REARRANGEMENT STUDIES WITH C14: XI. THE FORMOLYSIS OF 2-PHENYLETHYL-1-C14p-TOLUENESULPHONATE WITH OR WITHOUT ADDED SODIUM p-TOLUENESULPHONATE-S35

1961 ◽  
Vol 39 (7) ◽  
pp. 1510-1517 ◽  
Author(s):  
J. W. Clayton ◽  
C. C. Lee
Keyword(s):  
Experimental Data ◽  
Rate Constant ◽  
Reaction Times ◽  
Order Rate Constant ◽  
Covalent Bonding ◽  
Equimolar Amount ◽  
Rate Of Return ◽  
First Order ◽  
Ionic Intermediates

The formolysis of 0.350 M 2-phenylethyl-1-C14p-toluenesulphonate (I) was carried out at 74 ± 0.2 °C with or without the presence of an equimolar amount of sodium p-toluenesulphonate-S35 (III). The over-all first-order rate constant, k1, was found to be 2.6 × 10−5 sec−1 and 3.0 × 10−5 sec−1, respectively, for the reaction with and without added III. The determination of the degrees of rearrangement of the C14-labeled atoms from the C-1 to the C-2 positions in the 2-phenylethyl p-toluenesulphonate (Ir) recovered from the reaction mixture at various reaction times permitted the evaluation of k14, the rate of return from ionic intermediates to covalent bonding. Using the experimental data, it was possible to calculate ks and kΔ, the rates, respectively, for the anchimerically unassisted and assisted solvolysis. As expected, formolysis of I proceeded principally by the anchimerically assisted process. Calculations also showed that the fraction of the anchimerically assisted ionization returning to covalent bonding was about 15% for the reaction in the presence of III, while in the absence of III, the return was about 9%. For the formolysis of I in the presence of III, the extents of incorporation of S35 in the recovered sulphonate Ir were also determined. The S35 incorporation in Ir, when considered in conjunction with the C14 rearrangement in Ir, led to the conclusion that the return from ionic intermediates to covalent bonding during the formolysis of I included both internal and external returns, the extent of external return being the greater of the two.

scholarly journals Kinetic study on the removal of mercury by fly ash

2014 ◽  
Vol 16 (2) ◽  
pp. 385-392 ◽  
Keyword(s):  
Experimental Data ◽  
Fly Ash ◽  
Rate Constant ◽  
Contact Time ◽  
Order Rate Constant ◽  
First Order ◽  
Pseudo Second Order ◽  
Pseudo First Order ◽  
Percent Removal ◽  
Adsorbent Dose

<div> <p>The removal of mercury by adsorption process using fly ash was investigated in this study. Mercury removal capacity of fly ash was performed by batch mode adsorption experiment with the effect of various parameters i.e., contact time (0.5-3.5) h, pH of 2-10, concentration of adsorbate (1, 5 and 10)<br /> mg l<sup>-1</sup>, adsorbent dose (100-1000) mg per 100 ml solution and temperature (303, 313 and 323) K. Mercury concentration (10 mg l<sup>-1</sup>) was chosen for all parameters except adsorbent dose. The experimental data were showed that the adsorbent dose of 200, 400 and 600 mg per 100 ml were sufficient to maximum removal of mercury (98 percent) from aqueous solution of mercury (1, 5 and 10) mg.L<sup>-1</sup> at equilibrium and 89 percent mercury was removed when concentration was 10 mg l<sup>-1</sup> at 303K temperature. Adsorbent dose of 100 mg per 100 ml solution showed 74 percent removal of mercury for 2 hours contact time and 90 percent removal at pH 10. The experimental data were fitted with pseudo first order and pseudo second order kinetics which was proposed by Lagergreen. The value of pseudo first order rate constant, k<sub>1</sub> is 0.697 h<sup>-1</sup> and pseudo second order rate constant k<sub>2</sub> is 0.135 l mg<sup>-1</sup> h<sup>-1</sup>.</p> </div> <p>&nbsp;</p>

scholarly journals The determination of specificity constants in enzyme-catalysed reactions

1986 ◽  
Vol 239 (1) ◽  
pp. 221-224 ◽  
Author(s):  
I E Crompton ◽  
S G Waley
Keyword(s):  
Rate Constant ◽  
Competitive Inhibition ◽  
Order Rate Constant ◽  
Beta Lactamase ◽  
Initial Concentration ◽  
First Order ◽  
Order Rate ◽  
Accurate Procedure ◽  
Hydrolysis Of

A convenient and accurate procedure for determining the kinetic parameter Vmax./Km is described. This avoids the error in the usual method of taking the observed first-order rate constant of an enzymic reaction at low substrate concentration as Vmax./Km. A series of reactions is used in which the initial concentration of substrate is below Km (e.g. from 5% to 50% of Km). Measurements are taken over the same extent of reaction (e.g. 70%) for each member of the series, and treated as if the kinetics were truly first-order. The reciprocal of the observed first-order rate constant is then plotted against the initial concentration of substrate: the reciprocal of the ordinate intercept is Vmax./Km. The procedure, as well as being applicable to simple reactions, is shown to be valid when there is competitive inhibition by the product, or when the reaction is reversible, or when there is competitive or mixed inhibition. The hydrolysis of cephalosporin C by a beta-lactamase from Pseudomonas aeruginosa is used to illustrate the method.

Improvement of a direct spectrophotometric assay for routine determination of superoxide dismutase activity

1991 ◽  
Vol 37 (11) ◽  
pp. 1993-1999 ◽  
Author(s):  
B J Bolann ◽  
R J Ulvik
Keyword(s):  
Superoxide Dismutase ◽  
Rate Constant ◽  
Spectrophotometric Method ◽  
Order Rate Constant ◽  
Spectrophotometric Assay ◽  
Alkaline Ph ◽  
First Order ◽  
Pseudo First Order ◽  
Superoxide Dismutase Mimics

Abstract The growing interest in measuring superoxide dismutase (EC 1.15.1.1) in many diseases calls for useful routine assays. For this purpose, the direct spectrophotometric method of Marklund (J Biol Chem 1976;251:7504-7) was improved to offer an alternative to the imprecise, indirect assays currently used. The decay of O2.- (from KO2) at pH 9.5 was monitored as the decrease in delta A (delta A = A250nm-A360nm). Superoxide dismutase was determined from the pseudo-first-order rate constant of O2.- dismutation. The precision of the assay was improved by increasing the concentration of O2.- and expanding the interval for measurements of O2.- concentrations to 4-16 mumol/L. Other assay characteristics, including temperature, were also optimized. In hemolysate the assay had a within-day CV of 5.5-13% and a between-day CV of 4%. Mn-superoxide dismutase and some superoxide dismutase mimics are inhibited at alkaline pH. Therefore, the method is primarily recommended for Cu,Zn-superoxide dismutase.

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

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

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.

scholarly journals Population Pharmacokinetic Model and Meta-analysis of Outcomes of Amphotericin B Deoxycholate Use in Adults with Cryptococcal Meningitis

2018 ◽  
Vol 62 (7) ◽  
Author(s):  
Katharine E. Stott ◽  
Justin Beardsley ◽  
Sarah Whalley ◽  
Freddie Mukasa Kibengo ◽  
Nguyen Thi Hoang Mai ◽  
...  
Keyword(s):  
Amphotericin B ◽  
Rate Constant ◽  
Cryptococcal Meningitis ◽  
Drug Exposure ◽  
Meta Analysis ◽  
Central Compartment ◽  
Order Rate Constant ◽  
Peripheral Compartment ◽  
First Order ◽  
Amphotericin B Deoxycholate

ABSTRACT There is a limited understanding of the population pharmacokinetics (PK) and pharmacodynamics (PD) of amphotericin B deoxycholate (DAmB) for cryptococcal meningitis. A PK study was conducted in n = 42 patients receiving DAmB (1 mg/kg of body weight every 24 h [q24h]). A 2-compartment PK model was developed. Patient weight influenced clearance and volume in the final structural model. Monte Carlo simulations estimated drug exposure associated with various DAmB dosages. A search was conducted for trials reporting outcomes of treatment of cryptococcal meningitis patients with DAmB monotherapy, and a meta-analysis was performed. The PK parameter means (standard deviations) were as follows: clearance, 0.03 (0.01) × weight + 0.67 (0.01) liters/h; volume, 0.82 (0.80) × weight + 1.76 (1.29) liters; first-order rate constant from central compartment to peripheral compartment, 5.36 (6.67) h−1; first-order rate constant from peripheral compartment to central compartment, 9.92 (12.27) h−1. The meta-analysis suggested that the DAmB dosage explained most of the heterogeneity in cerebrospinal fluid (CSF) sterility outcomes but not in mortality outcomes. Simulations of values corresponding to the area under concentration-time curve from h 144 to h 168 (AUC144–168) resulted in median (interquartile range) values of 5.83 mg · h/liter (4.66 to 8.55), 10.16 mg · h/liter (8.07 to 14.55), and 14.51 mg · h/liter (11.48 to 20.42) with dosages of 0.4, 0.7, and 1.0 mg/kg q24h, respectively. DAmB PK is described adequately by a linear model that incorporates weight with clearance and volume. Interpatient PK variability is modest and unlikely to be responsible for variability in clinical outcomes. There is discordance between the impact that drug exposure has on CSF sterility and its impact on mortality outcomes, which may be due to cerebral pathology not reflected in CSF fungal burden, in addition to clinical variables.

The Dephosphorylation of Adenosine 5′ -Triphosphate in a Binary and Ternary Zn2+ Complex

1974 ◽  
Vol 29 (11-12) ◽  
pp. 680-682 ◽  
Author(s):  
Peter Amsler ◽  
David Buisson ◽  
Helmut Sigel
Keyword(s):  
Rate Constant ◽  
Ternary Complex ◽  
Order Rate Constant ◽  
Reactive Species ◽  
Ph Optimum ◽  
First Order ◽  
Order Rate

The dephosphorylation of ATP was characterized by determining the dependence of the first-order rate constant on pH in the absence and presence of Zn2+ and together with Zn2+ and 2,2′-bipyridyl. The Zn2+-accelerated reaction passes through a pH optimum at about 8. The decrease in the rate at higher pH is due to the formation of Zn(ATP) (OH)3-; this species is relatively insensitive towards dephosphorylation. It is concluded that Zn(ATP)2- is the reactive species and that the interaction between N (7) and Zn2+ in this complex is crucial for its reactivity. In the presence of 2,2′-bipyridyl (Bipy) the ternary complex, Zn (Bipy) (ATP)2-, is formed which is rather stable towards dephosphorylation. It is suggested that the described effects of acceleration and inhibition are helpful for understanding the recycled processes in nature.

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.

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