Tuning and Dissecting Electronic and Steric Effects in Ammonium Receptors: Nonactin vs Artificial Receptors
摘要:
Ion selective electrodes (ISE) based on three different tripodal receptors (5, 6, and 7) have been investigated for sensing ammonium ion. Each receptor is based on three pyrazole groups that can accept three H-bonds from the bound ammonium ion. The receptor based on 4-bromo-3,5-dimethylpyrazole (6) is the most sensitive with a detection limit for ammonium ion of 2.5 x 10(-5) M at pH 8. The detection limits for the receptors based on 2,3-dimethylpyrazole (5) and unsubstitued pyrazole (7) are 1,0 x 10(-4) and 2.0 x 10(-4) M, respectively. The selectivities of the receptors 5, 6, and 7 for sensing ammonium ion over potassium ion (logK(NH4)(-)/(+)(K)) are -2.8, -2.3, and -1.7, respectively. In contrast, the detection limit and the selectivity of a nonactin-based ISE are 2.2 x 10(-5) M and -1.3, respectively. Crystallographic studies reveal that 6 accepts three H-bonds from the bound ammonium and singly protonated receptor 5 forms three H-bonds with the bound water molecule.
Synthesis of Tripodal and Hexapodal Pyrazole- and Benzimidazole-Bearing Compounds
作者:Monika Mazik、Niklas Koch
DOI:10.1055/s-0033-1338518
日期:——
The syntheses of eight new tripodal and hexapodal benzimidazole- and pyrazole-bearing compounds, which are all potentially applicable for use as artificial receptors, are described. The prepared compounds contain either bromo-substituted heteroaromatic rings, able to participate in halogen-bonding interactions, or their analogues lacking the bromo substituents. Furthermore, the preparation of a new trisbenzimidazolium cage is included in this work. All used practical synthetic procedures are facilely accomplishable and provide the products in good to excellent yields. In addition, slightly modified, simplified synthetic procedures for five known tripodal compounds, which lead to better yields than those previously reported, are also detailed.