Molecular structure, quantum mechanical calculation and radical scavenging activities of (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3- methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3- methoxyphenol compounds

Article abstract of DOI:10.1016/j.saa.2014.03.069

In this study, (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3- methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3- methoxyphenol compounds have been synthesized and characterized by using X-ray crystallographic method, FT-IR an

Full text of DOI:10.1016/j.saa.2014.03.069

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Molecular structure, quantum mechanical calculation and radical
scavenging activities of (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)
methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-
[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds
b
c
d
e
Can Alaßsalvar a, , Mustafa Serkan Soylu , Aytaç Güder , Çig˘dem Albayrak , Gökhan Apaydın ,
⇑
Nefise Dilek f
a Giresun University, Technical Science Vocational High School, Department of Electric and Energy, 28100 Giresun, Turkey
b Giresun University, Faculty of Art and Science, Department of Physics, 28100 Giresun, Turkey
c Giresun University, Vocational High School of Health Services, Department of Medical Services and Techniques, 28100 Giresun, Turkey
d Sinop University, Faculty of Arts and Sciences, Department of Chemistry, 57000 Sinop, Turkey
e Karadeniz Technical University, Faculty of Arts and Sciences, Department of Physics, 61080 Trabzon, Turkey
f Aksaray University, Faculty of Arts and Sciences, Department of Physics, 68100 Aksaray, Turkey
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
The title compounds were
characterized using experimental and
theoretical methods.
Antioxidant properties were
determined by using different
methods.
Observed and calculated values were
compared.
(a) Compound I (b) Compound II
a r t i c l e i n f o
a b s t r a c t
Article history:
In
this
study,
(E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxyphenol
and
Received 30 January 2014
Received in revised form 3 March 2014
Accepted 21 March 2014
Available online 13 April 2014
(E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds have been syn-
thesized and characterized by using X-ray crystallographic method, FT-IR and Density functional method.
The molecular geometry, vibrational frequencies of the title compounds in the ground state have been
calculated by using B3LYP with the 6-31G(d,p) basis set. The tautomeric form of the compounds has been
demonstrated by using single crystal X-ray method, FT-IR spectrometer and DFT method. In addition,
HOMO–LUMO energy gap, molecular electrostatic potential map and NBO analysis of the compounds
are performed at B3LYP/6-31G(d,p) level. It may be remarked that the free radical scavenging activities
of the title compounds were assessed using DPPHꢀ, DMPDꢀ+, and ABTSꢀ+ assays. The obtained results show
Keywords:
Schiff base
Crystal structure
DFT method
Radical scavenging activities
that especially compound 2 has effective DPPHꢀ (SC50 1.52 0.14 g/mL), DMPDꢀ+ (SC50 1.22 0.21
l lg/
mL), and ABTSꢀ+ (SC50 3.32 0.17
and trolox).
l
g/mL) scavenging activities compared with standards (BHA, rutin,
Ó 2014 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +90 0454 310 14 00; fax: +90 0454 310 14 77.
E-mail address: canalasalvar@hotmail.com (C. Alaßsalvar).
http://dx.doi.org/10.1016/j.saa.2014.03.069
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

358
C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
compound 1 and 2 were solved by Direct methods [14] using
Introduction
SHELXS-97 and refined with SHELXL-97 [14]. The molecular figures
were prepared by the help of Olex 2 program packages.
All non-hydrogen atoms were refined anisotropically. The
refinement was carried out using the full matrix least squares
method on the positional and anisotropic temperature parameters
of non-hydrogen atoms corresponding to 194 crystallographic
parameters for 1 and 193 parameters for 2. H1A atom was located
in the difference maps, and their positions were refined using
freely and Hydrogen atoms bonding to C atoms were refined using
a riding model with fixed isotropic U values for compound 1. All H
atoms were refined using a riding model with fixed isotropic U val-
ues for compound 2.
Schiff bases are used as starting materials in the synthesis of
important drugs such as antibiotics, antiallergics, antifungals and
antitumors because of their biological activities [1,2]. On the indus-
trial scale, they have a wide range of applications, such as in dyes
and in pigments [3].
o-Hydroxy Schiff bases are of interest because they have long
been known to show photochromism and thermochromism in
the solid state, which can involve reversible proton transfer from
an oxygen atom to the neighboring nitrogen atom. Based on
thermochromic and photochromic Schiff bases, it was proposed
that the molecules exhibiting thermochromism are planar while
the molecules exhibiting photochromism are non-planar [4–6].
Photochromic compounds are used as optical switches and optical
memories, variable electrical current, ion transport through
membranes [7].
Details of the data collection conditions and the parameters of
the refinement process are given in Table 1.
Determination of free radical scavenging activities
In general, Schiff bases have two possible tautomeric forms, the
phenol-imine (OH) and the keto-amine (NH) forms. Depending on
the tautomers, two types of intramolecular hydrogen bonds are
observed in Schiff bases: OAHꢁ ꢁ ꢁN in phenol-imine [8,9] and
NAHꢁ ꢁ ꢁO in keto-amine [10,11] tautomers. Another structure of
Schiff base compounds is their zwitterionic form and this is rarely
seen for hydroxy derivatives. The characteristic property of this
form is the presence of ionic N+AHꢁ ꢁ ꢁOꢂ hydrogen bond [12].
In this work, we first synthesized and determined structure
of the molecular of (E)-4,6-dibromo-2-[(3,5-dimethylphe-
nylimino)methyl]-3-methoxyphenol (compound 1) and (E)-4,6-
dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol
(compound 2) compounds by using X-ray technique, FT-IR spectra
and theoretical methods. Properties of investigated molecules
were compared with each other. In addition, the free radical
scavenging activities of the title compounds were evaluated by
using a 2,2-diphenyl-1-picryl-hydrazyl (DPPHꢀ), N,N-dimethyl-p-
phenylenediamine (DMPDꢀ+), and 2,20-azino-bis(3-ethylbenzthiaz-
oline-6-sulfonic acid) (ABTSꢀ+) scavenging activity assays.
DPPHꢀ radical scavenging activity assay
The DPPH radical scavenging activities of compounds and stan-
dards were evaluated according to previously method described by
Blois (1958) [15] with minor modifications. Serially diluted sam-
ples (200 lL) at the different concentrations (1–10 lg/mL) was
added to DPPHꢀ solution (2.8 mL, 0.2 mM) in ethanol. The mixtures
were shook forcefully and allowed to stand at room temperature
during 30 min. Then, absorbance was recorded at 517 nm in a
spectrophotometer. The results were expressed as SC50 by linear
regression analysis.
DMPDꢀ+ radical scavenging activity assay
DMPD radical scavenging activity assays were performed
according to method of Fogliano et al. (1999) [16]. DMPDꢀ+ solu-
tions (100 mM) was prepared by using a deionized water. This
Table 1
Crystal data, data collection and refinement detail of the title compounds.
Experimental details
Compound 1
16H15Br2NO2
413.11
296(2)
orthorhombic
Pbca
16.987(13)
b = 6.884(6)
c = 27.533
90.00
90.00
90.00
3220(3)
8
1.704
Compound 2
Materials and measurements
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
C
C16H15Br2NO2
413.11
296(2)
orthorhombic
Pnna
8.6731(3)
15.3199(5)
24.1525(7)
90.00
90.00
90.00
3209.17(18)
8
1.710
FT-IR spectra of compounds were recorded on a Perkin–Elmer
spectrometer using KBr pellets. The melting points were deter-
mined by using StuartMP30 apparatus.
b/Å
c/Å
Synthesis
a
/°
b/°
/°
The compound (E)-4,6-dibromo-2-[(3,5-dimethylphenylimi-
no)methyl]-3-methoxyphenol (1) was prepared by refluxing
a mixture of a solution containing 3,5-dibromo-2-hydroxy-6-
methoxybenzaldehyde (0.5 g 1.65 l mmol) in 20 ml ethanol and a
solution containing 3,5-dimethylaniline (0.20 g, 1.651 mmol) in
20 ml ethanol. The mixture was stirred for 2 h under reflux. The
crystals of compound 1 suitable for X-ray analysis were obtained
by slow evaporation from CH3CN (yield = 83%, m.p. = 456–459 K).
The same procedure was followed in synthesizing compound 2.
The crystals of compound 2 were obtained from EtOH (yield = 87%,
m.p. = 358–360 K).
c
Volume/Å3
Z
qcalc mg/mm3
l
m mꢂ1
5.04
1632
5.055
1632.0
F(000)
Crystal size/mm3
0.91 ꢃ 0.43 ꢃ 0.25
0.868 ꢃ 0.718 ꢃ 0.200
3.38–57.02°
ꢂ11 6 h 6 8,
ꢂ20 6 k 6 20,
ꢂ32 6 l 6 32
31510
4055 [Rint = 0.0812,
Rsigma = 0.0506]
4055/0/194
1.191
2h range for data collection 2.96–52°
Index ranges
ꢂ20 6 h 6 20,
ꢂ8 6 k 6 8,
ꢂ33 6 l 6 33
29616
Reflections collected
Independent reflections
3161 [Rint = 0.0900,
Rsigma = 0.0535]
3161/0/194
1.181
Data/restraints/parameters
Crystal data for the compounds
Goodness-of-fit on F2
Final R indexes [I P 2
r
(I)]
R1 = 0.0705,
wR2 = 0.2044
R1 = 0.1266,
wR2 = 0.2429
R1 = 0.0770,
wR2 = 0.1353
R1 = 0.1217,
wR2 = 0.1472
1.32/ꢂ0.44
X-ray diffraction data were recorded on Bruker SMART BREEZE
CCD diffractometer (purchased under Grant No. 2010K120480 of
the State of Planning Organization). Absorption correction applied
to collected data by multi scan, SADAPS V2012/1 software [13]. The
Final R indexes [all data]
Largest diff. peak/hole/e Åꢂ3 0.96/ꢂ0.55

C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
359
solution (1 mL) was added to acetate buffer (100 mL, 0.1 M, pH
Results and discussions
5.25), and the colored radical cation (DMPDꢀ+) was obtained by
adding 0.2 mL of a of ferric chloride solution (0.05 M) (the final
Crystallographic studies
concentration was 0.01 mM). This solution (225 lL) was trans-
ferred directly to the tube and absorbance values were measured
at 505 nm (absorbance of control tube). Different concentrations
Olex-2 [23] view of compounds is shown in Fig. 1(a and b) and
crystal data, data collection and refinement details of compounds
are given in Table 1. While molecule 1 is nearly planar and dihedral
angles between the two rings (C2AC7 and C8AC13) in the mole-
cule is 8.353 (6)° molecule 2 is not planar and dihedral angles
between the two rings (C2AC7 and C8AC13) is 42.5389 (18)°. It
is also known that Schiff bases may exhibit photochromism
depending on the planarity or non-planarity, respectively [24].
Therefore, it can be said that compound 1 may exhibit thermochro-
mism and compound 2 may exhibit photochromism. Compound 1
is stabilized by C16AH16ꢁꢁꢁOi1 (Fig. 2) and C16AH16CꢁꢁꢁOi1 (Fig. 3)
weak intermolecular hydrogen bond interactions (Table 2), as well
as N+AHꢁ ꢁ ꢁOꢂ strong intramolecular interaction (Table 2). On the
other hand, molecule 2 is stabilized by OAHꢁ ꢁ ꢁN intramolecular
interaction (Table 2). Bond parameters of the compounds were
given in Table 3. The C7AO1 (1.296 (8) Å) and C1AN1 (1.319
(7) Å) bond distances are the most important indicators for deter-
mination of the tautomeric form of compounds. While the C7AO1
bond is of a double bond for the keto-amine tautomer, this bond
displays single bond character in phenol-imine tautomer. In addi-
tion, the C1AN1 bond is also a double bond in phenol-imine tauto-
mer and of single bond length in keto-amine tautomer [25,26].
However, these bond lengths have intermediate values between
single and double CAO (1.362 and 1.222 Å, respectively) and
CAN (1.339 and 1.279 Å, respectively) bond distance [27]. Besides,
zwitterionic forms of Schiff bases have an intramolecular ionic
hydrogen bond (N+AHꢁ ꢁ ꢁOꢂ), and their N+AH bond lengths are
(1–10
l
g/mL) of the title compounds or standards (15
lL) and
DMPDꢀ+ (210
lL) were added to all tubes. After all tubes were
stirred and left to stand for 10 min, a decrease in absorbance was
measured at 505 nm in a spectrophotometer (absorbance of sam-
ples or standards). The buffer solution was used as a blank sample.
The results were expressed as SC50 by linear regression analysis
using four different concentrations in triplicate and represent
mean of the data.
ABTSꢀ+ radical scavenging activity assay
ABTS radical cation scavenging activities of the title compounds
and standards was carried out by using a chemical method
described by Re et al. [17] with slight modification. For this exper-
iment, ABTSꢀ+ radical cation was generated by a reaction of
2.0 mmol/L ABTS and 2.45 mmol/L potassium persulfate. The reac-
tion mixture was allowed to stand in the dark for 16 h at room
temperature and used within 2 days. Prior to assay, the ABTSꢀ+
solution was diluted with a PBS (0.1 M pH 7.4) to give an absor-
bance of 0.750 0.020 at 734 nm in a 1 cm cuvette and equili-
brated to 30 °C, the temperature at which all the assays were
performed. Then, the diluted ABTSꢀ+ solution (1.0 mL) was added
to the title compounds or standards (3.0 mL) solution in PBS at dif-
ferent concentrations (1–10 lg/mL). The percentage inhibition of
ABTSꢀ+ was calculated for each concentration relative to a blank
absorbance. The results were expressed as SC50 by linear regression
analysis using four different concentrations in triplicate and repre-
sent mean of the data.
Statistical analysis
Experimental results were given as mean S.D. of the three par-
allel measurements. Analysis of variance was performed by ANOVA
procedures. Significant differences between means were deter-
mined by Duncan’s Multiple Range tests. P values of <0.05 were
regarded as significant and P values of <0.01 very significant. Both
operations were done with SPSS (version 15.0.0; SPSS Inc., Chicago,
IL, USA) for windows.
Computational details
All calculations were carried out with the Gauss-View molecu-
lar visualization program and Gaussian03 [18,19] program pack-
age. Starting geometries of compounds were taken from X-ray
refinement data. The molecular structures of the compounds in
the ground state are optimized by using B3LYP/6-31G(d,p) level.
In DFT calculation, hybrid functional are also used, the Becke’s
three parameter functional (B3) [20] which defines the exchange
functional as the linear combination of Hartre–Fock, local and gra-
dient – corrected exchange terms. The B3 hybrid functional was
used in combination with the correlation functional of Lee, Yang
and Parr [21]. For the compound, vibrational frequencies were cal-
culated by using B3LYP/6-31G(d,p) level. The Calculated frequen-
cies were scaled by 0.9627 [22]. To investigate the reactive sites
of the structure the molecular electrostatic potential was evaluated
using the B3LYP/6-31G(d,p) method. In addition, the distributions
and energy levels of HOMO–LUMO orbitals and NBO analysis were
computed at the B3LYP/6-31G(d,p) level for the compounds.
Fig. 1. (a) Olex 2 diagram of compound 1 and (b) Olex 2 diagram of compound 2.

360
C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
Fig. 2. C16AH16AꢁꢁꢁO1# hydrogen bond interaction of compound 1 (#:1/2 + x, y, 1/2ꢂz).
longer than those observed in neutral NAH bond lengths (0.87 Å)
[28,29]. These bond lengths are compatible with similar zwitter-
ionic Schiff base molecules [30,31]. Considering all these, it can
be said that the structure of the compound 1 has zwitterionic form.
According to Table 3, C7AO1 and C1@N1 bond lengths of com-
pound 2 were given as [1.336 (6) Å] and [1.285 (6) Å], respectively.
When considering these values, C7AO1 has single bond and
C1@N1 has double bond character. Hence, tautomeric form of the
compound 2 is phenol-imine form. These bond distances are com-
patible with similar Schiff base molecules [32–38].
these bond lengths are calculated as 1.258, 1326 Å and 1.330,
1.289 Å for B3LYP method, respectively. CABr bond lengths are
observed between 1.880 and 1.895 Å for the molecules and these
bonds are computed at the interval 1.900–1.906 Å for the B3LYP.
The compounds were optimized for both tautomeric forms
using B3LYP/6-31G(d,p). According to these results, OAH form
for compound 1 is more stable than NAH form and energy different
between two states is 1.687 kcal/mol. This result is not compatible
with the results of X-ray. Because of this inconsistency, it can be
C16AH16ꢁ ꢁ ꢁOi1 and C16AH16Cꢁ ꢁ ꢁOi1 intermolecular interactions
given in Table 2. It is well known that the experimental results
belong to solid phase of molecules while the theoretical results
are related to the gas phase of the isolated molecules. On the other
hand, OAH form for compound 2 is more stable than NAH form
and energy different between two states is 2.064 kcal/mol and this
supports the results of X-ray.
Optimized geometry
Optimized geometry parameters of the compounds were given
together with experimental values in Table 3. As seen from Table 4,
there are deviations between the calculated and experimental val-
ues for C7AO1 and C1AN1 bond distances in compound 1 but
there is a good agreement between the calculated and experimen-
tal values for the compound 2. These bonds are the bonds most
affected by charge transfer. Therefore, these deviations are normal.
The C7AO1 and C1AN1 bond lengths of compound 1 and 2 are
found to be 1.319 (7) 1.296 (8) Å and 1.336 (6), 1.285 (8) Å and
FT-IR spectra analyses
FT-IR spectra of the compounds were shown in Fig. 4(a and b).
Vibrational frequencies of the compounds were calculated by using

C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
361
Fig. 3. C16AH16CꢁꢁꢁO1$ hydrogen bond interaction of compound 1 ($:1ꢂx, ꢂ1/2 + y, 1/2ꢂz).
Table 2
Hydrogen-bond geometry (Å, °) of the compounds.
Compound 1
DAHꢁꢁꢁA
DAH (Å)
0.96
0.96
HꢁꢁꢁA (Å)
2.38
2.51
DꢁꢁꢁA (Å)
3.336 (7)
3.394 (9)
2.522 (8)
DAHꢁꢁꢁA (°)
176
152
Table 3
C16AH16Aꢁ ꢁ ꢁOi1
C16AH16Cꢁ ꢁ ꢁOii1
N1AH1AꢁꢁꢁO1
Selected molecular structure parameters of the title compounds.
1.13 (14)
1.39 (14)
174 (10)
Compound 1
Bond length
C1AC2
C1AN1
C7AO1
X-ray (Å)
1.428 (9)
1.296 (8)
1.319 (7)
1.419 (9)
1.517 (11)
1.508 (10)
1.431 (8)
1.882 (7)
1.887 (6)
1.13 (14)
1.39 (14)
(Å)
Compound 2
DAHꢁꢁꢁA
1.403
1.326
1.258
1.408
1.510
1.510
1.436
1.906
1.900
DAH (Å)
0.82
HꢁꢁꢁA (Å)
DꢁꢁꢁA (Å)
DAHꢁꢁꢁA (°)
O1AH1AꢁꢁꢁN1
1.82
2.555 (6)
148
C8AN1
(i) 1/2 + x, y, 1/2ꢂz, (ii) 1ꢂx, ꢂ1/2 + y, 1/2ꢂz.
C12AC15
C10AC14
O2AC16
C4ABr2
C6ABr1
N1AH1A
O1AH1A
DFT with 6-31G(d,p) basis set and were listed in Table 4, with their
experimental values.
The OACH3 stretching vibration bands of methoxy group for
compound 1 and 2 are observed at 1047 and 1053 cmꢂ1, and these
values are found at 1058 and 1061 cmꢂ1 in our B3LYP/6-31G(d,p)
calculations, respectively. The obtained results are in a good agree-
ment with literature [39–41].
Bond and dihedral angels
C2AC1AN1
C1AN1AC8
N1AC8AC13
N1AC8AC9
C1AC2AC3
C2AC7AO1
C2AC1AN1AC8
C1AC2AC3AO2
C1AC2AC7AO1
C1AN1AC8AC13
X-ray (°)
121.8 (6)
124.4 (6)
123.8 (7)
116.1 (7)
119.7 (6)
121.4 (6)
180.0 (5)
ꢂ2.0 (8)
(°)
122.30
128.25
123
116.9
119
According to Fig. 4a, the NAH vibration mode was observed as
3414 cmꢂ1 and this mode were calculated as 2911 cmꢂ1. The
stretching frequency (NAH) observed at 3414 cmꢂ1 in compound
1 shows the presence of NAHꢁ ꢁ ꢁO intramolecular hydrogen bond
given in Table 2. In the literature, some NAH modes observed for
the zwitterionic Schiff bases molecules are 3191–3371 cmꢂ1 [42],
3420 cmꢂ1 [43]. The CAN, C@C and CAO vibration modes were
observed as 1615, 1586 and 1311 cmꢂ1, while these modes are
computed as 1628, 1583 and 1606 cmꢂ1 for B3LYP method. The
NAH, CAO and CAN stretching values in the structure are compat-
ible with similar zwitterionic Schiff base molecules [42,43].
According to Fig. 4b, the OAH vibration mode was observed as
3414 cmꢂ1 and this mode were computed as 2858 cmꢂ1. The
stretching frequency (OAH) observed at 3414 cmꢂ1 in compound
1 shows the presence of OAHꢁ ꢁ ꢁN intramolecular hydrogen bond
given in Table 2. In the literature, some OAH modes observed for
the phenol imine Schiff bases molecules are 3414 cmꢂ1 [44],
3401 cmꢂ1 [5]. The CAN, C@C and CAO vibration modes were
found as 1612, 1590 and 1337 cmꢂ1 respectively and these modes
were calculated as 1618, 1579 and 1421 cmꢂ1 for B3LYP. The OAH,
CAO and CAN stretching values in the structure are compatible
with those of similar phenol imine Schiff base molecules [44,45].
Consequently, FT-IR results showed that compound 1 is zwitter-
ionic form and compound 2 is phenol imine form and this support
X-ray results.
122
ꢂ179.51
0.39
ꢂ3.1 (8)
ꢂ10.7 (10)
ꢂ1.77
ꢂ8.54
(Å)
Compound 2
C1AC2
C1AN1
C7AO1
C8AN1
C13AC15
C9AC14
O2AC16
C4ABr2
C6ABr1
X-ray (Å)
1.451 (7)
1.285 (6)
1.336 (6)
1.417 (6)
1.508 (8)
1.504 (8)
1.430 (7)
1.895 (5)
1.880 (6)
1.455
1.289
1.330
1.418
1.512
1.508
1.436
1.905
1.900
Bond and dihedral angels
C2AC1AN1
C1AN1AC8
N1AC8AC13
N1AC8AC9
C1AC2AC3
C2AC7AO1
C2AC3AO2
C2AC1AN1AC8
C1AC2AC3AO2
C1AC2AC7AO1
C2AC1AN1AC8
X-ray (°)
120.6 (5)
121.9 (4)
123.1 (5)
115.5 (5)
119.0 (4)
120.7 (5)
118.6 (4)
178.2 (4)
0.0 (7)
(°)
121.43
121.35
121.54
117
119.67
121.67
118.46
ꢂ179.56
0.68
2.4 (7)
178.2 (4)
1.41
ꢂ179.56

362
C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
Table 4
generated from the molecule electrons and nuclei and a positive
test charge(a proton) located at r. For the studied system, the
V(r) values are calculated by the equation [46],
Some experimental and calculated vibrational frequencies (cmꢂ1) and assignments of
the compounds on B3LYP/6-31G(d,p).
Assignments
Experimental (cmꢂ1
)
B3LYP/6-31G(d,p) (cmꢂ1
)
Z
t
t
t
t
t
t
t
t
(NAH)
3414
3013
2920
2852
1615
1586
1311
1047
2911
3057
2999
2918
1628
1583
1606
1058
ZA
jRA ꢂ rj
q
ðr0Þ
X
VðrÞ ¼
ꢂ
aromatik(CAH)s
(CAH3)as
(CAH3)s
(CAN)
(C@C)
(C@O)
jr0 ꢂ rjd3r0
where ZA is the charge of nucleus A located at RA,
q
ðr0Þ is the elec-
tronic density function of the molecule, and r0 is the dummy inte-
gration variable. To predict the reactive sites of electrophilic and
nucleophilic attack for the investigated compounds, the MEP at
the B3LYP/6-31G(d,p) optimized geometry was calculated and
shown in Fig. 5(a and b).
(OACH3)
Compound 2
Assignments
t
t
t
Experimental (cmꢂ1
)
B3LYP/6-31G(d,p) (cmꢂ1
)
(OAH)s
aromatik(CAH)s
(CAH3)as
3420
2998
2923
2852
1612
1590
1337
1053
2858
3083
3014
2917
1618
1579
1421
1061
As seen from Fig. 5a, the most negative region is located on the
O1 atom which can be considered as possible site for electrophilic
attack and its V(r) value is ꢂ0.054 a.u. According to Table 2, O1
atom is acceptor atom at inter and intramolecular interactions in
the molecule. Therefore, MEP map supports existence of inter
and intramolecular interactions given in Table 2 for the compound
1. However, the maximum positive region is located on the H atom
bonded C13 and V(r) value is 0.034 a.u. and this indicates a possible
site for nucleophilic attack.
As seen from Fig. 5b, the most negative region are located on the
O1 atom which can be considered as possible site for electrophilic
attack and its V(r) value is ꢂ0.043 a.u. MEP map supports existence
of intramolecular interaction given in Table 2 for the compound 2.
However, the maximum positive region is located on the methyl
t(CAH3)s
t
t
t
t
(C@N)
(C@C)
(C@O)
(OACH3)
Molecular electrostatic potential analysis
The molecular electrostatic potential (MEP), V(r) at a given
point r(x, y, z) in the vicinity of a molecule, is defined in terms of
the interaction energy between an electrical charge which is
Fig. 4. (a) Experimental and calculated FT-IR spectrum of compound 1 and (b) experimental and calculated FT-IR spectrum of compound 2.

C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
363
Fig. 4 (continued)
l2
groups bonded O2 atom and V(r) value is 0.024 a.u. and this
indicates a possible site for nucleophilic attack.
w ¼
ðElectrophilicity indexÞ
2g
where I and A is ionization potential and electron affinity, and is
I = ꢂEHOMO and A = ꢂELUMO, respectively [49–52].
HOMO–LUMO analysis
HOMO–LUMO orbitals of the compounds were calculated by
using B3LYP/6-31G(d,p) method in gas phase. HOMO–LUMO
energy gap, electronegativity, electrophilicity index and chemical
hardness and softness values of the structures were listed in
Table 5. 3D plots of highest occupied molecular orbitals (HOMO),
lowest unoccupied molecular orbitals (LUMO) for the molecule
were shown in Fig. 6(a and b). HOMO–LUMO energy gaps of the
molecules are calculated as 3.11 eV and 4.08 eV respectively.
According to Table 5, compound 2 has a good stability and a high
chemical hardness.
The most important orbitals in a molecule are the frontier
molecular orbitals, called HOMO and LUMO. These orbitals deter-
mine the way the molecule interacts with other species. The fron-
tier orbital gap helps characterize the chemical reactivity and
kinetic stability of the molecule. A molecule with a small frontier
orbital gap is more polarizable and is generally associated with a
high chemical reactivity, low kinetic stability and is also termed
as soft molecule [47,48]. The energy gap between HOMO and
LUMO is a critical parameter to determine molecular electrical
transport properties. By using HOMO and LUMO energy values
for a molecule, chemical hardness–softness, electronegativity and
electrophilicity index can be calculated as follows:
NBO analysis
I þ A
In order to investigate the intramolecular interactions, the
bond-antibond stabilization energies within the title compounds
are calculated in the NBO formalism by using second-order pertur-
bation theory. The results of second-order perturbation theory
analysis of the Fock Matrix at B3LYP/6-31G(d,p) level of theory
are presented in Table 5. For each donor NBO(i) and acceptor
NBO(j), the stabilization energy E(2) associated with electron delo-
calization between donor and acceptor is estimated as [53,54]
l
g
ꢄ ꢂ
v
¼ ꢂ
ðElectronegativityÞ
2
I ꢂ A
ꢄ
ðChemical hardnessÞ
ðSoftnessÞ
2
1
f ¼
2
g

364
C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
Fig. 5. (a) Molecular electrostatic potential map of compound 1 and (b) molecular electrostatic potential map of compound 2.
Therefore, we can say that these results are compatible with the
Table 5
obtained intra- molecular interactions from X-ray results of com-
pound 1. Similarly, NBO analysis is also performed for compound
II. But, in NBO analysis of compound II could not calculated
between nðN19Þ ! rꢅðO18 ꢂ H26Þ interactions because as seen
in Table 2, O1AH1Aꢁ ꢁ ꢁN1 intramolecular interaction of compound
II is very week.
The calculated HOMO, LUMO energy values, HOMO–LUMO energy gap, electrophi-
licity index, electronegativity, chemical hardness and softness of the molecules.
Parameters (eV)
Compound 1
Compound 2
HOMO
LUMO
ꢂ5.44
ꢂ2.32
3.11
3.88
1.56
6.04
1.96
4.08
4
2.04
0.245
3.92
EHOMO ꢂ ELUMO
v
g
(Electronegativity)
(Hardness)
Radical scavenging activity
f (Softness)
0.320
4.82
w
(Electrophilicity index)
Antioxidant properties, especially radical-scavenging activities,
are very important due to the deleterious role of free radicals in
foods and in biological systems. Excessive formation of free radi-
cals accelerates the oxidation of lipids in foods and decreases food
quality and consumer acceptance [55]. The involvement of free
radicals, especially their increased production, appears to be a fea-
ture of most, if not all, human diseases, including cardiovascular
disease and cancer [56]. In DPPH radical form absorbs at 517 nm.
When a hydrogen atom or electron was transferred to the odd elec-
tron in DPPHꢀ, the absorbance at 517 nm decreased proportionally
to the increases of nonradical forms of DPPH [57,58]. As a conse-
quence, DPPHꢀ is usually used as a substrate to evaluate the antiox-
idative activity of antioxidants [59]. In the manner of Table 7, the
2
ðFijÞ
Eð2Þ ¼ ꢂq
ð1Þ
, ej are diagonal elements
i ej
ꢂ
ei
where qi is the donor orbital occupancy, ei
(orbital energies) and Fij is the off-diagonal NBO Fock matrix
element.
In NBO analysis, the strongest stabilization in compound1 is
found in N31AH36ꢁ ꢁ ꢁO32. This value is calculated as 33.76 kcal/
mol in gas phase of the compound 1 and its calculated values are
given in Table 6. This interactions in NBO analysis is appeared from
lone pair electrons of O32 atom to antibonding sigma electrons of
N31AH36 bonding, that is, it is the form nðO32Þ ! rꢅðN31 ꢂ H36Þ.
SC50 values (lg/mL) of the title compounds and standards on the
Fig. 6. (a) 3D plots of the HOMO–LUMO of the compound 1 and (b) 3D plots of the HOMO–LUMO of the compound 2.

C. Alaßsalvar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 130 (2014) 357–366
365
Table 6
Second-order perturbation theory analysis of the Fock matrix in NBO basis, calculated at B3LYP/6-31G(d,p) level.
ED (e) (i)
Donor (i)
ED (e) (j)
Acceptor (j)
E(2) kcal mol
E(j) ꢂ E(i) a.u.
1.06
0.71
F(i,j) a.u.
1.80023
1.85489
n(O32)
n(O32)
0.08383
0.08383
rꢅ (N31AH36)
rꢅ (N31AH36)
6.75
27.01
0.076
0.125
Table 7
frequencies values of the title compounds were calculated by using
B3LYP method with 6-31G(d,p) basis set. Calculated values were
founded to be compatible with experimental data. Electrophilic
and nucleophilic attack sites of the title molecules were deter-
mined by using The MEP map. We have been calculated the param-
eters such as HOMO–LUMO energy gap, electronegativity,
electrophilicity index and chemical hardness and softness values
by means of HOMO–LUMO energy values for the title compounds.
Compound 2 has a good stability and a high chemical hardness
than compound 1. In addition, synthesized compounds have elec-
tron donating groups on the phenyl ring exhibiting good activity
with maximum scavenging free radical. Compound 2 has electron
donating groups at ortho and para positions of aromatic ring to
which a nitrogen atom is bonded. Methyl groups located at ortho
and para positions of aromatic ring have an important role in the
stabilization of radical occuring in phenol ring. For Compound 1,
the methyl groups are not effective in stabilizing phenol radical.
Therefore, the effect of Compound 2 is greater than Compound 1.
For this reason, this compound may be used in molecular design
of free-radical-scavenging drugs in pharmaceutical and medical
industry.
Comparison of the DPPHꢀ, ABTSꢀ+, and DMPDꢀ+ radical scavenging activities of title
compound and standards. BHA (butylated hydroxyanisole), RUT: rutin, TRO: trolox.
SC50
g/mL)
Compound 1 Compound 2 BHA
RUT
TRO
(l
DPPHꢀ
2.14 0.27
1.52 0.14
1.22 0.21
3.32 0.17
8.67 0.13 17.60 0.19 26.47 0.16
14.41 0.19 10.99 0.03 27.84 0.27
8.01 0.22 17.02 0.03 4.28 0.10
DMPDꢀ+ 2.08 0.07
ABTSꢀ+ 4.49 0.06
DPPHꢀ increased in that order: Compound 2 (1.52 0.14) > Com-
pound 1 (2.14 0.27) > BHA (8.67 0.13) > Rutin (17.60 0.19) >
Trolox (26.47 0.16) (P < 0.05).
The samples were analyzed for the ability to scavenge the
DMPD radicals. The discoloration of the DMPDꢀ+ solution was found
to increase with an increase in the concentration of the sample
[60]. The title compounds were an effective DMPDꢀ+ radical scaven-
ger in a concentration-dependent manner (1–10
value for the title compounds were 2.08 0.07 and 1.22
0.21 g/mL, respectively (Table 7). These values were found as
lg/mL). SC50
l
10.99 0.03, 14.41 0.19, and 27.84 0.27 lg/mL for rutin, BHA,
and trolox, respectively (P < 0.01).
ABTSꢀ+, a protonated radical, has a characteristic maximum
absorbance peak at 734 nm, which decreases with the scavenging
of the proton radicals. The ABTSꢀ+ radical cation can be prepared
employing different oxidants. Results obtained using potassium
persulfate as oxidant show that the presence of peroxodisulfate
increases the rate of ABTSꢀ+ autobleaching in a concentration-
dependent manner. ABTSꢀ+ radical cation was generated in the
ABTS/K2S2O8 system [61]. For radical scavenging activities, the
SC50 values of the title compounds and standards are reported in
Table 7. The results show that ABTSꢀ+ radical cation scavenging
activity of the title compound is very important as well as stan-
Supplementary material
Crystallographic data for the structures reported in this article
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication number 978729 (compound I)
– 978730 (compound II). Copies of the data can be obtained free
of charge on application to CCDC 12 Union Road, Cambridge
CB21 EZ, UK. Fax: +44 1223 336 033; e-mail: data_request@
ccdc.cam.ac.uk.
Acknowledgment
dards such as BHA and rutin. SC50 values (lg/mL) of the title com-
pounds and standards on the ABTSꢀ+ radical cation decreased in
that order: Compound 2 (3.32 0.17) < Trolox (4.28 0.10) < Com-
pound 1 (4.49 0.06) < BHA (8.01 0.22) < Rutin (17.02 0.03)
(P < 0.01).
The authors acknowledge the Aksaray University Science and
Technology Application and Research Center, Aksaray, Turkey, for
use of the Bruker SMART BREEZE CCD diffractometer (purchased
under grant No. 2010K120480 of the State of Planning
Organization). The synthesis of the compounds in this study was
financially supported by Sinop University in Turkey (Project No.
EGTF-1901-12-03).
Conclusion
(E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxy-
phenol (1) and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)-
methyl]-3-methoxyphenol (2) compounds have been characterized
by using FT-IR and X-ray technique experimentally and using
B3LYP method with 6-31G(d,p) basis set theoretically. According
to X-ray results, it was founded the molecule 1 is nearly planar
and zwitterionic form. Hence, it can be said the compound 1 has
thermochromism properties. However, it was founded the mole-
cule 2 is not planar and its tautomeric form is phenol-imine form.
Therefore, it can be said that the compound 2 has photochromic
properties. Intermolecular and intramolecular interactions of the
title compounds were determined by X-ray technique. According
to X-ray results, compound 1 is stabilized by C16AH16ꢁꢁꢁOi1 and
C16AH16CꢁꢁꢁOi1 weak intermolecular hydrogen bond interaction,
as well as N+A Hꢁ ꢁ ꢁOꢂ strong intramolecular interaction and com-
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