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Homochiral versus Racemic 2D Covalent Organic Frameworks
Get PDFThe synthesis of homochiral two dimensional covalent organic frameworks 2D COFs from chiral amp; 960; conjugated building blocks is challenging, as chiral units often lead to misaligned stacking interactions. In this work, we introduce helical chirality into 2D COFs using configurationally stable enantiopure and racemic [5]helicenes as linkers in the backbone of 2D [5]HeliCOFs as powders and films. Through condensation with 1,3,5 triformylbenzene TFB or 1,3,5 triformylphloroglucinol TFP , our approach enables the efficient formation of a set of homochiral and racemic 2D [5]HeliCOFs. The resulting carbon based crystalline and porous frameworks exhibit distinct structural features and different properties between homochiral and racemic counterparts. Propagation of helical chirality into the backbone of the crystalline frameworks leads to the observation of advanced chiroptical properties in the far red visible spectrum, along with a less compact structure compared with the racemic frameworks. Homogeneous thin films of [5]HeliCOFs disclosed photoluminescent properties arising from the controlled growth of highly ordered amp; 960; conjugated lattices. The present study offers insight into general chiral framework formation and extends the Liebisch Wallach rule to 2D COF
Pseudocapacitance Facilitates the Electrocatalytic Reduction of Carbon Dioxide
No full textElectroreduction of CO2 to value added products is a promising strategy for CO2 reuse, where copper has a unique ability to produce oxygenates and C2 products. Unfortunately, the electronic factors making copper so unique are unknown, which limits the ability to design improved catalysts. By combining in situ surface sensitive X ray resonant photoelectron spectroscopy with density functional theory calculations, the complex electronic structure of copper is uncovered during the electrocatalytic reduction of CO2. It is found that the pseudocapacitive charging of copper, produced by the incorporation of protons and electrons into the subsurface, facilitates the activation of CO2, while simultaneously increasing the barrier for H H coupling. The net result is that cathodic pseudocapacitive charge suppresses the hydrogen evolution reaction and promotes the production of hydrocarbons and oxygenated products on copper. These results represent a new paradigm in the understanding of CO2 reduction, highlighting the key role of pseudocapacitive charge in the reactio
Highly selective Ag foam gas diffusion electrodes for CO2 electroreduction by pulsed hydrogen bubble templation
Get PDFThe electrochemical reduction of carbon dioxide to valuable fossil free products opens up a way to close the carbon cycle, if based solely on renewable energy sources. Making the process industrially viable, however, needs high CO2 conversion rates, efficient electrodes, and high selectivity for desired products. To reach this goal, highly catalytically active porous electrodes with maximized surface areas are required. We combined pulsed electrochemical deposition of the Ag foam catalyst with ionomer infiltration of the electrode to produce Ag based gas diffusion electrodes GDEs in a facile and fast production process. Using the dynamic hydrogen bubble templation method DHBT , we utilized the parasitic hydrogen evolution reaction HER to aid the solvent free structuring of the 3D catalyst network and directly manufacture a GDE. Different deposition parameters and in particular pulse to pause ratios increased the amount of deposited catalyst and successfully reduced the overpotential during CO2RR operation. To inhibit electrode flooding and decrease CO2 mass transport limitations during CO2RR, we further infiltrated the electrode with a suitable perfluorosulfonic acid ionomer. SEM and EDS analyses showed a homogeneous Ag F distribution along the cross section of the electrodes. These electrodes catalyzed the conversion of CO2 to CO at industrially viable current densities of 500 mA cm 2 with an unprecedented faradaic efficiency up to 76 in 1 M KHCO
Domain nucleation across the metal insulator transition of self strained V2O3 films
No full textBulk V2 amp; 8290;O3 features concomitant metal insulator MIT and structural SPT phase transitions at amp; 119879;C amp; 8764;160 K. In thin films, where the substrate clamping can impose geometrical restrictions on the SPT, the epitaxial relation between the V2 amp; 8290;O3 film and substrate can have a profound effect on the MIT. Here, we present a detailed characterization of domain nucleation and growth across the MIT in 001 oriented V2 amp; 8290;O3 films grown on sapphire. By combining scanning electron transmission microscopy and photoelectron emission microscopy PEEM , we imaged the MIT with planar and vertical resolution. We observed that upon cooling, insulating domains nucleate at the top of the film, where strain is lowest, and expand downwards and laterally. This growth is arrested at a critical thickness of 50 nm from the substrate interface, leaving a persistent bottom metallic layer. As a result, the MIT cannot take place in the interior of films below this critical thickness. However, PEEM measurements revealed that insulating domains can still form on a very thin superficial layer at the top interface. Our results demonstrate the intricate spatial complexity of the MIT in clamped V2 amp; 8290;O3, especially the strain induced large variations along the amp; 119888; axis. Engineering the thickness dependent MIT can provide an unconventional way to build out of plane geometry devices by using the persistent bottom metal layer as a native electrod
7,8 Dihydroxyflavone is a direct inhibitor of human and murine pyridoxal phosphatase
No full textVitamin B6 deficiency has been linked to cognitive impairment in human brain disorders for decades. Still, the molecular mechanisms linking vitamin B6 to these pathologies remain poorly understood, and whether vitamin B6 supplementation improves cognition is unclear as well. Pyridoxal 5 phosphate phosphatase PDXP , an enzyme that controls levels of pyridoxal 5 phosphate PLP , the co enzymatically active form of vitamin B6, may represent an alternative therapeutic entry point into vitamin B6 associated pathologies. However, pharmacological PDXP inhibitors to test this concept are lacking. We now identify a PDXP and age dependent decline of PLP levels in the murine hippocampus that provides a rationale for the development of PDXP inhibitors. Using a combination of small molecule screening, protein crystallography, and biolayer interferometry, we discover, visualize, and analyze 7,8 dihydroxyflavone 7,8 DHF as a direct and potent PDXP inhibitor. 7,8 DHF binds and reversibly inhibits PDXP with low micromolar affinity and sub micromolar potency. In mouse hippocampal neurons, 7,8 DHF increases PLP in a PDXP dependent manner. These findings validate PDXP as a druggable target. Of note, 7,8 DHF is a well studied molecule in brain disorder models, although its mechanism of action is actively debated. Our discovery of 7,8 DHF as a PDXP inhibitor offers novel mechanistic insights into the controversy surrounding 7,8 DHF mediated effects in the brai
Nonpeptidic Irreversible Inhibitors of SARS CoV 2 Main Protease with Potent Antiviral Activity
No full textSARS CoV 2 infections pose a high risk for vulnerable patients. In this study, we designed benzoic acid halopyridyl esters bearing a variety of substituents as irreversible inhibitors of the main viral protease Mpro . Altogether, 55 benzoyl chloro bromo pyridyl esters were synthesized, with broad variation of the substitution pattern on the benzoyl moiety. A workflow was employed for multiparametric optimization, including Mpro inhibition assays of SARS CoV 2 and related pathogenic coronaviruses, the duration of enzyme inhibition, the compounds stability versus glutathione, cytotoxicity, and antiviral activity. Several compounds showed IC50 values in the low nanomolar range, kinact Ki values of gt;100,000 M 1 s 1 and high antiviral activity. High resolution X ray cocrystal structures indicated an important role of ortho fluorobenzoyl substitution, forming a water network that stabilizes the inhibitor bound enzyme. The most potent antiviral compound was the p ethoxy o fluorobenzoyl chloropyridyl ester PSB 21110, 29b, MW 296 g mol; EC50 2.68 nM , which may serve as a lead structure for broad spectrum anticoronaviral therapeutic
Structure based humanization of a therapeutic antibody for multiple myeloma
No full textThe optimal efficacy of xenogeneically generated proteins intended for application in humans requires that their own antigenicity be minimized. This necessary adaptation of antibodies to a humanized version poses challenges since modifications even distant from the binding sites can greatly influence antigen recognition and this is the primary feature that must be maintained during all modifications. Current strategies often rely on grafting and or randomization selection to arrive at a humanized variant retaining the binding properties of the original molecule. However, in terms of speed and efficiency, rationally directed approaches can be superior, provided the requisite structural information is available. We present here a humanization procedure based on the high resolution X ray structure of a chimaeric IgG against a marker for multiple myeloma. Based on in silico modelling of humanizing amino acid substitutions identified from sequence alignments, we devised a straightforward cloning procedure to rapidly evaluate the proposed sequence changes. Careful inspection of the structure allowed the identification of a potentially problematic amino acid change that indeed disrupted antigen binding. Subsequent optimization of the antigen binding loop sequences resulted in substantial recovery of binding affinity lost in the completely humanized antibody. X ray structures of the humanized and optimized variants demonstrate that the antigen binding mode is preserved, with surprisingly few direct contacts to antibody atoms. These results underline the importance of structural information for the efficient optimization of protein therapeutic
Perovskite Silicon Tandem Solar Cells Above 30 Conversion Efficiency on Submicron Sized Textured Czochralski Silicon Bottom Cells with Improved Hole Transport Layers
Get PDFIn perovskite silicon tandem solar cells, the utilization of silicon heterojunction SHJ solar cells as bottom cells is one of the most promising concepts. Here, we present optimization strategies for the top cell processing and their integration into SHJ bottom cells based on industrial Czochralski Cz Si wafers of 140 amp; 956;m thickness. We show that combining the self assembled monolayer [4 3,6 dimethyl 9H carbazol 9 yl butyl]phosphonic acid Me 4PACz with an additional phosphonic acid PA with different functional groups, can improve film formation when used as a hole transport layer improving wettability, minimizing shunt fraction and reducing nonradiative losses at the buried interface. Transient surface photovoltage and transient photoluminescence measurements confirm that the combined Me 4PACz PA layer has similar charge transport properties to Me 4PACz alone. Moreover, this work demonstrates the potential for thin, double side submicron sized textured industry relevant silicon bottom cells yielding a high accumulated short circuit current density of 40.2 mA cm2 and reaching a stabilized power conversion efficiency of gt;30 . This work paves the way toward industry compatible, highly efficient tandem cells based on a production compatible SHJ bottom cel
Nanoscale Surface and Bulk Electronic Properties of Ti3C2Tx MXene Unraveled by Multimodal X Ray Spectromicroscopy
Get PDF2D layered materials, such as transition metal carbides or nitrides, known as MXenes, offer an ideal platform to investigate charge transfer processes in confined environment, relevant for energy conversion and storage applications. Their rich surface chemistry plays an essential role in the pseudocapacitive behavior of MXenes. However, the local distribution of surface functional groups over single flakes and within few or multilayered flakes remains unclear. In this work, scanning X ray microscopy SXM is introduced with simultaneous transmission and electron yield detection, enabling multimodal nanoscale chemical imaging with bulk and surface sensitivity, respectively, of individual MXene flakes. The Ti chemical bonding environment is found to significantly vary between few layered hydrofluoric acid etched Ti 3 C 2 T x MXenes and multilayered molten salt MS etched Ti 3 C 2 T x MXenes. Postmortem analysis of MS etched Ti3 C 2 T x electrodes cycled in a Li ion battery further illustrates that simultaneous bulk and surface chemical imaging using SXM offers a method well adapted to the characterization of the electrode electrolyte interactions at the nanoscal
Mechanisms of permeation of helium, hydrogen, oxygen, and water vapor through silicate based composite barrier coating layers
Get PDFWhen considering coating of flexible films for the packaging of sensitive products, a common goal is to meet all gas barrier requirements in a single process step. One way to achieve this is to improve the barrier performance of polymeric coating layers by incorporating silicate particles. In order to tailor the gas barrier performance of the coatings, understanding the permeation mechanisms through these composite coating layers is required. In this study, polyethylene terephthalate films were coated with composite lacquers comprising montmorillonite particles and a polymer matrix. The compatibility of montmorillonite with polymer matrices of polypropylene, polyacrylate, polycarboxylic acid, and polyvinyl alcohol was tested. The permeation behavior of helium, hydrogen, oxygen, and water vapor in these coatings was investigated. For a composite coating layer comprising montmorillonite and polyvinyl alcohol at a mixing ratio of 1 1 by weight, barrier improvement factors of Image 1 compared with the pure polymer coating were found for helium, hydrogen, and oxygen, respectively. It was shown that the permeability coefficients of composite coating layers decrease with increasing permeant kinetic diameter. A comparison of calculated and measured permeability values indicated that the integration of montmorillonite leads to a tortuous permeation path and changes in the free volume and crystallinity of the polymer matrix. The permeation mechanism for water vapor turned out to be completely different from that for non polar helium, hydrogen, and oxygen and is determined by the so called polar path effec