Brady Kimberly G, Gilberg Laura, Sigwalt David, Bistany-Riebman Joshua, Murkli Steven, Klemm Jared, Kulhánek Petr, Šindelář Vladimír, Isaacs Lyle
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States.
Department of Chemistry and RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic.
Supramol Chem. 2020;32(9):479-494. doi: 10.1080/10610278.2020.1795173. Epub 2020 Aug 13.
We report the synthesis of the conformationally mobile S-shaped glycoluril pentamer building block and two new acyclic CB[n]-type receptors and . (9 mM) and (11 mM) have moderate aqueous solubility but their host•guest complexes are poorly soluble. Host does not undergo intermolecular self-association whereas does (K = 189±27 M). H NMR titrations show that and are poor hosts toward hydrophobic (di)cations - (: K = 375-1400 M; : K = 1950-19800 M) compared to and (: K = 3.09 × 10 to 4.69 × 10 M; : K = 4.59 × 10 to 1.30 × 10 M). Molecular modelling shows that and exist as a mixture of three different conformers due to the two S-shaped methylene bridged glycoluril dimer subunits that each possess two different conformations. The lowest energy conformers of and do not feature a well-defined central cavity. In the presence of guests, adapts its conformation to form 1:1 •guest complexes; the binding free energy pays the energetic price of conformer selection. This energetically unfavorable conformer selection results in significantly decreased K values of and compared to and .
我们报道了构象可移动的S形甘脲五聚体结构单元以及两种新型无环CB[n]型受体和的合成。（9 mM）和（11 mM）具有适度的水溶性，但其主客体配合物溶解性较差。主体不发生分子间自缔合，而主体会发生（K = 189±27 M）。1H NMR滴定表明，与主体和相比，主体和对疏水性（二价）阳离子 - （：K = 375 - 1400 M；：K = 1950 - 19800 M）的结合能力较差（主体和：K = 3.09×10至4.69×10 M；：K = 4.59×10至1.30×10 M）。分子模拟表明，由于两个S形亚甲基桥连甘脲二聚体亚基各自具有两种不同构象，主体和以三种不同构象的混合物形式存在。主体和的最低能量构象没有明确界定的中心腔。在客体存在的情况下，主体会调整其构象以形成1:1的主客体配合物；结合自由能支付了构象选择的能量代价。这种能量上不利的构象选择导致主体和的K值与主体和相比显著降低。
