Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 126, Issue 30, Pages 9248-9256Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja048299z
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Funding
- NCI NIH HHS [R21 CA084697, CA-84697, CA96019, R33 CA084697] Funding Source: Medline
- NCRR NIH HHS [RR-02584, P41 RR002584] Funding Source: Medline
- NIBIB NIH HHS [EB-04285, R21 EB004285, R21 EB004285-02, R21 EB004285-01] Funding Source: Medline
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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-DWAM) 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.
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