Structures of urea/thiourea 1,3-disubstituted thia[4]calixarenes and corresponding monofunctional receptors and their anion recognition properties
作者:Carol Pérez-Casas、Herbert Höpfl、Anatoly K. Yatsimirsky
DOI:10.1007/s10847-010-9798-0
日期:2010.12
Two thiacalix[4]arenes in 1,3-alternate conformation functionalized by two (CH2)2NH(C=X)NHC6H4-NO2-p groups (X = S,O) as well as two related monofunctional receptors MeO(CH2)2NH(C=X)NHC6H4-NO2-p were prepared and characterized by X-ray crystal structures. The thioureido and ureido derivatives have E,Z and E,E conformations respectively both in monofunctional receptors and thiacalixarenes. The thiacalixarene attached thiourea groups are well separated from each other, but respective urea groups are much closer to each other and have mutual parallel orientation making the bisurea derivative a better preorganized receptor as compared to bisthiourea. Binding of Cl−, F−, H2PO4 − and AcO− anions in chloroform and DMSO was studied by spectrophotometric and NMR titrations. In chloroform both bisurea and bisthiourea thiacalix[4]arenes bind anions 3–5 times stronger than corresponding monofunctional compounds in spite of better preorganization of the urea derivative. In DMSO simultaneous deprotonation of ureido NH groups of receptors and hydrogen bonding reactions are observed. Deprotonation by H2PO4 − is accompanied by a strong association between liberated H3PO4 and H2PO4 − (log K = 3.9). For hydrogen bonding associations the binding constants of H2PO4 − and AcO− with bisurea thiacalixarene are up to two orders of magnitude larger than those with corresponding monofunctional receptor, but with bisthiourea thiacalixarene the effect is less than two-fold. Thus in this solvent in contrast to chloroform the preorganization is an important factor.
通过 X 射线晶体结构,制备并表征了由两个 (CH2)2NH(C=X)NHC6H4-NO2-p 基团(X = S,O)官能化的 1,3 邻构象的两种硫杂六[4]烯,以及两种相关的单官能受体 MeO(CH2)2NH(C=X)NHC6H4-NO2-p。硫脲基和脲基衍生物在单官能团受体和硫杂六烯烃中分别具有 E,Z 和 E,E 构象。与双硫脲相比,硫杂六烯丙基脲上的硫脲基团彼此分离得很好,但各自的脲基团彼此更接近,并具有相互平行的取向,这使得双硫脲衍生物成为一种更好的预组织受体。通过分光光度法和核磁共振滴定法研究了氯仿和二甲基亚砜中 Cl-、F-、H2PO4 - 和 AcO - 阴离子的结合情况。在氯仿中,尽管脲衍生物的预组织能力更强,但双脲和双硫脲硫杂[4]烷与阴离子的结合力都比相应的单官能团化合物强 3-5 倍。在二甲基亚砜中,受体的脲基 NH 基团同时发生去质子化反应和氢键反应。H2PO4 - 的去质子化伴随着释放出的 H3PO4 和 H2PO4 - 之间的强结合(log K = 3.9)。就氢键结合而言,H2PO4 - 和 AcO- 与双脲噻卡力蒈烯的结合常数比与相应的单官能团受体的结合常数大两个数量级,但与双硫脲噻卡力蒈烯的结合常数则小于两个数量级。因此,与氯仿相比,在这种溶剂中,预组织是一个重要因素。