In situ-generated PVP-stabilized palladium(0) nanocluster catalyst in hydrogen generation from the methanolysis of ammonia-borane

Herein, we report the in situ generation of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized palladium(0) nanoclusters and their catalytic activity in hydrogen generation from the methanolysis of ammonia-borane (AB). The PVP-stabilized palladium(0) nanoclusters with an average particle size of 3.2 +/- 0.5 nm were formed from the reduction of palladium(II) acetylacetonate during the methanolysis of AB in the presence of PVP at room temperature. The palladium(0) nanoclusters are highly stable in solution for extended periods of time, can be isolated as solid materials, are redispersible in methanol and show catalytic activity after redispersion. The nanoclusters were characterized by TEM, XPS, FTIR, UV-Vis, XRD, and SAED techniques. Mercury poisoning experiments indicate that PVP-stabilized palladium(0) nanoclusters are heterogeneous catalysts in the methanolysis of ammonia-borane. The PVP-stabilized palladium(0) nanoclusters are highly active and stable catalysts as they provide 23 000 turnovers in hydrogen generation from the methanolysis of AB over 27 h before deactivation at room temperature. A kinetic study shows that the catalytic methanolysis of AB is first order with respect to catalyst concentration and zero order with respect to substrate concentration. The activation energy of the methanolysis of AB catalyzed by PVP-stabilized palladium(0) nanoclusters was determined to be E-a = 35 +/- 2 kJ mol(-1)

Hydrogen generation from the methanolysis of ammonia borane catalyzed by in situ generated, polymer stabilized ruthenium(0) nanoclusters

Addressed herein is the detailed study on in situ generation of poly(N-vinyl-2-pyrrolidone) (PVP) stabilized ruthenium(0) nanoclusters and their catalysis in the methanolysis of ammonia borane (AB). PVP-stabilized ruthenium(0) nanoclusters with an average particle size of 2.4 +/- 1.2 nm were generated in situ from the reduction of ruthenium(III) chloride during the methanolysis of AB in the presence of PVP at room temperature. The nanoclusters were characterized by UV-vis spectroscopy, TEM, XRD, XPS and FTIR techniques. PVP stabilized ruthenium(0) nanoclusters are highly active and stable catalyst in hydrogen generation from the methanolysis of AB with a turnover frequency (TOF) value of 4017 h(-1) and 71,500 turnovers over 25 h. Mercury poisoning experiments showed that the PVP-stabilized ruthenium(0) nanoclusters are the true heterogeneous catalyst in the methanolysis of AB. The report also includes the results of a detailed kinetic study on the hydrogen generation from the methanolysis of AB catalyzed by PVP stabilized ruthenium(0) nanoclusters investigating the effect of the catalyst concentration, substrate concentration, and temperature as well as the activation parameters of catalytic methanolysis of AB calculated from the kinetic data

L-Dopa Synthesis on Conducting Polymers

With regards to the synthesis of L-Dopa (l-3,4-dihydroxy phenylalanine) two types of biosensors were designed by immobilizing tyrosinase on conducting polymers; polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT). PPy and PEDOT were synthesized electrochemically and tyrosinase immobilized by entrapment during electropolymerization. The kinetic parameters of the designed biosensors, maximum reaction rate of the enzyme (Vmax) and Michaelis Menten constant (Km) were determined. Vmax were found as 0.013 for PPy matrix and 0.041 mol/min.electrode for PEDOT matrix. Km values were determined as 3.7 and 5.2mM for PPy and PEDOT matrices respectively. Calibration curves for enzyme activity vs. substrate concentration were drawn for the range of 0.8 to 2.5 mM L-Tyrosine. Optimum temperature and pH, operational and shelf life stabilities of immobilized enzyme were also examined

A fluorescently labeled dendronized polymer-enzyme conjugate carrying multiple copies of two different types of active enzymes

A hybrid structure of a synthetic dendronized polymer, two different types of enzymes (superoxide dismutase and horseradish peroxidase), and a fluorescent dye (fluorescein) was synthesized. Thereby, a single polymer chain carried multiple copies of the two enzymes and the fluorescein. The entire attachment chemistry is based on UV/vis-quantifiable bis-aryl hydrazone bond formation that allows direct quantification of bound molecules: 60 superoxide dismutase, 120 horseradish peroxidase, and 20 fluorescein molecules on an average polymer chain of 2000 repeating units. To obtain other enzyme ratios the experimental conditions were altered accordingly. Moreover, it could be shown that both enzymes remained fully active and catalyzed a two-step cascade reaction

Corynebacterium diphtheriaeMethionine Sulfoxide Reductase A Exploits a Unique Mycothiol Redox Relay Mechanism

Methionine sulfoxide reductases are conserved enzymes that reduce oxidized methionines in proteins and play a pivotal role in cellular redox signaling. We have unraveled the redox relay mechanisms of methionine sulfoxide reductase A of the pathogen Corynebacterium diphtheriae (Cd-MsrA) and shown that this enzyme is coupled to two independent redox relay pathways. Steady-state kinetics combined with mass spectrometry of Cd-MsrA mutants give a view of the essential cysteine residues for catalysis. Cd-MsrA combines a nucleophilic cysteine sulfenylation reaction with an intramolecular disulfide bond cascade linked to the thioredoxin pathway. Within this cascade, the oxidative equivalents are transferred to the surface of the protein while releasing the reduced substrate. Alternatively, MsrA catalyzes methionine sulfoxide reduction linked to the mycothiol/mycoredoxin-1 pathway. After the nucleophilic cysteine sulfenylation reaction, MsrA forms a mixed disulfide with mycothiol, which is transferred via a thiol disulfide relay mechanism to a second cysteine for reduction by mycoredoxin-1. With x-ray crystallography, we visualize two essential intermediates of the thioredoxin relay mechanism and a cacodylate molecule mimicking the substrate interactions in the active site. The interplay of both redox pathways in redox signaling regulation forms the basis for further research into the oxidative stress response of this pathogen

A Fluorescently Labeled Dendronized Polymer–Enzyme Conjugate Carrying Multiple Copies of Two Different Types of Active Enzymes

A hybrid structure of a synthetic dendronized polymer, two different types of enzymes (superoxide dismutase and horseradish peroxidase), and a fluorescent dye (fluorescein) was synthesized. Thereby, a single polymer chain carried multiple copies of the two enzymes and the fluorescein. The entire attachment chemistry is based on UV/vis-quantifiable bis-aryl hydrazone bond formation that allows direct quantification of bound molecules: 60 superoxide dismutase, 120 horseradish peroxidase, and 20 fluorescein molecules on an average polymer chain of 2000 repeating units. To obtain other enzyme ratios the experimental conditions were altered accordingly. Moreover, it could be shown that both enzymes remained fully active and catalyzed a two-step cascade reaction

Considerations for the selection of tests for SARS-CoV-2 molecular diagnostics

During the course of 2020, the outbreak of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) spread rapidly across the world. Clinical diagnostic testing for SARS-Cov-2 infection has relied on the real-time Reverse Transcriptase Polymerase Chain Reaction and is considered the gold standard assay. Commercial vendors and laboratories quickly mobilised to develop diagnostic tests to detect the novel coronavirus, which was fundamentally important in the pandemic response. These SARS-Cov-2 assays were developed in line with the Food Drug Administration-Emergency Use Authorization guidance. Although new tests are continuously being developed, information about SARS-CoV-2 diagnostic molecular test accuracy has been limited and at times controversial. Therefore, the analytical and clinical performance of SARS-CoV-2 test kits should be carefully considered by the appropriate regulatory authorities and evaluated by independent laboratory validation. This would provide improved end-user confidence in selecting the most reliable and accurate diagnostic test. Moreover, it is unclear whether some of these rapidly developed tests have been subjected to rigorous quality control and assurance required under good manufacturing practice. Variable target gene regions selected for currently available tests, potential mutation in target gene regions, non-standardized pre-analytic phase, a lack of manufacturer independent validation data all create difficulties in selecting tests appropriate for different countries and laboratories. Here we provide information on test criteria which are important in the assessment and selection of SARS-CoV-2 molecular diagnostic tests and outline the potential issues associated with a proportion of the tests on the market

TheCorynebacterium glutamicummycothiol peroxidase is a reactive oxygen species-scavenging enzyme that shows promiscuity in thiol redox control : The mycothiol peroxidase mechanisms kinetically unraveled

Cysteine glutathione peroxidases (CysGPxs) control oxidative stress levels by reducing hydroperoxides at the expense of cysteine thiol (-SH) oxidation, and the recovery of their peroxidatic activity is generally accomplished by thioredoxin (Trx). Corynebacterium glutamicum mycothiol peroxidase (Mpx) is a member of the CysGPx family. We discovered that its recycling is controlled by both the Trx and the mycothiol (MSH) pathway. After H2 O2 reduction, a sulfenic acid (-SOH) is formed on the peroxidatic cysteine (Cys36), which then reacts with the resolving cysteine (Cys79), forming an intramolecular disulfide (S-S), which is reduced by Trx. Alternatively, the sulfenic acid reacts with MSH and forms a mixed disulfide. Mycoredoxin 1 (Mrx1) reduces the mixed disulfide, in which Mrx1 acts in combination with MSH and mycothiol disulfide reductase as a biological relevant monothiol reducing system. Remarkably, Trx can also take over the role of Mrx1 and reduce the Mpx-MSH mixed disulfide using a dithiol mechanism. Furthermore, Mpx is important for cellular survival under H2 O2 stress, and its gene expression is clearly induced upon H2 O2 challenge. These findings add a new dimension to the redox control and the functioning of CysGPxs in general