Probing the Water Coordination of Protein-Targeted MRI Contrast Agents by Pulsed ENDOR Spectroscopy

A novel methodology based on electron–nuclear double resonance (ENDOR) spectroscopy is used for the direct determination of the water coordination number (q) of gadolinium‐based magnetic resonance imaging (MRI) contrast agents. Proton ENDOR spectra can be obtained at approximately physiological conc...

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Bibliographic Details
Published in:Chemphyschem 2005-12, Vol.6 (12), p.2570-2577
Main Authors: Zech, Stephan G., Sun, Wei-Chuan, Jacques, Vincent, Caravan, Peter, Astashkin, Andrei V., Raitsimring, Arnold M.
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Contrast Media - chemistry
Electron Spin Resonance Spectroscopy
ENDOR spectroscopy
Fundamental and applied biological sciences. Psychology
Gadolinium - chemistry
hyperfine couplings
Magnetic Resonance Imaging
metal complexes
Molecular Structure
Protein Binding
proteins
Proteins - chemistry
Solutions
transition metals
Water - chemistry
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Summary:A novel methodology based on electron–nuclear double resonance (ENDOR) spectroscopy is used for the direct determination of the water coordination number (q) of gadolinium‐based magnetic resonance imaging (MRI) contrast agents. Proton ENDOR spectra can be obtained at approximately physiological concentrations for metal complexes in frozen aqueous solutions either in the presence or absence of protein targets. It is shown that, depending on the structure of the co‐ligand, the water hydration number of a complex in aqueous solution can be significantly different to when the complex is noncovalently bound to a protein. From the ENDOR spectra of the exchangeable protons, precise information on the metal–proton distance can be derived as well. These essential parameters directly correlate with the efficacy of MRI contrast agents and should therefore aid the development of novel, highly efficient compounds targeted to various proteins. Electron–nuclear double resonance (ENDOR) spectroscopy is used for the direct determination of water coordination numbers and proton–metal distances of gadolinium‐based magnetic resonance imaging (MRI) contrast agents. It is shown that the water hydration number q of a complex in aqueous solution can be significantly different to when the complex is noncovalently bound to a protein (see picture; HSA= human serum albumin).
ISSN:1439-4235
1439-7641
DOI:10.1002/cphc.200500250