Abstract
We present a steady-state and time-resolved fluorescence emission spectra analysis of the membrane probe 1-myristoyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]- sn-glycero-3-phosphocholine (DANSYL) in 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and cholesterol multi-lamellar vesicles (MLV) prepared by modified rapid solvent exchange. We report that the dose-dependent cholesterol-induced blue shifts in the steady-state fluorescence emission spectra observed in DMPC MLV are due to complex solvent effects that include time-dependent dipolar relaxation and the formation of internal charge transfer (ICT) states. A key finding of this investigation is identification of two distinguishable DANSYL populations existing at both shallow and deep locations in the membrane; these two DANSYL populations are evidence of laterally phase-separated domains at cholesterol compositions between X chol = 0.30 and 0.60 at 30 °C in DMPC MLV.
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