Nucleophilic Reactivity of 4,4′-Disubstituted Diphenyl Sulfides Towards trans-Dichlorobis(pyridine)platinum(II)

1971 ◽  
Vol 49 (14) ◽  
pp. 2390-2393 ◽  
Author(s):  
J. R. Gaylor ◽  
C. V. Senoff
Keyword(s):  
Free Energy ◽  
Rate Constant ◽  
Driving Force ◽  
Order Rate Constant ◽  
Second Order ◽  
Energy Correlation ◽  
Linear Free Energy ◽  
Nucleophilic Reactivity ◽  
Kinetics Of ◽  
Divalent Sulfur

The kinetics of the reaction of trans-[PtCl2py2] with a series of 4,4′-disubstituted diphenyl sulfides, XC6H4SC6H4Y, have been studied at 30° in methanol. A linear free energy correlation has been obtained between the logarithm of the second order rate constant and the sum of the Hammett substituent parameters for X and Y. This result is consistent with the notion that bond making is the driving force when divalent sulfur functions as a nucleophile towards platinum(II) substrates and is consistent with the inability of 4,4′-dinitrodiphenyl sulfide to coordinate to platinum(II).

Comparison of the nucleophilicities of alcohols and alkoxides

2005 ◽  
Vol 83 (9) ◽  
pp. 1554-1560 ◽  
Author(s):  
Thanh Binh Phan ◽  
Herbert Mayr
Keyword(s):  
Free Energy ◽  
Key Words ◽  
Rate Constants ◽  
Correlation Equation ◽  
Linear Free Energy Relationship ◽  
Hydroxide Solution ◽  
Linear Free Energy ◽  
S Parameters ◽  
Nucleophilic Reactivity ◽  
Kinetics Of

The kinetics of the reactions of benzhydrylium ions with some alcohols and alkoxides dissolved in the corresponding alcohols were photometrically investigated. Using the correlation equation log k (20 °C) = s(E + N), the N and s parameters of methoxide, ethoxide, n-propoxide, and isopropoxide in alcohol–acetonitrile (91:9, v/v) were determined. The cosolvent acetonitrile has only a little influence on the rate constants of the reactions of alcohols and alkoxides. The order of N values (OH– << MeO– < EtO– < n-PrO– < i-PrO–) shows that alkoxides differ only moderately in reactivity but are considerably more nucleophilic than hydroxide. As a consequence, the nucleophilic reactivity of a 0.5 mmol/L aqueous hydroxide solution increases by a factor of 13 when 10% (v/v) methanol is added. In 1–10 mmol/L alkoxide solutions in alcohols, weak electrophiles react considerably faster with alkoxides than with the corresponding alcohols. With increasing electrophilicity, the preference for alkoxides decreases, and electrophiles of –3 < E < 3 react with alkoxides (1–10 mmol/L) and alcohols with comparable rates. Stronger electrophiles will react with alcohols exclusively when alkoxides are present in concentrations ≤10 mmol/L. Key words: kinetics, alcohol, alkoxide, linear free energy relationship, nucleophilicity.<

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

1973 ◽  
Vol 51 (4) ◽  
pp. 582-587 ◽  
Author(s):  
M. L. Cotton ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constant ◽  
Active Sites ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Compound I ◽  
Order Rate ◽  
Compound Ii ◽  
Kinetics Of

In order to investigate the nature of compounds I and II of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three different oxidizing agents. The pH dependence of the apparent second-order rate constant for ferrocyanide oxidation by compound I, prepared from ethyl hydroperoxide and m-chloroperbenzoic acid, was interpreted in terms of an ionization on the enzyme with a pKa = 5.3, identical to that reported previously for hydrogen peroxide. The second-order rate constant for the compound II-ferrocyanide reaction also showed the same pH dependence for the three oxidizing substrates. However, with more accurate results, the compound II-ferrocyanide reaction was reinterpreted in terms of a single ionization with pKa = 8.5. The same dependence of ferrocyanide oxidation on pH suggests structurally identical active sites for compounds I and II prepared from the three different oxidizing substrates.

scholarly journals Determination of the Mechanism of Nucleophilic Reaction of Fenitrothion Using Substituted Phenoxide Nucleophiles in Aqueous Media

2021 ◽  
pp. 40-46
Author(s):  
E. G. Amadi ◽  
C. I. Egwuatu ◽  
C. U. Okoro ◽  
F. O. Obumselu ◽  
M. U. Onuoha
Keyword(s):  
Transition State ◽  
Rate Constant ◽  
Aqueous Media ◽  
Order Rate Constant ◽  
Second Order ◽  
Bond Rupture ◽  
Linear Free Energy Relationship ◽  
Order Rate ◽  
Linear Free Energy ◽  
Nucleophilic Displacement

The mechanism of the nucleophilic displacement reaction at the phosphorus centre of organophosphates was determined. Phenoxide nucleophiles were reacted with fenitrothion (O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate) in water at 25oC and pseudo-first order rate constant measurements taken. Second-order rate constant (kNuc) was determined for the different concentrations of nucleophiles while the second-order rate constant (klg) for the investigation of 2,4-dichlorophenoxide ion with and series of aryl phosphorothioate esters was also determined. Linear free energy relationship was further determined using the Brϕnsted-type plot. The plots are linear over a range of pKaNuc of 7.15-11.10 that straddles the pKa of the leaving 3-methyl-4-nitrophenoxide ion (pKa = 7.20) with statistically acceptable linear correlations (R2 = 0.987) and (R2 = 0.980). The linearity in the traditional Brϕnsted-type plots shows the sensitivity of the nucleophilic displacement to the basicity of the nucleophiles and hence is consistent with a single transition-state mechanism whose barrier to decomposition is low hence concerted. Analysis of the values of βNuc, βLg and βeq (0.734) with the effective charge distribution in the transition state shows that it has no positive character. The Leffler index presents bond formation being slightly ahead of bond rupture.

THE KINETICS OF THE CHELATION OF NICKEL (II) AND 1,10-PHENANTHROLINE

1964 ◽  
Vol 42 (4) ◽  
pp. 934-940 ◽  
Author(s):  
P. F. Barrett ◽  
W. MacF. Smith
Keyword(s):  
Ionic Strength ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Hydrogen Ion ◽  
Kinetic Behavior ◽  
Ion Concentrations ◽  
Order Rate ◽  
Kinetics Of ◽  
Limiting Values

The kinetics of the formation of the bidentate monocomplex of 1,10-phenanthroline and nickel (II) have been examined spectrophotometrically at ionic strength 0.5 over the range of temperatures 8 to 37 °C and over the range of hydrogen ion concentrations 0.01 to 0.30 molar. The kinetic behavior over the range of conditions is consistent with that found at 25 °C by Margerum, Bystroff, and Banks. The limiting values for the second-order rate constant for the reaction at high acidities have been assessed and imply associated values of ΔH≠and ΔS≠ of 9.5 kcal mol−1 and −5.3 e.u. respectively.

Effect of Thrombomodulin on the Molecular Recognition and Early Catalytic Events in Thrombin-Protein C Interaction

1996 ◽  
Vol 76 (04) ◽  
pp. 556-560 ◽  
Author(s):  
Raimondo De Cristofaro
Keyword(s):  
Molecular Recognition ◽  
Perturbation Method ◽  
Rate Constant ◽  
Protein C ◽  
Order Rate Constant ◽  
Second Order ◽  
Concentration Addition ◽  
Order Rate ◽  
C Complex ◽  
Kinetics Of

SummaryA viscosity perturbation method allowed to compute the second order rate constant, k±15 for the formation of thrombin-Protein C complex, both in the absence and presence of thrombomodulin (TM) at pH 8.00 and 37° C. In the absence of TM the second order rate constant was found equal to 7.9 ± 0.6 × 103 M-1 sec-1, whereas it was enhanced to 9.9 ± 0.4 × 104 M-1 s-1 by a saturating (100 nM) TM concentration. Addition of 5 mM Ca++ to solution containing 100 nM TM induced a further increase of k+1 value up to 7.3 ± 0.5 × 105 M-1 s-1. Moreover, it was demonstrated that the thrombin-PC complex undergoes the acy-lation reaction more rapidly than it dissociates to form free thrombin and substrate (stickiness ratio = 2.4 ± 0.9). This tendency is even favored when thrombin is bound to TM both in the absence and presence of Ca++ (stickiness ratio = 9 ± 6 in the absence of Ca++ and 16 ± 10 in the presence of Ca++). Altogether these results demonstrate that TM is able to positively affect both the molecular encounter and the kinetics of the early catalytic events of the thrombin-Protein C interaction.

Kinetics of the Reaction of Nickel(II) and 2,2′-Bipyridine in Ethanol

1973 ◽  
Vol 51 (23) ◽  
pp. 3975-3977 ◽  
Author(s):  
M. L. Sanduja ◽  
W. MacF. Smith
Keyword(s):  
Kinetic Parameters ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Stopped Flow ◽  
Ligand Specificity ◽  
Temperature Range ◽  
Kinetics Of Formation ◽  
The Difference ◽  
Kinetics Of

The kinetics of formation of the monobipyridine complex of nickel(II) in ethanol has been studied with stopped-flow methods over the temperature range 7 to 35 °C. The value of the second order rate constant kf at 25 °C of 6.6 × 10−3M−1 s1 and the values of ΔH≠ (10.1 ± 1.0 kcal mol−1) and of ΔS≠ (−7.3 ± 3.4 cal deg−1 mol−1) are close to the corresponding values for ethanol exchange on nickel(II) and suggest that the mechanism is dissociative interchange. However the difference in the values of the kinetic parameters of this reaction and those previously reported for the reactions involving the chemically similar phenanthroline imply a degree of ligand specificity for the reactions in ethanol which is considerably larger than is the case for reactions in water and methanol and that a common Id mechanism with monodentate formation being rate controlling is not applicable to both reactions.

scholarly journals Kinetics of the reaction of thrombin and α2-macroglobulin

1985 ◽  
Vol 231 (2) ◽  
pp. 417-423 ◽  
Author(s):  
R D Feinman ◽  
A I Yuan ◽  
S R Windwer ◽  
D Wang
Keyword(s):  
Rate Constant ◽  
Gel Electrophoresis ◽  
Bond Formation ◽  
Covalent Bond ◽  
Thiol Group ◽  
Order Rate Constant ◽  
Second Order ◽  
Order Rate ◽  
Covalent Bond Formation ◽  
Kinetics Of

The kinetics of the reaction of alpha 2-macroglobulin (alpha 2M) with human thrombin were studied by recording the appearance of thiol groups spectrophotometrically and by measuring the distribution of protein species by denaturing non-reducing gel electrophoresis. The goals were to study the relation between the formation of various covalent enzyme-inhibitor complex species and the appearance of free thiol, and from the kinetic analysis, to try to characterize the chemical nature of the protein complexes. The kinetics of thiol-group release were observed to be biphasic, the early phase showing second-order behaviour, results consistent with previous reports in the literature. The observed second-order rate constant for thiol-group release was found to be faster than the second-order rate constant for the disappearance of the band corresponding to native alpha 2M on gel electrophoresis. This may be a reflection of the multiple products formed from the thioester. Alternatively, it is possible that covalent-bond formation is slower than some enzyme-induced change in the thioester centre, and this may be suggestive evidence for a reactive alpha 2M centre that does not contain an intact thioester. The kinetics of covalent-bond formation were found to be consistent with the internal cross-link of several alpha 2M chains by the bound proteinase, providing further evidence that the very-high-Mr species seen on gels may arise from dimers of the alpha 2M molecule held together by covalent bonds to the enzyme.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

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