Dissociation kinetics of the solvated electron species in methylamine and methylamine–ammonia mixtures

1982 ◽  
Vol 60 (4) ◽  
pp. 445-455 ◽  
Author(s):  
Y. Harima ◽  
H. Kurihara ◽  
Y. Nishiki ◽  
S. Aoyagui ◽  
K. Tokuda ◽  
...  
Keyword(s):  
Rate Constant ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Formation Constants ◽  
Dissociation Rate ◽  
Theoretical Treatment ◽  
Solvated Electron ◽  
Dissociation Kinetics ◽  
Potential Sweep ◽  
The One

Potential-sweep voltammetric and potential-step chronoamperometric experiments were made at −50 °C with solvated electrons in methylamine containing LiCl, KI, or CsI. The dissociation rate constants of the ion pairs, (M+•es−), M being alkali metal and es− free solvated electron, were greater than 103 s−1. The pseudo-first-order rate constant of the dissociation of K− into the one-electron species, es− and (K+•es−) in rapid equilibrium, was determined as 40 s−1 by chronoamperometry with 0.5 M KI solutions. The formation constants of K− from the one-electron species determined by chronoamperometry and voltammetry were 4.5 × 104 M−1 and 5.6 × 104 M−1, respectively. An addition of a small amount of ammonia to methylamine caused a decrease in the formation constant of K− and an increase in its dissociation rate constant. The appendix deals with a theoretical treatment of chronoamperograms for an electrode process preceded by the dissociation of a dimer. The boundary value problem was solved by the explicit finite difference method and the analytical method which was based on the concept of reaction layer.

Dissociation kinetics of potassium anion in methylamine

1980 ◽  
Vol 58 (11) ◽  
pp. 1151-1153 ◽  
Author(s):  
Y. Harima ◽  
H. Kurihara ◽  
S. Aoyagui
Keyword(s):  
Rate Constant ◽  
Supporting Electrolyte ◽  
Order Rate Constant ◽  
Dissociation Kinetics ◽  
Potential Sweep ◽  
Solvated Electrons ◽  
Potential Step ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

The potential-sweep voltammograms of solvated electrons in methylamine containing KI as the supporting electrolyte demonstrate the coexistence of one- and two-electron species in equilibrium. The it1/2 vs. log t curve obtained with potential-step chronoamperometry exhibits a transient part between two plateaux. The analysis of this curve yields the approximate value of 102 s−1 for the first-order rate constant of the dissociation of the two-electron species, K−.

Observation of a radical intermediate in the one electron oxidation of 5-methyl-1-thia-5-azacyclooctane by •Br2−

1984 ◽  
Vol 62 (9) ◽  
pp. 1874-1876 ◽  
Author(s):  
Warren Kenneth Musker ◽  
Parminder S. Surdhar ◽  
Rizwan Ahmad ◽  
David A. Armstrong
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Half Life ◽  
Cation Radical ◽  
Order Rate Constant ◽  
Type Structure ◽  
Radical Intermediate ◽  
Text Type ◽  
First Order ◽  
The One

The one electron oxidant •Br2− reacts with 5-methyl-1-thia-5-azacyclooctane (4) in aqueous solution at high pH with an overall rate constant of ~2 × 108 M s−1. The radical intermediate produced has a broad maximum at 500 nm with ε = 2400 M−1 cm−1 and at pH 10 decays with a first order rate constant of 2.3 ± 0.3 × 104 s−1, first half-life of 30 ± 5 μs. Its characteristics do not correspond to those of the [Formula: see text] species reported by Asmus and co-workers. The species appears to be the same as the cation radical reported earlier in the one electron oxidation of 4 in acetonitrile. This species is considered to have an [Formula: see text] type structure, which provides transannular stabilization.

The homogeneous decomposition reactions of gaseous formic acid

1960 ◽  
Vol 255 (1283) ◽  
pp. 444-455 ◽  
Keyword(s):  
Formic Acid ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Second Order ◽  
Unimolecular Decomposition ◽  
Order Component ◽  
First Order ◽  
Homogeneous Decomposition

By use of reaction vessels with specially treated surfaces the homogeneous decomposition of formic acid has been studied kinetically in the range 436 to 532°C. Neither of the two simultaneous reactions ( a ) HCOOH = CO 2 + H 2 , ( b ) HCOOH = CO + H 2 O, is retarded by the usual inhibitors of chain processes. Each appears to be molecular. Reaction ( a ) is of the first order in the range 3 to 650 mm, the first-order rate constant being given by k CO 2 = 10 4⋅8 exp (–30600/ RT )s -1 . It is suggested tentatively that the abnormal kinetic parameters might be explained by regarding the reaction as a decarboxylation of (H + ) (HCOO¯) ion pairs present in minute concentration. Reaction ( b ) shows a pressure dependence most simply explained by a superposition of a predominant second-order component with a small first-order component. The most satisfactory interpretation of the second-order reaction is that it represents the unimolecular decomposition of dimer molecules, known to be present in formic-acid vapour. On this basis the rate constant is given by k CO dimer = 10 13⋅58 exp (–42600/ RT )s -1 , the kinetic parameters thus being in the normal range. The various alternative interpretations are discussed.

scholarly journals Effects of charged lipids on the interaction of cholesteryl ester transfer protein with lipid microemulsions

1997 ◽  
Vol 322 (1) ◽  
pp. 159-165 ◽  
Author(s):  
Otthakal V. RAJARAM ◽  
William H. SAWYER
Keyword(s):  
Cholesteryl Ester ◽  
Surface Charge ◽  
Rate Constant ◽  
Cholesteryl Ester Transfer Protein ◽  
Egg Yolk ◽  
Order Rate Constant ◽  
Cholesteryl Oleate ◽  
Dissociation Rate ◽  
Excimer Fluorescence ◽  
Transfer Protein

This study reports the effects of charged lipids on the transfer of cholesteryl-1-pyrene decanoate (Py-CE) between apolipoprotein-free microemulsion particles mediated by cholesteryl ester transfer protein (CETP). The surface charge characteristics of microemulsion particles composed of cholesteryl oleate and egg yolk phosphatidylcholine were altered by incorporating phosphatidylserine, oleate or stearylamine into the phosphatidylcholine that forms the surface monolayer of the particle. The transfer of Py-CE was measured continuously by following the decrease in excimer fluorescence that accompanies the transfer of the probe from donor to acceptor particles [Rajaram, Chan and Sawyer (1994) Biochem. J. 304, 423Ő430]. The inclusion of 20 mol% phosphatidylserine relative to the phospholipid in the surface monolayer of the emulsion caused a 64% decrease in the first-order rate constant describing the transfer. An increase in ionic strength caused a partial reversal of this effect, indicating that electrostatic factors are only partially responsible for the interaction with lipid. Complete inhibition of transfer was observed when 10 mol% sodium oleate was incorporated into the surface monolayer. The incorporation of stearylamine into the emulsion caused a 32% increase in the transfer rate. The binding of CETP to the different emulsion surfaces was also examined using a surface plasmon resonance biosensor. The presence of negatively charged lipid (phosphatidylserine or oleic acid) decreased the rate of association of CETP with the emulsion without a significant change in the dissociation rate constant. The presence of the positively charged lipid stearylamine increased the rate of association of CETP with the lipid surface. It is concluded that a negative surface charge on the monolayer decreases the rate of transfer by decreasing the affinity of CETP for these particles.

scholarly journals A fragment of antithrombin that binds both heparin and thrombin

1986 ◽  
Vol 237 (3) ◽  
pp. 639-646 ◽  
Author(s):  
L Rosenfeld ◽  
I Danishefsky
Keyword(s):  
Rate Constant ◽  
Inhibitory Activity ◽  
Order Rate Constant ◽  
Neutralizing Activity ◽  
Unique Fragment ◽  
High Concentrations ◽  
The One ◽  
A Site ◽  
Polypeptide Chains ◽  
Inhibition Of Thrombin

In order to identify the regions of antithrombin that interact with heparin and thrombin, it was degraded with CNBr and the activities of the isolated products were investigated. These fragments did not exhibit direct thrombin-neutralizing activity; however, one unique fragment was found to bind to heparin-Sepharose and also to interfere with the inhibition of thrombin by intact antithrombin. This fragment was identified as the one consisting of three disulphide-linked polypeptide chains containing residues 1-17, 104-251 and 424-432. At a concentration of 46 nM, this product decreased the heparin-enhanced thrombin-inhibitory activity of antithrombin by half, and completely abolished this inhibition when above 300 nM. In the absence of heparin, the action of antithrombin was not completely nullified by the fragment, even when present at relatively high concentrations. At a given fragment concentration, the extent of inhibition was independent of antithrombin concentration over the range tested. It was found that the fragment decreased the second-order rate constant for the antithrombin-thrombin reaction. Reduction and alkylation of the fragment showed that the above properties reside primarily in the peptide with residues 104-251. It is concluded that this peptide possesses portions of the antithrombin molecule that bind to heparin as well as to a site on thrombin.

scholarly journals The rates of formation and dissociation of actin-myosin complexes. Effects of solvent, temperature, nucleotide binding and head-head interactions

1982 ◽  
Vol 203 (2) ◽  
pp. 453-460 ◽  
Author(s):  
S B Marston
Keyword(s):  
Rate Constant ◽  
Protein Concentration ◽  
Order Rate Constant ◽  
Dissociation Rate ◽  
Dissociation Rate Constant ◽  
Light Scatter ◽  
Association Rate Constant ◽  
Heavy Meromyosin ◽  
Association Rate ◽  
Low Protein

The rates of formation and dissociation of actin-subfragment 1 and actin-heavy mero-myosin complexes were measured by using light-scatter and the change in fluorescence of N-iodoacetyl-N'-(5-sulpho-1-naphthyl)ethylenediamine (IAEDANS)-labelled acting as probes. Association rate measurements were made at low protein concentration, where the transients approximated to single exponentials with rate constants proportional to the concentration of reactant in excess. Dissociation rate measurements were made by displacing IAEDANS-actin from myosin with excess native actin and by a salt jump. The second-order rate constant of association for actin-subfragment 1 was 3 × 10(6) M-1 . s-1 in 60 mM-KCl at 13 degree C. It was decreased 10-fold in 500 mM-KCl and in 50% (v/v) glycol. It was decreased 6-fold when MgADP or Mg[beta gamma-imido]ATP bound to myosin. The dissociation rate constant was 0.012 s-1 in 60 mM-KCl at 13 degree C. It was increased 4-fold by 500 mM-KCl, 25-fold by 50% glycol, 8-fold by MgADP binding and 170-fold by Mg[beta gamma-imido]ATP binding. Ea for association was 70 kJ . mol-1 and for dissociation 35 kJ . mol-1. Heavy meromyosin associated at twice the rate observed for subfragment 1 and dissociated at less than one-twentieth of the rate for subfragment 1 (60 mM-KCl, 25 degree C), but when Mg[beta gamma-imido]ATP bound actin-heavy meromyosin dissociated at one-half the rate for subfragment 1. There were significant correlations between increase in the dissociation rate constant, decrease in binding constant and increase in magnitude of conformational change. The association rate constant did not correlate with any property of the actin-myosin complex.

ON THE KINETICS OF THE INHIBITION OF PLASMINOGEN ACTIVATORS BY THE PLASMINOGEN ACTIVATOR INHIBITOR PAI-1

1987 ◽  
Author(s):  
J Chmielewska ◽  
B Wiman
Keyword(s):  
Plasminogen Activator ◽  
Rate Constant ◽  
Rate Constants ◽  
Plasminogen Activator Inhibitor ◽  
Plasminogen Activators ◽  
Order Rate Constant ◽  
Association Reaction ◽  
The One ◽  
Kinetics Of ◽  
Pai 1

The kinetics of the inhibition of the following plasminogen activators: one- and two-chain tissue plasminogen activator (t-PA) and low and high molecular weight urokinase (UK) by PAI-1 was studied. For this purpose direct systems were employed and the reactions were studied in the presence of different concentrations of plasminogen activator chromogenic substrates. The second-order rate constant of the association reaction was estimated from the initial decline in plasminogen activator activity. Determination of the rate constants in the absence of substrates was performed by plotting the rate constants versus the substrate concentrations and extrapolation to zero concentration. The rate constants with all plasminogen activators were very similar and estimated as 2 - 4 x 107 M-1 x s-1. The reactions were also studied in the presence of 6-aminohexanoic acid, lysine, arginine, guanidinium chloride (final concentrations for all substances about 1 mmol/L) and heparin (10 mg/L), without any significant effect on the rate constants. The effect of soluble fibrin (bathroxobin-digested fibrinogen in urea) at 10 - 300 nmol/L was also studied. With one-chain t-PA the rate constant was decreased about 10-fold with the highest fibrin concentration and about 2-fold at 30 nmol/L. In contrast, the reactions with urokinase or two-chain t-PA were not influenced by fibrin at these concentrations. These findings may have a physiological significance: the one-chain t-PA adsorbed to the fibrin surface and actively involved in fibrinolysis would be protected against inactivation by PAI. This phenomenon adds further to the physiological fibrin specificity of one-chain t-PA.

Formation and Decay of the Vanadate Complex of the Sarcoplasmic Reticulum Calcium Transport Protein

1985 ◽  
Vol 40 (11-12) ◽  
pp. 876-879 ◽  
Author(s):  
Pankaj Medda ◽  
Wilhelm Hasselbach
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Transport ◽  
Dissociation Rate ◽  
Decay Kinetics ◽  
Dissociation Kinetics ◽  
Ligand Binding Sites ◽  
Sequential Mode ◽  
Quaternary Complex ◽  
The One ◽  
Sarcoplasmic Reticulum Calcium

Abstract The calcium free sarcoplasmic reticulum calcium transport ATPase incorporates in the presence of magnesium ions approx. 8 nmol monovanadate per mg protein, indicating the formation of a complex containing one vanadate residue per enzyme molecule. On ligand-removal or dilution, the saturated enzyme complex displays biphasic decay kinetics, while the unsaturated complex slowly dissociates monophasically. - Ligand competition by raising the concentrations of unlabeled vanadate results in a progressive decrease of the dissociation rate of the unsaturated enzyme. The complicated dissociation kinetics indicate a sequential mode of interaction between two ligand binding sites. The one to one stoichiometry of the complex suggests that the two sites are located at adjacent ATPase molecules. - It appears unlikely that the decay of the enzyme, vanadate complex is retarded by the formation of a stable quaternary complex between the enzyme, magnesium, mono-and polyvanadate.

Trajectory study of dissociation reactions. Br2 in Ar at 3500 K

1977 ◽  
Vol 55 (3) ◽  
pp. 380-382 ◽  
Author(s):  
D. T. Chang ◽  
George Burns
Keyword(s):  
High Temperatures ◽  
Rate Constant ◽  
Rate Coefficient ◽  
Dissociation Rate ◽  
Experimental Results ◽  
Dissociation Rate Constant ◽  
Trajectory Calculations ◽  
Order Of Magnitude ◽  
Nonequilibrium Effects ◽  
The One

Dissociation of Br2 in Ar was studied at 3500 K using classical 3-D trajectory technique, and compared with earlier trajectory calculations. Some of the assumptions used previously were eliminated, while others were studied in some detail. The one-way flux, equilibrium rate coefficient, obtained from over 8400 trajectories, was found to be over an order of magnitude larger than the experimental rate constant. This was taken as an indication that at high temperatures the nonequilibrium effects are important in dissociation reactions. In order to understand these effects better, additional calculations using an improved set of assumptions were performed. The calculated dissociation rate constant for Br2 + Ar → 2Br + Ar reaction, which accounted for nonequilibrium effects, agrees reasonably well with experimental results.

Development of Sustained Release Multi-Component Microparticulate System of Diclofenac Sodium and Tizanidine Hydrochloride

1970 ◽  
Vol 1 (1) ◽  
pp. 97-105
Author(s):  
Kamlesh Dashora ◽  
Shailendra Saraf ◽  
Swarnalata Saraf
Keyword(s):  
Particle Size ◽  
Sustained Release ◽  
Cellulose Acetate ◽  
Rate Constant ◽  
Diclofenac Sodium ◽  
Order Rate Constant ◽  
Anomalous Transport ◽  
First Order ◽  
Sem Study ◽  
Transport Type

Sustained released tablets of diclofenac sodium (DIC) and tizanidine hydrochloride (TIZ) were prepared by using different proportions of cellulose acetate (CA) as the retardant material. Nine formulations of tablets having different proportion of microparticles developed by varied proportions of polymer: drug ratio ‘’i.e.’’; 1:9 -1:3 for DIC and 1:1 – 3:1 for TIZ. Each tablet contained equivalent to 100 mg of DIC and 6mg of TIZ. The prepared microparticles were white, free flowing and spherical in shape (SEM study), with  the particle size varying from 78.8±1.94 to 103.33±1.28 µm and 175.92± 9.82 to 194.94±14.28µm for DIC  and TIZ, respectively.  The first order rate constant K1 of formulations were found to be in the range of  K1 = 0.117-0.272 and 0.083- 0.189 %hr-1for DIC and TIZ, respectively. The value of exponent coefficient (n) was found to be in the range of 0.6328-0.9412  and 0.8589-1.1954 for DIC and TIZ respectively indicates anomalous  to  non anomalous transport type of diffusions among different formulations

Sign in / Sign up

Export Citation Format

Share Document