Synthesis, crystal structure, vibration spectral, and DFT studies of 4-Aminoantipyrine and its derivatives

Article abstract of DOI:10.3390/molecules18010877

Three compounds derived from 4-Aminoantipyrine (AA) were synthesized and their structures confirmed by melting point, elemental analysis, FT-IR, and 1H-NMR. The molecular structures of the four compounds were characterized by single-crystal X-ray diffraction and calculated by using the density functional theory (DFT) method with 6-31G (d) basis set. The calculated molecular geometries and the vibration frequencies of the AA derivatives in the ground state have been compared with the experimental data. The results show that the optimized geometries can reproduce well the crystal structural parameters, and the theoretical vibration frequencies show good agreement with the experimental data, although the experimental data are different from the theoretical ones due to the intermolecular forces. Besides, the molecular electrostatic potential (MEP) and the frontier molecular orbital (FMO) analysis of the compounds were investigated by theoretical calculations.

Full text of DOI:10.3390/molecules18010877

Molecules 2013, 18, 877-893; doi:10.3390/molecules18010877
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis, Crystal Structure, Vibration Spectral, and
DFT Studies of 4-Aminoantipyrine and Its Derivatives
1
,2
3
4
2,
1,
4,
Yi Li , Yuanyuan Liu , Haowei Wang , Xiaohui Xiong *, Ping Wei * and Fangshi Li *
1
College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology,
Nanjing 210009, China
2
College of Food Science and Light Industry, Nanjing University of Technology, Nanjing 210009, China
3
Department of Chemical and Pharmaceutical Engineering, Southeast University ChengXian College,
Nanjing 210088, China
4
College of Science, Nanjing University of Technology, Nanjing 210009, China
*
Authors to whom correspondence should be addressed; E-Mails: xxh@njut.edu.cn (X.X.);
weiping@njut.edu.cn (P.W.); fangshi.li@njut.edu.cn (F.L.); Tel./Fax: +86-25-5813-9432 (X.X.);
+
86-25-5813-9908 (P.W.); +86-25-8358-8933 (F.L.).
Received: 26 November 2012; in revised form: 2 January 2013 / Accepted: 5 January 2013 /
Published: 11 January 2013
Abstract: Three compounds derived from 4-aminoantipyrine (AA) were synthesized and
1
their structures confirmed by melting point, elemental analysis, FT-IR, and H-NMR. The
molecular structures of the four compounds were characterized by single-crystal X-ray
diffraction and calculated by using the density functional theory (DFT) method with 6-31G
(
d) basis set. The calculated molecular geometries and the vibration frequencies of the AA
derivatives in the ground state have been compared with the experimental data. The results
show that the optimized geometries can reproduce well the crystal structural parameters,
and the theoretical vibration frequencies show good agreement with the experimental data,
although the experimental data are different from the theoretical ones due to the intermolecular
forces. Besides, the molecular electrostatic potential (MEP) and the frontier molecular
orbital (FMO) analysis of the compounds were investigated by theoretical calculations.
Keywords: 4-aminoantipyrine derivatives; X-ray structure determination; IR spectroscopy;
DFT calculations; electronic structure properties

Molecules 2013, 18
. Introduction
878
1
4
-Aminoantipyrine (AA) and its derivatives (Figure 1) have potential biological activities [1–7],
such as analgesic, anti-inflammatory, antimicrobial, and anticancer properties. Recently, AA and
-methylantipyrine (MAA) were found to correlate with the analgesic effect of dipyrone [8]. A study
4
demonstrated for the first time that dipyrone and some AA derivatives have a high potential to
attenuate or prevent the anti-platelet effects of aspirin [9]. This was confirmed by docking studies,
which revealed that MAA forms a strong hydrogen bond with serine 530 within the COX-1 enzyme,
thereby preventing enzyme acetylation by aspirin. The three-dimensional structures of COX-1 and
COX-2 have been solved by X-ray crystallography [10,11].
Although there have been many studies of the synthesis and biological activities of AA and its
derivatives, there are only a few articles concerning the structures of these compounds. To our
knowledge, there are no articles describing their complete structural analysis. Since AA and its
derivatives are biologically active compounds, information about their 3-dimensional structures,
especially their crystal structures, may be of great interest for rational drug design. On the other hand,
we also aimed to obtain and analyze the electronic structures of AA and its derivatives. B3lyp theory
with 6-31G* basis set was used since it is known to be quite a reliable method [12].
Figure 1. Structures of AA and some of its derivatives.
In this study, we present results of a detailed investigation of the structural characterization of AA
and its three derivatives (FAA, MMAA, MCAA) using single crystal X-ray diffraction, IR
spectroscopy, and quantum chemical methods. The geometrical parameters, fundamental frequencies of
the three derivatives in the ground state have been calculated by using the DFT (B3LYP) method with
6
-31G (d) basis set. This calculation is valuable for providing insight into molecular parameters and
the vibration spectrum. The aim of this work was to explore the molecular dynamics and the structural
parameters that govern the chemical behavior, and to compare predictions made from theory with
experimental observations.

Molecules 2013, 18
879
2
. Results and Discussion
2
.1. Crystallographic Results
Crystal data of AA, MMAA, and MCAA are listed in Table 1. The selected molecular structure
parameters (bond lengths and bond angles) are listed in Tables 2–5. The hydrogen bonds are listed in
Table 6. The molecular structures and the packing diagrams are shown in Figures 2–5.
Table 1. Crystal and structure refinement data.
AA
MMAA
MCAA
empirical formula
formula weight
temperature [K]
wavelength [Å]
crystal system,
space group
unit cell dimensions
a [Å]
C
11
H
13
N
3
O
C
13
H
15
N
3
O
3
28 38 6 8
C H N O
203.24
293 (2)
261.28
293 (2)
0.71073
586.64
293 (2)
0.71073
0.71073
hexagonal
P65
monoclinic
monoclinic
P2 /c
Cc
1
7.5160 (11)
7.5160 (11)
32.005 (6)
90.00
6.7180 (13)
17.305 (4)
11.455 (2)
90.00
12.044 (2)
11.961 (2)
20.724 (4)
90.00
b [Å]
c [Å]
α [º]
β [º]
90.00
97.33 (3)
90.00
97.47 (3)
90.00
γ [º]
120.00
3
volume [Å ]
1565.7 (5)
6
1320.8 (5)
4
2960.1 (10)
4
Z
−
3
ρcalcd [g cm ]
1.293
1.314
1.316
−
1
μ [mm ]
F (000)
0.087
0.095
0.098
648
552
1248
3
crystal size [mm ]
θ range [º] for data collection
index ranges
0.05 × 0.10 × 0.20
3.13 to 25.31
0 ≤ h ≤ 7
0.10 × 0.10 × 0.20
2.14 to 25.27
0 ≤ h ≤ 8
0 ≤ k ≤ 20
−13 ≤ l ≤ 13
2,603
0.10 × 0.10 × 0.20
1.98 to 25.27
0 ≤ h ≤ 14
0 ≤ k ≤ 14
−24 ≤ l ≤ 24
2,956
0
≤ k ≤ 7
−
38 ≤ l ≤ 38
reflections collected
independent reflections
max. and min. transmission
data/restraints/parameters
2,331
1898 [R = 0.097]
2392 [R = 0.023]
2818 [R = 0.084]
int
int
int
0.9957/0.9829
1898/1/136
1.005
0.9905/0.9812
0.9903/0.9807
2392/0/173
1.000
2818/3/387
1.009
2
goodness-of-fit on F
final R indices [I > 2σ (I)];
R1, wR2
0
.0638, 0.1667
0.0552, 0.1488
0.0886, 0.1704
0.239 and −0.188
0.0651, 0.1526
0.0969, 0.1716
0.224 and −0.273
R , wR (all data)
0.0992, 0.1901
1
2
largest diff. peak and hole
0
.153 and −0.160
−
3
[
e·Å ]

Molecules 2013, 18
880
Table 2. Selected molecular structure parameters of AA.
Parameters
AA
Bond lengths (Å) Experimental B3LYP/6-31G (d)
O1-C7
N1-C7
N1-C6
N1-N2
N2-C9
1.229 (6)
1.379 (6)
1.418 (6)
1.431 (5)
1.402 (6)
1.459 (6)
1.365 (7)
1.228
1.400
1.417
1.420
1.421
1.475
1.394
N2-C10
N3-C8
Bond angles ()
C7-N1-C6
C6-N1-N2
C9-N2-C10
N1-N2-C10
C1-C6-N1
C5-C6-N1
O-C7-N1
O-C7-C8
N1-C7-C8
C9-C8-N3
N3-C8-C7
N2-C9-C11
126.9 (4)
119.3 (4)
117.9 (4)
110.3 (4)
122.7 (5)
117.2 (4)
125.1 (4)
129.2 (5)
105.7 (4)
129.9 (5)
121.4 (5)
119.3 (4)
125.11
119.28
115.26
111.49
120.76
119.23
126.98
127.79
105.17
132.14
119.44
119.85
Table 3. Selected molecular structure parameters of FAA.
Parameters
FAA
Bond lengths (Å) Experimental B3LYP/6-31G (d)
O1-C9
N1-C9
N1-C6
N1-N2
N2-C7
N2-C10
N3-C8
N3-C12
O2-C12
C9-N1-C6
C6-N1-N2
C7-N2-C10
N1-N2-C10
C1-C6-N1
C5-C6-N1
O1-C9-N1
O1-C9-C8
N1-C9-C8
C7-C8-N3
N3-C8-C9
N2-C7-C11
C12-N3-C8
O2-C12-N3
1.248 (5)
1.384 (5)
1.424 (5)
1.412 (5)
1.359 (5)
1.463 (5)
1.419 (5)
1.305 (6)
1.228 (5)
124.3 (3)
118.3 (3)
123.0 (4)
117.4 (4)
119.4 (4)
120.4 (4)
123.6 (4)
131.7 (4)
104.7 (4)
127.8 (4)
122.7 (4)
120.4 (4)
122.2 (4)
124.7 (5)
1.226
1.405
1.420
1.413
1.405
1.474
1.396
1.382
1.217
124.92
119.36
116.78
112.61
119.25
120.57
125.40
130.29
104.27
127.35
124.17
120.17
127.67
121.89

Molecules 2013, 18
881
Table 4. Selected molecular structure parameters of MMAA.
Parameters
MMAA
Bond lengths (Å) Experimental B3LYP/6-31G (d)
O3-C4
N2-C4
N2-C8
N2-N3
N3-C5
N3-C6
N1-C3
N1-C2
O2-C2
1.235 (3)
1.396 (3)
1.422 (3)
1.408 (3)
1.384 (3)
1.476 (3)
1.407 (3)
1.346 (3)
1.208 (3)
1.342 (3)
1.428 (4)
1.228
1.400
1.418
1.415
1.411
1.474
1.397
1.374
1.217
1.357
1.433
O1-C2
O1-C1
Bond angles ()
C4-N2-C8
C8-N2-N3
C5-N3-C6
N2-N3-C6
C13-C8-N2
C9-C8-N2
O3-C4-N2
O3-C4-C3
N2-C4-C3
C5-C3-N1
N1-C3-C4
N3-C5-C7
C2-N1-C3
O2-C2-N1
O1-C2-N1
O2-C2-O1
C2-O1-C1
125.2 (2)
118.9 (2)
119.8 (2)
114.1 (2)
120.7 (3)
119.2 (2)
123.9 (2)
130.6 (2)
105.5 (2)
129.6 (2)
121.5 (2)
120.3 (2)
124.0 (2)
126.1 (2)
109.5 (2)
124.4 (2)
116.8 (2)
125.32
119.58
116.43
112.43
120.77
119.11
127.11
127.96
104.86
133.63
117.07
118.98
125.31
126.26
109.11
124.62
114.74
Table 5. Selected molecular structure parameters of MCAA.
Parameters
MCAA
Bond lengths (Å) Experimental B3LYP/6-31G(d)
O3-C6
N3-C6
N3-C9
N2-N3
N2-C5
N2-C8
N1-C4
N1-C2
O2-C2
O1-C2
O1-C1
N1-C3
1.240 (8)
1.386 (9)
1.420 (7)
1.420 (7)
1.373 (8)
1.459 (8)
1.412 (8)
1.367 (10)
1.215 (8)
1.351 (9)
1.411 (10)
1.456 (9)
1.225
1.415
1.419
1.414
1.396
1.472
1.409
1.378
1.218
1.361
1.434
1.468

Molecules 2013, 18
882
Table 5. Cont.
Parameters
MCAA
Bond lengths (Å) Experimental B3LYP/6-31G (d)
Bond angles ()
C6-N3-C9
C9-N3-N2
C5-N2-C8
N3-N2-C8
C10-C9-N3
C14-C9-N3
O3-C6-N3
O3-C6-C4
N3-C6-C4
C5-C4-N1
N1-C4-C6
N2-C5-C7
C2-N1-C4
O2-C2-N1
O1-C2-N1
O2-C2-O1
C2-O1-C1
C2-N1-C3
C4-N1-C3
126.3 (5)
120.6 (5)
123.9 (6)
118.2 (5)
120.6 (5)
117.6 (6)
123.1 (6)
131.6 (6)
105.2 (5)
125.6 (6)
125.0 (6)
120.8 (6)
120.7 (6)
125.0 (7)
111.2 (6)
123.8 (8)
114.9 (7)
120.0 (6)
118.5 (6)
124.67
119.17
117.83
113.26
119.01
120.91
125.21
130.54
104.21
128.24
123.01
120.67
123.23
124.89
111.66
123.45
114.12
118.43
117.53
Figure 2. Crystal structure (Left), packing diagram (Middle), and theoretical optimized
geometric structure (Right) of AA.
Figure 3. Crystal structure (Left), packing diagram (Middle), and theoretical optimized
geometric structure (Right) of FAA.

Molecules 2013, 18
Figure 4. Crystal structure (Left), packing diagram (Middle), and theoretical optimized
883
geometric structure (Right) of MMAA.
Figure 5. Crystal structure (Left), packing diagram (Middle), and theoretical optimized
geometric structure (Right) of MCAA.
Regarding the crystal structure of AA (Figure 2, Table 6), there is one intermolecular N3-H3•••O
hydrogen bond, between the carbonyl oxygen atoms of the pyrazole rings and the hydrogen atoms of
the amide groups, and two C-H•••π interactions (C11-H11•••Cg1, and C11-H13•••Cg1), between the
methyl hydrogen of the pyrazole ring and the center of phenyl ring, to form a three-dimensional
network. The dihedral angle between the pyrazole ring and the phenyl ring is 42.39°.
Table 6. Hydrogen bonding geometries (Å, ).
D-H···A
AA
D-H H···A
D···A
D–H···A
Symmetry codes
N3-H3A···O
0.86 2.23 3.039 (6)
156.0
98.2
x − y, −1 + x, −1/6 + z
x − y, −1 + x, −1/6 + z
x − y,−1 + x, −1/6 + z
C11-H11A···Cg1 0.96 3.21 3.476 (6)
C11-H11C···Cg1 0.96 2.99 3.476 (6)
FAA
112.7
N3-H3A···O1
0.86 2.01 2.864 (5)
172.0
153.0
125.0
−x, y + 1/2,−z + 3/2
−x − 1, y + 3/2, −z + 3/2
−x, y+ 3/2, −z + 3/2
C10-H10B···Cg1 0.96 2.85 3.733 (5)
C12-H12A···Cg1 0.93 3.03 3.647 (5)

Molecules 2013, 18
884
Table 6. Cont.
D-H···A
MMAA
D-H H···A
D···A
D–H···A
Symmetry codes
N1-H1A···O3
C9-H9A···O3
0.86 2.01 2.850 (3)
0.93 2.52 2.960 (3)
0.96 3.11 3.686 (4)
0.96 3.23 3.763 (3)
166.0
109.0
120.1
116.7
1 − x, 1 − y, 2 − z
C1-H1C···Cg1
C7-H7B···Cg1
MCAA
x, 1/2 − y, 1/2 + z
2 − x, 1− y, 2− z
OW1-HW1B···O3
C17-H17A···O5
OW2-HW2B···O3
OW2-HW2A···O3
OW2-HW2A···O6
C3-H3A···O2
1.01 1.90 2.850 (9)
0.96 2.34 2.766 (10)
0.85 2.51 2.860 (7)
0.85 2.55 2.860 (7)
0.85 2.41 2.871 (8)
0.96 2.43 2.806 (10)
156.0
106.0
106.0
102.0
114.0
103.0
159.0
118.0
151.0
171.0
151.0
147.0
165.3
113.0
127.4
160.5
109.4
OW1-HW1A···O6#1 0.96 1.90 2.823 (9)
C8-H8C···OW1#2 0.96 2.49 3.056 (10)
C10-H10A···OW2#2 0.93 2.52 3.358 (9)
C22-H22A···O5#2 0.96 2.56 3.510 (8)
C28-H28A···OW2#2 0.93 2.54 3.384 (9)
1/2 + x, 1/2 + y, z
−1/2 + x, 1/2 + y, z
−1/2 + x, 1/2 + y, z
−1/2 + x, 1/2 + y, z
−1/2 + x, 1/2 + y, z
x, y, z
C3-H3B···Cg1#3
C8-H8B···Cg1#1
0.96 3.20 4.038 (9)
0.96 2.80 3.737 (8)
1/2 + x, 1/2 + y, z
1/2 + x,1/2 + y, z
x, y, z
C14-H14A···Cg2#1 0.93 3.11 3.582 (7)
C17-H17B···Cg3#3 0.96 3.36 4.020 (9)
C22-H22B···Cg3#4 0.96 2.90 3.814 (8)
C24-H24A···Cg4#4 0.93 3.12 3.539 (8)
−1/2 + x,−1/2 + y, z
−1/2 + x, −1/2 + y, z
The molecular conformation of MMAA (Figure 4, Table 6) is stabilized via the intermolecular
N1-H1•••O3 hydrogen bonds, between the carbonyl oxygen atoms of the pyrazole rings and the
hydrogen atoms of the amide groups to form a ten-member-ring, and two C-H•••π interactions,
between the methoxy hydrogen and the phenyl ring (C1-H1•••Cg1, C7-H7•••Cg1), to form dimers.
In the crystal of MCAA (Figure 5, Table 6), water molecules are involved in the intermolecular
hydrogen bonds between two molecules of MCAA. The water molecules were confirmed in the IR
(
Figure 6). There are three C-H•••π interactions (C3-H3•••Cg1, C8-H8•••Cg1, C14-H14•••Cg2) to
reinforce the crystal packing. The crystal structure of FAA has been reported by us [13].
2
.2. Vibration Spectra
Vibration spectroscopy is used extensively in organic chemistry for the identification of functional
groups of organic compounds, the study of molecular conformations, reaction kinetics, etc. The
vibration spectral data obtained from the solid phase FT-IR spectra are assigned based on the results of
the normal coordinate calculations. The experimental and the simulated infrared spectra, where the
intensity (km/mol) is plotted against the vibration frequencies, are shown in Figure 6. The resulting
vibration wave numbers for the optimized geometry and the proposed assignments are given in Table 7.
As seen from Table 7, the observed and the calculated spectra are in good agreement with each other.

Molecules 2013, 18
Figure 6. Experimental (above) and Theoretical (below) FT-IR of the compounds.
885
−1
Table 7. Experimental and Theoretical FT-IR and assignments for the compounds (cm ).
FAA
MMAA
B3LYP/
6-31G *
3210
MCAA
B3LYP/
6-31G *
3055
B3LYP/
Vibrational
assignments
Vibrational
Vibrational
Exp.
Exp.
Exp.
6
-31G *
assignments
assignments
νN-H
νN-H
ν=C-H
3
3
190ms
049ms
3187
3213s
3056w
2948m
as
ν=
as
C-H
ν=C-H
as
ν
3044
3053m
3057
C-H
νC=O
ν
ν
2
2
925ms
878ms
C-H
2948w
1725vs
C-H
1700vs
1676vs
1690
s
νC=O
νC=O
ν
C-H
1727
1659
1659
1643
νC=O
νC=O
νC=O
νC=C
1
689vs
636vs
1690
1643
1659vs
1629vs
1639s
νC=C
νC=C
1
1593ms
νC=C
N-H
1
545s
490s
1544
1480
1395
1211
1129
1593s
1541s
1544w
1493s
1546
1498
1455
1340
1209
νC=C
s
νC=C
N-H
1
1538
1492
1449
1346
νC=C
νC=C

1
1
386ms
216ms
C-H
1494s
1452vs
1331vs
1205ms
s
νC-N
νC-N
νC=C

1456ms
1347m
C-H
s
νC-N

1
140m
C-H
νC-N
νC-N
νC-N
νC-N
νC-O
νC-N
1
106w
020w
1113
1017
850
774
708
659
632
1290s
1253vs
1185w
1139w
1109w
1067s
765s
1187ms
1165ms
1137ms
1111ms
1073w
1051w
996m
1188
1169
1141
1108
1072
1045
991
νC-O
1
νC-N
8
56w
68ms
98ms
1188
1141
1117
1065
758
γ=
C-H
νC-N
νC-N
7
6
γN-H
γ=
νC-N
νC-O
νC-O
γ=
νC-N
6
66w
38w
C-H
6
C-H
γ=
C-H
7
7
6
35m
14m
94m
740
769s
773
γN-H
γ=
709
725m
728
703
C-H
6
52w
661

Molecules 2013, 18
886
vs, very strong; s, strong; ms, medium strong; m, medium; w, weak; vw, very weak; ipb, in plane bending;
opb, out plane bending.
FAA or MMAA have one N-H bond. The characteristic IR band of the synthesized FAA or MMAA
−1
appears the peak in the 3190 and 3213 cm regions due to the (N-H) stretching vibrations. This is
interpreted as a result of their conjugated resonance with the pyrazole ring, besides the carbonyl group
is connected to the imine group. The calculated (N-H) stretching vibrations are observed at 3187 and
−1
3
210 cm , respectively.
There are aromatic moieties in the molecules of FAA, MMAA, and MCAA. The stretching bands
−1
of C-H (Ar-H) appear at 3049, 3053, and 3056 cm , respectively. These values have been calculated
−1
as 3044, 3057, and 3055 cm , respectively.
FAA, MMAA, and MCAA have two kinds of carbonyl (C=O) groups. The very strong stretching
−1
bands of amide carbonyl appear at 1689, 1725, and 1700 cm , respectively, while they are calculated
−1
at 1690, 1727, and 1690 cm ; The very strong stretching bands of pyrazole carbonyl appear at 1636,
−
1
1
659, and 1676 cm , respectively, apparently decreasing in frequencies compared with the carbonyl
−1
−1
absorption of AA (1679 cm ), while they are calculated at 1643, 1659, and 1659 cm . The
assignment of the experimental frequencies is based on the observed band frequencies in the infrared
spectra (Table 7).
2
.3. Theoretical Structures
The optimized parameters (bond lengths and bond angles) of AA, FAA, MMAA, and MCAA were
obtained by using B3LYP/6-31G (d) method and listed in Tables 2–5 to compare with the X-ray
experimental data.
As seen from Table 2, the biggest difference between the X-ray and calculated values of the bond
lengths of AA is at N3-C8. The calculated value is 0.0291 Å longer than the X-ray value. The biggest
difference between the X-ray and calculated values of the bond angles of AA is at C9-N2-C10. The
calculated value is 2.2356 smaller than the X-ray value. It is because there are intermolecular
N3-H3•••O hydrogen bond and the C-H•••π interactions (Figure 2), there are such differences between
the X-ray and calculated values.
As seen from Table 3, for the same reason, the biggest differences between the X-ray and the
calculated values of the bond length and angles of FAA is at N3-C12 and at C7-N2-C10, respectively.
The differences are 0.0773 Å and 6.2166, respectively.
As seen from Table 4, the biggest difference between the X-ray and the calculated values of the
bond lengths and angles of MMAA is at N1-C2 and at N1-C3-C4, respectively. The differences are
0.0278 Å and 4.4298, respectively. The reasons could be that the carbonyl oxygen atom of the
pyrazole ring is involved not only in the intermolecular hydrogen bond (N1-H1•••O3) but also in
the intramolecular hydrogen bond (C9-H9···O3), and that there are C-H•••π interactions between
the molecules.
As seen from Table 5, the biggest difference between the X-ray and the calculated values of the
bond lengths and angles of MCAA is at N3-C6 and at C5-N2-C8, respectively. The differences are
0.0285 Å and 6.0658, respectively. When the X-ray structures of the compounds are compared with
their optimized counterparts (Figure 7), conformational discrepancies are observed between them.

Molecules 2013, 18
887
Figure 7. Atom-by-atom superimposition of the calculated structure (red) over the X-ray
structure (black) for the compounds.
The most notable discrepancies exist in the orientation of the methyl groups, which are attached to
N(2) and C(3) of the pyrazole ring in the compounds. For AA, FAA, MMAA, and MCAA, the
orientation of the methyl groups were defined by the torsion angles in X-ray data [134.5 (4)°,
−148.5 (4)°, 139.3 (2)°, and −151.4 (6)°] and [177.0 (5)°, 178.8 (5)°, −179.9 (3)°, and 175.0 (7)°],
respectively. They were calculated as 133.06°, −135.19°, 131.28°, and 134.18°, and −179.8981°, 178.92°,
179.43°, and −177.90°, respectively.
The molecular structures of the compounds are nonplanar. According to the X-ray study, the
dihedral angles between the pyrazole ring and the benzene ring are 42.39°, 50.03°, 36.99°, and 41.17°
for AA, FAA, MMAA, and MCAA, respectively, whereas the dihedral angles have been calculated as
4
5.22°, 74.47°, 25.43°, and 38.91°, respectively.
We noted that the experimental results correspond to the solid phase of the compounds and that the
theoretical calculations are for the gas phase. In the solid state, there are intermolecular hydrogen
bonds between molecules, and the experimental results are related to molecular packing, while isolated
molecules are considered in the theoretical calculations. In spite of these small differences, calculated
geometric parameters represent a good approximation and they are the basis for calculating other
parameters, such as frontier orbitals and energy, and molecular electrostatic potential, as we describe later.
2
.4. Frontier Molecular Orbital Analysis
Molecular orbital and their properties, like energy, are very useful for physicists and chemists and
their frontier electron density used for predicting the most reactive position in -electron systems and
also explained several types of reaction in conjugated system [14]. Moreover, eigenvalues of the lowest
unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) and their
energy gap reflect the chemical activity of the molecule. Recently the energy gap between HOMO and
LUMO has been used to prove the bioactivity from intramolecular charge transfer (ICT) [15,16]. The
HOMO-LUMO energy gaps for the four compounds were calculated by B3LYP/6-31G (d). From the
HOMO-LUMO orbital picture (Figure 8), it is found that the filled -orbital (HOMO) is mostly

Molecules 2013, 18
888
located on the pyrazole ring and -N(H) group of the compounds, while the unfilled anti-orbital
LUMO) is on the benzene ring. When electron transitions take place, electrons are mainly transferred
(
from the pyrazole ring and -N(H) group to the phenyl ring. Therefore, introduction of an electron
withdrawing group into the -N(H) group will reduce the energy of the HOMO. It can be seen from
Figure 8 and Table 8 that the HOMO energy of AA is highest (−0.192 a. u.), and that the gap is the
smallest (0.174 a. u.). It implies that the electronic transfer in AA is easier.
Figure 8. Frontier molecular orbital of the compounds.
Table 8. Frontier orbital energy (a.u.).
Compound E(HOMO)
E (LUMO) E (LUMO−HOMO)
AA
−0.192 (54a) −0.018 (55a)
−0.210 (61a) −0.034 (62a)
0.174
FAA
0.176
0.182
0.185
MMAA
MCAA
−0.207 (69a) −0.025 (70a)
−0.211 (73a) −0.026 (74a)
2
.5. Molecular Electrostatic Potential
Molecular electrostatic potential (MEP) is related to the electronic density and is a very useful
descriptor in understanding sites for electrophilic attack and nucleophilic reactions as well as hydrogen
bonding interactions [17–19]. The electrostatic potential V(r) are also well suited for analyzing
processes based on the “recognition” of one molecule by another, as in drug-receptor and
enzyme-substrate interactions, because it is through their potentials that the two species first “see” each
other [20,21]. Being a real physical property, V(r)s can be determined experimentally by diffraction or
by computational methods [22].
Many researchers have used graphic models, especially MEP, as a tool in conformational analysis [23].
The fundamental application of this study is the analysis of noncovalent interactions [24–27], mainly
by investigating the electronic distribution in the molecule. Thus, this methodology was used to
evaluate the electronic distribution around molecular surface for the four compounds.
To visually consider the most probable sites of the molecules for an interaction with electrophilic
and nucleophilic species, MEP was calculated at the B3LYP/6-31G (d) optimized geometry. While
electrophilic reactivities are visualized by red color which indicates the negative regions of the

Molecules 2013, 18
889
molecule, the nucleophilic reactivities are colored in blue, indicating the positive regions of the
molecule, as shown in Figure 9. The nitro and carbonyl oxygen atoms are surrounded by a greater
negative charge surface, becoming these sites potentially more favorable for electrophilic attack. As
can be seen from the results, the MEP map confirms the existence of intra- and intermolecular
interactions observed in the solid state.
Figure 9. Molecular electrostatic potential map of the compounds.
In the MEP of AA, the main negative center includes the nitrogen atom attacked at C(4) of pyrazole
ring and the pyrazole carbonyl group, which should be responsible for the interaction with the active
drug-receptor sites [28]. It is clear in the MEPs that around the nitrogen atoms attached at C(4) of the
pyrazole ring, FAA, MMAA and MCAA show an electronic density lower than those of AA. That is,
there is a larger electronic concentration in the active sites of AA. It could be the reason for the
preferential COX -drug binding and in agreement with the activity observed in AA. A significant
2
change in the molecular structure of the compounds is the presence of a different substituent attached
to C(4). For AA, the substituent at C(4) is -NH
2
, while for FAA, MMAA, and MCAA, the substituents
, respectively. The amide carbonyl substituents
are -NHCHO, -NHCOOCH , and -NH(CH )COOCH
3
3
3
should increase the electronic delocalization in the molecules. The electronic density of the atoms is
shown in Figure 10.
Figure 10. Electronic density of the atoms.

Molecules 2013, 18
890
3. Experimental
3.1. General
Melting points were measured on an X-4 microscope electro-thermal apparatus (Taike, Nanjing,
1
China) and were uncorrected. H-NMR spectra were recorded on a Bruker spectrometer at 500 MHz
3
using CDCl as the solvent, with tetramethylsilane as an internal standard. IR spectra were recorded in
KBr disk using a Nicolet 380 FT-IR spectrophotometer. Elemental analyses were performed with a
Flash EA-1112 elemental analyzer. Crystal data were collected on a Nonius CAD-4 diffractometer by
using MoKα (0.71073 Å) irradiation.
3.2. Synthesis
AA was a commercial product (Yacoo Corperation, Suzhou, China). FAA, MMAA, and MCAA
were synthesized as follows: AA (10 mmol), formic acid (60 mmol), and ZnO (5 mmol) were placed in
a 25 mL three-necked round bottom flask. The reaction was started by stirring and heating to 70 °C.
The reaction was monitored by TLC (eluent: ether/acetone, 1:2 v/v). CH Cl (20 mL) was added after
2
2
the reaction was completed. ZnO was removed by filtration. The filtrate was washed with H
2
O (2 × 10 mL)
followed dry saturated aqueous sodium bicarbonate (2 × 10 mL), and dried over anhydrous Na
2 4
SO .
Yellow powder of FAA was got Yield: 12%. M.p. 192–194 °C; Elemental analysis: Anal. Calcd for
1
C
12
H
13
N
3
O
2
: C 62.33, H 5.67, N 18.17; found C 62.56, H 5.64, N 18.11; H-NMR (CDCl
3
) δ: 9.09
), 2.25 (s, 3H, CH );
IR (KBr, cm ) υ: 3190 (νN-H), 3049 (ν=C-H), 2925 (νC-H), 2878 (νC-H), 1689 (νC=O), 1636 (νC=O), 1545
(
s, 1H, CHO), 8.23 (s, 1H, NH), 7.48–7.31 (m, 5H, Ar-H), 3.09 (s, 3H, CH
3
3
−1
(
N-H), 1490 (νC=C), 1386 (C-H), 1216 (νC-N), 1140 (νC-N), 768 (=C-H), 698 (N-H).
AA (10 mmol) was added to a mixture of Me
25 mmol). The reaction mixture was heated in an oil bath to 50 °C. The reaction was monitored by
CO was evaporated under reduced pressure after the
reaction was completed. The residue was mixed with 150 mL water. The insoluble solid was removed
by filtration. The liquid was extracted with CH Cl . The combined organic extracts were dried
) and evaporated under reduced pressure to give MMAA as a light yellow powder. Yield:
3%. M.p. 180–182 °C; Elemental analysis: Anal. Calcd for C H N O : C 59.76, H 5.79, N 16.08;
2 3
CO (18 mL), 18-crown-6 (0.1 mmol), and NaH
(
TLC (eluent: acetone:chloroform, 2:1 v/v). Me
2
3
2
2
2 4
(Na SO
7
1
3
15
3
3
1
found C 59.98, H 5.82, N 16.02; H-NMR (CDCl
3
) δ: 7.46–7.27 (m, 5H, Ar-H), 3.71 (s, 3H, OCH
3
),
−1
3
1
1
.05 (s, 3H, CH ), 2.23 (s, 3H, CH ); IR (KBr, cm ) υ: 3213 (νN-H), 3053 (ν=C-H), 2948 (νC-H),
3 3
725 (νC=O), 1659 (νC=O), 1629 (νC=C), 1593 (νC=C), 1541 (N-H), 1494 (νC=C), 1456 (νC=C), 1347 (C-H),
290 (νC-N), 1253 (νC-O), 1139 (νC-N), 1067 (νC-O), 765 (=C-H), 714 (N-H).
K
2
3
CO (30 mmol) and dimethyl carbonate (36 mL) was added to a mixture of AA (10 mmol) and
1
8-crown ether-6 (0.6 mmol). The mixture was stirred and heated in an oil bath at 90 °C. The reaction
was monitored by TLC (eluent: acetone/chloroform, 2:1 v/v). The excess dimethyl carbonate was
removed in vacuum after the reaction was completed. CH Cl (20 mL) was added to the residue. The
2
2
insoluble solid was filtrated. After removal of the solvent, the brown residue was recrystallized from
the mixed solvent of ether and petroleum ether. A brown solid of MCAA was obtained. Yield: 80%. M.p.
1
20–121 °C; Elemental analysis: Anal. Calcd for C14
H
17
N
3
O
3
: C 61.08, H 6.22, N 15.26; found C
), 3.20
1
60.88, H 6.19, N 15.32; H-NMR (CDCl
3
) δ: 7.48–7.26 (m, 5H, Ar-H), 3.71 (s, 3H, OCH
3

Molecules 2013, 18
891
−1
(
s, 3H, CH ), 3.09 (s, 3H, CH ), 2.15 (s, 3H, CH ); IR (KBr, cm ) υ: 3056 (ν=C-H), 2948 (νC-H),
3
3
3
1
700 (νC=O), 1676 (νC=O), 1639 (νC=C), 1593 (νC=C), 1493 (νC=C), 1452 (νC=C), 1331 (C-H), 1165 (νC-O),
137 (νC-N), 1073 (νC-O), 769 (=C-H).
1
3
.3. Crystallography
Single crystals of AA, MMAA, and MCAA were prepared by recrystallization from acetonitrile,
acetone, and diethyl ether, respectively. The X-ray diffraction data were collected on an automated
Enraf-Nonius CAD-4 diffractometer (Mo-Ka radiation, 0/20 scanning technique). The positions and
thermal parameters of the non-hydrogen atoms were refined anisotropically. H atoms were positioned
geometrically and refined as riding groups, with N-H = 0.86Å (for NH), C-H = 0.93, 0.93 and 0.96Å
(
for aromatic, aldehydic and methyl H), respectively, and constrained to ride on their parent atoms,
with Uiso (H) = xUeq (C), where x = 1.2 for aromatic H, and x = 1.5 for other H. The positions of the
hydrogen atoms were located according to the difference of electron density. All calculations were
carried out with the use of the SHELXL-97 program package. Details of the parameters are given in
Table 1. CCDC-660447, 801822, 801827, 801826 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html
[
or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ,
UK; Fax: +44(0) 1222-336033; email: deposit@ccdc.cam.ac.uk].
3.4. Theoretical Calculation
The molecular structures of the compounds in the ground state (in vacuo) were optimized using
DFT (B3LYP) method with the 6-31G (d) basis set with the Gaussian 03 software package. The initial
configurations for calculation were constructed according to the X-ray data. Frequency calculations at
the same levels of theory revealed no imaginary frequencies, indicate that the B3LYP/6-31G (d)
method was the optimal one in our system.
4
. Conclusions
In this study, three AA derivatives (FAA, MMAA, and MCAA) have been synthesized and
1
characterized by elemental analysis, FT-IR, and H-NMR spectroscopy. AA and the three derivatives
were characterized by single-crystal X-ray diffraction techniques. The theoretical calculations of AA
and the derivatives have been performed by using the density functional theory (DFT) method with the
6
-31G(d) basis set. Although differences were observed in the geometric parameters, the general
agreement is in a good range and the theoretical calculations support the solid-state structures. The
experimental vibration frequencies are in a good agreement with the results of the B3LYP method. The
calculated MEP map verifies the solid-state interactions.
Acknowledgements
This work was supported by the Project of Food Fast Detection Technology (BM2012026) and the
supporting project of the Twelfth Five Year Plan of China (2012BAK17B09).

Molecules 2013, 18
892
References
1
.
.
Cechinel Filho, V.; Correa, R.; Vaz, Z.; Calixto, J.B.; Nunes, R.J.; Pinheiro, T.R.; Andricopulo, A.D.;
Yunes, R.A. Further studies on analgesic activity of cyclic imides. Farmaco 1998, 53, 55–57.
Sondhi, S.M.; Sharma, V.K.; Verma, R.P.; Singhal, N.; Shukla, R.; Raghubir, R.; Dubey, M.P.
Synthesis, anti-inflammatory, and analgesic activity evaluation of some mercapto pyrimidine and
pyrimidobenzimidazole derivatives. Synthesis 1999, 1999, 878–884.
2
3
4
.
.
Mishra, A.P. Physicochemical and antimicrobial studies on nickel(II) and copper(II) Schiff base
complexes derived from 2-furfuraldehyde. J. Indian Chem. Soc. 1999, 76, 35–37.
Raman, N.; Kulandaisamy, A.; Jeyasubramanian, K. Synthesis, spectral, redox, and antimicrobial
activity of Schiff base transition metal(II) complexes derived from 4-aminoantipyrine and benzil.
Syn. React. Inorg. Met. Org. Chem. 2002, 32, 1583–1610.
5
.
.
Raman, N.; Kulandaisamy, A.; Jeyasubramanian, K. Synthesis, Structural Characterization,
Redox, and Antibacterial Studies of 12-Membered Tetraaza Macrocyclic Cu(II), Ni(II), Co(II),
Zn(II), and VO(IV) Complexes Derived from 1,2-bis(imino-4'-antipyrinyl)-1,2-diphenylethane
and o-Phenylenediamine. Syn. React. Inorg. Met. Org. Chem. 2004, 34, 17–43.
6
Sondhi, S.M.; Singhal, N.; Verma, R.P.; Arora, S.K.; Dastidar, S.G. Synthesis of hemin and
porphyrin derivatives and their evaluation for anticancer activity. Indian J. Chem. Sect. B 2001,
4
0B, 113–119.
7.
8.
9.
Sutcliffe, J.A. Antibacterial Agents: Solutions for the Evolving Problems of Resistance.
Bioorg. Med. Chem. Lett. 2003, 13, 4159–4161.
Ergun, H.; Frattarelli, D.A.C.; Aranda, J.V.J. Characterization of the role of physicochemical
factors on the hydrolysis of dipyrone. J. Pharm. Biomed. Anal. 2004, 35, 479–487.
Hohlfeld, T.; Zimmermann, N.; Weber, A.A.; Jessen, G.; Weber, H.; Schroer, K.; Hoeltje, H.D.;
Ebel, R. Pyrazolinone analgesics prevent the antiplatelet effect of aspirin and preserve human
platelet thromboxane synthesis. J. Thromb. Haemost. 2008, 6, 166–173.
1
0. Picot, D.; Loll, P.J.; Garavito, R.M. The x-ray crystal structure of the membrane protein
prostaglandin H2 synthase-1. Nature 1994, 367, 243–249.
1
1. Kurumbail, R.G.; Stevens, A.M.; Gierse, J.K.; McDonald, J.J.; Stegeman, R.A.; Pak, J.Y.;
Gildehaus, D.; Miyashiro, J.M.; Penning, T.D.; Seibert, K.; et al. Structural basis for selective
inhibition of cyclooxygenase-2 by anti-inflammatory agents. Nature 1996, 384, 644–648.
2. Li, Y.; Zhang, H.B.; Liu, Y.Y.; Li, F.S.; Liu, X.N. Synthesis, characterization, and quantum
chemical calculation studies on 3-(3-nitrophenylsulfonyl)aniline. J. Mol. Struct. 2011, 997, 110–116.
3. Wang, H.W.; Yang, M.M.; Lu, Q.S.; Li, F.S. N-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-
1
1
1
1
4-yl) formamide. Acta Crystallogr. Sect. E Struct. Rep. Online 2011, E67, o1310.
4. Fukui, K.; Yonezawa, T.; Shingu, H.J. A molecular-orbital theory of reactivity in aromatic
hydrocarbons. J. Chem. Phys. 1952, 20, 722–725.
5. Padmaja, L.; Ravikumar, C.; Sajan, D.; Hubert Joe, I.; Jayakumar, V.S.; Pettit, G.R.; Neilsen, F.O.
Density functional study on the structural conformations and intramolecular charge transfer from
the vibrational spectra of the anticancer drug combretastatin-A2. J. Raman Spectrosc. 2009, 40,
4
19–428.

Molecules 2013, 18
893
1
1
1
6. Ravikumar, C.; Hubert Joe, I.; Jayakumar, V.S. Charge transfer interactions and nonlinear optical
properties of push-pull chromophore benzaldehyde phenylhydrazone: A vibrational approach.
Chem. Phys. Lett. 2008, 460, 552–558.
7. Scrocco, E.; Tomasi, J. Electronic molecular structure, reactivity and intermolecular forces: An
euristic interpretation by means of electrostatic molecular potentials. Adv. Quantum Chem. 1978,
11, 115–121.
8. Luque, F.J.; Lopez, J.M.; Orozco, M. Perspective on “Electrostatic interactions of a solute with a
continuum. A direct utilization of ab initio molecular potentials for the prevision of solvent
effects”. Theor. Chem. Acc. 2000, 103, 343–345.
1
2
2
2
2
9. Okulik, N.; Jubert, A.H. Theoretical analysis of the reactive sites of non-steroidal
anti-inflammatory drugs. Internet Electron. J. Mol. Des. 2005, 4, 17–30.
0. Politzer, P.; Laurence, P.R.; Jayasuriya, K. Molecular electrostatic potentials: An effective tool for
the elucidation of biochemical phenomena. Environ. Health Perspect. 1985, 61, 191–202.
1. Scrocco, E.; Tomasi, J. Topics in Current Chemistry; Springer: Berlin, Germany, 1973; Volume 7,
p. 95.
2. Politzer, P.; Truhlar, D.G. Chemical Applications of Atomic and Molecular Electrostatic Potentials;
Basic Books: New York, NY, USA, 1981.
3. Bocca, C.C.; Basso, E.A.; Gauze, G.F. Substituent effects on the reduction of 2-OMe, 2-SMe and
2
-SeMe cyclohexanones by LiAlH4: An investigation of conformational equilibrium and
transition states. Chem. Phys. Lett. 2005, 413, 434–439.
2
4. Politzer, K.C.D. The Force Concept in Chemistry; Van Nostrand Reinhold Publisher: New York,
NY, USA, 1981; Chapter 6.
2
5. Politzer, S.M. Reviews in Computational Chemistry; VCH Publishers: New York, NY, USA, 1991;
Chapter 7.
2
6. Naray-Szabo, G.; Ferenczy, G.G. Molecular Electrostatics. Chem. Rev. 1995, 95, 829–847.
7. Murray, S.; Politzer, P. Molecular Orbital Calculations for Biological Systems; Oxford University
Press: New York, NY, USA, 1998; Chapter 3.
2
2
8. Michaux, C. A new potential cyclooxygenase-2 inhibitor, pyridinic analogue of nimesulide. Eur. J.
Med. Chem. 2005, 40, 1316–1324.
Sample Availability: Samples of the compounds, AA, FAA, MMAA, and MCAA, are available from
the authors.
©
2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
http://creativecommons.org/licenses/by/3.0/).
(