ChemRxiv
Not a member yet
27047 research outputs found
Sort by
Why are some pnictogen(III) pincer complexes planar and others pyramidal?
No full textGeometrically-constrained pnictogen pincer complexes have emerged in recent years as platforms for unique stoichiometric and catalytic chemical transformations. These complexes feature dynamic conformations ranging from fully planar at the pnictogen centre to distorted-pyramidal geometries, as well as variation between phases. Although the valued reactivity of pnictogen pincer complexes is ascribed to their geometries, there is no unified model to explain the observed conformational outcomes across different ligands and pnictogen centres. Here we propose such a model through computational analysis of more than 1300 structures across 64 complexes (16 ligands and 4 heavy pnictogens), explaining the experimental observations and making new predictions. By looking at signatures of bond stability (bond lengths, Wiberg bond indices) and delocalization (NPA charges, Hirshfeld charges), our framework posits a pnictogen-based σ-bonding effect that favours pyramidalization and exists in competition with a ligand-based π-bonding effect that favours planarity. Variations in structure as a function of pnictogen identity, ligand tethering, electronics, and aromaticity can be reconciled with reference to a balance between these two opposing forces. Careful consideration of the σ/π-bonding effects may aid in the rational design of future pnictogen pincer complexes with predictable geometries and reactivities
Synergistic Processes for Enhanced Functionality and Microstructure Engineering in PVDF-based Systems
No full textVinylidene Fluoride (VDF)-based polymers are renowned for their remarkable electroactive properties, including piezoelectric, pyroelectric, and ferroelectric features. These properties make them highly sought-after in a wide range of applications, such as sensors and energy storage. The modulation of their dielectric characteristics is intricately linked to the crystalline polymorphism, which is contingent upon specific processing conditions. Herein, we delve into the potential for enhancing these dielectric functionalities through modifications of the processing conditions (i.e., solvent casting and evaporation rate). Our findings demonstrate that superior structural characteristics and enhanced dielectric properties are achieved when casting from highly polar solvents followed by vacuum annealing. This simple and efficient method, eliminates the need for extensive processing and excessive energy consumption and it holds promise for streamlining industrial processing on a larger scale by reducing duration, energy, and complexity
Improvements in fast mass microscopy for large-area samples
No full textMass spectrometry imaging (MSI) is a technique that analyzes chemical information and spatial distribution of surface analytes. Most MSI studies are conducted in microprobe-mode, in which a mass spectrum is collected for each pixel to create a mass image. Thus, spatial resolution, sample imaging area, and imaging speed are linked. In this mode, halving the pixel size quadruples the analytical time, which presents a practical limit on high spatial resolution MSI throughput. Fast mass microscopy (FMM) is, in contrast, a microscope-mode MSI technique which decouples spatial resolution and imaging speed. FMM circumvents the linear-quadratic relationship of pixel size and analytical time which enables increased the imaging size area and the analytical speed achievable. In this study, we implement instrument modifications to the FMM system including the addition of linear encoders that enable roughly 8.5× faster imaging than was previously achieved, allowing a 42.5 × 26 mm2 sample area to be imaged at a 1 µm pixel size in < 4.5 min. Linear encoders also enable the alignment of multi-pass images that increase image homogeneity and chemical signal. The applicability of FMM to large area samples has made it important to define the tolerance to height variations of the technique, which was determined to be at least 218 µm
Clustering of the Membrane Protein by Molecular Self-assembly Downregulates Signaling Pathway for Cancer Cell Inhibition
No full textThis work reports a cyclic peptide appended self-assembled scaffold that recognizes the membrane protein EGFR and arrests the EGFR signaling by assembly induced aggregation through multivalent interactions. Being incubating with cells, the oligomers of PAD-1 first recognize overexpressed EGFR on cancer cell membrane for arresting EGFR, which then initiate cellular uptake through endocytosis. The accumulation of PAD-1 and EGFR in the lysosome results in the formation of nanofibers, leading to lysosomal membrane permeabilization (LMP). These processes disrupt the homeostatic of EGFR and inhibit the downstream signaling transduction of EGFR for cancer cell survive. Moreover, LMP induced the releasing of protein aggregates could generate endoplasmic reticulum (ER) stress, resulting in cancer cell death selectively. In vivo studies indicate the efficient anti-tumor efficiency of PAD-1 in tumor bearing mice. As a first example, this work provides an alternative strategy for controlling protein behavior for tuning cellular events in living cells
Leveraging Asymmetric Catalysis Data for Mechanistic Interrogation of Nickel-Photoredox THF Arylation
No full textThis manuscript details the development of an asymmetric variant for the Ni-photoredox α-arylation of tetrahydrofuran (THF), which was originally reported in a racemic fashion by Doyle and Molander. Leveraging the enantioselectivity data that we obtained, a complex mechanistic scenario different from those originally proposed is uncovered. Specifically, an unexpected dependence of the product enantiomeric ratio on both the halide identity (aryl chloride vs. bromide substrates) and the Ni source was observed. Stoichiometric experiments and time course analyses of the evolution of product enantioselectivity with time revealed a different initial behavior for reactions carried out with Ni(II) and Ni(0) pre-catalysts that later converge into a common mechanism. For studying the predominant pathway, this paper describes a rare example of the syntheses of chiral bisoxazoline Ni(II) aryl halide complexes, which proved essential for probing enantioselectivity via stochiometric experiments. These experiments identify the Ni(II) aryl halide complex as the primary species involved in the key THF radical trapping event. A multivariate linear regression model is presented that further validates the dominant mechanism and delineates structure-selectivity relationships between ligand properties and enantioselectivity. EPR analysis of Ni(0)/aryl halide mixtures highlights the fast access to a variety of Ni complexes in 0,+1, and +2 oxidation states that are proposed to be responsible for the initial divergence in mechanism observed when using Ni(0) pre-catalysts. More broadly, beyond advancing the mechanistic understanding of this THF arylation protocol, this work underscores the potential of leveraging enantioselectivity data to unravel intricate mechanistic manifolds within Ni-photoredox catalysis
Consolidating LC×LC-HRMS/MS Technique for the Non-targeted Analysis of Poly- And Perfluorinated Substances: a Trial on Aqueous-Film Forming Foams.
No full textTo date, poly- and perfluoroalkyl substances (PFASs) represent a real threat for both their environmental persistence, wide physicochemical variability, and their potential toxicity. Thus far a large portion of these chemicals remain structurally unknown. These chemicals, therefore, require the implementation of complex non-targeted analysis workflows using high resolution mass spectrometry coupled with liquid chromatography (LC-HRMS) for their comprehensive detection and monitoring. This approach, even though comprehensive, does not always provide the much needed analytical resolution for the analysis of complex PFAS mixtures such as fire-fighting aqueous-film forming foams (AFFFs). This study consolidates the advantages of LC×LC technique hyphenated with high-resolution tandem mass spectrometry (HRMS/MS) for the identification of PFASs in AFFF mixtures. A total of 57 PFAS homologue series (HSs) were identified in 3M and Orchidee AFFF mixtures thanks to the (i) high chromatographic peak capacity (n’2D,c~300) and the (i) increased mass domain resolution provided by the “remainder of Kendrick Mass” (RKM) analysis on the HRMS data. Then, we attempted to annotate PFASs of each HSs exploiting the available reference standards and the FluoroMatch workflow in combination with the RKM defect by different fluorine repeating units, such as CF2, CF2O, and C2F4O. This approach resulted in 12 identified PFAS HSs, including compounds belonging to the HSs of PFACAs, PFASAs, SF5-PFASAs, N-SPAmP-FASA, and N-CMAmP-FASA. The annotated categories of perfluoroalkyl aldehydes, and chlorinated PFASAs represent a first record of PFAS HSs in the investigated AFFF samples
A DyIII2 Dimer in a Radical Straitjacket: The Importance of Dipolar Interactions in Dysprosium Single Molecule Magnets
No full textWe present three air-stable radical-containing compounds [MIII2(phsq)4(NO3)2(MeOH)2]∙2MeOH (M = Dy (1), Y (2), Gd (3); Hphsq = 9,10-phenanthrenesemiquinone) in which strong intramolecular inter-radical interactions force two lan-thanide ions into close proximity and isolate them from the lattice. Magnetic measurements on (1) showed it to be an SMM with maxima in the ac susceptibility up to 18 K (1000 Hz). Modeling the magnetic data using three different analytical approaches reveals the absence of zero-field quantum tunneling of magnetization (ZFQTM) as a relaxation pathway. This is a result of significant internal magnetic fields identified by ab initio calculations that appear to quench the ZFQTM. This can be verified from the measurements performed on a Y-doped sample (1a) in which one of the DyIII ions is largely replaced by diamagnetic YIII and switches ZFQTM back on
A domino reaction strategy for facile and modular construction of synthetically challenging functionalized ortho-fluoroanilines
No full textThe selective formation of ortho-fluoroanilines, representing versatile intermediates for the pharmaceutical and fine chemical industries, relies to date on, e.g., transition-metal-catalyzed fluorination of azobenzenes, which must be pre-formed from aniline derivatives. While few efficient methods for aniline synthesis were reported, sustainable, straightforward, and selective synthesis of fluoroanilines, and in particular ortho-fluoroanilines, remains challenging. Herein, we describe a domino approach that involves the simultaneous construction of a benzene ring and the installation of both amine and fluorine groups in a single operation under metal-free conditions, starting from readily available acyclic compounds. The developed atom- and cost-efficient, highly convenient, selective, and environmentally friendly four-step domino process allows the formation of a variety of functionalized ortho-fluoroanilines with yields of up to 80% and bypasses the selectivity issues of transition-metal-catalyzed aniline fluorination reactions. Furthermore, we show that the new domino products can efficiently be utilized to synthesize fluorinated azo dye and (tetrahydro)quinazoline derivatives in a bioactive form, i.e., possessing a first-time proven micromolar antiviral activity and high selectivity (EC50 (HCMV) down to 1.9 ± 0.7 µM, CC50 up to >100 µM), under conventional and/or visible-light mediated conditions
Overlooked Role of Electrostatic Interactions in HER Kinetics on MXenes: Beyond the Conventional Descriptor ΔG~0 to Identify the Real Active Site
No full textUnderstanding the atomic-level mechanism of the hydrogen evolution reaction (HER) on MXene materials is crucial for developing affordable HER catalysts, while their complex surface terminations present a substantial challenge. Herein, employing constant-potential grand canonical density functional theory (GC-DFT) calculations, we elucidate the reaction kinetics of HER on MXenes with various surface terminations by taking experimentally reported Mo2C as a prototype. We observe a contradictory scenario on Mo2C MXene when using the conventional thermodynamic descriptor ΔGH* (hydrogen binding energy): both competing surface phases that emerge close to the equilibrium potential meet the ΔGH*~0 criterion, while they exhibit distinctly different reaction kinetics. Contrary to previous studies that identified surface *O species as active sites, our research reveals that these *O sites are kinetically inert for producing H2 but easily reduced to H2O. Consequently, the surface Mo atoms, exposed from the rapid reduction of the surface *O species, serve as the actual active site catalyzing HER via the Volmer-Heyrovsky mechanism, as confirmed by the experimental studies. Our findings highlight the overlooked role of electrostatic repulsion in HER kinetics, a factor not captured by the thermodynamic descriptor ΔGH*. This work provides new insights into the HER mechanism and emphasizes the importance of kinetic investigation for a comprehensive understanding of HER
Ni-Catalyzed Asymmetric Reductive Arylation of ⍺-Substituted Imides
No full textα-Aryl imides are common structural motifs in bioactive molecules and proteolysis-targeting chimeras designed for targeted protein deg-radation. An asymmetric Ni-catalyzed reductive cross-coupling of imide electrophiles and (hetero)aryl halides has been developed to synthesize enantioenriched α-arylglutarimides from simple starting materials. Judicious selection of electrophile pairs allows for coupling of both electron-rich and electron-deficient (hetero)aryl halides in good yields and enantioselectivities