title: Host-Guest Inclusion Complexation of α-Cyclodextrin and Triiodide Examined Using UV-Vis Spectrophotometry.
abstract: The historically relevant host-guest complexation of α-cyclodextrin (α-CD) and triiodide (I3(-)) in aqueous solution was examined using a systematic UV-vis spectrophotometric approach. This particular system is experimentally challenging because of the coupled equilibria, namely, I2 + I(-) ⇌ I3(-) and α-CD + I3(-) ⇌ α-CD·I3(-). We therefore developed a unique experimental approach that allowed us to determine the concentration of all iodine species. This enabled us to unequivocally demonstrate that the large increase in the UV absorbance with added α-cyclodextrin is due to an increase in the overall triiodide concentration as α-CD essentially converts iodine to triiodide according to the coupled equilibria. Herein we report (a) the complexation stoichiometry is 1:1 (i.e., the host-guest complex is α-CD·I3(-)), (b) the binding constant is KH-G = (1.35 ± 0.05) × 10(5) M(-1) at room temperature, and
authors.affiliation: Department of Chemistry, Trinity University , One Trinity Place, San Antonio, Texas 78212, United States.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Pursell
authors.affiliation: Department of Chemistry, Trinity University , One Trinity Place, San Antonio, Texas 78212, United States.|Okinawa Institute of Science and Technology Graduate University , 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa, Japan 904-0495.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Pursell