Excited-state proton transfer of protonated 1-aminopyrene complexes with .beta.-cyclodextrin Academic Article uri icon

abstract

  • Excited-state proton transfer in inclusion complexes of 1-aminopyrene and a-naphthol with cyclodextrins was studied by time-resolved spectroscopy. We find that the kinetic studies are much more sensitive to the complexation than are steady-state spectroscopic measurements. Our data suggest two distinct binding orientations for 1 -aminopyrene bound to 8-cyclodextrin. The rate of proton transfer is increased by a factor of 2-3 compared to pure water with the inclusion complex resembling a water-ethanol mixture near the 75% by volume alcohol composition. Deuteration enhances the dissociation rate by a factor of 3.5 in both 80% (by volume) ethanol water mixtures and ion the complex with 8-cyclodextrin. In the case of a-naphthol the rate of proton transfer slows considerably in the inclusion complex and has the rate expected for an 80% by volume ethanoi-water mixture. We suggest that the water near the cavity rim of 8-cyclodextrin is modified by the extensive network of OH groups in such a way as to increase its basicity. Similar effects may occur in enzymic systems.

publication date

  • January 1, 1992