Cucurbit[7]uril Host–Guest Complexes with Biguanidinium Cations in Aqueous Solution. Issue 13 (13th March 2013)

• Record Type: Journal Article
• Authors: MacGillivray, Brendan C.; Macartney, Donal H.
• Is Part Of: European journal of organic chemistry. Issue 13(2013)
• Page Start: 2573
• Page End: 2582
• Publication Date: 2013-03-13
• Subjects: Supramolecular chemistry -- Host–guest system -- Rotaxanes -- Reaction mechanisms; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.201201655
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract: The host–guest complexations of a series of biguanidinium cations (metformin and phenformin) and bis(biguanidinium) dications (chlorhexidine and alexidine) by the host molecule cucurbit[7]uril (CB[7]) in aqueous solution have been investigated by 1 H NMR spectroscopy and ESI mass spectrometry. Metformin forms both 1:2 and 1:1 host–guest complexes, whereas phenformin forms only a 1:1 complex. The two bis(biguanidinium) dications both form sequential 1:1, 2:1 and 3:1 host–guest complexes, however, the mechanism is different in each case. With chlorhexidine, the first CB[7] binds to the central hexamethylene chain, followed by sequential complexation of the terminal 4‐chlorophenyl groups. With alexidine, the two terminal 2‐ethylhexyl groups are bound first, with the third CB[7] adding only with a concomitant relocation of one CB[7] to the central hexamethylene binding site. The stability constants of the various host–guest complexes were determined by 1 H NMR titrations and competitive binding experiments, as well as by the application of a statistical binding model. Abstract : Biguanidinium (metformin, phenformin) and bis(biguanidinium) (chlorhexidine, alexidine) guests form very stable host–guest complexes with cucurbit[7]uril in water. The bis(biguanidinium) guests may be complexed by up to three hosts, with the first binding to the central hexamethylene chain of chlorhexidine, whereas with alexidine, the first two hosts bind to the terminal 2‐ethylhexyl groups.