Photoelectron Circulardichroism in the Photodetachment of Electrosprayed Anions

Research aiming at the quantification of molecular chirality by chiroptical techniques continues to attract a significant amount of interest in chemistry, physics, biology and pharmacology. Over the last decades some focus has been put on the measurement and analysis of the photo ion circular dichroism (PICD) – a total ion yield effect – and the Photoelectron Circular Dichroism (PECD) – a molecular frame angular distribution effect, ultimately culminating in a true coincidence experiment, where the PICD and the PECD have been simultaneously measured in one and the same (single) ionization event [1,2].

It is probably fair to state, that most of that work has been limited to relatively small molecules, exhibiting sufficient vapor pressure for standard chiroptical techniques. A breakthrough was reached a couple of years ago, when the measurement of PICD in the photodetachment of electro-sprayed anions was introduced by Daly et al. [3] and subsequently the measurement of PECD in the photodetachment of electrospray anions was demonstrated by Krüger et al., e.g., for the Gramicidin A peptide, with a mass of approx. 2000 Da [4,5]. Since then, the photodetachment of anions has received considerable attention, e.g., by Triptow et al. [6]. Here, we further report on recent progress in the Weitzel group demonstrating

i.) the quantification of enantiomeric excess in ESI-PECD of tryptophane monomer and dimer anions as well as phenylalanine anions [7], and

ii.) the implementation of the photoelectron elliptical dichroism (PEELD). Basically, PEELD is the extension of PECD considering a systematic variation of the elliptical polarization of light [8].

If time permits, an example will be presented, where ESI-PECD allows the distinction of folding isomers of mini proteins, where ion mobility spectrometry fails to provide the distinction.

References

[1] C.S. Lehmann, K.-M. Weitzel, Phys. Chem. Chem. Phys., 2020, 22, 13707.

[2] C.S. Lehmann, D. Botros, K.-M. Weitzel, Phys. Chem. Chem. Phys., 2022,24, 15904.

[3] S. Daly, F. Rosu, V. Gabelica, Science, 2020, 368, 1465-1468.

[4] P. Krüger, K.-M. Weitzel, Angew. Chem. Int. Ed., 2021, 60, 17861 – 17865.

[5] P. Krüger, J. H. Both, U. Linne, F. Chirot, K.-M. Weitzel, J. Phys. Chem. Lett., 2022, 13, 6110 – 6116.

[6] J. Triptow, A. Fielicke, G. Meijer, M. Green, Angew. Chem. Int. Ed., 2022, 62, e202212020.

[7] J. H. Both, A. Beliakouskaya, K.-M. Weitzel, Analytical Chemistry, 2025, in press, (https://doi.org/10.1021/acs.analchem.4c05964).

[8] J. H. Both, K.-M. Weitzel, work to be published (2025).