Solution structure of physiological Cu(His)2: novel considerations into imidazole coordination
Yamini P Ginotra1, Prasad P Kulkarni
1Biometry and Nutrition Group, Animal Sciences Division, Agharkar Research Institute, Pune 411 004, India.
Inorganic Chemistry
|September 3, 2009
Summary
The copper(II) bis(histidine) complex in solution is confirmed to be a neutral, five-coordinate structure. This finding resolves ongoing debates regarding histidine binding and copper complex geometry.
Area of Science:
- Coordination Chemistry
- Biophysical Chemistry
- Spectroscopy
Background:
- Discrepancies exist regarding the coordination mode of histidine binding to copper(II) and the solution structure of the [Cu(2+)(His)(2)] complex.
- Spectroscopic data suggest a six-coordinate species with N4O2 donor atoms, contrasting with X-ray crystallography findings of a five-coordinate N3O2 donor set.
Purpose of the Study:
- To elucidate the precise structure and coordination of the [Cu(2+)(His)(2)] complex in aqueous solution.
- To resolve the conflicting structural data obtained from spectroscopic and crystallographic methods.
Main Methods:
- Chemical modification of the [Cu(2+)(His)(2)] complex in solution using diethyl pyrocarbonate (DEPC).
- Monitoring of reaction products using spectrophotometry.
- Characterization of modified complexes via mass spectrometry.
Main Results:
- Spectrophotometric analysis indicated the presence of a free imidazole moiety within the [Cu(2+)(His)(2)] complex.
- Mass spectral analysis of DEPC-modified [Cu(2+)(His)(2)] revealed a peak at 587.8 amu, consistent with three DEPC adducts.
- These findings collectively support a specific structural model for the complex in solution.
Conclusions:
- The [Cu(2+)(His)(2)] complex in solution exists as a neutral, five-coordinate species.
- The coordination environment is characterized by N3O2 donor atoms, aligning with X-ray crystallographic data.
- This study provides critical evidence resolving the structural ambiguity of this important copper-histidine complex.
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