UHV Deposition of the Gly-Pro Dipeptide on Cu(110) by Sublimation or Electrospray Ionization
Résumé
While most of the peptide adsorption studies, in vacuum, are achieved by sublimation, we demonstrate here the possible use of electrospray ionization (ESI) to deposit entire peptides, possibly surrounded by solvated ions, on a surface in ultra high vacuum (UHV) conditions. This paper is then focused on the possible differences, depending on the way the peptide is sent onto the surface, sublimation or electrodeposition, in the resulting adsorption chemical state and geometry. As a matter of fact, both the chemical state of the molecule, and its anchoring points with the surface, significantly change: from sublimation, the Gly-Pro molecules are adsorbed under an anionic form (COO-/NH2) and bound to the copper surface via both COO- and NH2 groups; whereas, after deposition by ESI under positive voltage, the adsorbed peptides are under their zwitterionic form (COO-/NH3+); and only interact with the surface via one oxygen atom of the carboxylate groups. These changes modify both the geometry of the adsorbed molecules but also the growth of further layers.
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