Complexation of phosphine ligands with peracetylated beta-cyclodextrin in supercritical carbon dioxide: spectroscopic determination of equilibrium constants.
The interaction between peracetylated beta-cyclodextrin and several triphenyl phosphine derivatives was studied in supercritical carbon dioxide (scCO2) by UV-visible spectroscopy. The equilibrium constant for a 1:1 complexation reaction was obtained from titration spectra and calculated using two established mathematical models. The values of the equilibrium constants are 1-3 orders of magnitude smaller than those obtained in aqueous solution with analogous phosphines. This is likely due to the absence in scCO2 of the hydrophobic effect, which is replaced by a corresponding, but weaker, CO2-phobic effect. The largest value of Kf was found for complexes of diphenyl(4-adamantylphenyl)phosphine, which is rationalized on the basis of the excellent fit of the phosphine in the cyclodextrin cavity, leading to enhanced host-guest van der Waals interactions. This study can be considered the first step toward the comprehension of the complexation thermodynamics of modified cyclodextrins soluble in scCO2.
Galia
Alessandro
A
Dipartimento Ingegneria Chimica Processi e Materiali, Università di Palermo, Viale delle Scienze Ed. 6, 90128 Palermo, Italy. galia@dicpm.unipa.it
Navarre
Edward C
EC
Scialdone
Onofrio
O
Ferreira
Michel
M
Filardo
Giuseppe
G
Tilloy
Sebastien
S
Monflier
Eric
E