LIQUID-CRYSTALLINE SOLVENTS AS MECHANISTIC PROBES .36. DEPTH PROFILES FOR PERMEATION OF WATER AND OXYGEN IN VESICLES AND TUBULE PHASES BY FLUORESCENCE QUENCHING STUDIES

Static and dynamic fluorescence data from three structurally related probe molecules [(1‐pyrenyl)acetic acid, 4‐(l‐pyrenyl)butanoic acid, and 12‐(l‐pyrenyl)dodecanoic acid] were employed to determine the influence of phase structure on oxygen and water permeability in small unilamellar vesicles and microtubules of l,2‐bis(tricosa‐10,12‐diynoyl)‐in‐glycero‐3‐phosphocholine (DC23PC). Since the pyrenyl units of the three reporter molecules probe environments at different depths in DC23PC bilayers, the aggregated information provides a depth profile of both small‐molecule permeability and order. The results indicate that the probe sites are somewhat more available to water molecules immediately below the chain melting transition temperature than above it: singlet lifetimes of the pyrenyl groups undergo a clear increase as the temperature is raised in the region of the transition. This observation is consistent with melted chains being able to wrap themselves more efficiently around pyrenyl units (and thereby protect them better from water molecules) than stiff chains. The gross picture that emerges is one in which pyrenyl groups experience water and oxygen quenching via opposing concentration gradients. The concentration of oxygen is greatest near the bilayer midplane and decreases toward the aqueous interface; the concentration of water increases from the midplane to the interface. Copyright © 1990, Wiley Blackwell. All rights reserved