title: Diphenylhexatriene membrane probes DPH and TMA-DPH: A comparative molecular dynamics simulation study.
abstract: Fluorescence spectroscopy and microscopy have been utilized as tools in membrane biophysics for decades now. Because phospholipids are non-fluorescent, the use of extrinsic membrane probes in this context is commonplace. Among the latter, 1,6-diphenylhexatriene (DPH) and its trimethylammonium derivative (TMA-DPH) have been extensively used. It is widely believed that, owing to its additional charged group, TMA-DPH is anchored at the lipid/water interface and reports on a bilayer region that is distinct from that of the hydrophobic DPH. In this study, we employ atomistic MD simulations to characterize the behavior of DPH and TMA-DPH in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and POPC/cholesterol (4:1) bilayers. We show that although the dynamics of TMA-DPH in these membranes is noticeably more hindered than that of DPH, the location of the average fluorophore of TMA-DPH is only ~3-4Å more shallow than that of DPH. The hindrance observed in the translational and rotational motions of TMA-DPH compared to DPH is mainly not due to significant differences in depth, but to the favorable electrostatic interactions of the former with electronegative lipid atoms instead. By revealing detailed insights on the behavior of these two probes, our results are useful both in the interpretation of past work and in the planning of future experiments using them as membrane reporters.
authors.affiliation: Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal.
authors.forename: António M T M
authors.initials: AMTM
authors.lastname: do Canto
authors.affiliation: Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal; Theory and Bio-Systems Department, Max Planck Institute of Colloids and Interfaces, Wissenschaftspark Golm, D-14424 Potsdam, Germany.
authors.forename: João R
authors.initials: JR
authors.lastname: Robalo
authors.affiliation: Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal.
authors.forename: Patrícia D
authors.initials: PD
authors.lastname: Santos
authors.affiliation: Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal.
authors.forename: Alfredo J Palace
authors.initials: AJP
authors.lastname: Carvalho
authors.affiliation: Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal.
authors.forename: J P Prates
authors.initials: JPP
authors.lastname: Ramalho
authors.affiliation: Faculdade de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, P-3000-548 Coimbra, Portugal; Centro de Química de Coimbra, Largo D. Dinis, Rua Larga, P-3004-535 Coimbra, Portugal. Electronic address: lloura@ff.uc.pt.
authors.forename: Luís M S
authors.initials: LMS
authors.lastname: Loura
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D004161:Diphenylhexatriene / Q000031:analogs & derivatives* / Q000737:chemistry*; D005453:Fluorescence; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry; D008560:Membrane Fluidity; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry*; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D014867:Water; D004161:Diphenylhexatriene; C033628:1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine
keywords: Diphenylhexatriene; Fluorescence; Lipid bilayer; Membrane probe; Molecular dynamics simulation