Kinetics of hydrogen-transfer isomerizations of butoxyl radicals

2010 ◽  
Vol 12 (28) ◽  
pp. 7782 ◽  
Author(s):  
Jingjing Zheng ◽  
Donald G. Truhlar
Keyword(s):  
Hydrogen Transfer ◽  
Kinetics Of

Charakterisierung und Kinetik des in der Rattenplacenta vorkommenden mikrosomalen Enzyms, das den Wasserstoff-Transfer von Oestradiol auf Androstendion katalysiert / Characterization and Kinetics of the Microsomal Enzyme of Rat Placenta which Functions as a “Transhydrogenase” between Estradiol-17β and Androstenedione

1971 ◽  
Vol 26 (7) ◽  
pp. 710-719 ◽  
Author(s):  
Kunhard Pollow ◽  
Barbara Pollow
Keyword(s):  
Hydrogen Transfer ◽  
Microsomal Fraction ◽  
Close Relation ◽  
Inhibitory Effect ◽  
Magnesium Ions ◽  
Michaelis Constant ◽  
Temperature Optimum ◽  
Optimum Ph ◽  
Kinetics Of ◽  
Estradiol 17Β

The microsomal fraction of rat placenta contains a 17β-hydroxysteroid-oxidoreductase which transfers hydrogen from position 17 of estradiol to androstenedione. This hydrogen transfer is dependent on NAD, NADP as cofactor is without effect. The optimum pH is at 6,9. In the presence of NAD the Michaelis constant for estradiol is 4,17 · 10-5м at pH 7,4. In the presence of androstenedione in the incubation medium the Km-value for estradiol is decreased, which indicates an increased affinity for the enzyme. The temperature optimum of the enzyme is 38 °C. Addition of SH-blocking agents inhibited the enzyme activity. Zinc and magnesium ions had an inhibitory effect on the “transhydrogenase” and B-NADPT specifically labelled from [1-T]-glucose showed that the non-effect of NADP on transhydrogenation from estradiol to androstenedione resulting in reduction of position 17 is not due to different stereospecifity.The results show a close relation between the oxidative metabolism of estradiol and the reduction of androstenedione, indicating that estradiol-17β, as the preferred hydrogen-donating substrate, is an essential component of the androstenedione-hydrogenating system in the microsomal fraction of rat placenta.

Pyrolysis of Hexadecane

1997 ◽  
Vol 62 (7) ◽  
pp. 1057-1069 ◽  
Author(s):  
Elena Barteková ◽  
Martin Bajus
Keyword(s):  
Hydrogen Transfer ◽  
Coke Formation ◽  
Tubular Reactor ◽  
Frequency Factor ◽  
Mass Ratio ◽  
Pyrolysis Products ◽  
Alkyl Radicals ◽  
Secondary Reactions ◽  
Increasing Temperature ◽  
Kinetics Of

The kinetics of thermal decomposition of hexadecane was studied in a flow tubular reactor from stainless steel. The experiments were performed in the temperature range of 700 to 780 °C for the mass ratio of steam to hydrocarbon 3 : 1. The hexadecane pyrolysis took place according to the first-order reaction with a frequency factor of 3.5 . 109 s-1 and an activation energy of 162 kJ mol-1. In the pyrolysis products there were above all 1-alkenes. From alkanes, methane and ethane and less propane were formed in a higher degree. The prevailing compounds are ethene and propene whose amount increases with increasing temperature and residence time. The content of 1-alkenes higher than 1-pentene decreases with increasing conversion which gives evidence of their decomposition owing to their lower stability in comparison with the lighter 1-alkenes. The formation of dienes (1,3-butadiene and propadiene) and benzene also confirmed the course of secondary reactions. The observed higher formation of hydrogen results from the reaction of steam with coke deposited on the walls of the reactor or with hydrocarbon radicals. The evidence of the coke formation is given also by the presence of carbon oxides whose amount grew with the pyrolysis severity. The high content of 1-hexene in comparison with the other higher 1-alkenes is probably caused by the isomerization of alkyl radicals by 1,5-hydrogen transfer.

Substituent effects upon the kinetics of hydrogen transfer from triorganotin hydrides to the 5-hexen-1-yl radical

1988 ◽  
Vol 7 (10) ◽  
pp. 2220-2223 ◽  
Author(s):  
Philip W. Pike ◽  
Vernon. Gilliatt ◽  
Michael. Ridenour ◽  
James W. Hershberger
Keyword(s):  
Hydrogen Transfer ◽  
Substituent Effects ◽  
Kinetics Of

Hydrogen transfer reactions in viscous media — Potential and free energy surfaces in solvent–solute coordinates and their kinetic implications

2013 ◽  
Vol 91 (9) ◽  
pp. 787-794
Author(s):  
Heather Wiebe ◽  
Melissa Prachnau ◽  
Noham Weinberg
Keyword(s):  
Free Energy ◽  
Hydrogen Transfer ◽  
Transfer Reactions ◽  
Molecular Dynamics Calculations ◽  
Viscous Media ◽  
Solvent Systems ◽  
Energy Surfaces ◽  
Kinetics Of ◽  
Viscosity Dependence ◽  
Hydrogen Transfer Reactions

Two-dimensional potential energy and free energy surfaces are obtained using quantum mechanical and molecular dynamics calculations for four hydrogen transfer reactions in n-hexane solvent: the methyl–methane, n-propyl–n-propane, n-pentyl–n-pentane, and t-butyl–isobutane systems. The resultant surfaces have similar landscapes despite the fact the equilibrated solvent cavities for these systems are notably different in size and shape. The kinetic implications of these landscapes are discussed. The Arrhenius and tunneling kinetics of hydrogen transfer in nonpolar hydrocarbon solute–solvent systems are not expected to show any significant viscosity dependence.

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