Boron acid complexation reactions: Equilibria, thermodynamics and metal ion binding.
Item
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Title
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Boron acid complexation reactions: Equilibria, thermodynamics and metal ion binding.
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Identifier
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AAI9510711
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identifier
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9510711
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Creator
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Ricatto, Pascal John.
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Contributor
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Adviser: Richard Pizer
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Date
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1994
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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 | Environmental Sciences
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Abstract
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The application of both {dollar}\sp1{dollar}H and {dollar}\sp{11}{dollar}B NMR to the study of boron acid complexation reactions is demonstrated in this work. Variable temperature FTNMR is shown to be a reliable technique for the determination of thermodynamic parameters ({dollar}\Delta\rm H\sp\circ{dollar} and {dollar}\Delta\rm S\sp\circ{dollar}) for the complexation reactions of borate with a wide range of ligands. Results for the reactions of aliphatic diols with various borate ions show that all of these reactions are quite similar. The reactions are all exothermic with an average value of {dollar}\Delta\rm H\sp\circ{dollar} {dollar}\sim{dollar} {dollar}-{dollar}20 kJ/mol. All of the entropy changes are quite negative ({dollar}\Delta\rm S\sp\circ{dollar} {dollar}\sim{dollar} {dollar}-{dollar}60 J/mol K) and this can be attributed to the loss of ligand configurational entropy on complexation.;Results for reactions of borate ion with {dollar}\alpha{dollar}-hydroxy carboxylic acids and dicarboxylic acids show that the large increase in K{dollar}\sb1{dollar} for {dollar}\alpha{dollar}-hydroxy carboxylic acids compared with K{dollar}\sb1{dollar} for the reaction of borate with diols is entirely due to a much more favorable {dollar}\Delta\rm H\sp\circ{dollar}. The second complexation reaction here is emphatically different from the first. K{dollar}\sb2{dollar} is much smaller than K{dollar}\sb1{dollar} and extremely large differences in both {dollar}\Delta\rm H\sp\circ{dollar} and {dollar}\Delta\rm S\sp\circ{dollar} are observed.;The results for these systems as well as those presented for the formation of mixed ligand complexes show the important effect the first ligand has on subsequent bis complex formation. Many of these results can be explained by the significant differences found in boron - oxygen bonds of the various borates as determined by AM1 calculations.;The synergic binding of both Ca{dollar}\sp{lcub}2+{rcub}{dollar} and Sr{dollar}\sp{lcub}2+{rcub}{dollar} is demonstrated in the ternary M{dollar}\sp{lcub}2+{rcub}{dollar}/borate/tartrate system. Ca{dollar}\sp{lcub}2+{rcub}{dollar} and Sr{dollar}\sp{lcub}2+{rcub}{dollar} show a large preference for coordination to 1:2 borotartrate complexes (BT{dollar}\sb2\sp{lcub}5-{rcub}{dollar}) compared with 1:1 complexes (BT{dollar}\sp{lcub}3-{rcub}{dollar}) or free tartrate (T{dollar}\sp{lcub}2-{rcub}{dollar}). Stability constants for these synergic interactions were determined for both the BT{dollar}\sb2\sp{lcub}5-{rcub}{dollar} (I - tartrate) and BT{dollar}\sb2\sp{lcub}5-{rcub}{dollar} (meso - tartrate) complexes. On the other hand, Mg{dollar}\sp{lcub}2+{rcub}{dollar} binds preferentially to free tartrate, T{dollar}\sp{lcub}2-{rcub}{dollar}, and shows little if any interaction with the borotartrate complex ions. A terdentate metal ion binding site on the BT{dollar}\sb2\sp{lcub}5-{rcub}{dollar} complex is proposed which is consistent with both our experimental results and molecular mechanics (MM2) calculations.
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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.
