Synthesis, crystal structure, spectral and DFT studies of potent isatin derived metal complexes

Article abstract of DOI:10.1016/j.molstruc.2018.03.132

The isatin-core in compounds offers exciting perspectives in medicinal and pharmacological research. The present study reports the successful development of new isatin-core transition metal based anti-bacterial complexes via conventional refluxing method.

Full text of DOI:10.1016/j.molstruc.2018.03.132

Accepted Manuscript
Synthesis, crystal structure, spectral and DFT studies of potent isatin derived metal
complexes
Sajjad Hussain Sumrra, Aftab Hussain Atif, Muhammad Naveed Zafar, Muhammad
Khalid, Muhammad Nawaz Tahir, Muhammad Faizan Nazar, Muhammad Arif
Nadeem, Ataualpa A.C. Braga
PII:
S0022-2860(18)30429-0
10.1016/j.molstruc.2018.03.132
MOLSTR 25071
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 18 August 2017
Revised Date: 28 March 2018
Accepted Date: 30 March 2018
Please cite this article as: S.H. Sumrra, A.H. Atif, M.N. Zafar, M. Khalid, M.N. Tahir, M.F. Nazar, M.A.
Nadeem, A.A.C. Braga, Synthesis, crystal structure, spectral and DFT studies of potent isatin derived
metal complexes, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.03.132.
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Synthesis, Crystal Structure, Spectral and DFT Studies of Potent Isatin Derived Metal
Complexes
Sajjad Hussain Sumrra*1, Aftab Hussain Atif1, Muhammad Naveed Zafar2, Muhammad
Khalid*3, Muhammad Nawaz Tahir4, Muhammad Faizan Nazar1, Muhammad Arif Nadeem5,
Ataualpa A. C. Braga6
1Department of Chemistry, University of Gujrat 50700, Pakistan.
2Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan.
3Department of Chemistry, Khwaja Fareed University of Engineering & Information
Technology, Rahim Yar Khan, Pakistan.
3Department of Chemistry, University of Education Lahore, Faisalabad Campus, Pakistan.
4Department of Physics, University of Sargodha, Sargodha, Pakistan.
5Department of Chemistry, University of Gujrat 50700, Pakistan.
6Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av.
Prof. LineuPrestes, 748, São Paulo, 05508-000, Brazil
ABSTRACT
The isatin-core in compounds offers exciting perspectives in medicinal and pharmacological
research. The present study reports the successful development of new isatin-core transition
metal based anti-bacterial complexes via conventional refluxing method. The bidentate nature of
as-synthesized isatin-core ligand was confirmed using various analytical techniques such as
1
13
FTIR, H NMR, C NMR, EIMS, and single crystal X-ray diffraction. The computed analysis
i.e. IR, UV-Visible, NBO (Natural Bond Orbital) and FMO (Frontier Molecular Orbital) of
crystalline isatin-core ligand reflect its dimer nature and predict the conjugative interaction
among molecules. Moreover, metal complexes of isatin-core ligand using metallic salts of first
transition series i.e. VO(IV), Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) were
prepared and further screened against bacterial strains. Octahedral geometry was proposed for all
the complexes except vanadium which had square-pyramidal geometry. All the as-prepared
metal complexes are found potentially active entities against both of the gram-positive and gram-
negative bacterial strains. Additionally, the bacterial screened data revealed that metal complexes
have better bactericidal activities compared to their parent ligand.
Keywords: Bidentate Ligand, Metal Chelates, Computed Analysis, Conjugative Interaction,
Bactericidal
Corresponding authors E-mail address: sajjadchemist@uog.edu.pk (Sajjad Hussain Sumrra)
muhammad.khalid@kfueit.edu.pk (Muhammad Khalid)
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Introduction
Isatin (1H-Indole-2,3-dione) is a natural compound found in most plants. It is a unique class of
heterocycles acting as biological agents [1]. Isatin derived compounds have extensive
applications in the pharmacological and medicinal field due to the presence of bioactive indole
moiety containing both keto and lactum groups [2-5]. Isatin and its derivatives have a number of
biological applications including nervous system activities and as a metabolic derivatives of
humans [6, 7]. Isatin and its derived compounds also possess broad range of pharmacological
effects [8], such as antifungal [9, 10], antibacterial [11, 12], anti HIV [13] and antiviral [14-16].
Isatin also shows enzyme inhibition activity [17, 18] and act as cytotoxic agent against tumor
cells [19-22]. Moreover, Isatin derived compounds have a number of actions in the brain against
different types of infections [23]. It also exhibit antiproliferative [24] and caspase inhibitor
activities [25, 26]. Compounds of isatin possess SARS protease [27], antismall pox [28], kinase
activator [29], and inflammatory activities [30]. These biological functions validated isatin as a
starting point for the design and preparation of chemical libraries [31, 32]. Metal complexes of
isatin based ligands attracted much attention nowadays because of their diagnostic and
therapeutic properties [33]. Copper (II) complexes of isatin based ligand are used as
antimicrobial agents [34]. Cobalt complexes derived from isatin ligands possess good
antibacterial activity against different strains of bacteria [24]. These versatile functions of isatin
based compounds and their complexes compelled us to extend this chemistry and synthesize new
compound, 3-(2-hydroxyethyl)quinazoline-2,4(1H,3H)-dione (E9) by reacting isatin with
ethanolamine and its metal complexes with transition metals (V, Cr, Mn, Fe, Co, Ni, Cu and
Zn). The DFT calculations are being performed for ligand to check the molecular interactions in
a compound and its stability. Finally, antibacterial activity against different bacterial strains has
been performed for all the synthesized compounds.
Scheme 1: Synthesis of 3-(2-hydroxyethyl)quinazoline-2,4(1H,3H)-dione (E9)
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Results and Discussion
The reaction of 1H-Indole-2,3-dione with ethanolamine in an equimolar ratio afforded brown
color product (Scheme 1). The brown crystals of isatin based ligand were grown successfully.
The compound was moisture and air stable, soluble in methanol and DMSO. The melting point
of the compound was 248ºC. The bidentate isatin based ligand reacted readily with first series of
following transition metals; VO(IV), Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) to
form metal complexes (Scheme 2-4).
Scheme 2: Synthesis of Oxovanadium(IV) Complex
Scheme 3: Synthesis of Chromium(III) Complex
Scheme 4: Synthesis of Metal(II) Complexes
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All the metal complexes were intensely colored except Zn(II) and Cr(III) which were of off
white color. All the complexes were soluble in DMSO and having decomposition temperature in
the range 258-290 except Fe(II) which showed greater than 300ºC.
1H NMR of E9
The proton NMR spectrum was recorded using DMSO-d6 as a solvent. The careful study of
spectrum (Table 1) demonstrated one signal of proton as singlet at 11.32 ppm confirming the
presence of N-H proton. Two signals appeared as triplet at 3.54-3.99 ppm for four CH2 aliphatic
protons indicating the presence of ethyl group of ethanolamine. The isatin aromatic protons were
appeared as multiplet at 7.15-7.93 ppm. The O-H proton appeared at 4.72 ppm. These all proton
signals supported the proposed structure of E9 [35].
Table 1. 1H NMR Data of E9
Sr. #
Position of peak
N-H proton
Signal values (ppm)
11.32 (s, 1H)
1
2
3
4
Aliphatic protons
Aromatic protons
O-H proton
3.54-3.99 (t, 4H)
7.15-7.93 (m, 4H)
4.72 (s, 1H)
s = singlet, t = triplet, m = multiplet
13C NMR of E9
The 13C NMR spectrum of ligand was recorded in DMSO solvent. The examination of spectrum
revealed that the signal of C2 appeared at 42 ppm and a downfield signal at 57.6 ppm appeared
due to attachment of OH group at C1. The six signals displayed between 113-139 ppm were due
to the presence of phenyl carbons (C4-C9) of isatin moiety. Due to the electronegative effect of
oxygen and inductive effect of nitrogen, C3 carbon appeared as downfield at 150.2 ppm. The
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downfield shift of C10 at 162 ppm was observed indicating the presence of C=O carbon. This
downfield shift was also due to attachment of electronegative oxygen and nitrogen atoms. All the
carbon peaks were in good agreement with proposed structure [35].
Mass Spectrum of E9
The mass fragmentation pattern of E9 compound is showed the existence of molecular ion peak
at m/z = 206 which indicated the formation of said compound. The base peak of 100% intensity
was observed at m/z = 163, by the loss of all three oxygen from parent compound through C-O
and C=O bond cleavage. The other mass fragments formed as shown in figure were produced by
the cleavage of C-C, C-O, C=O, C-N bonds.
Single Crystal Analysis of E9
The data in Table 2 showed that all the bond lengths and angles were within normal range.
Hydrogen bonding in Table 2 and Figure 2 showed that two types of intermolecular hydrogen
bonding O1—H1···O3 and N2—H2···O1 were present in crystal structure forming dimer and
stabilizing the crystal molecular system.
The solid state structure of E9 was resolved using X-ray diffraction technique (Table 2). ORTEP
diagram of single molecule and unit cell packing are given in Figure 1 and 2, respectively. The
selected bond lengths, bond angles, torsion angles and H-bonding are shown in Table 3.
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Table 2. Crystal Data of E9 Compound
Crystal data
CCDC
Compound (E9)
1515138
Chemical formula
Mr
C10H10N2O3
206.20
Crystal system, space group
Temperature (K)
a, b, c (Å)
Monoclinic, P21/c
296
13.1382 (16), 4.7630 (5), 14.9136 (19)
95.035 (4)
929.65 (19)
4
β (°)
V (Å3)
Z
Radiation type
µ (mm-1)
Mo Kα
0.11
Crystal size (mm)
0.45 × 0.22 × 0.18
Data collection
Bruker Kappa
APEXII CCD
Diffractometer
Multi-scan
(SADABS; Bruker, 2005)
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
7771, 2012, 1546
Rint
0.026
0.639
(sin θ/λ)max (Å-1)
Refinement
R[F2 > 2σ(F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
∆〉max, ∆〉min (e Å-3)
0.060, 0.177, 1.21
2012
138
H-atom parameters constrained
0.90, -1.02
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Figure 1. ORTEP Diagram of Single Unit of E9
Figure 2. Unit Cell Packing of E9
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Table 3. Hydrogen Bond Parameters (Å) of Ligand (E9)
D—H···A
D—H (Å)
0.82
0.86
H···A (Å)
1.98
1.95
D···A (Å)
2.7242 (17)
2.7953 (17)
D—H···A (°)
151.1
168.6
O1—H1···O3i
N2—H2···O1ii
Symmetry code(s): (i) −x, −y+2, −z; (ii) x, −y+3/2, z+1/2.
DFT Calculations of E9 Crystal
Computed and Experimental FT-IR Characterization of E9
The experimental and theoretical frequencies along with intensity and vibrational assignment are
given in Table 4.Vibrational frequencies of E9 compound were designed with the help of
DFT/B3LYP with 6-31G(d,p) basis set.
C-H Vibrations
The C-H stretching vibrations of the aromatic ring are commonly observed in the 3000-3100 cm-
1
region of FT-IR spectrum [36], and are easily predicted using DFT frequencies. The
experimental C-H stretching frequencies of E9 ligand are observed at 3150 and 3100 cm-1, which
are in good agreement with scaled frequencies at 3105 and 3081 cm-1. The small differences
between DFT and experimental frequencies are maybe due to interactions in the solid state
sample used for spectral data, and no interactions in gaseous sample used for DFT calculations.
The C-H bending vibrations are usually observed in 1000-1300 cm-1 region [37]. The weak to
medium bending bands are observed at 1100, 1150 and 1200 cm-1 in spectral data, these bands
are well correlated to the computed bands predicted at 1096, 1146 and 1192 cm-1. These bands
are actually C-H bending rocking vibrations coupled with scissoring vibrations. The C-H
aliphatic bands are observed at 2930 and 2980 cm-1 resulted from the symmetric stretch of
aliphatic CH2 group in the compound, these vibrations are supported by computed frequencies
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appeared at 2926 and 2992 cm-1 showing good correlation between spectral and theoretical
results. The banding vibrations of CH2 appeared at 1330 and 1350 cm-1 as medium bands in the
experimental data, these frequencies are due to rocking and twisting bending modes. The
computed frequencies at 1323 and 1350 cm-1 supported the spectral bending modes (Table 4).
Ring Vibrations
Stretching vibrations of C-C in a ring generally appeared at 1430-1650 cm-1. FT-IR vibrations
appeared at 1550 and 1600 cm-1 as weak bands are in good agreement with computed data at
1580 and 1600 cm-1 showing of carbon-carbon single and double bond vibrations (Table 4).
N-H Vibrations
N-H stretching vibration at 3200 cm-1 as weak band is appeared in the spectral data, the
computed vibration was at 3506 cm-1. The N-H bending vibration is observed at 1400 cm-1 as
weak band in experimental showing rocking vibrations, well agreed with computational band at
1402 cm-1 (Table
4).
C=O Vibrations
The C=O stretching vibration are appeared at 1650, 1700 cm-1 as strong band in the spectral data,
and these bands are fully supported by DFT vibrations at 1663, 1708 cm-1. It is interesting to
note that these vibration are mixed with other mode of vibrations appeared in the same region
(Table 4).
Hydrogen Bond Vibrations
It is well known that spectral frequency of O-H is always decreased from expected value during
intermolecular hydrogen bonding [38]. The O-H symmetric stretching vibration is observed at
3430 cm-1 as medium broad band, not correlated with computed band appeared at 3706 cm-1,
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downward shift in frequency indicating the presence of intermolecular hydrogen bonding in
dimer form. The O-H bending vibration is observed experimentally at 1050 cm-1 as strong band,
and theoretically at 1088 cm-1 due to the rocking bending mode of vibration. The difference
between actual and theoretical frequency may be assigned to intermolecular hydrogen bonding.
The Figure 3 clearly shows the presence of O-H···O hydrogen bonding in dimer, as in dimer
form the intensity of band of O-H in monomer at 3706 cm-1 increased and frequency is shifted
downward. This increase in intensity along with decrease in frequency of the dimer form as
compared to the monomer form, what clearly indicate the presence of O-H···O hydrogen bonds.
Table 4. Experimental and Theoretical Frequencies of IR along with Intensity and
Vibrational Assignment
I
IR
Frequency Scaled Experimental
Vibrational assignments
C-HAromatic + O-H + αC-Haliphatic
1088
1096
1139
1146
1192
1229
1242
1253
1306
1314
1323
1350
1365
1385
1402
1423
1463
1478
1481
1580
1050s
1100m
1145
13.426
C-HAromatic + O-H + αC-Haliphatic
C-HAromatic + C-N
C-HAromatic
12.3653
6.9042
1150m
1200w
14.7788
10.3409
17.981
C-HAromatic + N-H
C-HAromatic + N-H + αC-Haliphatic
C-HAromatic + N-H + αC-Haliphatic
C-HAromatic
1250m
1300w
37.2941
10.2608
15.6821
8.4198
C-HAliphatic
C-HAromatic + C-HAliphatic
C-HAliphatic
1330m
1350m
12.2977
172.9735
60.6736
123.1791
31.4672
59.9851
3.772
αC-Haliphatic + O-H
C-HAromatic + C-HAliphatic + O-H
C-HAromatic + C-HAliphatic
C-HAromatic + N-H
C-HAliphatic
1400m
1450s
C-HAliphatic
C-HAromatic
81.2011
55.5871
17.2222
C-HAromatic
1500w
1550w
(s)C-C=C + C-C=C
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C-HAromatic + N-H
(s)C=O + N-H + C-HAliphatic
(s)C=O + N-H + C-HAliphatic
(s)C-HAliphatic
1600
1663
1708
2926
2992
3004
3052
3067
3081
3092
3105
3508
3706
1600w
1650s
1700s
2930m
2980m
119.8445
687.0003
457.6824
30.4821
12.3452
15.9051
1.1975
(s)C-HAliphatic
(as)C-HAliphatic
(as)C-HAliphatic
(as)C-HAromatic
3100w
3150w
3.4707
(as)C-HAromatic
7.7816
(as)C-HAromatic
5.3436
(s)C-HAromatic
5.3392
(s)N-H
3400w
3430m
68.6926
37.4498
(s)O-H
Frequencies are given in cm-1, = stretching, α=twisting =scissoring, =rocking,
s=symmetric, as=asymmetric, w= weak, m= medium, s= strong.
Figure 3. FT-IR Absorption Spectra Calculated at B3LYP/6-31G(d,p) Level of Theory
NBO Analysis of E9
It is well known that NBO analysis is a handy tool for measuring molecular interaction among
molecules. These are mostly hyper conjugative interactions, charger transfer and hydrogen
bonding. In these interactions the electron density transfer from donor orbital to acceptor orbital
and give stabilization energy to whole of the system. The magnitude of interactions is related to
values of stabilization energy, greater values of energy show more interactions among molecular
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system [39]. Table 5 shows the NBO donor and acceptor orbital along with stabilization energy
values. The charge transfer from σ (O29-C50)→ σ*(C45-H46) and σ (O29-C50)→ σ*(C47-H48)
shows the larger stabilization energy values of 99.49 and 89.59 kJ/mol respectively, indicating
strong conjugative interaction between C-O bonding to C-H antibonding sigma orbital. In the
similar way the electron transfer from σ (N31-C50)→ σ*(C45-H46) and σ (N30-C50)→ σ*(C47-
H48) give stabilization energy of 66.78 and 53.26 kJ/mol respectively. The charge transfer from
π bonding orbital to π* antibonding orbital gives stabilization energy values of 32.96 and 31.98
kJ/mol for C16-C18→ C20-C22 and C20-C22→ C15-C24, respectively, these interactions are
due to the π electron delocalization in a system. The interaction between lone pair 1 (O4), lone
pair 2 (O4), lone pair 1 (O29) and lone pair 2 (O29) to antibonding σ* O26-H27, O26-H27, O1-
H2 and O1-H2 give stabilization energies of 5.01, 2.35, 5.04 and 2.38 kJ/mol, respectively,
indicating the presence of intermolecular O-H···O hydrogen bonding. The interaction of lone
pair 2 (O3) and lone pair 2 (O4) to σ* (N5-C14) and (N5-C25) give stabilization values of 34.68
and 28.93 kJ/mol respectively showing conjugative interaction between O to C-N. The
interaction of lone pair 1 (N5), lone pair 1 (N6) and lone pair 1 (N30) to π* (O4-C25), (O4-C25)
and (O29-C50) give stabilization energies of 69.97, 66.32 and 70.04 kJ/mol respectively showing
hyper conjugative interaction in which charge delocalization occur from lone pair of N to C-O
bond. The charge transfer between lone pair 2 (O28) and lone pair 1 (O29) to antibonding σ*
(C39-C40) and (C47-H48) give stabilization energy values of 21.32 and 50.68 kJ/mol,
respectively, indicating conjugative interaction between O to C-C and O to C-H. The NBO
analysis shows that molecular system contain O-H···O hydrogen bonding and strong conjugative
interactions (Table 5).
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Table 5. NBO analysis of E9 with Second-Order Perturbation Theory
Donor NBO
(i)
Type
Acceptor NBO Type
(j)
E(2)a
(kj/mol)
25.44
28.28
32.96
31.98
34.68
28.93
59.25
69.97
66.32
46.4
E(j) - E(i)b
(a.u.)
0.38
0.38
0.35
0.35
0.79
0.82
0.37
0.37
0.39
0.38
1.37
0.91
1.37
0.91
4.29
4.21
3.88
4.05
3.99
3.92
4
F(i,j)c
(a.u.)
0.089
0.094
0.097
0.098
0.149
0.139
0.137
0.143
0.145
0.122
0.074
0.043
0.074
0.043
0.584
0.549
0.29
C15-C24
C15-C24
C16-C18
C20-C22
O3
π
π
π
π
O3-C14
C16-C18
C20-C22
C15-C24
N5-C14
π*
π*
π*
π*
σ*
σ*
π*
π*
π*
π*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
π*
π*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
π*
π*
π*
π*
LP (2)
LP (2)
LP (1)
LP (1)
LP (1)
LP (1)
LP (1)
LP (2)
LP (1)
LP (2)
σ
O4
N5
N5
N6
N6
O4
O4
O29
N5-C25
O3-C14
O4-C25
O4-C25
C15-C24
O26-H27
O26-H27
O1-H2
5.01
2.35
5.04
2.38
O29
O1-H2
O29-C50
O29-C50
N30-C36
N30-C39
N30-C50
N31-H32
N31-C49
N31-C50
C40-C49
C41-C43
O28
C45-H46
C47-H48
C47-H48
C45-H46
C47-H48
C45-H46
C47-H48
C45-H46
C41-C43
C45-C47
N30-C39
C39-C40
C45-H46
C47-H48
N30-C50
N31-C50
C45-H46
C47-H48
O28-C39
O29-C50
O29-C50
C40-C49
99.49
89.59
27.07
20.85
53.26
27.03
20.37
66.78
28.28
31.78
34.4
21.32
46.19
50.68
30.63
30.25
33.2
σ
σ
σ
σ
σ
σ
σ
π
0.26
0.412
0.291
0.255
0.466
0.094
0.097
0.149
0.123
0.383
0.397
0.144
0.144
0.314
0.279
0.137
0.143
0.145
0.123
4.08
0.38
0.37
0.79
0.86
3.96
3.88
0.82
0.84
3.51
3.42
0.37
0.37
0.39
0.39
π
LP (2)
LP (2)
LP (1)
LP (1)
LP (2)
LP (2)
LP (2)
LP (2)
LP (1)
LP (1)
LP (1)
LP (1)
O28
O29
O29
O29
O29
O29
O29
N30
26.89
59.24
70.04
66.13
46.35
N30
N31
N31
a E(2) means energy of hyper conjugative interaction (stabilization energy).
b Energy difference between donor and acceptor i and j NBO orbital.
c F(i, j) is the Fork matrix element between i and j NBO orbital.
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UV Visible Analysis of E9
In the experimental graph the maximum obtained at 264 nm indicated the presence of HOMO→
LUMO (90%) transition as calculated by computational analysis and this is due to π to π*
transition in a compound. There are some other transitions which were calculated using
computational analysis are shown in Table 6.
Table 6. Experimental and Calculated Electronic Bands for E9
Experimental
wavelength (nm)
264
Calculated
wavelength (nm)
264
Oscillator strength
Major contribution
(%)
H-2→ L+2 (3%), H-1→ L+2 (5%),
H→ L (90%)
(f)
0.068
250
224
214
202
201
0.001
0.015
0.0001
0.204
0.796
H-5→ L (7%), H-3→ L (68%),
H-3→ L+9 (10%), H-3→ L+13 (3%)
H-2→ L (7%), H-1→ L (28%),
H→ L+2 (58%)
H→ L+1 (86%), H→ L+3 (4%),
H→ L+5 (3%)
H-4→ L (3%), H-2→ L (78%),
H→ L+2 (8%), H→ L+9 (3%)
H-1→ L (62%), H→ L+2 (28%)
Frontier Molecular Orbital of E9
The frontier molecular orbital theory is very helpful to calculate electric and optical parameters.
In this, HOMO orbital acts as donor and LUMO as electron acceptor. The excitation of electron
occurs from HOMO to LUMO. Figure 4-6 shows frontier HOMO and LUMO orbitals surfaces
with energy gap between occupied and unoccupied orbital. The energies for HOMO and LUMO
are calculated as -8.283 eV and -0.996 eV, respectively. The orbital energies of HOMO-1 and
LUMO+1 are -8.284 eV and -0.992 eV, respectively. The energies -8.854 eV and -0.181 eV
belongs to HOMO-2 and LUMO+2 orbitals. In HOMO and HOMO-1 orbital, the electron
density is mainly delocalized on phenyl ring and N-H of E9 compound, where, as in HOMO-2,
the electrons are delocalized through the nitrogen, oxygen and methylene groups. In LUMO and
LUMO+1 orbital, electrons are delocalized on phenyl ring and carbonyl group, where as in
LUMO+2, electrons are concentrated on phenyl ring and nitrogen atom. These frontier HOMO,
LUMO orbital energies are used in the calculation of global reactivity parameters as shown in
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Table 7. These parameters tell us about the chemical reactivity and stability of E9 compound
[40].
Figure 4. Molecular Orbital Surfaces and Energy Level Gap for the HOMO and LUMO of
E9 Dimer
Figure 5. Molecular Orbital Surfaces and Energy Level Gap for the HOMO-1 and
LUMO+1 of E9 Dimer
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Figure 6. Molecular Orbital Surfaces and Energy Level Gap for the HOMO-2, and
LUMO+2 of E9 Dimer
Table 7. Ionization Potential (I), Electron Affinity(A), Electro negativity (X) Chemical
Potential (ꢀ) Global Hardness (η) Global Softness (s) and Global Electrophilicity
(ω) of E9 Dimer
Combinations
Ionization potential (I)
Electron affinity (A)
Electro negativity (X)
Chemical potential (ꢀ)
Global hardness (η).
Global softness (s)
A
B
8.283
0.996
4.639
-4.639
3.643
0.1372
2.954
8.284
0.992
4.638
-4.638
3.646
0.1371
2.950
Global electrophilicity (ω)
A= HOMO & LUMO; B= HOMO-1 & LUMO+1
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Molecular Electrostatic Potential (MEP)
Molecular electrostatic potential (Figure 7) at a point around molecule tell us about the
electrostatic effect of electron and proton in molecule which relate with the chemical reactivity
and electronegativity of compound. The red color shows that there is negative electrostatic
potential and blue color shows that there is positive electrostatic potential. The red color mostly
contains electronegative oxygen and nitrogen atoms, whereas blue color contains mostly phenyl
ring hydrogen and carbonyl carbon atoms. The potential values show that oxygen act as
nucleophilic center and phenyl hydrogen as well as carbonyl carbon act as electrophilic center.
These electrostatic potential values tell us about the presence of molecular interactions in a
compound [40].
Figure 7. MEP Map of Dimer Calculated at B3LYP/6-31G(d,p) Basis Set
Spectral Characterization of Metal Complexes
FT-IR Characterization of Complexes
The data obtained by FT-IR for characterization of the metal complexes is reported in Table 8.
The metal coordination with isatin derived ligand was confirmed by the disappearance of O-H
peak at 3430 cm-1 and shifting of ν(C-O) peak from 1055 cm-1 to lower frequency by 10-19 cm-1,
showing the coordination of the oxygen to respective metal [41]. The ν(C=O) peak of isatin
moiety was also shifted from 1700 cm-1 to 1650-1670 by 30-40 cm-1, indicating the presence of
M-O bond [42]. The examination of data showed that ν(C-N) and ν(N-H) peaks are unchanged
during complex formation indicating the absence of M-N bond formation. Furthermore the
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appearance of new weak peaks of ν(M-O) at 473-495 cm-1, showing the formation of metal-
ligand bond through oxygen [41]. The origin of a new peak at 3336-3363 cm-1 indicated the
presence of coordinated water molecule [43]. All these peaks confirmed the formation of metal
complexes with isatin derived ligand.
Table 8. FT-IR Data of Metal Complexes
Compounds
Bond Vibrations (cm-1)
ν(H2O)
3345
3347
3336
-
ν(N-H) ν(C=O) ν(C-N) ν(C-O) ν(M=O) ν(M-O)
E13
E15
E18
E19
E21
E22
E23
E24
3201
3202
3189
3180
3181
3189
3202
3206
1657
1663
1670
1661
1652
1669
1658
1627
1141
1146
1139
1140
1143
1137
1143
1132
1045
1036
1044
1043
1041
1037
1040
1043
-
495
478
487
473
491
475
486
478
-
-
801
3349
3360
3358
3363
-
-
-
-
Magnetic Moments of Metal Complexes
The magnetic moment values were recorded using Gouy method for all the metal complexes
(Table 9). The copper and vanadium complexes (E13, E19) possessed magnetic moments values
of 1.95 and 1.78 BM, respectively, showing the presence of one unpaired electron [43]. The
magnetic moment of nickel (E15) was 3.19 BM showing the presence of two unpaired electrons.
The cobalt metal complex (E18) showed the magnetic moment of 4.38 BM indicating the
presence of three unpaired electrons [42]. The chromium complex (E22) showed magnetic
moment value of 3.92 BM indicating the presence of three unpaired electrons. The manganese
complex (E23) showed magnetic moment value of 5.85 BM indicating the presence of five
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unpaired electrons. The iron complex (E24) possessed magnetic moment value of 5.09 BM
showing the presence of four unpaired electrons [41]. The zinc complex (E21) was diamagnetic
in nature with zero magnetic moment value due to d10 system.
Table 9. Magnetic Moments of Metal Complexes
Sr #
1
Code
E13
E15
E18
E19
E22
E23
E24
E21
Metal
Cu(II)
Ni(II)
B.M (µeff)
1.95
3.19
4.38
1.78
3.92
5.85
5.09
0
2
3
Co(II)
VO(IV)
Cr(III)
Mn(II)
Fe(II)
4
5
6
7
8
Zn(II)
Antibacterial Bioassay of Ligand (E9) and Metal Complexes
The antibacterial bioassay was performed on four different bacterial strains as A (Escherichia
coli), B (Staphylococcus aureus), C (Neisseria gonorrhoeae) and D (Pseudomonas syringae) to
check the inhibitory activity of ligand and its metal complexes. The agar well diffusion method
was used for antibacterial assay in which diameters of inhibition zone were measured in
millimeter. The data in Table 10 and Figure 8 showed the results of antibacterial activity and
these results were compared with standard drug kanamycin. DMSO was used as solvent showing
no inhibition against any bacterial strain. The bacterial results showed that ligand exhibited
remarkable (12 mm) activity against D, which was higher than isatin and standard drug
kanamycin. This showed that ligand was more bactericidal than precursor isatin against D
bacterial strain. The ligand displayed significant (8-9 mm) activity against B and C, respectively
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while weaker (3 mm) activity was observed against A strain. The metal complex (E13) possessed
significant (8-10 mm) activity against B, C and D strains and no activity against A strain. Also,
significant (10 mm) inhibition zone was shown by E15 against C and D strain and significant (8
mm) against A and B strain. The complex E17 showed significant (8 mm) activity against A, B
and D and showed no activity against C strain. Similarly, the E18 complex displayed significant
(8-9 mm) activity C and D and moderate (6 mm) activity was shown by B and inactive against A
bacterial strain. The compound E19 showed significant (8 mm) activity against D and C, and
moderate (6 mm) activity against B, respectively. However, E19 complex demonstrated weaker
(4 mm) activity against A strain. The compound E21 possessed significant (10 mm) activity
against B and moderate (7 mm) activity against D, respectively. The complex E22 was also
inactive against A and C, and showed significant (8 mm) activity against D and B, respectively.
The E23 complex exhibited significant (9 mm) activity against C, moderate (7 mm) activity
against B and D, and no activity was observed against A strain. Similarly, E24 complex showed
significant (8 mm) activity against B, moderate (7 mm) activity was shown by C and D strains
and weaker (4 mm) activity against A strain. The E25 complex exhibited significant (9-10 mm)
activity against B and C, and no activity against A and D bacterial strain. The examination of
antibacterial data revealed that complexes showed promising activity against B and C strain as
compared to ligand. This increase in activity in complexes was due to metal chelation property
[44].
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Table 10. Antibacterial Bioassay of Ligand (E9) and Metal Complexes
Sr #
Compounds
Inhibitions Zone (mm)
A
B
C
D
1
2
3
E9
E13
E15
03
Inactive
08
09
08
08
08
10
10
12
08
10
4
5
6
E17
E18
E19
08
Inactive
04
08
06
06
Inactive
09
08
08
08
08
7
8
9
10
11
12
13
14
E21
E22
E23
E24
Inactive
Inactive
Inactive
04
Inactive
12
10
08
07
08
10
13
10
Inactive
Inactive
09
07
08
07
07
07
09
13
12
E25
Inactive
08
08
Inactive
Isatin
Kanamycin
DMSO
12
Inactive
Inactive
Inactive
Figure 8. Antibacterial Activity of Ligand (E9) and Metal Complexes Against Four
Bacterial Strains
Conclusion
The present research work describes the design and synthesis of isatin based ligand and its metal
complexes with first transition series. The ligand was designed by reacting equimolar amount of
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isatin and ethanolamine in ethanol at high temperature. The high temperature broke the C-C
single bond between two carbonyl carbons of isatin moiety and formation of C-N bond between
carbonyl carbons and nitrogen of ethanolamine occurred. The resulting six membered ring
formation took place. The structure of ligand was supported by physical (m.p, colour and
1
1
solubility) and spectral (IR, mass, HNMR, CNMR and single crystal analysis) data. The DFT
calculations were performed for the synthesized crystalline ligand. The computational IR results
were compared with experimental IR and hydrogen bonding in ligand was proved with FT-IR
findings. The Natural Bond Orbital (NBO) analysis supported the hydrogen bonding results
established from IR and explained the inter and intra molecular interactions. The Frontiar
Molecular Orbital (FMO) analysis showed the energies of HOMO and LUMO orbitals and these
energies were used to find out the global reactivity parameters of ligand. The computed U.V
analysis explained the π to π* transition in compound. The bidentate ligand was reacted with
transition metal salt of first series to prepare metal complexes. The complexes were characterized
by FT-IR and magnetic moment measurements. The octahedral geometry of complexes was
observed except vanadium which had square-pyramidal geometry. All the compounds were
tested against four bacterial strains and results concluded that most of the metal complexes were
more bactericidal than ligand against B and C bacterial strains due to chelating property of
complexes.
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Experimental
Materials and Methods
All the required chemicals were of analytical grade and no purification steps were performed
except for solvents like ethanol and methanol which were purified. Isatin and ethanolamine were
purchased from Sigma Aldrich and Merck, respectively, and used in reaction scheme without
further purification. Melting points were taken on Staurt SMP 10, for solvent evaporation
purpose rotary evaporator made of Heidolyph was used. For checking the progress of the
reaction, TLC was performed using Ultraviolet lamp (UVGL-58, Cambridge, UK). The UV
spectra of compounds were recorded on UV-4000, and vibrational characterization was
performed on Shimadzu FTIR-8400S Spectrophotometer. Electron impact mass spectrometer
instrument made of JEOL MS Route was used to collect fragmentation pattern. 1H and 13C NMR
was carried out using Bruker Spectrospin Avance DPX-400MHz using TMS as internal standard
and d6-DMSO as a solvent. The single crystal analysis was performed on Bruker Kappa APEXII
CCD diffractometer. ESCO made Laminar Flow Cabinet and Memmert made Incubator was
used for antibacterial activity.
Chemistry of Ligand Synthesis
1H-Indole-2,3-dione was added in 250 mL two-necked round bottom flask containing 30 mL of
ethanol and refluxed for 30 minutes until all the isatin was dissolved until yellowish color
solution appeared. Hot ethanolic solution of ethanolamine was added in refluxed isatin solution
in an equimolar ratio giving purple color solution which was refluxed for 10 hours and
monitored with TLC until brown precipitates produced. The reaction was cooled to room
temperature and precipitates collected, washed with ethanol and dried in vacuum to give pure E9.
The product was further recrystallized in methanol to give pure brown crystals of E9.
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3-(2-hydroxyethyl)quinazoline-2,4(1H,3H)-dione (E9)
Yield: (60%); mp 248°C; color (brown); IR (KBr, cm-1): 3430 (O-H), 3200 (NH), 3150 (C-
1
Haromatic), 2930 (C-Haliphatic), 1700 (C=O), 1550 (C=C), and 1145 (C-N); H NMR (ppm d6-
13
DMSO): δ 3.54 (t, 2H), 3.99 (t, 2H), 4.71 (s, 1H), 7.15-7.92 (m, 4H), 11.31 (s, NH); C NMR
(DMSO-d6): δ 42.1, 57.6, 113.8, 114.9, 122.3, 127.3, 134.8, 139.3, 150.2, 162.0; Mass Spectrum
(EIMS): [M]+ = 206.
Chemistry of Metal Complexes Synthesis
All complexes were prepared using following standard procedure. Ligand (1 mmol) was added in
50 mL two-necked round bottom flask containing 20 mL of methanol. To it added dropwise 10
mL of methanolic solution of respective metal salt (0.5 mmol) and solution was refluxed. Colour
changes and precipitate formation occurred during refluxing. The reaction was monitored with
TLC. After 7 hours reflux, the mixture was cooled to room temperature, precipitates were
collected, washed with fresh methanol, dried in vacuo and recrystallized in mixture of methanol :
ethanol (1:1) to give TLC pure respective metal complex.
Computational Procedure
All DFT calculations were carried out with the help of Gaussian 09 program package [45], at the
M06-2x/6-31G(d,p) level of theory. The UV–Visible calculations were performed using TD-
DFT with B3LYP/6-31G(d,p) method in the gas phase [46, 47]. All the input data files were
prepared, using GaussView 5.0 [48, 49]. Finally Chemcraft [50], Avogadro [51] and GaussView
5.0 programs have been used to analyze the output data files.
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Biological Studies
In-vitro Antibacterial Bioassay
The antibacterial screening was performed by agar well diffusion method on four different
bacterial strains as A (Escherichia coli), B (Staphylococcus aureus), C (Neisseria gonorrhoeae)
and D (Pseudomonas syringae). In these bacteria the B was gram-positive and A, C, D were
gram-negative. The media (20 g agar, 20 g glucose, 0.2 g (NH4)2SO4, 0.2 g KH2PO4, 0.05 g
CaCl2, 0.05 g MgSO4.7H2O, 1000 mL dist. H2O) for bacterial growth was prepared by adding
o
these ingredients in a 2000 mL conical flask and autoclaved at 121 C for one hour. The petri
dishes, micropipette tips and filter paper strips were also autoclaved. The recommended samples
of concentration 10 mg/250 µL DMSO was prepared. The semi-liquid media was poured in petri
dishes, bacterial inoculums were dispersed on the media present in petri dishes with the help of
cotton swab. The filter paper strips were placed on each petri dish and samples (10 µL, 400
µg/disc) were injected on these strips with the help of micropipette tips. The control (Kanamycin,
10 µL) was also placed on one filter paper strip to see the comparative effect of test sample and
control on the inhibition of respective bacteria. The wrapped petri dishes were placed in
incubator at 37oC for 24 hours. After 24 hours, the diameters of inhibition zone were measured in
millimeter (mm). The separate DMSO solution was subjected to bacterial activity and results
showed that DMSO itself has no activity against any bacteria [52].
Acknowledgments
A.A.C.B (grants #2015/01491-3 and 2014/25770-6) is thankful to Fundação de Amparo à
Pesquisa do Estado de São Paulo for financial support. Moreover, Muhammad Khalid (grant #
2017/1314) is thankful to HEC Islamabad Pakistan for financial support.
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