Synthesis, characterization, molecular modeling, antioxidant and microbial properties of some Titanium(IV) complexes of schiff bases

Article abstract of DOI:10.1016/j.molstruc.2018.04.025

The titanium(IV) complexes of Schiff bases derived from aroylhydrazine e.g. benzoylhydrazine, salicyloylhydrazine, nicotinic acid hydrazide with aldehyde or ketone are reported and characterized based on UV–vis spectroscopy, (Infra-red) IR spectra, ¹H NMR spectra, mass spectra, magnetic susceptibility and molar conductance measurements. Complexes are found to possess 1:2 (metal:ligand) stoichiometry. The prepared ligands were act as dibasic tridentate ligands. On the basis of experimental evidences octahedral geometry has been proposed for prepared complexes. Geometry was confirmed by the optimized structure obtained from computational study. The synthesized ligands, in comparison to their titanium(IV) complexes, were also screened for their microbial and antioxidant properties.

Full text of DOI:10.1016/j.molstruc.2018.04.025

Accepted Manuscript
Synthesis, Characterization, Molecular Modeling, Antioxidant and Microbial
Properties of Some Titanium(IV) Complexes of Schiff Bases
Mohammad Nasir Uddin, Sonia Khandaker, Moniruzman, Shaharier Amin, Wahida
Sumi, Md. Atiar Rahman, Sheikh Mahbubur Rahman
PII:
S0022-2860(18)30456-3
10.1016/j.molstruc.2018.04.025
MOLSTR 25098
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
24 January 2018
04 April 2018
04 April 2018
Please cite this article as: Mohammad Nasir Uddin, Sonia Khandaker, Moniruzman, Shaharier
Amin, Wahida Sumi, Md. Atiar Rahman, Sheikh Mahbubur Rahman, Synthesis, Characterization,
Molecular Modeling, Antioxidant and Microbial Properties of Some Titanium(IV) Complexes of
Schiff Bases, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.04.025
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ACCEPTED MANUSCRIPT
Synthesis, Characterization, Molecular Modeling, Antioxidant
and Microbial Properties of Some Titanium(IV) Complexes of
Schiff Bases
1
1
1
Mohammad Nasir Uddin* , Sonia Khandaker , Moniruzman, Shaharier Amin , Wahida
2
3
4
Sumi , Md. Atiar Rahman , Sheikh Mahbubur Rahman
1
2
3
Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh
Department of Microbiology, University of Chittagong, Chittagong-4331, Bangladesh
Department of Biochemistry & Molecular biology, University of Chittagong, Chittagong-
4
331, Bangladesh
4
UL Laboratories, Dhaka, Bangladesh
Corresponding author: nasircu72@gmail.com
Abstract
The titanium(IV) complexes of Schiff bases derived from aroylhydrazine e.g.
benzoylhydrazine, salicyloylhydrazine, nicotinic acid hydrazide with aldehyde or ketone are
1
reported and characterized based on UV-vis spectroscopy, (Infra-red) IR spectra, H NMR
spectra, mass spectra, magnetic susceptibility and molar conductance measurements.
Complexes are found to possess 1:2 (metal:ligand) stoichiometry. The prepared ligands were
act as dibasic tridentate ligands. On the basis of experimental evidences octahedral geometry
has been proposed for prepared complexes. Geometry was confirmed by the optimized
structure obtained from computational study. The synthesized ligands, in comparison to their
titanium(IV) complexes, were also screened for their microbial and antioxidant properties.
Keywords: Schiff bases, titanium(IV) complexes, aroylhydrazine, nicotinic acid hydrazide,
dibasic tridentate ligands, computational study, octahedral geometry, anti-microbial and
antioxidant properties.
1
. Introduction
Schiff base ligands are considered as ‘‘privileged ligands’’ [1] because they are easily
prepared by condensation between aldehydes and primary amines. The chemistry of
transition metal complexes with Schiff bases has played an important role in the development
of coordination chemistry as a whole. The field of Schiff base complexes is fast developing
because of the wide variety of possible structures for the ligands, depending on the aldehyde
and amines used. Many Schiff bases and their complexes have been widely studied because
1

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of their industrial and biological applications [2, 3]. Hydrazones are the condensation
products of hydrazine derivatives with carbonyl compounds, they contain an acyclic group
>
C=N-N<. It is long since hydrazones and their derivatives, due to their high complexing
ability, have attracted the attention of scientists. Depending on various factors (the nature of
the hydrazone and the metal atom, reaction conditions, the ratio of reactants etc.) hydrazones
form either mono- or polynuclear coordination compounds with metal atoms [4]. Aroyl
hydrazones and their metal derivatives often possess biological activity and can inhibit
enzymatic reactions in the cell [5-7]. The remarkable biological activity of acid hydrazides,
R-CO-NH-NH , a class of Schiff bases, their corresponding aroylhydrazones, R-CO-NH-
2
N=CH-R and their dependence of their mode of chelation with transition metal ion present in
the living system have been of significant interest. Isonicotinic acid hydrazide is a drug of
proven therapeutic importance and is used bacterial ailments e.g. tuberculosis [8]. Diketones
have been widely used as intermediates in the preparation of large number of biologically
important heterocyclic compounds and as precursors of potential anti-diabetic drugs [9].
Metal complexes of S-, N-, and O-chelating ligands have attracted considerable attention
because of their interesting physico-chemical properties, pronounced biological activities and
their use as models for metalloenzyme active sites [10,11]. In this investigation, titanium(IV)
complexes were synthesized from some new Schiff base ligands. They are characterized in
terms of conventional techniques. Geometry of the ligands and complexes was optimized by
computational chemistry study. Selected ligands and complexes were tested against the
growth of bacteria and fungi. Also their antioxidant property was to evaluate.
2
. Experimental
2
.1 Instrumentation and Apparatus
Electronic weighing balance, Microwave oven, Magnetic stirrer, Reflux condenser, Round
bottom flasks, Beakers, Pipettes, Funnels, Water bath, Burners, Test tubes, Desiccator,
Melting point apparatus, UV-Vis spectrophotometer, IR spectrometer, 1H NMR
Spectrometer, Mass Spectrometer, pH Meter, NMR spectrometer, Autoclave, Conical flask
(250 ml), Test tubes, Micropipettes, Horizontal Laminar Flow Unit, Incubator, Micro tips etc.
2
.2 Chemicals and solvents
Methanol, Ethanol, Nicotinic Acid Hydrazide, Ethyl Acetoacetate, Benzoyl Acetone, 2-
Hydroxy-1-Naphthaldehyde, Dimethyl Sulfoxide, Dimethyl Formamide, Acetone,
Chloroform, Diethyl ether, Titanium tetrachloride, Beef Extract, Peptone, 95% Ethanol, 70%
2

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Ethanol, Sterile Water, Potato, Dextrose, Agar, Distilled Water, Folin Ciocalteu Reagent
(
FCR), Na CO (20 % solution), Standard gallic acid, DPPH solution (2,2-diphenyl-1-
2 3
picrylhydrazyl), Ascorbic acid etc.
2
.2.1 Benzoyl Hydrazine (C H CONHNH )
6
5
2
This compound was prepared (12) by refluxing an equimolar mixture of ethylbenzoate and
hydrazine hydrate for 21 hours. The product thus obtained was recrystallized twice from
ethanol. Melting point 112o.
2
.2.2 Salicyloylhydrazine (2-OH-C H CO-NHNH )
6 4 2
An equimolar mixture of ethylsalicylate and hydrazine hydrate was refluxed for 5 hours
where after the white solid mass obtained was recrystallized twice from hot water (12).
Melting point 146o.
2
.2.3 Synthesis of Ligands
The Schiff Base ligands were synthesized by the following general procedure. The aliphatic
or aromatic amine compound was dissolved in absolute methanol in a round bottom flask
with constant stirring and heating. Then ketone or aldehyde was added drop wise. The
mixture was heated under reflux for 2 hours. The volume was allowed to reduce placing the
reaction mixture in a water bath. After about one hour heating the reaction mixture was
allowed to cool at room temperature for 20 minutes. The solid precipitated was filtered off,
and washed several times using absolute methanol. Then the solid precipitate dried over silica
gel.
2
.2.4 Synthesis of Complexes
The ligand (10 mmol) was dissolved in absolute ethanol and 10 mmol TiCl was added drop
4
wise in it. Then the reaction mixture was refluxed for 3 hours and allowed to cool at room
temperature. Colour change was occurred for each complex. Then the metal complexes were
separated by filtration and washed thoroughly with ethanol and dried in vacuo over silica gel
and CaCl2.
2
.3 Computational Study
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The ligands and complexes were designed depending on quantum mechanical (QM)
calculation. QM methods allow us to calculate different types of energies precisely and
interpret various types of complicated interaction between ligands and metal in the formation
of complexes [13]. In the present work, Density functional theory with Becke’s, exchange
functional combining Lee, Yang and Paee’s correlation functional [14] in Gaussian 09
program package for the ligands and complexes [15]. Pople’s 6-31G (d,p) basis set has been
employed to optimize the ligands and complexes to elucidate their thermodynamic properties
such as; thermal energy, enthalpy, Gibb’s free energy, entropy, dipole moment and their
electronic properties e.g. frontier molecular orbital features (HOMO, LUMO, HOMO-LUMO
gap), hardness and softness [16].
Hardness and softness of all ligands and complexes were also calculated from the energies of
frontier HOMOs and LUMOs considering Parr and Pearson interpretation [17] of hamess in
DFT and Koopmans theorem [16] on the correlation of ionization potential (IP) and electron
affinities (EA) with HOMO and LUMO energy. The following equations are used to
calculate the Hardness (η) and Softness (S);
η = [휀LUMO-휀HOMO] /2; S = 1/ η
2
.4 Microbial Property
All measurements of antifungal and antibacterial activities have been carried out and the test
tube cultures of the bacterial pathogens were collected from the Department of Microbiology,
University of Chittagong, Bangladesh.
2
.4.1 Anti-bacterial property
List of test organisms which used in present research are Staphylococcus aureus, Bacillus
cereus, Salmonella paratyphi and Candida albicans. Standard Nutrient Broth media
consisting peptone (5g), beef extract (3g), NaCl (0.5g), distilled water (1000mL) was used
throughout the study. 0.2%, 0.5% and 0.8% solutions were prepared by dissolving 0.002 g,
0
.005 g and 0.008 g solid samples in 1 mL DMSO respectively. Small amount of the
collected microorganisms were transferred to the nutrient agar containing test tubes with the
o
help of sterilized needles. The inoculated tubes were incubated for 24 hours at 37 C.
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A number of test tubes were freshly cleaned and 10 mL of prepared nutrient broth were
placed in every test tube. The test tubes were then capped with cotton and sterilized by
o
autoclaving at 15-lbs. pressure/sq. inch at 121 C for 20 minutes. Then 100 µL prepared test
sample solutions were added to the sterilized nutrient broth containing test tubes by
micropipette. Then the 100 µL incubated selected microorganisms (freshly cultured) were
carefully inoculated to these test tubes by micropipette. After inoculation, test tubes were
o
incubated at 37 C. Then the absorbance of every incubated solution was recorded by UV-
Spectrophotometer at 600 nm after 6 hours to 24 hours.
2
.4.2 Antifungal Activities
The prepared ligands and complexes were tested in vitro against fungi by two methods. One
was by liquid medium method against Fusarium and another was by disc diffusion technique
against Aspergillus niger. 0.8% solutions were prepared by dissolving 0.008 g solid samples
in 1 mL DMSO.
2
.4.3 Culture media
PDA (Potato-Dextrose-Agar) medium was used as culture media and it was prepared by the
composition of Potato (200 g), Dextrose (20 g), Agar (15 g), Distilled Water (1000 mL).
To prepare PDA medium, potatoes were cut into pieces and weighed about 200 g and boiled
in 1000 mL of distilled water for an hour, filtered and volume was made up to 1000 mL by
adding more distilled water. Glucose and agar were then added and stirred. The pH of the
o
medium was checked and recorded. The medium was then sterilized at 121 C temperature
and 15 lb pressure 25 minutes.
2
.4.4 Liquid Medium Method
A number of conical flasks were freshly cleaned and 20 mL of prepared LPD media [18] was
taken in every conical flask. The conical flasks were then capped with cotton and sterilized
o
by autoclaving at 15-lbs. pressure/sq. inch at 121 C for 20 minutes. Then 200 µL prepared
sample solutions were added to the sterilized LPD media containing conical flasks by
micropipette. Then selected microorganism was carefully added to these conical flasks by a
loop. After adding the microorganism test tubes were incubated for 3 days. Same procedure
was performed without adding microorganism and was recorded pH instant and after 3 days
to observe the activity of the sample and the solvent. After 3 days all the organism containing
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solutions were filtered and separated the growing organism from the solutions. The filtered
0
growing organism dried in oven at 60 C. Then pH of the filtered solutions was taken by pH
meter.
2
.4.5 Cup Plate Technique
The prepared ligands and complexes were tested in vitro against fungi Aspergillus niger by
cup plate technique also [19]. PDA was used as culture media. The culture media prepared
without agar powder is called nutrient broth. Nutrient broth was inoculated with the fungal
suspension with the help of an inoculating loop in an aseptic condition, mixed thoroughly and
o
kept in shaker for 2 days in order to facilitate the case of homogeneous distribution at 37 C.
This type of liquid culture is called broth culture. Fresh culture of this type was always used
throughout the sensitivity testing.
The test ligands and complexes were mixed with sterilized liquid media. The medium was
poured into sterile petridishes in an aseptic condition on a leveled horizontal surface so as to
give a uniform depth of approximately 4 mm. Then the medium had been allowed to cool to
room temperature in order to solidify the medium. Sterilized cork borer was taken and the test
fungus (Aspergillus niger) plate were cut by the borer. One colony with the help of sterilized
needle was transferred into the prepared solid plate. After transferring, the plates were
o
incubated at 27 C for 2-3 days. The zone of growth or zone of inhibition was measured and
recorded.
2
.5 Antioxidant Properties
Some prepared Schiff base ligands and complexes were tested for antioxidant property. This
experiment was carried out at Department of Biochemistry and Molecular Biology,
University of Chittagong. Total Phenolic Content Determination (TPC) and DPPH Free
Radical Scavenging Activity experiments were done to evaluate the antioxidant property of
ligands and complexes.
2
.5.1 Determination of Total Phenolic Content (TPC)
Total phenolic content of test samples were determined by a method established by with
some modification using FCR (Folin Ciocalteu Reagent) [20]. The test samples were
oxidized with FCR and the reaction was neutralized with sodium carbonate. The absorbance
was measured at 760 nm. The phenolic content was expressed as Gallic acid equivalents
6

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using the following linear equation based on the calibration curve. The result was expressed
in micrograms equivalent gallic acid by grams of the powder dry mass of the test samples (µg
GAE/g).
At first 20 μL sample or 20 μL standard solution was taken in screw cap tube and then added
1
.58 mL distilled water to the tube. After that 100 μL FC reagent was added and incubated at
room temperature for 1–8 minutes. Then 300 μL Na CO solutions was added into the tube
2
3
and incubated at room temperature for 2 hrs. Finally optical density (OD) of the solution was
measured at 760 nm (Note: Used distilled water as blank).
2
.5.2 DPPH Free Radical Scavenging Activity
A certain amount of sample was dissolved in DMSO to prepare the stock solution. Standard
solution: 1000 mg of ascorbic acid was dissolved in 10 mL of solvent (by which extract
prepared) to prepare 1 µg\mL. 0.4 mM DPPH solution: 0.158 g of DPPH (MW 394.32) was
dissolved in 100 mL of methanol and the solution was kept in conical flask. It was protected
from the light by covering the flask with aluminium foil.
Procedure [21]: A 2.5 mL of different concentrations of ascorbic acid (30, 60, 120, 240 and
-1
4
80 µg mL ) were taken in triplicate numbers of test tubes. Then 2.5 mL of different
-1
concentrations of test sample (30, 60, 120, 240 and 480 µg mL ) were taken in triplicate
numbers of test tubes. A 2.5 mL of distilled water was taken in duplicate pair of test tubes for
control in case of standard, and 2.5 mL of DMSO was taken in duplicate pair of test tubes for
control in case of test samples. 1.5 mL of 0.4 mM DPPH solution was mixed in all of the
above test tubes. The test tubes were kept in dark for 30 minutes at room temperature for
complete reaction. The degree of DPPH decolourisation to yellow indicates the scavenging
efficiency of the extracts. Then the absorbance of the solution was measured at 517 nm using
a spectrophotometer against blank (methanol). Lower absorbance of the reaction mixture
indicated higher free radical-scavenging activity.
DPPH radical scavenging activity was calculated according to the following equation:
퐴푠
DPPH radical scavenging (%) = [1 ‒ ( ) 푥 100]
퐴푐
Here,
Ac = absorbance of control,
As = absorbance of sample solution.
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Then % of inhibition was plotted against respective concentrations used and from graph IC50
was calculated.
3
. Results and Discussion
3
.1 Physical Properties of Prepared Ligands and Complexes
All the prepared ligands and complexes were coloured compound with high melting point
o
>
200 C.The melting point of most of the ligands was less than the prepared complexes. Both
ligands and complexes were quite stable at room temperature and can be stored for a long
time. They were insoluble in water but completely soluble in both DMSO and DMF. The
physical properties of prepared Schiff base ligands and complexes are given in table-1.
3
.2 Infrared Spectra
-1
The bands obtained in the region 3160-3270 cm for the aroylhydrazones bases are attributed
-1
to v-N-H. Pickard and Polly [11] reported the vN-H frequencies near 3200 cm for a number
of ketimines. Association of the N-H group with ketonic group gives absorption in the range
-1
3
240-3320 cm . The β-diketone hydrazone ligands seem to exist in the keto form and do not
show enolic OH bands. In o-hydroxycarbonyl-hydrazones there is no band above 3270 cm-1
due to the free OH group thus showing it to be hydrogen bonded with the azomethine
nitrogen [12]. In the infrared spectra of the free ligands, generally two bands are observed in
-1
-1
the region 3040-3380 cm . One of these two bands above 3000 cm is due to the hydrogen
OH group and the other being due to the free of hydrogen bonded N-H [4]. The broad band
-1
around 3200 cm might be a mixture of vN-H and H-bonded phenolic/ enolic OH stretches.
-1
-1
The bands observed between 1640 cm and 1675 cm for the free ligands are due to vC=O
-1
and that obtained at 1600-1632cm are due to vC=N of the azomethine group [6,8]. The
-1
bands obtained at 1530-1580 cm are due to the vC=C aromatic [6,12].
In the infrared spectra of the TiL complexes, the absence of the vO-H frequency indicates
2
deprotonation of both are replaceable hydrogen atoms and the dibasic character of the
benzoylhydrazone Schiff bases. A representative IR spectrum is shown in Fig. 1. The spectra
of the complexes show no characteristic bands for the vN-H and vC=O in agreement with the
ligands being coordinated in the enolic form. This mode of coordination is further supported
-1
in each case by the appearances of the vC=N band at about 1600 cm . The vC=N present in
-1
the free ligand show a downward shift of 10-35 cm indicating the involvement of the
nitrogen of the azomethine group in coordination [11]. The bands appearing around 1600cm-1
8

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seems to originate from the stretching mode of the conjugate >C=N-N=C< grouping [7,12]
4
+
suggesting the enolization of the ligand in presence of Ti and the participation of the enolic
oxygen in coordination. Also, as stated above, the disappearance of all bands above 3000cm-1
confirms the participation of the phenolic and enolic oxygen in coordination on
-1
deprotonation. The bands appearing at 1250-1372cm have been assigned as due to vC-O
phenolic/enolic). The formation of the TiL compounds is also indicated by the appearance
(
2
of the vN-N at a higher frequency as compared to that in the free ligand [11,12].
The bands characteristic of vTi=O were absent in the TiL complexes thus indicating the
2
presence of the non-oxotitanium (IV) in these present metal chelates. Based on the previous
-1
-
results [11, 12], the bands appearing for the present systems at 530-600 cm and 400-470 cm
1
have been assigned tentatively to Ti-N and Ti-O stretching frequencies respectively. These
vTi-N and vTi-O band regions seem reasonable on the basis of some other M-N and M-O
band regions observed for some other metal complexes of related systems [4-7]. These vTi-N
and vTi-O assignments (Table-4) are less definitive and tentative. The presence of a smaller
number of bands in this region was an advantage for attempts of the present assignments.
Some infrared spectral data along with their tentative assignments for the free ligands and for
the TiL complexes of these ligands are given in table 2.
2
3
.3 Electronic Spectra
The electronic spectra of the some prepared TiL complexes were run in DMF and some were
2
in DMSO solutions recorded in the 250-500 nm region (table 2). The electronic spectral data
of the free ligands and the TiL complexes are given in table-5. The spectra of the Schiff
2
base LH exhibit three main peaks at around 270, 320 and 370 nm. The first and second
2
peaks around 270, 320 nm were attributed to aryl π-π*and iminoπ-π* (-C=N) transitions
respectively [22]. The first band of the other complexes of the Schiff base LH was not
2
significantly affected by chelation. The second band was shifted to a shorter wavelength by
chelation. The third in the spectra of LH (~370 nm) was assigned to n-π* transitions [23].
2
This band was shifted to a longer wavelength along with an increase in its intensity. This shift
may be attributed to the donation of the lone pairs of the nitrogen atoms of the Schiff base
LH to the metal ion (N-M). Similar observation was observation was obtained for the
2
prepared complexes. The electronic spectra of the complexes showed bands similar to those
observed for the free ligands. There is no evidence of any d-d transition, for the TiL2
complexes, over the visible region. The bands in the longer wavelength region may be
9

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attributed to be LMCT transition. The complexes are coloured only through these intense
0
charge transfer absorptions tailing in from the ultraviolet. Being a d system, the present
complex system should not show any d-d but C.T transitions. The other bands (table 2)
observed are all intense and may be assigned to the π--->π* (benzoid and azomethine) and n--
->π* (azomethine) transitions as well as to the C.T. The electronic spectral behaviour of the
0
complexes suggests that the complexes are genuine d -Ti(IV) species rather than any Ti(III).
Representative electronic spectra of a ligand and its complex have been shown in fig. 2.
3
.4 Conductance and Magnetic Measurements
Magnetic measurements were performed at room temperature. The measured magnetic
0
susceptibility values (table 3) suggest diamagnetic behaviour supporting 3d electronic
configuration consistent with the 4+ oxidation state of central metal ion in complexes. The
−
1
2
−1
very low molar conductance values obtained in the 2.81–16.50 ohm cm mol range [24],
in DMF and DMSO solutions, for the complexes show them to be non-electrolyte in nature.
Thus it is evident that there were no inorganic anions present outside the coordination sphere.
The very low molar conductance values in DMF solutions also support the neutralization of
the 4+ oxidation state of the central titanium ion by the two coordinated dinegatively charged
tridentate ligands in these complex systems. Table-6 also shows the molar conductance
values of the complexes.
1
3
.5 H NMR Spectra
1
The H NMR spectra of the compounds were obtained in DMSO at room temperature using
1
TMS as an internal standard. The H NMR data and assignments of the compounds are
presented in table 3. The free LH ligands exhibit a peak between 11.116-13.19 ppm, which
2
is due to hydrogen-bonded phenolic protons. This peak is due to hydrogen bonded phenolic
protons and the integration is generally less than 2.0 due to this intramolecular hydrogen
bonding. The chemical shift observed for the OH protons in the ligands was not observed in
1
any of the complexes. The disappearance of the singlet signals for the OH proton in the H
NMR spectra of the complexes indicating the enolic oxygen atoms are coordinated to the
central metal atom via deprotonation. The same result was confirmed by the IR spectra. The
presence of a sharp singlet for the CH=C proton at 5.7 ppm and 6.047 ppm respectively
clearly showed a up field shift compared to the free ligand and indicated that the magnetic
1
environment is equivalent for all such protons. The H NMR spectra of all the complexes
showed a downfield shift in the frequency of azomethine protons confirming coordination of
1
0

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the metal ion [25]. This down field shift observation may be assigned to the deshielding of
protons as a result of the reduction of electron density after coordination [26]. The multiplets
of aromatic protons appeared within the range 7.4-8.2 ppm and they were not affected by
chelation. The azomethine (H C-C=N) resonance signal is appeared at 2.27 ppm for Ti(Etac-
3
NH) [11,12]. This downfield chemical shift observation showed the coordination of the
2
azomethine nitrogen to central atom [27].On the basis of the physical and spectral data of the
Schiff bases and the complexes discussed above, it is assume that the metal ions are bonded
to the Schiff bases via the phenolic oxygen and the iminonitrogen. Fig-3 shows the NMR
spectrum of Ti(Etac.NH)2.
3
.6 Mass Spectra
The mass spectra of Etac.NHH , Ti(Etac.NH) , BH.HNPH and Ti(BH.HNP) show
2
2
2
2
molecular ion peak at m/z =250.6, m/z=542.4, m/z=289.2 and m/z=622.6 respectively which
correspond to the molecular weight of the respective compound, corresponds to [M+1]
supports to the structure of the complexes and confirms the ML type stoichiometry of the
metal chelates. The series of peaks, in the ranges of 109.1, 147.1, 162.2, 175.2, 204.2, 221.2
and 234.2 may be corresponding to various fragments of Etac.NHH and their intensity gives
2
an idea of stability fragments. The mass Spectrum of Ti(Etac.NH) shows the series of peaks
2
at 260.1, 322.1, 350.1, 386.1, 422.2, 452.2, 486.3, 514.3 may correspond to various fragments
and their intensity gives an idea of the stability of these fragments. Fig-4 shows the mass
spectrum of Ti(Etac.NH) figure 5 shows mass fragmentation pattern of this comple. The
2
series of peaks, in the ranges of 110.60, 161.2, 173.2, 198.2, 210.2, 262.3 and 274.3 may be
corresponding to various fragments of BH.HNPH and their intensity gives an idea of
2
stability fragments. An ‘isotope’ of any given element is an atom with the same number of
protons but a different number of neutrons, resulting in a different overall mass. Almost all
elements have a variety of naturally occurring isotopes. For isotopic abundance, some
fragments were found in which one or two units were less or more than the calculated value.
3
.7 Computational Studies
The thermodynamic properties of the ligands and and complexes are also computed at
PBEPBE/SDD level of theory, and the results are summerizes in table 4. The thermal
energy,enthalpy, Gibb’s free energy of ligand Etac-NHH is greater than the ligand BH-
2
HNPH and the complex Ti(Etac-NH) is greater than the complex Ti(BH-HNP) . Dipole
2
2
2
1
1

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moment is another important parameter in the study of ligand and complex formation system,
drug-receptor systems and plays a significant role for the formation of hydrogen bond in the
biological system. With the increase of dipole moment there is an increase of polarity of the
compound. As a result increase the tendency of hydrogen bond formation, and also show a
better effect in nonbonding interaction with selected protein in biological system [28]. It has
been observed that there is an increase of dipole moment in ligand BH.HNPH as compare to
2
ligand Etac.HNPH . On the other hand there is a significant increase of dipole moment in
2
complex Ti(Etac.NH) as compare to other complex Ti(BH.HNP) . Optimized structure of
2
2
two ligands and their respective complexes has been shown in Fig-6.
.7.1 Frontier Molecular Orbital
3
Frontier Molecular orbitals calculation is performed with the optimized structures of all
ligands and coplmexes by using PBEPBE/SDD level of theory. Frontier orbitals energy
values are important to determine chemical reactivity and the extent to which a drug interacts
with a particular receptor which is defined as a highest occupied molecular orbital (HOMO)
lowest unoccupied molecular orbital (LUMO) [29]. The energy gap between HOMO and
LUMO predicts of a molecule’s kinetic and chemical stability [30]. Larger the FO gap, higher
the kinetic stability, as it is energetically unfavourable for an electron to have it elevated from
a low energy HOMO to a relatively high-lying LUMO. The pictorial presentation of HOMO
and LUMOs of some ligands and their complexes are shown in the fig. 7. Energy (eV) of
HOMO, LUMO, Gap, hardness, and softness of all ligands are given in table 5. Among the
ligands and complexes it is found that the HOMO and LUMO energy gap for Etac-NHH is
2
the highest and for Ti(BH-HNP) is the lowest. Chemical hardness and softness of a molecule
2
also depend on HOMO-LUMO gap of a molecule. In this analysis, we found that ligand
BH.HNPH has the lowest HOMO-LUMO gap and the highest softness, which may
2
contribute to its higher chemical activity than other. A decreased HOMO-LUMO gap in
ligands and complexes promotes softness which makes them relatively more polarizable and
chemically more reactive compare to others [17].
3
3
.8 Microbial properties
.8.1 Antibacterial Activities
Antibacterial activities were done by liquid medium method by measuring absorbance by
spectrophotometer at 600nm. Bacterial growth was evaluated after 6 hours to 24 hours
1
2

ACCEPTED MANUSCRIPT
incubation in presence of ligands and complexes. The optical density of Bacillus cereus,
Staphylococcus aureus, Candida albicans and Salmonella paratyphi were recorded for all
ligands and complexes. Fig. 8 is the representative Presentation of bacterial activity of Etac-
NHH2.
Etac-NHH ligand showed nearly the same activity as the control against Bacillus cereus,
2
Staphylococcus aureus and Salmonella paratyphi. Maximum growth of bacteria was found at
higher concentration against Candida albicans after both 6 hours and 24 hours incubation.
Whereas its complex Ti(Etac-NH) showed maximum enhancing capacity at 0.2 %
2
concentration and minimum at 0.8 % concentration against the four test organisms.
In case of Bzac-NHH ligand inducing capacity was increased with increasing concentration
2
of sample against Salmonella paratyphi. Maximum enhancing capacity was found after 24
hours incubation and minimum was found after 6 hours incubation against the test organisms.
Maximum growth for Ti(Bazc-NH) was found at 0.5% and 0.8% concentration after both 6
2
hours and 24 hours incubation against Salmonella paratyphi. In case of Candida albicans and
Staphylococcus aureus this complex showed higher enhancing capacity after 24 hours
incubation. But it showed higher inducing capacity at lower concentration against Bacillus
cereus.
Ligand NH.HNPH showed nearly the same activity as the control after 24 hours incubation
2
against Staphylococcus aureus and Candida albicans and showed slightly inhibiting capacity
against Bacillus cereus after 24 hours incubation. Maximum inducing capacity was found
after both 6 hours and 24 hours incubation at 0.5 % concentration in case of Salmonella
paratyphi. Its Ti(NH-HNP) complex showed maximum enhancing capacity at 0.8 %
2
concentration after 24 hours incubation and minimum was found in both 0.2 % and 0.8 %
concentration against the test organisms.
BH.HNPH ligand showed slightly inhibiting capacity after 6 hours incubation but showed
2
inducing activity after 24 hours incubation against Bacillus cereus, Candida albicans and
Salmonella paratyphi. In case of Staphylococcus aureus inducing capacity was increasing
with increasing concentration of sample. Ti(BH.HNP) complex induced the growth of test
2
organism. It showed minimum enhancing capacity at 0.5 % concentration with Bacillus
cereus and Staphylococcus aureus, whereas maximum inducing capacity at 0.8 %
concentration with Candida albicans and Salmonella paratyphi.
1
3

ACCEPTED MANUSCRIPT
It is seen that the growth of bacteria in sample solutions was higher than the growth of
bacteria growth in control. That indicates that ligands and complexes were showing the
inducing activity rather than the inhabiting activity against the test organisms.
3
.8.2 Antifungal Activities
3
.8.2.1 Liquid Medium Method
The prepared ligands and complexes were tested by liquid media method by measuring pH of
the solutions against Fusarium. Fig-9 shows the pH data of prepared ligands and
complexes against Fusarium species. Figure shows that with the presence of fungal
biomass showed higher pH (alkaline) after 3 days incubation. In the control Fusarium species
became acidic (after 3 days), however in presence of test ligands and complexes the fungal
medium became alkaline that means, pH of the sample S-1, S-2, S-3, S-4, S-6, S-7, S-8
became 7.96, 7.34, 6.92, 8.19, 7.32, 8.12, 6.24, 7.82 respectively. The fig.10 shows the fungal
biomass result which was measured by dry weight measured technique. This figure showed
that the test sample expressed more or less biomass after 3 days incubation. From the biomass
of Fusarium species it is seen that S-1 and S-7 have the inducing capacity to enhance the
aerial growth of this species whereas S-5 and S-6 have similar activity as the control. On the
other hand S-2, S-3, S-4 and S-8 have the lower enhancing ability than the S-1 and S-7. The
result indicated the test ligands and complexes have the tendency to increase microbial
biomass of the Fusarium species.
3
.8.2.2 Cup Plate Technique
The prepared ligands and complexes were also tested in vitro against fungi Aspergillus niger
by cup plate technique. After incubation, the diameter of the zone of inhibition and zone of
growth were measured in mm by a transparent scale. The ligand NH.BzacH was showing
2
growth inhibition activity against the tested fungi with respect to control. Rest of the ligands
and the complexes were showing growth stimulation activity.
3
3
.9 Antioxidant Properties
.9.1 Total Phenolic Content
In this investigation, TPC of Etac-NHH , Ti(Etac-NH) , Bzac-HNPH and BH-HNPH were
2
2
2
2
5
07.37 ± 1.227 mg/g dry weight, 271.08 ± 1.184 mg/g dry weight, 502 ± 3.287 mg/g dry
1
4

ACCEPTED MANUSCRIPT
weight and 416.48 ± 3.287 mg/g dry weight respectively. These test ligands and complex
contain very high amount of phenolic content (table 6) which means they have good
antioxidant properties.
3
.9.2 DPPH free radical scavenging activity
The DPPH assay is considered to be mainly based on an ET reaction, and hydrogen-atom
abstraction is a marginal reaction pathway. DPPH is a source of free radical. So when a test
sample is added in DPPH solution, the free radical is neutralized by the test sample which,
either donate hydrogen or an electron which result in neutralization of free radical, and at 517
nm DPPH show absorbance due to this free radical. When the free radical is neutralized by
test sample less free radical will be available. Due to this reason OD decreases and we
calculate percentage of free radical neutralized/scavenged. Control should be greater than the
sample, if its lower means, there is no inhibition takes place, instead of inhibit, it induces the
activity. The absorbance of sample is higher than it might be due to the presence of color
compound or compound with their self-absorbance power. DPPH is stable nitrogen radical
that bears no similarity to the highly reactive and transient peroxyl radicals involved in lipid
peroxidation. Many antioxidants that react quickly with peroxyl radicals may react slowly or
may even be inert to DPPH due to steric inaccessibility. In this experiment, the IC values of
5
0
Etac-NHH , Ti(Etac-NH) , NH-BzacH , BH-HNPH and standard ascorbic acid were found
2
2
2
2
to be 5.74 μg/mL, 1.29 μg/mL, 1.32 μg/mL, 0.8 μg/mL and 1.34 μg/mL respectively. The
values were anti-oxidative. The percentage of scavenging activity is very high as IC value is
5
0
lower. Fig. 11 presents the comparison of DPPH free radical scavenging activity of
selected ligands and their respective complexes with ascorbic acid (standard) in terms
of IC .
5
0
4
. Conclusion
-1
-1
From the IR spectra it is seen that, the bands observed between 1640 cm and 1675 cm for
-1
the free ligands were due to vC=O and that obtained at 1600-1632cm were due to vC=N of
-1
the azomethine group. The peak found for vTi-O at the range of 420-470 cm indicating the
complex formation. In the electronic spectral data, three main peaks were found for the
ligands at around 270, 320 and 370 nm. There was no evidence of any d-d transition, for the
TiL complexes, over the visible region. Absence of δ(-OH) peak in complexes and presence
2
1
in ligands in the H NMR spectra indicating the complex and ligand formation. Mass spectral
1
5

ACCEPTED MANUSCRIPT
evidence of the ligands and complexes showed relatively correct fragmentation pattern. All
the prepared ligands in the enolic form have the potential to act as dinegative tridentate
ligands in forming TiL complexes. The computational study confirmed the octahedral
2
geometry of the complexes. The test ligands and complexes have the inducing capacity to
enhance the aerial growth of bacterial and fungal species. Antioxidant data indicated that
Schiff base ligands have good antioxidant potential. They show more antioxidant properties
than their Schiff base complexes.
References
1
. J.F. Lawrence, R.W. Frei, Chemical Derivatization in Chromatography. Elsevier.
Amsterdam. 1976.
2
3
4
. H.A. El-Borae, J. Therm, Anal. Calorim., 81(2005)339.
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5. A.D. Becke, Phys. Rev. A. 38(1988)3098.
6. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R Cheeseman., et
al., Gaussian 09, Revision A. 02. Gaussian Inc., Wallingford, CT, Http//www. Gaussian.
Com. (2009).
1
6

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1
7. R.G. Pearson, Proc Natl Acad Sci., 83(1986)8440.
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4
(2012)273.
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0. C. Johannes, S. Tuschy, I. Lamprecht, G. Obe, Biol. Zentralbl, 108(1989)15.
1. C. Lin, C. Yu, S. Wu, K. Yih, J. Food and Drug Analysis, 17(2009)386.
2. A. M. Hamil, K.M. Khalifa, A. Al-Houni, M.M. El-ajaily, Rasayan J. Chem. 2(2009)261.
3. U. M. Rabie, A. S. Assran, M. H. M. Abou-El-Wafa, J. Mol. Struct., 872(2008)113.
4. F.M. Morad, M.M. El-Sjaily, S. B. Gweirif, J. Sci. Appl.1(2007)72.
5. H. Yin, H. Xu, K. Li, G. Li, J Inorg & Organomet Polym& Mat., 15(2005)319.
6. M. Tuncel, S. Serin, M. Tuncel, Trans Met Chem, 31(2006)805.
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0. J. Aihara, J. Phys. Chem. A. 103(1999)7487.
1
7

ACCEPTED MANUSCRIPT
Fig-1: IR spectrum of Ti(NH.Bzac)2
Fig-2: Electronic spectra of NH.HNP, Red-Complex and Blue-Ligand

ACCEPTED MANUSCRIPT
Fig-3: NMR spectrum of Ti(Etac.NH)2
Fig-4: Mass spectrum of Ti(Etac-NH)2

ACCEPTED MANUSCRIPT
CH
3
H
H
C
2
C
N
N
C
C
C
C
N
N
C
C
H
C
O
CH3
O
O
N2
N
Ti
N
Ti
H
C
2
O
O
C
N
N
C
C
C
O
CH3
H
C
H
C
N
N
C
C
CH
3
5
42.4 m/z
422.2 m/z
H C
2
N
N
O
O
C
H
2 5
H
C
C
C
H
H
Ti
CH
3
H
C
O
C
N
O
N
C
C
C
N
N
C
C
H
C
OH
H C
2
N
Ti
N
Ti
OH
O
C
N
NH
87.1 m/z
H
H
C
2
2
32.1 m/z
C
N
N
C
C
C
O
CH
3
3
CH
3
N
C
C CH
H
N
514.3 m/z
3
H
2 5
C H
H
C
N
O
NH
OH
CH
C
3
N
H
Ti
C
N
N
C
C
OH
O
O
OH
O
C
N
NH
N
Ti
3
53.1 m/z
N
O
O
C
N
N
C
C
C
OH
H
HN N
CH
3
N
C N NH
O
4
86.3 m/z
OH
OH
2
OH
N
Ti
CH
3
O
2
H C
C
N
N
C
C
H
C
O
O
3
24 m/z
N
HN
N
N
Ti
2
OH
O
O
H2
C
H
C
C
N
N
C
C
O
CH
52.2 m/z
3
N
Ti
4
N
O
2CH
3
2
H C
N
2
60.1 m/z
Fig-5: Mass fragmentation pattern of Ti(Etac.NH)2

ACCEPTED MANUSCRIPT
Ligands
Complexes
Etac-NHH2
Ti(Etac-NH)2
BH-HNPH2
Ti(BH-HNP)2
Fig-6: Optimized structure of two ligands and their respective complexes

ACCEPTED MANUSCRIPT
Fig. 7: The HOMO and LUMO of the ligands and complexes are showing below.
휀HOMO
휀LUMO
Molecule
Etac-NHH2
Ti(Etac-NH)2
HNP-BHH2
Ti(HNP-BH)2

ACCEPTED MANUSCRIPT
Fig. 8: Representative Presentation of bacterial activity of Etac-NHH2

ACCEPTED MANUSCRIPT
9
8
7
6
5
4
3
2
1
0
Initial pH
Final pH
Test pH
C
S-1 S-2 S-3 S aS m- 4p le (S 0- .58 % S) -6 S-7 S-8
Fig-9: pH data of prepared ligands and complexes against Fusarium species
1
.1
1
0
0
.05
1
.95
0
.9
.85
.8
0
Control S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8
Sample 0.8 %
Fig-10: Biomass of Fusarium species

ACCEPTED MANUSCRIPT
3
2
2
1
1
0
5
0
5
0
5
0
Fig. 11: Comparison of DPPH free radical scavenging activity of selected ligands and
their respective complexes with ascorbic acid (standard) in terms of IC50

ACCEPTED MANUSCRIPT
Highlights




Nine Schiff bases were derived from aroylhydrazine with aldehyde or ketone.
The titanium(IV) complexes of prepared Schiff bases were synthesised.
Both Schiff bases and Ti-complexes were characterized by conventional methods.
Octahedral geometry of the complexes was elucidated on the basis of experimental
evidences.


Geometry was optimized by computational study.
The synthesized ligands and complexes were screened for their microbial and antioxidant
properties.

ACCEPTED MANUSCRIPT
Table-1: The physical properties of prepared Schiff base ligands and complexes
Serial Ligands/complexes
No
Molecular
Formula
Melting point Solubility
Colour
Yield
%
70
o
1
2
3
4
5
6
7
8
9
Etac-BHH2
Bzac-BHH2
Etac-SalHH2
Bzac-SalHH2
Etac-NH H2
Bzac-NHH2
HNP-BHH2
HNP-SalHH2
HNP-NHH2
C H N O
245 C
DMF
DMF
Pink
13
16
2
3
2
4
3
3
2
2
o
C H N O
133 C
White
70
90
75
65
78
75
80
74
17
16
2
o
C H N O
134 C
DMF
Cream
13
16
2
o
C H N O
206 C
DMF
Yellow
17
16
2
o
C H N O
(193-197) C
DMSO
DMSO
DMSO
DMSO
DMSO
Off White
Yellow
12
15
3
o
C H N O
(130-135) C
16
15
3
o
C H N O
>200 C
Chocolate
Chocolate
18
14
2
o
>200 C
o
C H N O
>200 C
Light
Chocolate
Cream
17
13
3
2
o
1
2
3
4
5
6
7
8
9
Ti (Etac-BH)2
Ti (Bzac-BH)2
Ti (Etac-SalH)2
Ti (Bzac-SalH)2
Ti (Etac-NH)2
Ti(Bzac-NH)2
Ti(HNP-BH)2
Ti (HNP-SalH)2
Ti(HNP-NH)2
TiC H N O
>250 C
DMF
DMF
60
70
75
65
60
75
81
84
80
26
28
4
6
4
6
4
6
4
4
o
TiC H N O
250 C
Black
Orange
Black
34
28
4
o
TiC H N O
>250 C
DMF
26
26
4
o
TiC H O N
>260 C
DMF
34
28
6
o
TiC H N O
>200 C
DMSO
DMSO
DMSO
DMSO
DMSO
Brown
24
26
6
TiC H N O
(192-196)°C
White
32
26
6
o
TiC H N O
>200 C
Wine red
Chocolate
Chocolate
36
24
4
o
>200 C
o
TiC H N O
>200 C
34
22
6
4

ACCEPTED MANUSCRIPT
-1
Table-2: Some characteristic infrared frequencies (cm ) and electronic spectral
data (nm) for the Schiff base ligands.
-
1
Ligands/
complexes
Infrared frequencies (cm )
Electronic
spectra (nm)
300flsh, 270
350, 341, 299,
vC=O
1670m
vC=N
1632s
1595s
vC=C
vC-O
1285vs
1290m
vN-N
925m
vTi-N
vTi-O
Etac-BHH2
1580s
Ti(Etac-BH)2
1520ms
1020m
580w
430w
2
54
430flsh, 342,
30flsh, 271
421flsh, 355sh,
99, 287flsh
365flsh, 301sh,
73
370flsh, 308sh,
77
420, 356sh,
21, 302flsh,
72
419, 359, 301,
75flsh
308sh, 267,
58, 238
Bzac-BHH2
Ti(Bzac-BH)2
Etac-SalHH2
Ti(Etac-SalH)2
Bzac-SalHH2
1660s
1720vs
1635m
1600m
1590vs
1625s
1550ms
1545s
1280s
1290s
1275s
920vs
950m
905s
3
595s
430m
460m
2
1550s
2
1595s
1500sbr 1250vs
1530ms 1300ms
1030s
870vs
530w
6
00ms
2
1600m
3
2
Ti(Bzac-SalH)2
Etac-NHH2
1590s
1651s
1520ms
1372m
1020m
929m
670m
470ms
400w
5
80w
2
1678w
1685vs
1604m
1535m
1570w
1265m
1307s
1
597w
2
Ti(Etac-NH)2
Bzac-NHH2
1604w
1469s
1261w
1014m
1040w
929s
594.w
621m
474w
459m
420m
260, 242, 232
1
280s
1593s
1577ms
1292w
589, 335, 233,
8
79s
2
09
Ti(Bzac-NH)2
HNP-BHH2
1593.20s 1531ms 1265vs
396m
1010w
652w
671ms
498, 340, 271
1
1573s
1597vs
1507s
1465s
1288s
914m
376, 363, 326,
8
60m
3
13, 259
361, 353, 327,
11, 264
346, 307, 300,
44
386, 353, 307,
34
364, 327, 314,
59
410, 330, 262,
32
Ti(HNP-BH)2
HNP-SalHH2
Ti(HNP-SalH)2
HNP-NHH2
1408s
1288ms
914m
1037w
582s
648ms
1
338s
3
1633vs
1693vs
1416ms
1407s
1268s
1259s
856m
958ms
910m
2
1501ms
1577s
625w
462m
2
1516ms 1288vs
8
60m
2
Ti(HNP-NH)2
1601ms
1577s
1280s
319vs
1030m
952ms
621w
655m
420m
474w
1
2

ACCEPTED MANUSCRIPT
1
Table-3: H NMR spectral data, Magnetic and conductance data of the selected
ligands and titanium complexes
Complexes
1H NMR (DMSO)
-CH2- -CH= =CH-
Conductance
Solvent
µ
-CH3
-OH
Ar-H
Ʌ
(B.M)
M
-1
2
(Ar)
Ohm cm
mole
-1
Ti(Etac-BH)2
Ti(Bzac-BH)2
Ti(Etac-SalH)2
Ti(Bzac-alH)2
Etac.NHH2
DMF
DMF
DMF
DMF
5.0
2.5
4.8
8.5
Dia
Dia
Dia
Dia
2.079
.509
1.29
3.71
5.7
-
-
11.116 7.7-9.2
2
Ti(Etac-NH)2
3.451
6.047
-
7.46-9.1
DMSO
DMSO
7.7
Dia
Dia
2
.27
BH.NHH2
Ti(Bzac-NH)2
-
-
-
-
-
-
7.175
6.4
13.19
-
7.5-7.9
7.02-
10.4
8
.210
Ti(HNP-NH)2
Ti(HNP-BH)2
DMSO
DMSO
6.4
4.4
Dia
Dia