Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 53

Electron transfer in 12-mer double-stranded DNA by muon
spectroscopy and scanning tunneling microscopy
H. Rozak,∗1,∗2 S. Sulaiman,∗2 W. N. Zaharim,∗2 N. E. Ismail,∗2 S. N. Abu Bakar,∗2 M. R. Samian,∗4I. Miyazaki,∗3 K. Ichimura,∗3 and I. Watanabe∗1,∗2,∗324
2220
Asymmetry(%)

Electron transport through DNA plays a pivotal
role in biological systems. Processes that use electron transfer include scanning the damaged sites inDNA and DNA repair.1,2) To understand these biological phenomena, it is necessary to investigate theelectron transfer process in normal and damaged DNA
at the microscopic level. The main questions of thisstudy are: what is the diﬀerence in the characteristics of electron transfer between normal and damaged
DNA, and how much the diﬀerence in the quantitative value for electron diﬀusion along the normal anddamaged DNA helix.
In order to answer those questions, muon spin relaxation (µSR) measurements were performed at theArgus spectrometer RIKEN RAL. This µSR technique
has been suggested as a good probe to study the motion of electron transfer in DNA because the muon
spin relaxation could characterize or model the diﬀusion of electrons along the DNA helix via hyperﬁneinteraction without producing any radiation eﬀect on
the sample.3)
In this study, 12-mer double-stranded synthetic
DNA GC (12 mer-dsDNA GC) was used to portraythe conditions for normal DNA. The measurements
were performed at room temperature and the external longitudinal magnetic ﬁelds were applied up toFig. 1. STM image of 12 mer-dsDNA GC molecules alignedin one-dimensional chain structure.
∗1∗2∗3∗418 16

 140G20 G
100 G
200 G
500 G1000 G

121080246Time(PS)810Fig. 2. Raw data of muon spin relaxation for 12-merdouble-stranded synthetic DNA GC dependence overtime.

3400 G. The 80 mg powder sample of 12 mer-dsDNA
GC was wrapped in a thin silver foil with the diameterof 1.5 cm.
In addition, scanning tunneling microscopy (STM)
measurements were conducted to probe the molecular
structure of 12 mer-dsDNA GC. From the STM measurements, the images of 12 mer-dsDNA GC molecules
were successfully observed as shown in Fig. 1. The
image in Fig. 1, was taken in constant current modeat room temperature and it corresponds to the surface map of electron tunneling from HOMO tip to theLUMO of the sample.4)
Figure 2 shows the raw data of muon spin relaxation
spectra dependence over time. The asymmetry is increased as the applied magnetic ﬁeld increases. Themuon spin relaxation becomes suppressed at the highest external magnetic ﬁelds. This result indicates thatthe spin relaxation of a muon is interacting with anelectron that is rapidly diﬀusing along the molecule.
At higher applied ﬁeld, the muon-electron hyperﬁne
coupling starts to be quenched. Accordingly, the muon
spin relaxation is decreased, as illustrated in Fig. 2.
References

1) E. O’brien et al., Science 355(6327), eaag1789 (2017).
2) M. A. Grodick et al., Biochemistry 54(4), 962 (2015).
3) M. Iain, J. Phys. Chem. B 123(21), 4540 (2019).
4) R. Harison et al., Mater. Sci. Forum. 966, (2019).

RIKEN Nishina Center
School of Distance Education, Universiti Sains Malaysia
Department of Engineering, Hokkaido University
School of Biological Sciences, Universiti Sains Malaysia- 157 -