Highly Unsaturated CrII/SiO2Single-Site Catalysts for Reducing Nitrogen Oxides with CO: Reaction Intermediates and Catalytic Cycle

ChemCatChem ◽  
2010 ◽  
Vol 2 (3) ◽  
pp. 259-262 ◽  
Author(s):  
Adriano Zecchina ◽  
Carlos Otero Areán ◽  
Elena Groppo
Keyword(s):  
Nitrogen Oxides ◽  
Catalytic Cycle ◽  
Reaction Intermediates

scholarly journals Unstable Reaction Intermediates and Hysteresis during the Catalytic Cycle of 5-Aminolevulinate Synthase

2014 ◽  
Vol 289 (33) ◽  
pp. 22915-22925 ◽  
Author(s):  
Bosko M. Stojanovski ◽  
Gregory A. Hunter ◽  
Martina Jahn ◽  
Dieter Jahn ◽  
Gloria C. Ferreira
Keyword(s):  
Catalytic Cycle ◽  
Reaction Intermediates ◽  
Aminolevulinate Synthase

scholarly journals Stabilization of Reaction Intermediates in the Catalytic Cycle of Nitric Oxide Synthases

2009 ◽  
Vol 23 (S1) ◽  
Author(s):  
Jesus Tejero ◽  
Ashis Biswas ◽  
Zhi‐Qiang Wang ◽  
Richard C. Page ◽  
Mohammed Mahfuzul Haque ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Nitric Oxide Synthases ◽  
Catalytic Cycle ◽  
Reaction Intermediates

scholarly journals Cryotrapped Reaction Intermediates of Cytochrome P450 Studied by Radiolytic Reduction with Phosphorus-32

2001 ◽  
Vol 276 (15) ◽  
pp. 11648-11652 ◽  
Author(s):  
Ilia G. Denisov ◽  
Thomas M. Makris ◽  
Stephen G. Sligar
Keyword(s):  
Cytochrome P450 ◽  
Catalytic Cycle ◽  
Internal Source ◽  
Reaction Intermediates ◽  
Compound I ◽  
Γ Irradiation ◽  
Rate Limiting Step ◽  
Type Spectrum ◽  
Radiolytic Reduction ◽  
Electron Reduction

Unstable reaction intermediates of the cytochrome P450 catalytic cycle have been prepared at cryogenic temperatures using radiolytic one-electron reduction of the oxy-P450 CYP101 complex. Since a rate-limiting step in the catalytic cycle of the enzyme is the reduction of the ferrous oxygenated heme protein, subsequent reaction intermediates do not normally accumulate. Using60Co γ-irradiation, the primary reduced oxy-P450 species at 77 K has been identified as a superoxo- or hydroperoxo-Fe3+-heme complex (Davydov, R., Macdonald, I. D. G., Makris, T. M., Sligar, S. G., and Hoffman, B. M. (1999)J. Am. Chem. Soc.121, 10654–10655). The electronic absorption spectroscopy is an essential tool to characterize cytochrome P450 intermediates and complements paramagnetic methods, which are blind to important diamagnetic or antiferromagnetically coupled states. We report a method of trapping unstable states of redox enzymes using phosphorus-32 as an internal source of electrons. We determine the UV-visible optical spectra of the reduced oxygenated state of CYP101 and show that the primary intermediate, a hydroperoxo-P450, is stable below 180 K and converts smoothly to the product complex at ∼195 K. In the course of the thermal annealing, no spectral changes indicating the presence of oxoferryl species (the so-called compound I type spectrum) was observed.

Analyzing reactions of single mechanoenzyme molecules by light microscopy

1992 ◽  
Vol 50 (1) ◽  
pp. 426-427
Author(s):  
Jeff Gelles
Keyword(s):  
Image Processing ◽  
Reaction Mechanisms ◽  
Transient State ◽  
Nanometer Scale ◽  
Reaction Intermediates ◽  
Enzyme Molecule ◽  
Directed Movement ◽  
Enzyme Molecules ◽  
Individual Enzyme ◽  
Single Reaction

Mechanoenzymes are enzymes which use a chemical reaction to power directed movement along biological polymer. Such enzymes include the cytoskeletal motors (e.g., myosins, dyneins, and kinesins) as well as nucleic acid polymerases and helicases. A single catalytic turnover of a mechanoenzyme moves the enzyme molecule along the polymer a distance on the order of 10−9 m We have developed light microscope and digital image processing methods to detect and measure nanometer-scale motions driven by single mechanoenzyme molecules. These techniques enable one to monitor the occurrence of single reaction steps and to measure the lifetimes of reaction intermediates in individual enzyme molecules. This information can be used to elucidate reaction mechanisms and determine microscopic rate constants. Such an approach circumvents difficulties encountered in the use of traditional transient-state kinetics techniques to examine mechanoenzyme reaction mechanisms.

The Structure and Rearrangements of a Complete Polyketide Synthase Module During its Catalytic Cycle

Planta Medica ◽  
2013 ◽  
Vol 79 (10) ◽  
Author(s):  
DH Sherman ◽  
G Skiniotis ◽  
JL Smith ◽  
K Håkansson ◽  
S Dutta ◽  
...  
Keyword(s):  
Polyketide Synthase ◽  
Catalytic Cycle

WET BURNING – THE MODERN TREND IN ENVIRONMENTAL BENIGN FUEL COMBUSTION AND IN SOLUTION TO THE PROBLEM OF SUSTAINABLE DEVELOPMENT OF THE POWER GENERATION

2018 ◽  
pp. 96-117 ◽  
Author(s):  
B. S. Soroka
Keyword(s):  
Numerical Simulation ◽  
Nitrogen Oxides ◽  
Chemical Kinetics ◽  
Fuel Combustion ◽  
Transport Processes ◽  
Cfd Modeling ◽  
Furnace Chamber ◽  
Modern Trend ◽  
Atmospheric Air ◽  
No Formation

The article considers the role and place of water and water vapor in combustion processes with the purpose of reduction the effluents of nitrogen oxides and carbon oxide. We have carried out the complex of theoretical and computational researches on reduction of harmful nitrogen and carbon oxides by gas fuel combustion in dependence on humidity of atmospheric air by two approaches: CFD modeling with attraction of DRM 19 chemical kinetics mechanism of combustion for 19 components along with Bowman’s mechanism used as “postprocessor” to determine the [NO] concentration; different thermodynamic models of predicting the nitrogen oxides NO formation. The numerical simulation of the transport processes for momentum, mass and heat being solved simultaneously in the united equations’ system with the chemical kinetics equations in frame of GRI methane combustion mechanism and NO formation calculated afterwards as “postprocessor” allow calculating the absolute actual [CO] and [NO] concentrations in dependence on combustion operative conditions and on design of furnace facilities. Prediction in frame of thermodynamic equilibrium state for combustion products ensures only evaluation of the relative value of [NO] concentration by wet combustion the gas with humid air regarding that in case of dry air – oxidant. We have developed the methodology and have revealed the results of numerical simulation of impact of the relative humidity of atmospheric air on harmful gases formation. Range of relative air humidity under calculations of atmospheric air under impact on [NO] and [CO] concentrations at the furnace chamber exit makes φ = 0 – 100%. The results of CFD modeling have been verified both by author’s experimental data and due comparing with the trends stated in world literature. We have carried out the complex of the experimental investigations regarding atmospheric air humidification impact on flame structure and environmental characteristics at natural gas combustion with premixed flame formation in open air. The article also proposes the methodology for evaluation of the nitrogen oxides formation in dependence on moisture content of burning mixture. The results of measurements have been used for verification the calculation data. Coincidence of relative change the NO (NOx) yield due humidification the combustion air revealed by means of CFD prediction has confirmed the qualitative and the quantitative correspondence of physical and chemical kinetics mechanisms and the CFD modeling procedures with the processes to be studied. A sharp, more than an order of reduction in NO emissions and simultaneously approximately a two-fold decrease in the CO concentration during combustion of the methane-air mixture under conditions of humidification of the combustion air to a saturation state at a temperature of 325 K.

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