Transverse location of new fluorene based depth dependent fluorescent probes in membranes--quenching studies with 9,10-dibromostearic acid

Fluorescence quenching technique has been used to determine the transverse location of the fluorescent fluorenyl fatty acids in single bilayer vesicles prepared from phosphatidylcholine. The fluorenyl fatty acids used here are 2-fluorenyl acetic, butyric, hexanoic and octanoic acid. In addition a new type of fluorescent probe, 7-n-butyl-fluorene-2-butyric acid, wherein a hydrophobic tail is attached to 2-fluorenyl-butyric acid has also been used to study its effect on alignment of these probes in the membrane. The association properties of the quencher 9,10-dibromostearic acid have been analysed. It is observed that the quencher association involves partitioning into the vesicles and does not involve any binding to the vesicles. The absolute partition coefficient of the 9,10-dibromostearic acid which partitions between the aqueous and the lipid phases of the phospholipid dispersion has been evaluated. Using this information the corrected Stern-Volmer plots were drawn and the bimolecular quenching constant evaluated.