Nonpolar media, kinetics

In nonpolar solvents, Eu chelates studied in the present work exhibited luminescence kinetics closely following the single exponential decay law over the intensity range of about three orders of magnitude. In agreement with the previous observations [5, 6], an increase in the refractive index of the nonpolar medium leads to a systematic decrease in the excited-state lifetime of the Eu ion. This effect is accounted for by the well-known refractive-index dependence of the radiative rate y where and are radiative rates in a dielectric medium and in vacuo, respectively, n is the refractive index of the medium, and/[ ) is the local-field correetion factor [4, 5]. 

Biological cell membranes are multi-component systems consisting of a fluid bilayer lipid membrane (BLM) and integrated membrane proteins. The main structural features of the BLMs are determined by a wide variety of amphiphilic lipids whose polar head groups are exposed to water while hydrocarbon tails form the nonpolar interior. The BLMs act as the medium for biochemical vectorial membrane processes such as photosynthesis, respiration and active ion transport. However, they do not participate in the corresponding chemical reactions which occur in membrane-dissolved proteins and often need redox-active cofactors. BLMs were therefore mostly investigated by physical chemists who studied their thermodynamics and kinetic behaviour . ... 

During the degradation of tert.-butlybenzene only nonpolar free radicals are formed with low interaction with the solvent. Oxygen-containing radicals can interact much more with water, which is important, for example, for oxidation reactions. In these cases specific solvent effects are of more importance and significant difference in the chemical kinetics of the reaction in water compared with nitrogen as reaction medium could be assumed. 

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