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Correlation of structure and function in oligonuclear zinc(II) model phosphatases
Bernhard Bauer-Siebenlist1, Franc Meyer, Etelka Farkas
1Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, D-37077 Göttingen, Germany.
Inorganic Chemistry
|July 9, 2004
Summary
This study explores dizinc(II) complexes as phosphoesterase models. Hydrolytic activity depends on the zinc-metal distance, hydroxide position, and coordination, with nonbridging hydroxides and sufficient coordination sites enhancing activity.
Area of Science:
- Bioinorganic Chemistry
- Coordination Chemistry
- Enzyme Mimicry
Background:
- Phosphoesterases are crucial enzymes catalyzing the hydrolysis of phosphoester bonds.
- Developing functional models of these enzymes aids in understanding their mechanisms and designing new catalysts.
- Dizinc(II) complexes offer a promising platform for mimicking the active sites of binuclear metalloenzymes.
Purpose of the Study:
- To synthesize and characterize pyrazolate-based dizinc(II) complexes as functional models for phosphoesterases.
- To investigate the structure-activity relationships governing the hydrolytic activity of these bimetallic complexes.
- To elucidate the role of molecular parameters, such as metal-metal distance and hydroxide nucleophile positioning, in catalytic efficiency.
Main Methods:
- Synthesis and characterization of pyrazolate-based dizinc(II) complexes.
- Potentiometric titrations for determining species distributions in solution.
- X-ray crystallography for elucidating solid-state structures.
- Hydrolysis kinetics studies using bis(p-nitrophenyl)phosphate (BNPP) as a substrate.
- Electrospray ionization mass spectrometry (ESI-MS) for monitoring substrate coordination.
Main Results:
- Dizinc(II) complexes exhibit varying hydrolytic activities influenced by the Zn...Zn distance, ligand topology, and hydroxide nucleophile positioning.
- A nonbridging hydroxide nucleophile and sufficient coordination sites for substrate and water activation enhance hydrolytic activity.
- Product inhibition by (p-nitrophenyl)phosphate was observed and characterized crystallographically.
- A decreased pK(a) of zinc-bound water was noted for intramolecularly hydrogen-bonded hydroxides.
Conclusions:
- The topology of the ligand scaffold critically controls the molecular parameters of the dizinc(II) core, impacting hydrolytic activity.
- Nonbridging hydroxide nucleophiles are more effective than bridging ones for phosphoesterase activity.
- Effective phosphoesterase models require adequate coordination sites to bind both the substrate and the nucleophile.