Photoelectron circular dichroism on chiral amino-acids based systems: From free molecules to nanoparticles

Within a bottom-up approach of biomolecular complexity, substrate- and solvent-free dilute matter in the gas phase offers unique opportunity to template intrinsic structural and dynamical properties of small neutral biomolecules, the so-called elementary bricks of life. One important investigation method is by interaction with short wavelength photons, leading to photoionization processes which can be unraveled by angle-resolved photoelectron spectroscopy (ARPES), a sensitive, universal and background-free technique.

Recently, a new observable in ARPES, linked to Photoelectron Circular Dichroism (PECD) have been introduced in the case of randomly-oriented chiral species, leading to very intense (up to 35 %) forward/backward asymmetries with respect to the photon axis in the angular distribution of photoelectrons produced by circularly-polarized light ionization of pure enantiomers. PECD happens to be an orbital-specific, photon energy dependent chiroptical effect and is a subtle probe of the molecular potential being very sensitive to static molecular structures such as conformers, chemical substitution, clusters, as well as to vibrational motion, much more so than other observables in photoionization such as the cross section or the b asymmetry parameter (for a review see [1]). PECD has also been suggested as a possible process involved in the origin of life’s homochirality, the fact that only L-amino-acids and D-sugars are found in the biosphere [2].

After an introduction to chirality and PECD, I will present several recent results of valence-shell PECD obtained via double imaging electron/ion coincidence, on various systems based upon amino-acids, the chiral building blocks of proteins:

• Alanine, the simplest chiral proteic amino-acids, with astrochemical implications [3,4]
• Proline, on which we could observed directly a conformer-specific PECD [5]
• The effect of condensation on Serine homochiral nanoparticles [6]

References
[1] L. Nahon, G. A. Garcia, and I. Powis, J. Elec. Spec. Rel. Phen. 204, 322 (2015).
[2] R. Hadidi, D. Bozanic, G. Garcia, and L. Nahon, Advances in Physics: X 3, 1477530 (2018).
[3] M. Tia, B. Cunha de Miranda, S. Daly, F. Gaie-Levrel, G. Garcia, I. Powis, and L. Nahon, J. Phys. Chem. Lett. 4, 2698 (2013).
[4] M. Tia, B. Cunha de Miranda, S. Daly, F. Gaie-Levrel, G. A. Garcia, L. Nahon, and I. Powis, J. Phys. Chem. A 118, 2765 (2014).
[5] R. Hadidi, D. K. Božanić, H. Ganjitabar, G. A. Garcia, I. Powis, and L. Nahon, Commun. Chemi. 4, 72 (2021).
[6] S. Hartweg, G. A. Garcia, D. K. Božanić, and L. Nahon, The Journal of Physical Chemistry Letters 12, 2385 (2021).