title: Electrostatic switching of biopolymer layers. Insights from combined electrokinetics and reflectometric interference.
abstract: Structural integrity and functional characteristics of biomacromolecules are largely defined by electrostatic forces between ionized moieties, which are often altered at interfaces. Unraveling these changes requires access to charge state and structure of surface-confined biopolymers in aqueous environments. We therefore combined electrokinetic measurements of interfacial electrical potentials with the simultaneous determination of the optical layer thickness by reflectometric interference spectroscopy. Two examples are summarized to demonstrate the resulting options: The pH-switching of grafted poly(l-glutamic acid) layers caused by dissociation-dependent helix-coil transitions was studied; potential distribution and ion mobility within the grafted polyelectrolyte were unraveled using an new theoretical model for the charging of polyelectrolyte layers. The charge-driven modulation of biopolymers at interfaces was furthermore analyzed in the adsorption of fibronectin onto polymer substrates with varied charge density; the results permit us to reach a conclusion about the relevance of electrostatic matching for orientation and anchorage of the protein. Altogether, the introduced methodology was found suitable to follow the electrosurface characteristics of biomacromolecules in situ.
authors.affiliation: Max Bergmann Center of Biomaterials Dresden, Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Zimmermann
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Osaki
authors.forename: Thomas
authors.initials: T
authors.lastname: Kratzmüller
authors.forename: Günter
authors.initials: G
authors.lastname: Gauglitz
authors.forename: Stanislav S
authors.initials: SS
authors.lastname: Dukhin
authors.forename: Carsten
authors.initials: C
authors.lastname: Werner
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D004553:Electric Conductivity; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D013057:Spectrum Analysis / Q000379:methods*; D055672:Static Electricity
chemical_list: D001704:Biopolymers