Woods Mark, Zhang Shanrong, Ebron Von Howard, Sherry A Dean
Department of Chemistry, University of Texas at Dallas, P.O. Box 803066, Richardson, Texas 75083, USA.
Chemistry. 2003 Oct 6;9(19):4634-40. doi: 10.1002/chem.200305159.
The lanthanide(III) complexes of three tetraamide DOTA bearing pyridyl, phenolic and hydroxypyridyl substituents have been studied by NMR, luminescence and cyclic voltammetry. The relaxivity profiles of the gadolinium complexes of the pyridyl and phenolic ligands were flat and essentially the same between pH 2 and 8. The hydroxypyridyl ligand, however, exhibited two regions of enhanced relaxivity. The small relaxivity enhancement (25 %) at lower pH (pH 2-4) has been attributed to an increase in the prototropic exchange of the coordinated water molecule while the slightly larger enhancement (84 %) at higher pH (pH 6-9) reflects deprotonation of the ligand amide protons. Deprotonation of the amides results in the formation of an intramolecular acid-base pair interaction with the phenolic protons and this, in turn, causes a highly organized second hydration sphere to come into effect, thereby increasing the relaxivity. The water relaxivity of the Gd(3+)-hydroxypyridyl complex is further enhanced upon binding to serum albumin.
通过核磁共振、发光和循环伏安法研究了三种带有吡啶基、酚基和羟基吡啶基取代基的四酰胺DOTA的镧系元素（III）配合物。吡啶基和酚基配体的钆配合物的弛豫率曲线在pH 2至8之间是平坦的，并且基本相同。然而，羟基吡啶基配体表现出两个弛豫率增强的区域。在较低pH值（pH 2-4）下弛豫率的小幅增强（25%）归因于配位水分子的质子转移交换增加，而在较高pH值（pH 6-9）下稍大的增强（84%）反映了配体酰胺质子的去质子化。酰胺的去质子化导致与酚质子形成分子内酸碱对相互作用，这反过来又导致高度有序的第二水合层起作用，从而提高弛豫率。Gd（3+）-羟基吡啶基配合物与血清白蛋白结合后，水弛豫率进一步提高。
