Co-ordination chemistry and molecular mechanics study of the magnesium(II) and calcium(II) complexes of trisubstituted 1,4,7-triazacyclononane derivatives
作者:Jurriaan Huskens、A. Dean Sherry
DOI:10.1039/a703640j
日期:——
The affinities of 1,4,7-tris(2-hydroxyalkyl)-1,4,7-triazacyclononane derivatives for MgII and CaII were found to differ greatly. Whereas 1,4,7-tris(2-hydroxyethyl)- (L1), 1,4,7-tris(2-hydroxy-2-methylpropyl)- (L2) and the unsymmetrical 1,4,7-tris(2-hydroxypropyl)-1,4,7-triazacyclononane derivative L3b barely discriminated between MgII and CaII, the symmetrical isomer L3a was more than 500 times more selective for MgII than for CaII. Similar selectivity differences were observed between the diastereomers of 1,4,7-tris(2-hydroxy-2-phenylethyl)- (L4) and 1,4,7-tris(2-hydroxydodecyl)-1,4,7-triazacyclononane (L5). These selectivities were related to the structure of the magnesium complexes as shown by molecular mechanics (MMX) calculations. Only those ligands favoring the formation of a magnesium complex with a large twist angle between the planes of co-ordinating oxygens and ring nitrogens resulting in a small, tight cavity showed a large preference for MgII over CaII. The MMX calculations predicted large twist angle structures for phosphinate derivatives, and for a phosphonate monoester derivative, and these ligands were found to have a high selectivity for MgII. Similarly, the calculated preference for the smaller twist angle correctly predicted the lack of MgII/CaII selectivity for acetate and amide derivatives and for a phosphonate diester derivative. Equilibration of the complexes of the ligands in the presence of both MgII and CaII was slow, as shown for example by kd,0 = 2.1 × 10–4 s–1 for CaL3a. These dissociation rates were a factor of 100 times larger at the boundary of a two-phase (water–chloroform) system.
发现1,4,7-三(2-羟烷基)-1,4,7-三氮杂环壬烷衍生物对MgII和CaII的亲和力差异很大。而 1,4,7-三(2-羟乙基)- (L1)、1,4,7-三(2-羟基-2-甲基丙基)-(L2) 和不对称 1,4,7-三(2 (羟丙基)-1,4,7-三氮杂环壬烷衍生物L3b几乎无法区分MgII和CaII,对称异构体L3a对MgII的选择性比对CaII的选择性高500倍以上。在 1,4,7-三(2-羟基-2-苯基乙基)-(L4) 和 1,4,7-三(2-羟基十二烷基)-1,4,7-三氮杂环壬烷的非对映异构体之间观察到类似的选择性差异(L5)。正如分子力学 (MMX) 计算所示,这些选择性与镁络合物的结构有关。只有那些有利于形成镁配合物的配体,该配合物在配位氧和环氮平面之间具有大扭转角,从而形成小而紧密的空腔,才显示出对 MgII 的优先选择超过 CaII。 MMX 计算预测了次膦酸酯衍生物和膦酸酯单酯衍生物的大扭转角结构,并且发现这些配体对 MgII 具有高选择性。类似地,计算出的对较小扭转角的偏好正确地预测了 MgII/CaII 对乙酸酯和酰胺衍生物以及膦酸酯二酯衍生物缺乏选择性。在 MgII 和 CaII 存在的情况下,配体复合物的平衡很慢,如 CaL3a 的 kd,0 = 2.1 × 10–4 s–1 所示。在两相(水-氯仿)系统的边界处,这些解离速率是原来的 100 倍。