Diazo coupling reactions in acetonitrile: an apparent increase in kinetic isotope effect with temperature

1979 ◽  
pp. 819 ◽  
Author(s):  
John R. Penton ◽  
Heinrich Zollinger
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Coupling Reactions ◽  
Apparent Increase ◽  
Kinetic Isotope ◽  
Diazo Coupling

scholarly journals Investigation of C1 + C1 Coupling Reactions in Cobalt-Catalyzed Fischer-Tropsch Synthesis by a Combined DFT and Kinetic Isotope Study

Catalysts ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 551 ◽  
Author(s):  
Yanying Qi ◽  
Jia Yang ◽  
Anders Holmen ◽  
De Chen
Keyword(s):  
Isotope Effect ◽  
Thermodynamic Stability ◽  
Kinetic Isotope Effect ◽  
Theoretical Calculations ◽  
Tropsch Synthesis ◽  
Chain Growth ◽  
Coupling Reactions ◽  
Fischer Tropsch ◽  
Fischer Tropsch Synthesis ◽  
Kinetic Isotope

Understanding the chain growth mechanism is of vital importance for the development of catalysts with enhanced selectivity towards long-chain products in cobalt-catalyzed Fischer-Tropsch synthesis. Herein, we discriminate various C1 + C1 coupling reactions by theoretical calculations and kinetic isotope experiments. CHx(x=0−3), CO, HCO, COH, and HCOH are considered as the chain growth monomer respectively, and 24 possible coupling reactions are first investigated by theoretical calculations. Eight possible C1 + C1 coupling reactions are suggested to be energetically favorable because of the relative low reaction barriers. Moreover, five pathways are excluded where the C1 monomers show low thermodynamic stability. Effective chain propagation rates are calculated by deconvoluting from reaction rates of products, and an inverse kinetic isotope effect of the C1 + C1 coupling reaction is observed. The theoretical kinetic isotope effect of CO + CH2 is inverse, which is consistent with the experimental observation. Thus, the CO + CH2 pathway, owing to the relatively lower barrier, the high thermodynamic stability, and the inverse kinetic isotope effect, is suggested to be a favorable pathway.

Quantum electrocatalysts: theoretical picture, electrochemical kinetic isotope effect analysis, and conjecture to understand microscopic mechanisms

2020 ◽  
Vol 22 (20) ◽  
pp. 11219-11243 ◽  
Author(s):  
Ken Sakaushi
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Effect Analysis ◽  
Kinetic Isotope

The fundamental aspects of quantum electrocatalysts are discussed together with the newly developed electrochemical kinetic isotope effect (EC-KIE) approach.

scholarly journals l-mandelate dehydrogenase from Rhodotorula graminis: comparisons with the l-lactate dehydrogenase (flavocytochrome b2) from Saccharomyces cerevisiae

1993 ◽  
Vol 290 (1) ◽  
pp. 103-107 ◽  
Author(s):  
O Smékal ◽  
M Yasin ◽  
C A Fewson ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Lactate Dehydrogenase ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Dimensional Structure ◽  
Striking Difference ◽  
Kinetic Properties ◽  
Proton Abstraction ◽  
Rate Determining Step ◽  
Kinetic Isotope

L-Lactate dehydrogenase (L-LDH) from Saccharomyces cerevisiae and L-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis are both flavocytochromes b2. The kinetic properties of these enzymes have been compared using steady-state kinetic methods. The most striking difference between the two enzymes is found by comparing their substrate specificities. L-LDH and L-MDH have mutually exclusive primary substrates, i.e. the substrate for one enzyme is a potent competitive inhibitor for the other. Molecular-modelling studies on the known three-dimensional structure of S. cerevisiae L-LDH suggest that this enzyme is unable to catalyse the oxidation of L-mandelate because productive binding is impeded by steric interference, particularly between the side chain of Leu-230 and the phenyl ring of mandelate. Another major difference between L-LDH and L-MDH lies in the rate-determining step. For S. cerevisiae L-LDH, the major rate-determining step is proton abstraction at C-2 of lactate, as previously shown by the 2H kinetic-isotope effect. However, in R. graminis L-MDH the kinetic-isotope effect seen with DL-[2-2H]mandelate is only 1.1 +/- 0.1, clearly showing that proton abstraction at C-2 of mandelate is not rate-limiting. The fact that the rate-determining step is different indicates that the transition states in each of these enzymes must also be different.

Isotope effect profiles in the N-demethylation of N,N-dimethylanilines: a key to determine the pKa of nonheme Fe(iii)–OH complexes

2015 ◽  
Vol 51 (24) ◽  
pp. 5032-5035 ◽  
Author(s):  
Alessia Barbieri ◽  
Martina De Gennaro ◽  
Stefano Di Stefano ◽  
Osvaldo Lanzalunga ◽  
Andrea Lapi ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Kinetic Isotope

pKa of [(N4Py)FeIII–OH]2+ is obtained from the kinetic isotope effect profiles in the N-demethylation of N,N-dimethylanilines promoted by [(N4Py)FeIVO]2+.

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