Depolarisation of fluorescence

Between 1960 and 1972 several new models for membrane structure were put forward. The incentives for this were that the special biochemistry of membranes was starting to become accessible to study and physical-chemical techniques, such as nuclear magnetic resonance, electron-spin resonance and depolarisation of fluorescence, were showing the fluid and dynamic nature of at least parts of plasma membranes. It became clear that in many cells the plasmalemma is rapidly turned over and even in non-growing cells a basal level of turnover persists. Such dynamism accorded well with the behaviour of cells such as macrophages or fibroblasts and with the emergence of modem immunology the importance and mutability of the cell surface achieved a massive, new emphasis. 

Multi-step transfer occurs by successive elementary single-step processes with or without correlation between them. It requires a high density of molecules of the same kind, such as present in more concentrated solutions or in crystals. The so-called concentration depolarisation of fluorescence in isotropic solutions has been explained by such repeated step singlet-singlet transfer between differently oriented molecules. In typical transfer experi-... 

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