title: Evaluating the sensitivity of lipid headgroup-bound chromophores to their local environment.
abstract: We report on the steady state and time-resolved fluorescence behavior of the chromophore 1,2-dimiryristoyl-sn-glycero-3-phosphoethanolamine-N-lissamine rhodamine B sulfonyl ammonium salt (SR-DMPE) in a series of solution phase and lipid bilayer environments. The issue of interest is whether or not the lipid headgroup-bound chromophore is sensitive to its local environment under conditions where vesicles have not been formed in lipid-containing mixtures and where unilamellar vesicles have been formed by extrusion. Our data point to the strong interaction of SR-DMPE with 1,2-dimirystoyl-sn-glycero-phosphocholine (DMPC) in solution whether or not the solution has undergone extrusion. The amount of SR-DMPE in the lipid-containing systems affects both the steady state and time-resolved spectroscopic response. Excitation of the chromophore to the S(2) state deposits sufficient excess energy into the system to influence its rotational diffusion dynamics, demonstrating significant interactions between SR-DMPE and DMPC. Comparison of SR-DMPE reorientation dynamics in DMPC-containing solutions with corresponding data on SR-DMPE in aqueous solution indicates that the lipids impose a restrictive local environment on the chromophore that is a factor of ca. 10 more viscous than an aqueous environment. The similarity of the reorientation data in all DMPC-containing solutions suggests that SR-DMPE is a local probe that is not sensitive to longer range organization.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, Michigan 48824-1322, USA.
authors.forename: Iwan
authors.initials: I
authors.lastname: Setiawan
authors.forename: G J
authors.initials: GJ
authors.lastname: Blanchard
mesh_terms: D016880:Anisotropy; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D015394:Molecular Structure; D010714:Phosphatidylethanolamines / Q000737:chemistry; D012235:Rhodamines / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008055:Lipids; D010714:Phosphatidylethanolamines; D012235:Rhodamines; C046703:lissamine-rhodamine-phosphatidylethanolamine; D004134:Dimyristoylphosphatidylcholine; C018525:1,2-dimyristoylphosphatidylethanolamine