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. 2007 Jun 15;93(8):2877–2891. doi: 10.1529/biophysj.106.100743

FIGURE 5.

FIGURE 5

Schematic representation of DPPC monolayers with PMI-COOH molecules. (A) The electrical field generated by the transition-induced dipole moment of the dye (Inline graphic green arrow) determines an induced dipole moment in the polarizable molecule placed in its vicinity (Inline graphic blue arrow). The resulting transition dipole moment of the dye (Inline graphic red arrow) is the sum of the two vectors and has smaller amplitude. (B) Lo phase. Due to the tight packing of molecules in this phase, a cholesterol molecule (representing the polarizable element) was placed near a PMI-COOH molecule. (C) The calculated decay time variation when cholesterol is placed near PMI-COOH, as a function of distance. The line is drawn at a distance of ∼4 Å between the centers of the molecules; smaller values are less probable due to steric effects. At a distance of 5 Å from PMI-COOH, the cholesterol molecule produces an increase in the dye lifetime of ≈1.3 times, comparable with the experimental value. (D) Ld phase. Because of the less tight packing of the molecules in this phase and of the presence of a high proportion of free volume (∼40% as demonstrated in molecular dynamics simulation studies (67)), a void is placed near the dye. This does not influence the decay time of PMI-COOH.