Molecular binding behaviors between tetrasulfonated bis(m-phenylene)-26-crown-8 and bispyridinium guests in aqueous solution.
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.
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China.
Ling
L
Chen
Ying-Ming
YM
Zhang
Yu
Y
Liu