2004 Bader Award LectureMetal-ion-catalyzed acyl and phosphoryl transfer reactions to alcohols: La3+-promoted alcoholysis of activated amides, carboxylate esters, and neutral organophosphorus esters

2004 ◽  
Vol 82 (12) ◽  
pp. 1791-1805 ◽  
Author(s):  
R Stan Brown ◽  
Alexei A Neverov ◽  
Josephine SW Tsang ◽  
Graham TT Gibson ◽  
Pedro J Montoya-Pelaez
Keyword(s):  
Rate Constant ◽  
Metal Ion ◽  
Active Form ◽  
Transfer Reactions ◽  
Nucleophilic Attack ◽  
Phosphoryl Transfer ◽  
Solution Ph ◽  
Activated Esters ◽  
Neutral Ph ◽  
Kinetics Of

Unlike metal-ion-catalyzed hydrolysis processes, metal-ion-catalyzed methanolysis processes have received scant attention in the literature particularly from the standpoint of mechanistic studies. La3+, introduced into methanol solution as its triflate or perchlorate salt, is particularly effective in promoting methanolysis reactions of unactivated and activated esters, phosphate triesters, and activated amides such as acetyl imidazoles and lactams. Studies of the kinetics of methanolysis of these substrates as a function of solution pH and [La3+] indicate that the solution comprises lanthanum dimers with one to five associated methoxides (La23+(–OCH3)1–5), the most catalytically active form being La23+(–OCH3)2, which is produced at near neutral pH in methanol (8.4). Mechanisms for all the acyl and phosphoryl transfer reactions are proposed where the metal ion serves a dual role of acting as a Lewis acid to activate the C=O or P=O system to nucleophilic attack by a metal-coordinated methoxide nucleophile. In cases where direct comparisons can be made, the La23+ catalyst system is more active for the methanolysis of nonactivated substrates than for activated substrates. Another general characteristic of this system is that the catalytic rate constant for the metal complex exceeds the second-order rate constant for free methoxide, in some cases by as much as 4600-fold. Overall the catalytic effects exhibited by the La23+ system is spectacular for such substrates as paraoxon, where as little as 2 mmol L–1 La(OTf)3 in the presence of equimolar NaOCH3 accelerates the methanolysis by 109-fold relative to the background reaction at neutral pH and ambient temperature.Key words: kinetics of methanolysis, metal ion catalysis, lanthanides, methanolysis of carboxylate esters and phosphate esters.

Two-Metal Ion Catalysis in Enzymatic Acyl- and Phosphoryl-Transfer Reactions

1996 ◽  
Vol 35 (18) ◽  
pp. 2024-2055 ◽  
Author(s):  
Norbert Sträter ◽  
William N. Lipscomb ◽  
Thomas Klabunde ◽  
Bernt Krebs
Keyword(s):  
Metal Ion ◽  
Transfer Reactions ◽  
Phosphoryl Transfer ◽  
Metal Ion Catalysis

Correlation analysis of reactivity in the addition of substituted benzylamines to β-nitrostyrene

1996 ◽  
Vol 74 (4) ◽  
pp. 625-629 ◽  
Author(s):  
Neeta Jalani ◽  
Seema Kothari ◽  
Kalyan K. Banerji
Keyword(s):  
Activation Energy ◽  
Correlation Analysis ◽  
Rate Constant ◽  
Steric Hindrance ◽  
Nucleophilic Addition ◽  
Regression Coefficients ◽  
Nucleophilic Attack ◽  
Arrhenius Activation Energy ◽  
First Order ◽  
Kinetics Of

The kinetics of addition of a number of ortho-, meta-, and para-substituted benzylamines to β-nitrostyrene (NS) in acetonitrile have been studied. The reaction is first order with respect to NS. The order with respect to the amine is higher than one. It has been shown that the reaction follows two mechanistic pathways, uncatalyzed and catalyzed by the amine. The Arrhenius activation energy for the catalyzed path is negative, indicating the presence of a pre-equilibrium (k1, k−1) leading to the formation of a zwitterion. The values of the rate constant, k1, for the nucleophilic attack have been determined for 28 benzylamines. The rate constant k1 was subjected to correlation analysis using Charton's LDR and LDRS equations. The polar regression coefficients are negative, indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho substituents. Key words: nucleophilic addition, benzylamines, correlation analysis, kinetics, alkene.

Cobalt, Iron and Ruthenium Complexes of Picolinic and Dipicolinic Acids: Syntheses, Solution Properties and Kinetics of Electron Transfer Reactions With Cytochrome C(II) and Some Inorganic Reductants

1989 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
RM Ellis ◽  
JD Quilligan ◽  
NH Williams ◽  
JK Yandell
Keyword(s):  
Exchange Rate ◽  
Cytochrome C ◽  
Rate Constant ◽  
Order Rate Constant ◽  
The Self ◽  
Transfer Reactions ◽  
Solution Properties ◽  
Cobalt Iron ◽  
Exchange Rate Constant ◽  
Kinetics Of

Tris picolinate complexes of CO111 and RU111 have been synthesized, and their standard potentials measured (432 �10, 403 �2 mV) at 25�C and ionic strength 0.1 mol dm-3. The self-exchange rate constant of Ru ( pic )3O/- was found to be (1 .4 �0.9)×108 dm3 mol-1 s-l, from reaction with cytochrome C(II), Co( bpy )32+ and ~Co( phen )32+. For the reaction between Fe( dipic )2- and cytochrome ~(II), at 2S260C, pH 5.5 and I 0.1 mol dm-3 (KNO3), the second-order rate constant was (3.2 �0.l)×105 dm3 mol-1 s-1,with ΔH+ 19.9 �0.9 kJ mol-1 and ΔS+ -72.8 �.7 J K-1 mol-l. The self-exchange rate constant of Fe( dipic )2-/2- was reevaluated as (5.8 �0.2)×106 dm3 mol-l s-1.

ChemInform Abstract: Two-Metal Ion Catalysis in Enzymatic Acyl- and Phosphoryl-Transfer Reactions

ChemInform ◽  
2010 ◽  
Vol 28 (1) ◽  
pp. no-no
Author(s):  
N. STRAETER ◽  
W. N. LIPSCOMB ◽  
T. KLABUNDE ◽  
B. KREBS
Keyword(s):  
Metal Ion ◽  
Transfer Reactions ◽  
Phosphoryl Transfer ◽  
Metal Ion Catalysis

Bio-inspired approaches to accelerating metal ion-promoted reactions: enzyme-like rates for metal ion mediated phosphoryl and acyl transfer processes

2015 ◽  
Vol 87 (6) ◽  
pp. 601-614 ◽  
Author(s):  
Robert Stan Brown
Keyword(s):  
Metal Ion ◽  
Catalytic Efficiency ◽  
Acyl Transfer ◽  
Transfer Reactions ◽  
Medium Effect ◽  
Phosphoryl Transfer ◽  
Leaving Group ◽  
Bonding Properties ◽  
Catalyzed Reactions ◽  
Phosphate Diesters

Abstract Intense efforts by many research groups for more than 50 years have been directed at biomimetic approaches to understand how enzymes achieve their remarkable rate accelerations. Nevertheless, it was noted in 2003 that, despite numerous efforts to design models for catalyzing the cleavage of such species as phosphate diesters, “none of the several models so far described approaches the enormous catalytic efficiency of natural enzymes”. The same could be said for biomimetics of other enzymes promoting acyl or phosphoryl transfer reactions, particularly those mediated by metal ions such as Zn(II). Clearly other important factors were being overlooked or awaiting discovery. In this manuscript we describe two important effects that we have implemented to accelerate metal ion catayzed phosphoryl and acyl transfer reactions. The first of these relates to a medium effect where the polarity of the solution, as measured by dielectric constant, is reduced from that of water (ε = 78) to values of 31.5 and 24.3 when the solvent is changed to methanol or ethanol. Among organic solvents these light alcohols are closest to water in terms of structure and properties as well as retaining important H-bonding properties. The second important effect involves a known but difficult to demonstrate mode of catalysis where the leaving group (LG) in a solvolysis reaction is accelerated as it becomes progressively poorer. In the cases described herein, the LG’s propensity to depart from a substrate during the course of reaction is accelerated by coordination to a metal ion in a process known as leaving group assistance, or LGA. These two effects can each impart accelerations of 109–1017 for certain metal ion catalyzed reactions relative to the corresponding solvent, or base induced reactions.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1005-1008
Author(s):  
Ayla Khan ◽  
Alexei A Neverov ◽  
Anatoly K Yatsimirsky ◽  
R S Brown
Keyword(s):  
Rate Constant ◽  
Metal Ion ◽  
Order Rate Constant ◽  
Water Proton ◽  
First Order ◽  
Catalytic Rate Constant ◽  
Equilibrium Binding ◽  
Metal Ion Catalysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of methanolysis of acetyl imidazole (1) and acetyl pyrazole (2) have been investigated under anhydrous conditions in the presence of Zn(ClO4)2, Co(ClO4)2, and HClO4 at 25°C. In all cases, the plots of the pseudo-first-order rate constant for methanolysis (kobs) vs. [metal ion] or [HClO4] show saturation behavior indicative of equilibrium binding of the M2+ or H+ to the amide. Relative to the spontaneous methanolysis rate constant (ko), the catalytic rate constant obtained at saturation, kcat, is larger for metal-ion catalysis than for H+ catalysis. The (kcatH+/ko) ratio is 10.7 and 1.25 for 1 and 2, respectively, while the (kcatM2+/ko) for these divalent metals varies from 150-fold for 1 to between 700 and 5700-fold for 2. By contrast, in water, proton is far more effective at promoting the hydrolysis of 1 than are metals, the aqueous (kcatH+/ko) ratio being 560, while the (kcatZn2+ /ko) and (kcatNi2+/ko) ratios are 15 and 3.2, respectively.Key words: methanolysis, kinetics, metal-ion catalysis, acetyl imidazole, acetyl pyrazole.

scholarly journals The kinetics of substrate-induced inactivation

1991 ◽  
Vol 279 (1) ◽  
pp. 87-94 ◽  
Author(s):  
S G Waley
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Initial Rate ◽  
Active Form ◽  
Partition Ratio ◽  
Enzymic Activity ◽  
Progress Curve ◽  
Inactive Form ◽  
Reversible Formation ◽  
Kinetics Of

The kinetics of a branched-pathway mechanism for a simple enzymic reaction were studied. In this mechanism there is reversible formation of an inactive form of the second complex along the pathway. This substrate-induced inactivation typically results in the progress curve showing a burst. Three parameters can be obtained from the progress curve: the initial rate, the final rate and the rate constant characterizing the transient. The rate constant for the conversion of the inactive form of the complex into the active form can be obtained either from these parameters or by measuring the regain of enzymic activity. The partition ratio can also be obtained from the three parameters; this is the ratio of the rate of conversion of complex into product to the rate of conversion of complex into inactive form. Simulations give guidance to the conditions required for accurate determinations of the rate constants.

Sign in / Sign up

Export Citation Format

Share Document