Activation of diatomic molecules at solid surfaces

2005 ◽  
Vol 363 (1829) ◽  
pp. 955-958 ◽  
Author(s):  
Gerhard Ertl
Keyword(s):  
Active Sites ◽  
Crystal Surface ◽  
Dissociative Adsorption ◽  
Solid Surfaces ◽  
Oxidation Of Co ◽  
Elementary Processes ◽  
Mechanism And Kinetics ◽  
Kinetics Of ◽  
Present Understanding

The interaction of a diatomic molecule with a well-defined single crystal surface represents the prototype of the elementary processes involved in heterogeneous catalysis, and it can be studied down to atomic length and extremely short (fs) time-scales. Our present understanding is illustrated by examples concerning the activation of hydrogen (including also the breakdown of thermal equilibrium during rapid laser-induced associative desorption), the role of steps as ‘active sites’ in the dissociative adsorption of NO or N 2 , and the mechanism and kinetics of the catalytic oxidation of CO.

Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures

1993 ◽  
Vol 58 (5) ◽  
pp. 1001-1006 ◽  
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Transfer Functions ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Oxidation Of Co ◽  
Kinetics Of Oxidation ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Alcohol Mixtures ◽  
Kinetics Of

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.

Mechanism and kinetics of catalytic oxidation of CO to CO2 over Ptn+and MPtn-1+, (M=Sn, Rh &Ru; n=3, 4) clusters

2021 ◽  
Vol 509 ◽  
pp. 111638
Author(s):  
Satyajit Dey Baruah ◽  
Subrata Paul ◽  
Nand Kishor Gour ◽  
Nishant Biswakarma ◽  
Ramesh Chandra Deka
Keyword(s):  
Catalytic Oxidation ◽  
Oxidation Of Co ◽  
Catalytic Oxidation Of Co ◽  
Mechanism And Kinetics ◽  
Kinetics Of

scholarly journals Evolutionary Expansion of the Amidohydrolase Superfamily in Bacteria in Response to the Synthetic Compounds Molinate and Diuron

2015 ◽  
Vol 81 (7) ◽  
pp. 2612-2624 ◽  
Author(s):  
Elena Sugrue ◽  
Nicholas J. Fraser ◽  
Davis H. Hopkins ◽  
Paul D. Carr ◽  
Jeevan L. Khurana ◽  
...  
Keyword(s):  
Active Site ◽  
Metal Ion ◽  
Active Sites ◽  
Evolutionary Transition ◽  
Functional Changes ◽  
Metal Ion Analysis ◽  
Amidohydrolase Superfamily ◽  
Kinetics Of ◽  
Hydrolysis Of

ABSTRACTThe amidohydrolase superfamily has remarkable functional diversity, with considerable structural and functional annotation of known sequences. In microbes, the recent evolution of several members of this family to catalyze the breakdown of environmental xenobiotics is not well understood. An evolutionary transition from binuclear to mononuclear metal ion coordination at the active sites of these enzymes could produce large functional changes such as those observed in nature, but there are few clear examples available to support this hypothesis. To investigate the role of binuclear-mononuclear active-site transitions in the evolution of new function in this superfamily, we have characterized two recently evolved enzymes that catalyze the hydrolysis of the synthetic herbicides molinate (MolA) and phenylurea (PuhB). In this work, the crystal structures, mutagenesis, metal ion analysis, and enzyme kinetics of both MolA and PuhB establish that these enzymes utilize a mononuclear active site. However, bioinformatics and structural comparisons reveal that the closest putative ancestor of these enzymes had a binuclear active site, indicating that a binuclear-mononuclear transition has occurred. These proteins may represent examples of evolution modifying the characteristics of existing catalysts to satisfy new requirements, specifically, metal ion rearrangement leading to large leaps in activity that would not otherwise be possible.

scholarly journals Kinetic analysis of the role of lipoic acid residues in the pyruvate dehydrogenase multienzyme complex of Escherichia coli

1980 ◽  
Vol 187 (2) ◽  
pp. 393-401 ◽  
Author(s):  
Mary C. Ambrose-Griffin ◽  
Michael J. Danson ◽  
William G. Griffin ◽  
Geoffrey Hale ◽  
Richard N. Perham
Keyword(s):  
Escherichia Coli ◽  
Lipoic Acid ◽  
Pyruvate Dehydrogenase ◽  
Active Sites ◽  
Catalytic Mechanism ◽  
Pyruvate Dehydrogenase Complex ◽  
Enzymic Activity ◽  
Complex Activity ◽  
Kinetics Of

The catalytic roles of the two reductively acetylatable lipoic acid residues on each lipoate acetyltransferase chain of the pyruvate dehydrogenase complex of Escherichia coli were investigated. Both lipoyl groups are reductively acetylated from pyruvate at the same apparent rate and both can transfer their acetyl groups to CoASH, part-reactions of the overall complex reaction. The complex was treated with N-ethylmaleimide in the presence of pyruvate and the absence of CoASH, conditions that lead to the modification and inactivation of the S-acetyldihydrolipoic acid residues. Modification was found to proceed appreciably faster than the accompanying loss of enzymic activity. The kinetics of the modification were fitted best by supposing that the two lipoyl groups react with the maleimide at different rates, one being modified at approximately 3.5 times the rate of the other. The loss of complex activity took place at a rate approximately equal to that calculated for the modification of the more slowly reacting lipoic acid residue. The simplest interpretation of this result is that only this residue is essential in the overall catalytic mechanism, but an alternative explanation in which one lipoic acid residue can take over the function of another was not ruled out. The kinetics of inactivation could not be reconciled with an obligatory serial interaction between the two lipoic acid residues. Similar experiments with the fluorescent N-[p-(benzimidazol-2-yl)phenyl]maleimide supported these conclusions, although the modification was found to be less specific than with N-ethylmaleimide. The more rapidly modified lipoic acid residue may be involved in the system of intramolecular transacetylation reactions that couple active sites in the lipoate acetyltransferase component.

Theory of Dissociative Adsorption Kinetics of Homonuclear Diatomic Molecules on Solid Surfaces

2002 ◽  
Vol 106 (45) ◽  
pp. 11784-11794 ◽  
Author(s):  
Ernst D. German ◽  
Irena Efremenko ◽  
Alexander M. Kuznetsov ◽  
Moshe Sheintuch
Keyword(s):  
Adsorption Kinetics ◽  
Diatomic Molecules ◽  
Dissociative Adsorption ◽  
Solid Surfaces ◽  
Homonuclear Diatomic Molecules ◽  
Kinetics Of

scholarly journals Comparison of kinetic and enzymatic properties of intracellular phosphoserine aminotransferases from alkaliphilic and neutralophilic bacteria

2020 ◽  
Vol 18 (1) ◽  
pp. 149-164
Author(s):  
Marianne Koivulehto ◽  
Natalia Battchikova ◽  
Saara Korpela ◽  
Elvira Khalikova ◽  
Anton Zavialov ◽  
...  
Keyword(s):  
Active Sites ◽  
Structural Data ◽  
Acid Base ◽  
Ph Optimum ◽  
E Coli ◽  
Internal Ph ◽  
Specific Activities ◽  
Activity Loss ◽  
Kinetics Of

AbstractIntracellular pyridoxal 5´-phosphate (PLP) -dependent recombinant phosphoserine aminotransferases (PSATs; EC 2.6.1.52) from two alkaliphilic Bacillus strains were overproduced in Escherichia coli, purified to homogeneity and their enzymological characteristics were compared to PSAT from neutralophilic E. coli. Some of the enzymatic characteristics of the PSATs from the alkaliphiles were unique, showing high and sharp pH optimal of the activity related to putative internal pH inside the microbes. The specific activities of all of the studied enzymes were similar (42-44 U/mg) as measured at the pH optima of the enzymes. The spectrophotometric acid-base titration of the PLP chromophore of the enzymes from the alkaliphiles showed that the pH optimum of the activity appeared at the pH wherein the active sites were half-protonated. Detachment of PLP from holoenzymes did not take place even at pH up to 11. The kinetics of the activity loss at acid and alkaline pHs were similar in all three enzymes and followed similar kinetics. The available 3-D structural data is discussed as well as the role of protons at the active site of aminotransferases.

Electron Microscope Study of the Effect of Substrate Metal Dislocation Structure on the Structure of Electrodeposited Nickel

1975 ◽  
Vol 33 ◽  
pp. 94-95
Author(s):  
I. Gundiler ◽  
L.E. Murr
Keyword(s):  
Dislocation Structure ◽  
Growth Parameters ◽  
Growth Patterns ◽  
Dislocation Mechanism ◽  
Free Surfaces ◽  
Substrate Metal ◽  
Electrodeposited Nickel ◽  
Mechanism And Kinetics ◽  
Kinetics Of

The role of dislocations on crystal growth was first introduced by Frank and an extensive treatment of the theory was developed by Burton, et al. The growth parameters pertaining to electro-crystallization have been defined, and theories on the mechanism and kinetics of electrodeposition have been developed. The formation of spirals and pyramidal growth patterns are both explained by the screw-dislocation mechanism. Two dimensional nucleation on displacement-free surfaces and step-bunching mechanisms have also been suggested.Although a surface-diffusion-to-dislocation-steps mechanism for electrocrystallization is generally accepted, the effect of dislocation structure and density in the substrate on the microstructure of electrodeposited metals has not been systematically studied.

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