Photodehydroxylation of methoxybenzyl alcohols: rate constants for solvent and hydronium ion catalyzed photodehydroxylation and applicability of Förster cycle calculations

1989 ◽  
Vol 46 (1) ◽  
pp. 49-57 ◽  
Author(s):  
Peter Wan ◽  
Becky Chak ◽  
Erik Krogh
Keyword(s):  
Rate Constants ◽  
Hydronium Ion

Gas-phase proton-transfer reactions of the hydronium ion at 298 K

1979 ◽  
Vol 57 (12) ◽  
pp. 1518-1523 ◽  
Author(s):  
Gervase I. Mackay ◽  
Scott D. Tanner ◽  
Alan C. Hopkinson ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Flowing Afterglow ◽  
Hydronium Ion ◽  
Proton Transfer Reactions

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.

Stability of NADPH: effect of various factors on the kinetics of degradation.

1986 ◽  
Vol 32 (2) ◽  
pp. 314-319 ◽  
Author(s):  
J T Wu ◽  
L H Wu ◽  
J A Knight
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Degradation Rate ◽  
Neutral Ph ◽  
Degradation Reactions ◽  
Hydronium Ion ◽  
Effects Of Ph ◽  
Reaction Orders ◽  
Kinetics Of Degradation ◽  
Kinetics Of

Abstract Seeking to minimize degradation of NADPH during storage, reagent preparation, and assays, we investigated the effects of pH, temperature, and ionic strength as well as the effects of phosphate and acetate. NADH was also included for comparison. Our results indicate that the rate of degradation of NADPH is proportional most importantly to temperature and concentrations of hydronium ion, but also to concentrations of phosphate and acetate. The degradation rate decreased with increasing ionic strength at neutral pH, but increased slightly at lower pH. NADPH generally is less stable than NADH under the same conditions. The reaction orders with respect to hydronium ion and anions were near 1 for NADH degradation reactions, about 0.5 for NADPH. Rate constants for NADH and NADPH differed more at higher pH and lower phosphate and acetate concentrations.

Mutarotation of some biologically important 2-substituted hexoses

1974 ◽  
Vol 337 (1610) ◽  
pp. 317-332 ◽  
Keyword(s):  
Acetic Acid ◽  
Transition State ◽  
Rate Constants ◽  
Activation Parameters ◽  
Water Molecules ◽  
Concerted Mechanism ◽  
Hydronium Ion ◽  
Thermodynamic Activation Parameters

Catalysis by water, hydronium ion, acetate ion, acetic acid, pyridine and 3-hydroxypyridine of the mutarotation of D-glucose, 2-deoxy-D-glucoso, 2-amino-2-deoxy-D-glucose and 2-acetamido-2-deoxy-n-glucose has been studied polarimetrically. Rate constants were measured at 298 and 308 K and the thermodynamic activation parameters have been calculated for each case. It is concluded that the mutarotation reaction probably takes place by a concerted mechanism in which two or more water molecules are involved in the transition state.

Kinetics of acid-catalyzed hydration in aqueous solution of 1-methoxy- and 1-methylthio-2-phenylethyne and some related acetylenes

1987 ◽  
Vol 65 (2) ◽  
pp. 441-444 ◽  
Author(s):  
N. Banait ◽  
M. Hojatti ◽  
P. Findlay ◽  
A. J. Kresge
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Isotope Effect ◽  
Rate Constants ◽  
Acid Catalysis ◽  
The Other ◽  
Buffer Solutions ◽  
Hydronium Ion ◽  
Acid Catalyzed ◽  
Kinetics Of

The rates of conversion of C6H5C≡COCH3 to C6H5CH2CO2CH3 were measured in dilute HClO4/H2O, DCIO4/D2O, and H3PO4–H2PO2−/H2O buffer solutions, and the rates of conversion of C6H5C≡CSCH3 to C6H5CH2COSCH3, C6H5C≡CH to C6H5COCH3, 2,4,6-(CH3)3C6H2C≡CH to 2,4,6-(CH3)3C6H2COCH3, and p-CH3OC6H4C≡CCH3 to p-CH3OC6H4COCH2CH3 were measured in concentrated HClO4/H2O solutions, all at 25 °C. The reaction of C6H5C≡COCH3 showed general acid catalysis and gave the isotope effect [Formula: see text], which indicates that it proceeds through rate-determining proton transfer from catalyst to substrate. The hydronium ion catalytic coefficient for this reaction is [Formula: see text], and those for the other four, in the order given above, are [Formula: see text], and 8.5 × 10−6 M−1 s−1. Relative reactivities based on these rate constants are discussed.

The kinetics and mechanisms of the acid-catalysed hydrolysis of t-butyl formate in aqueous solution.

1969 ◽  
Vol 22 (1) ◽  
pp. 19 ◽  
Author(s):  
RA Fredlein ◽  
I Lauder
Keyword(s):  
Aqueous Solution ◽  
Acid Solution ◽  
Rate Constants ◽  
Aqueous Acid ◽  
Hydronium Ion ◽  
Low Concentrations ◽  
Order Of Magnitude ◽  
Catalytic Rate ◽  
Hydrolysis Of ◽  
Tracer Experiments

The hydrolysis of t-butyl formate in aqueous acid solution has been studied over the range 35-83�. At low concentrations of catalysing acid, specific hydronium-ion catalysis is enhanced by the formic acid produced during the reaction. A series of oxygen-18 tracer experiments was performed, taking into account the formation of isobutylene, which is a by-product of hydrolysis by alkyl-oxygen fission. ��� The percentage alkyl-oxygen fission varies from 3 at 35� to 40 at 76�. Catalytic rate constants for reactions by the AAL1 and the AAC2 mechanisms are expressed respectively by the equations ���������������� k?1 = 1016.6exp(-28000/RT)�� 1. mole-1 sec-1���������������� k?2 = 107.8exp(-13600/RT)�� 1. mole-1 sec-1����������������� The rate constants found for the BAL1 mechanism are of order-of- magnitude significance only.

Inhibition in Purified Systems and in Human Plasma of Chimaeric Plasminogen Activators Consisting of the NH2-Terminal Region of Tissue-Type Plasminogen Activator and the COOH-Terminal Region of UrokinaseType Plasminogen Activator

1988 ◽  
Vol 60 (02) ◽  
pp. 247-250 ◽  
Author(s):  
H R Lijnen ◽  
L Nelles ◽  
B Van Hoef ◽  
F De Cock ◽  
D Collen
Keyword(s):  
Plasminogen Activator ◽  
Rate Constants ◽  
Plasminogen Activators ◽  
Second Order ◽  
Tissue Type ◽  
Single Chain ◽  
Chain Molecules ◽  
Order Rate ◽  
Type Plasminogen Activator ◽  
Urokinase Type Plasminogen Activator

SummaryRecombinant chimaeric molecules between tissue-type plasminogen activator (t-PA) and single chain urokinase-type plasminogen activator (scu-PA) or two chain urokinase-type plasminogen activator (tcu-PA) have intact enzymatic properties of scu-PA or tcu-PA towards natural and synthetic substrates (Nelles et al., J Biol Chem 1987; 262: 10855-10862). In the present study, we have compared the reactivity with inhibitors of both the single chain and two chain variants of recombinant u-PA and two recombinant chimaeric molecules between t-PA and scu-PA (t-PA/u-PA-s: amino acids 1-263 of t-PA and 144-411 of u-PA; t-PA/u-PA-e: amino acids 1-274 of t-PA and 138-411 of u-PA). Incubation with human plasma in the absence of a fibrin clot for 3 h at 37° C at equipotent concentrations (50% clot lysis in 2 h), resulted in significant fibrinogen breakdown (to about 40% of the normal value) for all two chain molecules, but not for their single chain counterparts. Preincubation of the plasminogen activators with plasma for 3 h at 37° C, resulted in complete inhibition of the fibrinolytic potency of the two chain molecules but did not alter the potency of the single chain molecules. Inhibition of the two chain molecules occurred with a t½ of approximately 45 min. The two chain variants were inhibited by the synthetic urokinase inhibitor Glu-Gly-Arg-CH2CCl with apparent second-order rate constants of 8,000-10,000 M−1s−1, by purified α2-antiplasmin with second-order rate constants of about 300 M−1s−1, and by plasminogen activator inhibitor-1 (PAI-1) with second-order rate constants of approximately 2 × 107 M−1s−1.It is concluded that the reactivity of single chain and two chain forms of t-PA/u-PA chimaers with inhibitors is very similar to that of the single and two chain forms of intact u-PA.

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