Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: An allosteric regulation of the first metal ion for stepwise extraction of the second ion
Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: An allosteric regulation of the first metal ion for stepwise extraction of the second ion
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DOI：
10.1039/c1an15199a
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发表时间：
2011-01-01
期刊：
影响因子：
4.2
通讯作者：
Ohto, Keisuke
中科院分区：
文献类型：
--
作者：
Adhikari, Birendra Babu;Gurung, Manju;Ohto, Keisuke
开发了一种基于杯[5]芳烃的溶剂萃取试剂3，在下缘附加了羧酸基团，并研究了其对一些过渡金属离子的络合行为。主体3可以在pH 1.8以上选择性地、定量地提取Pb(II)离子，而其他二价离子如Cu(II)、Zn(II)、Co(II)、Ni(II)仅在pH 3.0以上被定量提取。 3优异的Pb(II)选择性来自于杯[5]芳烃空腔中Pb(II)离子的尺寸配合互补效应。一个 3 分子逐步提取两个 Pb(II) 离子。第一个 Pb(II) 离子被提取到由苯氧基氧原子定义的杯[5]芳烃的深腔中。第一个络合的 Pb(II) 离子充当模板，使主体形成锥形构象，并诱导正变构效应，以在由羧基组成的富氧配位位点提取第二个 Pb(II) 离子。两种 Pb(II) 离子都通过离子交换机制被萃取，有机相中的电中性络合物是通过将等量的氢离子释放到水溶液中而形成的。使用稀酸溶液可以轻松地从 Pb(II) 络合物 3 中反萃取负载的 Pb(II)。
A calix[5] arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5] arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5] arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.