title: Conformation of self-assembled porphyrin dimers in liposome vesicles by phase-modulation 2D fluorescence spectroscopy.
abstract: By applying a phase-modulation fluorescence approach to 2D electronic spectroscopy, we studied the conformation-dependent exciton coupling of a porphyrin dimer embedded in a phospholipid bilayer membrane. Our measurements specify the relative angle and separation between interacting electronic transition dipole moments and thus provide a detailed characterization of dimer conformation. Phase-modulation 2D fluorescence spectroscopy (PM-2D FS) produces 2D spectra with distinct optical features, similar to those obtained using 2D photon-echo spectroscopy. Specifically, we studied magnesium meso tetraphenylporphyrin dimers, which form in the amphiphilic regions of 1,2-distearoyl-sn-glycero-3-phosphocholine liposomes. Comparison between experimental and simulated spectra show that although a wide range of dimer conformations can be inferred by either the linear absorption spectrum or the 2D spectrum alone, consideration of both types of spectra constrain the possible structures to a "T-shaped" geometry. These experiments establish the PM-2D FS method as an effective approach to elucidate chromophore dimer conformation.
authors.affiliation: Department of Physics, Oregon Center for Optics, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Lott
authors.forename: Alejandro
authors.initials: A
authors.lastname: Perdomo-Ortiz
authors.forename: James K
authors.initials: JK
authors.lastname: Utterback
authors.forename: Julia R
authors.initials: JR
authors.lastname: Widom
authors.forename: Alán
authors.initials: A
authors.lastname: Aspuru-Guzik
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Marcus
mesh_terms: D019295:Computational Biology; D008081:Liposomes / Q000378:metabolism*; D008954:Models, Biological; D011166:Porphyrins / Q000378:metabolism*; D011487:Protein Conformation; D055503:Protein Multimerization / Q000502:physiology*; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D008081:Liposomes; D011166:Porphyrins