The solution and solid-state structures of lanthanide complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetryltetramethylenetetra(benzylphosphinate), L1a, and of its o-, m- and p-methoxybenzyl analogues (L2, L3, L4) have been investigated by NMR, relaxometry, crystallographic and photophysical methods. It has been shown that the number of proximate water molecules is dependent on the size of the bound lanthanide ion: the complex [LaL1a]– is nine-co-ordinate and adopts a twisted square-antiprismatic structure with one bound water molecule. The analogous [YL1a]–, [YbL1a]–, [GdL1a]– and [EuL1a]– complexes also adopt a twisted square-antiprismatic geometry, but are eight-co-ordinate, with no metal-bound water. Relaxivity studies with the gadolinium complexes showed that they are purely ‘outer-sphere’ contrast agents, but they associate strongly with proteins leading to a pronounced relaxivity enhancement. Detailed biodistribution studies with [GdL1a]– revealed avid biliary uptake at low doses and a well defined tendency for the complex to be cleared more slowly from tumour tissue, allowing tissue differentiation.
利用NMR、弛豫测量、晶体学和光物理方法研究了1,4,7,10-四
氮杂环十二烷-1,4,7,10-四乙撑四(苄基
膦酸酯), L1a及其邻、间、对甲氧基苄基类似物(
L2、L3、L4)的
镧系配合物的溶液和固态结构。结果表明,邻近的
水分子数目取决于结合的
镧系离子的大小:配合物[LaL1a]–是九配位的,具有一个结合
水分子,呈扭曲的方形反棱柱结构。类似的[YL1a]–、[YbL1a]–、[GdL1a]–和[EuL1a]–配合物也采取扭曲的方形反棱柱几何结构,但为八配位,没有
金属结合
水。对
钆配合物的弛豫率研究表明,它们是纯粹的“外球”对比剂,但与蛋白质强相互作用导致弛豫率显著提高。详细
生物分布研究揭示[GdL1a]–在低剂量下有强烈胆汁摄取,且该配合物从肿瘤组织中的清除速度较慢,这有利于组织区分。