Temperature dependence of positronium reactivities with charge transfer molecules in bilayer membranes

摘要

Rate constants for positronium atoms reacting chemically with chargehyphen;transfer molecules such asphyphen;benzoquinone, nitrobenzene, and coenzymeQhyphen;10 in a model bilayer membrane, dipalmitoylphosphatidylcholine (DPPC), have been measured at temperatures between 23 and 65thinsp;deg;C. A strong variation of the positronium chemical reactivities,kPswas observed in these systems:kPsincreases with increasing temperature until the pretransition temperature of the membrane reaches a maximum value near the main transition temperature and decreases at temperatures higher than the main transition temperature. This variation is interpreted in terms of fluidity and permeability changes associated with the phase transitions of membranes and in terms of chargehyphen;transferhyphen;complex formation between the solubilized molecules and the polar head of the membrane. These results demonstrate that positronium and its annihilation characteristics can be employed to investigate charge transport phenomena and microstructural changes of real biological membranes.