7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Synchrotron Radiation Chiral Spectroscopy and Biomolecules
Koichi Matsuo
Synchrotron Radiation Center, Hiroshima Universitye-mail: pika@hiroshima-u.ac.jp
2-313 Kagamiyama, Higashi-Hiroshima, Japan.
Circular dichroism (CD), which is defined as thedifference in absorbance between left- andright-circularly polarized light (LCPL and RCPL), is theestablished technique to monitor the steric structures ofchiral molecules such as biomolecules (amino acid,natural product, protein, DNA, and polysaccharide). The
usage of synchrotron radiation (SR) as a light source has
further enhanced the usefulness of this spectroscopy
through the extension of the wavelength region of CD
spectrum into vacuum-ultraviolet (VUV) region (downto 140 nm), the developments of new VUV-CD
analytical methods combined with computational science[1], and the installation of the linear dichroism (LD) [2]and spatial- and time-resolved measurement systems. In
this study, we introduce the CD techniques using SR andits applications to the characterization of the structures ofchiral molecules.
The relationship between chromophores of stericconfigurations and their substituents in organic
compounds can be analyzed from the sign of CD(positive or negative), and when targeting thechromophores that has an absorbance only in the VUVregion (~200 nm), the SR-CD becomes effective tool.
For example, the absorption of allene exhibits around180 nm and hence the absolute configuration of its
substituents is determined from the CD sign around 180nm, not in the wavelength region above 200 nm [3]. The
acetal bonds and hydroxyl groups of sugars also have theCD peak around 170 nm, reflecting their configurations.
Since, even for mono-saccharide, sugar in solution takes
an equilibrium state of two anomers and three rotamers,
it is difficult to determine the configurations from the CD
sign. However molecular dynamics (MD) simulation andtime-dependent density functional theory can disclose
the unique CD of each isomer and the situations of theirintramolecular hydrogen bonding [4], and further canreveal the relationships between isotope effect andhydration [5]. Thus, it is possible to discuss the stericconfiguration and the hydrogen bonding network ofmonosaccharide at the isomer level.
The CD analysis of globular proteins combined withbioinformatics and LD allowed us to estimate thecontents, numbers of segments, sequences, andorientations of secondary structures of proteins. The
combination method was applied to the elucidation of themechanism of protein-membrane interaction related todrug transportation into cell, myelin formation aroundneuron cell, antimicrobial activity in immune system,
and amyloid fibril formation [6,7]. The antimicrobial
peptide magainin 2 interacts with the bacterial membrane,
causing damage to its structure. The CD analysis
revealed that the M2 peptides assembled in themembrane and turned into oligomers with a β-strandstructure. LD and fluorescence anisotropy suggested thatthe oligomers are inserted into the hydrophobic core of
the membrane, disrupting the bacterial membrane. Thus,VUVCD and its combination with other polarization
experimental methods pave the way for unraveling themolecular mechanisms of biological phenomena related
to protein-membrane interactions. The time-resolved
system installed into the CD instrument realized thekinetics analysis of conformation change of protein
under the interactions with other biomolecules. Microbeam using the schwarzschild objective made it possible
to measure the CD with microvolume sample and theposition-dependent CD [8]. This system was used forrevealing a part of mechanism of DNA damage response
in X-ray irradiated human HeLa cells [9] and formeasuring the spatial-resolved CD of solid sample.
Origin of homochirality in terrestrial biomolecules(L-amino acids and D-sugars dominant) remains anunresolved problem. The CD spectroscopy can easily
detect the emergence of optical anisotropy due to theasymmetric reaction. The thin solid films of racemic
alanine (L/D = 1) were prepared by the vacuum
evaporation system and irradiated by the LCPL andRCPL generated from SR undulator, and the emergenceof amino acid homochirality were investigated by the CD
measurements. The SR-CD spectroscopy was also used
for the study of biochemical effects by loss ofhomochirality [10].
The CD technique with SR light source would further
enhance the performance of chiral spectroscopy andopen a pathway of next-generation of molecular chirality
research.
Acknowledgments
This work was funded by Japan Society for thePromotion of Science (grant numbers 22 K06163 and19 K06587).
References[1] K. Matsuo and K. Gekko, Bull. Chem. Soc. Jpn. 6,675 (2013)[2] M. Kumashiro et al, Membranes 12, 131 (2022)[3] T. Umezawa et al, Molecules 26, 1296 (2021)[4] K. Matsuo and K. Gekko J. Phys. Chem. A 124, 642(2020)[5] Y. Kanematsu et al, Sci. Rep. 5, 17900 (2015)[6] K. Matsuo et al, Chirality 32, 594 (2020)[7] M. Kumashiro et al, Proteins 8 9, 1251 (2021)[8] Y. Izumi and K. Matsuo, Molecules 23, 2865 (2018)[9] Y. Izumi et al, Chirality 35, 165 (2023)[10] A. Banreti et al, Nat. Comm. 13, 7059 (2022)