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Control of Heparin Surface Density in Multilayers of Partially Hydrolyzed Poly(2-ethyl-2-oxazoline) by Degree of Hydrolysis
No full textControlling the surface density of heparin in active anticoagulant coatings is important in applications where an optimum is required. An approach based on tuning the degree of hydrolysis of poly(2-ethyl-2-oxazoline) (PEOX) is presented to control the surface density of heparin in layer-by-layer (LbL) assembled films. Multilayers are prepared at pH5 in 0.5M aqueous NaCl solutions by electrostatic interactions between negatively charged heparin and the positively charged amine groups in hydrolyzed PEOX. Characterization of the multilayers by QCM-D, TBO assay and XPS all show that the amount of heparin deposited increases with the degree of hydrolysis. While non-hydrolyzed PEOX/Heparin multilayers do not grow, the average deposited mass per area per bilayer, as determined by QCM-D measurements, increases with the degree of hydrolysis. At 50% hydrolysis, ITC measurements exhibit an exothermic enthalpy below -500 kJ/mol, TBO assay gives a heparin surface density of 1.03 ug/cm2 and atomic % of sulfur as determined by XPS leveled off at ~14%. These results show the potential of acidic hydrolysis of PEOX combined with LbL assembly of heparin as a reproducible method for controlling the surface density of heparin in anticoagulant coatings
Advancing Organic Photoredox Catalysis: Mechanistic Insight through Time-Resolved Spectroscopy
No full textThe rapid development of light-activated organic photoredox catalysts has led to the proliferation of powerful synthetic chemical strategies with industrial and pharmaceutical applications. Despite the advancement in synthetic approaches, a detailed understanding of the mechanisms governing these reactions has lagged. Time-resolved optical spectroscopy provides a method to track organic photoredox catalysis processes and reveal the energy pathways that drive reaction mechanisms. These measurements are sensitive to key processes in organic photoredox catalysis such as charge or energy transfer, lifetimes of singlet or triplet states and solvation dynamics. The sensitivity and specificity of ultrafast spectroscopic measurements can provide a new perspective on the mechanisms of these reactions, including electron-transfer events, the role of solvent, and the short lifetimes of radical intermediates
Engineering Robust Battery Interphases with Dilute Fluorinated Cations
No full textControlling solid electrolyte interphase (SEI) in batteries is crucial for their efficient cycling. Herein, we demonstrate an approach to enable robust battery performance that does not rely on high fractions of fluorinated species in electrolytes, thus substantially decreasing the environmental footprint and cost of high-energy batteries. In this approach, we use very low fractions of readily reducible fluorinated cations in electrolyte (~0.1 wt.%) and employ electrostatic attraction to generate a substantial population of these cations at the anode surface. As a result, we can form a robust fluorine-rich SEI that allows for dendrite-free deposition of dense Li and stable cycling of Li metal
full cells with high-voltage cathodes. Our approach represents a general strategy for delivering desired chemical species to battery anodes through electrostatic attraction while using minute amounts of additive
Impact of Symmetry and Donor Set on the Electronic Energy Levels in Nine-coordinated Eu(III) and Sm(III) Crystals Structures Determined from Single Crystal Luminescence Spectra
No full textLanthanide luminescence is characterised by “forbidden” 4f-4f transitions and a complicated electronic structure. Our understanding of trivalent lanthanide(III) ions luminescence is centered on Eu3+ because absorbing and emitting transition in Eu3+ occur from a single electronic energy levels. In Sm3+ both absorpbing and emitting multiplets have a larger multiplicity. A transition from the first emitting state multiplet to the ground state multiplet will result in nine lines for a Sm3+ complex. In this study, high resolution emission and excitation spectra were used to determine the electronic energy levels for the ground state multiplet and first excited state multiplet in four Sm3+ compounds with varying donor set and site symmetry. This was achieved by the use of Boltzmann distribution population analysis and experimentally determined transition probabilities from emission and excitation spectra. Using this analysis it was possible to show the effect of changing three oxygen atoms with three nitrogen atoms in the tricapping donor set for compounds with the same Trigonal Tricapped Prism (TTP) site symmetry on the crystal field splitting in both Eu3+ and Sm3+ crystals. This work celebrates the 40 year annivesary for the first report of [Eu(ODA)3]3- luminescence by Kirby and Richardson
A Scalable Synthesis of Adjuvanting Antigen Depots Based on Met-al-Organic Frameworks
No full textVaccines have saved countless lives by preventing and even irradicating infectious diseases. Commonly used subunit vaccines comprising one or multiple recombinant proteins isolated from a pathogen demonstrate a better safety profile than live or attenuated vaccines. However, the immunogenicity of these vaccines is weak, and therefore, subunit vaccines require a series of doses to achieve sufficient immunity against the pathogen. Here, we show that the biomimetic mineralization of the inert model antigen, ovalbumin (OVA), in zeolitic imidazolate framework-8 (ZIF-8) significantly improves the humoral immune response over three bolus doses of OVA (OVA 3×). Encapsulation of OVA in ZIF-8 (OVA@ZIF) demonstrated higher serum antibody titers against OVA than OVA 3×. OVA@ZIF vaccinated mice displayed higher populations of germinal center (GC) B cells and IgG1+ GC B cells as opposed to OVA 3×, indicative of class-switching recombination. We show that the mechanism of this phenomenon is at least partly owed to the metalloimmunological effects of the zinc metal as well as the sustained release of OVA from the ZIF-8 composite. The system acts as an antigen reservoir for antigen-presenting cells to traffic into the draining lymph node, enhancing the humoral response. Lastly, our model system OVA@ZIF is produced quickly at the gram scale in a laboratory setting, sufficient for up to 20,000 vaccine doses
Molten Salt-Assisted synthesis of Titanium Nitride
No full textTitanium nitride is an exciting plasmonic material, with optical properties similar to gold. However, synthesizing TiN nanocrystals is highly challenging and typically requires solid-state reactions at very high temperatures (800-1000°C). Here, we achieve the synthesis of TiN nanocrystals at temperatures as low as 350°C, in just three hours. The strategy comprises molten salt, Mg as reductant and Ca3N2 as nitride source. This brings TiN from the realm of solid-state chemistry into the field of solution-based synthesis in regular, borosilicate glassware
Electret-Nanopore Ionic Flux Generator
No full textTowards the development of in-vivo autonomous technology, this paper proposes and investigates an electret-nanopore based ionic flux generator (IFG). The Poisson-Nernst-Planck equations were used to develop a one-dimensional analytical model under circulatory electrolytic conditions characterizing enhanced power density as electret charge saturation or pore length increased due to greater counterion flux. An approximate Electret-Nanopore IFG power density of 11.3 (W/m2) was calculated for a 500 nm pore length, 10 nm pore radius and 80% electret charge saturation system.
Comparative Study of the Photocatalytic Activity of g C3N4/MN4 (M=Mn, Fe, Co) for Water Splitting Reaction
No full textIn this study, novel nanocomposites of g C3N4/MN4 (where M is Mn, Fe, or Co) were designed using advanced density functional theory (DFT). The cutting edge DFT method was employed to evaluate the photocatalytic activity of the g C3N4/MN4 (M=Mn, Fe, and Co) composites. A comprehensive analysis was conducted on the geometry, electronic, optical properties, work function, charge transfer interaction, and adhesion energy of the g C3N4/MN4 (M=Mn, Fe, and Co) heterostructure. Lastly, the potential of the g C3N4/MN4 (M=Mn, Fe, and Co) heterojunction as a photocatalyst for the water splitting reaction was assessed by examining its band alignment for the water splitting reaction. Ideally, for water splitting, the valence band maximum (VBM) band position should be higher than the O2/H2O potential (0 V vs. NHE), and the conduction band minimum (CBM) band position should be lower than the H+/H2 potential (1.23 V vs NHE). The g C3N4/FeN4 and g C3N4/CoN4 composites meet this requirement, making them suitable for use as photocatalysts for water splitting
Synthesis, studies electrochemical of complexes hydrazones containing a ferrocene fragment : a short review.
No full textComplexes hydrazones containing ferrocene fragments used in aqueous or non-aqueous solution have been widely studied in recent times. Good results of electrochemical properties were found. The present work consists of bringing these results together by doing a comparison study, but also by serving as a solid basis for the development of new chemo sensor ligands in the coming years
Pathways of Quantum Dot Degradation during Photocatalysis
No full textCdS QDs are widely employed as photocatalysts for reactions such as hydrogen evolution, and its degradation under aerobic, aqueous conditions is well understood. However, despite evidence of aggregation and precipitation of CdS QD photocatalysts under inert conditions, catalyst speciation and degradation are under-explored. In this work, we demonstrate that during a reductive dehalogenation reaction, CdS QDs undergo surface ligand etching, leading to loss of colloidal stability and the formation of micro-crystalline cadmium metal deposits. We hypothesize that this results from the accumulation of electrons on the QD surface. In addition, we demonstrate a high catalytic TOF of 0.67 s-1 and show evidence of mild surface sulfur oxidation and formation of an ammonium salt by-product of the hole quencher. This work adds to our atomic-level understanding of the reactions occurring at the QD surface during photocatalysis and ultimately uncovers design principles that will allow the design of more stable and efficient catalysts