title: pH-induced protonation of lysine in aqueous solution causes chemical shifts in X-ray photoelectron spectroscopy.
abstract: We demonstrate the applicability of X-ray photoelectron spectroscopy to obtain charge- and site-specific electronic structural information of biomolecules in aqueous solution. Changing the pH of an aqueous solution of lysine from basic to acidic results in nitrogen 1s and carbon 1s chemical shifts to higher binding energies. These shifts are associated with the sequential protonation of the two amino groups, which affects both charge state and hydrogen bonding to the surrounding water molecules. The N1s chemical shift is 2.2 eV, and for carbon atoms directly neighboring a nitrogen the shift for C1s is approximately 0.4 eV. The experimental binding energies agree reasonably with our calculated energies of lysine(aq) for different pH values.
authors.affiliation: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2a, D-12489 Berlin, Germany. nolting@mbi-berlin.de
authors.forename: Dirk
authors.initials: D
authors.lastname: Nolting
authors.forename: Emad F
authors.initials: EF
authors.lastname: Aziz
authors.forename: Niklas
authors.initials: N
authors.lastname: Ottosson
authors.forename: Manfred
authors.initials: M
authors.lastname: Faubel
authors.forename: Ingolf V
authors.initials: IV
authors.lastname: Hertel
authors.forename: Bernd
authors.initials: B
authors.lastname: Winter
mesh_terms: D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D012015:Reference Standards; D012996:Solutions / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods / Q000592:standards*; D014867:Water / Q000737:chemistry; D014965:X-Rays
chemical_list: D011522:Protons; D012996:Solutions; D014867:Water; D008239:Lysine