INHIBITION OF THERMAL ELECTRON TRANSFER REACTIONS BY SHORT SATURATED BARRIERS.
Item
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Title
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INHIBITION OF THERMAL ELECTRON TRANSFER REACTIONS BY SHORT SATURATED BARRIERS.
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Identifier
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AAI8401888
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identifier
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8401888
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Creator
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ANDERES, BERTA.
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Contributor
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David K. Lavallee
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Date
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1983
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Inorganic
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Abstract
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Numerous studies have determined the general adequacy of the theories of Marcus and Hush for rationalizing trends in rates of adiabatic outer-sphere electron transfer reactions. However, it is likely that the sizes of biological molecules often preclude the adiabatic mechanism that is typical of smaller molecules. Reactions in biological systems for which a tunneling mechanism has been discussed include photosynthesis and the conversion of oxygen to water. The latter electron transfer reactions involve a series of membrane-bound proteins, the cytochromes. The objective of this project is to try to understand how the separation of the cytochromes would affect the rate at which the electron is transferred from one site to the next. In order to study the electron transfer reactions, I synthesized model molecules which had to satisfy several criteria: (1) inert metal atoms, and (2) a rigid ligand so that the metal ions would be separated by a known distance and, (3) the reduction potentials for the reactions should be of the same order of magnitude as those of biological reactions, about 0.5V or less. One of the ligands I used was 1,4-dicyano{lcub}2.2.2{rcub}bicyclooctane. This ligand is rigid, providing a well-defined separation of the metal atoms. The inert metals used were Co(III) and Ru(III). The bimetallic complexes were synthesized by mixing the ligand with a chloro complex of Co(III) in the presence of (CF(,3)SO(,2))(,2)O to form the corresponding Co(III)-nitrile complex, followed by a second reaction in which the Ru(III) moeity was added using {lcub}Ru(NH(,3))(,5)(CF(,3)SO(,3)){rcub}(CF(,3)SO(,3))(,2). The relatively inert solvent sulfolane was used throughout. The reactions are rapid and the products stable for months. The Ru(III)-CN group does undergo acid-independent hydrolysis, but very slowly (t(, 1/2) > 5 h at 25(DEGREES)C). The Ru(III) site was rapidly reduced using Ru(NH(,3))(,6)('2+). Intramolecular reduction of Co(III) is very slow (< 10% after 10 h at 25(DEGREES)C). The inhibition of the electron transfer rate by the 4 (ANGSTROM) barrier is estimated to be at least a factor of 10('4).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Chemistry
