Metal ion- and vitamin B₆-catalyzed transamination and dephosphonylation of 2-amino-3-phosphonopropionic acid.
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1984.
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| Subjects: | |
| Online Access: | Link to OAKTrust Copy Link to ProQuest Copy |
| Abstract: | Schiff base formation between pyridoxal 5'-phosphate (PLP) and 2-amino-3-phosphonopropionic acid (APP) has been investigated by measurement of the corresponding NMR and electronic absorption spectra. The cis and trans forms of the Schiff bases were distinguished with the aid of the nuclear Overhauser effect. The equilibria in D(,2)O and H(,2)O between PLP, APP, PLP-APP Schiff base (SB), Zn(II) and the secondary liqand 2,6-pyridinedicarboxylic acid (PDA), have been determined by potentiometric H('+) and D('+) measurements, proton magnetic resonance, and ('31)P magnetic resonance. The ('31)P magnetic resonance of the Zn(II)-SB-PDA complex and the Zn(II)-SB'-PDA complex, where SB' is the Schiff base formed between 2-aminoethylphosphonic acid (2-AEP) and PLP, shows that at p D values < 8.50 Zn(I) is coordinated to the carboxylate group of the amino acid moiety of the SB, while at p D values > 8.50 the phosphonate group is coordinated to the Zn(II) ion. Aldimine and carbinolamine structures are proposed for the completely deprotonated 1:2 A1(III)-SB complex at p H values above 8.80. ('31)P NMR and ('1)H NMR were employed to show that the first protonation site of this species occurs at the phosphonate group of the carbinolamine part of the complex, and there is no second protonated species for the 1:2 A1(III)-SB in this p H range. Consequently the monoprotonated form is considered to have two terdentate ligands, one with a phosphonate group coordinated to the A1(III) ion and the other with a coordinated carboxylate group. The major species for the 1:2:2 Ga(III)-PLP-APP system are the 1:2 Ga(III)-SB complexes. Seven forms of the 1:2 Ga(III) Schiff base complexes are identified. The protonation sites are assigned as follows: the first two occur at the phosphonate groups, then two at the phosphate, followed by two protonations at the pyridine nitrogens of the two terdentate coordinated Schiff bases. Kinetic studies revealed that Ga(III), Al(III), Zn(II) and vitamin B(,6) catalyze transamination and dephosphonylation of APP in two steps: the first is transamination with formation of a ketimine intermediate, and the second is a dephosphonylation step. The rate constant of the dephosphonylation reaction is an order of magnitude higher for the species in which the carboxylate group is coordinated to the metal ion, compared with the species in which the two phosphonate groups are coordinated to the metal center. Thus the most active species in the metal-catalyzed systems are those in which the phosphonate groups are not coordinated to the metal ion. A complete reaction mechanism for these catalytic systems will be described. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xviii, 199 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 189-198). |