Chemical and functional characterization of metal-binding pseudotripeptides with different functionalized N-alkyl residues Dedicated to Professor Dr. Ernst-Gottfried Jaeger on occasion of his 65th birthday |
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Authors: | Seyfarth Lydia Greiner Georg Kuenzel Sebastian Poppitz Wolfgang Reissmann Siegmund |
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Institution: | (1) Institute of Biochemistry and Biophysics, Friedrich-Schiller-University Jena, Jena, Germany;(2) Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, Jena, Germany |
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Abstract: | Summary Pseudotripeptide ligands with 4 different N-functionalized glycine residues were qualitatively, semiquantitatively and quantitatively
tested for their complexation of the bivalent transition metal ions Zn2+, Cu2+, Co2+, Ni2+ and Mn2+. The functional side chains have different length and different groups available for complexation. MALDI-MS and ESI-MS were
used for more qualitative or semiquantitative estimation of the complex formation tendencies. The found ranking differs by
these two methods only for Zn2+ and Ni2+. For one of the pseudotripeptide ligands, the ligand L1, complex formation with certain transition metal was estimated quantitatively
by potentiometric titration. The Zn-complex of that ligand polarizes bound water strongly, resulting in a low pK
a
-value. Complexes of pseudotripeptide ligand L1 with certain metal ions were tested for their hydrolytic activity. The pseudo
first order rate constants of the hydrolysis of the substrates 4-nitrophenyl acetate and bis(4-nitrophenyl)phosphate were
compared to complexes with the same metal ions formed with a very well studied ligand from the literature, the 1,4,7,10-tetraaza
cyclododecane (cyclen). The hydrolysis of the phosphate ester occurs very slowly compared to the acetate ester. No correlation
exists between the estimated pK
a
values of complexes formed from ligand L1 with different metal ions and the phosphate ester hydrolysis. The Ni ions give
totally different hydrolytic activities for pseudotripeptide ligand L1 and cyclen. With one exception, the Ni-cyclen complex,
all other complexes have only a low or moderate catalytic activity.
Dedicated to Professor Dr. Ernst-Gottfried Jaeger on occasion of his 65th birthday. |
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Keywords: | complexation complex stability hydrolytic activity metal ions potentiometric titration pseudotripeptides |
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