Induction of optical activity in an oligothiophene synchronized with pH-sensitive folding of amylose.
Control of the helical sense in alpha-sexithiophene (6T) through pH-responsive wrapping with left-handed-helical amylose is demonstrated. A change in pH of the medium caused a significant conformational change in amylose as the host polymer, which resulted in either supramolecular complexation with 6T as the guest molecule to induce optical activity or decomplexation leading to loss of optical activity. Furthermore, we observed that chirality reversal in 6T does not require hosts of opposite helical chirality, but can be made possible simply by taking advantage of the pH sensitivity of the amylose folding, which is dependent on the pH history of the aqueous medium. In helical amylose, 6T assumes a clockwise-twisted conformation when the pH is changed from acidic to neutral, but assumes an anticlockwise-twisted conformation when the aqueous solution is acidified from very basic conditions.
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-13 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. sanji@res.titech.ac.jp
Takanobu
T
Sanji
Nobu
N
Kato
Masato
M
Tanaka