The interaction of fluorescent DPH probes with unsaturated phospholipid membranes: A molecular dynamics study

Abstract DPH (1,6-diphenyl-1,3,5-hexatriene) is one of the most used fluorescent molecules for the study of hydrophobic domain of membranes. Its fluorescence polarization is high in the absence of rotational motion and it is sensitive to reorientation of the long axis resulting from interactions with surrounding lipids. The steady-state anisotropy depends both on the fluorescence lifetime and order parameters. The aim of the present study was to gain insights, by means of computational methods (molecular dynamics simulation), about the orientation and location preference of DPH molecules in different regions of the bilayer and the influence they may exert on the structure of 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) membranes. The computed bilayer properties such as area/lipid and the order parameters 〈 P 2 〉 and 〈 P 4 〉 for DPH showed good agreement with known experimental data. A representative population of DPH molecules was found to be localized in the acyl-chain region of the bilayer immediately beneath the DOPC/water interface oriented parallel to the bilayer plane. This can give an explanation for the fluorescence quenching experimentally observed for the unsaturated lipid membranes.