Zhang S, Wu K, Sherry AD
Department 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).
Angew Chem Int Ed Engl. 1999 Nov 2;38(21):3192-3194.
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.
一种具有酰胺配位基团和伸展的非配位膦酸酯基团的1,4,7,10-四氮杂环十二烷四取代衍生物与钆(III)形成一种配合物（如图所示），该配合物含有一个缓慢交换的内球水分子（τ(M)=21微秒）。发现该配合物的20兆赫水质子弛豫率高度依赖于pH值。非配位膦酸酯基团的质子化似乎催化了结合水质子的质子转移交换，从而提供了一种在pH值低于7时增强水对比度的机制。
