The urea hydrolysis method allowed to prepare well-crystallized Ni–Co–Zn–Al Layered Double Hydroxides to be used as precursors of mixed oxide catalysts for the Ethanol Steam Reforming (ESR) reaction. ...The calcination of the layered precursors gives rise to high surface area mixed oxides, being actually a mixture of a rock salt phase (NiO), a wurtzite phase (ZnO) and a spinel phase.
The steam reforming of ethanol has been investigated over these catalysts after calcination at 973
K in flow reactor experiments. All these catalysts are active for ESR. At 820
K the selectivity to hydrogen increases with cobalt content. The most selective catalyst is the Ni-free Co–Zn–Al mixed oxide essentially constituted by a single spinel type phase Zn
0.55Co
0.45Al
0.45Co
0.55
2O
4. At 770 K the most active catalyst is constituted by a predominant spinel phase with composition near Zn
0.58Ni
0.42Al
0.44Co
0.56
2O
4 and small amounts of NiO and ZnO. Yield to hydrogen exceeding 90% is obtained with this catalyst at 823
K with a water to ethanol feed ratio of 6. The most relevant selectivity determining step is supposed to be the evolution of acetate ions, assumed to be the key intermediate. The high selectivity to hydrogen and CO
2 obtained in the 770–870
K range is attributed to the less reduced state of cobalt in reaction conditions, allowing the evolution of acetate species to CO
2 and hydrogen. On more or completely reduced surfaces (with Ni and/or less water in the feed) acetates decompose preferentially producing CH
4 and COx.
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•Oxidation of amine to imine over type-II WO3/BiOBr is studied for the first time.•WO3/BiOBr with O2 as a green oxidant shows excellent activity at room temperature.•Superior activity ...is due to high oxygen vacancy amount and potent charge transfer.•Reaction proceeds via electron transfer route involving O2− radical.•Band energy line-up and redox potential at solid-liquid interface are proposed.
The visible-light-driven WO3/BiOBr heterojunction was for the first time determined for its photocatalytic activity toward oxidative coupling of amines at room temperature using molecular oxygen as a green oxidant. The WO3/BiOBr heterojunction exhibits superior photocatalytic activity and photostability compared with pure BiOBr and WO3 due to an increased oxygen vacancy concentration, an effective separation of photogenerated electron-hole pairs and an efficient interfacial charge transfer. Additionally, the WO3/BiOBr also shows 2.3 and 41.1 times higher activity than that of TiO2 P25 and BiVO4 Alfa Aesar, respectively. Determination of energy band line-up indicates that the WO3/BiOBr is a type II-heterojunction where electron-hole pairs are efficiently separated. Mechanistic studies based on radical quenching experiment, EPR trapping study and Hammett plot reveal that the main reaction pathway is the electron transfer route mediated by superoxide radical. A possible surface reaction mechanism, the insightful information on the structure-activity relationship and the involvement of reactive oxygen species elucidated in this work lay an important background for the material design and encourage a further development of highly efficient photocatalysts toward organic fine chemical syntheses.
A common solution for precise magnetic field sensing is to employ spin-active defects in semiconductors, with the NV center in diamond as a prominent example. However, the three-dimensional nature of ...diamond limits the obtainable proximity of the defect to the sample. Two-dimensional boron nitride, which can host spin-active defects, can be used to overcome those limitations. In this work, we study spin properties of sp2-bonded boron nitride layers grown using Metal Organic Chemical Vapor Deposition at temperatures ranging from 700 °C to 1200 °C. With Electron Spin Resonance (ESR) we show that our layers exhibit spin properties, which we ascribe to carbon related defects. Supported by photoluminescence and Fourier-transform infrared spectroscopy, we distinguish three different regimes: (i) growth at low temperatures with no ESR signal, (ii) growth at intermediate temperatures with a strong ESR signal and a large number of spin defects, (iii) growth at high temperatures with a weaker ESR signal and a lower number of spin defects. The observed effects can be further enhanced by an additional annealing step. Our studies demonstrate wafer-scale boron nitride that intrinsically hosts spin defects without any ion or neutron irradiation, which may be employed in spin memories or magnetic field detectors.
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•Spin properties in boron nitride can be induced by MOCVD growth.•Changes in spin properties can be correlated with precursor temperature pyrolysis.•Spin properties originate from unpaired electrons on carbon within boron nitride.
Proteins comprise a majority of the dry weight of a cell, rendering them a major target for oxidative modification. Oxidation of proteins can result in significant alterations in protein molecular ...mass such as breakage of the polypeptide backbone and/or polymerization of monomers into dimers, multimers, and sometimes insoluble aggregates. Protein oxidation can also result in structural changes to amino acid residue side chains, conversions that have only a modest effect on protein size but can have widespread consequences for protein function. There are a wide range of rate constants for amino acid reactivity, with cysteine, methionine, tyrosine, phenylalanine, and tryptophan having the highest rate constants with commonly encountered biological oxidants. Free tryptophan and tryptophan protein residues react at a diffusion-limited rate with hydroxyl radical and also have high rate constants for reactions with singlet oxygen and ozone. Although oxidation of proteins in general and tryptophan residues specifically can have effects detrimental to the health of cells and organisms, some modifications are neutral, whereas others contribute to the function of the protein in question or may act as a signal that damaged proteins need to be replaced. This review provides a brief overview of the chemical mechanisms by which tryptophan residues become oxidized, presents both the strengths and the weaknesses of some of the techniques used to detect these oxidative interactions, and discusses selected examples of the biological consequences of tryptophan oxidation in proteins from animals, plants, and microbes.
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•Proteins are a major target for oxidative modification.•Tryptophan residues are highly susceptible to oxidation by radicals, singlet oxygen, and ozone.•Oxidation of tryptophan residues is studied using a variety of techniques.•Oxidation of tryptophan residues can be necessary for normal physiology or be neutral or deleterious in effect.
Since their discovery and development in the 20th century, acrylic polymers have become an integral part of numerous industries and are used in a myriad of applications. As is true for many polymers, ...the suitability of a particular polyacrylate for a given application comes from its structure, which is determined during its synthesis in the reactor, long before commercial use. Uniquely, the radical polymerization of acrylic monomers is strongly affected by radical transfer events which dictate reaction kinetics and lead to a range of distinct macromolecular structures, a fact that went unknown for many years and continues to generate unexpected results. In this review, we aim to present the current picture of the various competitive processes which occur during polymerization of acrylic monomers, as well as the ongoing issues that hinder our complete comprehension of this complicated monomer family.
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•Single-chip ESR detectors operating at 50GHz, 92GHz, and 146GHz.•Spin sensitivity down to 2×107spins/Hz1/2 at 146GHz with BDPA at 300K.•Experiments up to 360GHz using the higher ...harmonics of the 92GHz oscillator.
We report on the design and characterization of single-chip electron spin resonance (ESR) detectors operating at 50GHz, 92GHz, and 146GHz. The core of the single-chip ESR detectors is an integrated LC-oscillator, formed by a single turn aluminum planar coil, a metal-oxide-metal capacitor, and two metal-oxide semiconductor field effect transistors used as negative resistance network. On the same chip, a second, nominally identical, LC-oscillator together with a mixer and an output buffer are also integrated. Thanks to the slightly asymmetric capacitance of the mixer inputs, a signal at a few hundreds of MHz is obtained at the output of the mixer. The mixer is used for frequency down-conversion, with the aim to obtain an output signal at a frequency easily manageable off-chip. The coil diameters are 120μm, 70μm, and 45μm for the U-band, W-band, and the D-band oscillators, respectively. The experimental frequency noises at 100kHz offset from the carrier are 90Hz/Hz1/2, 300Hz/Hz1/2, and 700Hz/Hz1/2 at 300K, respectively. The ESR spectra are obtained by measuring the frequency variations of the single-chip oscillators as a function of the applied magnetic field. The experimental spin sensitivities, as measured with a sample of α,γ-bisdiphenylene-β-phenylallyl (BDPA)/benzene complex, are 1×108spins/Hz1/2, 4×107spins/Hz1/2, 2×107spins/Hz1/2 at 300K, respectively. We also show the possibility to perform experiments up to 360GHz by means of the higher harmonics in the microwave field produced by the integrated single-chip LC-oscillators.
•Prepared Co, ni and fe strontium borate glass systems reveal similar characterization against γ-irradiation.•Close Eopt, density, molar volume, FTIR and ESR spectra, chemical durability, ac ...conductivity, dielectric constant and dielectric loss values, provide the stable behavior of the glasses against ionizing radiation.•Presence of TM ions e.g. Co, ni or fe enhances the stable behavior of the glasses to gamma radiation by healing defect color centers through their variable electronic configuration and then the possible use of glasses for radiation shielding applications up to 5 kGy.
Co2+/ Ni2+/ Fe3+ borate glasses were prepared by melting-annealing procedure and extensively characterized towards gamma irradiation (up to 8 kGy). UV–visible spectra revealed Co2+ (3d7) in octahedral and tetrahedral coordinations, while Ni2+ (3d8) and Fe2+ (3d6) favored the octahedral coordination. Optical energy gap (Eopt) appeared dependent on glass density in a direct relation. ESR spectra revealed values of g// ∼ 2.01 and g┴ ∼ 2.025 correlated to the transition metal (TM) ion valence state. Chemical durability in H2O, HCl, and NaOH revealed good behavior from 15 to 35 days. Trigonal BO3 units appeared more extensive than tetrahedral BO4 on FTIR spectra after irradiation. AC conductivity, dielectric constants and dielectric loss revealed rising with incorporating TM ions and irradiation. TM ions provide the glasses stable behavior to irradiation because of their flexible configuration to heal radiation defects affording the possible use of glasses as radiation shielding materials (up to 5 kGy).
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•SARS-2 FP is more hydrophobic than SARS-1 FP.•SARS-2 FP induces greater membrane ordering than SARS-1 FP.•SARS-CoV-2 FP induces membrane ordering in a specific Ca2+-dependent ...fashion.•SARS-2 FP binds two Ca2+ and the binding sites are positively cooperative.•SARS-1 PP is even more effective in inducing membrane ordering than separate FPs.
Coronaviruses are a major infectious disease threat, and include the zoonotic-origin human pathogens SARS-CoV-2, SARS-CoV, and MERS-CoV (SARS-2, SARS-1, and MERS). Entry of coronaviruses into host cells is mediated by the spike (S) protein. In our previous ESR studies, the local membrane ordering effect of the fusion peptide (FP) of various viral glycoproteins including the S of SARS-1 and MERS has been consistently observed. We previously determined that the sequence immediately downstream from the S2′ cleavage site is the bona fide SARS-1 FP. In this study, we used sequence alignment to identify the SARS-2 FP, and studied its membrane ordering effect. Although there are only three residue differences, SARS-2 FP induces even greater membrane ordering than SARS-1 FP, possibly due to its greater hydrophobicity. This may be a reason that SARS-2 is better able to infect host cells. In addition, the membrane binding enthalpy for SARS-2 is greater. Both the membrane ordering of SARS-2 and SARS-1 FPs are dependent on Ca2+, but that of SARS-2 shows a greater response to the presence of Ca2+. Both FPs bind two Ca2+ ions as does SARS-1 FP, but the two Ca2+ binding sites of SARS-2 exhibit greater cooperativity. This Ca2+ dependence by the SARS-2 FP is very ion-specific. These results show that Ca2+ is an important regulator that interacts with the SARS-2 FP and thus plays a significant role in SARS-2 viral entry. This could lead to therapeutic solutions that either target the FP-calcium interaction or block the Ca2+ channel.
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