title: Atom-scale depth localization of biologically important chemical elements in molecular layers.
abstract: In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.
authors: Biomaterials Department, Max Planck Institute of Colloids and Interfaces, 14476 Potsdam, Germany; Institut Laue-Langevin, 38000 Grenoble, France; schneck@mpikg.mpg.de.
authors: Emanuel
authors: E
authors: Schneck
authors: Institut Laue-Langevin, 38000 Grenoble, France; Institut de Chimie Séparative de Marcoule UMR 5257 Commissariat à l'énergie atomique/CNRS/École Nationale Supérieure de Chimie de Montpellier, Université Montpellier, 30207 Bagnols sur Cèze, France;
authors: Ernesto
authors: E
authors: Scoppola
authors: European Synchrotron Radiation Facility (ESRF), 38000 Grenoble, France;
authors: Jakub
authors: J
authors: Drnec
authors: Synchrotron SOLEIL, 91192 Gif-sur-Yvette Cedex, France;
authors: Cristian
authors: C
authors: Mocuta
authors: European Synchrotron Radiation Facility (ESRF), 38000 Grenoble, France;
authors: Roberto
authors: R
authors: Felici
authors: Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany.
authors: Dmitri
authors: D
authors: Novikov
authors: Institut Laue-Langevin, 38000 Grenoble, France;
authors: Giovanna
authors: G
authors: Fragneto
authors: Synchrotron SOLEIL, 91192 Gif-sur-Yvette Cedex, France;
authors: Jean
authors: J
authors: Daillant
mesh_terms: D000880:Anthraquinones / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D011510:Proteolipids / Q000737:chemistry*; D000075462:Serum Albumin, Human / Q000737:chemistry; D012996:Solutions; D013052:Spectrometry, X-Ray Emission / Q000295:instrumentation / Q000379:methods*
chemical_list: D000880:Anthraquinones; D006027:Glycosides; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D011510:Proteolipids; D012996:Solutions; C479846:sulfemodin 8-O-beta-D-glucopyranosyl-6-O-sulfate; C010942:1,2-distearoyllecithin; D000075462:Serum Albumin, Human
keywords: X-ray scattering; interfaces; lipid membranes; protein adsorption; surfaces