Assessment of conformational, spectral, antimicrobial activity, chemical reactivity and NLO application of Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydrazone)

Article abstract of DOI:10.1016/j.saa.2014.12.080

An orange colored pyrrole dihydrazone: Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydrazone) (PDBO) has been synthesized by reaction of oxalic acid dihydrazide with 2,5 diformyl-1H-pyrrole and has been characterized by spectroscopic analysis (¹H, ¹³C NMR, UV-visible, FT-IR and DART Mass). The properties of the compound has been evaluated using B3LYP functional and 6-31G(d,p)/6-311+G(d,p) basis set. The symmetric (3319, 3320 cm^-1) and asymmetric (3389, 3382 cm^-1) stretching wave number confirm free NH₂ groups in PDBO. NBO analysis shows, inter/intra molecular interactions within the molecule. Topological parameters have been analyzed by QTAIM theory and provide the existence of intramolecular hydrogen bonding (N-H?O). The local reactivity descriptors analyses determine the reactive sites within molecule. The calculated first hyperpolarizability value (β₀ = 23.83 × 10^-30 esu) of pyrrole dihydrazone shows its suitability for non-linear optical (NLO) response. The preliminary bioassay suggested that the PDBO exhibits relatively good antibacterial and fungicidal activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pyogenes, Candida albicans, Aspergillus niger. The local reactivity descriptors - Fukui functions (f_k⁺, f_k^-), local softnesses (s_k⁺, s_k^-) and electrophilicity indices (ω_k⁺, ω_k^-) analyses have been used to determine the reactive sites within molecule.

Full text of DOI:10.1016/j.saa.2014.12.080

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Assessment of conformational, spectral, antimicrobial activity,
chemical reactivity and NLO application of Pyrrole-2,5-dicarboxaldehyde
bis(oxaloyldihydrazone)
⇑
Poonam Rawat, R.N. Singh
Department of Chemistry, University of Lucknow, Lucknow 226007, U.P., India
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
ꢀ
ꢀ
Solid state FT-IR spectrum
characterization of PDBO.
Experimental and calculated
spectroscopic analysis confirm the
formation of product.
ꢀ
ꢀ
The calculated first
0
hyperpolarizability (b ) value of PDBO
ꢂ30
is 23.83 ꢁ 10
esu.
Antimicrobial efficiency of PDBO was
analyzed by ‘‘Disc Diffusion Assay’’.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2014
Received in revised form 15 December 2014
Accepted 17 December 2014
Available online 25 December 2014
An orange colored pyrrole dihydrazone: Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydrazone) (PDBO)
has been synthesized by reaction of oxalic acid dihydrazide with 2,5 diformyl-1H-pyrrole and has been
1
13
characterized by spectroscopic analysis ( H, C NMR, UV–visible, FT-IR and DART Mass). The properties
of the compound has been evaluated using B3LYP functional and 6-31G(d,p)/6-311+G(d,p) basis set. The
ꢂ1
ꢂ1
symmetric (3319, 3320 cm ) and asymmetric (3389, 3382 cm ) stretching wave number confirm free
NH groups in PDBO. NBO analysis shows, inter/intra molecular interactions within the molecule. Topo-
2
Keywords:
Hydrogen bond
NBO analysis
QTAIM calculation
Reactivity descriptors
logical parameters have been analyzed by QTAIM theory and provide the existence of intramolecular
hydrogen bonding (N–Hꢃ ꢃ ꢃO). The local reactivity descriptors analyses determine the reactive sites within
ꢂ30
molecule. The calculated first hyperpolarizability value (b
0
= 23.83 ꢁ 10
esu) of pyrrole dihydrazone
shows its suitability for non-linear optical (NLO) response. The preliminary bioassay suggested that
the PDBO exhibits relatively good antibacterial and fungicidal activity against Escherichia coli, Pseudomo-
nas aeruginosa, Staphylococcus aureus, Streptococcus pyogenes, Candida albicans, Aspergillus niger. The local
+
ꢂ
+
ꢂ
+
reactivity descriptors – Fukui functions (f
k
, f
k
), local softnesses (s
k
, s
k
) and electrophilicity indices (
) analyses have been used to determine the reactive sites within molecule.
x
k
,
ꢂ
x
k
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
enzymes [1] and development of novel functional materials show-
ing molecular ferromagnetism [2] and specific catalytic properties
[3]. Heteroatoms influence various properties of material and their
applications [4–6].
Mono- and bishydrazones find wide application in medicine as
active physiological preparations, due to their antibacterial, tuber-
culostatic, fungicidal properties as well as activities against certain
types of cancers. The dihydrazones are capable of giving rise to
The chemistry of polyfunctional metal complexes has become a
fascinating area of research in contemporary coordination chemis-
try following the discovery of multinuclear sites in several
⇑
Corresponding author. Tel.: +91 9451308205.
E-mail address: rnsvk.chemistry@gmail.com (R.N. Singh).
http://dx.doi.org/10.1016/j.saa.2014.12.080
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
345
monometallic [7], homobimetallic [8] and heterobimetallic [9]
complexes. Bis-acylhydrazones and their metal complexes have
attracted great and growing interest due to chemical properties,
therapeutic activity, biological significance, industrial importance
and structural variety and Fe overload disease. They have also been
used as fluorescent materials, pigments, analytical reagents and
polymer-coating [10]. Bis-acylhydrazones held a special place in
the field of hydrazone chemistry [11] due to (i) the presence of
two coordinating unit in these ligands may yield supramolecular
architectures or better coordinative properties than those a sole
coordinative unit, (ii) a ditopic ligand enables the properties of
its complexes to be modulated by the degree of deprotonation,
and (iii) Metal complexes of dihydrazones may be able to mimic
bimetallic sites in various enzymes. The biocidal properties of
dihydrazones dependent on the organic group and the ligand
attached to metal [11].
plates pre-coated with silica gel (Kieselgel 60 F256, 0.2 mm,
Merck). The product was separated by column chromatography
on silica using hexane and ethylacetate as eluent. Thus pure orange
color product was obtained along with other side products. Yield:
60.41%, Melting point: decompose above 243 °C. UV–visible
ꢂ5
ꢂ3
(DMSO, c = 10 mol dm ): Elemental Analysis: for C10
13 9 4
H N O
calcd. C, 37.15; H, 4.05; N, 39.00; Obs. C, 37.45; H, 4.09; N, 39.08;
MS (DART) for C10
(M+H ).
H
13
N
9
O
4
: calcd. m/z = 323.10, obs. m/z = 324.20
+
Synthesis of macrocyclic bis-hydrazone of pyrrole (6)
The reaction mixture of 2,5 diformyl–1H–pyrrole (0.100 g,
1
.219 mmol) and oxalic acid dihydrazide (0.0498 g, 1.219 mmol)
in ratio 1:1 were taken in methanol with small amount of conc.
HCl. The reaction was refluxed for eight hour, orange color precip-
itate was obtained. Color: Orange, Yield: 58%. Solubility: Poor sol-
Previously, wide series of hydrazones of 2-formylpyrrole have
been synthesized and studied [12–15], while the data on bis-
hydrazones of 2,5-diformylpyrrole are extremely rare [16–18].
However, less attention has been paid to synthesis, metal com-
plexes or organometallic complexes with diacylhydrazones as
multidentate ligands of diformyl pyrrole [19].
1
ubility in organic solvents. Elemental analysis, H NMR and Mass
spectra of the formed macrocyclic bis-hydrazone (6) are reported
as: Elemental analysis for C16
H
14
N
10
1
O
4
calc. C, 46.83; H, 3.44; N,
3
4.13; obs. C 46.79, H 3.41, N 34.13. H NMR (300 MHz, DMSO–d6):
Organic materials are molecular materials that consist of chem-
ically bonded molecular units interacting in the bulk media
through weak van-der Waal interactions and possess ease of fabri-
cation and integration into devices, relatively low cost, fast
response, intrinsic tailorability which is responsible for NLO prop-
erties [20,21]. NLO materials have gained attention in recent years
with respect to their future potential applications in the field of
optoelectronic such as optical communication, optical computing,
optical switching and dynamic image processing [22]. The vibra-
tional spectral studies of the molecule can provide deeper knowl-
edge about the relationships between molecular architecture,
nonlinear response and hyperpolarizability.
As per literature survey synthesis and study on pyrrole dihyd-
razones of oxalic acid hydrazide were not found reported. The
interest, therefore, arouse in this work. The objectives of the pres-
ent investigation are synthesis, structural elucidation, spectral
characterization, evaluation of NLO properties and chemical reac-
tivity. In addition to this antimicrobial activity of PDBO has also
been evaluated against antibacterial (Escherichia coli, Pseudomonas
aeruginosa, Staphylococcus aureus, Streptococcus pyogenes) and fun-
gal (Candida albicans, Aspergillus niger) species. In this study molec-
ular parameters have been computed using B3LYP functional and
d 11.623 (s, 2H, pyrrolic NH), 11.049 (s, 4H, hydrazone-NH), 8.884
s, 4H, azomethine CH@NA), 6.396–6.369 (4H, pyrrolic ring
CH). The MS for C16 calc. 410.12 amu, found m/z 411
(
14 10 4
H N O
+
[
M+H ].
Quantum chemical calculations
The structure of the compound was drawn on Chemdraw ultra
D software and the quantum chemical calculations were carried
3
out with Gaussian 03 program package [25] to predict the molec-
1
ular structure, H NMR chemical shifts, vibrational wavenumbers
and energies of the optimized structures using DFT(B3LYP) method
and 6-31G(d,p), B3LYP/6-311+G(d,p) basis set [26,27]. All the
molecular structures are visualized using software Gauss-view
[
[
28]. Internal coordinate system recommended by Pulay et al.
29] is used for the assignment of vibrational modes. Potential
energy distribution along internal coordinates is calculated by
Gar2ped software [30]. The topological properties at the BCPs have
been calculated by using the Bader’s theory of ‘Atoms in Molecules
(
AIM), implemented in AIM 2000 software [31].
6
-311+G(d,p) basis set. This method predicts relatively accurate
molecular structure with moderate computational effort. The cal-
culated FT-IR spectrum was analyzed on the basis of the potential
energy distribution (PED) of each vibrational mode, which allowed
obtaining a quantitative as well as qualitative interpretation of the
infrared spectrum. In addition to this, weaker interactions and
intramolecular charge transfer has been studied with the help of
Quantum theory of Atoms in Molecules (QTAIM) [23] and Natural
bond analysis (NBO), respectively.
Evaluation of antimicrobial activity
The antimicrobial activity has been study with the help of disc
plate diffusion assay procedures. The compound (PDBO), reactant:
2,5-diformyl-1H-pyrrole and oxalic acid dihydrazide were dis-
solved in DMSO. Proper drug Chloramphenicol and Nystatin were
used as control. All compound and reactants were taken at concen-
tration of 100 and 200 lg/ml for testing antibacterial activity and
antifungal activity. The compounds diffused into the medium pro-
duced a concentration gradient. After the incubation period, the
zones of inhibition were measured in mm. The tabulated results
represent the actual readings control. The compound was tested
against E. coli, P. aeruginosa (gram negative bacteria), S. aureus,
S. pyogenes (gram positive bacteria), C. albicans and A. niger (fungi).
The plates were placed in an incubator at 37 °C within 30 min of
preparation for bacteria and 22 °C for fungal. After 48 h incubation
for bacteria and 7-days for fungal, the diameter of zone (including
the diameter disc) was measured and recorded in mm. The mea-
surements were taken with a ruler, from the bottom of the plate,
without opening the lid.
Experimental details
Synthesis of Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydrazone)
(
5 = PDBO)
2
,5-diformyl-1H-pyrrole [24] (0.1000 gm, 0.47 mmol) and oxa-
lic acid dihydrazide (0.1110 gm, 0.94 mmol) were dissolved in
methanol and water by ( /v = 1/3) solution. The above mixture
v
was allowed to stir for 4 h. The color of the solution changes to
orange and completion of reaction was analyzed using thin layer
chromatography (TLC). TLC analysis was carried out using glass

3
46
P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Result and discussion
Conformational and topological analysis
Depending on ratio of reactants 2,5-diformyl-1H-pyrrole (4)
and oxalic acid dihydrazide (3) as well as used solvents and reac-
tion conditions, the products such as Pyrrole-2,5-dicarboxaldehyde
bis(oxaloyldihydrazone), macrocycle and polymeric products were
formed [18]. The general route for synthesis of PDBO (5) and (6) are
shown in Supplementary Scheme S1. When 2,5-diformyl-1H-pyr-
role react with oxalic acid dihydrazide in a stoichiometric ratio of
The molecular geometry and conformational analysis plays a
very important role in determining the structure–activity relation-
ship [32]. The potential energies was determined by calculating the
variation in the total energy of the molecule with change in dihe-
dral angle
s (C3C2C8N9 and C4C5C6N7) at intervals of 10° by DFT/
6–31G(d,p) method. Two conformer I and II were obtained on
potential surface scan. The enolic conformer III was obtained by
moving N–H proton to oxygen atom. The enolic conformer III, gen-
erally predominates during metal complex formation. The lower
energy conformer corresponds to the most stable conformer I.
The enthalpy difference between conformer I and II is 0.855 kcal/
mol. In principle, the existence of stable compounds would corre-
spond to lower energy conformer. All three conformers are shown
in Fig. 1 and molecular graph of lower energy conformer I is shown
in Fig. 2. The symmetry observed in N1–C2 and N1–C5 bonds occur
due to identical substituents at 2- and 5-positions of pyrrole ring in
PDBO. As a result of symmetry in N1–C2 and N1–C5 bonds, delo-
calization of electron is seen in pyrrole ring and toward azome-
1
:2, compound Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydraz-
one) (5 = PDBO), is formed as major product along with (6) as
minor. The compound (5 = PDBO) was orange in color, stable and
stored at room temperature for longer period of time. The com-
pound decomposes above 243 °C without melting. If 2,5-difor-
myl-1H-pyrrole was reacted with oxalic acid dihydrazide in
stoichiometric ratio of 1:1, at higher temperature macrocyclic
bis-hydrazone (6) was obtained. The macrocyclic bis-hydrazone
(
6) has poor solubility in most of the organic solvents. Therefore,
the spectral analysis, biological activity and all quantum chemical
calculations have been performed on PDBO compound.
I
II
III
Fig. 1. Optimized geometries for conformers of PDBO.

P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
347
Fig. 2. Molecular graph of PDBO.
ꢂ1
thine carbon of PDBO. These effects are observed in quantum cal-
culation and single crystal structure of pyrrole derivatives [33–
it is calculated at 3482 cm [37]. In the experimental FT-IR spec-
trum, asymmetric and symmetric NH
2
stretching vibrations are
ꢂ1
3
4]. The presence of C@N, make PDBO to show E and Z stereoiso-
observed at 3382, 3320 cm , with very low intensity corresponds
ꢂ1
mers. The E-configuration is more stable than Z. Considering the
thermodynamic stability; E isomer is predominant in the mixture.
to theoretically calculated wavenumber at 3389, 3319 cm
respectively. A combined theoretical and experimental symmetric
,
ꢂ1
ꢂ1
The C@NANHA(C(@O))
2
ANHNH
2
frame is planar and has intra-
(3319, 3320 cm ) and asymmetric (3389, 3382 cm ) stretching
wave number analysis confirms free NH groups in the solid phase
scissoring is assigned at
molecular hydrogen bonding between oxygen of carbonyl group
and hydrogen of >C@NNH azomethine frame. Popov et al. [24] have
reported the crystal structure of pyrole diisoniazid hydrazone
showing the E configuration. The calculated optimized bond
lengths and bond angles of PDBO using DFT(B3LYP) methods at
2
of PDBO. The weak band of NH
2
ꢂ1
1580 cm
, corroborate well with the observed mode at
1639 cm in FT-IR spectrum. The observed NH
agrees well with the calculated wavenumber at
894 cm . The observed NH
ꢂ1
2
wagging mode
ꢂ1
at 855 cm
ꢂ1
ꢂ1
6
-31G(d,p) and 6-311+G(d,p) basis set are given in Supplementary
Tables S1 and Table S2. The bond length calculated by DFT at 6-
11+G(d,p) method are more closer with experimental values
17]. Molecular graph of PDBO using AIM program is shown in
2
rocking mode at 1298 cm agrees
ꢂ1
well with the calculated wavenumber at 1300 cm . The vibra-
tional analysis indicates the formation of intramolecular hydrogen
bonding (N–Hꢃ ꢃ ꢃO). A combined theoretical and experimental sym-
3
[
ꢂ1
ꢂ1
Fig. 1 and calculated topological parameters is given in Supple-
mentary Table S3. Topological parameters for bonds of interacting
atom is calculated at B3LYP/6-31G(d,p) method. The N–Hꢃ ꢃ ꢃO
metric (3386 cm ) and asymmetric (3458 cm ) stretching wave
2
number analysis confirms free NH groups in the solid phase of
PDBO. The absence of symmetric and asymmetric stretching vibra-
tions in (6) confirms the cyclic product formation that is macrocy-
clic bis-pyrrole hydrazone.
C–O Vibrations: The observed stretching vibration of carbonyl
) absorption band at 1645 cm agrees well with the
calculated wavenumber at 1703 cm which also closely correlates
interaction visualized in molecular graph is classified as weak
2
intramolecular hydrogen bond due to (
r
qBCP) > 0 and HBCP > 0.
According to AIM calculations, the classical intramolecular hydro-
gen bond (N–Hꢃ ꢃ ꢃO) energy is calculated as 5.1 kcal mol
ꢂ1
ꢂ1
.
group (
m
@
C O
ꢂ1
ꢂ1
with reported hydrogen bonded
m
C
@
O
vibration at 1665 cm for
Vibrational assignments
pyrrole-2-carbaldehyde isonicotinoyl hydrazone [36]. This stretch-
ing vibrational waveumber of carbonyl group again confirms the
formation of hydrogen bond (N–Hꢃ ꢃ ꢃO) by the involvement of
C@O group through intramolecular attraction.
C–N Vibrations: The observed C@N stretching vibration (
agrees well with the calculated wavenumber at
615 cm . In FT-IR spectrum, the presence of C@N band confirms
FT-IR spectroscopy is not only frequently used in the literature
for the identification of functional group but also used for identifi-
cation of weaker interaction present in the molecule. In the present
study experimental and theoretical data have been compared and
presences of weaker interactions have been identified. The experi-
mental and theoretical (selected) vibrational wavenumbers of
PDBO and their assignments using PED are given in Table 1. Calcu-
m
C
@
N
)
ꢂ1
at 1540 cm
ꢂ1
1
the formation of hydrazone linkage in PDBO and macrocyclic bis-
pyrrole hydrazone. The C–N stretches is assigned at 1237 cm
ꢂ1
ꢂ1
.
lated and experimental IR spectra in the region 4000–400 cm are
shown in Fig. 3. The calculated wavenumbers at B3LYP/6–31G(d,p)
level are scaled down using single scaling factor 0.9608 to discard
the anharmonicity present in real system [35]. The value of corre-
lation coefficient (r = 0.99) shows that there is good agreement
between experimental and calculated wavenumbers.
1
H NMR spectroscopy
2
Pyrrole-2,5-dicarboxaldehyde bis(oxaloyldihydrazone) (5 = PD
BO) and macrocyclic bis-hydrazone (6) product were obtained
depending on the amount of stoichiometric ratio, solvent and reac-
tion conditions. The experimental and calculated H and C NMR
chemical shifts (d in ppm) of PDBO are given in Table 2 and exper-
imental spectrum is shown in Supplementary Figs. S1 and S2,
respectively. The chemical shifts have been calculated by using
DFT (B3LYP) methods with 6-31G(d,p) and 6-311+G(d,p) basis
N–H Vibrations: In solid state experimental FT-IR spectrum,
1
13
the N–H stretching vibration of pyrrole (
m
N–H) is observed at
ꢂ1
ꢂ1
3
490 cm and calculated as 3502 cm in PDBO. The reported
ꢂ1
wavenumber of N–H stretching vibration at 3358 cm indicates
the involvement of N–H group in weaker bonding as seen in the
crystals of pyrrole-2-carbaldehyde isonicotinoyl hydrazone in KBr
ꢂ1
1
pellet [36]. The absence of N–H wagging mode at 772 cm con-
set, employing GIAO approach. The experimental H NMR spec-
forms free N–H group of pyrrole. The N–H stretch of hydrazide
trum of PDBO shows the presence of singlet at d 4.16 ppm for
two free NH protons. The calculated NH signal at d 9.766 ppm cor-
2
ꢂ1
(
CONHNH
2
) part of molecule is observed at 3480 cm , whereas

3
48
P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Table 1
Experimental and calculated vibrational wavenumbers of PDBO at B3LYP/6–31G(d,p) level and their assignments: Wavenumbers (mꢀ/cmꢂ1), Intensity (km mol ).
ꢂ1
m
ꢀ
m
ꢀ
Intensity
m
ꢀ
Assignment (PED P 5%)
Unsc
Scal
Obs
3645
3624
3528
3477
3477
3454
3268
3254
3076
3076
1808
1800
1773
1706
1681
1668
1604
1591
1567
1546
1538
1521
1466
1461
1378
1353
1331
1287
1287
1275
1240
1240
3502
3482 113.96
62.19
3490
3480
3382
m
m
m
m
m
m
m
m
m
m
m
m
m
d
(N1H24)(99)
(N15H30)(69)
as(NH )(90)
2
(N14H29)(53)
(N23H36)(53)-
m
(N21H23)(30)
(N23H36)(46)
3389
3341
3341
3319
3140
3126
2956
2955
1737 410.09
1729 134.09
1703 635.08
1639 100.16
1615 139.08
1.46
9.59
87.26
0.97
2.7
5.21
m
m
asN14H29)(46)
3320
2
(NH )(80)
(pyCH)(49)
m
(pyCH)(49)
as(pyCH)(50)
(C6H27)(36)-das(C2C9)(18)
(C6H27)(31)-das(C2C9)(20)
(C18N23)(36)- (C18N23)(6)-
(C18N23)(34)- (C@O)(34)- (C10N14)(5)
(C@O)(71)- (C17N21)(7)- (C11N15)(7)
sc(NH )(51) dsc(NH2)(39)
3015
2970
(pyCH)(50)-
m
14.61
84.11
(C8H28)(41)
m
(C8H28)(45)-
m
1690
1650
1645
1580
(C@O)(36)
m
m
m
m
m
m
(C10N14)(6)
(C18N23)(5)
m
m
2
1540 d(N23N9C8)(25)-
m
m
(C@N)(16)das(C2C9)(C2C9)(16)
(C@N)(18)das(C2C9)(17)- (C@N)(16)
(C@N)(11)- (C@N)(10)-d(C5H24N1)(8)d(C10H29N14)(5)d(N9H36N23)(5)
1479 d(N9H36N23)(13)-d(C10H29N14)(13)das(C2C9)(9) (C18N23)(5) (C10N14)(5)
1420 d(C10H29N14)(13) d(N9H36N23)(13)78(6)- (C10N14)(6) (C18N23)(6)-d(C18C17O20)(5)d(C18N23O20)(5)
(C11N15)(9)- (C17N21)(9)
(C17N21)(9) (C11N15)(9)
(C2C8)(8)+d(C10H29N14)(7)-d(N9H36N23)(7)
(N1C2)(22)-d(Pyring)(11)-d(C5H24N1)(10)- (C2C8)(9) (C2C3)(9)
(C2C8)(13)-d(N23N9C8)(11)- (N1C2)(10)- (N1C5)(10)
(C3C4)(25)-das(C2C9)(22)-d(N23N9C8)(10)
(NH )(99)
as(C2C9)(46)d(N23N9C8)(37) d(C5C6N7)(8)
m(C@N)(14)-m(C5C6)(6)
1603
1541
36.29
97.23
1532 d(N23N9C8)(27)-
m
m
(C6H27)(12)-
m
(C2C3)(12)
m
m
1528 164.34
1506 102.19
1485 248.54
1478 623.62
1462 160.72
1409 144.62
1404
1324
1300
1279
1237
1237
1225
m
m
m
m
1410
1390
q
q
m
m
m
m
q
d
q
q
(NH)(15)-
q
(NH
(NH
(C5C6)(8)+
(N1C5)(22)+
(C2C3)(13)
2
)(15)d(NH
2
)(9)-
m
m
(NH)(16)
q
2
)(16)-
m
m
(C3C4)(8)+
m
m
m
m
m
m
30.74
31.81
1.13
52.23
8.26
m
m
1355
1298
1279
2
(NH2)(16)-d(O13C11N15)(13) d(O13C11C10)(10)-
(NH)(16)-d(C@O)(14) (C@O)(11) (C17N21)(8) (NH2)(7)-d(O13C11N15)(5)
(C5H27N7C6)(6)
(C18N23)(8)-d(C18C17O20)(7)- (C10N14)(7)-d(N9H36N23)(7)-d(C10H29N14)(6)
(C10N14O12)(12)-d(C18N23O20)(11)- (C10N14)(8)d(C18C17O20)(7)- (C18N23)(7)-
m(C6-N7)(9)-q(NH)(7) d(C@O)(6)
33.28
97.98
1230
q
m
q
1205 d(C5H24N1)(33)-d(C@N)(11)- d(Pyring)(9)-d(Pyring)(9)das(C2C9)(8)
1168 d(C18N23O20)(11) d(O12C10C11)(10)-79(9)
1135 d(O12C10C11)(12)-
x
1192 146.27
1192
m
m
54.51
q
m
m
d(C10H29N14)(7)d(N9H36N23)(6)
1
1
1
1
1
1
1
1
1
1
9
9
9
9
8
8
8
8
7
7
7
6
6
6
5
5
5
4
4
226
191
182
112
112
073
042
037
010
008
57
55
31
31
51
49
15
05
91
66
01
78
31
16
49
28
12
98
19
1178
1144
1136
1068
1068
1031
1001
996
970
968
919
917
76.02
36.08
57.75
33.34
42.1
47.55
0.06
0.27
54.33
22.5
25.76
0
d(N23N9C8)(25) das(C2C9)(24)-d(Pyring)(7)-d(Pyring)(7) m(C5C6)(6)
m
m
m
m
(N9N23)(15)
(N7N14)(13)-
(N7N14)(19)-
m
m
m
m
(N7N14)(15)
(N9N23)(13)
(N9N23)(17) d(N14N7C6)(8)-d(N23N9C8)(7)d(C@N)(5)
(N7N14)(16)d(N23N9C8)(7)- (C17N21)(5)
m
m
(N21N22)(6)
(N15N16)(5)-
m
m
(N15N16)(6)d(N23N9C8)(5)das(C2C9)(5)
(N21N22)(5)- (C10N14)(5) (C18N23)(5)
m
m
(N9N23)(18)
m
1012 d(Pyring)(32)-das(C2C9)(Pyring)(32)
d(Pyring) (16)- (Pyring)(6)- as(Pyring) (6)-d(O12C10C11)(5)
(Pyring) (9)- (Pyring)(9)d(C5H24N1)(8) d(O12C10C11)(5)
986 d(Pyring)(13)- (NH )(6)- (NH )(6)- (N21N22)(5)- (N15N16)(5)d(C@O)(5)
d(Pyring)(9) (NH )(5)- (NH )(5) (N15N16)(5)- (N21N22)(5)
(C8H28C2N9)(35)- (H27C6C5N7)(34)- (C6N7)(12)
(C8H28C2N9)(33) (H27C6C5N7)(33)- (C8N9)(11)-
)(17) (N21N22)(14)
)(17) (N15N16)(14)-
m
m
m
m
x
2
x
2
m
m
x
2
x
2
m
m
x
x
x
x
x
x
s
s
s
s
(C8N9)(12)
(C6N7)(11)
894 128.17
894 161.98
855
843
(NH
(NH
2
)(19)
x
x
(NH
(NH
2
m
m
m(N15N16)(13)d(C18C17O20)(6) d(O12C10C11)(6)
2
)(20)-
2
m(N21N22)(13)d(O12C10C11)(7)-d(C18C17O20)(6)
817
816
783
773
760
736
674
34.46
20.66
34.04
1.58
72.39
3.2
d(O13C11C10)(16)-d(C@O)(16)-d(O12C10C11)(10) d(C18C17O20)(10)-d(O13C11N15)(8)-d(C18N23O20)(7)d(Pyring)(6)
d(O13C11C10)(17) d(C@O)(16)-d(O12C10C11)(11)-d(C18C17O20)(11)-d(O13C11N15)(8)d(C18N23O20)(8) (C10N14O12)(5)
d(Pyring)(20) das(C2C9)(19)-d(C@N)(18) (C5H27N7C6)(9) d(C18C17O20)(5)
d(N16C11N15)(27) (N21C17C18O19)(24) (C@O)(23) (C10N7N14H29)(21)
(Pyring)(38) (Pyring)(38)
d(C@N)(23)-das(C2C9)(17) (C5H27N7C6)(12)-d(Pyring)(10) -d(N23N9C8)(5)
(Pyring)(30)
(N15C16)(19)-
(Pyring)(20)
(N21C17)(27)
(C10N14O12)(17) das(C2C9)(13)-d(C18N23O20)(11)-d(C@N)(7)d(N23N9C8)(6)-d(O12C10C11)(5)
(C10N14O12)(23) (C@O)(17) d(C18N23O20)(14) d(O13C11N15)(10)-d(O12C10C11)(5)
(N21C17C18O19)(42) (Pyring)(30)- (Pyring)(20)
as(C2C9)(28)-d(C@N)(14)- (C5H27N7C6)(8) d(C5C6N7) (5)
d(C18C17O20)(18)-d(O12C10C11)(15)d(N14N7C6)(10)-d(C18N23O20)(7)-49(6)43(6)17(5)
q
x
x
x
x
x
x
x
26.68
s
s
x
(Pyring) (65)-
(N23C18)(20)-
(Pyring)(63)-
(N15C11)(28)-
x
s
s
s
651 202.45
634
558
x
(H29C10N7N14)(18)
606
592
528
508
492 158.97
479
403
24.76
79.53
0.41
s
x
(C@O) (18) x(C10N7N14H29)(6)
q
q
2.31
q
x
x
s
2.82
2.81
d
x
Proposed assignment and potential energy distribution (PED) for vibrational modes: Types of vibrations:
d – deformation, d – symmetric deformation, das – asymmetric deformation, – torsion.
m – stretching, dsc – scissoring, q – rocking, x – wagging,
s
s
responds to hydrazone (C@NNH) linkage at d 11.980 ppm in exper-
imental spectrum. Again appearance of singlet at d 11.895 ppm in
experimental spectrum corresponding to calculated signal at d
d 6.47–6.69 confirms two vacant b position of pyrrole ring. Sharp
singlet at d 8.771 ppm corresponds to protons of azomethine group
directly attached to carbon of hydrazone (ACH)@NNHA) linkage.
1
8
.003 ppm of pyrrolic NHNH
2
proton. The signal appears as singlet
The disappearance of NH
2
peak in H NMR of macrocyclic bis-
at d 12.191 ppm in experimental spectrum corresponding to calcu-
lated signal at d 9.810 ppm of pyrrolic NH. Appearance of triplet at
hydrazone (6) indicates that (6) exist in cyclic form as shown in
Supplementary Fig. S3.

P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
349
TD-DFT/B3LYP calculation using 6-31G(d,p)/6-311+G(d,p) basis
set have been used to determine the low-lying excited states of
PDBO. The experimental values and calculated electronic transi-
tions of high oscillatory strength are listed in Table 4. Comparison
between experimental and theoretical UV–visible spectrum is
shown in Fig. 4. The TD–DFT calculations predict one intense elec-
tronic transitions at kmax = 382 nm, f = 0.796 (B3LYP/6-31 g(d,p))
and kmax = 397 nm, f = 0.7959 (B3LYP/6-311+g(d,p)). The calculated
electronic transitions at k = 266 nm (B3LYP/6-31g(d,p)) and 274 nm
(
B3LYP/6-311+g(d,p)) are correspond to the experimental
electronic transitions observed at k = 287 nm. According to the
TD–DFT calculations, the experimental bands at 287 nm originate
mainly due to the electronic excitations H-3 ? L. The difference
between the theoretical and experimental UV–visible spectra is
due to solvation.
Chemical reactivity
Fig. 3. Comparison between experimental and theoretical IR spectrum for PDBO.
The most fruitful and promising framework so far is probably
the Density Functional Theory of chemical reactivity so called con-
ceptual DFT [40]. Conceptual DFT is a subfield of DFT in which one
tries to extract from the electronic density relevant concepts and
principles that help to understand and predict the chemical behav-
ior of a molecule. The calculated global parameters [41,42] are
given in Table 5.
Additional support for the structure of the synthesized com-
pound was provided by its 13C NMR spectrum. The chemical shift
values of the carbon atom attached to nitrogen found to be at
1
38.03 ppm (C(H)@N) corroborated well with reported hydrazone
1
compound [38]. The values of correlation coefficient for H and
1
3
2
C NMR (r = 0.99, 0.99) show that there are good agreement
According to Mulliken [52] chemical potential and the electro-
negativity is calculated as
1
between experimental and calculated results. In addition to H,
1
3
C NMR chemical shifts, Mass spectrum is shown in Supplemen-
tary Figs. S4 and S5 also confirms the presence of molecular ion
peak at M+1, corresponds to the molecular formula C10
and C16 of PDBO and macrocyclic bis-hydrazone (6),
respectively.
l
g
¼ ꢂ
v
¼ ꢂ1=2ðI þ AÞ
ð1Þ
ð2Þ
13 9 4
H N O
¼ 1=2ðI ꢂ AÞ
14 10 4
H N O
where I and A are the first ionization energy and electron affinity,
respectively. The chemical potential and the absolute electronega-
tivity are molecular properties and not the orbital properties.
According to Koopman’s [53] theorem the I is simply the eigenvalue
of HOMO with change of sign and A is the eigenvalue of LUMO with
change of sign, hence the Eq. (1) can be written as
Natural bond orbital analysis and UV–visible spectrum
The NBOs provides an accurate method for studying intra-, inter-
molecular bonding, interaction among bonds and charge transfer or
conjugative interaction in various molecular systems [39]. The sec-
ond-order perturbation theory analysis of Fock Matrix, in the NBO
basis for PDBO, calculated at B3LYP/6-31G(d,p) are presented in
ꢂ
v
¼ ꢂ1=2ð
¼ 1=2ð LUMO ꢂ
The electrophilicity index, (
e
HOMO þ
e
LUMOÞ
ð3Þ
ð4Þ
g
e
e
HOMOÞ
x
) =
l
2/2
g
which measures the capacity
Table 3. The delocalization of
p
electron from
p
(C2–C3) ?
r
⁄(C2–
of an electrophile to accept the maximal number (a fractional of or
more than one) of electrons in a neighboring reservoir of electron sea.
The local reactivity descriptors [40–51] such as Fukui functions
C8)/
r
⁄(N1–C2)/
p
⁄(C4–C5)/
p
⁄(C8–N9) stabilized the molecule up
ꢂ1
to 21.46 kcal mol
another
⁄(C18–N23),
due to strong conjugative interactions. The
conjugative
interactions
⁄(C11–N15)/
⁄(C17–C21) stabilized the molecule up
n
2
(O20) ?
r
⁄(C17–C18)/
+
ꢂ
k
k
f (r), f (r) are calculated using the following equations as:
p
n
1
(O13) ?
r
r
⁄(C10–C11)
and
n
1
(O19) ?
r
⁄(C11–C18)/
r
þ
f ðrÞ ¼ ½q ðN þ 1Þ ꢂ q ðNÞꢄ; for nucleophilic attack
ð5Þ
ð6Þ
ꢂ1
k
k
k
to 24.39 kcal mol . The structure allow strong
p
–
p
⁄ and n– ⁄ tran-
p
ꢂ
f ðrÞ ¼ ½q ðNÞ ꢂ q ðN ꢂ 1Þꢄ; for electrophilic attack
sitions in the UV–visible region with high extinction coefficients.
k
k
k
Table 2
Calculated and experimental 1H NMR and 13C NMR chemical shifts (d/ppm) in chemical shifts (d/ppm) in DMSO of (5 = PDBO).
Atom no.
d calcd.
-31G(d,p)
d exp.
Assignment
Atom no.
d calcd.
d exp.
Assignment
6
6-311+G(d,p)
6-31G(d,p)
6–311+G(d,p)
2
2
2
2
2
4H
5H
6H
7H
8H
9.382
6.133
6.133
7.075
7.074
9.810
6.411
6.411
7.617
7.617
12.19
(s, 1H, pyrrole–NH)
(d, 2H, pyrrole–CH)
(d, 2H, pyrrole–CH)
(s, 1H, ACH@N)
2C
3C
4C
5C
6C
126.06
139.018
121.436
121.4363
139.019
139.649
123.63
117.99
117.99
129.27
138.00
(pyrrole ring)
(pyrrole ring)
(pyrrole ring)
(pyrrole ring)
6-48-6.69
6-48-6.69
8.77
110.798
110.797
126.061
128.482
8.77
(s, 1H, ACH@N)
(
hydrazone–CH@N–NH
hydrazone–CH@N–NH
2
3
3
3
3
9H
0H
1H
2H
3H
9.388
7.699
2.786
2.785
7.699
9.766
8.002
3.206
3.205
8.002
11.98
11.89
4.16
(s, 1H, hydrazide–C@NANH
8C
128.482
145.896
154.834
154.836
145.895
139.649
157.351
167.696
167.6989
157.350
138.00
161.57
157.43
157.43
161.57
(
10C
11C
17C
18C
(
s, 1H, hydrazide–NH–NH2)
(amidic–NH–COCONH)
(s, 1H, –NH2)
(
(
amidic–NH–COCONH)
amidic–NH–COCONH)
4.16
(s, 1H, –NH2)
11.89
(
s, 1H, hydrazide–NH–NH2)
(amidic–NH–COCONH)
3
3
3
4H
5H
6H
2.787
2.784
9.388
3.207
3.203
9.766
4.16
4.16
11.98
(s, 1H, –NH2)
(s, 1H, –NH2)
(s, 1H, hydrazide–C@NANH)

3
50
P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Table 3
Second-order perturbation theory analysis of the Fock matrix in NBO basis for monomer: Donar (i), Acceptor (j), Occupancy (O), Percentage electron density over bonded atoms
(
2)
(
EDX, %), Stabilization energy of charge delocalization interactions(E ) in (kcal/mol) and NBO hybrid orbitals of bonded atoms of (5 = PDBO).
Donor
i)/O (i)
Acceptor
E(2)
(
ED
ED
A
B
NBO hybrid
orbitals
(j) / O (j)
ED
ED
A
(%)
(%)
NBO hybrid
orbitals
(%)
B
r
(N1–
H24)
.988
74.24
25.76
0.8616(sp2.33)
N
+
+
r
⁄(N1–C2)
0.08889
⁄(C4–C5)
.01546
⁄(C11–O13)
0.01316
68.72
31.28
51.34
48.66
64.89
35.11
0.8290 (sp2.59
)
N
–0.5593(sp2.04
)
H
0.68
0
0.5075(sp )
H
1
r
0
r
0.7165(sp2.03
)
N
–0.6976(sp1.72
)
H
H
1.99
5.09
0.8559(sp .15)
2
0.8056(sp2.01
)
–0.5925(sp1.48
)
r(N15–
H30)
73.26
26.74
N
N
0
0.5171(sp )
H
1
.984
(N1–C2)
1.983)
1
.86
0.6190(sp1.86
–0.7854(sp2.71
–0.7165(sp2.03
–0.7148(sp1.82
–0.7148(sp1.82
–0.7148(sp1.82
–0.6976(sp1.72
–0.7148(sp1.82
–0.7148(sp1.82
–0.7854(sp2.71
r
61.68
38.32
0.7854 (sp
)
N
+
r
⁄(N1–C5)
0.02340
⁄(C2–C3)
.01546
⁄(C5–C6)
.02570
⁄(C2–C8)
.02570
⁄(C2–8)
0.02570
⁄(C4–C5)
.01546
⁄(C5–C6)
.02570
⁄(C2–C8)
0.02570
⁄(N1–C2)
.02340
⁄(C4–C5)
.41417
⁄(C8–N9)
.23441
⁄(C2–C3)
0.41417
⁄(C6–N7)
.23441
⁄(N1–H24)
.01759
⁄(C5–C6)
.02570
⁄(C2–C8)
0.02570
⁄(C5–C6)
.02570
⁄(N9–N23)
0.02154
⁄(C2–C3)
.01546
⁄(C4–C5)
0.01546
⁄(N7–N14)
.02154
⁄(C2–C3)
0.01546
⁄(C4–C5)
0.01546
⁄(C6–N7)
0.00692
38.32
61.68
48.66
51.34
48.90
51.10
48.90
51.10
48.90
51.10
51.34
48.66
48.90
51.10
48.90
51.10
38.32
61.68
50.00
50.00
56.76
43.24
50.00
50.00
56.76
43.24
25.76
74.24
48.90
51.10
48.90
51.10
48.90
51.10
53.16
46.84
48.66
51.34
51.34
48.66
53.16
46.84
48.66
51.34
51.34
48.66
59.36
40.64
)
N
N
N
N
N
N
N
N
N
)
)
)
)
)
)
)
)
)
H
H
H
H
H
H
H
H
H
H
1.96
1.39
3.82
1.28
3.08
1.39
1.28
3.14
3.43
19.95
21.46
19.95
21.46
3.43
3.41
5.74
5.74
4.44
3.01
3.01
4.44
10.35
10.35
1.98
(
0.6190 (sp2.71)
H
r
0
r
0
r
0
r
0.6976(sp1.72
0.6993(sp1.76
0.6993(sp1.76
0.6993(sp1.76
0.7165(sp2.03
0.6993(sp1.76
0.6993(sp1.76
0.6190(sp1.86
)
)
)
)
)
)
)
)
1
.86
r
(N1–C5)
1.983)
61.68
38.32
0.7854 (sp
)
N
+
+
(
0.6190 (sp2.71)
H
r
0
r
0
1
.00
p
(C2–C3)
1.712)
50.00
50.00
0.7071 (sp
)
N
r
(
0.7071 (sp1.00)
H
r
0
p
0
p
0
p
0.7071(sp1.00
0.7534(sp1.00
0.7071(sp1.00
0.7534(sp1.00
0.5075(sp2.33
)
–0.7071(sp1.00
–0.6576(sp1.00
–0.7071(sp1.00
–0.6576(sp1.00
–0.8616(sp0.00
)
N
N
N
N
N
)
)
)
)
)
H
1
.00
p
(C4–C5)
50.00
50.00
0.7071 (sp
)
N
+
)
H
(
1.712)
0.7071 (sp1.00)
H
p
0
r
0
r
0
r
)
H
H
)
0.6993(sp1.76
0.6993(sp1.76
0.6993(sp1.76
0.7291(sp3.06
0.6976(sp1.72
0.7165(sp2.03
0.7291(sp3.06
0.6976(sp1.72
0.7165(sp2.03
)
N
)
N
)
N
)
N
)
N
)
N
)
N
)
N
)
N
N
–0.7148(sp1.82
–0.7148(sp1.82
–0.7148(sp1.82
–0.6844(sp2.82
–0.7165(sp2.03
–0.6976(sp1.72
–0.6844(sp2.18
–0.7165(sp2.03
–0.6976(sp1.72
–0.6375(sp1.44
)
)
)
)
)
)
)
)
)
)
1
.95
r
r
r
(C3–C4)
50.00
50.00
0.7071 (sp
)
N
+
+
+
H
H
H
H
H
H
H
H
H
(
1.975)
0.7071 (sp1.95)
H
r
0
r
1
.76
(C2–C8)
1.976)
51.10
48.90
0.7148 (sp
)
N
(
0.6933 (sp1.82)
H
r
0
r
1
.76
(C5–C6)
1.976)
51.10
48.90
0.7148 (sp
)
N
(
0.6933 (sp1.82)
H
r
0
r
1.00
1.00
1.00
1.00
2.08
1.66
p
p
r
(C8–N9)
1.712)
(C6–N7)
1.918)
43.24
56.76
43.24
56.76
37.18
62.82
0.6576 (sp
0.7534 (sp
0.6576 (sp
0.7534 (sp
0.6098 (sp
0.7926 (sp
)
)
)
)
)
)
N
H
N
H
N
H
+
+
+
(
r
(
(C10–
N14)
r
0.7705(sp2.05
0.7705(sp2.05
0.7926(sp2.08
0.7926(sp2.08
)
)
)
)
(
1.988)
0.6098 (sp2
0.7926 (sp
.08
.66
)
)
+
+
+
r
⁄(C8–N9)
59.36
40.64
–0.6375(sp1.44
–0.6098(sp1.66
–0.6098(sp1.66
)
)
)
1.98
1.25
1.25
r
r
r
(C18–
N23)
37.18
62.82
N
N
N
N
H
H
H
1
H
0.00692
(
1.988)
2
.08
(C17–
N21)
38.23
61.77
0.6183 (sp
)
N
r
⁄(C18–N23)
62.82
37.18
0.7860 (sp1.66)
0.07745
H
(
1.982)
2
.08
(N15–
C11)
38.23
61.77
0.6183 (sp
)
N
r
⁄(C10–N14)
62.82
37.18
0.7860 (sp1.66)
0.07745
H
(
1.982)
n
2
O12
1
O20
1
sp99.99
p
⁄(C10–C11)
48.29
51.71
49.72
50.28
62.82
0.6949(sp1.85
0.7051(sp1.95
0.7926(sp2.08
)
N
)
N
)
N
–0.7191 (sp1.53
)
H
2.64
22.89
27.32
.852
0.05521
n
2
sp99.99
r⁄(C17–C18) 0.12286
–0.7091(sp1.99
–0.6098(sp1.66
)
H
H
.852
p⁄(C18–N23) 0.08889
)
37.18

P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
351
Table 3 (continued)
Donor
Acceptor
E(2)
(i)/O (i)
ED
ED
A
B
NBO hybrid
orbitals
(j) / O (j)
ED
ED
A
B
(%)
(%)
NBO hybrid
orbitals
(%)
n
2
O13
sp99.99
r
r
r
r
⁄(C11–N15) 0.35496
⁄(C10–C11) 0.12285
⁄(C11–C18) 0.03449
⁄(C17–C21)
72.85
27.15
50.28
0.8535 (sp1)
N
–0.5210 (sp1)
H
24.39
21.54
21.25
24.39
1
.860
0.7091(sp1.99
0.7051(sp1.95
0.7860(sp2.03
)
N
)
N
)
N
–0.7051(sp1.95
)
)
)
H
49.72
n
2
O19
sp99.99
49.72
50.28
61.77
38.23
–0.7091(sp1.99
–0.6183(sp1.57
H
1
.860
0.07719
Table 4
Calculated and experimental electronic excitations for (5 = PDBO).
6
-31G(d,p)
6-311+G(d,p)
Excitations
Excitations
k calcd.
k calcd
k obs.
Assignment
8
8
8
7
4 ? 85 (H ? L)
382.98
322.15
266.40
248.78
84–>85
84–>86
81–>85
78–>85
397.45
329.83
274.18
242.83
381
p
?
p
⁄
4 ? 86 (H ? L+1)
1 ? 85(Hꢂ3 ? L)
8 ? 85 (Hꢂ7 ? L)
287
p
?
p⁄
treatment of the frontier molecular orbitals separately from the
other orbitals is based on the general principles governing the nat-
ure of chemical reactions. The energy of the HOMO is directly
related to the ionization potential and characterizes the suscepti-
bility of the molecule toward attack of electrophiles. The energy
of LUMO is directly related to the electron affinity and character-
izes the susceptibility of the molecule toward attack of nucleo-
philes. The concept of hard and soft nucleophiles and
electrophiles has been also directly related to the relative energies
of the HOMO and LUMO orbitals.
Electrophilic charge transfer [54] (ECT) = (
D
N
max
)
A
ꢂ (
max B
DN )
is defined as the difference between the max values of interact-
D
N
ing molecules. If we consider two molecules 1 and 2 approach to
each other (i) if ECT > 0, charge flow from 2 to 1 (ii) if ECT < 0,
charge flow from 1 to 2. The calculated high value of electrophilic-
ity index shows that reactant 1 is a strong electrophile than reac-
tant 2. The Electrophilic charge transfer ECT is calculated as
0
.6496 for reactant molecules 1 and 2, which indicates that charge
+
Fig. 4. Comparison between experimental and theoretical UV–visible spectra for
PDBO.
k
flows from 2 to 1. Selected electrophilic reactivity descriptors (f ,
+
+
ꢂ
k k
s
k
,
x
x
k
k
) for reactant 1 and nucleophilic reactivity descriptors (f
,S
-
ꢂ
ꢂ
,
) for reactant 2, using Hirshfeld population analyses are listed
where, q is the gross charge of atom k in the molecule and N, N+1,
Nꢂ1 are electron systems containing neutral, anion, cation form of
molecule, respectively. Using Fukui functions, other local reactivity
in Table 6. In reactant 1, the maximum values of the local electro-
philic reactivity descriptors (f
site is prone to nucleophilic attack. In the same way, for reactant
2
+
+
+
k k k
, s , x ) at C (6/7) indicate that this
+
ꢂ
k
descriptors as local softnesses (s
k
, s
) and electrophilicity indices
, the maximum values of the local nucleophilic reactivity descrip-
+
ꢂ
k
(x
k
,
x
) are calculated using following equations as
ꢂ
ꢂ
ꢂ
k
tors (f
k
, s
k
,
x
) at N (6) indicate that this is more nucleophilic site.
þ
þ
ꢂ
ꢂ
s
¼ Sf ; s ¼ Sfk
ð7Þ
ð8Þ
Therefore, local reactivity descriptors for reactants 1 and 2 confirm
the formation of product by nucleophilic attack of N (6) site of
reactant 2 on the more electrophilic C (6/7) site of reactant 1.
k
k
k
þ
þ
ꢂ
ꢂ
x
¼
x
f ;
x
¼
xf
k
k
k
k
+
ꢂ
k
where, + and ꢂ sign show nucleophilic, electrophilic attack,
Selected reactivity descriptors as Fukui functions (f
k
, f
), local
+
ꢂ
+
ꢂ
respectively.
softnesses (s
k
, s
k
), local electrophilicity indices (
x
k
,
x
k
) for
The orbitals play a major role in governing many chemical reac-
tions, and are also responsible for charge transfer complexes. The
(5 = PDBO), using Hirshfeld atomic charges are given in Table 7.
In PDBO, the maximum values of the electrophilic reactivity
Table 5
Calculated
e
HOMO
,
e
LUMO, energy band gap (
e
L
ꢂ
H
e ), chemical potential (l), electronegativity (v), global hardness (g), global softness (S) and global electrophilicity index (x) for
(1), (2), and (5 = PDBO), Electrophilicity based charge transfer (ECT) for reactant system [(1) M (2)].
e
H
e
L
(
e
L
ꢂ
e
H
)
v
l
g
S
x
ECT
0.6496
(1)
(2)
(3)
ꢂ6.8410
–6.7803
ꢂ5.5493
ꢂ2.3647
–1.1461
ꢂ2.1388
4.4763
5.6341
3.4104
4.6028
3.9632
3.8440
ꢂ4.6028
–3.9632
ꢂ3.8440
2.2382
2.8170
1.7052
0.2234
0.1774
0.2932
4.7330
2.7878
4.3328
ꢂ1
e
H,
e
L,
(e
H
–
e
L ,
)
v,
l,
g
,
x
(in eV) and S (in eV ).

3
52
P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Table 6
Table 7
+
+
+
+
+
+
Selected electrophilic reactivity descriptors (f
philic reactivity descriptors (f
k
, s
k
,
x
k
) for reactant (1) and nucleo-
Selected electrophilic reactivity descriptors (f
descriptors (f
k
, s
k k
, x ) and nucleophilic reactivity
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
k
k
, s
k
,
x
k
) for reactant (2) using Hirshfeld population
k
, s
k
,
x
) for (5 = PDBO) using Hirshfeld population analyses charges.
analyses charges.
+
+
+
ꢂ
ꢂ
ꢂ
k
Sites
f
k
s
k
x
k
Sites
f
k
s
k
x
Reactant (1)
Reactant (2)
C6/C8
O12/
O20
O13/
O19
0.1492 0.0437 0.6464 N1
0.0715 0.0209 0.3097 N14/
0.3368 0.0987 1.4592
0.2676 0.0784 1.1594
+
+
+
ꢂ
ꢂ
ꢂ
k
Sites
f
k
s
k
x
k
Sites
f
k
s
k
x
N23
C6
C7
0.1053 0.0235 0.4989 N5
0.1053 0.0235 0.4989 N6
0.056658 0.010056 0.157954
0.119492 0.021207 0.333126
0.066731 0.011843 0.186036
0.131873 0.023405 0.367642
0.0418 0.0122 0.1811 N15/
0.3102 0.0909 1.3440
0.5576 0.1634 2.4159
N21
N16/
N22
N7
N8
ꢂ
+
ꢂ
ꢂ1
+
ꢂ
k
f
k
+, f
k
(in e); s
k
, s
k
(in eV ) and
x
k
,
x
(in eV).
ꢂ
+
ꢂ
ꢂ1
+
ꢂ
k
f
k
+, f
k
(in e); s
k
, s
k
(in eV ) and
x
k
,
x
(in eV).
descriptors (f+
, s , x ) at C6/C8 indicate that this site is more prone
+
+
k k k
to nucleophilic attack. Therefore, local reactivity descriptors of
PDBO favor the formation of new heterocyclic compounds such
as thiadiazoline, thiazolidinones and azetidinones etc. by attack
of nucleophilic part of the dipolar reagent on the C6/C8 site of
C8@N9/C6@N7 bond. In the same way, for PDBO the maximum
ꢂ ꢂ
ꢂ
k
values of the nucleophilic reactivity descriptors (f , s , x ) at
k k
nitrogen atom of N16/N22 indicate that this site is more prone to
electrophilic attack and favor the formation of Schiff base and
hydrazide-hydrazones compounds.
Atomic charges
The charge distribution of PDBO was calculated from the atomic
charges by NBO and Mulliken population analysis (Fig. 5). The
atomic charges are calculated using B3LYP method with 6-31G
(
d,p)/6-311+G(d,p) basis set and the values are tabulated in Sup-
plementary Table S4. The charges changes with basis set presum-
ably occur due to polarization. These two basis set does not
predict the same trend i.e., among the nitrogen atoms N1 and
N16/22, N16/22 is considered as basic site, opposite trend is
observed in case of MPA charges [55]. The charge distribution
shows that the more negative charge is concentrated on N16/22
Fig. 5. Bar diagram representing the charge distribution of PDBO using NPA and
MPA methods.
atom of NH
gen atoms. Among the oxygen atoms O12/20 and O13/19, O13/
9 is considered more electronegative than O12/20. The negative
charge concentrated at O12/20 share with hydrogen atom of
N14-H29/N23-H36 due to intramolecular hydrogen bonding. All
the hydrogen atoms have a net positive charge. Considering both
bases sets used in the atomic charge calculation; the oxygen atoms
exhibit a negative charge, which are donor atoms. Hydrogen atom
exhibits a positive charge, which is an acceptor atom, may suggest
the presence of intra-molecular bonding in the gas phase.
2
group whereas the positive charge resides at hydro-
where, ZA is the charge on nucleus A located at RA and q(r) is the
electron density. The first term in the expression represents the
effect of the nuclei and the second represents that of electrons.
The two terms have opposite sign and therefore opposite effects.
V(r) is their resultant at each point r and it is an indication of the
net electrostatic effect produced at the point r by the total charge
distribution (electron+nuclei) of the molecule.
1
The molecular electrostatic potential is related to electron
density and a very useful descriptor for determining sites for elec-
trophilic attack and nucleophilic reactions as well as hydrogen-
bonding interactions. To predict reactive sites for electrophilic
and nucleophilic attack for the investigated molecule, the MEP at
the B3LYP/6-31G(d,p) optimized geometry was calculated and
shown in Fig. 6. The different values of the electrostatic potential
at the surface are represented by different colors. Potential
increases in the order red < orange < yellow < green < blue. The
negative (red, orange and yellow) regions of the MEP are related
to electrophilic reactivity. The maximum positive region is local-
ized on the NH bonds, indicating a possible site for nucleophilic
attack. The MEP map (Fig. 6) shows that the negative potential
sites are on electronegative O atom and the positive potential sites
are around the hydrogen atoms of azomethine (CH@NNH) frame.
These sites give information about the region from where the com-
pound can have intermolecular interactions. This predicted the
most reactive site for both electrophilic and nucleophilic attack.
Molecular electrostatic potential surface
Molecular electrostatic potential are useful quantities to illus-
trate the charge distributions of molecules and used to visualize
variably charged regions of a molecule. Therefore, the charge dis-
tributions can give information about how the molecules interact
with another molecule. Molecular electrostatic potential is widely
used as a reactivity map displaying most probable regions for the
electrophilic attack of charged point-like reagents on organic mol-
ecules [56].
ESP provides a visual method to understand the relative polarity
of a molecule. It also serves as a useful quantity to explain electro-
negativity, partial charges, site of chemical reactivity, structure–
activity relationship, hydrogen bonding and other interactions of
molecules including biomolecules and drugs. Molecular electro-
static potential [V(r)] of a molecule is expressed by the following
equation [57] given as:
First hyperpolarizability
Z
X
0
0
VðrÞ ¼
Z
A
=jR
A
ꢂ rj ꢂ
q
ðrÞdr =jr ꢂ rj
Experimental measurements and theoretical calculations on
molecular hyperpolarizability b is one of the key factors in the

P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
353
Fig. 6. Molecular electrostatic potential (ESP) map for PDBO.
Table 8
Calculated dipole moment (
First hyperpolarizability (b
properties. Polarizabilities and hyperpolarizabilities are described
to response of a system in the presence of an applied electric field
l
0
), polarizability (|
0
a |), anisotropy of polarizability (Da),
0
) and their components calculated at B3LYP/6–31G(d,p) of
[
58]. They determine the strength of molecular interactions (long-
(5 = PDBO).
range intermolecular induction, dispersion forces, etc.), cross sec-
tions of different scattering and collision processes, as well as the
non-linear optical (NLO) properties of the system. The DFT-based
methods can be of great aid and adequate in searching for new
nonlinear chemical compounds [59]. Theoretical methods have
been considered as useful techniques for prediction of polarizabil-
ities and hyperpolarizabilities avoiding an expensive large amount
of experimental synthetic work that precedes the measuring of
NLO properties, what may not lead to a desired compound for prac-
tical applications [58]. The search for molecules possessing a large
value of static first hyperpolarizability is a key step toward the
optimization of new materials for NLO response applications.
Hybrid functional, B3LYP, tend to be the most commonly used
methods for computational chemistry practitioners [60]. In order
to investigate the relationship between molecular structure and
Dipole moment
Polarizability
Hyperpolarizability
l
x
l
y
l
z
l
0
0.0003
4.5484
0.1935
4.5525
a
a
a
xx
yy
zz
381.699
20.75
26.302
21.1803
111.436
b
xxx
b
xxy
b
xyy
b
yyy
b
xxz
b
xyz
b
yyz
b
xzz
b
yzz
b
zzz
b
0
3.4924
ꢂ2486.11
ꢂ1.339
ꢂ283.69
ꢂ2.545
ꢂ2.126
ꢂ1.485
0.374
|a
0
|
D
a
10.730
ꢂ1.690
23.836
Para nitro aniline (p-NA)
B3LYP/6-31G(d,p)
l
0
7.5769
|a
0
|
D
a
12.798
b
0
11.546
3
8.396
ꢂ24
ꢂ30
NLO response, first hyperpolarizability (b ) of this novel molecular
system, and related properties (| | and Da) are calculated using
0
l
0
/Debye;|
a
0
| and
D
a
/10
esu; b
0
/10
esu.
a
0
B3LYP/6-31G(d,p), based on the finite-field approach and their cal-
second order NLO materials design. Theoretical determination of
hyperpolarizability is quite useful both in understanding the rela-
tionship between the molecular structure and nonlinear optical
culated values are given in Table 8. It is well known that if the mol-
ecule has many delocalization
p electrons, bigger change of dipole
moment from ground state to excited state, large transition
Table 9
The antimicrobial activity of reactants (r1, r2) and product (P = PDBO)) at different concentration.
Antibacterial activity
Zone of inhibition(mm)
Gram positive
Gram negative
S. aureus
g/ml
S. pyogenes
g/ml
E. coli
P. aeruginosa
g/ml
l
l
lg/ml
l
Comp
100
200
100
200
100
200
100
200
r1
r2
P
6
9
11
14
11
12
18
20
6
9.3
10
13
10
12
17
20
5
7
9
9
13
17
23
4
7
8
9
13
17
19
Control
13
13
chloramphenicol
Antifungal activity
C. albicans
A. niger
r1
r2
P
6
7
10
12.5
9
11
17
22
8
10
11
14
11
14
21
25
Nystatin

3
54
P. Rawat, R.N. Singh / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 344–355
Conclusions
A PDBO has been synthesized and characterized by combined
experimental and theoretical quantum chemical calculations using
B3LYP/6-31G(d,p) and B3LYP/6-311+g(d,p) basis set. By comparing
calculated electronic transitions, chemical shifts and wavenumbers
values with experimental value, it have been observed that B3LYP/
6
-311+G(d,p) estimate better results. NBO analysis investigation
indicates the various types of interactions within molecule. A com-
ꢂ1
bined theoretical and experimental symmetric (3319, 3320 cm
)
ꢂ1
and asymmetric (3389, 3382 cm ) stretching wave number anal-
2
ysis confirms free NH groups in the solid phase of PDBO. Topolog-
ical parameters have been analyzed by Bader’s ‘Atoms in
molecules’ AIM theory and provide the existence of intramolecular
hydrogen bonding (N–Hꢃ ꢃ ꢃO). The first hyperpolarizability (b
0
) of
esu indicates
ꢂ30
the title compound is calculated as 23.83 ꢁ 10
that PDBO is suitable for NLO applications. The preliminary bioas-
say suggested that the PDBO compound exhibits relatively good
antibacterial and fungicidal activity against E. coli, P. aeruginosa,
S. aureus, S. pyogenes, C. albicans, A. niger. The local reactivity
descriptors analyses have been used to determine the reactive sites
within molecule.
Acknowledgments
The authors are thankful to the DST and CSIR for providing
research fund and IIT Kanpur for spectral data.
Appendix A. Supplementary data
Fig. 7. Bar diagram represent the inhibition zone in mm of (a) against bacterial
strains (b) against fungal strains.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.12.080.
moment and noncentrosymmetry structure, the molecule will
have strong second order NLO response [61].
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optical properties. In PNA, the presence of a desirable resonance
structure, in addition to the intermolecular charge transfer, leads
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[
[
[
[
[
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and oxalic acid dihydrazide. The product PDBO was found more
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[
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2
[
even at 100
only at 200
l
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