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Development of a sampling protocol for collecting leaf surface material for multiphase chemistry studies
No full textPlant leaves and water drops residing on them interact with atmospheric oxidants, impacting the deposition and emission of trace gases and mediating leaf damage from air pollution. Characterizing the chemical composition and reactivity of the water-soluble material on leaf surfaces is thus essential for improving our understanding of atmosphere-biosphere interactions. However, the limited knowledge of sources and nature of these chemicals challenges sampling decisions. This work investigates how sampling variables and environmental factors impact the quantity and composition of water-soluble material sampled from wet leaves and proposes a flexible protocol for its collection. The ratio of solvent volume-to-leaf area, the solvent-to-leaf contact time, and environmental parameters – including the occurrence of rain, plant location and its metabolism – drive solute concentration in leaf soaks. Despite minor variations, UV-Vis absorption spectra of leaf soaks are comparable to authentic raindrops collected from the same tree and share features with microbial dissolved organic matter – including overall low aromaticity, low chromophore content, and low average molecular weight. In addition to guiding the development of a sampling protocol, our data corroborate recent hypotheses on the amount, origin, nature, and reactivity of water-soluble organics on wet leaves, providing new directions of research into this highly interdisciplinary topic
Enantioselective Arbuzov Reaction Enabled by Catalytic Ion-Pair Reorganization
No full textThe stereocontrolled synthesis of stereogenic-at-phosphorus compounds is a long-standing challenge in organic chemistry that has received heightened research attention in recent years. None of the catalytic approaches taken to date have leveraged the rich manifold of transformations proceeding through nucleophilic dealkylation of phosphonium ion intermediates (e.g. Michaelis–Arbuzov, Pudovik, and Appel reactions). Here, we report enantioselective hydrogen-bond-donor-catalyzed Michaelis–Arbuzov reactions of dialkylphosphonites with hydrogen chloride to afford H-phosphinates, which are versatile P-chiral building blocks. Mechanistic and computational investigations reveal that the catalyst diminishes the reactivity of the chloride nucleophile, yet accelerates the rate-determining dealkylation step by preorganizing the phosphonium chloride resting state into a geometry that is primed to enter the SN2 transition state
Edge Functionalization of Bulk γ-Graphyne Facilitates Mechanical Exfoliation and Modulates the Mode of Sheet Stacking
No full textWe have successfully achieved selective and efficient functionalization of sheet edges in microcrystalline multilayer γ-graphyne through two methods: cross-coupling with residual bromide edge groups, and copper-catalyzed azide-alkyne cycloaddition (CuAAC) with edge terminal alkyne groups. This modification significantly enhances the ease of mechanical exfoliation and dispersibility of the sheets of γ-graphyne. Specifically, C18-grafted γ-graphyne forms stable dispersions in compatible organic solvents, allowing for the imaging of atomically thin layers of γ-graphyne for the first time. Additionally, we have discovered that phenylacetylide edge groups alter the preferred stacking mode of γ-graphyne sheets. Few-layer flakes of Ph-edge γ-graphyne exhibit a preference for the symmetric R3m space group, contrasting with the aperiodic stacking of as-synthesized Br-edge γ-graphyne. These results open the door for an easy and scalable exfoliation of few-layer flakes of γ-graphyne with a high aspect ratio, enabling potential applications in carbon electronics
Synthesis and Medicinal Applications of N-Heterocyclic Carbene Complexes Based on Caffeine and Other Xanthines
No full textXanthines are purine derivatives predominantly found in plants. Xanthines include compounds such as caffeine, theophylline, and theobromine and exhibit a variety of pharmacological properties, demonstrating efficacy in treating neurodegenerative disorders, respiratory dysfunctions, and also in cancer. The versatile attributes of these materials render them privileged scaffolds for the development of compounds for various biological applications. Xanthines are N-heterocyclic carbene precursors that combine a pyrimidine and an imidazole ring. Owing to their biological relevance, xanthines have been employed as N-heterocyclic carbenes in the development of metallodrugs for anticancer and antimicrobial purposes. In this conceptual review, we examine key examples of N-heterocyclic carbene complexes derived from caffeine and other xanthines, elucidating their synthetic methods and describing their pertinent medicinal applications
Advanced nanomaterials for Organic Compounds detection and Oxidation by Electrochemical methods with the Aid of Active Catalysts
No full textThe coexistence of biomolecules in the living being blood, and urine plays a crucial function in the biological systems. For i.e., in human organism, generally there coexist Ascorbic Acid (AA) and Dopamine (DA) in the extracellular fluid. Moreover, in the human’s blood and urine, it coexists Uric Acid (UA) and (AA). Therefore, these compounds are of great interest in biomedical function which play a essential factor in the human metabolism, central nervous, renal systems, and beyond. However, abnormal levels of these molecules can lead to a drop-off in the biological system purpose. So, that, since long time ego, as described here, there are many materials in diverse forms that have been designed and developed for both biomolecules oxidation and detection. However, it still some issues to master this concern such the materials costs, the process optimization and cost, the environmental friendliness of the suggested catalysts, and so on. Therefore, there is a higher need in the development of a new and powerful platforms for the early and facile sensing of these biomolecules with cost- effective, high selectivity, as well as best sensitivity, superior stability
Triethoxysilane-Catalyzed Sequential Regioselective Hydroboration of Terminal Alkynes: Sustainable Access to E-Alkenylboronate and Alkyl Gem-Diboronate Esters
No full textThe commercial reagent, HSi(OEt)3, was an efficient catalyst for the synthesis of E-alkenylboronate esters and alkyl gem-diboronate esters by single or double hydroboration of terminal alkynes with HBPin (pinacolborane). The reaction time controlled whether a single or a double addition of HBPin to the alkynes occurred. Aromatic terminal alkynes containing strong electron-donating or -withdrawing substituents at different positions as well as aliphatic alkynes were efficiently mono- and dihydroborated. Mechanistic studies suggested that the formation of diboronate esters proceeds by a double hydroboration with the second hydroboration cycle being the rate determining. The reaction of HSi(OEt)3 with HBPin has been identified as a catalyst deactivation pathway operative in catalysis. Screening of other silicon compounds for this transformation supported that the steric and electronic profile of HSi(OEt)3 is key to promote the second hydroboration step
The Third CACHE Challenge – Finding Ligands Targeting the Macrodomain of SARS-CoV-2 NSP3 Using AI-inspired and Knowledge-Based Approaches.
No full textThe SARS-CoV-2 virus contains a host of nonstructural proteins (NSPs) that contribute to its structure and viral function. Among them is the nonstructural protein 3 (NSP3), which contains a macrodomain (Mac1) that interferes with antiviral adenosine diphosphate (ADP)-ribosylation signaling. Catalytic mutations in Mac1 render viruses nonpathogenic, making this enzyme a promising target for antiviral development. For this reason, the third CACHE challenge focused on identifying binders of the Mac1 domain of NSP3 for the development of novel antivirals against SARS-CoV-2. To this end, we used available structural data of the NSP3 Mac1 domain in complex with known fragment binders as starting points for ligand discovery; our efforts were primarily focused on sub-sites of the ADP binding site in the NSP3 macrodomain. Then, using Artificial intelligence (AI)-guided and knowledge-based fragment merging and expansion approaches, we generated novel molecules that would serve as templates to identify highly similar compounds in the Enamine REAL database that would be commercially available. Our design yielded a library of 12,800 molecules, which was docked with our program FITTED to a representative crystal structure of NSP3. We ranked the predicted binding poses based on docking score, followed by visual pose analysis of the best 200 compounds. We finally selected and proposed 150 compounds for testing, followed by further shortlisting to yield a final list of 107 molecules. 91 compounds were purchased from Enamine and are being tested at the Structural Genomics Consortium (SGC). Our approach and findings will further contribute to our open science efforts, and we aim to continue to engage the scientific community
From Humorous Post to Detailed Quantum-Chemical Study: Isocyanate Synthesis Revisited
No full textIsocyanates play an essential role in modern manufacturing processes, especially in polyurethane production. There are numerous synthesis strategies for isocyanates both in industrial and laboratory conditions, which do not prevent searching for alternative highly efficient synthetic protocols. Here, we report a detailed theoretical investigation of the mechanism of sulfur dioxide-catalyzed rearrangement of the phenylnitrile oxide into phenyl isocyanate, which was first reported in 1977. The DLPNO-CCSD(T) method and up-to-date DFT protocols were used to perform a highly accurate quantum-chemical study of the rearrangement mechanism. An overview of various organic and inorganic catalysts has revealed other potential catalysts, such as sulfur trioxide and selenium dioxide. Furthermore, the present study elucidated how substituents in phenylnitrile oxide influence reaction kinetics. This study was performed by a self-organized collaboration of scientists initiated by a humorous post on the VK social network
Enforcing Metal‒Arene Interactions in Bulky p-Terphenyl Bis(anilide) Complexes of Group 2 Metals (Be‒Ba): Potential Precursors for Low Oxidation State Alkaline Earth Metal Systems
No full textAn extremely bulky p-terphenyl bis(aniline), p-C6H4{C6H4[N(H)TCHP]-2}2 (TCHP = 2,4,6-tricyclohexylphenyl) TCHPTerphH2, has been developed. Deprotonation of a less bulky analogue, DipTerphH2 (Dip = 2,6-diisopropylphenyl), with BePh2 affords the bimetallic system, [(BePh)2(-DipTerph)] 1. Treating either TCHPTerphH2 or DipTerphH2 with Mg{CH2(SiMe3)}2 gives the monomeric bis(anilide) complexes [Mg(ArTerph)] (Ar = Dip 2, TCHP 3) which display rare examples of eta-6-arene coordination to the metal centre. Treating 2 with THF leads to partial dissociation of the Mg···arene interaction, and formation of [Mg(DipTerph)(THF)] 4. Reactions of the bis(aniline)s with the group 2 metal amides [M{N(SiMe3)2}2] affords dimeric, isostructural compounds [{M(ArTerph)}2] (Ar = Dip, M= Ca 5, Sr 6, Ba 7; Ar = TCHP, M= Ca 8, Sr 9, Ba 10) which display intermolecular M···arene interactions in the solid-state. Computational studies have shown that the intramolecular M···arene interactions in models of the ether free metal bis(anilide) compounds are largely electrostatic in nature. Reductions of these compounds with alkali metals led to mixtures of unidentified products
Spin Polarized Electron Dynamics Enhance Water Splitting Efficiency by Yttrium Iron Garnet Photoanodes: A New Platform for Spin Selective Photocatalysis
No full textThis work presents a spectroscopic and photocatalytic comparison of water splitting using yttrium iron
garnet (Y3Fe5O12, YIG) and hematite (α-Fe2O3) photoanodes. Despite similar electronic structures,
YIG significantly outperforms widely studied hematite, displaying more than an order of magnitude
increase in photocurrent density and a factor of two increase in Faradaic efficiency. Probing the
charge and spin dynamics by ultrafast, surface-sensitive XUV spectroscopy reveals that the enhanced
performance arises from 1) reduced polaron formation in YIG compared to hematite and 2) an intrinsic
spin polarization of catalytic photocurrents in YIG. Ultrafast XUV measurements show a reduction
in the formation of surface electron polarons compared to hematite due to site-dependent electronphonon
coupling. This leads to spin polarized photocurrents in YIG where efficient charge separation
occurs on the Td sub-lattice compared to fast trapping and electron/hole pair recombination on the
Oh sub-lattice. These lattice-dependent dynamics result in a long-lived spin aligned hole population
at the YIG surface, which is directly observed using XUV magnetic circular dichroism. Comparison
of the Fe M2,3 and O L1-edges show that spin aligned holes are hybridized between O 2p and Fe 3d
valence band states, and these holes are responsible for highly efficient, spin selective water oxidation
by YIG. Together, these results point to YIG as a new platform for highly efficient, spin selective
photocatalysis