Catalytic upgrading of ethanol to n-butanol using an aliphatic Mn–PNP complex: theoretical insights into reaction mechanisms and product selectivity

AbstractThe existence of post-transition state bifurcations on potential energy surfaces for organic and biological reaction mechanisms has been known for decades, but recently, new reports of bifurcations have been occurring at a much higher rate. Beyond simply discovering bifurcations, computational chemists are developing techniques to understand what aspects of molecular structure and vibrations control the product selectivity in systems containing bifurcations. For example, the distribution of products seen in simulations has been found to be extremely sensitive to the local environment of the reacting system (i.e. the presence of a catalyst, enzyme, or explicit solvent molecules). The outlook for the future of this field is discussed, with an eye towards the application of the principles discussed here by experimental chemists to design a reaction setup to efficiently generate desired products.

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An Interactive Classroom Activity Demonstrating Reaction Mechanisms and Rate-Determining Steps

Journal of Chemical Education ◽

10.1021/ed082p549 ◽

2005 ◽

Vol 82 (4) ◽

pp. 549 ◽

Cited By ~ 2

Author(s):

Laura D. Jennings ◽

Steven W. Keller

Keyword(s):

Reaction Mechanisms ◽

Classroom Activity ◽

Interactive Classroom ◽

Rate Determining Steps

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Critical Analysis of Kinetic Modeling Procedures

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2796 ◽

2011 ◽

Vol 9 (1) ◽

Cited By ~ 4

Author(s):

José Carlos Pinto ◽

Marcos W. Lobao ◽

Andre L. Alberton ◽

Marcio Schwaab ◽

Marcelo Embiruçu ◽

...

Keyword(s):

Experimental Data ◽

Kinetic Models ◽

Reaction Mechanisms ◽

Critical Analysis ◽

Kinetic Data ◽

Statistical Analyses ◽

Statistical Tools ◽

Combinatorial Explosion ◽

Kinetic Rate ◽

Rate Determining Steps

In this work, issues related to the mathematical modeling and statistical analyses of kinetic data are discussed. Firstly, problems related to the combinatorial explosion of the number of plausible kinetic models are analyzed, when complex reaction mechanisms are taken into consideration and distinct rate determining steps are assumed. Although modeling procedures based on rate-determining steps can lead to oversimplification of kinetic models, these procedures are still very popular because the existence of multiple rate-determining steps usually renders the analytical derivation of kinetic rate expressions impossible. However, if the derived kinetic models are too simple, one can face serious difficulties to fit the proposed models to available experimental data. Secondly, problems related to the statistical analyses of experimental data are discussed. Particularly, very often statistical tools are used even when some of the fundamental assumptions required for their validity are violated. For this reason, the fundamental grounds that support some of the most popular statistical tools are discussed in the framework of the kinetic analysis.

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Analyzing reactions of single mechanoenzyme molecules by light microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122538 ◽

1992 ◽

Vol 50 (1) ◽

pp. 426-427

Author(s):

Jeff Gelles

Keyword(s):

Image Processing ◽

Reaction Mechanisms ◽

Transient State ◽

Nanometer Scale ◽

Reaction Intermediates ◽

Enzyme Molecule ◽

Directed Movement ◽

Enzyme Molecules ◽

Individual Enzyme ◽

Single Reaction

Mechanoenzymes are enzymes which use a chemical reaction to power directed movement along biological polymer. Such enzymes include the cytoskeletal motors (e.g., myosins, dyneins, and kinesins) as well as nucleic acid polymerases and helicases. A single catalytic turnover of a mechanoenzyme moves the enzyme molecule along the polymer a distance on the order of 10−9 m We have developed light microscope and digital image processing methods to detect and measure nanometer-scale motions driven by single mechanoenzyme molecules. These techniques enable one to monitor the occurrence of single reaction steps and to measure the lifetimes of reaction intermediates in individual enzyme molecules. This information can be used to elucidate reaction mechanisms and determine microscopic rate constants. Such an approach circumvents difficulties encountered in the use of traditional transient-state kinetics techniques to examine mechanoenzyme reaction mechanisms.

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X-Ray Microanalysis of Nickel and Cobalt Intensified Peroxidase- Antiperoxidase For Verification of Reaction Sites

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119168 ◽

1985 ◽

Vol 43 ◽

pp. 468-469

Author(s):

A. Angel ◽

K. Miller ◽

V. Seybold ◽

R. Kriebel

Keyword(s):

Reaction Mechanisms ◽

Visual Discrimination ◽

Osmium Tetroxide ◽

Ultrastructural Level ◽

Microscopic Level ◽

Electron Microscopic Level ◽

Electron Microscopic ◽

X Ray ◽

Insoluble Polymer ◽

Cytochemical Reaction

Localization of specific substances at the ultrastructural level is dependent on the introduction of chemicals which will complex and impart an electron density at specific reaction sites. Peroxidase-antiperoxidase(PAP) methods have been successfully applied at the electron microscopic level. The PAP complex is localized by addition of its substrate, hydrogen peroxide and an electron donor, usually diaminobenzidine(DAB). On oxidation, DAB forms an insoluble polymer which is able to chelate with osmium tetroxide becoming electron dense. Since verification of reactivity is visual, discrimination of reaction product from osmiophillic structures may be difficult. Recently, x-ray microanalysis has been applied to examine cytochemical reaction precipitates, their distribution in tissues, and to study cytochemical reaction mechanisms. For example, immunoreactive sites labelled with gold have been ascertained by means of x-ray microanalysis.

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