Abstract
Excimer formation of pyrene (PY) and 16-(1-pyrenyl)hexadecanoic acid (C 16PY) incorporated into small unilamellar vesicles of phosphatidylcholine (SUV-PC) was studied by absorption and fluorescence spectroscopy. We also examined the spectra of C 16PY dissolved in ethanol and in binary mixtures of ethanol and buffer to compare the characteristics of ground state aggregated and monomeric forms of the probe. The experiments performed in ethanol—buffer mixtures give evidence of aggregation of the pyrenyl moieties of C 16PY. In contrast, with up to about 4.0 mol.% of probe incorporated (PY or C 16PY) into SUV-PC, no ground state dimers, or any other type of molecular aggregate, could be detected. We conclude that under these experimental conditions the mechanism of excimer formation in SUV-PC is a purely dynamic process, most probably a diffusion-controlled probe—probe interaction. An important point to arise from this work is that the incorporated probe concentration relative to the membrane lipid content should be taken into account in order to distinguish between true excimer emission and excimer-like emission from ground state aggregates.
Published Version
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