Speaker
Description
Liquid microjets (liquid jets, LJ), introduced in the 80s–90s by M. Faubel, S. Schlemmer and J.P. Toennies, enabled the investigation of volatile liquids under high-vacuum conditions and opened a breadth of new fields [1]. One of such fields is the combination of LJs with photoelectron spectroscopy, LJ–PES, capable of revealing subtle energy shifts in molecular-orbital binding energies (BEs) of both solvent and solute [2]. Here we present our most recent LJ-PES study applied to proline solutions [3].
Proline is one of the proteinogenic amino acids, being the only one with a heterocyclic amine group, which imparts higher rigidity and reduces its conformational space. As happens with many biomolecules, proline is found as a zwitterion in the neutral aqueous phase. PES studies of such molecules in the gas phase can only bring limited insight about its electronic structure when in aqueous solution, which is its biologically relevant environment. We can also easily switch to proline’s cationic and anionic forms by changing the solution’s pH to low and high values, respectively. These assisted us to interpret our XPS (X-rays Photoelectron Spectroscopy) results.
Even though theoretical and indirect experimental evidence on the evaporation dynamics of water using LJs have been gathered in the last decades, no direct study on that matter has been reported. We are setting up a novel experiment: crossing a supersonic beam of metastable carbon monoxide (CO($a^3$Π) or CO$^*$) with a LJ. By detecting the projection of the beam or imaging its fluorescence, one can determine the density profile of the vapor phase around a LJ.
[1] M. Faubel, S. Schlemmer, and J. P. Toennies, A molecular beam study of the evaporation of water from a liquid jet, Z. Phys. D: At. Mol. Clusters 10, 269 (1988).
[2] B. Winter and M. Faubel, Photoemission from liquid aqueous solutions, Chem. Rev. 106, 1176 (2006).
[3] B. Credidio, S. Thürmer, D. Stemer, M. Pugini, F. Trinter, J. Vokrouhlický, P. Slavíček, and B. Winter, From gas to solution: The changing neutral structure of proline upon solvation, J. Phys. Chem. A (2024).
