Study of the inclusion complexes of β-cyclodextrin with the sodium salt of trisulfonated triphenylphosphine

The formation of inclusion complexes between the sodium salt of trisulfonated triphenylphosphine and beta-cyclodextrin has been investigated at two temperatures by high field nuclear magnetic resonance, electrospray mass and UV-vis spectroscopies. At 268 K, titration experiments and Job's method suggest that the major species in solution is a 1 : 1 inclusion complex. The molecular geometry of this inclusion complex was studied using the ROESY NMR technique complemented by molecular modelling. All these methods converged towards the structure attained by inserting one aromatic ring into the hydrophobic cavity of the host from the side of the secondary hydroxyls. At 298 K, a higher proportion of 2 : 1 and 3 : 1 complexes induces strong alterations of the NMR signals, preventing an easy and reliable determination of association constants. Nevertheless, an apparent association constant can be determined from UV-vis data by assuming a 1 : 1 equilibrium. The geometry of the 2 : 1 and 3 : 1 complexes is also briefly discussed from ROESY NMR experiments.