Triplet excited states of polycyclic aromatic compounds as probes of their microenvironment in serum albumin complexes.

Using flash photolysis techniques, the triplet excited states of benzo(a)pyrene, pyrene, benz(a)anthracene and other aromatic hydrocarbons have been detected in complexes of bovine (and human) serum albumin dissolved in aqueous solutions at room temperature. The triplet lifetimes can be adjusted to any value within the microsecond-millisecond time domains by varying the partial pressure of oxygen from zero to one atmosphere, thus providing a useful probe on these time scales. Local oxygen concentrations as low as ～ 2 × 10^?7M can be detected. In air saturated solutions, the triplet lifetimes are sensitive to pH dependent conformational changes of the host bovine serum albumin molecules.