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Role of catalyst shape and reactor performance for relating the catalytic activity and the chemical structure of active sites for emission control catalysis
No full textPacked powder beds and coatings are two relevant forms of catalysts, applied in industrial heterogeneous catalysis. Both types have their individual advantages and disadvantages in regard to the performance and characterisation causing some complexity in the resulting
flow patterns, possible temperature inhomogenities in the reactor and the dynamic evolution of chemical state of the noble metal during the reaction along the catalytic bed. The well-known CO oxidation reaction over Pt/Al2O3 catalysts was used in this study to uncover the influence of the gas phase compositions, the influence of the temperature and the evolution of the electronic structure of Pt for powdered and coated catalysts at comparable length scales. Advanced operando investigations were used to demonstrate the influence of spatial gradients in the gas phase for washcoatings in contrast to packed powder beds. Additionally, transient gradients in the chemical state of Pt, which occurred more pronounced for packed powder beds than for coated monoliths were followed and traced back to heat and mass transfer effects. Finally, the catalytic activity can be linked to the temperature distributions for both types of samples. These findings will be valuable for planning and evaluating future combinations of spectroscopic and catalytic experiments on industrially relevant systems
Unraveling C4 selectivity in the light-driven C–H fluoroalkylation of pyridines and quinolines
No full textGiven the prevalence of pyridine motifs in FDA-approved drugs, selective fluoroalkylation of pyridines and quinolines is essential for preparing diverse bioisosteres. However, conventional Minisci reactions often face challenges in achieving precise regioselectivity due to competing reaction sites of pyridine and the limited availability of fluoroalkyl radical sources. Herein, we present a light-driven, C4-selective fluoroalkylation of azines utilizing N-aminopyridinium salts and readily available sulfinates. Our approach employs electron donor-acceptor complexes, achieving highly C4-selective fluoroalkylation under mild conditions without an external photocatalyst. This practical method not only enables the installation of CF2H groups but also allows for the incorporation of CF2-alkyl groups with diverse functional entities, surpassing the limitations of previous methods. The versatility of the radical pathway is further demonstrated through straightforward three-component reactions involving alkenes and [1.1.1]propellane. Detailed experimental and computational studies have elucidated the origins of regioselectivity, providing profound insights into the mechanistic aspects
POTASSIUM HEXATITANATE FIBER FREE. A NEW CLASS OF ALKALI TITANATES WITH TITANIUM OXIDATION NUMBER DIFFERENT FROM +4
No full textA new class of Titanates are presented with Titanium oxidation N° different from +4. The Titanates thus obtained presents a non-fibrous morphology. Ways of synthesis are reported. SEM pictures and fiber analysis showing an absolutely fiber free material. A new structure, unknown till now, is displayed, recovered through a dedicated software, through which a new formula has been calculated. An hypothesis of structure stabilization is proposed, confirmed by TGA and DSC. The new material has been tested in brake pads, confirming with good performances
PCET-driven Reactivity of Neptunyl(VI) Yields Oxo-bridged Np(V) and Np(IV) Species
No full textA reaction sequence based upon the principles of proton-coupled electron transfer (PCET) has been used to access two unconventional oxo-deficient polynuclear complexes of neptunium (Np). The complexes featuring mono-μ2-oxo motifs assemble under ambient atmosphere upon dissolution of neptunyl(VI) diacetate dihydrate (NpO2(OAc)2(H2O)2·HOAc) in methanol followed by addition of a supporting pentadentate ligand (LNM); one complex is a mixed-valent [NpV,NpIV,NpV ] trimer with two bridging μ2-oxos and the other is a [NpV,NpV ] dimer featuring a single μ2-oxo. The outer Np centers are also capped with terminal oxo ligands. Spectroscopic and spectrokinetic findings show that intermediate [NpV O2(OAc)]n species form prior to metal chelation by LNM; electrolysis experiments demonstrate that production of Np(V) gives rise to asynchronous proton transfer that does not occur otherwise (in the Np(VI) state) as well as condensation (loss of H2O) and formation of the polynuclear complexes. The oxo-deficient nature of these products is attributable to the reduction/condensation reaction sequence of PCET. Consequently, PCET reactivity appears poised to complement more established techniques for interconverting actinide oxidation states, a prospect with considerable applications in fuel recycling for low-carbon nuclear energy
One-step Hydrothermal Synthesis of Sn-doped Sb2Se3 for Solar Hydrogen Production
No full textAntimony selenide (Sb2Se3) has recently been intensively investigated and has achieved significant advancement in photoelectrochemical (PEC) water splitting. In this work, a facile one-step hydrothermal method for the preparation of Sn-doped Sb2Se3 photocathodes with improved PEC performance was investigated. We present an in-depth study of the performance enhancement in Sn-doped Sb2Se3 photocathodes using capacitance-voltage (CV), drive level capacitance profiling (DLCP), and electrochemical impedance spectroscopy (EIS) techniques. The incorporation of Sn2+ into the Sb2Se3 results in increased carrier density, reduced surface defects, and improved charge separation, thereby leading to improved PEC performance. With a thin Sb2Se3 absorber layer (270 nm thickness), the Sn-doped Sb2Se3 photocathode exhibits an improved photocurrent density of 17.1 mA cm−2 at 0 V versus RHE (VRHE) compared to that of the undoped Sb2Se3 photocathode (14.4 mA cm−2). This work not only highlights the positive influence of Sn doping on Sb2Se3 photocathodes but also showcases a one-step method to synthesize doped Sb2Se3 with improved optoelectronic properties
Probing the Intramolecular Folding of Nucleic Acids with Native Ion Mobility Mass Spectrometry: Strategies and Caveats
No full textThe goal of native mass spectrometry is to obtain information on non-covalent interactions in solution through mass spectrometry measurements in the gas phase. Characterizing intramolecular folding re-quires using structural probing techniques such as ion mobility spectrometry. However, inferring solu-tion structures of nucleic acids is difficult because the low-charge state ions produced from aqueous solutions at physiological ionic strength get compacted during electrospray. Here we explored whether native supercharging could produce higher charge states that would better reflect solution folding, and whether the voltage required for collision-induced unfolding (CIU) could reflect preserved intramolec-ular hydrogen bonds. We studied pH-responsive i-motif structures, with or without a hairpin in the loop, and unstructured controls. We also implemented a multivariate curve resolution procedure to extract physically meaningful pure components from the CIU data and reconstruct unfolding curves. We found that the relative unfolding voltages reflect preserved intramolecular hydrogen bonds, espe-cially at higher charge states. However, we uncovered several caveats in data interpretation: (1) un-structured controls also undergo unfolding, and the base composition influences the unfolding voltage, (2) changing the solution pH also unexpectedly changed the unfolding voltage, and (3) the ion mobility patterns become more complicated when two structures are present simultaneously, such as an i-motif and a harpin, because of opposite effects on the collision cross section upon activation. Reaching phos-phate charging densities over 0.25 makes it easier to discriminate between structures, and the use of native supercharging agents is thus essential. In short, we investigated in detail the potential and limi-tations of native ion mobility to deduce solution folding of nucleic acids structures
Alzheimer\u27s Disease: Exploring the Landscape of Cognitive Decline
No full textAlzheimer\u27s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and impaired daily functioning. The pathology of AD is marked by the accumulation of amyloid-beta plaques and tau protein tangles in brain, along with neuroinflammation and synaptic dysfunction. Genetic factors, such as mutations in APP, PSEN1, and PSEN2 genes, as well as APOE ε4 allele, contribute to increased risk of acquiring AD. Currently available treatments provide symptomatic relief but do not halt disease progression. Research efforts are focused on developing disease-modifying therapies that target the underlying pathological mechanisms of AD. Advances in identification and validation of reliable biomarkers for AD hold great promise for enhancing early diagnosis, monitoring disease progression, and assessing treatment response in clinical practice, in effort to alleviate the burden of this devastating disease.
In this paper, we analyze data from the CAS Content Collection to summarize the research progress in Alzheimer’s disease. We examine the publication landscape in effort to provide insights into current knowledge advances and developments. We also review the most discussed and emerging concepts and assess the strategies to combat the disease. We explore the genetic risk factors, pharmacological targets, and comorbid diseases. Finally, we inspect clinical applications of products against AD with their development pipelines and efforts for drug repurposing. The objective of this review is to provide a broad overview of the evolving landscape of current knowledge regarding AD, to outline challenges, and evaluate growth opportunities to further efforts in combating the disease
An ex situ gaseous reagent for multicomponent amine bioconjugation
No full textBioconjugation is a large field with many diverse goals, needs, and challenges, that requires a broad toolbox of fundamentally different synthetic approaches. As nucleophilic groups are prevalent in biomolecules, the ability to crosslink two nucleophilic sites offers an attractive approach to construct useful bioconjugates. New technologies for crosslinking with gaseous reagents and with minimal perturbation of natural structure could provide new ways to think about bioconjugation in complex environments. We report a minimalist gaseous sulfonyl chloride-derived reagent for multicomponent bioconjugation with amine, phenol, or aniline reagents to afford urea or carbamate products. In utilizing a gas-phase reagent for a reaction mediated by metal ions, a variety of biologically relevant molecules such as saccharide, PEG, fluorophore, and affinity tag can be efficiently crosslinked to the N-terminus or lysine side chain amines on natural polypeptides or proteins. The application of this method to the production of functional, modified proteins was demonstrated by fluorescence imaging of a cancer cell line and by the facile preparation of a peptide–protein conjugate
Synthesis of chiral boranes via asymmetric insertion of carbenes into B-H bonds catalyzed by the rhodium(I) diene complex
No full textAsymmetric insertion of arydiazoacetates into B-H bonds of NHC-BH2R adducts gives rare compounds with chiral boron centers. The reaction is catalyzed by the rhodium(I) complex with the chiral diene ligand tBu2-TFB, which can be conveniently synthesized by diastereoselective coordination of the racemic diene with (S-Salox)Rh(CO)2. The target boranes were obtained typically in 75−90% yields with 90-95% ee and 2:1-5:1 dr
Hydrogenolysis of epoxy resins by a reusable CeO2-supported Ni−Pd bimetallic catalyst toward recycling of epoxy thermosets
No full textRecycling of epoxy composites, one of the most widely utilized thermoset plastics, is of importance for achieving circular economy as demand for the lightweight materials in the field of sustainable technologies is soaring. Although catalytic hydrogenolysis of epoxy resins provides a promising approach to recover valuable fillers and phenolic compounds from the composites, there is a lack of a reusable heterogeneous catalyst for this purpose. Here, we report a robust Ni−Pd bimetallic nanoparticles supported on CeO2 (Ni−Pd/CeO2) for the hydrogenolysis of epoxy resins under mild conditions (180 °C, 1 atm of H2). Mechanistic studies revealed that Pd-induced reduction of Ni2+ to Ni0 is the key for the high efficiency of the bimetallic catalyst. Benefiting from its heterogeneous nature, Ni−Pd/CeO2 can be easily recycled and reused for several times. The catalyst is also applicable to decomposition of carbon fiber-reinforced epoxy resins to recover carbon fibers and bisphenol A, indicating the potential application of our catalyst system toward recycling of epoxy composites