Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 1. Polynuclear Hydroxyaluminum Cations

1971 ◽  
Vol 49 (10) ◽  
pp. 1683-1687 ◽  
Author(s):  
R. C. Turner ◽  
Wan Sulaiman
Keyword(s):  
Acetic Acid ◽  
Rate Constant ◽  
Empirical Equation ◽  
Decomposition Reaction ◽  
Order Rate Constant ◽  
Acetate Concentration ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Kinetics Of

The effect of varying 8-quinolinol and acetate concentration on the rate of decomposition of poly-nuclear hydroxyaluminum cations was studied. It was found that the concentration of the undissociated 8-quinolinol and acetic acid molecules determined the magnitude of the first order rate constant for the decomposition of the polynuclear hydroxyaluminum cations, except when the acetate concentrations were relatively high. With high acetate concentrations, it appeared that polynuclear acetate species were involved in the reactions. An empirical equation was developed showing the effect of 8-quinolinol and acetic acid molecule concentrations on the pseudo first order rate constant for the decomposition reaction.

Kinetics of reconstitution of apotyrosinase by copper

1990 ◽  
Vol 68 (2) ◽  
pp. 476-479
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constant ◽  
Copper Concentration ◽  
Copper Ions ◽  
Copper Ion ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

scholarly journals Inactivation of the endogenous argininosuccinate lyase activity of duck δ-crystallin by modification of an essential histidine residue with diethyl pyrocarbonate

1993 ◽  
Vol 293 (2) ◽  
pp. 537-544 ◽  
Author(s):  
H J Lee ◽  
S H Chiou ◽  
G G Chang
Keyword(s):  
Enzyme Activity ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Histidine Residue ◽  
Argininosuccinate Lyase ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Order Rate ◽  
Lyase Activity ◽  
Pseudo First Order

The argininosuccinate lyase activity of duck delta-crystallin was inactivated by diethyl pyrocarbonate at 0 degrees C and pH 7.5. The inactivation followed pseudo-first-order kinetics after appropriate correction for the decomposition of the reagent during the modification period. The plot of the observed pseudo-first-order rate constant versus diethyl pyrocarbonate concentration in the range of 0.17-1.7 mM was linear and went through the origin with a second-order rate constant of 1.45 +/- 0.1 M-1.s-1. The double-logarithmic plot was also linear, with slope of 1.13, which suggested a 1:1 stoichiometry for the reaction between diethyl pyrocarbonate and delta-crystallin. L-Arginine, L-norvaline or L-citrulline protected the argininosuccinate lyase activity of delta-crystallin from diethyl pyrocarbonate inactivation. The dissociation constants for the delta-crystallin-L-arginine and delta-crystallin-L-citrulline binary complexes, determined by the protection experiments, were 4.2 +/- 0.2 and 0.12 +/- 0.04 mM respectively. Fumarate alone had no protective effect. However, fumarate plus L-arginine gave synergistic protection with a ligand binding interacting factor of 0.12 +/- 0.02. The double-protection data conformed to a random Uni Bi kinetic mechanism. Fluorescence-quenching studies indicated that the modified delta-crystallin had minimum, if any, conformational changes as compared with the native delta-crystallin. Inactivation of the enzyme activity was accompanied by an increasing absorbance at 240 nm of the protein. The absorption near 280 nm did not change. Treatment of the modified protein with hydroxylamine regenerated the enzyme activity to the original level. These results strongly indicated the modification of an essential histidine residue. Calculation from the 240 nm absorption changes indicated that only one histidine residue per subunit was modified by the reagent. This super-active histidine residue has a pKa value of approximately 6.8 and acts as a general acid-base catalyst in the enzyme reaction mechanism. Our experimental data are compatible with an E1cB mechanism [Raushel (1984) Arch. Biochem. Biophys. 232, 520-525] for the argininosuccinate lyase with the essential histidine residue close to the arginine-binding domain of delta-crystallin. L-Citrulline, after binding to this domain, might form an extra hydrogen bond with the essential histidine residue.

Kinetics of Exchange of Dimethylsulfoxide between Hexakis(dimethylsulfoxide)chromium(III) and Solvent: Pressure Effect and Mechanism

1973 ◽  
Vol 51 (22) ◽  
pp. 3795-3798 ◽  
Author(s):  
Debra Lynn Carle ◽  
Thomas Wilson Swaddle
Keyword(s):  
Rate Constant ◽  
Pressure Effect ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

For the exchange of all six dimethylsulfoxide (DMSO) ligands in Cr(DMSO)63+ with perdeuterated DMSO solvent, the first-order rate constant (75°) = 5.5 × 10−5 s−1, while ΔH* = 23.1 kcal mol−1, ΔS* = − 11.8 cal deg−1 mol−1, and ΔV* = − 11.3 cm3 mol−1. These and other data are indicative of an associative interchange mechanism for substitution in Cr(III) DMSO complexes in DMSO.

Oxidation of the mercurous ion by peroxidase

1986 ◽  
Vol 64 (5) ◽  
pp. 969-972 ◽  
Author(s):  
Donald C. Wigfield ◽  
Season Tse
Keyword(s):  
Elemental Mercury ◽  
Order Rate Constant ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Cold Vapour ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Mercurous Ion

The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.

Optical kinetic method for calibration of spectrophotometer temperature: demonstration with the Cobas-Bio analyzer.

1987 ◽  
Vol 33 (10) ◽  
pp. 1891-1895 ◽  
Author(s):  
E K Armitage ◽  
W G Miller
Keyword(s):  
Analysis Of Variance ◽  
Rate Constant ◽  
Kinetic Method ◽  
Order Rate Constant ◽  
Time Intervals ◽  
First Order ◽  
Order Rate ◽  
Analytical Imprecision ◽  
Pseudo First Order ◽  
Temperature Errors

Abstract The pseudo-first-order rate constant for the Jaffé reaction with creatinine varies logarithmically with temperature and was calibrated in the range 25 to 37 degrees C to measure the temperature of the liquid in the lightpath of spectrophotometric instrumentation. The reagent concentrations can be adjusted to permit rate-constant measurements in time intervals from a few seconds to several minutes. The temperature increment that can be resolved is limited only by the analytical imprecision of the instrumentation used to measure the rate constant and the calibration temperature. In this investigation, a temperature SD of 0.03 degrees C could be measured. Two Cobas-Bio centrifugal analyzers, used to demonstrate the utility of this technique, were found to have temperature errors from -1.0 to -1.7 degrees C in the 30 to 37 degrees C range and overall temperature SD of 0.19 and 0.36 degree C, respectively, at 37 degrees C. Analysis of variance gave between-rotor SD of 0.14 and 0.34 degrees C and within-rotor SD of 0.13 and 0.11 degree C, respectively. We found temperature differences of 0.3 degree C between cuvets in a rotor, and gradients of 0.3 and 0.4 degree C, respectively, from the top to bottom of an individual cuvet in the two instruments.

Inactivation Of Purified Human Platelet Cyclic Amp Phosphodiesterase By The Affinity Label 2’-O-Iodohydrin-P-Cyclic Amp

1981 ◽  
Author(s):  
P G Grant ◽  
R F Colman ◽  
A K Sinha ◽  
R W Colman
Keyword(s):  
Cyclic Amp ◽  
Rate Constant ◽  
Active Site ◽  
Human Platelet ◽  
Order Rate Constant ◽  
Supernatant Fraction ◽  
First Order ◽  
Cyclic Amp Phosphodiesterase ◽  
Order Rate ◽  
Pseudo First Order

Cyclic AMP phosphodiesterase (PDE) is a regulatory enzyme in human platelets. Inhibitors of this enzyme raise intracellular cAMP which prevents platelet activation. Little is known about the biochemistry of this enzyme. PDE was isolated from human platelet concentrates by nitrogen bomb cavitation. The specific activity of PDE in cell lysate was 0.064 nmoles cAMP hydrolysed/min/mg protein at 22° , 1 µM cAMP. Eighty percent of the activity appeared in the 100,000 × g supernatant fraction. Chromatography was performed on DEAE cellulose equibrated with 50 mM Tris- acetate pH 6.0, 3.75 mM 2-mercaptoethanol. A linear gradient with a limiting salt concentration of 1.0 M Na acetate separated two peaks of PDE activity. The first had a for cAMP of >100 µM; the second had a Km for cAMP of 5 µM. The lower enzyme was further purified by adsorption on blue dextran Sepharose in 50 mM Tris pH 7.5, 2 mM MgCl2 followed by affinity elution with 1 mM cAMP in the same buffer. These steps resulted in a 1700 purification of the enzyme (113 nmoles/min/mg). The compound 2’-0-iodohydrin- p-cAMP (IH-cAMP) is a cAMP derivative with an alkylating side chain. Incubation of PDE with 5 mM IH-cAMP at 37° resulted in 88% inactivation of the enzyme at 15 hours, compared to a control, with a corrected pseudo-first-order rate constant of 0.144 h-1. When cAMP (100 µM) was included in the inactivation mixture the corrected pseudo-first-order rate constant decreased to 0.064 h-1l. Thus, a 20-fold excess of cAMP protected 56% against inactivation by IH- cAMP. The inhibition was not reversed by gel filtration of the inactivated enzyme which removed IH-cAMP. These results suggest that IH-cAMP reacts with the active site of PDE to irreversibly inactivate the enzyme. IH-cAMP should prove to be a useful tool in understanding the chemistry of the active site of this important enzyme.

scholarly journals Application of polymer-coated Macadamia integrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Malvin Moyo ◽  
Sekomeng Johannes Modise ◽  
Vusumzi Emmanuel Pakade
Keyword(s):  
Formic Acid ◽  
Rate Constant ◽  
Redox Reaction ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Chromium Vi ◽  
Relative Standard ◽  
Pseudo First Order ◽  
Catalyst Dosage

AbstractFreely suspended and porous basket restrained granules of palladium nanoparticles supported on polymer-grafted Macadamia nutshell biomass (Pd@Polym-MNS) composite were used for the treatment chromium(VI)-containing water. In the presence of formic acid, the Pd@Polym-MNS demonstrated its activity in the adsorption-reduction-based conversion of noxious chromium(VI) to less toxic chromium(III) with a low activation energy of 13.4 kJ mol–1, ΔH0 (+ 10.8 kJ mol–1), ΔS0 (−270.0 J mol–1 K–1), and ΔG0 (+ 91.3 to + 98.0 kJ mol–1) indicated the exothermic, endergonic and non-spontaneous nature of the catalytic redox reaction. In addition to facilitating easy recovery, rinsing, and reuse, restraining the Pd@Polym-MNS in the basket reactor helped maintain the integrity of the catalysts by preventing violent collisions of suspended granules with the mixing apparatus and the walls of the reaction vessel. Whereas the pseudo-first-order rate constant was recorded as 0.157 min–1 upon initial use, values of the mean and relative standard deviation for the second, third and fourth consecutive uses were found to be 0.219 min–1 and 1.3%, respectively. According to a response surface methodological approach to batch experimentation, the initial concentration of chromium(VI) and catalyst dosage had the greatest impact on the redox reaction rate, accounting for 85.7% and 11.6% of the variability in the value of the pseudo-first-order rate constant, respectively. Mutually beneficial effects of the combinations of high formic acid and low chromium(VI) concentration, high temperature and catalyst dosage as well as high formic acid and catalyst dosage were recorded.

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−.

scholarly journals Kinetics of the interaction of chymotrypsin with eglin c

1991 ◽  
Vol 280 (1) ◽  
pp. 27-32 ◽  
Author(s):  
B Faller ◽  
J G Bieth
Keyword(s):  
Rate Constant ◽  
Proteinase Inhibitor ◽  
Enzyme Inhibitor ◽  
Order Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Wide Range ◽  
Eglin C ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of binding of recombinant eglin c to bovine pancreatic chymotrypsin was studied by conventional and stopped-flow techniques. With nanomolar enzyme and inhibitor concentrations, the inhibition was fast and pseudo-irreversible (k(assoc.) = 4 x 10(6) m-1.s-1 at 7.4 and 25 degrees C). Reaction of the enzyme-inhibitor complex with alpha 1-proteinase inhibitor, an irreversible chymotrypsin ligand, resulted in a slow release of free eglin c, which was monitored by electrophoresis (k(dissoc.) approximately 1.6 x 10(-6) s-1, t1/2 approximately 5 days). The proflavin displacement method and a stopped-flow apparatus were used to monitor the association of chymotrypsin with eglin c under a wide range of inhibitor concentration and under pseudo-first-order conditions. At pH 7.4 and 25 degrees C or 5 degrees C, or at pH 5.0 and 25 degrees C, the pseudo-first-order rate constant of proflavin displacement increased linearly with eglin c up to the highest concentration tested, suggesting a one-step bimolecular association reaction: E + I in equilibrium with EI. However, kassoc. is much lower than the rate constant for a bimolecular reaction and its activation energy (66 kJ.mol-1 at pH 7.4 and 78 kJ.mol-1 at pH 5.0) is far too high for a diffusion-controlled step. The enzyme-inhibitor association may therefore occur via a loose pre-equilibrium complex EI* (Ki* much greater than 5 x 10(-4) M) that rapidly isomerizes (k2 much greater than 2 x 10(3) s-1) into an extremely stable final complex (Ki approximately 4 x 10(-13) M). Unlike other proteinase-inhibitor systems, the chymotrypsin-eglin association is virtually pH-independent.

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