Description
Molecular chirality is central to biology and chemistry. Identification of enantiomers of chiral molecules is based on optical circular dichroism (CD), which was developed starting from the XIXth century and it measures the absorption difference of left and right circularly polarised light by the sample [1].
CD signals are intrinsically weak, usually 0.1% of the linear absorption, which makes them challenging to measure. Extending CD spectroscopy into the X-ray regime (XNCD) [2] offers key advantages, including elemental specificity and the possibility to probe site-selective chiral responses within a molecule. In particular, XNCD can distinguish inequivalent atomic sites not only via chemical shifts but also through their local chiral environment.
Although several theoretical studies [3-5] have underlined the advantages of soft X-ray natural CD (XNCD), its measurement on disordered media (powders) has remained a challenge with only few studies performed on amino-acid residues and organic molecules in amorphous films [6-8].
With the advent of the liquid microjet technique [9], it has become possible to inject liquid samples into vacuum and investigate their soft X-ray absorption both in steady-state and time-resolved studies. We have extended the use of the flat liquid microjets to perform XNCD studies of chiral molecules in solution.
We will present for the first-time evidence of XNCD spectra of such systems in the case of fenchone [10] in ethanol. The measurements were carried out at the O K-edge of the molecule, at the carbonyl O 1s → π* resonance which exhibits a clear enantiomer-dependent sign inversion and vanishes for the racemic mixture within experimental uncertainty, providing a self-consistent validation of its chiral origin. Notably, the probed oxygen atom is not itself a stereogenic centre, demonstrating that the observed response arises from the chiral electronic environment of the molecule. The results show a good agreement with theoretical results which are also presented.
References:
[1] L. D. Barron, Chem. Soc. Rev. 15, 189 (1986).
[2] C. Brouder et al. J. Synchrotron Rad. (1999). 6, 261-263
[3] A. Jiemchooroj et al., J. Chem. Phys. 127, 16 (2007).
[4] A. Jiemchooroj et al., J. Chem. Phys. 128, 234304 (2008).
[5] Y. Nam et al., J. Phys. Chem. Lett. 16, 4652 (2025).
[6] M. Tanaka et al., Phys. Scr. 2005, T115 (2005).
[7] A. Agui et al., Rev. Sci. Instrum. 72, 8 (2001).
[8] Y. Izumi et al., J. Chem. Phys. 138, 7 (2013).
[9] M. Ekimova et al. Struct. Dyn. 2, 5 (2015)
[10] Y.Nam et al. J. Phys. Chem. Lett. 2025, 16, 19, 4652–4661
