Molecular binding behavior of water-soluble calix[4]arenes with asymmetric 4,4′-bipyridinium guests in aqueous solution: regioselective recognition or not?Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ob02105k

• Main Authors: Wang, Kui, Cui, Jian-Hua, Xing, Si-Yang, Dou, Hong-Xi
• Format: Article
• Language: English
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c6ob02105k

The molecular binding behavior of water-soluble calix[4]arenes ( p -sulfonatocalix[4]arene (SC4A) and p -sulfonatothiacalix[4]arene (STC4A)) with two asymmetric 4,4′-bipyridinium guests ( N -methyl- N ′-adamantane carbomethyl-4,4′-bipyridinium dibromide (MVAd 2+ ) and N -methyl- N ′-(naphthalen-2-ylmethyl)-4,4′-bipyridinium bromide iodide (MVNp 2+ )) was systematically studied using NMR spectroscopy and microcalorimetry in a neutral aqueous solution. Either the methyl group or the adamantane moiety in MVAd 2+ could enter into the SC4A and STC4A cavities, without regioselectivity. The STC4A cavity can also accommodate MVNp 2+ , either through incorporation of the methyl group or the naphthalene moiety, without regioselectivity. However, we were surprised to find that MVNp 2+ could only be included within the SC4A cavity through incorporation of the methyl group, with regioselectivity, which is rare for a flexible host. Furthermore, both SC4A and STC4A can form stable inclusion complexes with the two investigated asymmetric 4,4′-bipyridinium guests, driven by very favorable enthalpy changes, and the thermodynamic origins of the host selectivities for MVAd 2+ and MVNp 2+ can be well explained through their binding modes. The finding of this novel regioselective recognition is promising for potential applications in the development of more sophisticated biomimetic materials. A unique regioselective recognition of N -methyl- N ′-(naphthalen-2-ylmethyl)-4,4′-bipyridinium bromide iodide using a p -sulfonatocalix[4]arene was found.