| Abstract
| - Information about the transition states of metal-catalyzed hydrolysis reactions of model phosphatecompounds has been obtained through determination of isotope effects (IEs) on the hydrolysis reactions.Metal complexation has been found to significantly alter the transition state of the reaction from the alkalinehydrolysis reaction, and the transition state is quite dependent on the particular metal ion used. For thediester, ethyl p-nitrophenyl phosphate, the nonbridge 18O effect for the hydrolysis reactions catalyzed byCo(III) 1,5,9-triazacyclononane and Eu(III) were 1.0006 and 1.0016, respectively, indicative of a slightlyassociative transition state and little net change in bonding to the nonbridge oxygen. The reaction catalyzedby Zn(II) 1,4,7,10-tetraazacyclododecane had an 18O nonbridge IE of 1.0108, showing the reaction differssignificantly from the reaction of the noncomplexed diester and resembles the reactions of triesters. Reactionwith Co(III) 1,4,7,10-tetraazacyclododecane showed an inverse effect of 0.9948 reflecting the effects ofbonding of the diester to the Co(III). Lanthanide-catalyzed hydrolysis has been observed to have unusuallylarge 15N effects. To further investigate this effect, the 15N effect on the reaction catalyzed by Ce(IV) bis-Tris propane solutions at pH 8 was determined to be 1.0012. The 15N effects were also measured for thereaction of the monoester p-nitrophenyl phosphate by Ce(IV) bis-Tris propane (1.0014) and Eu(III) bis-Trispropane (1.0012). These smaller effects at pH 8 indicate that a smaller negative charge develops on thenitrogen during the hydrolysis reaction.
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