JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

2-08
ESR Study on Carboxymethyl Chitosan Radicals
in Aqueous Solution
S. Saiki a) , N. Nagasawa a) , A. Hiroki a) , N. Morishita a) , M. Tamada a) ,
H. Kudo b) and Y. Katsumura b)
a) Environment and Industrial Materials Research Division, QuBS, JAEA,
b) Graduate School of Engineering, The University of Tokyo
Carboxymethylated polysaccharides such as
carboxymethyl cellulose, carboxymethyl starch and
carboxymethyl chitosan (CMCTS, as shown in Fig. 1) at
highly concentrated aqueous solution undergo crosslinking
reactions by ionizing irradiation, though polysaccharides are
generally classified to radiation-degradation polymer 1) .
Radiation-induced crosslinking and degradation of polymer
aqueous solution are generally caused by OH radical derived
from water radiolysis. In order to understand the
radiation-induced reaction mechanism in carboxymethyl
polysaccharide aqueous solution, it is important that the
initially-formed radical by the hydrogen abstraction of OH
radical is identified. In this study, to identify CMCTS
radical produced by reaction with OH radical in an aqueous
solution, ESR spectra of CMCTS radical were observed
using UV photolysis of H 2O 2.
ESR measurements were carried out at room temperature
with an X-band ESR spectrometer (JES-TE200, JEOL Ltd.).
Ten mM CMCTS/10 mM H 2O 2 aqueous solution was
prepared at room temperature as a sample solution. The
solution was bubbled with N 2 gas in a continuous flow
system through a flat cell set in the ESR cavity by a
peristaltic pump at a rate of 0.2 mL/min (Fig. 2).
Measurements were taken continuously during irradiation
with ultra high mercury lamp (USH-250D, 350 W, Ushio
Inc.).
ESR spectrum of CMCTS radicals were successfully
observed as shown in Fig. 3. As it can be seen, there are
large split and small split, and the left-and-right spectra are
not of the same shape. It was assumed that a number of
radicals were overlapped in this spectrum.
To assign the radical site, we should consider the
candidate of radical sites from a point of view of chemical
structure. Considering the hydrogen abstraction of OH
radical, radicals are possibly located on carbon atom of
glucopyranose rings or of carboxymethyl group or of
acetoamido group, or on nitrogen atom of amino group or of
acetoamido group. Comparing the splitting pattern and
width of the experimental spectra with those of the radicals
which have similar chemical structure around radicals with
these candidates, the case of radicals on nitrogen atom and
on carbon atom of glucopyranose rings and of acetoamido
group were not coincident with experimental results.
Therefore, it was speculated that those radicals were not
included in experimental results. On the other hand, as for
radicals on carboxymethyl groups, the splitting pattern and
width of the similar radical, benzyl ethyl ether radicals, were
JAEA-Review 2010-065
- 48 -
almost coincident with experimental results.
In conclusion, experimental ESR spectrum of CMCTS
radicals was identified as radicals on carboxymethyl groups.
Reference
1) F. Yoshii et al., Nucl. Instrum. Meth. Phys. Res. B 208
(2003) 320-324.
N2
Intensity /a.u.
R : CH2COO - O
CH2OR
O
RO
O
(NHCOCH3)
NH2
O
O
RO NH2
CH2OR
(NHCOCH3)
or H
Fig. 1 Structure of carboxymethyl chitosan.
ESR cavity
Peristaltic pump
Sample server
quartz cell
lens
Fig. 2 ESR measurement system.
0.5 mT
magnetic field /mT
Mercury lamp
Fig. 3 ESR spectra of CMCTS radicals.