Specific Interactions in the Inclusion Complexes of Pyronines Y and B with β-Cyclodextrin

Abstract

The aim of this work is to analyze the role of specific interactions in host-guest association processes. The formation of inclusion complexes between pyronines Y and B and beta-cyclodextrin and the nature of the interactions involved have been studied using absorption, steady-state fluorescence, and time-resolved fluorescence spectroscopies. The two pyronines form 1:1 complexes with beta-cyclodextrin, with the association equilibrium constant being much higher in the case of pyronine B. Complexation causes a slight red shift of the emission spectra of the pyronines but decreases significantly their fluorescence quantum yields and lifetimes. To explain this atypical behavior, the photophysical properties of the pyronines in different solvents were determined and compared with those of the complexes. The similarities observed between the pyronines in dioxane and in the interior of the cyclodextrin cavity suggest that there are important specific interactions of the pyronines with the electron-rich oxygens present in these media. A possible explanation for the increase in the nonradiative rate constants in these media involves the existence of a charge-transfer excited state with the location of the positive charge at the xanthene moiety, which would be stabilized by the mentioned interactions. The observed differences between pyronine Y and B can be understood on the basis of these specific interactions.

Dynamics of Supramolecular Association Monitored by Fluorescence Correlation Spectroscopy

“…The much lower dissociation rate constant of the PB:b-CD complex as compared to that of PY:b-CD confirms that PB interacts more strongly with the interior of the b-CD cavity, as proposed on the basis of fluorescence studies. [32] The authors mentioned above have also reported values of the dissociation rate constants of these systems, but they are not in accordance with our results due to the great disagreement between their and our values of the association equilibrium constants. [41,42] There are several reasons for this, but the most important is the high ionic strength used in those works (aqueous 1.00 mol dm À3 NaCl) that can have a large effect on the equilibria under study.…”

“…[33] The stoichiometry of the inclusion complexes and the association equilibrium constants between the two pyronines and the two CDs were determined by electronic absorption and fluorescence spectroscopies. [32,35] In all cases 1:1 pyronine:CD complexes are formed, although 2:1 complexes are also observed in the absorption studies for the two pyronines with g-CD due to the enhancement of pyronine dimerization inside the cavity. Nevertheless, at the extremely low dye concentrations used in FCS the presence of 2:1 pyronine:CD complexes is negligible.…”

Fluorescence tuning of 2D montmorillonite optically active layers with beta-cyclodextrine/dye supramolecular complexes

“…This is possible due to the fact that the structure of PY allows 3 resonance conformations of the molecule. In the case where positive charge is present on the oxygen of the central ring of PY molecule, it can be stabilised through the glycosidic oxygens of the glucopyranose rings (Reija et al, 2005). Such interactions are indicated by the detection of higher negative values of ΔH and ΔS than in the case of C522 molecule, where hydrophobic interactions in the cavity of βCD/QAβCD molecule play a dominant role ( Table 2).…”

“…The formation of supramolecular complexes is a supposed act against the formation of dimers and higher aggregates, and can provide well-defined optical properties of dye/montmorillonite films with regard to the presence of dye monomer species (Reija et al, 2005). Experimental X-ray diffraction patterns confirmed that the modified MFs which were prepared from equilibrium mixtures of βCD/PY and QAβCD/C522 exhibit higher interlayer spacing (2.39 and 2.14 nm, respectively) in comparison with other samples (Fig.…”

Influence of the substituent on amide nitrogen atom of N-acetyl tyrosine on interactions with β-cyclodextrin

“…Apart from the fluorescence intensity (fluorescence quantum yield) other photophysical properties proportional to the concentration of the free and bound guest molecule can be used for stoichiometry and binding constant calculation [5,6,14,48,53,54]. For two components system, normalized pre-exponential factors of the fluorescence lifetime (a) for all forms present in the solution obtained from the global analysis of the fluorescence intensity decays as well as the average fluorescence lifetime defined by Eq.…”