Dynamics of probe complexation to bile salt aggregates

Excited triplet naphthalene and xanthone were employed as probe molecules to study the dynamics of incorporation into sodium cholate, taurocholate, and deoxycholate aggregates. The association and dissociation rate constants and the quenching rate constants for the incorporated probes were recovered from the dependence of the observed triplet decay rate constants on quencher concentrations (nitrite and cupric ions). Triplet naphthalene was incorporated into a site offering a high degree of protection from quenchers and from which dissociation was relatively slow. Triplet xanthone was incorporated into a less protected site from which dissociation was an order of magnitude faster than from the naphthalene site. We propose that naphthalene was incorporated into the hydrophobic site of primary aggregates, and xanthone was located in the region containing the hydroxyl groups in the secondary aggregates.