Determination of Absolute Structure of Chiral Crystals Using Three-Wave X-ray Diffraction

Ksenia Kozlovskaya,Francois Guillou,Alisa F Konstantinova,Fabrice Wilhelm,Elena Ovchinnikova,Jun Kokubun,Francois De Bergevin,Vladimir E Dmitrienko,Andrei Rogalev

doi:10.3390/cryst11111389

Ksenia Kozlovskaya, Francois Guillou + Show 7 more

Open Access

https://doi.org/10.3390/cryst11111389

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Abstract

We propose a new method to determine the absolute structure of chiral crystals, which is based on the chiral asymmetry of multiple scattering diffraction. It manifests as a difference in the azimuthal dependence of the forbidden Bragg reflection intensity measured with left and right circularly polarized X-ray beams. Contrary to the existing ones, the suggested method does not use X-ray anomalous dispersion. The difference between the Renninger scans with circularly polarized X-rays has been experimentally demonstrated for the 001 reflection intensities in the right- and left-handed quartz single crystals. A Jmulti-based code on model-independent three-wave-diffraction approach has been developed for quantitative description of our experimental results. The proposed method can be applied to various structures including opaque, organic and monoatomic crystals, even with only light elements. To determine the type of isomer, the Renninger plot of a single forbidden reflection is sufficient.

Highlights

Many biomolecules and medicines are chiral, i.e., can exist as right- or left-handed optical isomers
We propose a new X-ray method to determine the absolute atomic structure of crystals using only one crystal, one reflection and giving some flexibility in a choice of the wavelength of the incident radiation
The sign of this circular dichroism is opposite for two enantiomorphous structures, which allows the determination of the absolute structure of a sample

Summary

Introduction

Many biomolecules and medicines are chiral, i.e., can exist as right- or left-handed optical isomers. Recent development of XNCD was demonstrated in the visualization of chiral domain distribution by scanning over the sample surface with a small beam with circular polarization [20,21] Another way to determine the absolute crystal structure is a study of the energy and azimuthal dependence of forbidden reflections in REXS (Resonant Elastic X-ray Scattering) [22,23,24,25]. Using right or left circularly polarized beams, we can see that the azimuthal dependence of the forbidden reflection intensity looks different for two opposite helicities of the incident radiation or for the right- or left-handed crystal samples (Figure 2) This kind of measurement is available at the modern synchrotrons and can be realized for the forbidden Bragg reflections.

Method Description

Experiment Details

Modelling of Three-Wave Multiple Reflections with Circular Polarizations

Conclusions