P28
23AU007

BL-12

Optical Activity Measurement of Circularly Polarized
Lyman-α Light Irradiated and Magnetic Field Applied
Amino-acid Films
Jun-ichi Takahashia, Masahiro Kobayashib, Gen Fujimoric, Hiroshi Otad
Koichi Matsuoe, Yoshitaka Tairad, Masahiro Katohd,e, Kensei Kobayashic,fYoko Kebukawaf, Hiroaki NakamurabaDoshisha University, 1-3 Tatara Miyakodani, Kyotanabe 610-0394, Japan
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, JapancYokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, JapandUVSOR Synchrotron Facility, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, JapaneHiroshima Synchrotron Radiation Center, 2-313 Kagamiyama, Higashi-Hiroshima 739-0046, Japanf
Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8511, Japanb

Keywords: Homochirality, Amino Acid, Optical Activity, Circularly Polarized Light, Lyman-α, Circular Dichroism.

The origin of homochirality in terrestrial biomolecules (L-amino acid and D-sugar dominant) remains
one of the most mysterious problems in the research for the origins of life. Rational explanations for thechiral asymmetry introduction into biomolecules are required through interdisciplinary collaborations. Oneof the most attractive hypotheses in the context of astrobiology is cosmogenic scenario; Asymmetric
reactions of prebiotic molecules on interstellar dust surfaces in molecular cloud circumstances wereintroduced by polarized quantum radiation sources in space, that is “chiral radiations” [1, 2].
Among the polarized quantum radiation sources, circularly polarized light (CPL) in the spaceenvironment is thought to be one of the most likely causes of the enantiomeric excesses of terrestrial
bioorganic molecules. A cosmogenic scenario has attracted attention, which proposes that the radiation fieldsof CPL induce new optical activity in organic molecules produced in the interstellar environment, leading to
the enantiomeric excesses. The radiation fields of CPL are assumed to exist in the scattered light by magnetic
field-aligned dust in massive star-forming regions [3] and in synchrotron radiation (SR) or gamma-ray bursts
from neutron stars with strong magnetic fields [2]. Ultraviolet light with a wavelength shorter than 230 nm
is highly absorbed by bioorganic molecules such as amino acids. Furthermore, this is in the region where theoptical response to left- (L-) and right- (R-) CPL is of opposite sign, that is, optical activity is prominent.
To validate the cosmogenic scenario, several ground simulating experiments have been investigatedusing ultraviolet CPL from high-energy particle accelerators. In this study, we focused on a hydrogen Lymanα wavelength of 121.6 nm, where strong emission lines are observed in star-forming regions. Furthermore,
it is predicted by recent theoretical calculations that the hydrogen Lyman-α light is circularly polarized by
the magnetic field-aligned dust scattering in massive star-forming regions. We have carried out irradiation
experiments by using circularly polarized hydrogen Lyman-α light to investigate the further photon energy
dependence of chiral asymmetric reactions. We formed thin solid film samples of racemic mixture of alanine(DL-alanine) on quartz substrates from crystal powders of DL-alanine by using a thermal-crucible vacuumevaporation system. The samples were irradiated with L- or R-CPL in hydrogen Lyman-α wavelength of
121.6 nm using the undulator beam line BL1U of UVSOR-III. The irradiated CPL wavelength corresponds
to photon absorption bands with the chromophores from the electronic transitions of carboxyl and aminogroups (π-σ*) of alanine molecule [4, 5]. The samples were set in a vacuum sample chamber preventing
attenuation by air absorption. The 121.6 nm wavelength radiation from the undulator is reflected by a goldcoated mirror located in the mirror chamber directly beam upstream of the sample chamber and then enters
the sample chamber. On the beam entrance side of the vacuum sample chamber, a gate valve with an MgF2vacuum sealing window (0.5 mm in thickness) was mounted. The use of gold-coated mirror reflections hasmade it possible to suppress high-energy higher-order light from the undulator source expecting to reduce
the transmittance loss of the MgF2 window due to high-energy radiation induced defects. The sample
substrate was set in the sample holder, in which magnetic field can be applied to perpendicularly to thesample surface (Figure 1). The total photon beam intensity irradiated on the sample was monitored withphotoelectron current of a silicon photodiode settled at the beam downstream side of the sample holder.
CD spectra of the CPL irradiated films were measured using the SR-CD beam line BL-12 of HiSOR toclarify the optical activity emergence by CPL irradiation. CD spectroscopy can detect optical activity with ahigh accuracy because CD spectra sensitively reflects the steric structures of chiral molecules. To delete theeffects of linear dichroism components, the CD spectra at sample rotation angles (0, 45, 90, and 135 degrees)from both back and front directions of each were individually measured and averaged them. We alreadyreported the results of the first feasibility study conducted as application proposals to collaborate withUVSOR and HiSOR in FY2022 (6). The measured CD spectra of DL-alanine films irradiated with CPL at
121.6 nm in wavelength indicated the emergence of optical activity depending on the irradiated CPL
polarization helicity (L- or R-CPL). In addition, we examined the effect of applying a magnetic field to thesample to investigate the effect of the magnetic field in interstellar space. Comparing with CD spectra ofirradiations at 215, 180 and 155 nm in wavelength in our previous study [7, 8], the aspects of the opticalactivity emergence strongly depend on the irradiated CPL wavelength.
In the experiments for the FY2023 collaborative application proposals, we focused on accumulating
reproducibility data of the previous FY2022 results and improving the accuracy of quantification in thequantum efficiency of the emergence of optical activity. Figure 2 shows CD spectra of DL-alanine films afterright (R-) and left (L-) circularly polarized Lyman-α (121.6 nm) irradiation with magnetic field (0, ±0.7 T).
As shown in this figure, we found a clear emergence of optical activity and a significant magnetic field
application effect. The clarification of full mechanism of the optical activity emergence potentially has
relevance to the origin of terrestrial bioorganic homochirality stimulated by “chiral photon radiation”.
This work is supported by the Astrobiology Center Program of National Institutes of Natural Sciences(NINS) (Grant Number AB041014 and AB0515) and Frontier Photonic Sciences Project of National
Institutes of Natural Sciences (NINS) (Grant Number 01212202 and 01212304).

FIGURE 1. Schematic view of circularly polarized Lymanα (121.6 nm) irradiation system.

FIGURE 2. CD spectra of on DL-alanine films after right(R-) and left (L-) circularly polarized Lyman-α irradiation
with magnetic field (0, ±0.7 T).

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