Introduction to Catalysis
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Enzyme Activity and Assays Introductory Article
Enzyme Activity and Assays Introductory article Robert K Scopes, La Trobe University, Bundoora, Victoria, Australia Article Contents . Factors that Affect Enzymatic Analysis Enzyme activity refers to the general catalytic properties of an enzyme, and enzyme assays . Initial Rates and Steady State Turnover are standardized procedures for measuring the amounts of specific enzymes in a sample. Measurement of Enzyme Activity . Measurement of Protein Concentration Factors that Affect Enzymatic Analysis . Methods for Purifying Enzymes . Summary Enzyme activity is measured in vitro under conditions that often do not closely resemble those in vivo. The objective of measuring enzyme activity is normally to determine the exactly what the concentration is (some preparations of amount of enzyme present under defined conditions, so unusual substrates may be impure, or the exact amount that activity can be compared between one sample and present may not be known). This is because the rate another, and between one laboratory and another. The measured varies with substrate concentration more rapidly conditions chosen are usually at the optimum pH, as the substrate concentration decreases, as can be seen in ‘saturating’ substrate concentrations, and at a temperature Figure 1. In most cases an enzyme assay has already been that is convenient to control. In many cases the activity is established, and the substrate concentration, buffers and measured in the opposite direction to that of the enzyme’s other parameters used previously should be used again. natural function. Nevertheless, with a complete study of There are many enzymes which do not obey the simple the parameters that affect enzyme activity it should be Michaelis–Menten formula. -
Opportunities for Catalysis in the 21St Century
Opportunities for Catalysis in The 21st Century A Report from the Basic Energy Sciences Advisory Committee BASIC ENERGY SCIENCES ADVISORY COMMITTEE SUBPANEL WORKSHOP REPORT Opportunities for Catalysis in the 21st Century May 14-16, 2002 Workshop Chair Professor J. M. White University of Texas Writing Group Chair Professor John Bercaw California Institute of Technology This page is intentionally left blank. Contents Executive Summary........................................................................................... v A Grand Challenge....................................................................................................... v The Present Opportunity .............................................................................................. v The Importance of Catalysis Science to DOE.............................................................. vi A Recommendation for Increased Federal Investment in Catalysis Research............. vi I. Introduction................................................................................................ 1 A. Background, Structure, and Organization of the Workshop .................................. 1 B. Recent Advances in Experimental and Theoretical Methods ................................ 1 C. The Grand Challenge ............................................................................................. 2 D. Enabling Approaches for Progress in Catalysis ..................................................... 3 E. Consensus Observations and Recommendations.................................................. -
Dehydrogenation by Heterogeneous Catalysts
Dehydrogenation by Heterogeneous Catalysts Daniel E. Resasco School of Chemical Engineering and Materials Science University of Oklahoma Encyclopedia of Catalysis January, 2000 1. INTRODUCTION Catalytic dehydrogenation of alkanes is an endothermic reaction, which occurs with an increase in the number of moles and can be represented by the expression Alkane ! Olefin + Hydrogen This reaction cannot be carried out thermally because it is highly unfavorable compared to the cracking of the hydrocarbon, since the C-C bond strength (about 246 kJ/mol) is much lower than that of the C-H bond (about 363 kJ/mol). However, in the presence of a suitable catalyst, dehydrogenation can be carried out with minimal C-C bond rupture. The strong C-H bond is a closed-shell σ orbital that can be activated by oxide or metal catalysts. Oxides can activate the C-H bond via hydrogen abstraction because they can form O-H bonds, which can have strengths comparable to that of the C- H bond. By contrast, metals cannot accomplish the hydrogen abstraction because the M- H bonds are much weaker than the C-H bond. However, the sum of the M-H and M-C bond strengths can exceed the C-H bond strength, making the process thermodynamically possible. In this case, the reaction is thought to proceed via a three centered transition state, which can be described as a metal atom inserting into the C-H bond. The C-H bond bridges across the metal atom until it breaks, followed by the formation of the corresponding M-H and M-C bonds.1 Therefore, dehydrogenation of alkanes can be carried out on oxides as well as on metal catalysts. -
Sustainable Catalysis
Green Process Synth 2016; 5: 231–232 Book review Sustainable catalysis DOI 10.1515/gps-2016-0016 Sustainable catalysis provides an excellent in-depth over- view of the applications of non-endangered elements in Michael North (Ed.) all aspects of catalysis from heterogeneous to homogene- Sustainable catalysis: with non-endangered metals ous, from catalyst supports to ligands. The Royal Society of Chemistry, 2015 Four volumes of the book series are divided into RSC Green Chemistry series nos. 38–41 two sub-topics devoted to (i) metal-based catalysts and Part 1 (ii) catalysts without metals or other endangered ele- Print ISBN: 978-1-78262-638-1 ments. Each sub-topic comprises of two books due to the PDF eISBN: 978-1-78262-211-6 detailed analysis of catalytic applications described. All Part 2 chapters are written by the world-leading researchers in Print ISBN: 978-1-78262-639-8 the area; however, covering far beyond the scope of their PDF eISBN: 978-1-78262-642-8 immediate research interests, which makes the book par- ticularly valuable for a wide range of readers. Sustainable catalysis: without metals or other Sustainable catalysis: with non-endangered metals endangered elements begins with a very brief chapter which describes the Part 1 concept of elemental sustainability, overviewing the Print ISBN: 978-1-78262-640-4 abundance of the critical elements and perspectives on PDF eISBN: 978-1-78262-209-3 sustainable catalysts. The chapters follow the groups of EPUB eISBN: 978-1-78262-752-4 the periodic table from left to right, from alkaline metals to Part 2 lead spanning 22 chapters. -
The Early History of Catalysis
The Early History of Catalysis By Professor A. J. B. Robertson Department of Chemistry, King’s College, London One hundred and forty years ago it was Berzelius proceeded to propose the exist- possible for one man to prepare an annual ence of a new force which he called the report on the progress of the whole of “catalytic force” and he called “catalysis” the chemistry, and for many years this task was decomposition of bodies by this force. This undertaken by the noted Swedish chemist is probably the first recognition of catalysis J. J. Berzelius for the Stockholm Academy of as a wide-ranging natural phenomenon. Sciences. In his report submitted in 1835 and Metallic catalysts had in fact been used in published in 1836 Berzelius reviewed a num- the laboratory before 1800 by Joseph Priestley, ber of earlier findings on chemical change in the discoverer of oxygen, and by the Dutch both homogeneous and heterogeneous sys- chemist Martinus van Marum, both of whom tems, and showed that these findings could be made observations on the dehydrogenation of rationally co-ordinated by the introduction alcohol on metal catalysts. However, it seems of the concept of catalysis. In a short paper likely that these investigators regarded the summarising his ideas on catalysis as a new metal merely as a source of heat. In 1813, force, he wrote (I): Louis Jacques Thenard discovered that ammonia is decomposed into nitrogen and “It is, then, proved that several simple or compound bodies, soluble and insoluble, have hydrogen when passed over various red-hot the property of exercising on other bodies an metals, and ten years later, with Pierre action very different from chemical affinity. -
Physical Organic Chemistry
CHM 8304 Physical Organic Chemistry Catalysis Outline: General principles of catalysis • see section 9.1 of A&D – principles of catalysis – differential bonding 2 Catalysis 1 CHM 8304 General principles • a catalyst accelerates a reaction without being consumed • the rate of catalysis is given by the turnover number • a reaction may alternatively be “promoted” (accelerated, rather than catalysed) by an additive that is consumed • a heterogeneous catalyst is not dissolved in solution; catalysis typically takes place on its surface • a homogeneous catalyst is dissolved in solution, where catalysis takes place • all catalysis is due to a decrease in the activation barrier, ΔG‡ 3 Catalysts • efficient at low concentrations -5 -4 -5 – e.g. [Enz]cell << 10 M; [Substrates]cell < 10 - 10 M • not consumed during the reaction – e.g. each enzyme molecule can catalyse the transformation of 20 - 36 x 106 molecules of substrate per minute • do not affect the equilibrium of reversible chemical reactions – only accelerate the rate of approach to equilibrium end point • most chemical catalysts operate in extreme reaction conditions while enzymes generally operate under mild conditions (10° - 50 °C, neutral pH) • enzymes are specific to a reaction and to substrates; chemical catalysts are far less selective 4 Catalysis 2 CHM 8304 Catalysis and free energy • catalysis accelerates a reaction by stabilising a TS relative to the ground state ‡ – free energy of activation, ΔG , decreases – rate constant, k, increases • catalysis does not affect the end point -
Concepts and Tools for Mechanism and Selectivity Analysis in Synthetic Organic Electrochemistry
Concepts and tools for mechanism and selectivity analysis in synthetic organic electrochemistry Cyrille Costentina,1,2 and Jean-Michel Savéanta,1 aUniversité Paris Diderot, Sorbonne Paris Cité, Laboratoire d’Electrochimie Moléculaire, Unité Mixte de Recherche Université–CNRS 7591, 75205 Paris Cedex 13, France Contributed by Jean-Michel Savéant, April 2, 2019 (sent for review March 19, 2019; reviewed by Robert Francke and R. Daniel Little) As an accompaniment to the current renaissance of synthetic organic sufficient to record a current-potential response but small electrochemistry, the heterogeneous and space-dependent nature of enough to leave the substrates and cosubstrates (of the order of electrochemical reactions is analyzed in detail. The reactions that follow one part per million) almost untouched. Competition of the the initial electron transfer step and yield the products are intimately electrochemical/chemical events with diffusional transport under coupled with reactant transport. Depiction of the ensuing reactions precisely mastered conditions allows analysis of the kinetics profiles is the key to the mechanism and selectivity parameters. within extended time windows (from minutes to submicroseconds). Analysis is eased by the steady state resulting from coupling of However, for irreversible processes, these approaches are blind on diffusion with convection forced by solution stirring or circulation. reaction bifurcations occurring beyond the kinetically determining Homogeneous molecular catalysis of organic electrochemical reactions step, which are precisely those governing the selectivity of the re- of the redox or chemical type may be treated in the same manner. The same benchmarking procedures recently developed for the activation action. This is not the case of preparative-scale electrolysis accom- of small molecules in the context of modern energy challenges lead to panied by identification and quantitation of products. -
Materials Science
Materials Science Materials Science is an interdisciplinary field combining physics (fundamental laws of nature), chemistry (interactions of atoms) and biology (how life interacts with materials) to elucidate the inherent properties of basic and complex systems. This includes optical (interaction with light), electrical (interaction with charge), magnetic and structural properties of everyday electronics, clothing and architecture. The Materials Science central dogma follows the sequence: Structure—Properties—Design—Performance. This involves relating the nanostructure of a material to its macroscale physical and chemical properties. By understanding and then changing the structure, material scientists can create custom materials with unique properties. The goal of the materials science minor is to create a cross-disciplinary approach to fundamental topics in basic and applied physical sciences. Students will gain experience and perspectives from the disciplines of chemistry, physics and biology. The minor places a strong emphasis on current nanoscale research methods in addition to the basics of electronic, optical and mechanical properties of materials. Any student with an interest in pursuing the cross-disciplinary minor in materials science should consult with the coordinator of the minor. Students are encouraged to declare their participation in their sophomore year but no later than the end of the junior year. Students also should seek an adviser from participating faculty. Degree Requirements for the Minor General College requirements -
Recitation Section 4 Answer Key Biochemistry—Energy and Glycolysis
MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 4 Answer Key February 14-15, 2005 Biochemistry—Energy and Glycolysis A. Why do we care In lecture we discussed the three properties of a living organism: metabolism, regulated growth, and replication. Today we will focus on metabolism and biosynthesis. 1. It was said in lecture that chemical reactions are the basis of life. Why do we say that? Being alive implies being able to change your state in response to a change in internal or environmental conditions. We discussed previously that any change in the observable characteristics of a cell begins as and is propagated by molecular interactions. Molecular interactions propagate the signal by changing the state of molecules, i.e. by reactions. 2. Why is metabolism required for life? A cell is subject to all laws of chemistry and physics, including the first and second law of thermodynamics. Changing the state of molecules dissipates energy along the way, so getting or making new energy is essential to life. The energy is then used for many purposes, including making the building blocks and precursors and then using them to build macromolecules that make up cells—biosynthesis. 3. Can an entity that performs no chemical reactions be considered “alive?” In general, no. But there are special cases of the cells that do not perform reactions right at the moment, but have the potential to perform reactions if they encounter particular conditions. Some examples of such cells are spores in nature or frozen permanents in laboratory. If they experience certain conditions, such as availability of food for spores, or defrosting and food source for frozen permanents, these cells will again perform metabolism. -
2.4 the Breakdown Chemical Reactions Bonds Break and Form During Chemical Reactions
DO NOT EDIT--Changes must be made through “File info” CorrectionKey=B 2.4 Chemical Reactions KEY CONCEPT VOCABULARY Life depends on chemical reactions. chemical reaction MAIN IDEAS reactant Bonds break and form during chemical reactions. product Chemical reactions release or absorb energy. bond energy equilibrium activation energy Connect to Your World exothermic When you hear the term chemical reaction, what comes to mind? Maybe you think endothermic of liquids bubbling in beakers. You probably do not think of the air in your breath, but most of the carbon dioxide and water vapor that you breathe out are made by chemical reactions in your cells. MAIN IDEA Bonds break and form during chemical reactions. Plant cells make cellulose by linking simple sugars together. Plant and animal cells break down sugars to get usable energy. And all cells build protein mol- ecules by bonding amino acids together. These are just a few of the chemical reactions in living things. Chemical reactions change substances into different substances by breaking and forming chemical bonds. Although the matter changes form, both matter and energy are conserved in a chemical reaction. Reactants, Products, and Bond Energy Your cells need the oxygen molecules that you breathe in. Oxygen (O2) plays a part in a series of chemical reactions that provides usable energy for your cells. These reactions, which are described in detail in the chapter Cells and Energy, break down the simple sugar glucose (C6H12O6). The process uses oxygen and glucose and results in carbon dioxide (CO2), water (H2O), and usable energy. Oxygen and glucose are the reactants. -
Electrochemistry and Photoredox Catalysis: a Comparative Evaluation in Organic Synthesis
molecules Review Electrochemistry and Photoredox Catalysis: A Comparative Evaluation in Organic Synthesis Rik H. Verschueren and Wim M. De Borggraeve * Department of Chemistry, Molecular Design and Synthesis, KU Leuven, Celestijnenlaan 200F, box 2404, 3001 Leuven, Belgium; [email protected] * Correspondence: [email protected]; Tel.: +32-16-32-7693 Received: 30 March 2019; Accepted: 23 May 2019; Published: 5 June 2019 Abstract: This review provides an overview of synthetic transformations that have been performed by both electro- and photoredox catalysis. Both toolboxes are evaluated and compared in their ability to enable said transformations. Analogies and distinctions are formulated to obtain a better understanding in both research areas. This knowledge can be used to conceptualize new methodological strategies for either of both approaches starting from the other. It was attempted to extract key components that can be used as guidelines to refine, complement and innovate these two disciplines of organic synthesis. Keywords: electrosynthesis; electrocatalysis; photocatalysis; photochemistry; electron transfer; redox catalysis; radical chemistry; organic synthesis; green chemistry 1. Introduction Both electrochemistry as well as photoredox catalysis have gone through a recent renaissance, bringing forth a whole range of both improved and new transformations previously thought impossible. In their growth, inspiration was found in older established radical chemistry, as well as from cross-pollination between the two toolboxes. In scientific discussion, photoredox catalysis and electrochemistry are often mentioned alongside each other. Nonetheless, no review has attempted a comparative evaluation of both fields in organic synthesis. Both research areas use electrons as reagents to generate open-shell radical intermediates. Because of the similar modes of action, many transformations have been translated from electrochemical to photoredox methodology and vice versa. -
2. Electrochemistry
EP&M. Chemistry. Physical chemistry. Electrochemistry. 2. Electrochemistry. A phenomenon of electric current in solid conductors (class I conductors) is a flow of electrons caused by the electric field applied. For this reason, such conductors are also known as electronic conductors (metals and some forms of conducting non-metals, e.g., graphite). The same phenomenon in liquid conductors (class II conductors) is a flow of ions caused by the electric field applied. For this reason, such conductors are also known as ionic conductors (solutions of dissociated species and molten salts, known also as electrolytes). The question arises, what is the phenomenon causing the current flow across a boundary between the two types of conductors (known as an interface), i.e., when the circuit looks as in Fig.1. DC source Fig. 1. A schematic diagram of an electric circuit consis- flow of electrons ting of both electronic and ionic conductors. The phenomenon occuring at the interface must involve both the electrons and ions to ensure the continuity of the circuit. metal metal flow of ions ions containing solution When a conventional redox reaction occurs in a solution, the charge transfer (electron transfer) happens when the two reacting species get in touch with each other. For example: Ce4+ + Fe 2+→ Ce 3+ + Fe 3+ (2.1) In this reaction cerium (IV) draws an electron from iron (II) that leads to formation of cerium (III) and iron (III) ions. Cerium (IV), having a strong affinity for electrons, and therefore tending to extract them from other species, is called an oxidizing agent or an oxidant.