Determining the Conformation of an Adsorbed Br−PEG−Peptide by Long Period X-Ray Standing Wave Fluorescence

Abstract

Long period x-ray standing wave fluorescence (XSW) and x-ray reflectivity techniques are employed to probe the conformation of a Br-polyethylene glycol (PEG)-peptide adsorbate at the hydrated interface of a polystyrene substrate. The Br atom on this Br-PEG-peptide construct serves as a marker atom allowing determination by XSW of its position and distribution with respect to the adsorption surface with angstrom resolution. Adsorption occurs on native or ion beam modified polystyrene films that are spin coated onto a Si substrate and display either nonpolar or polar surfaces, respectively. A compact, oriented monolayer of Br-PEG-peptide can be formed with the peptide end adsorbed onto the polar surface and the PEG end terminating with the Br tag extending into the aqueous phase. The 108 -141 Å distance of the Br atom from the polystyrene surface in this oriented monolayer is similar to the estimated ~150 Å length of the extended Br-PEG-peptide. This Brpolystyrene distance depends upon adsorption time and surface properties prior to adsorption. Incomplete multilayers form on the polar surface after sufficient adsorption time elapses. By contrast, adsorption onto the nonpolar surface is submonolayer, patchy, and highly disordered with an isotropic Br distribution. Overall, this combination of x-ray surface scattering techniques with a novel sample preparation strategy has several advantages as a real space probe of adsorbed or covalently bound biomolecules at the liquid-solid interface.

Brominated Tyrosine and Polyelectrolyte Multilayer Analysis by Laser Desorption Vacuum Ultraviolet Postionization and Secondary Ion Mass Spectrometry

“…Elemental content of the PEMs was determined by monochromatic X-ray photoelectron spectroscopy using instrumentation and procedures previously described. 18 Details of the preparation and verification of the PEMs are given in Supporting Information.…”

“…PEMs were prepared on gold-coated substrates as described previously. , PEMs were verified by attenuated total reflection Fourier transform infrared spectroscopy. Elemental content of the PEMs was determined by monochromatic X-ray photoelectron spectroscopy using instrumentation and procedures previously described . Details of the preparation and verification of the PEMs are given in the Supporting Information.…”

Laser Desorption Postionization Mass Spectrometry and X-ray Surface Scattering for the Analysis of Bacterial Biofilms

“…However, XSW can be used to determine the spatial resolution of a molecular species in the condensed phase with ~1 nm resolution. XSW was previously used to probe the conformation of a bromine labeled-polyethylene glycol-peptide construct (Br-PEG-peptide) adsorbed at the liquid-solid interface of a modified polystyrene surface [6].…”

“…Bacillus subtilis biofilms were grown for several days (see above), then transferred to either Br-PEG-peptide or Br-tyrosine coated polystyrene and cultured for ~3 hours. XSW measurements of the Br distribution were then performed as previously described [6] except that the ChemMatCARS beamline was utilized at the Advanced Photon Source. The Br distribution was determined by XSW as the Br-tagged analyte spread into the biofilm.…”