Characterization of bile salt aggregates using singlet and triplet excited probe molecules
Date
1995
Authors
Ju, Changqing
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Abstract
Bile salt aggregation was studied by employing photophysical techniques to better understand the mechanism for the aggregates formation. Fluorescence of excited singlet probe molecules was used to investigate the location sites of the probes in the sodium cholate aggregates. Naphthalene, anthracene and pyrene were employed as the probes. Both steady-state and time-resolved quenching studies were performed to investigate the extent of protection of the incorporated probes in bile salt aggregates from aqueous quencher. The quenching rate constants of the probes in sodium cholate aggregates were ca. 20-50 times smaller than in water. The highest protection was observed for the smallest molecule, naphthalene, followed by pyrene and anthracene. The pattern of bile salt aggregation and the number of bile salt molecules necessary to solubilize each probe was suggested to be dependent on the size and the shape of the probe molecules.
Excited triplet probe molecules were employed to establish the dynamics of association and dissociation or the probes in bile salt aggregates. The entry/exit dynamics was studied by following the quenching of the excited triplet naphthalene and xanthone by nitrite or cupric ions. Excited triplet xanthone was quenched much faster in bile salt aggregates than excited triplet naphthalene. In addition, the association and dissociation rate constants of xanthone in sodium cholate aggregates were greater than naphthalene. This work established that dynamics of excited triplet probe molecules can be studied in bile salt aggregates and that the location of the probe incorporated in sodium cholate aggregates can be different.