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Journal of the American Chemical Society

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Contrast media (Diagnostic imaging) -- Synthesis, Ligands (Biochemistry), Magnetic resonance imaging, Hydrogen-ion concentration


Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 mM-1 s-1 at pH 9 to 7.0 mM-1 s-1 at pH 5 as a result of acid-catalyzed dissociation of the nitrophenol from the lanthanide. The nitrophenol group in Gd(NP-DO3AM) does not dissociate from the metal center even at pH 5; therefore, the very modest increase in relaxivity in this complex must be ascribed to an increase in prototropic exchange rate of the bound water and/or phenolic protons.


This is the authors' version of a paper that subsequently appeared in the Journal of the American Chemical Society, vol. 126, no. 30: 9248-9256. The version of record may be found at

Copyright ©2004 American Chemical Society

Note: At the time of writing Mark Woods was affiliated with the University of Texas at Dallas.



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