The synthesis and characterization of a resorcinarene-based tetra(imidazole) ligand is reported. The properties of the corresponding Zn^II complex are studied in depth, notably by NMR spectroscopy. In MeCN, acid–base titration reveals that one out of the four imidazole arms is hemi-labile and can be selectively protonated, thereby opening a coordination site in the exo position. Quite remarkably, the 4^th imidazole arm promotes binding of an acidic molecule (a carboxylic acid, a β-diketone or acetamide), by acting as an internal base, which allows guest binding as an anion to the metal center in the endo position. Most importantly, the presence of this labile imidazole arm makes the Zn^II complex active for the catalyzed hydration of acetonitrile. It is proposed that it acts as a general base for activating a water molecule in the vicinity of the metal center during its nucleophilic attack to the endo-bound MeCN substrate. This system presents a unique degree of biomimetism when considering zinc enzymes: a pocket for guest binding, a similar first coordination sphere, a coordination site available for water activation in the cis position relative to the substrate and finally an internal imidazole residue that plays the role of a general base.

中文翻译：

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的3^次biomimetism度：关联所述腔效应，锌^II协调和客人结合和激活内部基极援助†

报道了基于间苯二甲烯的四（咪唑）配体的合成和表征。深入研究了相应的Zn ^II配合物的性质，尤其是通过NMR光谱。在MeCN中，酸碱滴定表明，四个咪唑臂中的一个是半不稳定的，可以选择性地质子化，从而在exo位置打开一个配位点。相当显着的，这4^个咪唑臂促进酸性分子的（一个羧酸，β二酮或乙酰胺）结合，通过作为内部基极，这使得旅客结合作为阴离子在金属中心内的位置。最重要的是，这个不稳定的咪唑臂的存在使Zn ^II对乙腈催化水合具有活性的络合物。提出了它作为在金属中心附近对内结合的MeCN底物的亲核攻击期间活化金属中心附近的水分子的一般基础。考虑到锌酶，该系统具有独特的仿生度：一个用于客体结合的口袋，一个类似的第一配位球，一个可在相对于底物的顺式位置上被水活化的配位位点，最后是一个内部咪唑残基一般基础。