Label-free monitoring of immuno-specific interactions of adsorbed multilayer of proteins.

Protein-protein interactions in adsorbed multilayer of an immuno-specific system of proteins that include staphylococcal protein A (SpA), bovine serum albumin (BSA), anti-chicken immunoglobulin Y (ac-IgG), chicken serum IgG (cs-IgG), and rabbit serum IgG (rs-IgG) on polystyrene (PS) were studied using attenuated total reflection-Fourier transform infrared spectroscopy. A systematic analysis allowed a direct qualitative and quantitative determination of protein interactions at each step of specific and nonspecific binding conditions at the molecular level. The study also provided information about (1) the adsorption behavior of the proteins, (2) the role of SpA in enabling correct orientation of the adsorbed IgG and maintaining the stability of the adsorbed SpA/ac-IgG system on the PS surface, (3) the function of BSA as both blocking reagent and promoter of specific and selective binding, and (4) the bioactivity conserved accommodation of SpA molecules on the PS surface.

Site-specific electronic structure of imidazole and imidazolium in aqueous solutions.

The occupied and unoccupied electronic structure of imidazole (CNH) and imidazolium (CNH) in aqueous solutions is studied by X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). Both systems show distinct RIXS fingerprints with strong resonant effects. A comparison with calculated X-ray emission spectra of isolated imidazole and imidazolium suggests only a small influence of hydrogen bonding in the aqueous solution on the electronic structure of imidazole and imidazolium, and allows the attribution of specific spectral features to the non-equivalent nitrogen and carbon atoms in the molecules.

X-ray Emission Spectroscopy of Proteinogenic Amino Acids at All Relevant Absorption Edges.

Nonresonant N K, O K, C K, and S L X-ray emission spectra of the 20 most common proteinogenic amino acids in their solid zwitterionic form are reported. They represent a comprehensive database that can serve as a reliable basis for the X-ray absorption spectroscopy (XES) studies of peptides and proteins. At the most important N and O K edges, clear similarities and differences between the spectra of certain amino acids are observed and associated with the specific chemical structure of these molecules and their functional groups.

Investigation of the Ionic Hydration in Aqueous Salt Solutions by Soft X-ray Emission Spectroscopy.

Understanding the molecular structure of the hydration shells and their impact on the hydrogen bond (HB) network of water in aqueous salt solutions is a fundamentally important and technically relevant question. In the present work, such hydration effects were studied for a series of representative salt solutions (NaCl, KCl, CaCl2, MgCl2, and KBr) by soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). The oxygen K-edge XES spectra could be described with three components, attributed to initial state HB configurations in pure water, water molecules that have undergone an ultrafast dissociation initiated by the X-ray excitation, and water molecules in contact with salt ions.

Ion-Solvation-Induced Molecular Reorganization in Liquid Water Probed by Resonant Inelastic Soft X-ray Scattering.

The molecular structure of liquid water is susceptible to changes upon admixture of salts due to ionic solvation, which provides the basis of many chemical and biochemical processes. Here we demonstrate how the local electronic structure of aqueous potassium chloride (KCl) solutions can be studied by resonant inelastic soft X-ray scattering (RIXS) to monitor the effects of the ion solvation on the hydrogen-bond (HB) network of liquid water. Significant changes in the oxygen K-edge emission spectra are observed with increasing KCl concentration.