Neutral CH bond vs. electron pair of N(sp2): A binding site effect study of macrocycle anion receptor

To evaluate the effect of neutral CH bond or electron pair of nitrogen atom with sp2 hybridization (N(sp2)) involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine) [2](1,3-dimethylenebenzene) (14+), and cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine)[2](2,6-di methylenepyridine) (24+) were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl−, N3−, NO3−, and H2PO4−. The host–guest interactions were characterized via1H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites (14+ with neutral CH vs.24+ with N (sp2)) vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.

Graphical abstractThis paper mainly discussed the effect of two binding site (neutral CH vs. N(sp2)) in similar anion receptor on anion binding.Figure optionsDownload full-size imageDownload as PowerPoint slide