Reactions of hydrogen atoms with hexafluoroacetone

1978 ◽  
Vol 56 (20) ◽  
pp. 2638-2645 ◽  
Author(s):  
D. W. Grattan ◽  
K. O. Kutschke
Keyword(s):  
Rate Constant ◽  
Cross Sections ◽  
The Other ◽  
Hydrogen Atoms ◽  
Kinetics Of

Attempts were made to study the kinetics of the reaction of atomic H with (CF3)2CO vapour (HFA). Atomic H was generated from H2 by mercury photosensitization in the presence of C2H4 and HFA but the system was complicated by the loss of C2H5 radicals by addition to HFA and the kinetic results were intractable. When atomic H was generated from C3H8, the kinetics again were obscured by some unidentified reaction(s) which became more important at higher [HFA]/[C3H8]. An estimate of the rate constant for the addition of H to HFA obtained at low [HFA]/[C3H8] yielded k9 = 8.5 × 105 l mol−1 s−1. Trifluoroacetaldehyde was identified with some reliability but many of the other heavier products formed in the H2 + HFA reaction could not be identified. Quenching cross-sections were determined for C2H4, C3H8, C4H10, and HFA relative to that for N2O.

Kinetics of the reaction H + C2H6 → H2 + C2H5 in the temperature region of 1000 K

1984 ◽  
Vol 62 (1) ◽  
pp. 86-91 ◽  
Author(s):  
J.-R. Cao ◽  
M. H. Back
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Temperature Region ◽  
Recent Measurement ◽  
Hydrogen Atoms ◽  
Elementary Reactions ◽  
Temperature Range ◽  
Hydrogen Molecules ◽  
Kinetics Of ◽  
Rate Controlling Step

A system for the measurement of rate constants for elementary reactions of hydrogen atoms in the temperature region of 1000 K is described. The concentration of hydrogen atoms is controlled by the equilibrium constant for dissociation of hydrogen molecules. The kinetics of the rate of conversion of ethane to ethylene in this system has been studied over the temperature range 876–1016 K. The results show that the rate-controlling step is[Formula: see text]and the value obtained for the rate constant is[Formula: see text](R = 1.987 cal mol−1 deg−1). This value is compared with values obtained from other methods over the temperature range 300–1400 K. Combination with a recent measurement of the rate constant for the reverse reaction yields an experimental value for the equilibrium constant for the reaction.

scholarly journals The synthesis of inhibitors for processing proteinases and their action on the Kex2 proteinase of yeast

1993 ◽  
Vol 293 (1) ◽  
pp. 75-81 ◽  
Author(s):  
H Angliker ◽  
P Wikstrom ◽  
E Shaw ◽  
C Brenner ◽  
R S Fuller
Keyword(s):  
Rate Constant ◽  
Potent Inhibitor ◽  
Protein Processing ◽  
The Other ◽  
Peptide Sequence ◽  
Cleavage Sites ◽  
Precursor Processing ◽  
Inactivation Rate Constant ◽  
Potential Inhibitors ◽  
Kinetics Of

Peptidyl chloromethane and sulphonium salts containing multiple Arg and Lys residues were synthesized as potential inhibitors of prohormone and pro-protein processing proteinases. The potencies of these compounds were assayed by measuring the kinetics of inactivation of the yeast Kex2 proteinase, the prototype of a growing family of eukaryotic precursor processing proteinases. The most potent inhibitor, Pro-Nvl-Tyr-Lys-Arg-chloromethane, was based on cleavage sites in the natural Kex2 substrate pro-alpha-factor. This inhibitor exhibited a Ki of 3.7 nM and a second-order inactivation rate constant (k2/Ki) of 1.3 x 10(7) M-1.s-1 comparable with the value of kcat./Km obtained with Kex2 for the corresponding peptidyl methylcoumarinylamide substrate. The enzyme exhibited sensitivity to the other peptidyl chloromethanes over a range of concentrations, depending on peptide sequence and alpha-amino decanoylation, but was completely resistant to peptidyl sulphonium salts. Kinetics of inactivation by these new inhibitors of a set of ‘control’ proteinases, including members of both the trypsin and subtilisin families, underscored the apparent specificity of the compounds most active against Kex2 proteinase.

scholarly journals Intra-axonal transport and turnover of neurophysins in the rat. A proposal for a possible origin of the minor neurophysin component

1973 ◽  
Vol 136 (4) ◽  
pp. 1047-1052 ◽  
Author(s):  
Graham D. Burford ◽  
Brian T. Pickering
Keyword(s):  
Axonal Transport ◽  
Rate Constant ◽  
Half Life ◽  
Minor Component ◽  
The Other ◽  
Metabolic Product ◽  
Exponential Rate ◽  
Neural Lobe ◽  
Intracisternal Injection ◽  
Kinetics Of

1. Radioactivity associated with the three neurophysins in the neural lobe of the rat was determined at intervals up to 5 weeks after an intracisternal injection of [35S]cysteine. 2. The radioactivity associated with the two major neurophysins (one supposedly associated with vasopressin and the other with oxytocin) increased linearly for 12h after the injection and the ratio of the rates of increase in the two proteins was very similar to the ratio of vasopressin to oxytocin in the gland. 3. From 12h onwards the radioactivity associated with each major neurophysin declined exponentially but the half-life of the supposed oxytocin–neurophysin (13.3 days) was shorter than that for the supposed vasopressin–neurophysin (19.8 days). 4. The kinetics of labelling of the minor neurophysin was quite different from that of the two major ones. It became slowly labelled during 3–5 days after injection and the radioactivity hardly decreased during the following 4 weeks. 5. The data could support the hypothesis that the minor neurophysin is a metabolic product of oxytocin–neurophysin. The exponential rate of disappearance of radioactivity from oxytocin–neurophysin and the minor component taken together has a rate constant similar to that for vasopressin–neurophysin (e.g. half-life=18.9 days).

scholarly journals Specificity and kinetics of triose phosphate isomerase from chicken muscle

1972 ◽  
Vol 129 (2) ◽  
pp. 301-310 ◽  
Author(s):  
Sylvia J. Putman ◽  
A. F. W. Coulson ◽  
I. R. T. Farley ◽  
B. Riddleston ◽  
J. R. Knowles
Keyword(s):  
Triose Phosphate Isomerase ◽  
Proton Exchange ◽  
The Other ◽  
Chicken Breast ◽  
Dihydroxyacetone Phosphate ◽  
Exchange Reactions ◽  
Hydrogen Atoms ◽  
Triose Phosphate ◽  
Chicken Muscle ◽  
Kinetics Of

The isolation of crystalline triose phosphate isomerase from chicken breast muscle is described. The values of kcat. and Km for the reaction in each direction were determined from experiments over wide substrate-concentration ranges, and the reactions were shown to obey simple Michaelis–Menten kinetics. With d-glyceraldehyde 3-phosphate as substrate, kcat. is 2.56×105min-1and Km is 0.47mm; with dihydroxyacetone phosphate as substrate, kcat. is 2.59×104min-1and Km is 0.97mm. The enzyme-catalysed exchange of the methyl hydrogen atoms of the ‘virtual substrate’ monohydroxyacetone phosphate with solvent2H2O or3H2O was shown. This exchange is about 104-fold slower than the corresponding exchange of the C-3 hydrogen of dihydroxyacetone phosphate. The other deoxy substrate, 3-hydroxypropionaldehyde phosphate, was synthesized, but is too unstable in aqueous solution for analogous proton-exchange reactions to be studied.

KINETICS OF THE ABSTRACTION OF HYDROGEN ATOMS FROM HYDROGEN SULFIDE BY TRIFLUOROMETHYL RADICALS

1966 ◽  
Vol 44 (12) ◽  
pp. 1445-1449 ◽  
Author(s):  
N. L. Arthur ◽  
T. N. Bell
Keyword(s):  
Hydrogen Sulfide ◽  
Rate Constant ◽  
Hydrogen Sulphide ◽  
Hydrogen Atoms ◽  
Kinetics Of

Trifluoromethyl radicals generated from the photolysis of hexafluoroacetone abstract hydrogen atoms from hydrogen sulphide.[Formula: see text]The rate constant of this reaction measured by comparing the rate with that for the recombination of trifluoromethyl radicals (k = 2.3 × 1013 cc mole−1 s−1) is given by,[Formula: see text]

Kinetics of the reaction C2H5 + H2 → C2H6 + H from 1111-1200 K

1982 ◽  
Vol 60 (24) ◽  
pp. 3039-3048 ◽  
Author(s):  
J.-R. Cao ◽  
M. H. Back
Keyword(s):  
Rate Constant ◽  
Equilibrium Concentration ◽  
Reverse Reaction ◽  
Elementary Reaction ◽  
Hydrogen Atoms ◽  
Temperature Range ◽  
Lower Temperature ◽  
Kinetics Of ◽  
Rate Controlling Step ◽  
Hydrogenation Of Ethylene

A system for the measurement of the rate constant for the elementary reaction[Formula: see text]in the temperature range 1111–1200 K is described and is based on the thermal production of an equilibrium concentration of hydrogen atoms. In a mixture of hydrogen with about 10 ppm ethylene this reaction is the rate-controlling step in the hydrogenation of ethylene. The product ethane undergoes rapid secondary dissociation and the final product is methane. The values obtained in the present work, which are represented by the following expression,[Formula: see text](R = 1.987 cal mol−1 deg−1) are compared to those obtained at lower temperature (820–350 K) and to those calculated from measurements of the reverse reaction.

Electron Irradiation Effects in Polyoxymethylene Crystals Grown Inside Trioxane Crystals

1971 ◽  
Vol 29 ◽  
pp. 78-79
Author(s):  
J. P. Colson ◽  
D. H. Reneker
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Detailed Examination ◽  
The Other ◽  
Electron Micrograph ◽  
Irradiation Effects ◽  
Threefold Axis ◽  
Typical Sample ◽  
Polymer Crystals ◽  
Chain Axis

Polyoxymethylene (POM) crystals grow inside trioxane crystals which have been irradiated and heated to a temperature slightly below their melting point. Figure 1 shows a low magnification electron micrograph of a group of such POM crystals. Detailed examination at higher magnification showed that three distinct types of POM crystals grew in a typical sample. The three types of POM crystals were distinguished by the direction that the polymer chain axis in each crystal made with respect to the threefold axis of the trioxane crystal. These polyoxymethylene crystals were described previously.At low magnifications the three types of polymer crystals appeared as slender rods. One type had a hexagonal cross section and the other two types had rectangular cross sections, that is, they were ribbonlike.

Kinetics of Substitution of 4-Methoxyphenylazo Groups of 2,6-Dioxo-5(3)-(4-methoxyphenylazo)-3(5)-(4-methoxyphenylhydrazono)-1,2,3,6-tetrahydropyridine-4-carboxylic Acid by Reaction with 4-Nitrobenzenediazonium Cation

1994 ◽  
Vol 59 (7) ◽  
pp. 1665-1672 ◽  
Author(s):  
Jaroslava Horáčková ◽  
Vojeslav Štěrba
Keyword(s):  
Carboxylic Acid ◽  
Rate Constant ◽  
Kinetics Of

Kinetics have been studied of gradual replacement of 4-methoxyphenylazo groups in 2,6-dioxo-5(3)-(4-methoxyphenylazo)-3(5)-(4-methoxyphenylhydrazono)-1,2,3,6-tetrahydropyridine-4-carboxylic acid (IIIa) by 4-nitrophenylazo groups using the reaction with 4-nitrobenzenediazonium cation (IIc) in acetate and phosphate buffers. The rate constant of replacement of the second methoxyphenylazo group is lower by a factor of ca 60. From the experimentally found pKa values of the corresponding azohydrazone compounds with methoxy, chloro, or nitro substituent at 4-position (IIIa - IIIf) it has been concluded that the 5(3)-(4-methoxyphenylazo)-3(5)-(4-nitrophenylhydrazono) derivative is formed in the first step.

The Reactivity of Different Active Forms of Sodium Carbonate with Respect to Sulfur Dioxide

1992 ◽  
Vol 57 (11) ◽  
pp. 2302-2308
Author(s):  
Karel Mocek ◽  
Erich Lippert ◽  
Emerich Erdös
Keyword(s):  
Thermal Decomposition ◽  
Liquid Phase ◽  
Sulfur Dioxide ◽  
Specific Surface ◽  
Surface Area ◽  
Sodium Carbonate ◽  
Room Temperature ◽  
Active Form ◽  
The Other ◽  
Kinetics Of

The kinetics of the reaction of solid sodium carbonate with sulfur dioxide depends on the microstructure of the solid, which in turn is affected by the way and conditions of its preparation. The active form, analogous to that obtained by thermal decomposition of NaHCO3, emerges from the dehydration of Na2CO3 . 10 H2O in a vacuum or its weathering in air at room temperature. The two active forms are porous and have approximately the same specific surface area. Partial hydration of the active Na2CO3 in air at room temperature followed by thermal dehydration does not bring about a significant decrease in reactivity. On the other hand, if the preparation of anhydrous Na2CO3 involves, partly or completely, the liquid phase, the reactivity of the product is substantially lower.

Rate Constants, Reactive Flux

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Correlation Function ◽  
Rate Constant ◽  
Cross Sections ◽  
Time Correlation ◽  
Time Correlation Function ◽  
Exact Expression ◽  
Reaction Cross ◽  
Dividing Surface ◽  
Definition Of ◽  
Reactive Flux

This chapter discusses a direct approach to the calculation of the rate constant k(T) that bypasses the detailed state-to-state reaction cross-sections. The method is based on the calculation of the reactive flux across a dividing surface on the potential energy surface. Versions based on classical as well as quantum mechanics are described. The classical version and its relation to Wigner’s variational theorem and recrossings of the dividing surface is discussed. Neglecting recrossings, an approximate result based on the calculation of the classical one-way flux from reactants to products is considered. Recrossings can subsequently be included via a transmission coefficient. An alternative exact expression is formulated based on a canonical average of the flux time-correlation function. It concludes with the quantum mechanical definition of the flux operator and the derivation of a relation between the rate constant and a flux correlation function.

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