Estimation of rate constants for near-diffusion-controlled reactions in water at high temperatures

1990 ◽  
Vol 86 (9) ◽  
pp. 1539 ◽  
Author(s):  
A. John Elliot ◽  
David R. McCracken ◽  
George V. Buxton ◽  
Nicholas D. Wood
Keyword(s):  
High Temperatures ◽  
Rate Constants ◽  
Diffusion Controlled

Measurements of the bimolecular rate constants for S + O2 ? SO + O and CS2 + O2 ? CS + SO2 at high temperatures

1986 ◽  
Vol 18 (8) ◽  
pp. 871-884 ◽  
Author(s):  
Ko Saito ◽  
Yuji Ueda ◽  
Reiko Ito ◽  
Terumitsu Kakumoto ◽  
Akira Imamura
Keyword(s):  
High Temperatures ◽  
Rate Constants

Modulation spectroscopy. Kinetics for the self-reactions of some α-aminoalkyl radicals in solution

1982 ◽  
Vol 60 (3) ◽  
pp. 274-278 ◽  
Author(s):  
Paul R. Marriott ◽  
Arlindo L. Castelhano ◽  
David Griller
Keyword(s):  
Absorption Spectrum ◽  
Reaction Kinetics ◽  
Unpaired Electron ◽  
Rate Constants ◽  
Lone Pair ◽  
The Self ◽  
Modulation Spectroscopy ◽  
Alkyl Radicals ◽  
Diffusion Controlled ◽  
Kinetics Of

The optical spectra and reaction kinetics of some a-aminoalkyl radicals, RĊHN(CH2R)2; R≡H, Me, Ph, were measured in solution using the technique of modulation spectroscopy. These radicals undergo diffusion controlled self-reaction with rate constants [Formula: see text]. When R≡Ph, the absorption spectrum has a well defined maximum at 346 nm; ε = 3390 M−1 cm−1, while the spectra when R≡H or Me were less intense [Formula: see text] and tailed into the visible. These spectra are substantially red-shifted when compared with those of simple alkyl radicals, an effect which is thought to be due to the interaction between the unpaired electron and the lone pair of electrons on nitrogen.

scholarly journals Effect of heparin on the glia-derived-nexin-thrombin interaction

1989 ◽  
Vol 257 (1) ◽  
pp. 191-196 ◽  
Author(s):  
A Wallace ◽  
G Rovelli ◽  
J Hofsteenge ◽  
S R Stone
Keyword(s):  
Rate Constants ◽  
Antithrombin Iii ◽  
Kinetic Properties ◽  
Association Rate ◽  
High Affinity ◽  
Diffusion Controlled ◽  
Different Types ◽  
Human Thrombin ◽  
Alpha Beta ◽  
Association Rate Constants

In order to determine the specificity of the interaction between thrombin and glia-derived nexin (GdN), the inactivation of proteolytically modified human thrombin species by GdN has been studied. The second-order rate constants for the inactivation of alpha-, beta T-, gamma T- and epsilon-thrombin by GdN were 1.41, 0.63, 0.33 and 1.91 microM-1.s-1 respectively. The kinetic properties of gdN were also investigated in the presence of different types of heparin, fractionated according to antithrombin III-binding affinity. Association rate constants of both gdN and antithrombin III with alpha-thrombin were obtained using unfractionated, low- and high-affinity heparin types. The different heparin types gave optimal rates of inhibition at similar heparin concentrations for both inhibitors. At optimal heparin concentrations, the rate of inactivation of alpha-thrombin by GdN was 0.5-1.2 nM-1.s-1, which suggests that, under these conditions, the interaction is diffusion-controlled.

CHEMICALLY-CONTROLLED REACTION KINETICS ON FRACTALS: APPLICATION TO HYDROGEN EXCHANGE IN LYSOZYME

Fractals ◽  
1995 ◽  
Vol 03 (02) ◽  
pp. 251-267 ◽  
Author(s):  
T. GREGORY DEWEY
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Isotope Exchange ◽  
Time Course ◽  
Hydrogen Exchange ◽  
Chemical Processes ◽  
General Mechanism ◽  
Structure Information ◽  
Diffusion Controlled ◽  
Encounter Complex

The effect of time-dependent diffusional rate constants on chemically-controlled reactions in solution is considered. A general mechanism is examined that consists of a two step process. First the reactants diffuse together to form an “encounter complex.” This is followed by the collapse of the complex to the final product. The first step is diffusion controlled and the second step is chemically controlled. For reactions in restricted geometries or on fractals the rate constants associated with the diffusive process will scale with time as t−h where h is a constant between 0 and 1. The chemical processes are assumed to have time-independent rate constants. For reactions in which the encounter complex achieves a steady state, the differential equations governing the time course of the reaction can be solved exactly. At short times, the concentration of the reactants decays exponentially, reflecting the time constant of the chemical processes. At longer times, the decreasing diffusive rate constants result in the process being diffusion controlled. A stretched exponential of the form, exp{−kt1−h}, is observed. Approximate solutions for the pre-steady state behavior of the system are also determined using a Liouville transformation and corresponding asymptotic expansions. The short time regime shows power law decays of reactants. These decays will depend both on the dimensionality of the system as well as on the value of the rate constants associated with individual steps in the mechanism. Conditions can exist where a transformation to logarithmic oscillations will occur. Using this theoretical foundation a model is developed to analyze the kinetics of hydrogen isotope exchange kinetics in proteins. The exchange reaction is assume to occur in the boundary volume of the protein. Using the predicted fractal dimension of this boundary volume, scaling exponents are calculated and used as an unadjusted parameter. Highly accurate fits to the experimental data are achieved and activation energies are obtained that reflect the energetics of isotope exchange. This approach allows chemical kinetic behavior to be predicted from X-ray structure information.

Proton Transfer Kinetics in Medium-strong Inorganic Acids

1973 ◽  
Vol 51 (14) ◽  
pp. 2297-2305 ◽  
Author(s):  
David Charles Hodgkin ◽  
Peeter Kruus
Keyword(s):  
Proton Transfer ◽  
Aqueous Solutions ◽  
Rate Constants ◽  
Reasonable Agreement ◽  
Ultrasonic Absorption ◽  
Absolute Rate ◽  
Absorption Data ◽  
Inorganic Acids ◽  
Diffusion Controlled ◽  
Excess Absorption

A method of obtaining relative and absolute rate constants for proton transfer equilibria is described. It is suitable for equilibria of the type[Formula: see text]in dilute (< 0.1 M) solutions of medium strong inorganic acids. To obtain absolute values of kd, kr it is necessary to know the value of ΔV0 for the equilibrium. Ultrasonic absorption data for aqueous solutions of H3PO4, H3AsO4, and H2SO4 at 20, 10, and 0 °C are presented together with data at 20 °C for H3PO3, H2SeO3, HIO4, NaHSO4, KHSO4, and NH4HSO4. From analysis of the concentration dependence of the excess absorption, values of Ka are calculated for these acids, and values of kd, kr for those where ΔV0 is available. The Ka obtained are in reasonable agreement with literature values except for HIO4 and H2SeO4. The absolute values of kr for H3PO4, H3AsO4, and HSO4− indicate that the diffusion controlled recombination process postulated is complete when the ions are about 15 Å from each other.

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