Insights on Morphology and Thermal Stability of Hollow Pt Nanospheres by In Situ Environmental TEM.

The fields of catalysis and energy storage nowadays quote the use of nanomaterials with well-defined size, morphology, chemical composition, and thermal stability in the high-temperature range and under harsh conditions of reactions. We present herein an approach based on in situ environmental scanning transmission electron microscopy (STEM), combined with analytical STEM and electron tomography (ET), for the evaluation of the thermal stability of hollow Pt nanospheres under vacuum and high-pressure hydrogen environments. Spherical Pt hollow nanospheres (HNSs) with an average diameter of 15 and 34 nm were synthesized by a galvanic replacement-based procedure using either steep or continuous addition of Pt salts during synthesis.

Generative machine learning produces kinetic models that accurately characterize intracellular metabolic states.

Generating large omics datasets has become routine for gaining insights into cellular processes, yet deciphering these datasets to determine metabolic states remains challenging. Kinetic models can help integrate omics data by explicitly linking metabolite concentrations, metabolic fluxes and enzyme levels. Nevertheless, determining the kinetic parameters that underlie cellular physiology poses notable obstacles to the widespread use of these mathematical representations of metabolism.

Electroinduced Reductive and Dearomative Alkene-Aldehyde Coupling.

The direct coupling of alkene feedstocks with aldehydes represents an expedient approach to the generation of new and structurally diverse C(sp)-hybridized alcohols that are primed for elaboration into privileged architectures. Despite their abundance, current disconnection strategies enabling the direct coupling of carbon-carbon π-bonds and aldehydes remain challenging because contemporary methods are often limited by substrate or functional group tolerance and compatibility in complex molecular environments. Here, we report a coupling between simple alkenes, heteroarenes and unactivated aliphatic aldehydes via an electrochemically induced reductive activation of C-C π-bonds.

Interfacial Tuning of Electrocatalytic Ag Surfaces for Fragment-Based Electrophile Coupling.

Construction of C‒C bonds in medicinal chemistry frequently draws on the reductive coupling of organic halides with ketones or aldehydes. Catalytic C(sp)‒C(sp) bond formation, however, is constrained by the competitive side reactivity of radical intermediates following sp organic halide activation. Here, an alternative paradigm deploys catalytic Ag surfaces for reductive fragment-based electrophile coupling compatible with sp organic halides.

mRNA trans-splicing dual AAV vectors for (epi)genome editing and gene therapy.

Large genes including several CRISPR-Cas modules like gene activators (CRISPRa) require dual adeno-associated viral (AAV) vectors for an efficient in vivo delivery and expression. Current dual AAV vector approaches have important limitations, e.g.

Continuous nucleation of metallic nanoparticles photocatalytic reduction.

Whether in organic synthesis or solar energy conversion, light can be a powerful reagent in chemical reactions and introduce new opportunities for synthetic control including duration, intensity, interval, and energy of irradiation. Here, we report the use of a molecular photosensitizer as a reducing agent in metallic nanoparticle syntheses. Using this approach, we report three key findings.

Rupturing aromaticity by periphery overcrowding.

The balance between strain relief and aromatic stabilization dictates the form and function of non-planar π-aromatics. Overcrowded systems are known to undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. In this study we incremented the strain energy of an aromatic system beyond its aromatic stabilization energy, causing it to rearrange and its aromaticity to be ruptured.

A Metal-Free Cyclobutadiene Reagent for Intermolecular [4 + 2] Cycloadditions.

Cyclobutadiene is a highly reactive antiaromatic hydrocarbon that has fascinated chemists for over 60 years. However, its preparation and uses in chemical synthesis are sparing, in part due to its lengthy synthesis that generates hazardous byproducts including excess heavy metals. Herein, we report a scalable, metal-free cyclobutadiene reagent, diethyldiazabicyclohexene dicarboxylate, and explore its intermolecular [4 + 2] cycloaddition with various electron-deficient alkenes.

Elucidating electron-transfer events in polypyridine nickel complexes for reductive coupling reactions.

Polypyridine-ligated nickel complexes are widely used as privileged catalysts in a variety of cross-coupling reactions. The rapid adoption of these complexes is tentatively attributed to their ability to shuttle between different oxidation states and engage in electron-transfer reactions. However, these reactions are poorly understood in mechanistic terms.

Enantioselective C(sp)-H Functionalization of Oxacycles via Photo-HAT/Nickel Dual Catalysis.

The selective functionalization of ubiquitous but inert C-H bonds is highly appealing in synthetic chemistry, but the direct transformation of hydrocarbons lacking directing groups into high-value chiral molecules remains a formidable challenge. Herein, we develop an enantioselective C(sp)-H functionalization of undirected oxacycles via photo-HAT/nickel dual catalysis. This protocol provides a practical platform for the rapid construction of high-value and enantiomerically enriched oxacycles directly from simple and abundant hydrocarbon feedstocks.

Generating Fischer-Type Rh-Carbenes with Rh-Carbynoids.

We describe the first catalytic generation of Fischer-type acyloxy Rh(II)-carbenes from carboxylic acids and Rh(II)-carbynoids. This novel class of transient donor/acceptor Rh(II)-carbenes evolved through a cyclopropanation process providing access to densely functionalized cyclopropyl-fused lactones with excellent diastereoselectivity. DFT calculations allowed the analysis of the properties of Rh(II)-carbynoids and acyloxy Rh(II)-carbenes as well as the characterization of the mechanism.

The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere.

We revisit the hypothesis that there is life in the venusian clouds to propose a life cycle that resolves the conundrum of how life can persist aloft for hundreds of millions to billions of years. Most discussions of an aerial biosphere in the venusian atmosphere temperate layers never address whether the life-small microbial-type particles-is free floating or confined to the liquid environment inside cloud droplets. We argue that life must reside inside liquid droplets such that it will be protected from a fatal net loss of liquid to the atmosphere, an unavoidable problem for any free-floating microbial life forms.

Spatial differentiation of Brønsted acid sites by probe molecule in zeolite USY using synchrotron X-ray powder diffraction.

By combining synchrotron X-ray powder diffraction, Rietveld refinement and the use of a probe molecule, Brønsted Acid Sites (BAS) of different strengths in steam-treated USY zeolite can be for the first time spatially differentiated: this enables the analysis of different acid-catalysed reactions of dimethylfuran (biomass) by the zeolite using a definitive site blockage strategy.

Impact of Macroporosity on Catalytic Upgrading of Fast Pyrolysis Bio-Oil by Esterification over Silica Sulfonic Acids.

Fast pyrolysis bio-oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom- and energy-efficient route to upgrade pyrolysis bio-oils. Propyl sulfonic acid (PrSO H) silicas are active for carboxylic acid esterification but suffer mass-transport limitations for bulky substrates.

From Biomass-Derived Furans to Aromatics with Ethanol over Zeolite.

We report a novel catalytic conversion of biomass-derived furans and alcohols to aromatics over zeolite catalysts. Aromatics are formed via Diels-Alder cycloaddition with ethylene, which is produced in situ from ethanol dehydration. The use of liquid ethanol instead of gaseous ethylene, as the source of dienophile in this one-pot synthesis, makes the aromatics production much simpler and renewable, circumventing the use of ethylene at high pressure.