The analysis of time-dependent fluorescence shifts of the bilayer probe 6-hexadecanoyl-2-(((2-(trimethylammonium)ethyl)methyl)amino)naphthalene chloride (Patman) offers valuable information on the hydration and dynamics of phospholipid headgroups. Quenching studies on vesicles composed of four phosphatidylcholines with different hydrocarbon chains (18:1c9/18:1c9, DOPC; 16:0/18:1c9, POPC; 18:1c9/16:0, OPPC; 18:1c6/18:1c6, PCDelta6) show that the chromophore of Patman is defined located at the level of the sn-1 ester-group in the phospholipid, which is invariant to the hydrocarbon chain. The so-called solvent relaxation (SR) approach as well as solid-state 2H NMR reveals that DOPC and PCDelta6 are more hydrated than POPC and OPPC. A strong dependence of SR kinetics on the position of double bond in the investigated fatty acid chains was observed. Apparently, the closer the double bond is located to the hydrated sn-1 ester-group, the more mobile this group becomes. This work demonstrates that the SR approach can report mobility changes within phospholipid bilayers with a remarkable molecular resolution.
BACKGROUND: Fluorescence correlation spectroscopy (FCS) can be used for the determination of diffusion coefficients of single molecules. Since diffusion coefficients are correlated with size and shape of the labeled species, FCS provides information on conformational changes in plasmids aggregates. METHODS: A 10-kbp plasmid stained with PicoGreen was condensed by spermine or liposomes formulated from cationic lipid and egg phosphatidylcholine. RESULTS: The diffusion coefficient of DNA increases from 1.0 x 10(-12) m2/s to 3.2 x 10(-12) m2/s by the addition of spermine, whereas the addition of cationic liposomes leads to complexes characterized by diffusion coefficients with values ranging from 1.7 to 1.9 x 10(-12) m2/s. CONCLUSIONS: FCS experiments allow determining the diffusion coefficients of DNA-containing aggregates which provide information regarding the topology and homogeneity of the aggregate.
