The interaction of 02 with polycrystalline Pd was investigated; above 250 °C a significant amount of oxygen is incorporated into the bulk at pressures far below the dissociation pressure of PdO. The rate of uptake into previously unexposed Pd foil was pressure independent, suggesting (1) that penetration into the bulk occurred from an oxygen-saturated surface and (2) that the rate was limited by the process in which chemisorbed oxygen moved out of the surface layer toward the interior of the Pd. The temperature dependence of the uptake rate in this pressure-independent region was characterized by an Arrhenius A factor of 5.2 X 1020 atoms cm'2 min'1 and an activation energy of 17 kcal mol'1 (71 kJ mol'1). After about 100 monolayers of oxygen were incorporated, the uptake rate began to decline and became unobservable after about 350 monolayers were incorporated. Equilibrium oxygen pressures above such extensively oxygen-treated samples were much lower than the reported dissociation pressures of PdO indicating that the palladium-oxygen system under these conditions should be characterized as a solid solution of oxygen in palladium. The role which this incorporation of oxygen may play in catalytic processes is discussed.

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Measurement of the time-resolved fluorescence depolarization of 1,6-diphenylhexatriene (DPH) in artificial bilayers of microsomal membrane lipids from Tetrahymena gives detailed information concerning the molecular motion of this probe and fluid properties of the membrane lipids which are obscured with steady-state methods. The rotational motion of DPH in these lipids from cells acclimated to 15 and 39.5 degrees C growth temperatures was anisotropic, which agrees with recent time-resolved studies of this probe in synthetic phospholipid systems. Evaluation of DPH polarization data obtained from these lipid fractions at their respective growth temperatures showed differences in physical properties which suggest that "viscosity", per se, of the microsomal lipids is not a strictly regulated as it is in prokaryotic systems. Rotational relaxation of DPH in 39.5 degrees C microsomal lipids measured at 15 degrees C is more complex than that of either lipid fraction measured at its actual growth temperature, suggesting that the probe has partitioned into two dissimilar environments within the bilayer. Similar effects are observed in the microsomes of 39.5 degrees C cells by freeze-fracture electron microscopy following rapid cooling to 15 degrees C. Under these conditions, two distinct regions are observed on the fracture faces, suggesting a correlation between lipid phase changes and alterations in membrane structure.