Bond Scission in Sulfur Compounds. Part X. The Hydrazinolysis of Methyl p-Nitrophenyl Sulfate

1975 ◽  
Vol 53 (9) ◽  
pp. 1275-1280 ◽  
Author(s):  
Erwin Buncel ◽  
Claudio Chuaqui
Keyword(s):  
Kinetic Data ◽  
Order Rate Constant ◽  
Rate Data ◽  
Sulfate Ion ◽  
First Order ◽  
Nucleophilic Displacement ◽  
Bond Scission ◽  
Different Types ◽  
Acid Catalyzed ◽  
Pseudo First Order

Reaction of methyl p-nitrophenyl sulfate with the hydrazine – hydrazine hydrochloride system in methanol gives rise to different types of behavior depending on the state of ionization of the reagent. For the H2NNH2/H2NNH3+ combination the observed reaction is conversion of methyl p-nitrophenyl sulfate to p-nitrophenyl sulfate ion (alkyl–oxygen scission). For the H2NNH3+/+H3NNH3+ combination, or with +H3NNH3+ alone, one observes the consecutive processes methyl p-nitrophenyl sulfate → p-nitrophenyl sulfate ion → p-nitrophenol (alkyl–oxygen followed by sulphur–oxygen scission). For the alkyl–oxygen scission process, i.e. nucleophilic displacement on the alkyl carbon, the observed pseudo first-order rate constant is given by the contributions of several nucleophilic species; [Formula: see text] A method for the dissection of kobs into the constituent terms is given. The sulphur–oxygen scission process is an acid catalyzed reaction and the measured kinetic data have been utilized for the derivation of the pKa of +H3NNH3+ in methanol. Rate data for the conversion of sodium p-nitrophenyl sulfate to p-nitrophenol in methanol containing HCl have also been determined in this connection.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

Acid-catalyzed Solvolysis of Isonitriles. I

1971 ◽  
Vol 49 (14) ◽  
pp. 2455-2459 ◽  
Author(s):  
Y. Y. Lim ◽  
A. R. Stein
Keyword(s):  
Formic Acid ◽  
Acid Catalysis ◽  
Hydrolysis Product ◽  
Rate Dependence ◽  
Linear Rate ◽  
First Order ◽  
Methyl Amine ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of methyl isonitrile has been examined. The initial hydrolysis product is N-methylformamide which is further hydrolyzed to methyl amine and formic acid at a much slower rate. The hydrolysis to N-methylformamide is pseudo-first order in methyl isonitrile and shows a linear rate dependence on concentration of general (buffer) acid at fixed pH. The significance of general acid-catalysis in terms of the mechanism of the hydrolysis is considered and taken as evidence for carbon protonation rather than nitrogen protonation as the initiating step.

Nonlinear Hammett Relationships in the Reaction of Peroxomonosulfate Anion (HOOSO3-) with meta- and para-Substituted Anilines in Alkaline Medium

2001 ◽  
Vol 66 (6) ◽  
pp. 897-911 ◽  
Author(s):  
Subbiah Meenakshisundaram ◽  
Ramanathan Sockalingam
Keyword(s):  
Nitrogen Atom ◽  
Equilibrium Constant ◽  
Rate Equation ◽  
Kinetic Data ◽  
Formation Constant ◽  
Order Rate Constant ◽  
Reactive Intermediate ◽  
Substituted Anilines ◽  
Experimental Conditions ◽  
First Order

The HOOSO3- oxidation of eleven meta- and para-substituted anilines to the corresponding nitrosobenzenes at pH ≈ 11 was characterized by the rate equation v = kK[OX][An]/(1 + K[An]). Formation constant of the reactive intermediate and its rate of decomposition were evaluated separately for ascertaining the structure-reactivity relationships. Under the experimental conditions the dianion, -O-O-SO3- is probably the effective electrophile. Kinetic data can be rationalized by a bimolecular process which involves the attack of nucleophilic nitrogen atom on the peroxidic oxygen. The highlight of the study is the opposite curvatures observed in the nonlinear Hammett plots of first-order rate constant k and the "equilibrium" constant K, being concave downward and upward, respectively.

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 Acrolein, an irreversible active-site-directed inhibitor of deoxyribose 5-phosphate aldolase?

1976 ◽  
Vol 153 (2) ◽  
pp. 495-497 ◽  
Author(s):  
D C Wilton
Keyword(s):  
Schiff Base ◽  
Rate Constant ◽  
Active Site ◽  
Order Rate Constant ◽  
Lysine Residue ◽  
Prolonged Incubation ◽  
Enzyme Active Site ◽  
First Order ◽  
Substrate Analogue ◽  
Pseudo First Order

The enzyme deoxyribose 5-phosphate aldolase was irreversibly inactivated by the substrate analogue acrolein with a pseudo-first-order rate constant of 0.324 min-1 and a Ki (apparent) of 2.7 × 10(-4) m. No inactivation was observed after prolonged incubation with the epoxide analogues glycidol phosphate and glycidaldehyde. It is suggested that the acrolein is first activated by forming a Schiff base with the enzyme active-site lysine residue and it is the activated inhibitor that reacts with a suitable-active-site nucleophile.

An automated approach to characterize, in simple kinetic terms, the generation and inactivation of thrombin and the interaction of fibrinogen with thrombin.

1988 ◽  
Vol 34 (10) ◽  
pp. 1971-1975 ◽  
Author(s):  
D R Hoak ◽  
S K Banerjee ◽  
G Kaldor
Keyword(s):  
Prothrombin Time ◽  
Rate Constant ◽  
Thrombin Generation ◽  
Order Rate Constant ◽  
Clinical Use ◽  
First Order ◽  
Pathological Conditions ◽  
Pseudo First Order ◽  
Instantaneous Concentration

Abstract Here, we used a fully automated, computer-directed centrifugal analyzer (which permitted simultaneous turbidimetry and calculation of results) and purified thrombin, fibrinogen, and various inhibitors to study clot formation. The Km and Vm for these reactions were useful in detecting and partly characterizing anticoagulants. We also explored the generation and inactivation of thrombin, using the two-stage prothrombin time and antithrombin activity tests. The amount of thrombin instantaneously generated and inactivated was monitored under artificially created pathological conditions. The pseudo-first-order rate constant for thrombin generation and inactivation and the instantaneous concentration of enzymatically active and inactive thrombin were used in the characterization of these conditions. We believe this approach is suitable for routine clinical use.

Kinetics and mechanisms of oxidations by metal ions. Part IV. Oxidation of phenylphosphinic acid by aquavanadium(V) ions

1985 ◽  
Vol 63 (3) ◽  
pp. 663-666 ◽  
Author(s):  
Raj Narain Mehrotra
Keyword(s):  
Acidic Solution ◽  
Active Form ◽  
Equilibrium Mixture ◽  
Order Rate Constant ◽  
First Order ◽  
Inactive Form ◽  
Pseudo First Order ◽  
Independent Path ◽  
Kinetics Of ◽  
Vanadium Ion

The kinetics of the oxidation of phenylphosphinic acid by quinquevalent vanadium ion have been investigated in aqueous perchlorate media under pseudo-first order conditions (phenylphosphinic acid in excess). The reaction has a first order dependence in [V(V)] and [phenylphosphinic acid] and the observed pseudo-first order rate constant kobs is given by kobs = a + b[H+].The acid-independent path is considered to be due to the reaction between VO2+ (aq.) and C6H5P:(OH)2, the active form of phenylphosphinic acid, while the reaction between V(OH)32+ (aq.) and C6H5P(O)(OH)H, the inactive form of phenylphosphinic acid, is considered to explain the acid-dependent path. Phenylphosphinic acid in aqueous acidic solution is known to exist as an equilibrium mixture of the active and inactive forms. The composite activation and thermodynamic parameters associated with the constants a and b are reported.

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.

Decolorization of Methyl Orange Simulated Wastewater by Chlorine Dioxide with Ultrasound

2011 ◽  
Vol 255-260 ◽  
pp. 2904-2908
Author(s):  
Li Jie Huang ◽  
Ting Xu ◽  
Shuang Fei Wang
Keyword(s):  
Methyl Orange ◽  
Rate Constant ◽  
Chlorine Dioxide ◽  
Oxidation Process ◽  
Order Rate Constant ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Effective Technology ◽  
Simulated Wastewater ◽  
Pseudo First Order

Experiments were conducted to investigate the decolorization of methyl orange simulated wastewater in order to assess the effectiveness and feasibility of ultrasound(US) enhanced high-purity chlorine dioxide(ClO2) oxidation process. The results showed that in ClO2/US system the decolorization rate of methyl orange was up to 96%, which was increased by 8% as compared to ClO2treatment alone. The decolorization of methyl orange with/without ultrasonic irradiation follows apparent pseudo-first-order reaction kinetics. The apparent pseudo-first-order rate constant kappwas 0.19min-1in the ClO2/US system, which was a little higher than 0.13min-1of rate constant achieved in ClO2treatment alone. It shows that ClO2/US system can be an effective technology for the decolorization of azo dyes in wastewater.

scholarly journals The reaction of Pseudomonas aeruginosa cytochrome c oxidase with carbon monoxide

1975 ◽  
Vol 151 (1) ◽  
pp. 51-59 ◽  
Author(s):  
S R Parr ◽  
M T Wilson ◽  
C Greenwood
Keyword(s):  
Cytochrome Oxidase ◽  
Flash Photolysis ◽  
Order Rate Constant ◽  
Second Order ◽  
Stopped Flow ◽  
First Order ◽  
Order Rate ◽  
Co Concentration ◽  
Pseudo First Order ◽  
Two Phases

The binding of CO to ascorbate-reduced Pseudomonas cytochrome oxidase was investigated by static-titration, stopped-flow and flash-photolytic techniques. Static-titration data indicated that the binding process was non-stoicheiometric, with a Hill number of 1.44. Stopped-flow kinetics obtained on the binding of CO to reduced Pseudomonas cytochrome oxidase were biphasic in form; the faster rate exhibited a linear dependence on CO concentration with a second-order rate constant of 2 × 10(4) M-1-s-1, whereas the slower reaction rapidly reached a pseudo-first-order rate limit at approx. 1s-1. The relative proportions of the two phases observed in stopped-flow experiments also showed a dependency on CO concentration, the slower phase increasing as the CO concentration decreased. The kinetics of CO recombination after flash-photolytic dissociation of the reduced Pseudomonas cytochrome oxidase-CO complex were also biphasic in character, both phases showing a linear pseudo-first-order rate dependence on CO concentration. The second-order rate constants were determined as 3.6 × 10(4)M-1-s-1 and 1.6 × 10(4)M-1-s-1 respectively. Again the relative proportions of the two phases varied with CO concentration, the slower phase predominating at low CO concentrations. CO dissociation from the enzyme-CO complex measured in the presence of O2 and NO indicated the presence of two rates, of the order of 0.03s-1 and 0.15s-1. When sodium dithionite was used as a reducing agent for the Pseudomonas cytochrome oxidase, the CO-combination kinetics observed by both stopped flow and flash photolysis were extremely complex and not able to be simply analysed.

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