Gd3+ complexes with slowly exchanging bound-water molecules may offer advantages in the design of responsive MR agents.
OBJECTIVE
Slow water exchange in Gd3+ complexes is generally considered detrimental to their use as MR contrast agents. The objective of this work was to demonstrate how this feature may serve as a useful template for the design of responsive MR agents.


METHODS
Lanthanide (Ln) complexes of two 1,4,7,10-tetraazacyclododecane-N,N',N",N'"-tetraacetic acid (DOTA)-tetraamide phosphonate (1) and phosphonate ester (2) ligands were studied by multinuclear (1H, 13C, 31P, and 17O) nuclear MR spectroscopy.


RESULTS
The inner-sphere water lifetime in the Ln(2) complexes was much longer (tauM298 = 0.8-1.3 ms) than in the corresponding Ln(1) complexes. This allowed direct detection of the bound-water molecule in europium(2) in water at 40 degrees C by 1H nuclear MR. The water relaxivity of gadolinium(2) was independent of pH between 8.5 and 6.0, whereas the relaxivity of gadolinium(1) increased more than twofold in this pH range.


CONCLUSIONS
T1-weighted images of phantoms containing gadolinium(1) at different pH values demonstrate the efficacy of this complex as a pH-sensitive MR contrast agent.
Department of Chemistry, University of Texas at Dallas, Richardson, USA.
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Zhang
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Sherry
D003287:Contrast Media / Q000737:chemistry*; D005682:Gadolinium / Q000737:chemistry*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008674:Metals, Rare Earth / Q000737:chemistry; D014867:Water
D003287:Contrast Media; D008674:Metals, Rare Earth; D014867:Water; D005682:Gadolinium