The Experimental and Theoretical Determination of Combinatorial Kinetic Isotope Effects for Mechanistic Analysis PDF Download
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Author: Chad F. Christian
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Unfortunately, chemists can never experimentally unravel a full reaction pathway. Even our ability to define key aspects of mechanisms, such as short-lived intermediates and the even more ephemeral transition states, is quite limited, requiring subtle experiments and subtle interpretations. Arguably the most important knowledge to be gained about the mechanism of a reaction is the structure and geometry of the transition state at the rate-limiting step, as this is where a reaction0́9s rate and selectivity are generally decided. The Singleton group has developed a methodology for predicting the combinatorial kinetic isotope effects (KIEs) at every atomic position, typically carbon or hydrogen, at natural abundance. A combination of experimental isotope effects and density functional theory (DFT) calculations has greatly aided our ability to predict and understand a reaction0́9s pathway and transition state geometries. Precise application of this method has allowed for the mechanistic investigation of a myriad of bioorganic, organic, and organometallic reactions. The technique has been applied in the analysis of the catalytic borylation of arenes via C-H bond activation, dynamic effects in the enyne allene cyclization, palladium catalyzed allylic alkylation, the nature of proton transfer in orotate decarboxylase, and the epoxidation of enones with t-butyl hydroperoxide.
Author: Chad F. Christian
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Unfortunately, chemists can never experimentally unravel a full reaction pathway. Even our ability to define key aspects of mechanisms, such as short-lived intermediates and the even more ephemeral transition states, is quite limited, requiring subtle experiments and subtle interpretations. Arguably the most important knowledge to be gained about the mechanism of a reaction is the structure and geometry of the transition state at the rate-limiting step, as this is where a reaction0́9s rate and selectivity are generally decided. The Singleton group has developed a methodology for predicting the combinatorial kinetic isotope effects (KIEs) at every atomic position, typically carbon or hydrogen, at natural abundance. A combination of experimental isotope effects and density functional theory (DFT) calculations has greatly aided our ability to predict and understand a reaction0́9s pathway and transition state geometries. Precise application of this method has allowed for the mechanistic investigation of a myriad of bioorganic, organic, and organometallic reactions. The technique has been applied in the analysis of the catalytic borylation of arenes via C-H bond activation, dynamic effects in the enyne allene cyclization, palladium catalyzed allylic alkylation, the nature of proton transfer in orotate decarboxylase, and the epoxidation of enones with t-butyl hydroperoxide.
Author:
Publisher: Academic Press
ISBN: 0128122749
Category : Medical
Languages : en
Pages : 634
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Book Description
Experimental Analysis of Enzyme Mechanism Using Isotope Effects, Volume 596, the latest release in the Methods in Enzymology series, continues the legacy of this premier serial with quality chapters authored by leaders in the field. Chapters in this comprehensive update include Measurement of enzyme binding isotope effects, Chemical ligation and isotope labeling to locate dynamic effects, Measurement of heavy enzyme isotope effects, Extracting kinetic isotope effects from a global analysis of reaction progress curves, KIE of metabolic flux and enzymes, Solvent and Primary KIE on Flavin Enzymes, and The Rapid Determination of Primary Deuterium Isotope Effects on Enzyme-Catalyzed Proton Transfer at Carbon in 50/50 HOH/DOD. Readers who are interested in applying or understanding this research will find useful methods currently used for measuring isotope effects on solution and enzyme reactions. Written by pioneers of modern isotope effect research Is the only collection of modern kinetic isotope effect methods currently available
Author: Paul F. Cook
Publisher: CRC Press
ISBN: 9780849353123
Category : Medical
Languages : en
Pages : 656
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Book Description
Isotope effects have become one of the most powerful tools available to the enzymologist for probing enzymic mechanisms. Enzyme Mechanism from Isotope Effects presents the basic theory underlying isotope effects, including the latest findings on proton tunneling and coupled atomic notions. Specific theoretical applications are emphasized in regard to the types of information that can be obtained using isotope effects. The book also examines recent theoretical treatments of the product dependence of deuterium isotope effects, multiple isotope effects and isotope effects on intermediate partitioning. Other topics include a complete discussion of methods for measuring isotope effects, including a detailed description of the use of the isotope ratio mass spectrometer to obtain isotope effects, and a review of the literature regarding mechanistic information obtained from isotope effects for individual classes of enzyme-catalyzed reactions. Enzyme Mechanism from Isotope Effects is an excellent reference source for investigators using isotope effects in their research. The book is also valuable for reference libraries and instructors teaching courses in enzyme mechanism.
Author: Zhihong Wang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Several organic reactions that could potentially involve coarctate transition states were investigated by a combination of experimental and theoretical studies. In the thermal fragmentation of [delta]-1,3,4-oxadiazolines, the mechanism supported by kinetic isotope effects and theoretical calculations is a three-step process that does not demonstrate any special stabilization in coarctate transition states. Rather than undergoing a direct coarctate conversion to product, the mechanism avoids coarctate steps. The last step is a concerted coarctate reaction, but being concerted may be viewed as being enforced by the necessity to avoid high-energy intermediates. In the deoxygenation of epoxides with dichlorocarbene, the stabilization from the transition state aromaticity is not great enough to compete with the preference for asynchronous bonding changes. KIEs and calculations suggested that the reaction occurs in a concerted manner but with a highly asynchronous early transition state with much more C[alpha]-O bond breaking than C[beta]-O bond breaking. In the Shi epoxidation, a large [beta]-olefinic 13C isotope effect and small [alpha-carbon isotope effect indicated an asynchronous transition state with more advanced formation of the C-O bond to the [beta]-olefinic carbon. The calculated lowest-energy transition structures are generally those in which the differential formation of the incipient C-O bonds, the "asynchronicity," resembles that of an unhindered model, and the imposition of greater or less asynchronicity leads to higher barriers. In reactions of cis-disubstituted and terminal alkenes using Shi's oxazolidinone catalyst, the asynchronicity of the epoxidation transition state leads to increased steric interaction with the oxazolidinone when a [pi]-conjugating substituent is distal to the oxazolidinone but decreased steric interaction when the [pi]-conjugating substituent is proximal to the oxazolidinone. Dynamic effects were studied in Diels-Alder reaction between acrolein and methyl vinyl ketone. This reaction yields two products in a ratio of 3.0 " 0.5. Theoretical studies shows that only one transition structure is involved in the formation of both. Quasiclassical trajectory calculations on an MP2 surface give a prediction of a product ratio of 45:14 (3.2:1), which is in good agreement with the experimental observation.
Author: Mathew J. Vetticatt
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The mechanism of three important aldol reactions and a biomimetic transamination is investigated using a combination of experimental kinetic isotope effects (KIEs), standard theoretical calculations and dynamics trajectory simulations. This powerful mechanistic probe is found to be invaluable in understanding intricate details of the mechanism of these reactions. The successful application of variational transition state theory including multidimensional tunneling to theoretically predict isotope effects, described in this dissertation, represents a significant advance in our research methodology. The role of dynamic effects in aldol reactions is examined in great detail. The study of the proline catalyzed aldol reaction has revealed an intriguing new dynamic effect - quasiclassical corner cutting - where reactive trajectories cut the corner between reactant and product valleys and avoid the saddle point. This phenomenon affects the KIEs observed in this reaction in a way that is not predictable by transition state theory. The study of the Roush allylboration of aldehydes presents an example where recrossing affects experimental observations. The comparative study of the allylboration of two electronically different aldehydes, which are predicted to have different amounts of recrossing, suggests a complex interplay of tunneling and recrossing affecting the observed KIEs. The Mukaiyama aldol reaction has been investigated and the results unequivocally rule out the key carbon-carbon bond forming step as rate-limiting. This raises several interesting mechanistic scenarios - an electron transfer mechanism with two different rate-limiting steps for the two components, emerges as the most probable possibility. Finally, labeling studies of the base catalyzed 1,3- proton transfer reaction of fluorinated imines point to a stepwise process involving an azomethine ylide intermediate. It is found that dynamic effects play a role in determining the product ratio in this reaction.
Author: Jennifer Sue Hirschi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
A variety of biological and organic reaction mechanisms are studied using powerful tools from experimental and theoretical chemistry. These tools include the precise measurement of kinetic isotope effects (KIEs) and the use of theoretical calculations to predict KIEs as well as determine factors that contribute to reaction acceleration and selectivity. Theoretical analysis of the Swain-Schaad relationship involves the prediction of a large number of isotope effects and establishes the semiclassical boundaries of the relationship. Studies on the mechanism of oxidosqualene cyclase involve the determination of a large number of precise KIEs simultaneously. Transition state models for the Sharpless asymmetric epoxidation have been developed that explain the versatility, high selectivities, and ligand accelerated catalysis of the reaction. Theoretical predictions on the proposed enzymatic mechanism of flavin dependent amine oxidation suggest a hydride transfer mechanism and rules out mechanisms involving covalent intermediates. Finally, a theoretical analysis of Diels-Alder reactions successfully describes the unexpected exo selectivity in some of these reactions.
Author: Marvin J. Stern
Publisher:
ISBN:
Category : Chemical kinetics
Languages : en
Pages : 44
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Book Description
Author: Steven Ray Merrigan
Publisher:
ISBN:
Category :
Languages : en
Pages : 284
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Book Description
Author: Sungjin Kim
Publisher:
ISBN:
Category : Alkylation
Languages : en
Pages : 96
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Author:
Publisher:
ISBN:
Category : Chemical kinetics
Languages : en
Pages : 0
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Book Description
"Theoretical studies of hydrogen kinetic isotope effects are carried out with particular emphasis on the development of methods of analysis for the interpretation of experimental kinetic-isotope-effect data. Theoretical "exact" isotope-effect data are obtained by computer using a statistical-mechanical expression developed by Bigeleisen." -- Abstract.
