EPR study of gamma irradiated DL-methionine sulfone single crystals

Article abstract of DOI:10.1016/j.molstruc.2015.08.063

Electron paramagnetic resonance (EPR) study of gamma irradiated dl-2-amino-4-(Methylsulfonyl) butyric acid (dl-methionine sulfone, hereafter dl-ABA) single crystals and powder was performed at room temperature. It has been found that this compound indicates the existence of C.O2- and N.^H2 radicals after γ-irradiation. While g and hyperfine splitting values for the N.^H2 radical were observed, for the C.O2- radical, only the g factor was measured. The EPR spectra have shown that N.^H2 radical has two groups each having two distinct sites and C.O2- radical has one site. The principal g and hyperfine values for all sites were analyzed.

Full text of DOI:10.1016/j.molstruc.2015.08.063

Journal of Molecular Structure 1102 (2015) 186e189
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
EPR study of gamma irradiated DL-methionine sulfone single crystals
,
*
b
Bünyamin Karabulut a , Ilkay Yıldırım
_
a Department of Computer Engineering, Faculty of Engineering, Ondokuz Mayis University, Atakum 55139, Samsun, Turkey
b Department of Radiotherapy, Vocational School of Health Services, Biruni University, Topkapi 34010, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Electron paramagnetic resonance (EPR) study of gamma irradiated dl-2-amino-4-(Methylsulfonyl)
butyric acid (dl-methionine sulfone, hereafter dl-ABA) single crystals and powder was performed at
Received 4 February 2015
Received in revised form
27 August 2015
Accepted 28 August 2015
Available online 3 September 2015
:
:
room temperature. It has been found that this compound indicates the existence of COꢀ2 and NH2 radi:cals
:
after g
-irradiation. While g and hyperfine splitting values for the NH2 radical:were observed, for the CO2ꢀ
radical, only the g factor was measured. The EPR spectra have shown that NH2 radical has two groups
:
each having two distinct sites and COꢀ2 radical has one site. The principal g and hyperfine values for all
sites were analyzed.
Keywords:
© 2015 Elsevier B.V. All rights reserved.
EPR
Gamma-irradiation
Butyric acid
Amine radicals
dl-methionine sulfone
:
:
1. Introduction
proposal made for NH2 and COꢀ2 radicals in the literature. In this
study, as a result of the investigation of the line distributions in the
:
:
In order to get radicals from both organic and inorganic struc-
tures, they can be exposed to gamma rays. EPR technique is used to
identify the radical species formed in the structure [1]. The EPR
spectroscopy is the best way to determine the properties of radi-
cals; however, its application is limited by the lifetime of free
radicals produced by gamma-irradiation [2e5]. Dl-ABA is an
essential sulfur containing amino acid, which is not synthesized by
the body and must be obtained from food. It supplies mineral sulfur,
which improves the tone and pliability of the skin, conditions the
hair, strengthens the nails, and protects the cells from the airborne
pollutants. Radiation induced free radicals in amino acids and de-
rivatives have been investigated by many researchers [6e11].
Almanov et al. studied the radicals in irradiated DL-methionine
EPR spectra, the NH2 (amine) and COꢀ2 radicals were observed for
:
:
the first time. EPR study of the NH2 (amine) and COꢀ2 radicals
formed in dl-ABA was performed to get information about its
properties, the behavior and the environment of the radicals.
2. Experimental
The saturated solution of commercially obtained dl-ABA was
prepared and single crystals were obtained by using slow evapo-
ration technique. The selected single crystals were irradiated by a
60Co
g-ray source at room temperature at a dose of about 20 kGy,
then EPR spectra were recorded. The crystal structure of dl-ABA was
reported by Skvortsov et al. [17]. Due to the report, it crystallizes in
orthorhombic system with the unit cell parameters, a ¼ 5.353(1) Å,
b ¼ 5.353(1) Å, c ¼ 22.961 Å. The space group is P31/c and the unit
cell contains four molecules (Z ¼ 4). The EPR spectra were recorded
in the X-band frequency on a Varian E-109 C spectrometer with
100 kHz field modulation.
single crystals and as a result they proposed the formed radical
:
as CH3SCHCH2CHðNH2ÞCOOH [9]. Øyen et al. investigated the
radiation effects on L-asparagine and proposed three diff: erent
:
radicals as NH2COHCH2CHðNH3ÞCOO, NH2COCH2CHðNH3ÞCOOH,
:
and NH2COHCH2CHðNH3Þþ [10]. Osmanoglu et al. carried out
g-
ꢀ
irradiated L-glutamine hydrochloride and N-carbamoyl-L-glutamic
:
:
:
acid and proposed CH, NH2, CH2CðNH2ÞCOOH radicals [11]. How-
ever, no EPR report has been found specifically for dl-ABA and no
3. Results and discussion
The EPR spectra of gamma-irradiated dl-ABA (CH3SO2CH2CH2
CH(NH2)COOH) single crystal were recorded at room temperature
in three mutually perpendicular planes. The crystal was mounted
on a goniometer and rotated at 10ꢁ steps between 0ꢁ and 180ꢁ for
* Corresponding author.
E-mail address: bbulut@omu.edu.tr (B. Karabulut).
http://dx.doi.org/10.1016/j.molstruc.2015.08.063
0022-2860/© 2015 Elsevier B.V. All rights reserved.

_
B. Karabulut, I. Yıldırım / Journal of Molecular Structure 1102 (2015) 186e189
187
Table 2
:
:
The principal g and A values of NH2 and COꢀ2 radicals observed in various lattices
(D
g ¼ 0.0003 and A ¼ 0.05 mT).
D
Lattice
Radical
gx
gy
gz
giso
Aiso Reference
(mT)
_
dl-ABA
dl-ABA
dl-ABA
dl-ABA
NH2 ðI ꢀ IÞ 2.0001 2.0090 2.0025 2.0039 1.87 This study
_
NH2 ðI ꢀ IIÞ 2.0083 2.0045 1.9986 2.0038 1.84 This study
_
NH2 ðII ꢀ IÞ 2.0058 1.9986 2.0003 2.0016 1.87 This study
_
NH2 ðII ꢀ IIÞ 2.0054 1.9964 2.0031 2.0016 1.87 This study
:
L-Glutamine$ NH2
e
e
e
2.0037 2.04 [11]
HCl
:
Hydrazoic acid NH2
e
e
e
e
e
e
2.0038 2.39 [12]
2.0048 2.38 [13]
:
Ammonia
dl-ABA
Renal stone
Gypsum
NH2
:
COꢀ2
1.9976 1.9956 1.9985 1.9973
1.9973 1.9973 2.0025 1.9990
2.0029 2.0027 1.9973 2.0009
2.0018 2.0018 1.9973 2.0003
e
e
e
e
This study
[14]
[15]
:
COꢀ2
:
COꢀ2
:
Tooth enamel COꢀ2
[16]
thought to be formed due to the gamma irradiation as shown in the
:
Scheme 1. The NH2 radical has two identical protons and a single
14N nucleus. Proton and nitrogen have nuclear spins 1/2 and 1,
respectively. In an EPR spectrum, the identical two protons form a
1:2:1 intensity distribution and each line is splitted to a 1:1:1 in-
tensity distribution due to an additional 14N nucleus. As a result, a
total of 1:3:4:3:1 intensity distribution occurs in the spectrum.
Therefore, the two groups in the spectrum can be interpreted in
:
:
terms of NH2 radicals and the single line as COꢀ2 radical. The hy-
perfine lines resulting from 13C nucleus are not visible in the
spectrum at low and high field sides.
The EPR spectra of gamma-irradiated dl-ABA single crystal can
be expressed in terms of the spin Hamiltonian including g and A
(hyperfine) tensors as:
Fig. 1. EPR spectrum of the gamma irradiated dl-ABA single crystal. The magnetic field
is in the ac plane making 110ꢁ with the c axis.
H ¼ bB$g$S þ S$A$I
(1)
It includes only electronic Zeeman and hyperfine interactions.
The g and A (hyperfine) tensors were constructed and principal
values, i.e. gi and Ai (i ¼ x, y, z), were calculated by using the
diagonalization method as described in Ref. [18]. The calculated
values were given in Table 1.
Scheme 1.
The curve fitting procedure [18] was used to plot the magnetic
field values of all spectral lines against the rotation angle for all
planes (Table 2). Fig. 2 shows the graph and also represents the
all planes. Fig. 1 shows one of the recorded EPR spectra of gamma-
irradiated dl-ABA single crystal when the magnetic field makes
110ꢁ with the c axis in ca plane. In Fig. 1, the spectrum mainly
consists of 10 lines with an intensity distribution of two groups of
1:3:4:3:1 and a single line near the central field. Two radicals are
change in hyperfine values expresse:d in magnetic field units. The
:
sites of NH2 radical center I and the COꢀ2 radical were indicated for
the ca plane in Fig. 2.
From the spectral behavior, the gamma-irradiated dl-ABA single
Table 1
:
:
The EPR parameters of NH2 and COꢀ2 radicals in
g
-irradiated dl-ABA single crystals at room temperature (
Direction cosines
D
g ¼ 0.0003 and
D
A ¼ 0.05 mT).
Radical type
Site
g values
Hyperfine
Direction cosines
values (mT)
a
b
c
a
b
c
:
NH2ðIÞ
I
gx ¼ 2.0001
gy ¼ 2.0090
gz ¼ 2.0025
gx ¼ 2.0083
gy ¼ 2.0045
gz ¼ 1.9986
gx ¼ 2.0058
gy ¼ 1.9986
gz ¼ 2.0003
gx ¼ 2.0054
gy ¼ 1.9964
gz ¼ 2.0031
gx ¼ 1.9976
gy ¼ 1.9956
gz ¼ 1.9985
0.625
0.606
0.492
0.658
0.421
0.624
ꢀ0.735
0.511
ꢀ0.446
0.712
0.692
0.121
0.618
0.557
0.555
ꢀ0.380
0.787
ꢀ0.486
ꢀ0.655
0.729
ꢀ0.682
0.117
0.722
0.372
0.539
ꢀ0.756
0.029
0.680
0.732
0.425
ꢀ0.562
0.710
0.351
0.437
ꢀ0.828
Ax ¼ 1.89
Ay ¼ 1.57
Az ¼ 2.16
Ax ¼ 1.75
Ay ¼ 1.56
Az ¼ 2.22
Ax ¼ 1.81
Ay ¼ 1.42
Az ¼ 2.38
Ax ¼ 1.80
Ay ¼ 1.65
Az ¼ 2.17
e
ꢀ0.745
0.463
0.480
0.847
0.511
ꢀ0.148
0.836
0.451
0.311
0.977
0.186
0.103
e
ꢀ0.284
ꢀ0.872
0.400
ꢀ0.505
0.860
0.074
0.482
ꢀ0.876
ꢀ0.025
0.205
ꢀ0.952
0.227
e
0.604
0.161
0.781
0.165
0.012
0.986
0.261
0.171
ꢀ0.950
0.056
0.242
ꢀ0.969
e
II
I
0.199
:
NH2 ðIIÞ
ꢀ0.678
ꢀ0.525
0.515
II
e
ꢀ0.559
0.454
0.694
0.704
ꢀ
_
CO2
ꢀ0.706
ꢀ0.074

_
188
B. Karabulut, I. Yıldırım / Journal of Molecular Structure 1102 (2015) 186e189
Fig. 2. Variation of the magnetic field values of all lines due to rotation angle in three mutually perpendicular planes of the gamma irradiated dl-ABA single crystal.
crystal can be collected into two groups each having two sites as
the nitrogen atom, and one 14N nucleus. The interaction between
the unpaired electron of the radical and two identical protons,
namely H1a and H2a, gives 3 lines with a 1:2:1 intensity distribu-
tion. Hyperfine splitting of H1a and H2a are very close to each other,
so in some orientations the lines overlap. Each of the hyperfine
splitting of Ha protons is further separated to a 1:1:1 intensity
distribution due to 14N nucleus. The hyperfine interactions of the
shown in Fig. 2. The lines in the EPR spectrum were attributed to
:
two different NH2 paramagnetic centers. The source of this radical
is two equivalent protons, i.e. having the same bond lengths with
unpaired electron with the protons and the nitrogen nucleus in the
:
EPR spectra are almost equal to each other. For the NH2 radicals, the
intensity distribution in the EPR spectra was obtained as 1:3:4:3:1.
The hyperfine splitting values of 14N and protons appeared to be
equally for these two centers. It can be inferred from the EPR
spectra that the A and g values have small anisotropy. From Fig. 2, it
:
can be said that the COꢀ2 radical has a single line between 339 mT
and 341 mT and so has only one site. Compared to the non-oxidized
form of dl-ABA or dl-methionine [9], different radicals were ob-
tained as a result of irradiation.
The EPR spectra taken at the liquid nitrogen temperature have
not changed significantly compared to those at the room temper-
ature. Therefore, detailed comparison for the temperature range
has not been carried out. The results are shown in Table 1. Due to
the behavior of the spectrum, the complex is said to have two
groups and each group consists of two sites, as shown in Fig. 2.
Fig. 3 shows the recorded EPR spectrum of radiation induced dl-
ABA powder. The g values are 1.9958, 1.9941 and 1.9879 for the two
:
:
NH2 and one COꢀ2 paramagnetic centers, respectively. The hyper-
:
fine values for the group I and II of NH2 radicals are 2.13 and
1.80 mT, respectively. The protons and nitrogen have nearly the
same hyperfine values. The results are said to be compatible with
the single crystal values. The stick diagram under the figure rep-
resents the intensity distributions of the radicals. Solid lines and
:
dashed lines represent the NH2 radical centers I and II, respectively,
:
while the bold line represents COꢀ2 radical.
4. Conclusion
From the EPR spectra of gamma irradiated dl-ABA single crys-
tals; we conclude:
Fig. 3. Powder EPR spectrum of the gamma irradiated dl-ABA. Solid lines and dashed
:
lines represent the NH2 radical centers I and II, respectively, while the bold line rep-
:
resents COꢀ2 radical.
i. The site symmetry conforms the orthorhombic crystal system.

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B. Karabulut, I. Yıldırım / Journal of Molecular Structure 1102 (2015) 186e189
189
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groups has two distinct sites.
:
iii The EPR analysis shows that the NH2 radicals have rhombic
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ꢀ
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