title: Well-defined nanoparticles formed by hydrophobic assembly of a short and polydisperse random terpolymer, amphipol A8-35.
abstract: Amphipols are short amphilic polymers designed for applications in membrane biochemistry and biophysics and used, in particular, to stabilize membrane proteins in aqueous solutions. Amphipol A8-35 was obtained by modification of a short-chain parent polymer (poly(acrylic acid); PAA) with octyl- and isopropylamine, to yield an amphiphilic product with an average molar mass of 9-10 kg x mol(-1) (sodium salt form) and a polydispersity index of 2.0 to 3.1, depending on the source of PAA. The behavior of A8-35 in aqueous buffers was studied by size exclusion chromatography, static and dynamic light scattering, equilibrium and sedimentation velocity analytical ultracentrifugation, and small angle neutron scattering. Despite the variable length of the chains and the random distribution of hydrophobic groups along them, A8-35 self-organizes into well-defined assemblies. The data are best compatible with most of the polymer forming compact assemblies (particles) with a molar mass of approximately 40 kg x mol(-1), a radius of gyration of approximately 2.4 nm, and a Stokes radius of approximately 3.15 nm. Each particle contains, on average, four A8-35 macromolecules and 75-80 octyl chains. Neutron scattering reveals a sharp interface between the particles and water. A minor (approximately 0.1%) mass fraction of the material forms much larger aggregates, whose proportion may increase under certain conditions of preparation or handling, such as low pH. They can be removed by gel filtration.
authors.affiliation: Laboratoire de Physicochimie Moléculaire des Membranes Biologiques, UMR 7099, CNRS and Université Paris-7, Institut de Biologie Physico-Chimique, CNRS FRC 550, 13 rue Pierre et Marie Curie, F-75005 Paris, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Gohon
authors.forename: Fabrice
authors.initials: F
authors.lastname: Giusti
authors.forename: Carla
authors.initials: C
authors.lastname: Prata
authors.forename: Delphine
authors.initials: D
authors.lastname: Charvolin
authors.forename: Peter
authors.initials: P
authors.lastname: Timmins
authors.forename: Christine
authors.initials: C
authors.lastname: Ebel
authors.forename: Christophe
authors.initials: C
authors.lastname: Tribet
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Popot
mesh_terms: D002850:Chromatography, Gel; D008027:Light; D053758:Nanoparticles; D009502:Neutrons; D011108:Polymers / Q000737:chemistry*; D012542:Scattering, Radiation; D014461:Ultracentrifugation
chemical_list: D011108:Polymers