Supramolecular Assembly Interceded by C-H···O Hydrogen Bonds and Nitro···π(arene) Interactions of Antibacterial 4-Methyl-(2-nitro benzylidene)aniline using DFT and its Spectral Studies

Article abstract of DOI:10.14233/ajchem.2020.22517

4-Methyl-(2-nitrobenzylidene)aniline (MNBA) was grown and its structural as well as spectral analyses (FT-IR, FT-Raman, UV and NMR) using experimental and DFT computations were performed to understand its biological applications. Stability of molecule, ch

Full text of DOI:10.14233/ajchem.2020.22517

Asian Journal of Chemistry; Vol. 32, No. 5 (2020), 1048-1058
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22517
Supramolecular Assembly Interceded by C-H···O Hydrogen Bonds and Nitro···π(arene) Interactions
of Antibacterial 4-Methyl-(2-nitro benzylidene)aniline using DFT and its Spectral Studies
1
2
3
1,*
R. MINI , T. JOSELIN BEAULA , P. MUTHURAJA and V. BENA JOTHY
1
2
Department of Physics, Women′s Christian College (Affiliated to Manonmaniam Sundaranar University, Tirunelveli), Nagercoil-629001, India
Department of Physics, Malankara Catholic College (Affiliated to Manonmaniam Sundaranar University, Tirunelveli), Kaliakkavilai-629153,
India
3
P.G. and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya, College of Arts and Science, Coimbatore-641020, India
*
Corresponding author: E-mail: benaezhil@yahoo.com
Received: 16 October 2019; Accepted: 15 December 2019;
Published online: 29 April 2020;
AJC-19833
4-Methyl-(2-nitrobenzylidene)aniline (MNBA) was grown and its structural as well as spectral analyses (FT-IR, FT-Raman, UV and NMR)
using experimental and DFT computations were performed to understand its biological applications. Stability of molecule, charge delocalization,
charge analysis and charge transfer interactions had been explored to examine the structural analysis. Docking studies also suggested that
4
-methyl-(2-nitrobenzylidene)aniline exhibit antibacterial activity. Supramolecular assembly of 4-methyl-(2-nitrobenzylidene)aniline
molecule was interceded by C-H···O hydrogen bonds and nitro···π(arene) interactions.
Keywords: 4-Methyl-(2-nitrobenzylidene)aniline, Natural bond orbital, Structural analysis.
1
antibacterial activity. In H NMR, a substituent behaviour of NMR
INTRODUCTION
chemical shift centre has an application of using as a probe for
the electronic properties of delocalized π-system of benzylidene
aniline [5]. The dual replacement of parameters in azomethine,
Development of biologically active molecules require a
multidisciplinary effort by combining organic chemistry, crystal
growth, material science and physics. Organic base aniline is
generally used to make dyes, explosives and drugs. In medicinal
and biological chemistry fields, benzylidene anilines possess
an important class of Schiff bases. It may also possess signi-
ficant anticancer and anti-inflammatory activities which act
as reagents for various stereoselective organic synthesis [1].
Benzylidene aniline has the relieving property for inflamma-
tions in the warm-blooded animals and also consists of various
pharmaceutical compositions. It is also used for the treatment
of radiation induced by the topical administration. Benzylidene
aniline derivatives exhibit effective sun screening property [2].
Azomethine group enables attachment and extension of
π-donating groups [3]. Cyano (CN) group, gets adsorbed on
the metal surfaces easily due to planarity of π-bonding orbitals
and electrons from the attached electronegative atoms [4].
Hydrogen bonding interaction results in the formation of a
bridge of the sort C-H···O and nitro···π interactions causing
shift following bond stretching or contraction which compile
13
C NMR shift gave important insight into the special behaviour
of CN group as a substituent. The CN group inductively has a
strong electron-withdrawing group, whereas mesomerically it
also have the strong electron donating group [6]. In benzoic
complexes, the donor-acceptor groups are connected via varying
carbon-carbon single and double bonds. Benzylidene anilines
are isoelectronic which regards their π-electronic structure; their
properties can be strongly different [7]. Schiff bases have been
contemplated like versatile ligands which provide probability to
the design metal complexes for helpful in biological activities.
Several Schiff bases exhibit biological activities such as anti-
fungal, antibacterial, antitumor, anti-inflammatory and antipyretic
activities [8-10]. The antibacterial activity has been analyzed
more than antifungal activity because bacterium can obtain resis-
tance to antibiotics through biochemical and morphological
modifications [11,12]. In organic syntheses, a formation of carbon-
nitrogen double bond is important and the Schiff bases can be
synthesized from an amine and a carbonyl compound [13].
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Vol. 32, No. 5 (2020)
Spectral and DFT Studies of Crystal Growth of 4-Methyl-(2-nitrobenzylidene)aniline 1049
-
1
Quantum chemical computations has been carried out at
B3LYP / 6-311G(d) basis level to obtain optimized structure
which provides information about structural, spectral and elec-
tronic properties. Various spectral characterizations using UV-
visible, IR, Raman, H & C NMR techniques together with
X-ray diffraction analysis have been used to elucidate the struc-
ture of 4-methyl-(2-nitrobenzylidene)aniline (MNBA). NBO
analyses were carried out to identify the intra and intermole-
cular interactions. The reactive sites of the title molecule were
identified by the molecular electrostatic potential analysis
4000-400 cm by KBr pellet technique. FT-Raman spectral
studies was carried out using Bruker RFS 27 stand alone FT-
Raman spectrometer with laser source Nd:YAG 1064 nm in
-1
the spectral range of 4000-500 cm at room temperature. NMR
spectra was obtained using Bruker NMR spectrometer using
TMS as an internal standard. Thermal stability of the crystal
was examined using Thermogravimetric analysis. UV-visible
absorption spectrum of MNBA was recorded using methanol
solvent, JASCO UV-Vis spectrophotometer in the spectral region
of 200-400 nm.
1
13
(
MEP) and the group contribution of molecule was carried
Computational studies: DFT calculations were performed
using Gaussian 09 software [14] to obtain optimized geometry,
NBO analysis, HOMO-LUMO energy gap and charge analyses
at B3LYP/6-31G(d,p) level. Normal mode characterization was
performed with MOLVIB 7.0 program [15,16]. To improve
agreement between experimental and theoretical frequencies,
theoretical values were scaled using SQMFF procedure [17,
out by density of state (DOS) analysis.
EXPERIMENTAL
Synthesis of 4-methyl-(2-nitrobenzylidene)aniline
(
MNBA): Slow evaporation solution growth technique was
used for the growth of MNBA crystal. Analytical grades of
-methylaniline and 2-nitrobenzaldehyde were taken in 1:1 stoi-
18]. Electronic properties were determined by TD DFT approach,
4
by taking solvent effect into account [19-22] where the important
quantities were deduced from ionization potential and electron
affinity values [23-25]. GIAO method was used to calculate
NMR isotropic shielding [26,27] and AutoDock4 was used to
perform docking studies [28].
chiometric proportions and dissolved in methanol thoroughly
using mechanical stirrer for 5-6 h. Clear brown solution was
obtained and filtered off using Whatman 40 grade filter paper
to remove the suspended impurities (Scheme-I). The filtrate
was kept aside without any mechanical shake in a dust free
environment at room temperature. Bright brown 4-methyl-(2-
nitrobenzylidene)aniline (MNBA) single crystal (Fig. 1) was
obtained within 4-5 days and collected from the mother liquor.
The harvested MNBA crystals were recrystallized from ethanol
to get superior quality crystals.
RESULTS AND DISCUSSION
PXRD analysis: Purity and crystalline nature of MNBA
crystal had been confirmed by recording powder X-ray diffr-
action pattern. Powder X-ray diffraction pattern is shown in
Fig. 2. The well-defined and sharp Bragg peaks at specific 2θ
angles were in agreement with the theoretical data. All the
observed reflections were indexed by using CRYSFIRE soft-
ware package. Cell parameters and calculated 2θ for MNBA
are presented in Table-1. The given data clearly confirmed the
successful formation of MNBA.
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
Fig. 1. Photograph of the grown MNBA crystal
Characterization: Powder XRD data were collected in
a Bruker AXS instrument using CuKα radiation (λ = 1.5406
Å). Fourier transform infrared spectrum of MNBA crystal was
recorded using Shimazdu IR-affinity 1 instrument in the region
1000
0
3
10
20
30
40
(°)
50
60
70
80
2
θ
Fig. 2. Powder X-ray Diffraction spectrum of MNBA compound
O N
2
O N
2
H C
N
3
Methanol
H C
NH2
OHC
3
+
HC
Stirring/5-6 h
4
-Methylaniline
2-Nitrobenzaldehyde
4-Methyl-N-(nitrobenzylidene)aniline
Scheme-I: Synthetic reaction of 4-methyl-(2-nitrobenzylidene)aniline (MNBA)

1
050 Mini et al.
Asian J. Chem.
TABLE-1
POWDER X-RAY DATA OF SYNTHESIZED MNBA COMPOUND
(1.281 Å) lie between N-O single and N=O double bond length
values, indicating a electron delocalization within NO
Optimized geometry of MNBA compound revealed that NO
and CH groups were lying parallel with respect to benzene
2
group.
Unit cell parameters
k
2θ
2θ
‘d’
Observed
2
h
l
Observed Calculated
3
θ
1
2
2
2
4
2
5
2
2
θ
2
2
1
2
θ
3
2
1
4
1
0
θ
1
1
1
1
0
2
0
11.921
13.321
15.516
16.209
19.584
21.290
24.130
25.959
26.371
26.827
11.909
13.324
15.456
16.222
19.556
21.697
24.144
25.960
26.412
26.827
7.4179
6.6412
5.7064
5.4639
4.5293
4.0940
3.6853
3.4296
3.3770
3.3206
ring, which is recognized from their torsion angle values C4-
C3-N1-O2 (-180º), C2-C3-N1-O1 (180º) and C10-C12-C11-
C14 (179.9º).
Azomethine linkage forms a dihedral angle of 180º (C3-
C2-C1=N2, C1=N2-C8-C9) with aromatic ring of 2-nitro-
benzaldehyde moiety and 4-methylaniline moiety, which is
the clear proof for the planarity that exists between phenyl ring
and azomethine group. From the aforementioned bond length,
bond angle and torsion data, it is clearly understood that charge
transfer interaction is taking place from electron donor to
acceptor moiety through imine linkage. This intermolecular
charge transfer in the molecule generates two different mole-
cular domains within π-conjugated bridge. One of the domain
has partial quinonoid character and the other has an almost
pure aromatic character. So this π-electron cloud movement
from electron donor to acceptor is capable of highly polarizing
the molecule through the single-double path, when it changes
from the benzenoid form into the quinonoid form. Bond length
of C1-H19…O11, C4-H20…O10 and C13-H24…N8 were
2.2276 Å, 2.3690 Å and 2.43486 Å, respectively which are
shorter than van der Waals radii, confirming the presence of
Optimized geometry:An optimized structure of MNBA
is shown in Fig. 3 and the geometrical parameters have been
listed in Table-2. Phenyl rings were established to be planar
within 1º twist. Shortening of bond length C3-N4 (1.407 Å)
shorter than C-N single (1.465 Å) bond exposes the effect of
resonance in nitro group of molecule nonetheless C-N double-
bond length C1-N8 (1.289 Å) is longer than the normal C=N
bond (1.279 Å), exposing the effect of protonation of azome-
thine [29]. Asymmetry in phenyl rings exo-angles C4-C3-C9
and C2-C3-N9 were 117.8579º and 121.72º were deviated
from the normal value 120º which is due to the substitution of
nitro group. Endocyclic angles C12-C11-C10 (118.4 ) and C4-
C3-N1 (114.7 ) get shortened in addition to lengthening of
exo-cyclic angles C10-C11-C14 (121.3º) and C4-C3-C2
C-H···O hydrogen bonds and NO ···π(arene) interactions.
2
Natural bond orbital analysis: Second order perturbation
theory analysis and natural hybrid orbital in NBO basis are
shown in Table-3. Inter and intra-molecular hyper-conjugative
interactions n1(O11) with σ*(C1-H19), n3(O11) with σ*(C1-
H19), n1(N8) with σ*(C1-H19) and σ*(C7-H23) have
stabilization energies 0.63, 0.99, 12.02 and 0.89 kcal/mol
which revealed the presence of C-H···O and nitro···π (arene)
hydrogen bonds interactions. Natural hybrid orbital of
n2(O10), n2(O11) and n3(O11) have low occupation numbers
(1.89637, 1.89943 and 1.43979), substantial higher energy
orbital π-characters (99.82, 99.66 and 99.25 %) have lower
energies (-0.29439, -0.29696 and -0.28114 a.u.) and n1(O10),
n1(O11) and n2(N8) have high occupation numbers (1.98127,
(
121.7º) at the donor and acceptor side, respectively. This
asymmetry of angles clearly proves the charge-transfer
interaction within the system, nature of electron donor methyl
group, acceptor nitro group and also confirms the push-pull
nature of those two groups and hence this class of system is
known as push-pull chromophore. Large reduction in the endo-
cyclic angles C3-C2-C7 (116.8º) and C13-C8-C9 (118.6º) of
two phenyl rings at the junction of azomethine linkage obviously
proves the conjugation of two aromatic rings with C1=N2.
1
.97919, 1.89909) with energies, -0.80175, -0.80232, -0.34386
a.u. with lower energy orbital π-characters (25.08, 25.05, 72.50
). From these results, it can be inferred that pure p-type lone
%
pair orbital participates in electron donation which is very close
to the σ*(N-C) orbital for n2(O10) → σ*(N-C), n2(O11) →
σ*(N-C) and n2(O11) → σ*(N-C) orbital for n1(N8) → σ*(C-
C), n1(N6) → σ*(C-H) interactions in MNBA compound.
Vibrational analysis:Vibrational spectral assignment of
MNBA molecule fundamentals has been done based on normal
coordinate analysis. Fundamental band frequencies from experi-
mental IR and Raman spectra were scaled wavenumbers together
with the normal mode descriptions (Table-4). FT-IR and FT-
Raman spectra were exposed as overlayed with the corres-
ponding replicated spectra for optical comparison (Fig. 4).
Phenyl ring vibrations: Selection rule for ortho-disub-
stituted phenyl ring allows four C-H stretching vibrations, viz.
Fig. 3. Optimized molecular structure of synthesized MNBA molecule
An increase in the bond length values of C2-C3 (1.402
Å), C2-C7 (1.398 Å), C8-C9 (1.394 Å) and C8-C13 (1.398 Å)
compared to other CC lengths of aromatic rings also confirms
the hyper-conjugation of phenyl rings through C2-C1=N2-
C8 path, which was further evident from the partial double bond
nature of C1-N2 (1.281 Å). All these facts clearly revealed the
intramolecular charge transfer taking place within MNBA
compound. Bond length values of N1-O1 (1.277 Å), N1-O2
-1
2
, 7b, 20a and 20b in the range 3120-3010 cm [30]. Mode 2
-1
was observed in IR as weak band at 3095 cm , while mode
-1
2
0b was observed as a weak band at 3061 cm . In Raman, this

Vol. 32, No. 5 (2020)
Bond length
C1- C2
C1-N8
C1-H19
C2-C3
C2-C7
C3-C4
C3-N9
C4-C5
C4-H20
C5-C6
Spectral and DFT Studies of Crystal Growth of 4-Methyl-(2-nitrobenzylidene)aniline 1051
TABLE-2
OPTIMIZED BOND LENGTHS (Å), BOND ANGLES (°) AND DIHEDRAL
ANGLES (°) OF MNBA COMPOUND BY B3LYP/6-311G(d) BASIS SETS
(Å)
Bond angle
C2-C1-N8
C2-C1-H19
N8-C1-H19
C1-C2-C3
C1-C2-C7
C3-C2-C7
C2-C3-C4
C2-C3-N9
(°)
Dihedral angle
N8-C1-C2-C3
N8-C1-C2-C7
H19-C1-C2-C3
H19-C1-C2-C7
C2-C1-N8-C12
H19-C1-N8-C12
C1-C2-C3-C4
C1-C2-C3-N9
C7-C2-C3-C4
C7-C2-C3-N9
C1-C2-C7-C6
C1-C2-C7-H23
C3-C2-C7-C6
C3-C2-C7-H23
C2-C3-C4-C5
C2-C3-C4-H20
N9-C3-C4-C5
N9-C3-C4-H20
C2-C3-N8-O10
C2-C3-N9-O11
C4-C3-N9-O10
C4-C3-C9-O11
C3-C4-C5-C6
C3-C4-C5-H21
H20-C4-C5-C6
H20-C4-C5-H21
C4-C5-C6-C7
(°)
1.4782
1.2816
1.0901
1.4105
1.4068
1.396
1.4736
1.3896
1.0825
1.3983
1.0851
1.3893
1.0857
1.0839
1.4064
1.2303
1.2333
1.405
1.4047
1.3893
1.0854
1.4039
1.0873
1.4004
1.5098
1.3932
1.087
121.3912
113.9998
124.6007
121.6808
119.6064
118.6987
120.4195
121.7200
117.8579
119.7155
120.0448
120.2402
120.2043
119.5908
120.2028
120.1407
120.008
119.8446
120.8143
119.1098
120.0748
120.6073
118.4439
120.0993
121.4566
118.4269
122.9286
118.5508
120.2907
120.132
119.5141
120.9724
119.3471
119.6744
118.9195
121.0881
119.9881
120.8682
119.6137
119.5181
120.3914
119.9305
119.6526
109.7335
108.5571
109.5074
109.443
-129.8934
51.5171
49.1331
-129.48
178.0049
-0.8859
-120.4195
2.4364
C4-C3-N9
C3-C4-C5
0.603
-178.9361
177.6668
-1.9693
-0.9899
179.374
-0.1383
-179.9547
179.4183
-0.3981
-178.9258
1.2265
1.5238
-178.3239
0.0443
179.5238
179.8603
-0.6601
-0.4265
-179.4894
-179.9028
1.0342
C5-H21
C6-C7
C3-C4-H20
C5-C4-H20
C4-C5-C6
C4-C5-H21
C6-C5-H21
C5-C6-C7
C5-C6-H22
C7-C6-H22
C2-C7-C6
C2-C7-H23
C6-C7-23
C6-H22
C7-H23
N8-C12
N9-O10
N9-O11
C12-C13
C12-C17
C13-C14
C13-H24
C14-C15
C14-H25
C15-C16
C15-C18
C16-C17
C16-H26
C17-H27
C18-H28
C18-H29
C18-H30
C1-N8-C12
C3-N9-O10
C3-N9-O11
O10-N9-O11
N8-C12-C13
N8-C12-C17
C13-C12-C17
C12-C13-C14
C12-C13-H24
C14-C13-H24
C13-C14-C15
C13-C14-H25
C15-C14-H25
C14-C15-C16
C14-C15-C18
C16-C15-C18
C15-C16-C17
C15-C16-H26
C17-C16-H26
C12-C17-C16
C12-C17-H27
C16-C17-H27
C15-C18-H28
C15-C18-H29
C15-C18-H30
H28-C18-H29
H28-C18-H30
H29-C18-H30
1.0857
1.096
1.0964
1.0932
C4-C5-C6-H22
H21-C5-C6-C7
H21-C5-C6-H22
C5-C6-C7-C2
0.9108
C5-C6-C7-H23
H22-C6-C7-C2
H22-C6-C7-H23
C1-N8-C12-C13
C1-N8-C12-C17
N8-C12-C13-C14
N8-C12-C13-H24
C17-C12-C13-C14
C17-C12-C13-H24
N8-C12-C17-C16
N8-C12-C17-H27
C13-C12-C17-C16
C13-C12-C17-H27
C12-C13-C14-C15
C12-C13-C14-H25
H24-C13-C14-C15
H24-C13-C14-H25
C13-C14-C15-C16
C13-C14-C15-C18
H25-C14-C15-C16
H25-C14-C15-C18
C14-C15-C16-C17
C14-C15-C16-H26
C18-C15-C16-C17
C18-C15-C16-H26
C14-C15-C18-H28
C14-C15-C18-H29
C14-C15-C18-H30
C16-C15-C18-H28
C16-C15-C18-H29
C16-C15-C18-H30
C15-C16-C17-C12
C15-C16-C17-H27
H26-C16-C17-C12
H26-C16-C17-H27
-179.4566
179.9753
-0.3921
147.6777
-35.8963
177.2653
-2.9688
0.6802
-179.5539
-176.3624
1.7952
0.0594
178.2171
-0.8617
179.957
179.3708
0.2756
109.380
109.306
0.2864
179.5304
179.3787
1.3773
0.4637
179.6215
178.7888
1.126
22.3089
97.2589
143.4721
158.4551
81.9771
37.2919
0.6346
178.7974
179.4504
1.2877

1
052 Mini et al.
Asian J. Chem.
νCC (24), βCH1 (23), νCC1 (23)
βCHR2 (44), ASD2 (28), CC2 (15)
βCHR1 (77), νCC1 (18)
νCC1 (36), βCHR1 (34), νCN (14)
βCHR2 (59), νCC2 (32)
TD1 (30), νCC1 (18), νCN (14),
βCH1 (13)
TABLE-3
1
312
295
SECOND ORDER PERTURBATION THEORY ANALYSIS OF
FOCK MATRIX IN NBO BASIS OF MNBA COMPOUND
1
1
279s
1282
1255
1229
1161
ED(i)/
energy
E(2)
Donor
i)
1224w
1170s
S %
74.94
0.25
P %
Acceptor (j)
(kcal
(
-1
(
e)
n1(O11) 1.97919
0.80232
n2(O11) 1.89943
0.29696
n3(O11) 1.43979
0.28114
1.89909
0.34386
n1(O10) 1.89909
0.80175
n2(O10) 1.89637
0.29439
mol )
1162w
25.05
99.99
99.25
72.50
σ*(C -H )
0.63
1
19
-
σ*(C -N )
11.81
0.99
1126s
1135
1132
νCC1 (63), βCHR1 (19)
3
9
-
1
124w
096vs
076w
PK2 (33), ν CH (25), ATO2 (15),
R
3
0.54
σ*(C -H )
1
19
νROCH3 (11)
-
1
1090
1080
TD2 (47), ASD2 (19), ν CH3 (13),
RO
n1(N8)
27.37
σ*(C -H )
12.02
0.89
4.24
1
19
νCC2 (11)
TD2 (61), ASD2 (20)
GCHR1 (64), PK1 (10)
-
σ*(C -H )
7
23
1
74.92
0.08
25.08
99.82
σ*(C -N )
3
9
1011
-
9
98
ωCH (26), ATO2 (20), PK2 (16),
GCH1 (16)
GCHR1 (78)
σ*(N -O )
19.39
9
11
-
9
81
9
71w
978
967
959
942
905
898
848
839
ATO2 (22), TD2 (21), PK2 (18)
ATO2 (57), AT2 (24), GCH2 (14)
PK2 (51), GCHR2 (19), ATO2 (18)
TABLE-4
VIBRATIONAL ASSIGNMENTS OF MNBA COMPOUND
BY NORMAL COORDINATE ANALYSIS
956w
862vs
9
53s
Observed
939m
929m
8
νSDCO2 (45), TD1 (22), νSSNO (11)
GCHR1 (58), ASDO2 (10)
fundamentals
Selective scaled B3LYP/6-31G(d) force field
-
1
(
cm )
93s
ASDO2 (30), ASD2 (25), νCC2 (11)
ν
cal
GCHR2 (52), ATO2 (25), ν CN (14)
IR
Raman
Assignment with PED (≥ 100 %)
ν CH (71), ν CH (29)
AS
-
1
(
cm )
835w
NO DF (37), GCHR2 (26), AT2 (19),
2
3
3
125w
112w
3172
3140
OS
3
IS
3
PK2 (11)
ν CH (71), ν CH (29)
823
IS
3
OS
3
ASD2 (66), τD2 (19)
GCHR1 (41), GCO2 (22), GCN1 (15),
PK1 (10)
3129
3113
3098
νCHR1 (99)
νCHR1 (99)
νCHR1 (99)
νCHR2 (96)
νCHR2 (95)
νCHR1 (99)
νCHR2 (95)
νCHR2 (96)
ν CH (99)
807
751w
761
NO SC (23), ATO2 (20), GCH1 (17),
2
3
095w
3093
PK1 (13)
7
30w
12w
733
PK2 (35), ATO2 (33)
PK2 (50), ATO2 (47)
PK2 (47), ATO2 (43)
ASDO2 (52), ASD2 (15)
ASDO2 (50), ASDO1 (11)
PK2 (29), ATO2 (17), ASDO1 (13)
3089
3080
3063
726
7
713
670
660
616
561
547
518
502
433
6
6
6
67s
40s
02s
3
061w 3060w
968w
3061
970
2968
2
SS
3
2
νsCH (98)
νCNM (72), νCHR (13)
ASD2 (25), ASDO2 (21), νCC2 (15),
νCC (13), ν NO (11)
ASD2 (29), ASDO2 (27), νCC2 (20)
νCC2 (74)
553w
PK2 (39), AT2 (32), NO ROCK (12)
2
1
1
935
812
531w
AT2 (24), βCN2 (10)
ASDO2 (47), ASD2 (42)
AT2 (42), ATO2 (16)
AT1 (23), ATO2 (18), AT2 (13),
GCN1 (11), ATO1 (10)
ATO2 (54), AT2 (45)
ATO2 (52), AT2 (37)
ATO2 (42), AT2 (17), ASDO2 (10)
ATO2 (50), PK2 (28)
5
5
23vs
14vs
AS
2
1806
4
96w
23w
1
792vs
707vs
1770
762
1738
1
νCC1 (49), βCH1 (18)
νCC1 (50), βCH1 (12)
ASD2 (48), νCC2 (20), βCH2 (20)
βCHR1 (44), νCC1 (32)
ν CH (78)
4
422
1
4
3
08
86
1
1
697
641
377s
364
24
1620m
1625
612
AS
3
3
ASD2 (26), βCN1 (13), ASDO2 (12),
XCβCC2 (11)
ATO1 (23), AT2 (15)
AT2 (30), PK2 (21)
ASD2 (49), ASDO2 (22)
AT2 (54), ATO2 (19)
1
νASOCH (91)
3
1
609w
582vs
1553w
1607
1580
1574
βCHR1 (48), νCC1 (32)
2
2
73w
31w
293
241
1
νCC2 (32), βCHR2 (24), νCHR (15)
νCC2 (30), νCHR (19), βCH2 (14),
νCC1 (13)
210
163
143
1
537w
1559
ν NO (45), νCN (16), ν CO2 (15),
SS
2
SD
τCN1 (29), ASD2 (14)
AT2 (37), ATO2 (28)
νCHR (11), ν NO (10)
AS
2
121vvs
114
1547
1527
1510
ν CH (86), ν NO (13)
SD
3
AS
2
6
6
2
ATO2 (27), AT2 (27), τNO (24)
2
νCC2 (55), νCC1 (28)
νCC1 (44), νCC2 (30)
βCHR2 (74)
5
βCNC (21), βCN2 (15), τCN2 (13),
τCH (10)
ATO (26), ATO2 (22)
1
445s
1452
1412
1397
1320
45
28
24
20
1
398s 1399w
325w
434w
βCHR1 (43), νCC1 (12)
ASD2 (45), TD2 (17), νCN (15)
TD2 (33), ASD2 (24), νCC (15), νCC2
τCH (41), τNO (18)
2
1
τCH (44), GCC2 (17), PK2 (14)
3
1
τCH (27), τCH (23), GCC2 (15)
3
(11)

Vol. 32, No. 5 (2020)
Spectral and DFT Studies of Crystal Growth of 4-Methyl-(2-nitrobenzylidene)aniline 1053
(a)
(b)
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
1500
1000
500
–1
–1
Wavenumber (cm )
Wavenumber (cm )
Fig. 4. Experimental and stimulated FT-IR (a) and FT-Raman (b) spectra of MNBA compound
-
1
mode was observed at 3060 cm and the scaled value was at
3
changes in the intensity of IR spectrum. This indicates that
the hydrogen atoms of methyl group were directly involved in
donation of electronic change. Thus, hyperconjugation and
back donation of methyl group with the aromatic ring system
caused a changes in the intensity of IR spectrum clearly indicates
that methyl hydrogens were directly involved in the donation
of electronic change [31]. Methyl group yields to the strengt-
hening of C-H bond which is clearly seen in the experimental
value of C-H bond length (Table-4). The methyl group′s out-
-1
061 cm . These modes were generally pure and their contri-
butions are calculated as 99 % PED. Therewere six C-C stretching
vibrations (8a, 8b, 19a, 19b and 14) and considered as more
substituent dependent. The expected range of degenerate mode
a of ortho-disubstituted ring was 1609-1565 cm and 8b
extends from 1625-1586 cm with 8a smaller than 8b. Mode
-1
8
-1
-1
8
b was observed as strong band in Raman at 1792 cm and in
-1
addition strong band at 1707 cm in Raman is assigned to
mode 8a, which is coupled with C-H bending mode. Blue shift
of phenyl ring C-C stretching mode is due to steric interaction
that induces effective conjugation and charge carrier localization
resulting in phenyl ring twisting. Mode 19a was observed as
-1
of-plane bending mode was expected near 1460 cm and the
methyl group out-mode was coupled with CH in-plane bending
mode and observed as off-plane bending as a strong band at
3
-1
1445 cm in IR spectrum with major PED contribution of 99
%. Torsions and other modes are aslo shown in Table-4.
Azomethine vibrations: The C-H stretching vibrations
-1
strong band at 1582 cm in IR spectrum. This was coupled with
C-H bending mode. Mode 19b mode appeared as a weak band
-1
-1
at 1553 cm . In these vibrations, there was considerable per-
centage of C-H bend character. This arises as the hydrogen
and carbon move oppositely during C-C stretching. The increased
in intensities of these bands can be contributed to the methyl
substituent having electron-donor properties.
Another important ring mode is the in-plane C-H bending.
The small amount of C-C stretch interaction associated with
this mode usually appears in the region 1300-1100 cm . In
were observed in the region 3100-3000 cm and these vibra-
tions were not affected by the nature and position of substituent.
In MNBA, the symmetric stretching vibrations were observed
-1
-1
at 3061 cm in FT-IR and 3060 cm in FT-Raman. The C-N
stretching vibration was strongly spilt into an asymmetric and
a symmetric component. C-N stretching vibration of aromatic
-1
rings was observed at 1162cm in Raman spectrum.A downshift
of this vibration was a resonance structure of ortho-disubsti-
tuted benzaldehyde.
-1
-1
IR, weak band was observed at 1224 cm and in Raman, a strong
-
1
band was observed at 1279 cm correspond to this vibration.
Normal mode was active in IR as a weak intense band at 1224
The C=N stretching mode helps in the evaluation of bon-
ding configuration around amino N atom and the electronic
distribution of aromatic amine compounds. C=N stretching is
-1
-1
cm and as a strong band in Raman spectrum at 1126 cm . The
C-H out-of-plane bending vibrations were generally observed
in the region 1000-675 cm . These modes were designated as
-1
generally expected in the region 1670-1600 cm , but in MNBA
-1
-1
molecule, C=N stretching band was observed at 1610 cm .
gauche in internal coordinates definition. They were identified
Charge transfer interaction between the donor and acceptor
through -C=N-C skeleton causes downward shift of C=N stret-
ching frequency.
-1
as medium IR bands at 929 cm and as weak Raman bands at
-1
7
51, 835 and 956 cm .
Methyl vibrations: Methyl group contributes significantly
NO
2
Vibrations: A NO group was involved in the intra-
2
to the vibrational spectra of MNBA molecule. A downshift
caused by electronic effects in symmetric and asymmetric stret-
ching modes of methyl group attached to benzene ring was
molecular charge-transfer, intermolecular hydrogen bond and
dipole-dipole interactions. In aromatic nitro compounds, asym-
metric and symmetric vibrations of NO group gives rise to
2
-1
-1
expected near 2925 and 2865 cm , respectively. The weak
strong bands at 1550-1510 and 1365-1335 cm , respectively
-1
-1
band in Raman spectrum at 2968 cm was due to symmetric
stretching mode. This can direct to changing polarizability
and dipole moment due to electron delocalization, causing
[32]. A very strong band observed at 1582 cm which had
been assigned to the NO
2
asymmetric stretching vibration.
Intensity enhancement of these wavenumbers is due to the conju-

1
054 Mini et al.
Asian J. Chem.
gation with the aromatic ring [33]. Hence symmetric stretching
mode was observed as a strong band in IR spectrum at 1792
Signals of aromatic protons H
benzaldehyde moiety appeared in the range δ 7.7-8.2 ppm. H
and H proton signals appeared as doublets at δ 8.11 ppm and
δ 8.19 ppm, respectively. Similarly, H and H protons signals
5
, H
6
, H
7
and H
8
of 2-nitro-
5
-1
cm . A wagging mode, which is expected to occur at 740.50
6
-1
-1
cm was scaled at 807 cm .
A NO deformation vibration modes include scissoring,
rocking and wagging which usually occur at wavenumber below
7
8
2
appeared as triplets at δ 7.75 ppm and δ 7.85 ppm, respectively.
Solvent DMSO-d
6
peak appeared as a sharp signal at δ2.51 ppm.
-
1
13
13
9
7
00 cm [31]. Bands observed in IR as weak bands at 835,
C NMR analysis: C spectrum of MNBA compound is
-1
51 and 553 cm were assigned for in-plane bending defor-
group, respec-
stretching mode of aromatic nitro com-
shown in Fig. 6, where the appearance of fourteen distinct carbon
signals in the spectrum unambiguously confirmed the structure
of MNBA crystal. Methyl group carbon C14 signal appeared
at δ 24.55 ppm in the most up field region due to its +1 effect.
In this spectrum, a peak at δ155.59 ppm in the downfield region
pinpoints the existence of azomethine carbon C1. Aromatic
carbons gave a signal in overlapped areas of the spectrum with
chemical shift values from δ 100 to 150 ppm [34,35]. Carbon
mation modes, scissoring and rocking of NO
tively. Usually, C-NO
pounds is observed at 860-840 cm [31]. In MNBA compound,
2
2
-1
-1
C-N stretching was observed as a strong band at 862 cm .
NMR analysis: H & C NMR spectrum were recorded
by using DMSO-d and are presented in Table-5. H NMR
1
13
1
6
spectrum of MNBA compound displays eight signals, which
clearly proves the presence of eight different protons (Fig. 5).A
sharp singlet signal at δ 8.87 ppm was assigned for azomethine
proton, which obviously confirmed the formation of Schiff base
between 4-methylaniline and 2-nitrobenzaldehyde. In Fig. 5,
a sharp signal at δ 2.338 ppm with an integration equivalent to
three hydrogens corresponding to three methyl protons in the
compound. Protons labeled 2 and 3 exhibited signals at δ 7.26
ppm and δ 7.21 ppm. In fact, there were two sets of equivalent
protons present in ortho to nitro group (position 2) and meta
to nitro group (position 3). These signals do split into doublet
signals which were attached with azomethine nitrogen C
8
and
nitro group C appeared at deshielded region due to its attach-
3
ment with electron withdrawing nitrogen. The signals were seen
at δ 149.17 ppm and δ 148.13 ppm, respectively. Carbon signals
at δ 133.63 ppm and δ 131.62 ppm were assigned to carbons
C
6
, C which were geometrically present at the para-position
5
to the nitro group and azomethine linkage, respectively. In
Fig. 6, two high intensity signals were observed at δ 130.17
and δ 130.04 ppm due to carbon C10 and C12, which were ortho
to the methyl group in the 4-methylaniline moiety. Signal at δ
by the neighbouring protons. Compared to H
signals, H signal is upfield than H . Because H
3
and H
2
proton
121.11 ppm was assigned for carbons C and C13. The other
9
2
3
2
protons were
signals appeared in the shielded region were assigned for carbons
geometrically ortho to the methyl group in 4-methylaniline
moiety.
of 2-nitrobenzaldehyde moiety. Signals at δ 129.79, δ 129.39
and δ124.44 ppm were due to carbons C
7
, C
2
and C , respectively.
4
TABLE-5
1
13
OBSERVED AND PREDICTED ( H AND C) NMR ISOTROPIC
CHEMICAL SHIFTS OF SYNTHESIZED MNBA COMPOUND
7
6
4
1
3
1
C NMR
C1
Theor.
172
155
171
147
152
157
149
166
154
151
164
151
135
39
Exper.
155
131
149
–
H NMR
H19
H20
H21
H22
H23
H24
H25
H26
H27
H28
H29
H30
–
Theor.
Exper.
1
1
0
9
2
HC
5
8
8
8
8
8
8
7
7
7
2
2
3
–
–
11
9
8
8
9
8
8
8
8
2
3
3
–
–
11
H C
N
3
C2
C3
C4
C5
C6
C7
C12
C13
C14
C15
C16
C17
C18
3
8
1
4
2
O N
1
2
13
129
133
129
136
130
129
148
130
39
2
00 180 160 140 120 100 80
60
40
20
0 ppm
13
Fig. 6. C NMR spectrum of synthesized MNBA compound
29
–
UV-visible analysis: An optical absorption spectrum of
MNBA compound was recorded in the region 200-800 nm using
methanol as solvent (Fig. 7).An excitation energy and oscillator
strength for MNBA compound are listed in Table-6. UV-visible
spectrum of MNBA exhibited an absorption band at 440 nm,
and this may be attributed to π-π* and n-π* transitions taking
5
8
2
2
3
3
4
HC
7
H
3
C
N
6
1
2
O N
place within -C=N and NO
2
groups. Brown colour of the crystal
was mainly due to the presence of chromophore -NO
2
.
Frontier molecular orbital analysis:Total energy, energy
gap and dipole moment affect the stability of the molecule. The
conjugated molecules are characterized by highest occupied
molecular orbital (HOMO) and lowest-lying unoccupied orbital
1
0
9
8
7
6
5
4
3
2
1
0 ppm
1
Fig. 5. H NMR spectrum of synthesized MNBA compound

Vol. 32, No. 5 (2020)
Spectral and DFT Studies of Crystal Growth of 4-Methyl-(2-nitrobenzylidene)aniline 1055
TABLE-6
UV-VISIBLE EXCITATION ENERGY AND OSCILLATOR STRENGTH OF SYNTHESIZED MNBA COMPOUND
Wavelength (nm)
-
1
Energy (cm )
Oscillator strength
Symmetry
Major contributes
HOMO → LUMO (99 %)
H-2 → LUMO (91 %)
H-1 → LUMO (98 %)
H-5 → LUMO (73 %); H-2 → L+1 (18 %)
HOMO → L+1 (86 %)
H-3 → LUMO (85 %)
Cal
426
377
334
316
316
300
Exp
440
–
–
–
23446
26522
29850
31551
31636
33251
0.3768
0.0002
0.0057
0.0001
0.4412
0.0876
Singlet-A
Singlet-A
Singlet-A
Singlet-A
Singlet-A
Singlet-A
–
–
(
LUMO) separation. This arises due to significant degree of
1
0
0
0
0
.0
.8
.6
.4
.2
0
inter/intra molecular charge transfer from the electron-donor
to the efficient electron acceptor group through π-conjugated
path. HOMO-LUMO plot of MNBA molecule is shown in
Fig. 8 from which, it could be inferred that HOMO of π- nature
is mainly delocalized over the aromatic C=C part of 4-methyl-
aniline and 2-nitrobenzaldehyde moieties and CH
(
spread over the C=C part, NO (pull) group of 2-nitrobenzal-
dehyde moiety only. HOMO→LUMO transition implies that
an electron density was transferred from aromatic ring of the
3
group
push) and imine linkage. In LUMO, an electron density was
2
4
-methylaniline moiety to nitro group of 2-nitrobenzaldehyde
moiety through the single-double bond path in the conjugated
bridge involved in push-pull mechanism. Calculated energy
values of HOMO and LUMO in gas phase were -6.7024 eV
and 4.11194 eV, respectively with energy gap 2.590 eV. HOMO
200
400
600
Wavelength (nm)
Fig. 7. UV-visible absorbance spectrum of synthesized MNBA compound
800
1000
3.1320 eV
5.1399 eV
6.7029 eV
Fig. 8. HOMO LUMO orbitals of MNBA molecule (A), HOMO (B), LUMO (C), HOMO-1 (D), LUMO+1 (E), HOMO-2 and (F) LUMO+2

1
056 Mini et al.
Asian J. Chem.
2
.5
.0
.5
.0
.5
0
DOS spectrum
Occupied orbitals
Virtual orbitals
Methyl group
NO group
2
DOS
PDOS
Ring fragment
2
1
1
0
Azomethine group
Occupied orbitals
Virtual orbitals
COOP
Total (methyl group and NO
2
group)
Methyl group and ring fragment
Methyl group and azomethine group
NO
NO
2
group and ring fragment
2
group and azomethine group
-
0.5
1.0
Ring fragment and azomethine group
-
-20
-15
-10
Energy (eV)
-5
0
-20
-15
-10
Energy (eV)
-5
0
-20
-15
-10
-5
0
Energy (eV)
Fig. 9. DOS, PDOS and COOP diagrams of MNBA molecule
2
6H
→
LUMO transition implies an electron density transfer from
the highly aromatic part of π-conjugated system to the electron
2
7H
9
O
10O
1
9H
30H 29H
withdrawing NO group. Energy gap between HOMO and LUMO
2
8
N
2
0H
determines the kinetic stability, chemical activity, optical polari-
zability and chemical hardness-softness of the molecule. More-
over, lower HOMO and LUMO energy gap explains the eventual
charge transfer interaction taking place within the system.
Global reactivity descriptors: The global chemical react-
ivity descriptors of molecules such as hardness (η), chemical
potential (µ), softness (S), electronegativity (χ), electrophilicity
index (ω) can be determined using HOMO and LUMO energy
values and additional electronic charge ∆Nmax have been defined
1
6C
1
7C
12C
3C
C1
15C
1
8C
11N
C3
C4
C5
C2
14C
1
28H
2
1H
C7
C6
2
3H
2
5H
24H
2
2H
Fig. 10. Mulliken charge distribution of MNBA molecule
[
36]. Calculated values are shown in Table-7. Group contri-
butions to the density of state (DOS) are given in Fig. 9. When
there is a large HOMO-LUMO gap, the molecule is a hard
molecule and when the energy gap is small then it is a soft
molecule. Stability of molecule and hardness can be related
such that the molecule with least HOMO-LUMO gap is more
reactive and less stable.
0
.15
0.10
0.05
0
-
0.05
0.10
0.15
0.20
0.25
TABLE-7
CALCULATED ENERGIES VALUES OF
SYNTHESIZED MNBA MOLECULE
-
-
EHOMO
ELUMO
EHOMO-ELUMO
-6.7024 eV
4.11194 eV
2.590 eV
-6.7024
4.11194
-5.4071
1.2952
-
Ionisation potential (I)
Electron affinity (A)
Hardness (η)
11N
-
Atoms
Fig. 11. Mulliken charge distribution for MNBA molecule
Chemical potential (µ)
Softness (ζ)
2.7035
5.1809
0.1551
0.2395
on carbon atoms C11, C8, C1, C2 and C3 is a clear evidence
for intramolecular charge transfer (ICT), and it indicates the
direction of charge transfer from donor moiety 4-methylaniline
to acceptor 2-nitrobenzaldehyde through C1=N2 path. Negative
charge on atom C14 indicates its ionic nature. Negative charges
on other phenyl ring carbon atoms show its conjugation. All
hydrogen atoms of MNBA molecule have positive values (Table-
Electronegativity (χ)
Eletrophilicity index (ω)
Additional electronic charge ∆Nmax
Charge analysis
Atomic charge analysis:A charge distribution of MNBA
molecule is shown in Fig. 10, while its histogram is given in
Fig. 11. Charge distribution within various part of MNBA mole-
cule was calculated in order to understand the reactivity site.
Charge analysis revealed that the presence of two electronegative
oxygen atoms imposes large positive charge on the nitrogen
atom N8 of the nitro group. But atom N11 has highest negative
value due to its utmost contribution towards charge delocali-
zation which clearly spells out that the intramolecular charge
transfer occurred through this nitrogen atom. Positive charge
8
).Among these, atoms H19 and H20 showed highest positive
value due to the highest contribution towards delocalization
and their values are equal to 0.10 eV.
Electrostatic potential analysis: Electrophilic reactivity
is indicated by red, orange and yellow regions in the MEP map
(
Fig. 12). Maximum negative region is localized over nitro
group, methyl-substituted phenyl ring and the nitrogen atom
in the C=N group oxygen while the maximum positive region
is localized on CH group and C-H bonds indicating a possible
3

Vol. 32, No. 5 (2020)
Spectral and DFT Studies of Crystal Growth of 4-Methyl-(2-nitrobenzylidene)aniline 1057
TABLE-9
TABLE-8
NATURAL CHARGES OF SYNTHESIZED MNBA MOLECULE
ANTIMICROBIAL ACTIVITY OF
SYNTHESIZED MNBA COMPOUND
Atoms
C1
C2
C3
C4
C5
C6
C7
N8
Charge
1.4782
1.2816
1.0901
1.4105
1.4068
1.396
1.4736
1.3896
1.0825
1.3983
1.0851
1.3893
1.0857
1.0839
1.4064
Atoms
C16
C17
C18
H19
H20
H21
H22
H23
H24
H25
H26
H27
H28
H29
H30
Charge
1.2303
1.2333
1.405
1.4047
1.3893
1.0854
1.4039
1.0873
1.4004
1.5098
1.3932
1.087
Microorganism
Zone of inhibition (mm)
Salmonella paratyphi
Klebsiella pneumoniae
Staphylococcus aureus
Streptococcus pyogenes
Shigella sp.
17
15
15
16
14
Auto-docking analysis: Fig. 13 shows a different inhibitor-
residue interaction using molecular docking. In molecular
docking of protein-ligands residue interaction, energy for the
selected proteins are 1BB6, 1CX2, 4ENX and 3VQ7. Binding
energies (kcal/mol), bond distances (Å), Reference RMSD (Å)
and inhibition constants (M) had also obtained and tabulated
in Table-10. Protein-ligands interaction energies of four common
residues have a lowest binding energy among these 4ENX
had very low binding energy (-4.69 kcal/mol) which was binded
with N-H and N-O moieties. This result showed that 4ENX
has been the ligand for all the conformations to evaluate the
suitability relationship with its antibacterial activity.
N9
O10
O11
C12
C13
C14
C15
1.0857
1.096
1.0964
Fig. 12. MEP of MNBA molecule
site for nucleophilic attack. In most of MEPs, red colour indicates
the maximum negative region, which was the preferred site
for electrophilic attack. So, an approaching electrophile gets
attracted to highly negative regions, where electron distribution
effect was dominant. From MEP, it is evident that C=O groups
has negative charge and the rings and NH group had positive
charge.
1bb6
1cx2
Antimicrobial activity: 4-Methyl-(2-nitrobenzylidene)aniline
was also tested for its antimicrobial activity against human
pathogens of clinical isolates (Salmonella paratyphi, Shigella
sp., Staphylococcus aureus, Streptococcus pyogenesand Klebsiella
pneumonia). It showed a maximum zone of inhibition of 17 mm
exhibited by Salmonella paratyphi (Table-9). The least diameter
of zone of inhibition 14 mm was showed by Shigella sp.
4enx
3vq7
Fig. 13. MNBA molecule docked into the binding site of 1BB6, 1CX2,
ENX and 3VQ7
4
TABLE-10
HYDROGEN BONDING AND MOLECULAR DOCKING RESULTS OF
VARIOUS PROTEIN TARGETS WITH SYNTHESIZED MNBA COMPOUND
Number of
hydrogen bond
Bond distance
(Å)
Estimated inhibition
constant (µM)
Binding energy
(kcal/mol)
Reference
RMSD (Å)
45.96
Protein (PDB ID)
bb6
Bonded residues
1
TRP
ASN
GLU
ALA
ASP
ARG
ARG
HIS
1
3
3.0
2.6
2.0
2.4
2.1
2.2
1.9
1.9
1.6
99.29
-5.46
1
cx2
enx
13.24
-6.65
27.9
4
2
3
362.1
29.2
-4.69
-6.19
36.91
31.34
3vq7
LYS

1
058 Mini et al.
Asian J. Chem.
1
4. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark,
J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B.
Cross,V. Bakken, C.Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann,
O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L.
Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J.
Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman, J.V.
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https://doi.org/10.1016/0022-2860(90)80287-T
6. T. Sundius, Vib. Spectrosc., 29, 89 (2002);
https://doi.org/10.1016/S0924-2031(01)00189-8
7. P. Pulay, Mol. Phys.: An Int. J. Interf. Between Chem. Phys., 17, 197 (1969);
https://doi.org/10.1080/00268976900100941
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Conclusion
A grown compound 4-methyl-(2-nitrobenzylidene)aniline
MNBA) was optimized using DFT (B3LYP) method with 6-
(
3
11 G(d,p) basis sets. Bond length values of N1-O1 and N1-
O2 lie between N-O single and N=O double bond length values,
indicating electron delocalization within NO group. The π-
2
electron transfer from the electron donor to acceptor can make
the molecule highly polarized. From NBO results, it was clear
that pure p-type lone pair orbital participating in electron
donation was very close to σ*(N-C) orbital for n(O)→σ*(N-C),
interactions in MNBA molecule.A C-C stretching bands inten-
sities increases due to the methyl group substituent having
electron-donor properties. Downward shifting of C=N stret-
ching frequency was due to charge transfer interaction between
the donor and acceptor through -C=N-C skeleton. A 4ENX
protein truly reflects the features of MNBA inhibitors and this
can be used as fast and accurate tool to assist discovery of novel
antibacterial activity.
1
1
1
1
https://doi.org/10.1021/ja00362a005
1
2
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0. M. Petersilka, U.J. Gossmann and E.K.U. Gross, Phys. Rev. Lett., 76,
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
1212 (1996);
https://doi.org/10.1103/PhysRevLett.76.1212
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