Solvolysis of exo- and endo-Tricyclo[3,3,0,02,8]oct-4-yl p-Toluenesulphonates

1975 ◽  
Vol 28 (6) ◽  
pp. 1311 ◽  
Author(s):  
RG Buckeridge ◽  
KJ Frayne ◽  
BL Johnson
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Aqueous Acetone ◽  
Subsequent Formation ◽  
First Order ◽  
Order Rate ◽  
Hydrolysis Of

The structure of endo-tricyclo[3,3,0,02,8]octan-4-ol (3; X = OH) has been confirmed by hydrogenolysis which affords the known alcohols endo- (equatorial)-bicyclo[3,2,1]octan-2-(11) and cis-bicyclo[3,3,0]octan- anti-2-ol (12). Hydrolysis of derived p-toluenesulphonate (3; X = OTs) in 70% aqueous acetone at 21.6� proceeds with a first-order rate constant of 6.67�0.21x10-4s-1, and under buffered conditions yields endo- tricyclo[3,3,0,02,8]octan-4-ol (3; X = OH) as the only observable product. The results suggest that ionization of (3; X = OTs) proceeds with participation of the C 1 to C2 bonding electrons to give the intermediate trishomocyclopropenyl cation (4) which suffers stereospecific solvent capture to yield (3; X = OH). The results obtained with the monodeuterated isotopomer (17; X = OTs) are consistent with this mechanism. Hydrolysis of exo- tricyclo[3,3,0,02,8]oct-4-yl p-toluenesulphonate (5; X = OTs) is a little slower than its epimer(3; X = OTs), and proceeds with a first-order rate constant of (1.9�0.04)x 10-4s-1 at 49.9� in 70% aqueous acetone. The mechanism in this instance appears to involve anchimerically assisted ionization and subsequent formation of the intermediate tricyclo[3,2,1,02,7]oct-6-yl cation (24)which yields a characteristic mixture of products consisting of endo-tricyclo[3,2,1,02,7]octan-6-ol(20; X = OH) (mainly), its epimer (21; X = OH), exo-bicyclo[3,2,1]oct-6-en- 2-ol (18; X =OH)and exo-bicyclo[2,2,2]oct-5-en-2-ol (19; X = OH).��� A reinvestigation of the buffered acetolysis of exo- tricyclo[3,2,1,02,7]oct-6-yl p-nitrobenzoate(21; X = OPnb) has shown that, contrary to previous conclusions, there is no leakage from the L series to the G series in this system.

Studies on Sulphamic Acid and Related Compounds. II. Kinetics and Mechanism of Hydrolysis of Trimethylamine- and of Triethylamine Sulphur Trioxide Addition Compounds

1962 ◽  
Vol 15 (2) ◽  
pp. 251 ◽  
Author(s):  
BE Fleischfresser ◽  
I Lauder
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Aqueous Acetone ◽  
Second Order ◽  
Fluoride Ions ◽  
Order Rate ◽  
Mechanism Of Hydrolysis ◽  
Reaction With Water ◽  
Sulphamic Acid ◽  
Hydrolysis Of

The kinetics of hydrolysis of trimethylamine- and of triethylaminesulphur trioxide addition compounds have been studied in water and in aqueous acetone. Reaction occurs according to the equation,������������� f - + R,N.SO,+H,O-tR,XH+HSO~.The solvolysis reactions are first-order and are not catalyzed by acids. The halide ions, Cl', Br', and 1', show only a normal salt effect on the rate of hydrolysis of + - (CH,),N.SO, but in the presence of fluoride ions, the rate constant for the production + - of acid from (C,H,),N.SO, in water at 95 OC is about one-seventh of that in the absence of fluoride under the same conditions. It is suggested that the fluorosulphonate ion is formed rapidly, and that this ion then undergoes slow hydrolysis :�In the presence of alkali, using water as the solvent, second-order kinetics are observed, the equation for the reaction being,�������������� + - R,N.SO,+~OH-+R,X+SO~= +H,O. Assuming the reaction with water is bimolecular, the ratio of the (bimolecular) rate constants at 35 OC, ko~-/k~,o is approximately lo8 for each complex. In aqueous acetone, at low water concentrations, the hydrolysis reactions of the trialkylaminesulphur trioxide complexes show second-order kinetics. At 35 OC for the hydrolysis of + - (CH,),N.SO, the ratio of the second-order rate constant in aqueous acetone to the + - (calculated) second-order rate constant in water is approximately 550 ; for (C,H,),N.SO, the same ratio is 6900. It is considered that hydrolysis occurs in water and in aqueous acetone via a bi- molecular attack at sulphur.

Spontaneous hydrolysis of heroin in buffered solution

1978 ◽  
Vol 56 (4) ◽  
pp. 665-667 ◽  
Author(s):  
Paul T. Smith ◽  
M. Hirst ◽  
C. W. Gowdey
Keyword(s):  
Liquid Chromatography ◽  
Rate Constant ◽  
Phosphate Buffer ◽  
Internal Standard ◽  
Order Rate Constant ◽  
Gas Liquid Chromatography ◽  
First Order ◽  
Order Rate ◽  
Spontaneous Hydrolysis ◽  
Hydrolysis Of

Electron-capture gas–liquid chromatography was used to study the spontaneous hydrolysis of heroin in phosphate buffer (pH 6.4 and pH 7.4) at 23 °C. Aliquots of solution were taken over a 24-h period. After extraction at pH 8.9 into propan-2-ol (10%) – ethyl acetate, deacetylated products were made into heptafluorobutyrate derivatives which were analyzed quantitatively using nalorphine as the internal standard. Heroin decomposes to O6-monoacetylmorphine (O6-MAM) under these conditions. Further decomposition to morphine was not observed. Spontaneous hydrolysis was faster at pH 7.4 (first-order rate constant, 9.6 × 10−5 min−1) than at pH 6.4 (first-order rate constant, 3.0 × 10−5 min−1). In 24 h, the decomposition to O6-MAM was 13 and 4%, respectively.

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.

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.

The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C

2005 ◽  
Vol 83 (9) ◽  
pp. 1483-1491 ◽  
Author(s):  
Eduardo Humeres ◽  
Maria de Nazaré M. Sanchez ◽  
Conceição ML Lobato ◽  
Nito A Debacher ◽  
Eduardo P. de Souza
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
Hydrolysis Rate ◽  
Negative Slope ◽  
General Base ◽  
Order Rate ◽  
Basic Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH–rate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 2–6.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett–Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10–7 s–1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1–3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10–4 (mol/L)–1 s–1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.

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.

The Initial Stages of the Pyrolysis of Dimethyl Ether

1975 ◽  
Vol 53 (18) ◽  
pp. 2742-2747 ◽  
Author(s):  
Philip D. Pacey
Keyword(s):  
Dimethyl Ether ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Flow System ◽  
Order Rate Constant ◽  
Chain Termination ◽  
Rate Coefficients ◽  
First Order ◽  
Order Rate ◽  
Initiation Reaction

Dimethyl ether was pyrolized in a flow system at 782–936 K and 25–395 Torr with conversions from 0.2–10%. Product analyses were consistent with a simple Rice–Herzfeld mechanism with most chain termination by the recombination of CH3 radicals. The rate coefficients for both the initiation and termination reactions appeared to be slightly pressure dependent. The first-order rate constant for the initiation reaction,[Formula: see text]calculated from the rate of C2H6 formation, was k1 = 1015.0±0.5exp (−318 ± 8 kJ mol−1/RT) s−1, corresponding to ΔHf0(CH3O) = −5 ± 8 kJmol−1. Comparison of CH4 and C2H6 yields enabled calculation of the rate constant for the reaction of CH3 with dimethyl ether. From 373−936 K, the Arrhenius plot for this reaction is a curve.

On the Interaction Between Human Plasma Kallikrein and C1-Esterase Inhibitor

1983 ◽  
Vol 49 (03) ◽  
pp. 193-195 ◽  
Author(s):  
Torbjörn Nilsson
Keyword(s):  
Dissociation Constant ◽  
Human Plasma ◽  
Rate Constant ◽  
Enzyme Inhibitor ◽  
Order Rate Constant ◽  
Second Order ◽  
Plasma Kallikrein ◽  
First Order ◽  
Order Rate ◽  
Esterase Inhibitor

SummaryThe kinetics of the reaction between human plasma kallikrein and CĪ-esterase inhibitor was studied in a purified system. By monitoring the inhibition reaction for extended periods of time, it was found to proceed in two consecutive steps, a fast reversible second-order binding step followed by a slower, irreversible first-order transition. The rate constants in this reaction model were determined, as well as the dissociation constant of the initial, reversible enzyme-inhibitor complex. Thus, at 37° C the second-order rate constant was found to be 5 · 104 M -1 · s-1, the first order rate constant was 5 · 10-4 s-1 and the dissociation constant K was 1.5 · 10-8 M. Heparin (28 U/ml) and 6-aminohexanoic acid (10 mM) had no effect on the k1 of the of the reaction.

Kinetics and mechanism of the reaction of dimethyl acetylphosphonate with water. Expulsion of a phosphonate ester from a carbonyl hydrate

1978 ◽  
Vol 56 (13) ◽  
pp. 1792-1795 ◽  
Author(s):  
Ronald Kluger ◽  
David C. Pire ◽  
Jik Chin
Keyword(s):  
Rate Constant ◽  
Electronic Effect ◽  
Order Rate Constant ◽  
Ion Concentration ◽  
First Order ◽  
Cleavage Reactions ◽  
Ph Range ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of ◽  
Mechanism Of The Reaction

Dimethyl acetylphosphonate (DAP) is rapidly cleaved in water to acetate and dimethylphosphonic acid. The half time for reaction at pH 7, 25 °C is estimated to be 3 s. The reaction is first order in hydroxide ion concentration and first order in DAP concentration. Rates of reaction were measured over the pH range 3.8 to 6.5 at 25 °C, 6.5 and 7.0 at 5 °C, 4.5 to 6.5 at 35 °C, and 4.5 to 6.0 at 45 °C. The average observed second-order rate constant at 25 °C is 2.4 × 106M−1 s−1. DAP is converted rapidly to a hydrated carbonyl adduct. The mechanism for the formation of the observed products is proposed to be analogous to cleavage reactions of other carbonyl hydrates, proceeding from a monoanion conjugate in this case. The estimated rate constant for the unimolecular cleavage of the carbonyl hydrate anion is 2 × 103 s−1. The rapid hydrolysis of DAP results from energetically favourable formation of a hydrate due to the electronic effect of the phosphonate diester. This effect also promoles ionization of the hydrate. The ionized hydrate readily expels the phosphonate diester to achieve the overall rapid hydrolysis.

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