Molecular recognition of vesicles: host-guest interactions combined with specific dimerization of zwitterions.
The aggregation of beta-cyclodextrin vesicles can be induced by an adamantyl-substituted zwitterionic guanidiniocarbonylpyrrole carboxylate guest molecule (1). Upon addition of 1 to the cyclodextrin vesicles at neutral pH, the vesicles aggregate (but do not fuse), as shown by using UV/Vis and fluorescence spectroscopy, dynamic light scattering, zeta-potential measurements, cryogenic transmission electron microscopy, and atomic force microscopy. Aggregation of the vesicles is induced by a twofold supramolecular interaction. First, the adamantyl group of 1 forms an inclusion complex with beta-cyclodextrin. Second, at neutral pH the guanidiniocarbonylpyrrole carboxylate zwitterion dimerizes through the formation of hydrogen-bonded ion pairs. Because the dimerization of 1 depends on the zwitterionic protonation state of 1, the aggregation of the cyclodextrin vesicles is also pH dependent; the cyclodextrin vesicles do not interact at pH 5 or 9, at which 1 is either cationic or anionic and, therefore, not self-complementary. These observations are consistent with molecular recognition of the vesicles through a combination of two different supramolecular interactions, that is, host-guest inclusion and dimerization of zwitterions, at the bilayer membrane surface.
Voskuhl
Jens
J
Organic Chemistry Institute, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
Fenske
Tassilo
T
Stuart
Marc C A
MC
Wibbeling
Birgit
B
Schmuck
Carsten
C
Ravoo
Bart Jan
BJ
D003505:Cyclodextrins / Q000737:chemistry*; D019281:Dimerization; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D015394:Molecular Structure; D013050:Spectrometry, Fluorescence
D003505:Cyclodextrins