作者:Ivan Vatsouro、Ellen Alt、Myroslav Vysotsky、Volker Böhmer
DOI:10.1039/b719053k
日期:——
Ten tetra-urea calix[4]arene derivatives with different ether residues (methyl, pentyl, benzyl, all combinations of methyl and pentyl, 1,3-dibenzyl-2,4-dipentyl), including also the tetrahydroxy compound and the 1,3-dipentyl ether, were synthesised. Their urea groups were substituted with a lipophilic residue to ensure sufficient solubility in cyclohexane. Thus, kinetics for the exchange of the included guest (benzene) against the solvent (cyclohexane) could be followed by 1H NMR spectroscopy. The apparent first order rate constants decrease with increasing size of the ether residues from methyl to benzyl by more than three orders of magnitude. This can be understood by a decreasing flexibility/mobility of the calixarene skeleton. In line with this explanation is the rather slow exchange for the tetrahydroxy compound, where the cone conformation is stabilised by a cyclic array of intramolecular OH⋯OH hydrogen bonds.
我们合成了十种具有不同醚残基(甲基、戊基、苄基、甲基和戊基的所有组合、1,3-二苄基-2,4-二戊基)的四脲钙[4]炔衍生物,其中还包括四羟基化合物和 1,3- 二戊基醚。它们的脲基被亲脂残基取代,以确保在环己烷中有足够的溶解度。因此,可以通过 1H NMR 光谱跟踪所含客体(苯)与溶剂(环己烷)的交换动力学。随着醚残基(从甲基到苄基)大小的增加,表观一阶速率常数降低了三个数量级以上。这可以用卡利卡林骨架的柔韧性/流动性降低来解释。与这一解释相一致的是四羟基化合物的交换相当缓慢,锥形构象通过分子内 OH⋯OH 氢键的循环阵列而稳定。