Ion pairing between the chain ends induces folding of a flexible zwitterion in methanol

European Journal of Organic Chemistry

Volumn , Issue 20, 2007, Pages 3326-3330

  Schmuck, Carsten ^a   Dudaczek, Jürgen ^a  

^a UNIVERSITY OF WÜRZBURG   (Germany)

Author keywords

Amino acids; Foldamers; Guanidinium cations; Ion pairing; Supramolecular chemistry

Indexed keywords

EID: 34447537770     PISSN: 1434193X     EISSN: 10990690     Source Type: Journal    
DOI: 10.1002/ejoc.200700164     Document Type: Article

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37. The energy minimized structure in Figure 4 as obtained from the force field calculations contains one cis-amide linkage. Intramolecular ion pairing is not possible in the same way if that amide adopts a trans conformation. At least there is no energy minimum within 20 kJ/mol of the one shown here, which contains a trans linkage. Hence, the energetical cost for cis-amide formation is obviously more than overcome by the strong intramolecular ion pairing.
38. 1H NMR spectra of 10 do not change upon the addition of up to 50% water to the methanol solution. With even higher water contents precipitation occurs. Even though the exchanging acidic NH protons, which are most diagnostic for ion pairing, cannot be observed in the presence of water, there are no noticeable shift changes for any proton, suggesting that the loop most likely also exists in water/methanol mixtures.