-shell transition metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states instead correctly predicted as high-spin with a hybrid functional)...

The replacement of current petroleum-based plastics with sustainable alternatives is a crucial but formidable challenge for the modern society. Catalysis presents an enabling tool to facilitate the development of sustainable polymers. This review provides a system-level analysis of sustainable polymers and outlines key criteria with respect to the feedstocks the polymers are derived from, the manner in which the polymers are generated, and the end-of-use options. Specifically, we define sustainable polymers as a class of materials that are derived from renewable feedstocks and exhibit closed-loop life cycles...

Metallo-photoredox catalysis has redefined the available bond disconnections in the synthetic arsenal. By harnessing the one-electron chemistry of photoredox catalysis in tandem with low-valent cobalt catalysts, new methods by which functionalities may be stitched together become available. Herein we describe the coupling of photoredox-generated α-amino radical species with conjugated dienes using a unified cobalt and iridium catalytic system in order to access a variety of useful homoallylic amines from simple commercially available starting materials...

Readily available cyclodextrins (CDs) with an inherent hydrophobic internal cavity and hydrophilic external surface are macrocyclic entities that display a combination of molecular recognition and complexation properties with vital implications for host-guest supramolecular chemistry. While the host-guest chemistry of CDs has been widely recognized and led to their exploitation in a variety of important functions over the last five decades, these naturally occurring macrocyclic systems have emerged only recently as promising macrocyclic molecules to fabricate environmentally benign functional nanomaterials...

C2 symmetric chiral compounds overlap themselves when rotating with an axis of 180° with an axis and have important applications in chiral catalysis and chiral separation fields. A novel C2 symmetric stationary phase based on phenyl substituted L-proline derivatives was prepared and compared with the similar stationary phase based on mono-substituted brush-type stationary phase. The C2 symmetric stationary phase showed higher enantiodiscrimination capability than the mono-substituted stationary phase for 31 acidic, neutral and alkaline analytes...

Framework materials, both metal-organic frameworks (MOFs) and inorganic frameworks (zeolites), are porous systems with regular structures that provide valuable properties suitable for sorption, catalysis, molecular sieving, etc. Herein, we present an efficient, experimental/computational strategy allowing for the detailed characterization of a polycrystalline MOF system, ZBIF-1, with two integrated unit cells on the atomic-resolution level. Although high-resolution 1H, 11B, 13C and 15N MAS NMR spectra provided valuable structural information on the co-existence of two distinct asymmetric units in the investigated system, the utilized NMR crystallography approach combining XRPD, ssNMR and DFT calculations allowed us to firmly define the exact structure of the secondary crystalline phase and, furthermore, to resolve the mutual interconnectivity of the two crystalline frameworks...

Due to its extreme thinness, graphene can transmit some surface properties of its underlying substrate, a phenomenon referred to as graphene transparency. Here we demonstrate the application of the transparency of graphene as a protector of thin-film catalysts and a booster of their catalytic efficiency. The photocatalytic degradation of dye molecules by ZnO thin films was chosen as a model system. A ZnO thin film coated with monolayer graphene showed greater catalytic efficiency and long-term stability than did bare ZnO...

Erythrosine, a popular food dye, undergoes fast O2-sensitive bleaching in water when subjected to visible light illumi-nation. In dilute solution, Erythrosine undergoes photo-bleaching via first-order kinetics, where the rate of bleaching depends critically on the rate of photon absorption and on the concentration of dissolved oxygen. Kinetic studies indi-cate that this inherent bleaching is augmented by self-catalysis at higher concentrations of Erythrosine and on long exposure times. Under the conditions used, bleaching occurs by way of geminate attack of singlet molecular oxygen on the chromophore...

Enantioselective α-allylation of α-substituted β-ketoesters with allyl alcohols was successfully performed by synergistic catalysis with the catalyst combination of a chiral primary amino acid and an achiral palladium complex without additional promotors like acids or bases. The allylation reaction and generation of a chiral quaternary carbon stereocenter proceeded smoothly under mild reaction conditions to produce α,α-disubstituted β-ketoesters in high yields (91-99%) with high enantioselectivities (90-99% ee)...

A novel cascade Cp*Rh(III)-catalyzed C-H alkylation/Cu(II)-promoted α-oxygenation which enabled a three-component carboxygenation of activated alkene is reported. Mild reaction conditions, broad substrate scope, and good functional group tolerance were observed. The synthetic utility of the protocol was showcased by the facile transformations of the product to a variety of structurally diverse molecules. Preliminary mechanistic studies were conducted.

The use of transition metal catalysis to enable the coupling of readily available organic molecules has greatly enhanced the chemist's ability to access complex chemical structures. In this work, an intermolecular coupling reaction that unites organotriflates and aldehydes is presented. A unique catalyst system is identified to enable this reaction, featuring a Ni(0) precatalyst, a tridentate Triphos ligand, and a bulky amine base. This transformation provides access to a variety of ketone-containing products without the selectivity and reactivity-related challenges associated with more traditional Friedel-Crafts reactions...

Invited for this month's cover are researchers from the Division of Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, Uppsala University (Sweden). The research interests in the group span areas such as enzyme inhibitors, new antibiotics, angiotensin II AT2R ligands, PET tracers, palladium catalysis, heterocycle synthesis, and the development of novel multicomponent reactions. In particular, sequential carbonylation and cyclization appeal to us as a convenient and straightforward synthetic route for the synthesis of heterocycles...

Molecular nanodevices are computational assemblers that switch defined states upon external stimulation. However, interfacing artificial nanodevices with natural molecular machineries in living cells remains a great challenge. Here we delineate a generic method for programming assembly of enzyme-initiated DNAzyme nanodevices (DzNanos). Two programs including split assembly of two partzymes and toehold-exchange displacement assembly of one intact DNAzyme initiated by telomerase are computed. The intact one obtains higher assembly yield and catalytic performance ascribed to proper conformation folding and active misplaced assembly...

Here we report the employment of the quintuply bonded dichromium amidinates [Cr{κ2-HC(N-2,6-iPr2C6H3)(N-2,6-R2C6H3)}]2 (R = iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η6:η6-1,3,5-(Me3Si)3C6H3)[Cr{κ2-HC(N-2,6-iPr2C6H3)(N-2,6-R2C6H3)}]2 (R = iPr (5), Me (8))...

A methodology to access chiral 3,3'-spiro-phosphonylpyrazoline oxindoles via an asymmetric 1,3-dipolar cycloaddition reaction of substituted methyleneindolinones with α-diazomethylphosphonate in the catalysis of tertiary amine thiourea and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) has been established. This method exhibits high functional group compatibility, where a wide range of methyleneindolinones with various substituents and heterocyclic rings are accommodated by this reaction. The resulting chiral 3,3'-spiro-phosphonylpyrazoline oxindoles can be further transformed into spiro-phosphonylcyclopropane oxindoles by ring contraction...

In this study, we perform ultra-high vacuum (UHV) and arc-plasma synthesis of strain-controlled Pt(111) model shells on Pt-Co(111) layers with various atomic ratios of Pt/Co and an oxygen reduction reaction (ORR) activity enhancement trend against the surface strain induced by lattice mismatch between the Pt shell and Pt-Co alloy-core interface structures was observed. The results showed that the Pt(111)-shell with 2.0% compressive surface strain vs. intrinsic Pt(111) lattice gave rise to a maximum activity enhancement, ca...

Aldehyde dehydrogenase 7A1 (ALDH7A1) catalyzes the terminal step of lysine catabolism, the NAD+-dependent oxidation of α-aminoadipate semialdehyde to α-aminoadipate. Structures of ALDH7A1 reveal the C-terminus is a gate that opens and closes in response to the binding of α-aminoadipate. In the closed state, the C-terminus of one protomer stabilizes the active site of the neighboring protomer in the dimer-of-dimers tetramer. Specifically, Ala505 and Gln506 interact with the conserved aldehyde-anchor-loop in the closed state...

Photocatalytic CO₂ reduction into renewable hydrocarbon solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. This article focuses on the direct coupling of photocatalytic water splitting and thermo-catalytic hydrogenation of CO₂ in the conversion of CO₂-H₂O to fuels. Specifically, it was found that direct coupling of thermo- and photo-catalysis over Au-Ru/TiO₂ leads to 15 times higher activity (358 K, with ~99% CH₄ selectivity) in the conversion of CO₂-H₂O to fuels than that of photo-catalytic water splitting...

Conjugated microporous polymers (CMPs) are a class of crosslinked polymers that combine permanent micropores with π- conjugated skeletons and possess three-dimensional (3D) networks. Compared with conventional materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), the CMPs usually have superior chemical and thermal stability. CMPs have made significant progress in heterogeneous catalysis in the past seven years. With a bottom-up strategy, catalytic moieties can be directly introduced into in the framework to produce heterogeneous CMP catalysts...