PHOTOCHEMICAL INVESTIGATION OF PYRENE-LABELED MONOLAYERS

Mixed monolayers of dipalmitoylphosphatidic acid and two pyrene-labell ed fluorescent analogues of dipalmitoylphosphatidylcholine were studie d at the air-water interface, The pyrene moiety was covalently bound t o the phospholipids in two different positions: at the end of one of t he aliphatic chains and in the polar head group. Monolayers were chara cterized by measuring surface pressure- and surface potential-area iso therms, and the fluorescence and reflection spectra as a function of c ompression as well as monolayer composition. Information on the struct ural and dynamic properties of the monolayer were obtained from excime r-to-monomer intensity ratio, and from the change in the relative inte nsities of the vibronic peaks in the monomer emission bands. The photo induced electron transfer between the fluorescent probe and the absorb ed electron acceptor (methylviologen) depends on the pyrene location. When pyrene is located in the hydrophobic region of the monolayer, que nching of the excited state of pyrene occurs as a result of long-range photoinduced electron transfer between pyrene and methylviologen. How ever, when pyrene is located in the interfacial region of the monolaye r, the observed decrease in fluorescence intensity is also due to the formation of a ground state complex between pyrene and methylviologen.