ChemRxiv
Not a member yet
27047 research outputs found
Sort by
Scalable Synthesis of Accordion-Like Multilayered Titanium Nitride in Air with Enhanced Performance as Catalytic Support for Oxygen Reduction
No full textMXenes, recognized for their potential in energy storage and conversion, face significant challenges due to severe degradation in oxidative environments, which compromises their functional properties and limits further applications. To address this issue, we have developed an efficient pathway for transforming bulk titanium nitride (TiN) into multilayered titanium nitride (M-TiN). This method integrates the intrinsic properties of MXenes with the enhanced stability of TiN, offering a viable solu-tion to the pressing issue of oxidation stability for practical applications. The synthesis of M-TiN avoids the need for inert gas protection or chemical purification steps, making the process both practical and scalable. Notably, M-TiN exhibits inherent stability and improved performance, particularly in oxygen reduction reaction (ORR) when coupled with iron phthalocyanine (FePc). The oxidized surface layer of M-TiN enhances stability in corrosive and oxidative environments and facilitates the formation of Fe-O-Ti bonds, effectively modulating the spin states of the Fe center from low spin to medium spin, thereby improving ORR performance. M-TiN/FePc also delivers a greater power density of 270.31 mW cm-2 and better cyclability than Pt/C in a zinc-air battery. The simplicity of M-TiN\u27s synthesis, along with the inherent properties of both MXene and TiN, positions it as a promising material for the future of energy conversion and storage technologie
Characteristics and challenges of Poly(ethylene-co-vinyl acetate) solution electrospinning
No full textPoly(ethylene-co-vinyl acetate) (PEVA) is a versatile elastic, durable and biocompatible copolymer, which can be processed by melt extrusion or solvent casting, while electrospinning has been reported as challenging. Here, a spinnability window should be identified using a total of 10 different PEVA materials with increasing vinyl acetate content (~12 – 40 wt.%) and molecular weights (~60-130 kDa). Based on solubility predictions by calculating Hansen solubility parameters, candidate solvents were experimentally evaluated. Spinning experiments with systematic alteration of solution composition and processing parameters revealed the causes of material deposition at the spraying nozzle and multi-jet spinning characteristics. By introducing a spinnability score that accounts for product characteristics and reproducibility, the spinnability of PEVA could be rationalized. Overall, it was demonstrated that PEVA solutions with an apparent viscosity of 920-3500 mPa·s can be spun to bead-free fibers of ~10 µm. This size may allow suspension electrospinning to composite fibers in the future
Oxidative Cyclization and Enzyme-free Deiodination of Thyroid Hormones
No full textWe introduce the first non-enzymatic deiodination of thyroid hormones from a so far unknown hypervalent iodaoxinium state. After developing oxidative processes for thyroxine(T4)-derived model cyclic diaryliodonium salts, we successfully produced an iodaoxinium salt through the direct oxidation of O-and N-protected T4. DFT calculations revealed a novel halogen bonding-based deiodination mechanism, circumventing the traditional selenium-dependent pathways. Our findings open new avenues in thyroid hormone chemistry, suggesting alternative mechanisms for their involvement in metabolic processes, regulation of oxidative stress, and gene expression
One Touch Is All It Takes: the Supramolecular Interaction between Ubiquitin and Lanthanide Complexes Revisited by Paramagnetic NMR and Molecular Dynamics
No full textThe supramolecular interaction between lanthanide complexes and proteins is at the heart of numerous chemical and biological studies. Some of these complexes have demonstrated remarkable interaction properties with proteins or peptides in solution and in the crystalline state. Here we have used the paramagnetism of lanthanide ions to characterize the affinity of two lanthanide complexes for ubiquitin. As the interaction process is dynamic, the acquired NMR data only reflect the time average of the different steps. We have used molecular dynamics (MD) simulations to get a deeper insight into the detailed interaction scenario at the microsecond scale. This NMR/MD approach enabled us to establish that the tris-dipicolinate complex interacts specifically with arginines and lysines, while the crystallophore explores the protein surface through weak interactions with carboxylates. These observations shed new light on the dynamic interaction properties of these complexes, which will ultimately enable us to propose a crystallization mechanism
Periodic table screening for enhanced positive contrast in MRI and in vivo uptake in glioblastoma
No full textThe quest for nanomaterial-based imaging probes that can provide positive contrast in MRI is fueled by the necessity of developing novel diagnostic applications with potential for clinical translation that current gold standard probes cannot provide. Although interest in nanomaterials for positive contrast has increased in recent years, their study is less developed than that of traditional negative contrast probes in MRI. In our search for new magnetic materials with enhanced features as positive contrast probes for MRI, we decided to explore the chemical space to comprehensively analyze the effects of different metals on the performance of iron oxide nanomaterials already able to provide positive contrast in MRI. To this end, we synthesized 30 different iron-oxide-based nanomaterials. Thorough characterization was performed, including multivariate analysis, to study the effect of different variables on their relaxometric properties. Based on these results, we identified the best combination of metals for in vivo imaging and tested them in different experiments. First, we tested its performance on magnetic resonance angiography using a concentration ten times lower than that clinically approved for Gd. Finally, we studied the capability of these nanomaterials to cross the affected blood-brain barrier in a glioblastoma model. The results showed that the selected nanomaterials provided excellent positive contrast at large magnetic field and were able to accumulate at the tumor site, highlighting the affected tissue
A Reversible Four-electron Sn Metal Aqueous Battery
No full textSn is a promising metal anode for aqueous batteries due to its dendrite-free plating, large hydrogen evolution overpotential, and high theoretical capacity with up to four-electron redox per Sn atom. However, practically achieving the theoretical capacity for Sn remains challenging, with only limited cell energy densities demonstrated thus far. We validate a kinetically asymmetric [Sn(OH)6]2-/Sn redox pathway involving a direct four-electron plating and a stepwise 2+2 electron stripping through a [Sn(OH)3]- intermediate, which decreases the Coulombic efficiency (CE) by shuttling to the cathode and promoting chemical self-discharge. By using ion-selective membranes to suppress [Sn(OH)3]- crossover, we demonstrate Sn-Ni full cells with high round-trip efficiency (~80%) and energy density (143.1 Wh L-1). The results provide key understandings to the tradeoffs in engineering reversible multi-electron metal anodes and define a new benchmark for practical energy density that exceeds Sn-based aqueous batteries to date
Stereocontrol via Propeller Chirality in FLP-Catalyzed Asymmetric Hydrogenation
No full textUtilization of chiral frustrated Lewis pairs as catalysts in enantioselective hydrogenation of unsaturated molecules represents a promising approach in asymmetric synthesis. In our effort to improve our current understanding of the factors governing the stereoselectivity in these catalytic processes, herein we examined the mechanism of direct hydrogenation of aromatic enamines catalyzed by a binaphthyl-based chiral amino-borane. Our computational analysis reveals that only one particular conformer of the key borohydride reaction intermediate can be regarded as a reactive form of this species. This borohydride conformer has a well-defined chiral propeller shape, which induces facial selectivity in the hydride transfer to pro-chiral iminium intermediates. The propeller chirality of the reactive borohydride conformer is generated by the axially chiral binaphthyl scaffold of the amino-borane catalyst through stabilizing pi-pi stacking interactions. This new computational insight can be readily used to interpret the high degree of stereoinduction observed for these reactions. We expect that the concept of chirality relay could be further exploited in catalyst design endeavors
Accelerated Analysis of the Electrochemical Production Route for Biomass-derived Adiponitrile
No full textElectrochemical transformation of biomass feedstocks offers a promising route for sustainable production of fuels and chemicals, enhancing integration with renewable energy sources. Adiponitrile, a key intermediate in Nylon 6,6 production, is mainly produced through thermochemical processes or methods relying fossil fuel feedstocks. Alternatively, it can be produced through Kolbe coupling of biomass-derived 3-cyanopropanoic acid, with its practical implementation hinging on understanding and controlling factors that dictate reaction selectivity. In this study, we establish relationships between electrolyte composition, electrochemical conditions, and performance metrics in this approach, achieving a maximum Faradaic efficiency of 40% towards adiponitrile at current densities up to 500 mA cm-2. Implementing a semi- autonomous high-throughput electrochemical workflow, we tested hundreds of reaction conditions, accelerating the exploration of reaction parameters. Limitations and guidelines obtained from this study apply to a range of electrochemical decarboxylation reactions, and the accelerated research approach shows potential for speeding the development of sustainable electrochemical processes
Unveiling Stability Factors in Sn(II)-Containing Oxides: Discovery of a Polar Tin Titanate Perovskite and Photocatalytic Activity for Overall Water Splitting
No full textThe discovery of multinary Sn(II)-containing oxides has been severely limited by a lack of understanding of the factors leading to their thermodynamic stability, e.g., chemical compositions and structure types, as well as by the absence of productive synthetic routes. The relatively few reported Sn(II)-O-M (M = early transition metal cation) solids frequently decompose at moderate to low temperatures. Herein, a large-scale predictive modeling approach was used to assess the structural factors yielding their enhanced thermodynamic stability. This has resulted in ten predicted new Sn(II)-containing oxides that are proposed to fall within reasonable synthetic limits. Increasing stability was found for structures possessing smaller amounts of Sn(II) with local asymmetric coordination environments allowing expression of its stereoactive lone pair. As a test of these results, synthetic efforts to prepare one of the proposed compounds starting from BaLa4Ti4O15 yielded the predicted noncentrosymmetric layered perovskite SnLa4Ti4O15 (SLTO). The new SLTO crystallizes with hexagonal plate-shaped morphologies in the polar P3c1 space group (No. 158), as confirmed by Rietveld refinements of powder X-ray diffraction data and second harmonic generation activity. Full Sn(II) substitution was confirmed by 119Sn Mössbauer spectroscopy, SEM-EDS, and X-ray photoelectron spectroscopy. UV-vis diffuse reflectance data confirmed that SLTO has a visible-light bandgap of ~2.4 eV and is thus predicted to be promising photocatalyst for solar energy conversion. After loading its surfaces with a Rh/Cr2O3-CoOx dual-cocatalyst, SLTO is the first Sn(II)-containing oxide to show activity for overall water splitting into H2 and O2 with an apparent quantum yield of ~21.7%. Thus, these results highlight the synergistic combination of chemical intuition, predictive modeling, and synthetic design in the synthesis of new Sn(II)-containing oxides for promising optical properties and photocatalytic activities for water splitting
High-Efficiency Non-Thermal Plasma Synthesis of Imine Macrocycles
No full textMacrocycles are candidates for wide-ranging applications, yet their synthesis can be low-yielding, poorly reproducible, and resource-intensive, limiting their use. Here, we explore the use of Non-Thermal Plasma (NTP) as an efficient method for the synthesis of imine macrocycles. NTP-mediated macrocyclisations consistently achieved high yields of up to 97 % in reduced reaction times compared to the standard non-plasma method, and were successfully carried out with a range of different aldehyde substrates. Control experiments were performed to explore the origin of the observed improvements. The results indicate that NTP methods could be advantageous for macrocycle synthesis, particularly for substrates that are sensitive to elevated temperature, and other materials formed via imine condensation