Synthesis and spectral characterisation of dicyanopyrazine-related cyanoheterocycles

Article abstract of DOI:10.3184/174751913X13642346476213

Four dicyanopyrazine-related cyanoheterocycles have been synthesised and characterised; they show different absorption maxima values and molar absorptivity in absorption spectra. HOMO and LUMO energy levels have been obtained by electrochemical measurements and DMol3 calculation and show little difference in HOMO values but big differences in LUMO values. Their UV-Vis absorbance and fluorescence spectra have been investigated in chloroform and toluene and their aggregation decreases as the concentration decreases in toluene.

Full text of DOI:10.3184/174751913X13642346476213

268 RESEARCH PAPER
MAY, 268–272
JOURNAL OF CHEMICAL RESEARCH 2013
Synthesis and spectral characterisation of dicyanopyrazine-related
cyanoheterocycles
Cheol Jun Song, Chun Keun Jang, Wang Yao and Jae Yun Jaung*
Department of Organic and Nano Engineering, Hanyang University, 17, Haengdang-dong, Seongdong-gu, Seoul 133791, Korea
Four dicyanopyrazine-related cyanoheterocycles have been synthesised and characterised; they show different
absorption maxima values and molar absorptivity in absorption spectra. HOMO and LUMO energy levels have been
obtained by electrochemical measurements and DMol3 calculation and show little difference in HOMO values but big
differences in LUMO values. Their UV-Vis absorbance and fluorescence spectra have been investigated in chloroform
and toluene and their aggregation decreases as the concentration decreases in toluene.
Keywords: optical spectra, 2,3-naphthalene-dicarbonate, Wittig reaction, cyclic voltammetry, copper complex
with sodium sulfate. The solvent was removed under reduced pressure
and recrystallised with methanol. 2 was obtained as a white solid,
81% yield, m.p. 91 °C; 1H NMR (300 Mhz, CDCl3) δ 7.92 (d, 4H, J =
8.7 Hz) 7.53 (d, 4H, J = 9 Hz) 1.35 (s, 18H). Anal. Calcd for C22H26O2:
C, 81.95; H, 8.13; O, 9.92. Found: C, 81.73; H, 8.25; O. 10.02%.
6,7-Bis(4-tert-butylphenyl)naphthalene-2,3-dicarbonitrile (3a): tert-
BuOK (0.55 g, 4.9 mmol) in anhydrous N,N-dimethylformamide
(DMF) (3 mL) was added to a mixture of tetraethyl (4,5-dicyano-
1,2-phenylene)bis(methylene)diphosphonate7 (1 g, 2.3 mmol) and α-
diketone 2 (0.68 g, 2.1 mmol) in anhydrous DMF (10 mL) under an N2
atmosphere at 0–°C and the mixture refluxed overnight. When the
reaction was complete, the mixture was cooled and poured into ice
water. The mixture was extracted with ethyl acetate and dried with
sodium sulfate. The solvent was removed under reduced pressure and
crystallised with methanol. The crystal was chromatographed on silica
gel using EA:n-hexane = 1:5 as the eluent. 3a was obtained as a
white solid, 40% yield, m.p. 188 °C; IR (potassium bromide disc)
2233 cm−1 (C≡N); 1H NMR (300 MHz, CDCl3) δ 8.36 (s, 2H) 7.99 (s,
2H) 7.30 (d, 4H, J = 8.4 Hz) 7.13 (d, 4H, J = 8.7 Hz) 1.32 (s, 18H);
13C NMR (300 MHz, CDCl3) 151, 145, 137, 136, 133, 130, 129, 125,
116, 110, 35, 31. Anal. Calcd for C32H30N2: C, 86.84; H, 6.83; N, 6.33.
Found: C, 86.74; H, 6.90; N. 6.36%.
Rather than carbon atoms, pyrazine has two nitrogen atoms at
the 1 and 4 positions of the benzene ring.1–3 Pyrazine-oriented
colouring materials have more functional characteristics than
their benzene analogues. These characteristics include a strong
donor–acceptor chromophoric system, higher polarisability,
higher melting points, and higher solubility in polar solvents.
These dyes have a rather small molecular size but have a strong
intramolecular charge transfer system which induces a large
dipole moment in the excited state compared with the ground
state They also have a strong intramolecular charge transfer
system which induces a large dipole fluorescence in solution
and some have strong fluorescence even in the solid state. We
have been interested in how nitrile substitution affects the
chemical, electronic and physical properties of pyrazines.1–3
The present study is concerned with the design, synthesis and
characterisation of dicyanopyrazine-related heterocycles.4–6
Specifically, the solubility of a cyanoheterocyclic compound
has been improved by the introduction of a t-butylphenyl unit.
The spectral properties of these compounds are affected by
molecular aggregation and their functionalities are correlated
with their chemical structures.
2,3-Bis(4-tert-butylphenyl)quinoxaline-6,7-dicarbonitrile (3b): A
mixture of 4,5-diaminophthalonitrile8–9 (1 g, 6.3 mmol) and α-dike-
tone 2 (2 g, 6.3 mmol) in acetic acid was refluxed under an N2 atmo-
sphere. When the reaction was complete, the mixture was poured into
ice water, extracted with ethyl acetate, and dried by sodium sulfate.
The solvent was removed under reduced pressure and chromato-
graphed on silica gel using EA:n-hexane = 1:5 as the eluent. 3b was
obtained in 34% yield as a yellow solid, m.p. 190 °C; IR (potassium
Experimental
Flash chromatography was performed using a Merck-EM type 60
(230–400 mesh) silica gel (flash). Melting points were obtained with
a capillary melting point apparatus and were uncorrected. Elemental
analysis was obtained using a Flash EA-1112 analyser. 1H NMR and
13C NMR spectra were recorded on a VARIAN UnityInova 300 MHz
FT NMR spectrometer. MALDI-TOF mass-spectra were measured
using a SHIMADZU AXIMA Confidence instrument. UV-Vis
and fluorescence spectra were measured using Scinco S-4100 and
Shimadzu RF-5301PC spectrophotometers. Compounds 1 were
synthesised by literature methods.7–11
1
bromide) 2245 cm−1 (C≡N); H NMR (300 MHz, CDCl3) δ 8.59 (s,
2H) 7.55 (d, 4H, J = 9.0 Hz) 7.16 (d, 4H, J = 9.0 Hz) 1.33 (s, 18H);
13C NMR (300 MHz, CDCl3) 157, 154, 141, 137, 134, 130, 126, 115,
114, 35, 31. Anal. Calcd for C30H28N4: C, 81.05; H, 6.35; N, 12.60.
Found: C,81.56; H, 6.13; N. 12.31%.
6,7-Bis(4-tert-butylphenyl)quinoxaline-2,3-dicarbonitrile(3c):Sodium
hydride (0.7 g, 4.9 mmol) in anhydrous DMF (3 mL) was added to a
mixture of 2,3-bis(triphenylphosphonium methyl)-5,6-dicyanopyr-
azine dibromide10 (2 g, 2.38 mmol) in anhydrous DMF (5 mL) under
N2 at 0–5 °C and stirred for 1 h at room temperature. When the reac-
tion was complete, a solution of α-diketone 2 (0.95 g, 2.15 mmol) in
anhydrous DMF was added to the mixture and refluxed under N2.
After the reaction was complete, the mixture was cooled and poured
into 0.1N HCl solution. The mixture was filtered and washed with
distilled water. The residue was chromatographed on silica gel using
EA:n-hexane = 1:5 as the eluent. Compound 3c was obtained as a
yellow solid in 45% yield, m.p. 212 °C: IR (potassium bromide)
Synthesis of compounds 1 and 2 to give 3
Synthesis of benzoin derivative; general procedure
KCN (4.2 g, 0.065 mol) was added to a mixture of 4-tert-butylbenzal-
dehyde (50 g, 0.3 mol) in ethanol (40 ml) and H2O (25 ml) at room
temperature and refluxed for 5 h. The mixture was then cooled to
room temperature, filtered, and washed with water. The residue was
recrystallised with methanol. The benzoin derivative was obtained as
1
a white solid, 75% yield, m.p. 163 °C; H NMR (300 MHz, CDCl3)
δ 7.89 (d, 2H, J = 8.4 Hz) 7.34 (d, 2H, J = 8.4 Hz) 7.29 (d, 2H, J =
9.0 Hz) 7.28 (d, 2H, J = 9.0 Hz) 5.83(br, s, 1H) 1.56 (s, 1H) 1.31 (s,
9H) 1.29 (s, 9H). Anal. Calcd for C22H28O2: C, 81.44; H, 8.70; O, 9.86.
Found: C, 81.06; H, 8.98; O, 9.96%.
1,2-Bis(4-tert-butylphenyl)ethane-1,2-dione (2): A mixture of 1,2-
bis(4-tert-butylphenyl)-2-hydroxyethanone (37.3 g, 0.11 mol), copper
acetate monohydrate (45.9 g, 0.22 mol) and ammonium nitrate (4.6 g,
0.05 mol) in 80% acetic acid (AcOH) 500 mL was refluxed for 3hrs.
When the reaction was complete, the mixture was cooled to room
temperature, filtered and washed with distilled water, methanol, and
ethyl acetate. The organic layer of the filtrate was separated and dried
1
2265 cm−1 (C≡N); H NMR (300 MHz, CDCl3) δ 8.26 (s, 2H) 7.33
(d, 4H, J = 8.4 Hz) 7.16 (d, 4H, J = 8.4 Hz) 1.33 (s, 18H); 13C NMR
(300 MHz, CDCl3) 152, 150, 141, 136, 130, 129, 129, 126, 114, 35,
31. Anal. Calcd for C30H28N4: C, 81.05; H, 6.35; N, 12.60. Found: C,
81.88; H, 6.11; N. 12.01%.
6,7-Bis(4-tert-butylphenyl)pyrazino[2,3-b]pyrazine-2,3-dicarbonitrile
(3d): A mixture of 5,6-diaminopyrazine-2,3-dicarbonitrile11 (7.4 g,
46 mmol) and α-diketone 2 (10 g, 31 mmol) in a solution of AcOH
(30 mL), anhydrous THF (15 mL), and trifluoroacetic acid (6 mL)
was refluxed under N2. After 2 days, the mixture was cooled to room
temperature and poured into ice water. The mixture was extracted
* Correspondent. E-mail: jjy1004@hanyang.ac.kr

JOURNAL OF CHEMICAL RESEARCH 2013 269
with ethyl acetate and dried by sodium sulfate. The solvent was
removed under reduced pressure and chromatographed on silica gel
using benzene:n-hexane = 5:1 as the eluent to give 3d as an orange
solid, 25% yield, m.p. 255 °C. IR (potassium bromide) 2298 cm−1
H, 6.45; N, 12.59. Found: C, 80.37; H, 6.68; N, 12.95%. MALDI-TOF
mass-spectra: m/z 1780.67 (calcd 1780.30).
Synthesis of 4b (Cu complex); general procedure
1
A mixture of metal-free tetraquinoxalinoporphyrazine 0.3 g (0.17
mmole) and copper acetate monohydrate 0.14 g (0.68 mmole) in DMF
(5 mL) was refluxed for 6 h at 140 °C. When the reaction was com-
plete, the mixture was poured into distilled water, filtered, and washed
with methanol. The residue was chromatographed on silica gel using
chloroform:MeOH = 50:1 as the eluent to give 4b as a dark green
solid, yield 45%, m.p. > 300 °C. 1H NMR (300 MHz, CDCl3) δ 6.55–
6.62–7.79 (br, s, 40H) 1.06–1.46 (br, s, 72H); IR (potassium bromide,
cm−1): 1606, 1473 (C=C), 1348 (C-N), 1635 (C=N), 840, 721. Anal.
Calcd for C120H112CuN16: C, 78.25; H, 6.13; N, 12.17. Found: C, 78.46;
H, 6.21; N, 11.88%. MALDI-TOF mass-spectra: m/z 1841.62 (calcd
1841.83).
(C≡N); H NMR (300 MHz, CDCl3) δ 7.75 (d, 4H, J = 9 Hz) 7.45
(d, 4H, J = 9 Hz) 1.36 (s, 18H); 13C NMR (300 MHz, CDCl3) 162,
156, 144, 133, 132, 130, 126, 113, 35, 31. Anal. Calcd For C28H26N6:
C, 75.31; H, 5.87; N, 18.82. Found: C, 76.11; H, 5.54; N. 18.38%.
Synthesis of 4a, 4c and 4d
(4a): A mixture of compound 3a (0.4 g, 1.0 mmol), CuCl (85 mg,
0.5 mmole) and 1-chloronaphthalene (2 mL) was heated for 3 h at
200 °C. After cooling, methanol was poured in to the reaction mixture
and it was stirred for 30 mins. The mixture was filtered and washed
by methanol. The residue was chromatographed on silica gel using
chloroform:methanol = 30:1 as the eluent. 4a was obtained as a
green solid, yield 50%, m.p. > 300 °C, 1H NMR (300 MHz, CDCl3) δ
7.10–7.30 (br, s, 48H) 1.09–1.40 (br, s, 72H); IR (potassium bromide,
cm−1): 1608, 1475 (C=C), 1350 (C-N), 1635 (C=N), 840, 728. Anal.
Calcd For C128H120CuN8: C, 83.46; H, 6.83; N, 6.25. Found: C, 83.83;
H, 6.60; N, 6.11%; MALDI-TOF m/z 1833.65 (calcd 1833.92).
Results and discussion
The synthetic route is summarised in Scheme 2. Compounds 3
were synthesised by either condensation or the Wittig reaction
using the α-diketone with phthalonitrile or pyrazine.12–14
Compounds 1a and 1c in dry DMF reacted with 1,2-bis(4-tert-
butylphenyl)ethane-1,2-dione (2) in presence of 2.2 equiva-
lents of BuOK or NaH under reflux to give compounds 1b
and 1d in 40% and 45% yields, respectively. Reaction of
compounds 1b and 1d with compound 2 in acetic acid gave 3b
and 3d in moderate yields.12–14
Synthesised compounds 3a–d reacted with copper chloride
in o-dichlorobenzene or 1-chloronaphthalene to form a
tetramer.15–16 An alternative method was used for compound 4b
and the copper complex was not formed directly. Tetramerisa-
tion using magnesium turning and 1-butanol was performed
first. Then, metal-free phthalocyanine was produced using
p-toluenesulfonic acid in THF.13,17 By using copper(II) acetate
monohydrate in DMF, the metal centre of the tetramer
compound was substituted with copper.18
Synthesis of 4c and 4d
A mixture of compound 3c or 3d (1.12 mmol), CuCl (1.79 mmol) and
a catalytic amount of ammonium molybdate tetrahydrate in o-dichlo-
robenzene 5 mL was refluxed under N2. When the reaction was
complete, methanol was poured into the mixture and it was stirred
for 30 min. The mixture was filtered and washed with methanol.
The residue was chromatographed on silica gel using chloroform:
methanol = 20:1 as the eluent.
4c: Dark green solid, yield 45%, m.p. > 300 °C, 1H NMR (300 MHz,
CDCl3) δ 6.82–7.58 (br, s, 40H) 0.86–1.66 (br, s, 72H); IR (potassium
bromide, cm−1): 1606, 1475 (C=C), 1348 (C–N), 1637 (C=N), 840,
728. Anal. Calcd for C120H112CuN16: C, 78.25; H, 6.13; N, 12.17.
Found: C, 78.96; H, 6.04; N, 11.55%. MALDI-TOF mass-spectra: m/z
1842.17(calcd 1841.83).
4d: Dark green solid, yield 40%, m.p. > 300 °C, 1H NMR (300 MHz,
CDCl3) δ 6.89–7.43 (br, s, 32H) 0.91–1.73 (br, s, 72H); IR (potassium
bromide, cm−1): 1608, 1463 (C=C), 1363 (C-N), 1637 (C=N), 835,
730.Anal. Calcd for C112H104CuN24: C, 72.72; H, 5.67; N, 18.17 Found:
C, 72.51; H, 5.84; N, 18.21%. MALDI-TOF mass-spectra: m/z
1850.21 (calcd1849.73).
After synthesis, compound 3 was characterised by elemental
1
analysis, FT-IR, H NMR and 13C NMR spectroscopy. The
FT-IR peak at 2233–2298 cm−1 indicates a CN group.
1
The H NMR spectra showed the quinoxaline protons of
Synthesis of Mg complex; general procedure
compounds 3b and 3c at 8.59 and 8.26 ppm, while those of
compound 3a were observed at 8.36 and 7.99 ppm. The
downfield shifts of the quinoxaline proton of 3b and 3c were
attributed to the strong electron withdrawing effect of the
cyano-groups and the pyrazine moiety.
Compounds 4a–d were characterised by MALDI-TOF-MS
and 1H NMR spectroscopy. The 1H NMR spectra of the copper
complex compound showed peak differences depending on the
position of nitrogen, for the reason outlined above.
Optical properties are shown in Table 1. Compound 3 shows
absorption (λmax) and emission (Fmax) maxima at 299–450 nm
and 391–510 nm, respectively. The electronic character in the
naphthalene ring strongly reflects experimental results in
donor–acceptor systems. Due to aggregation, it is difficult to
compare the Q-bands of compounds 4a and 4b. However, the
nitrogen atoms result in a bathochromic shift in the B-band.
Also, for the cases of quinoxalinodicarbonitrile, like
compounds 3b and 3c, the position of the nitrogen affects the
wavelengths to give a difference of 23 nm. The nitrogen of
compound 3b is far from the cyano-group while the nitrogen
of compound 3c is closer.
A suspension of Mg turning (0.2 g, 9 mmol), one small crystal of
iodine and butanol (25 mL) was heated under reflux for 4 h. The reac-
tion mixture was then cooled to room temperature, and compound 3b
(0.8 g, 1.8 mmol) was added in one portion. The reaction mixture was
quickly reheated to reflux for 8 h. After approximately 10 min, the
reaction mixture became dark green. The mixture was cooled and
the solvent was removed in vacuo, yielding a crude dark green solid
product. The crude product was purified by chromatography using
chloroform:methanol = 30:1 as eluent to give the Mg complex as a
dark green solid, yield 48%, m.p. > 300 °C. Anal. Calcd for
C
120H112MgN16: C, 79.96; H, 6.26; N, 12.43. Found: C, 79.34; H, 6.28;
N, 12.03%; MALDI-TOF mass-spectra: m/z 1802.86 (calcd 1802.59).
Synthesis of metal-free tetraquinoxalinoporphyrazine; general
procedure
A mixture of Mg tetraquinoxalinoporphyrazine complex (0.6 g,
0.33 mmol) and p-toluenesulfonic acid (3.3 g, 16.5 mmol) in THF
(5 mL) was stirred for 1 h at room temperature. After this, the solvent
was removed under reduced pressure and the product crystallised with
methanol then chromatographed on silica gel, using chloroform:
MeOH = 30:1 as the eluent, to give the porphyrazine as a dark green
solid, yield 51%, m.p. > 300 °C. Anal. Calcd for C120H114N16: C, 80.96;
Scheme 1 Synthesis of compound 2.

270 JOURNAL OF CHEMICAL RESEARCH 2013
Scheme 2 Synthetic route of heterocycles 3.
Scheme 3 Synthetic route for compounds 4.
Table 1 Optical properties of compound 3 and 4
Cyclic voltammetry was used to find out how the introduced
nitrogen affected the HOMO and LUMO energy levels of
the molecules. CV data of compounds 3 are summarised in
Table 2. All measurements were carried out at room tempera-
ture with a conventional three-electrode configuration consist-
ing of platinum working electrode and an Ag/AgNO3 counter
electrode and reference electrode, respectively. The solvent in
all experiments was CH3CN and the supporting electrolyte was
0.1M tetra-n-butylammonium perchlorate (TBAP).
λmax/nm
Fmax/nm
Stoke Shift/nm
3a
3b
3c
3d
4a
4b
4c
4d
299
385
408
450
391
440
482
510
–
92
55
74
60
–
332/714/787
351/693/765
368/726
480/717
–
–
–
–
–
–
There is no big difference between the oxidation onset
values which is 2 0.15V. However, the difference of reduction
onset values from compound 3a to 3d goes up to 1.37V and
a In CHCl3 at room temperature.
b Fluorescence maximum excited at λmax value.

JOURNAL OF CHEMICAL RESEARCH 2013 271
Table 2 Electrochemical properties of compounds 3 in aceto-
nitrile containing 0.1M n-Bu4NClO4 at a scan rate of 100 mV s−1
peaks when diluted 10 times. No significant change is seen
with chloroform but with toluene, the broad Q-band peaks of
compounds 4a and 4b become sharper as the concentration
decreases. The Q-band spectra of the higher concentrations
show the characteristic patterns of aggregation species. At
lower concentrations this pattern is replaced by the spectral
envelope and the split Q-band. Comparison of the λmax peaks of
the Q-band in low concentration show that the introduction of
nitrogen atoms causes a hypsochromic shift. Aza-substitution
within the phthalocyanine macrocycle results in absorptions
at wavelengths lower than those in the unperturbed parent
systems.1–2 By the same principle, a hypsochromic shift occurs
when an aza-substitution takes place with the naphthalene
moiety of naphthalocyanine.18 With compound 4c in toluene,
the lowest λmax of the Q-band can be observed, but a different
result is observed when in chloroform. Comparison of 4c and
4d in chloroform shows that 4d has a lower λmax. However, 4c
has a lower λmax in toluene. It is possible that the compounds
are affected by solvatochromism.We are planning to investigate
the reasons for this phenomenon by comparing each HOMO
and LUMO energy value using electrochemical properties.
The X-ray crystal analysis of these compounds will be done
and these results connected with molecular stacking behaviour
will be reported in due course.
onset
onset
Compound
Eox
Ered
3a
3b
3c
3d
1.85a
2.03a
1.97a
2.14a
–1.59a
–0.81a
–0.62a
–0.22a
a Oxidation and reduction potentials versus ferrocene.
shows a cathodic shift. This can be explained by the introduced
nitrogen which makes the molecule more able to accept
electrons.
Compounds 3 were modelled using DMol3 at the GGA/
BLYP level in order to predict the relative HOMO and LUMO
energy levels. The levels could also be determined to some
extent experimentally using cyclic voltammetry. The relevant
data obtained from those analyses are contained in Table 3.
The HOMO energy levels of compounds 3 obtained from
the CV data are 6.35 0.15eV, for which the difference is small,
while the LUMO energy levels, which are 3.45 0.69 eV,
have a bigger difference. DMol3 calculation also shows the
tendency above as the HOMO values are 5.62 0.16 eV, while
the LUMO values are 3.33 0.61 eV.
The reason why this tendency appears for compounds 3 is
because there are no changes in the donor unit which decides
the HOMO energy level. However the nitrogen acts as an
acceptor unit, forming a stronger donor–acceptor system,
where stronger donor–acceptor systems lower the LUMO
energy level. As a result, the energy gap decreases which
increases the absorption maxima. The differences between the
experimentally determined values and the DMol3 calculations
are explained because DMol3 calculations were based on a
single molecule in vacuum and imperfection in the DMol3
model.
Conclusions
In this study, four different dicarbonatitrile compounds were
synthesised and characterised. Each compound shows differ-
ent absorption maxima values and molar absorptivity in the
absorption spectra. Also HOMO and LUMO energy levels
were obtained by electrochemical measurements and DMol3
calculation, which shows little difference in HOMO values
but big differences in LUMO values. This is caused by the
introduced nitrogen which is an electron withdrawing group,
lowering the LUMO energy values. The broad Q-bands of
compound 2a and 2b are shown to be due to the aggregation of
molecules, in which the aggregation degree varies with
different solvents. Especially in toluene, it can be seen that
aggregation decreases as the concentration decreases.
Figure 3 shows the effect of the concentration on the
absorption spectra of compound 4. A broad Q-band is observed
when compounds 4a and 4b are in either chloroform or toluene.
Compounds 4c and 4d show sharp peaks at the Q-band.
However, the spectrum of compound 4 shows a change in the
Table 3 Energy levels and band gap of the compounds 3 derived from experimental and computational data
CV
DMol3
CV
DMol3
CV
DMol3
Compound
EHOMO
EHOMO
ELUMO
ELUMO
EGAP
EGAP
3a
3b
3c
3d
–6.20
–6.38
–6.32
–6.49
–5.46
–2.76
–3.54
–3.73
–4.13
–2.72
3.44
2.84
2.59
2.36
2.74
–5.56
–5.62
–5.77
–3.30
–3.54
–3.94
2.26
2.08
1.83
Fig. 1 HOMO and LUMO structures of the compound 3.

272 JOURNAL OF CHEMICAL RESEARCH 2013
Fig. 2 Absorbance spectra of compound 4 (Cu complex).
6
7
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A.V. Ivanov, K.V. Kabanova, M.O. Breusova, I.V. Zhukov, L.G. Tomilova
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This research is supported by a collaborative research program
between industry, academia and research institutes through
The Korea Industrial Technology Association (KOITA), and is
funded by the Ministry of Education, Science and Technology
(MEST-2010).
8
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Received 26 December 2012; accepted 21 February 2013
Paper1201697 doi: 10.3184/174751913X13642346476213
Published online: 15 May 2013
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