Oligomere Harnstoffe - Synthese, Konformation und Anionenbindung

尿素功能(R-NH-CO-NH-R)能够与同一受体形成两个氢键，并已被用作豆荚类型的各种阴离子受体的结合部位。如果三个尿素官能团被结合在一个大小合适的大环中，阴离子应该被六个聚合的R-NH···X氢键结合，如示意图所示的硝酸盐。在第一次分子动力学模拟的基础上，预测了三方平面阴离子如硝酸盐或碳酸盐，特别是“三脚架”阴离子如磺酸盐和磷酸盐的高结合能。在这个项目的框架内，将合成这种一般类型的各种大环三脲，因为间隔基的大小或形状的细微变化很可能会对络合行为产生巨大的影响。这些配体的设计将主要基于分子动力学模拟，其次是对这些“铅结构”的合理修改。延伸到大环外的额外取代基将在非极性或水溶液中实现溶解，和/或产生显色或荧光性质。使用核磁共振滴定、UV-Vis光谱或电导法等技术，将确定一系列感兴趣的阴离子的结合常数。量热测量将完成络合反应的热力学数据集。所得结果将再次与计算值进行比较，以详细了解络合情况并检验理论/数学模型的有效性。在选定的案例中，我们还将尝试测量络合/解络动力学(动态核磁共振和停流技术)。为了比较，我们将合成和研究线性类似物(三到六脲)，它们应该呈螺旋构象，最终由络合阴离子诱导(S)。这些研究可能最终扩展到螺旋聚脲的构建。

Urea functions (R-NH-CO-NH-R) are able to form two hydrogen bonds to the same acceptor and have been used as binding sites in various anion receptors of the podand type. If three urea functions are incorporated in a suitably sized macrocycle anions should be bound by six convergent R-NH···X hydrogen bonds as indicated schematically for nitrate. High binding energies are predicted on the basis of first MD simulations for trigonal planar anions such as Nitrate or Carbonate and especially for "tripodal" anions such as Sulfonate and Phosphonate. In the frame of this project various macrocylic triureas of this general type will be synthesised, since subtle changes of the size or shape of the spacer groups will most probably have drastic influences on the complexation behaviour. The design of these ligands will be based primarily on MD simulations, and secondly on reasonable modifications of these "lead structures". Additional substituents extending the outside of the macrocycle will achieve solubility either in apolar or aqueous solutions and/or create chromo- or fluorophoric properties. Binding constants for the range of interesting anions will be determined, using techniques like NMR-titration, UV-Vis spectrometry or conductimetry. Calorimetric measurements will complete the set of thermodynamic data for the complexation. The results thus obtained will be compared again with calculated values, to understand the complexation in detail and to check the validity of the theoretical/mathematical model. In selected cases we will also try to measure the complexation/decomplexation kinetics (dynamic NMR and stoppped-flow techniques). For comparison we will synthesise and study linear analogues (tri- to hexa-ureas), which should assume a helical conformation, eventually induced by the complexed anion(s). These studies might be extended finally to the construction of helical poly-ureas.