Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Molecules. 2019 Aug 18;24(16):2990. doi: 10.3390/molecules24162990.
A series of ditopic ion pair receptors equipped with 4-nitrophenylurea and 1-aza-18-crown-6-ether linked by ortho-(), meta-(), and para-() substituted benzoic acid were readily synthesized in three steps from commercially available materials. The binding properties of these regioisomeric receptors were determined using UV-vis and H NMR spectroscopy in MeCN and in the solid state by single-crystal X-ray diffraction crystallography. The solution studies revealed that, apart from carboxylates, all the anions tested formed stronger complexes in the presence of sodium cations. Receptors and were found to interact with ion pairs with remarkably higher affinity than -substituted . H NMR titration experiments showed that both urea NH protons interacted with anions with comparable strength in the case of receptors and , but only one of the NHs was effective in anion binding in the case of receptor . X-ray analysis of the crystal structure of receptor and ·NaPF complex showed that binding was hampered due to the formation of an intramolecular hydrogen bond. Analysis of the crystal structures of ·NaBr and ·NaBr complexes revealed that proper mutual orientation of binding domains was responsible for the improved binding of the sodium salts.
一系列配备了 4-硝基苯脲和 1-氮杂-18-冠-6-醚的双位离子对受体，通过邻位（）、间位（）和对位（）取代苯甲酸连接，可从商业可得的材料通过三步法轻松合成。这些区域异构体受体的结合性质通过在 MeCN 中的 UV-vis 和 H NMR 光谱以及通过单晶 X 射线衍射晶体学在固态中进行测定。溶液研究表明，除了羧酸根外，所有测试的阴离子在钠离子存在下都形成了更强的配合物。发现受体和与离子对相互作用的亲和力明显高于取代的。H NMR 滴定实验表明，在受体和的情况下，两个脲基 NH 质子与阴离子以相当的强度相互作用，但在受体的情况下，只有一个 NH 对阴离子结合有效。受体和·NaPF 配合物的晶体结构分析表明，由于形成了分子内氢键，结合受到阻碍。对·NaBr 和·NaBr 配合物的晶体结构分析表明，结合结构域的适当相互取向是提高钠盐结合的原因。
