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

RIKEN Accel. Prog. Rep. 51 (2018)

Electron Transport Studies in Biological Moleculeswith respect to Ageing Science
H. Rozak,∗1 W. Zaharim,∗2 F. Astuti,∗1,∗3 R. Asih,∗1,∗4 R. Samian,∗2 S. Samsudin,∗2 S. N. Abu Bakar,∗2
N. Ismail,∗2 I. Watanabe,∗1,∗3,∗4 M. I. Mohamed-Ibrahim,∗2 and S. Sulaiman∗2
The electron transport process in deoxyribonucleic
acid (DNA) is a very important biological phenomenon
but the process itself is not fully understood at themicroscopic level. DNA is the molecule that storesgenetic information in a living cell and the structureof DNA consists of four bases. These four bases are
guanine (G), adenine (A), cytosine (C) and thymine(T).1) Damages in DNA can lead to various types ofdiseases such as cancers and neurological disorders.
There is a direct relationship between the damages in
DNA and ageing. We hypothesize that damages inthe DNA would alter the behavior of electron transfer
since DNA is well known as a good electron conductor.
If there are some defects in DNA, the electron transfer
in it will be disturbed, thus changing the electron motion. However, the degree and type of alterations areyet unknown at the microscopic level. In order to understand this phenomenon, systematic studies on thealteration of electron transfer in DNA are needed andµSR is known to be useful in this respect as has been
demonstrated in the past on one-dimensional organic
molecules.2–4)
In this project, we used simple model molecules of
DNA where the sequence is less than 12 bases, which
would make it easier to interpret the results.
Experiments on the µ+ relaxation in guanine andadenine have been conducted using an intense pulsed
beam µ+ at the RIKENRAL Muon Facility. All measurements were conducted on the powder sample andthe weight of each sample was 50 mg. We measured
the muon-spin relaxation rate under various longitudinal magnetic ﬁelds in the range between 0 T and 0.3 T
and the temperatures that we used to carry out ourexperiment were at 100 K and 300 K. The observed relaxation functions, G(t), were ﬁtted to the Risch-Kherfunction.
Based on the curve in Fig. 1, at temperatures 100 K,
the µ+ relaxation function was found to depend on
the external ﬁeld, where the initial asymmetry was increased as the external magnetic ﬁeld increased. Unfortunately, the muon spin precession did not show
clearly in this curve due to the limitation of the pulse
muon source at RAL. Therefore, it is better to repeat
the experiment involving guanine at PSI by using acontinuous beam to conﬁrm the existence of the diamagnetic muon components which are strongly bound
∗1
∗2
∗3
∗4

Fig. 1. µSR Time spectra in Guanine at 100 K under external longitudinal fields of 0, 200, 1000 and 2000 G.

Fig. 2. Relaxation parameter versus an external longitudinal magnetic field for µ+ in guanine at a temperaturesof 100 K.

to the molecules. For the curve in Fig. 2, the relation parameter (Γ ) was found to take an inverse-ﬁeld
dependence in guanine above 50 G, thus suggesting
existence of a quasi-1D rapid diﬀusion of electron in
DNA strands It is clear that the electron-transfer process at the microscopic level was directly detected in
the present experiments as shown in Fig. 2.
References1) S. P. Jackson et al., Nature (London) 461, 1071 (2009).
2) K. Ishida et al., Phys. Rev. Lett. 55, 2009 (1985).
3) K. Nagamine et al., Phys. Rev. Lett. 53, 1763 (1984).
4) E. Torikai et al., Hyperfine Interact. 138, 509 (2001).

RIKEN Nishina Center
School of Distance Education, Universiti Sains Malaysia
Department of Physics, Hokaido University
Department of Physics, Osaka University- 208 -