A temperature-annealing effect on the host–guest complexation with γ-cyclodextrin

Abstract

Pyrene binds to γ-cyclodextrin and forms host-guest complexes with different stoichiometries. The fluorescence of pyrene was employed as a qualitative signature for these different complexes. Solutions prepared at room temperature were shown not to be in thermodynamic equilibrium, since a heating cycle of 20 min at 80°C followed by cooling led to changes in the relative concentrations of the pyrene-γ-cyclodextrin complexes. This temperatureannealing effect has consequences when determining thermodynamic parameters such as equilibrium constants and host-guest stoichiometries.Résumé : Le pyrène se lie à la γ-cyclodextrine pour former des complexes hôte-invité de stoechiométries diverses. On a utilisé la fluorescence du pyrène comme signature qualitative de ces différents complexes. On a démontré que des solutions préparées à la température ambiante ne présentent pas d'équilibre thermodynamique puisqu'un cycle de chauffage de 20 min à 80°C, suivi par un refroidissement, conduit à des changements dans les concentrations relatives des complexes pyrène-γ-cyclodextrine. Cet effet d'annellation lié à la température a des conséquences lorsqu'on veut déter-miner des paramètres thermodynamiques, tels les constantes d'équilibre et les stoechiométries hôte-invité.

Molecular Organization, Structural Orientation, and Surface Topography of Monoacylated β-Cyclodextrins in Monolayers at the Air−Aqueous Interface

“…In turn, this discloses an important point, namely that the dynamic surface packing of the monoacylated β-CD derivative can contain, store, and transduce dynamic changes involving molecular information capacity that depends on the organization previously acquired at the interface. This organization can be related to the ability of native cyclodextrins to form aggregates in water. , …”

Supramolecular Dynamics Studied Using Photophysics

“…During these studies, we uncovered that the pyrene:γ-CD complexes present in solution, using the standard preparation methodology of stirring the solutions at room temperature for 12 h, were not at thermodynamic equilibrium. 74 This conclusion was reached when the pyrene/CD solutions were annealed at 80 °C for 20 min (Figure 9). Increasing the temperature of pyrene/γ-CD aqueous solutions led to a decrease in the excimer emission and an increase in the monomer fluorescence intensity.…”

“…Temperature studies were performed to establish if the slower dynamics for the 2:2 pyrene:γ-CD complex was of an enthalpic or entropic nature. During these studies, we uncovered that the pyrene:γ-CD complexes present in solution, using the standard preparation methodology of stirring the solutions at room temperature for 12 h, were not at thermodynamic equilibrium ).…”

“…The solid lines in the inset were included to guide the eye and do not have a physical meaning. Data from ref . …”

Supramolecular dynamics

“…This latter complex was initially assigned to a 1 : 2 complex, 41 but temperature studies showed that at high concentrations of g-cyclodextrin aggregates of the host are also present. 42 The formation of the 1 : n complex was confirmed by analyzing the emission spectra for the monomer of 14 where the ratio of the I and III bands is sensitive to the polarity of the solvent. The very low I/III ratio observed in the presence of 20 mM g-cyclodextrin ( Fig.…”