title: Quantitative determination of ion distributions in bacterial lipopolysaccharide membranes by grazing-incidence X-ray fluorescence.
abstract: A model of the outer membrane of Gram-negative bacteria was created by the deposition of a monolayer of purified rough mutant lipopolysaccharides at an air/water interface. The density profiles of monovalent (K(+)) and divalent (Ca(2+)) cations normal to the lipopolysaccharides (LPS) monolayers were investigated using grazing-incidence X-ray fluorescence. In the absence of Ca(2+), a K(+) concentration peak was found in the negatively charged LPS headgroup region. With the addition of CaCl(2), Ca(2+) ions almost completely displaced K(+) ions from the headgroup region. By integrating the experimentally reconstructed excess ion density profiles, we obtained an accurate measurement of the effective charge density of LPS monolayers. The experimental findings were compared to the results of Monte Carlo simulations based on a coarse-grained minimal model of LPS molecules and showed excellent agreement.
authors.affiliation: Physical Chemistry of Biosystems, Institute of Physical Chemistry, University of Heidelberg, D69120 Heidelberg, Germany.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Schneck
authors.forename: Thomas
authors.initials: T
authors.lastname: Schubert
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Konovalov
authors.forename: Bonnie E
authors.initials: BE
authors.lastname: Quinn
authors.forename: Thomas
authors.initials: T
authors.lastname: Gutsmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Brandenburg
authors.forename: Rafael G
authors.initials: RG
authors.lastname: Oliveira
authors.forename: David A
authors.initials: DA
authors.lastname: Pink
authors.forename: Motomu
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D002118:Calcium; D002412:Cations / Q000032:analysis*; D002462:Cell Membrane / Q000737:chemistry*; D003198:Computer Simulation; D006090:Gram-Negative Bacteria / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000737:chemistry*; D008954:Models, Biological; D009010:Monte Carlo Method; D011188:Potassium; D013052:Spectrometry, X-Ray Emission; D055672:Static Electricity
chemical_list: D002412:Cations; D008070:Lipopolysaccharides; D011188:Potassium; D002118:Calcium