Use of phosphorescent probes for studying model and biological membranes

Egg lecithin liposomes and rat liver microsomes have been used to analyse the possibilities of phosphorescent probes for investigating membranes. It is sho wn that to record the diffusion controlled quenching of phosphorescence of erythrosin by stable nitroxyl radicals it suffices to introduce into the liposomes one quencher molecule per 10⁴ lecithin molecules. This makes it possible to study the diffusion processes with D = 10^-5-10^-9 cm²·sec^-1. The use of quenchers of diffeent polarity suggests that the triplet probe erythrosin is incorporated into the liposomes in the region of the polar heads of phosphatidyl choline. The microviscosity of the membrane determined from the rate of quenching of the phosphorescence by the radicals at 20 °C is 0·1 N · sec/m². The coefficient of lateral diffusion of erythrosin in the liposomes determined from its concentration self-quenching is 1·1 × 10^-8 cm²·sec^-1. In the microsomes erythrosin is located in the hydrophobic portions of the proteins and is not accessible to the quencher molecules.