Amphiphilic 6-S-alkyl-6-thiocyclodextrins: unimolecular micellar and reverse micellar behaviour

Abstract

Micellar behaviour of the amphiphilic 6-S-alkyl-6-thiocyclomaltooligosaccharides (2) in chloroform has been measured by use of the fluorescent probe 8-anilinonaphthalene-1-sulfonate (ANS) as guest molecule, as well as by water–chloroform interfacial tension measurements. At low concentrations the amphiphiles show behaviour consistent with their being oligomers of monosaccharide amphiphiles, or ‘unimolecular micelles’. Thus, with ANS, 1∶1 complexes are formed for which the association constants are in proportion to the length of the chains. At higher concentrations, the long-chained (C₁₆, C₁₈) alkylthiocyclodextrins form inverted micellar aggregates. The NMR shift changes associated with inclusion of 1-naphthol indicate that even in these aggregates, the carbohydrate cavity plays a part in complexation, while the hydrophobic chains act as extensions of the more hydrophobic primary-hydroxy side of the cavity.