Consequences of transient heating on the motional dynamics of cholesterol-containing phospholipid vesicles.

We have investigated the effects of transient heating on the molecular reorientation dynamics of perylene incorporated into the nonpolar acyl chain region of 100 nm diameter unilamellar vesicles comprised of DMPC and cholesterol as a function of system temperature. We observe distinctly different reorientation behavior for perylene, depending upon whether it is excited to its S(1) or S(2) electronic state. This difference is due to the dissipation of excess excitation energy through nonradiative relaxation from the S(2) to the S(1) manifold.

Effects of energy dissipation on motional dynamics in unilamellar vesicles.

We have investigated the molecular reorientation dynamics of perylene incorporated into the nonpolar acyl chain region of 100 nm diameter phosphocholine unilamellar vesicles. When perylene is excited to the S(1) electronic manifold, it exhibits a different fluorescence anisotropy decay than when it is excited to its S(2) electronic manifold. In addition to differences in the polarization of the two transitions, there is a difference in the amount of excitation energy dissipated nonradiatively, because for both excitation conditions radiative emission is from the S(1) state.

Effects of ethanol on the organization of phosphocholine lipid bilayers.

We have investigated the consequences of the addition of ethanol to aqueous solutions containing 100 nm diameter phosphocholine unilamellar vesicles. We have studied the effect of ethanol addition on both gel phase and fluid phase phospholipid bilayers of 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC), using time-resolved fluorescence measurements of perylene incorporated into the vesicles. We observe an increase in the perylene rotational diffusion time constants for ethanol concentrations of ca.

Effect of hydrogen bonding on the rotational and translational dynamics of a headgroup-bound chromophore in bilayer lipid membranes.

We have studied the interactions of the chromophore 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-7-nitro-2-1,3-benzoxadiazol-4-yl (18:1 NBD-PE) imbedded in the headgroup region of bilayer lipid membranes consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DOPG). We have examined the molecular and mesoscale dynamics of the chromophore using time-correlated single photon counting (TCSPC) to measure rotational diffusion dynamics in lipid vesicles and fluorescence recovery after pattern photobleaching (FRAPP) to determine translational diffusion coefficients and mobile fractions in supported lipid bilayers. TCSPC data reveal that chromophore rotational diffusion rates in DOPG vesicles are statistically the same as in DOPC and mixed DOPC/DOPG vesicles, suggesting that the NBD-PE chromophore does not interact strongly with the headgroup region of these bilayers; however, FRAPP experiments show that lateral diffusion is statistically lower in mixed DOPC/DOPG-supported bilayers than in DOPC-supported bilayers.