Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China.
J Phys Chem B. 2012 Aug 9;116(31):9500-6. doi: 10.1021/jp305503e. Epub 2012 Jul 30.
A highly water-soluble crown ether bearing four sulfonate groups (1) was synthesized by sulfonation of neutral bis(m-phenylene)-26-crown-8. The complexation behavior of 1 with two bispyridinium-based guests, methyl viologen (MV(2+)) and 1,2-bis(pyridinium)ethane (BPE(2+)), was systematically investigated in both aqueous solution and the solid state by (1)H NMR spectroscopy, crystallography, and microcalorimetry. The crystallographic studies of superstructures MV(2+)⊂1 and BPE(2+)⊂1 show that MV(2+) forms an interpenetrated complex with 1, and conversely, BPE(2+) is bound outside the cavity of 1 as an electrostatic complex. Furthermore, microcalorimetric titration reveals the thermodynamic origins of this different binding process; that is, MV(2+) threads through the cavity of 1 with a significant enthalpy change, while BPE(2+) mainly associates with the sulfonate groups of 1, accompanied by a dominant entropy change. The obtained results demonstrate a structure-dependent binding process in complexes MV(2+)⊂1 and BPE(2+)⊂1, depending on the relative locations of positive charges on nitrogen atoms and the bridge linkers between two pyridinium moieties in the guest molecules.
一种高度水溶性的冠醚，带有四个磺酸根基团（1），通过中性双（间苯撑）-26-冠-8 的磺化反应合成。通过（1）H NMR 光谱、晶体学和微量热法，系统研究了 1 与两种双吡啶基客体，甲紫（MV(2+)）和 1,2-双（吡啶）乙烷（BPE(2+)）在水溶液和固态中的络合行为。超结构 MV(2+)⊂1 和 BPE(2+)⊂1 的晶体学研究表明，MV(2+)与 1 形成互穿络合物，相反，BPE(2+)作为静电络合物结合在 1 的腔体外。此外，微量热滴定揭示了这种不同结合过程的热力学起源；也就是说，MV(2+)通过 1 的腔以显著的焓变穿过，而 BPE(2+)主要与 1 的磺酸根基团结合，伴有主导的熵变。所得结果表明，在 MV(2+)⊂1 和 BPE(2+)⊂1 配合物中存在结构依赖性的结合过程，这取决于客体分子中氮原子上的正电荷和两个吡啶部分之间桥连基团的相对位置。
