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A Novel pH-Sensitive MRI Contrast Agent
1Department of Chemistry, University of Texas at Dallas, P.O. Box 830688, Richardson TX 75083-0688 (USA) (and) The Rogers Magnetic Resonance Center, Department of Radiology, University of Texas Southwestern Medical Center, 5801 Forest Park Road, Dallas, TX 75235-9085 (USA).
Abstract:
A tetrasubstituted derivative of 1,4,7,10-tetraazacyclododecane with amide coordinating groups and extended noncoordinating phosphonate groups forms a complex with gadolinium(III) (shown in the picture) which contains one slowly exchanging inner-sphere water molecule (tau(M)=21 µs). The 20-MHz water proton relaxivity of the complex was found to be highly pH dependent. Protonation of the noncoordinating phosphonate groups appears to catalyze prototropic exchange of the bound water protons, thereby providing a mechanism for enhanced water contrast below pH 7.