Urea-Functionalized M4L6 Cage Receptors: Anion-Templated Self-Assembly and Selective Guest Exchange in Aqueous Solutions

详细信息    查看全文

• 作者：Radu Custelcean ; Peter V. Bonnesen ; Nathan C. Duncan ; Xiaohua Zhang ; Lori A. Watson ; Gary Van Berkel ; Whitney B. Parson ; Benjamin P. Hay
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：May 23, 2012
• 年：2012
• 卷：134
• 期：20
• 页码：8525-8534
• 全文大小：409K
• 年卷期：v.134,no.20(May 23, 2012)
• ISSN：1520-5126

文摘

We present an extensive study of a novel class of de novo designed tetrahedral M₄L₆ (M = Ni, Zn) cage receptors, wherein internal decoration of the cage cavities with urea anion-binding groups, via functionalization of the organic components L, led to selective encapsulation of tetrahedral oxoanions EO₄^{n鈥?/sup> (E = S, Se, Cr, Mo, W, n = 2; E = P, n = 3) from aqueous solutions, based on shape, size, and charge recognition. External functionalization with tBu groups led to enhanced solubility of the cages in aqueous methanol solutions, thereby allowing for their thorough characterization by multinuclear (1H, 13C, 77Se) and diffusion NMR spectroscopies. Additional experimental characterization by electrospray ionization mass spectrometry, UV鈥搗is spectroscopy, and single-crystal X-ray diffraction, as well as theoretical calculations, led to a detailed understanding of the cage structures, self-assembly, and anion encapsulation. We found that the cage self-assembly is templated by EO₄n鈥?/sup> oxoanions (n 鈮?2), and upon removal of the templating anion the tetrahedral M₄L₆ cages rearrange into different coordination assemblies. The exchange selectivity among EO₄n鈥?/sup> oxoanions has been investigated with 77Se NMR spectroscopy using 77SeO₄2鈥?/sup> as an anionic probe, which found the following selectivity trend: PO₄3鈥?/sup> CrO₄2鈥?/sup> > SO₄2鈥?/sup> > SeO₄2鈥?/sup> > MoO₄2鈥?/sup> > WO₄2鈥?/sup>. In addition to the complementarity and flexibility of the cage receptor, a combination of factors have been found to contribute to the observed anion selectivity, including the anions鈥?charge, size, hydration, basicity, and hydrogen-bond acceptor abilities.}