Development of cryptand molecules of multiple ligation with allosteric binding behavior

这项工作旨在了解类隐形卟啉类化合物新的结合模式的机理，以及使变构结合成为可能的结构因素。合成了由6个吡咯和3个六元(杂)芳烃组成的类隐形卟啉化合物，并研究了它们与客体分子的多重结合行为。含有3个和2个吡啶的化合物分别与3个和2个羧酸结合，通过在CH2Cl2中的滴定实验观察到理想的正各向同性变构结合行为。在乙腈中观察到1：1或1：2主客比的中间络合物，表明在极性溶剂中基于多个氢键的变构结合是不利的。三个在吡咯-位上含有不同空间体积的烷基取代基的化合物被用来研究醇的结合行为。在氯化镉与乙醇的混合溶液上的VT-核磁共振实验显示了正的变构结合行为。吡啶旁边的大体积异丁基增加了平衡常数。桥头氰基取代的化合物大大提高了络合物的稳定性，从而扩大了变构结合的范围。

This work aimed at understanding the mechanistic aspect in the novel binding mode of cryptand-like porphyrinoids and also the structural factors that enables allosteric binding. A number of the cryptand-like porphyrinoids made of six pyrroles and three six-membered(hetero) aromatics were prepared and their multiple binding behavior of guest molecules was investigated. The cryptands containing three and two pyridines bind three and two carboxylic acids, respectively, where ideal positive homotropic allosteric binding behavior was observed through the titration experiments in CH_2Cl_2. The intermediate complexes of a one-to-one or a one-to-two host-guest ratio were observed in acetonitrile to show that allosteric binding based on multiple hydrogen bondings is unfavorable in polar solvents. Three cryptands containing alkyl substituents of a different steric bulk at the pyrrole.-positions were used to study binding behavior of alcohols. VT-NMR experiments on the dry CDCl_3 solution of a mixture of cryptand and alcohol revealed positive allosteric binding behavior. A bulky iso-butyl substituent next to the pyridine increased equilibrium constants. Cryptand with the cyano substituents at the bridgehead greatly improved the stability of the cryptand-like porphyrinoid, which expands the scope of allosteric binding.