Interaction of fluorescence quenchers with the n-(9-anthroyloxy) fatty acid membrane probes

The fluorescence quenching of the $\text{n-(9-}\text{anthroyloxy}\text{)}$ (AO) fatty acid probes has been investigated in aqueous dispersions, vesicles of egg phosphatidylcholine and vesicles formed from red cell ghosts. Negatively charged (KI), neutral (acrylamide) and positively charged (CuSO₄) quenchers were used to monitor the location of the probes. The fluorescence of the probes, with the exception of the shortest chain (11-(9-anthroyloxy)undecanoic acid) is not quenched by acrylamide when associated with vesicles. This indicates that in association with vesicles, the 9-anthroyloxy moiety of the long chain probes is buried within the hydrocarbon region and thus well shielded from the aqueous phase. Measurements with KI indicate that the probes are present in the membrane at depths corresponding to the position of the 9-anthroyloxy moiety on the fatty acid, and that the quencher itself forms a concentration gradient within the membrane. Very little or no CuSO₄ quenching was observed for $\text{n-}\text{(9-anthroyloxy)stearic}$ acid probes $\text{(n-}\text{AS)with}\text{n > 2}$, suggesting that in these vesicles Cu²⁺ does not significantly penetrate the bilayer.