title: On the origins of core-electron chemical shifts of small biomolecules in aqueous solution: insights from photoemission and ab initio calculations of glycine(aq).
abstract: The local electronic structure of glycine in neutral, basic, and acidic aqueous solution is studied experimentally by X-ray photoelectron spectroscopy and theoretically by molecular dynamics simulations accompanied by first-principle electronic structure and spectrum calculations. Measured and computed nitrogen and carbon 1s binding energies are assigned to different local atomic environments, which are shown to be sensitive to the protonation/deprotonation of the amino and carboxyl functional groups at different pH values. We report the first accurate computation of core-level chemical shifts of an aqueous solute in various protonation states and explicitly show how the distributions of photoelectron binding energies (core-level peak widths) are related to the details of the hydrogen bond configurations, i.e. the geometries of the water solvation shell and the associated electronic screening. The comparison between the experiments and calculations further enables the separation of protonation-induced (covalent) and solvent-induced (electrostatic) screening contributions to the chemical shifts in the aqueous phase. The present core-level line shape analysis facilitates an accurate interpretation of photoelectron spectra from larger biomolecular solutes than glycine.
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden. niklas.ottosson@fysik.uu.se
authors.forename: Niklas
authors.initials: N
authors.lastname: Ottosson
authors.forename: Knut J
authors.initials: KJ
authors.lastname: Børve
authors.forename: Daniel
authors.initials: D
authors.lastname: Spångberg
authors.forename: Henrik
authors.initials: H
authors.lastname: Bergersen
authors.forename: Leif J
authors.initials: LJ
authors.lastname: Sæthre
authors.forename: Manfred
authors.initials: M
authors.lastname: Faubel
authors.forename: Wandared
authors.initials: W
authors.lastname: Pokapanich
authors.forename: Gunnar
authors.initials: G
authors.lastname: Öhrwall
authors.forename: Olle
authors.initials: O
authors.lastname: Björneholm
authors.forename: Bernd
authors.initials: B
authors.lastname: Winter
mesh_terms: D004583:Electrons; D005998:Glycine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D056004:Molecular Dynamics Simulation; D056951:Photoelectron Spectroscopy; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D005998:Glycine