20 - Lecture 20: Catalytic Mechanisms 1 Monday, August 23,...

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Unformatted text preview: Lecture 20: Catalytic Mechanisms 1 Monday, August 23, 2010 Protein catalysts, which accelerate the rate at which a chemical reaction reaches equilibrium, are able to achieve their remarkable properties due to two distinct things: 1. They are able to very specifically recognize and bind their substrates with high anity. 2. They arrange the substrates in the optimal orientation for reaction. Monday, August 23, 2010 The specific mechanisms by which they perform catalysis are classified as: a. Acid-base catalysis b. Covalent catalysis c. Metal ion catalysis d. Electrostatic catalysis e. Proximity and orientation effects f. Preferential binding of the transition state complex Often, enzymes use a mixture of the above six methods in their specific mechanism of catalysis. Monday, August 23, 2010 GENERAL ACID-BASE CATALYSIS: A reaction that is accelerated by the participation of a general acid or base that serves to donate/abstract a proton during the chemical reaction. Example: keto-enol tautomerization: uncatalyzed, there is a significant buildup of negative charge on the carbonNOT GOOD! Monday, August 23, 2010 A general acid or base can stimulate this reaction by reducing the carbanion character of the transition state or by direct proton abstraction (above, general acid catalyzed; below, general base catalyzed)....
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20 - Lecture 20: Catalytic Mechanisms 1 Monday, August 23,...

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