ChemRxiv
Not a member yet
27047 research outputs found
Sort by
Alumina-Titania Nanolaminate Condensers for Hot Programmable Catalysis
No full textFor programmable catalysis applications, nanolaminates composed of thin alternating layers of alumina and titania (ATO) were engineered using atomic layer deposition (ALD) as the dielectric material for a Pt-on-carbon catalytic condenser. Systematic investigation assessed synthesis parameters such as deposition temperature, alumina and titania layer thicknesses, the total number of layers (and interfaces), and the presence of a capping alumina layer on the maximum achievable charge accumulation in the Pt catalyst layer. The highest capacitance ATO configuration demonstrated a specific capacitance of ~1,200 nF/cm2 with working voltages of ±5 V, enabling the storage of 4×10^13 electrons or holes per cm2 at room temperature. Adsorption of carbon monoxide on the Pt/C-ATO device characterized by grazing incidence infrared spectroscopy showed changes in the surface binding energy of 13.1 ± 0.8 kJ/mol for an applied external voltage bias of ±1 V. The results enhance our understanding of nanolaminate structures and provide a method for increasing charge condensation strength for higher temperature surface chemistries
Mechano-Adaptive Meta-Gels Through Synergistic Chemical and Physical Information-Processing
No full textGlobal functional adaptation after local mechanical stimulation, as in mechanobiology and the mimosa plant, is fascinating and ubiquitous in nature. This is achieved by locally sensing mechanical deformation with precise thresholds, processing this information via biochemical circuits, followed by downstream actuation. The integration of such embodied intelligence allowing for mechano-to-chemo-to-function information-processing remains elusive in man-made systems. By merging the fields of chemical circuits and metamaterials, we introduce adaptive metamaterial hydrogels (meta-gels) that can accurately sense mechanical stimuli (local touch and global strain), transmit this information over long distances via reaction-diffusion signaling, and induce downstream mechanical strengthening by growing nanofibril networks, or soft robotic actuation through competitive swelling. All elements of the sensor-processor-actuator system are embedded in the device, functioning autonomously without external feeding reservoirs. Our concept enables designing advanced life-like materials systems that synergistically combine two worlds – chemical circuits for chemical information-processing and metamaterial unit cells for physical information-processing
Structural and Mechanistic Insights into Oxidative Biaryl Coupling to form Arylomycin Core by an Engineered CYP450
No full textArylomycin, a potent antibiotic targeting bacterial signal peptidases, is difficult to synthesize experimentally due to poor to moderate yields and formation of mixture of compounds, Therefore, there is a need to focus on some greener catalyst. Enzymes are increasingly recognised as green catalysts for synthesis for new-to-nature reactions due to their chemo-selectivity and mild operating conditions, aligning with the principles of green chemistry. Cytochrome P450 enzymes, a group of heme-containing proteins, emerged as promising catalysts due to their ability to facilitate diverse oxidative transformations. Here, we discuss an engineered Cytochrome P450 enzyme from Streptomyces sp. for the synthesis of arylomycin core. Through molecular dynamics simulations, we investigated the impact of specific mutations: glycine101 to alanine mutation, which facilitates biaryl coupling by subtly pushing the substrate and glutamine306 to histidine mutation, exhibiting stable pi-pi interactions with substrate, which helps the two phenol rings of substrate to stay close to each other to undergo C-C coupling. Quantum mechanics/molecular mechanics (QM/MM) calculations investigated that variant 2 favours biradical mechanism of C-C bond formation over hydroxylation
Shallow Rate-Overpotential Scaling in Aqueous Molecular Oxygen Reduction Electrocatalysis Across a Family of Iron Macrocycles
No full textRate-overpotential scaling relationships have been employed widely to understand trends in oxygen reduction reaction (ORR) electrocatalysis by dissolved metal macrocycles in organic electrolytes. Similar scaling relationships remain unknown for surface-adsorbed ORR electrocatalysts in the acidic aqueous environments germane to proton-exchange membrane (PEM) fuel cells. Herein, we examine ORR catalysis in aqueous perchloric acid media for a structurally diverse array of iron macrocycle complexes adsorbed on Vulcan carbon black. The macrocycles encompass Fe–N4, Fe–N2N′2 and Fe–NxC4−x motifs bearing pyrrolic, pyridinic, and N-heterocyclic carbene (NHC) moieties in the primary ligation sphere, giving rise to a 530 mV range in Fe(III/II) redox potentials, EFe(III/II). Experimental Tafel data in the micropolarization regime were extrapolated to the EFe(III/II) to furnish estimated TOF values that span ~3 orders of magnitude across the family of compounds. Despite the structural diversity of this family of compounds, extrapolated TOF values correlate with Fe(III/II) redox potentials in a roughly log-linear fashion with a shallow scaling factor of approximately 180 mV/decade. These findings highlight that negative shifts in EFe(III/II) lead to diminishing returns in catalytic rate promotion and suggest that changes to the primary ligating environment in a macrocycle are insufficient to break fundamental rate-overpotential scaling relationships in aqueous ORR catalysis. Together these studies motivate the development of new higher-potential iron complexes that employ motifs beyond the equatorial ligation plane to enhance ORR catalysis
Differing Plasmonic Intra-nanoparticle and Inter-nanoparticle Molecular Reaction Rates at the Three-Phase Contact Line of an Evaporating Sessile Droplet
No full textIntra-nanoparticle and inter-nanoparticle heterogeneous chemical reaction pathways may involve different kinetic, dynamic natures and product selectivity like intramolecular and intermolecular counterparts in chemical synthesis and may involve rich chemistry. However, that is yet to be demonstrated. Herein, we utilized the phase change behavior of silver nanoparticles (AgNPs) from dispersion to deposition at the three-phase contact line (TPCL) in evaporating aqueous (H2O/D2O) droplet to experimentally monitor the plasmonic dimerization of 4-aminothiophenol (4-ATP) to 4,4´-dimercaptoazobenzene (DMAB) by surface-enhanced Raman spectroscopy (SERS). Raman signature of the solvent attached probe molecules in conjugation with density functional theory (DFT) calculations and DMAB formation in two steps suggested sequential intraparticle and interparticle DMAB formation, the former being ~3 times and ~1.5 times faster than the later in H2O and D2O, respectively
The Enol of Isobutyric Acid
No full textWe present the gas-phase synthesis of 2-methyl-prop-1-ene-1,1-diol, an unreported higher energy tautomer of isobutyric acid. The enol was captured in an argon matrix at 3.5 K and characterized using IR and UV/Vis spectroscopy, combined with density functional theory computations. Upon irradiation the enol rearranges to form isobutyric acid and dimethylketene. Moreover, we also identified propene, photochemically formed from dimethylketene
Targeting Plasmodium falciparum IspD in the Methyl-D-Erythritol Phosphate Pathway: Urea-Based Compounds with Nanomolar Potency on target with low micromolar whole-cell activity
No full textThe methyl-D-erythritol phosphate (MEP) pathway has emerged as an interesting target in the fight against antimicrobial resistance. The pathway is essential in many human pathogens, including Plasmodium falciparum (Pf), but is absent in human cells, reducing the risk of off-target side effects. In the present study, we conducted a high-throughput screening on the third enzyme of the pathway, IspD, and discovered a new chemical class for which we ran a structure–activity relationship investigation, resulting in low-nanomolar inhibitors of PfIspD. In addition, we determined the whole-cell activity (PfNF54 IC50 = 3.4 ± 1.0 μM), mode of inhibition, metabolic, and plasma stability of the new compound class. In vivo pharmacokinetic profiling of a selection of compounds demonstrated promising behavior for future development. Lastly, we disclosed a new MS-based enzymatic assay for direct IspD activity determination, circumventing the need for auxiliary enzymes. We used this assay to investigate the mode of inhibition of our new compound class. In summary, we have identified a readily synthesizable compound class, demonstrating excellent activity and a promising profile, positioning it as a valuable tool compound for advancing research on IspD
Light-induced quantum reconfiguration of oxyhydroxides for photoanodes with 4.24% efficiency and stability beyond 250 hours
No full textPhotoelectrochemical (PEC) water splitting is attracting significant research interest in addressing sustainable development goals in renewable energy for the future. Current state-of-the-art, however, cannot provide photoanodes with simultaneously high efficiency and long-lasting device lifetime. Here, we report a large-scale NiFe oxyhydroxides-alloy hybridized cocatalyst layer on photoanodes that exhibit a record value of applied bias photon-to-current efficiency (ABPE) of 4.24% in buried homojunction-free photoanodes and stability over 250 hours with above 88% retention of the initial current density. These performances represent an increase over the present highest-performing technology by 408% in stability and the
most stable competitor by over 330% in efficiency in alkaline media. These results originate from a previously unexplored mechanism of light-induced atomic reconfiguration and surface amorphization in NiFe-based materials. This process self-generates at low biases and, in short times, a catalytic-protective amorphous/crystalline heterostructure that provides abundant highly catalytic active sites for reaction and insulates the photoanode from performance degradation. NiFe oxyhydroxides generated by photons are more than 200% higher than the quantity that pure electrocatalysis would otherwise induce, overcoming the threshold for an efficient oxygen reduction reaction in the device. While of immediate interest in the industry of water splitting, the light-induced NiFe oxyhydroxides-alloy co-catalyst developed in this work provides a general strategy to enhance further the performances and stability of PEC devices for a vast panorama of chemical reactions, ranging from biomass valorization to organic waste degradation, and CO2-to-fuel conversion
TDDFT and the X-ray absorption spectrum of liquid water: finding the “best” functional
No full textWe investigate the performance of time-dependent density functional theory (TDDFT) for reproducing high-level reference X-ray absorption spectra of liquid water. For this, we apply the integrated absolute difference (IAD) metric, previously used for X-ray emission spectra of liquid water [J. Chem. Theory Comput. 19, 7333-7342 (2023)], in order to investigate which exchange-correlation (xc) functionals yield TDDFT spectra in best agreement to reference, as well as to investigate the suitability of IAD for XAS spectrum calculations. It is seen that long-range corrected xc-functionals are required to yield good agreement with reference coupled cluster (CC) and algebraic-diagrammatic construction (ADC) spectra, with 100% asymptotic Hartree−Fock exchange resulting in the lowest IADs. The xc-functionals with best agreement to reference have been adopted for larger water clusters, yielding results in line with recently published coupled cluster theory, but which still show some discrepancies in the relative intensity of the features compared to experiment
Targeted Protein Degradation in the Mitochondrial Matrix and Its Application to Chemical Control of Mitochondrial Morphology
No full textDysfunction of mitochondria is implicated in various diseases, including cancer and neurodegenerative disorders, but drug discovery targeting mitochondria and mitochondrial proteins has so far made limited progress. Targeted protein degradation (TPD) technologies represented by proteolysis targeting chimeras (PROTACs) are potentially applicable for this purpose, but most existing TPD approaches leverage the ubiquitin-proteasome system or lysosomes, which are absent in mitochondria, and TPD in mitochondria (mitoTPD) remains little explored. Herein, we describe the design and synthesis of a bifunctional molecule comprising TR79, an activator of the mitochondrial protease complex caseinolytic protease P (ClpP), linked to desthiobiotin. This compound successfully induced the degradation of monomeric streptavidin (mSA) and its fusion proteins localized to the mitochondrial matrix. Furthermore, in cells overexpressing mSA fused to short transmembrane protein 1 (mSA-STMP1), which enhances mitochondrial fission, our mitochondrial mSA degrader restored the mitochondrial morphology by reducing the level of mSA-STMP1. A preliminary structure-activity relationship study indicated that a longer linker length enhances the degradation activity towards mSA. These findings highlight the potential of mitoTPD as a tool for drug discovery targeting mitochondria and for research in mitochondrial biology, as well as the utility of mSA as a degradation tag for mitochondrial protein