the investigators proposed a mechanism of ester hydrolysis in which the ester group with a series of copper(II) substituted iminodiacetic acid complexes were
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R etrospective hTheses and Dissertations *1..!)%0!,-%.3+-.*)!-5!-!-) % M etal ion complex catalysis of amino acid esterh ydrolysisB ruce Eugene Leach F ollow this and additional works at:$
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)*,#)%$!(%-.,3*((*)-hThis Dissertation is brought to you for free and open access by the Iowa State University Capstones, hTheses and Dissertations at Iowa State University%
#%.'!+*-%.*,3.$-!!)!+.! "*,%)'/-%*)%)!.,*-+!.%0!5!-!-) %--!,..%*)-3)/.$*,%4! (%)%-.,.*,*"*1..!)%0!,-%.3%
#%.'!+*-%.*,3*,(*,!%)"*,(.%*)+'!-!*).. %#%,!+%-..!! /R ecommended CitationL each, Bruce Eugene, "Metal ion complex catalysis of amino acid ester hydrolysis " (1968). . 3487.6+-'% ,%-..!! /,.
I This dissertation has been microfilmed exactly as received69-4254 LEACH, Bruce Eugene, 1942-
METALION COMPLEX CATALYSIS OF AMINO
ACID ESTERHYDROLYSIS. Iowa State University,
Ph.D., 1968
Chemistry,
Inorganic University Microfilms, Inc., Ann Arbor, Michigan METAL ION COMPLEX CATALYSIS OF AMINO ACID ESTER HYDROLYSIS ADissertation Submitted
to theGraduate
Faculty
in Partial Fulfillment of TheRequirements
for the Degree ofDOCTOR
OF PHILSOPHY
MajorSubject: Inorganic Chemistry by
BruceEugene
LeachApproved :
Work ofGraduate College
IowaState University
Ames, Iowa1968 Signature was redacted for privacy.
Signature was redacted for privacy.
Signature was redacted for privacy.
iiTABLE OF CONTENTS Page
INTRODUCTION 1 EXPERIMENTAL 20 Instrumentation 20 Materials 22 Preparation and Characterisation of Compounds 25 Equilibrium
Measurements 4? Kinetic Measurements 46 RESULTS
52 Amino Acid Ester-N,N-diacetic Acids
52 Amino Acid Esters 81 DISCUSSION AND
CONCLUSION 102 Amino Acid Estei-N,N-diacetic Acids 102 Amino Acid Esters 117 BIBLIOGRAPHY 132 ACKNOWLEDGMENTS 1?7 VITA
138 APPENDIX
139 Derivation of a Calculable Expression for the
Formation
Constant
of Amino AcidEsters
with [MZ]o 139 Derivation of aCalculable
Expression
for the Formation Constant of Amino Acids with [MZ]° 141 1INTRODUCTION
Metal ion catalysis of the hydrolysis of a-amino acid esters was discovered in1952 by Kroll (1). Since that time
those reactions have been studied by a number of research groups with hopes of elucidating the nature of the hydrolytic process and the role of metal ions in biological systems. Esters of a-amino acids are an example of a class of impor tant biological compounds which are energy-rich. An energy- rich compound has been defined as one whose reaction with a substance commonly present in the environment is accompanied by a large negative free energy change at physiological pH (2). Amino acid esters which are important intermediates in the biosynthesis of proteins, have a standard free energy of hydrolysis which is comparable to that of adenosine triphosphate, ATP. At physiological pH in the absence of metal ions the rate of hydrolysis of amino acid esters is very slow. In general, four reactions must be considered. They involve water and hydroxide ion attack upon the protonated and free base esters. EH + HgO ^1 productsEH + OH" ^2 products
E + HgO *3 products
E + OH" ^4 products
2Conley
andMartin
(3) have investigated the hydrolysis of - 9 - 1 glycine ethyl ester and found = 5 ± 3 x 10 sec. ,
kg = 24 M~^ sec."^, kg = immeasurably slow, and k^ = 0.58 sec. . In agreement with the greater nucleophilicity of hydroxide ion, most of the hydrolysis near pH 7 is catalyzed by hydroxide ion. Hay, Porter and Morris (4) have studied the basic hydrolysis of ethyl glycinate, methyl glycinate, ethyl betaine ethyl ester, ethyl leucinate, methyl leucinate, methyl cysteinate, methyl serinate, ethyl phenylalaninate and dimethyl glutamate at25.0°
and ionic strength 0.1 M and determined the ionization constants of the esters. They found that the ionization constants for amino acid esters were approximately two pK units lower than those for the corresponding amino acids. Protonation of the amino group of an amino acid ester results in a much greater reactivity of the protonated species in alkaline hydrolysis. The effect of charge on ester hydrolysis was demonstrated (4) by comparison of the rates of hydrolysis for ethyl glycinate, ethyl betaine ethyl ester and cysteine methyl ester. Positively charged betaine ethyl ester, [(C2Hg)gNCHgC00C2Hg]^, hydrolyzes 36times faster than ethyl glycinate,