Synthesis and characterization of some arylhydrazone ligand and its metal complexes and their potential application as flame retardant and antimicrobial additives in polyurethane for surface coating

Article abstract of DOI:10.1016/j.jorganchem.2015.05.024

Hydrazones are versatile organic ligands and can be synthesized by condensation of hydrazides with carbonyl compounds (aldehydes/ketones). These compounds coordinate to the metal ions via azomethine nitrogen. Hydrazone Schiff's base ligands and their tran

Full text of DOI:10.1016/j.jorganchem.2015.05.024

Accepted Manuscript
Synthesis and characterization of some arylhydrazone ligand and its metal complexes
and their potential application as flame retardant and antimicrobial additives in
polyurethane for surface coating
H. Abd El-Wahab, M. Abd El-Fattah, Dr., Ayman H. Ahmed, Ahmed A. Elhenawy,
N.A. Alian
PII:
S0022-328X(15)00308-3
10.1016/j.jorganchem.2015.05.024
JOM 19064
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 26 February 2015
Revised Date: 29 April 2015
Accepted Date: 4 May 2015
Please cite this article as: H. Abd El-Wahab, M Abd El-Fattah, A.H Ahmed, A.A Elhenawy, N.A Alian,
Synthesis and characterization of some arylhydrazone ligand and its metal complexes and their potential
application as flame retardant and antimicrobial additives in polyurethane for surface coating, Journal of
Organometallic Chemistry (2015), doi: 10.1016/j.jorganchem.2015.05.024.
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Graphical abstract synopsis
The MBH ligand and its metal complexes showed excellent flame retardancy and
antimicrobial activity. The metal complexes were much more active than the original
ligand. The molecular modeling study revealed that molecular properties of MBH
ligand and its metal complexes are biologically safe, active and fulfill Lipinski’s rule
of five.

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Graphical abstract –pictogram
O
NH
N
MBH
OCH3
N
N
CuMBH
O
O
Cu
O
O
N
N
N
N
NiMBH
O
O
Ni
N
O
O
N

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Synthesis and characterization of some arylhydrazone ligand and its metal complexes
and their potential application as flame retardant and antimicrobial additives in
polyurethane for surface coating
a
b
a
a,c
d
H. Abd El-Wahab , M. Abd El-Fattah , Ayman H. Ahmed , Ahmed A. Elhenawy
, N. A. Alian
a
Chemistry Department, Faculty of Science, Al Azhar University, Cairo, Egypt
b
c
d
Production Department, Egyptian Petroleum Research Institute (EPRI), Cairo, Egypt
Chemistry Department, Faculty of Arts & Science, Almikhwah, AlBaha University, AlBaha, KSA
Chemistry Department, Faculty of Science (Girls), Al Azhar University, Cairo, Egypt
Corresponding author: Dr. Mohamed Abd El Fattah Moustafa
E- mail: eprimaf68@yahoo.com, telephone: +20 1006425240, Fax: +20 222747433
ABSTRACT
Hydrazones are versatile organic ligands and can be synthesized by condensation of
hydrazides with carbonyl compounds (aldehydes/ketones). These compounds
coordinate to the metal ions via azomethine nitrogen. Hydrazone Schiff’s base ligands
and their transition metal complexes possess a number of biological and flame
II
II
retardant applications. Some selected divalent metal (Cu and Ni ) complexes of
hydrazone Schiff base ligand, namely o-methoxybenzaldehyde benzoylhydrazone
1
(MBH) was synthesized and fully characterized by elemental analysis, FTIR, HNMR
and mass spectra. This work summarizes the application of the prepared MBH ligand
and its metal complexes. The prepared MBH ligand and its metal complexes were
physically incorporated in polyurethane coating and evaluated for their flame
retardancy and antimicrobial activity for surface coating. The flame retardancy of
these materials was characterized by the limiting oxygen index (LOI) test. The
antimicrobial activity of these materials was screened against Gram- positive bacteria,
Gram-negative bacteria and fungi. The physical, mechanical and chemical properties
were studied to ascertain any drawbacks. On the basis of experimental results of an
oxygen index (LOI) and the biological activity, the synthesized MBH ligand and its
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metal complexes showed excellent flame retardancy and antimicrobial activity. In
addition, the metal complexes were much more active than the original MBH ligand.
Quantum chemical calculations were also performed by Semiempirical PM3 method
to find the optimum geometry of the ligand and its metal complexes. The calculated
pharmacokinetic parameters in silico, showed promising futures for application of the
MBH ligand and its metal complexes as high antimicrobial potency agents.
Keywords: Hydrazones; Schiff base ligand; antimicrobial activity; flame retardant
activity; molecular modeling; polyurethane coating.
1. Introduction
Polymers such as polyurethane, polyester, and polyesteramide are susceptible
to microbial attack, when they are exposed to the atmosphere or used as an adhesive
or a coating material [1-4]. Generally, microorganisms have been found to cause dis-
bonding and blistering of coatings under various service conditions [5–7]. Paint
formulations traditionally containing biocidal species, are used to protect the coating
surface from microbial attack [8]. Up until the end of 1990’s, the most effective anti-
fouling paints were based on organotin compounds, mostly tributyltin compounds
(TBT-based paints). TBT and its derivatives were found to be harmful molecules to
marine eco-systems by Alzieu [9]. Thus, TBT- based paints were completely
prohibited by 1 January 2008 [10-11] and as a consequence promoted research into
new ecological paints. Modification of polyurethanes by the incorporation of metal
and Schiff base metal complex was found to enhance polyurethanes antimicrobial
activity, flame retardancy and the thermal stability [12]. Jayakumar et al. had
synthesized several petrobased transitional metals contained polymers from divalent
transition metal salts, these polymers have been found application as antibacterial
coatings [5-6, 13-16]. Hydrazones are versatile ligands occupied a central role in the
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development of coordination chemistry. This feature comes from the fact; they are
potential poly nucleating ligands possessing azomethine, amide, phenol or methoxy
functions which offer varying bonding possibilities in metal complexes. Studies of
metal chelates of hydrazone derivatives have been recognized [17]. Moreover, the
biological activity of complexes derived from hydrazones has been widely studied
and contrasted, acting in processes such as antibacterial, antitumoral, antiviral,
antimalarial and antituberculosis effects [18-20]. The most studied among
benzoylhydrazones are the benzoylhydrazones of salicylaldehyde or its substituted,
which hesitate in their coordination with the metal ions forming a five or six chelate
ring around the central metal. Indeed, several metal complexes of benzoylhydrazones
of salicylaldehyde, substituted-salicylaldehyde and 2-hydroxynapth-1-aldehyde have
been extensively studied [21-23]. Actually the investigation of new antimicrobial
agents is important; in this regard heterocyclic bases have great importance in
biological and industrial fields. In view of the importance of hydrazones and their
chelates, we have undertaken the synthesis and structural characterization studies on
o- methoxybenzaldehyde benzoylhydrazone (MBH) ligand and its bivalent (Cu, Ni)
metal complexes. The objective of this investigation is to establish whether the MBH
ligand and its metal complexes have a role in enhancing the flame retardancy and
antimicrobial activity properties of the polyurethane coating.
2. Experimental
2.1. Materials
All the chemicals used during the research project were sourced
internationally, or from local companies, and were of pure grade quality.
2.2. Methods and Techniques
2.2.1. Synthesis of o- methoxybenzaldehyde benzoylhydrazone (MBH) ligand
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Benzoylhydrazide (BH) was prepared following the method described in the
literature [24-25]. The MBH ligand used in this research work was prepared in a
similar manner according to the reported procedure [26] as given. Benzoylhydrazide
(3.0 g, 0.022 mole) was dissolved in absolute ethanol (50 ml) and the resulting
solution was then added to an ethanolic solution (50 ml) of o- methoxybenzaldehyde
(2.99 g, 0.022 mole). The reaction mixture was prolonged under reflux for 2 h in the
presence of 2 ~ 3 drops glacial acetic acid. The separated product was filtered, washed
with ethanol, crystallized using ethanol and finally dried in oven at 80 °C for 24 h.
The resulting ligand has the chemical formula C15H14N2O2 as shown in Scheme 1.
The authenticity of the ligand was proved by elemental analyses, mass, FTIR and
1HNMR spectroscopy. The synthesized hydrazone (MBH) ligand is insoluble in
petroleum ether and soluble in most common organic solvents, e.g. alcohol, acetone,
benzene, chloroform, DMF and DMSO.
2.2.2. Synthesis of the metal complexes of MBH ligand
All the isolated solid complexes were prepared by mixing equimolar amounts
of MBH ligand and metal (II) acetates [M = Cu (II) and Ni (II)] in 100 ml ethanol.
The reaction mixture was refluxed on hot plate for 3 h. Colored microcrystalline
solids were isolated by concentrating the solutions to their halves and then filtered on
hot. The obtained complexes were washed repeatedly with hot ethanol and finally
o
dried in oven at 80 C for 24 h. The complexes retain their colors for a long time,
insoluble in water and petroleum ether, and soluble in DMF and DMSO.
2.3. Characterization studies
The physical measurements were carried out using the methods and appliance
models reported earlier [27] as follows. The elemental analysis for carbon, hydrogen
and nitrogen was performed on Perkin Elmer 2400. Metal contents (wt. %) was
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estimated complexometrically by EDTA using xylenol orange as an indicator and
solid examine as a buffer (pH=6). FTIR spectra of the ligand as well as the complexes
were recorded as KBr pellet on a Bruker Vector 22, single beam spectrometer at a
1
spectral resolution of 2.0 cm-1. The HNMR spectra were recorded on a Varian
º
Mercury VX300 MHz spectrometer at 25 C using DMSO solvent and TMS as an
internal standard. Mass spectra of the MBH ligand was recorded on the Shimadzu-
GCMS-Q5050 instrument using the direct inlet system.
2.4. Preparation of polyurethane coating films containing MBH ligand and its metal
complexes for surface coating
The polyurethane coating compositions were prepared by means of
incorporating o-methoxybenzaldehyde benzoylhydrazone (MBH) ligand and its metal
complexes, in the ratio of 1.0, 1.5 and 2.0 wt. %, into polyurethane coating. The
composition of the polyurethane coating is tabulated in Table 1. The samples of
different molar ratio were then applied to both steel and glass panels by means of a
brush. All efforts were made to maintain a uniform film thickness of 100 ±5µm for
evaluating the physical and mechanical properties.
2.5. Flame retardant testing method
The performance of polyurethane coating incorporated MBH ligand and its
metal complexes as a flame retardant additives was evaluated in a limiting oxygen
index (LOI) chamber. LOI values can be determined by standardized tests such as
ASTM D: 2863-06, ISO 4589-1: 1996, DIN 4102-B2 and NF T51-071 procedures.
This test method was first proposed in 1966 by Fenimore and Martin [28]. Test panels
were prepared using a combustible material (wood specimen). It was important that
the panels were free of any surface contamination, or imperfections, prior to the
coating application. Hand tool cleaning (sand paper) was carefully used to treat the
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faces and edges of the panels. Final dry film thickness (DFT) was 100 ± 5µm. In all
cases, the film application was applied by means of brushing. Following 10 days of
air drying, the panels under study were heated at 50-60°C for 2h to eliminate any
remaining solvent.
2.6. Antimicrobial testing method
The synthesized MBH ligand and its metal complexes were screened for their
antimicrobial activity against eight different test organisms having environmental and
clinically importance. The microorganism`s inoculums were uniformly spread using a
sterile cotton swab on a sterile Petri dish Malt agar (for fungi) and nutrient agar (for
bacteria). 100 µL of each sample was added to each well (10 mm diameter holes cut
in the agar gel, 20 mm apart from one another). The systems were incubated for 24-48
h at 37 °C (for bacteria) and at 28 °C (for fungi). After incubation, microorganism
growth was observed. Inhibition of the bacterial and fungal growth were measured in
mm. Tests were performed in triplicate.
2.7. Physical and mechanical testing of films
A variety of physical and mechanical evaluations of the coating films were
carried out according to appropriate ASTM standard test methods. These included the
preparation of the steel panels (ASTM D: 609-00), measurement of film thickness
(ASTM D:1005-07), the degree of gloss for individual coating film (ASTM D: 523-
08), film hardness by pencil test (ASTM D: 3363-00), adhesion ‘cross hatch test’
(ASTM D: 3359-02), flexibility ‘bend’ test (ASTM D: 522-08) and resistance to
mechanical damage ‘impact resistance’ (ASTM D: 2794-04).
2.8. Molecular modeling studies
The conformational analysis of the target compounds has been performed
using the Merck molecular force field MMFF94 [29] (calculations in vacuo, bond
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dipole option for electrostatics, Polake Ribiere algorithm, RMS gradient of 0.01
kcal/mol) and then implemented in MOE [30]. The most stable conformer was fully
geometrical optimized with (PM3) semi-empirical Hamiltonian molecular orbital
calculation MOPAC-7 package [31]. The obtained electronic structural and
pharmakinetic parameters, such as, total energy, electronic energy, heat of formation,
the dipole moment of the molecules, the energy of the highest occupied molecular
orbital, the lowest unoccupied molecular orbital, total polar surface area, absorbance
percentage, lipophilicity, solubility, hydrogen bond acceptor, hydrogen bond donor,
and the molar refractivity was recorded.
3. Results and discussion
3.1. Synthesis and instrumental analysis of MBH ligand and its metal complexes
The chemical structure of the prepared MBH liagnd and its metal complexes
are represented in Scheme 1 and Figs.1-2. Elemental analysis and product color of the
prepared MBH ligand and its metal complexes were measured and listed in Table 2.
The good agreement between the experimental and theoretical values of the C, H, N
and M levels reveals that the methods of synthesis and purification of the products
were performed successfully.
3.2. Spectral analysis of MBH ligand and its metal complexes
The positions of the significant FTIR bands of the prepared MBH ligand as
well as its metal complexes are summarized in Table 3. The FTIR spectra of the free
MBH ligand exhibit strong absorptions at 3188, 1643, 1606 and 700-800 cm-1
assignable to υ (NH), υ (C=O), υ (C=N) and the out of plane deformation of the
aromatic ring, respectively. The observation of the (C=N) band ascertains the
formation of the azomethine linkage and thus the requested hydrazones. The positions
of other bands assigned to υ(CH)
and δ(NH)
amide
are observed at
aromatic, aliphatic
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-1
3028, 2950 and 1252 cm respectively. The position of bands assigned to the metal
complexes is demonstrated in Table 3. Finally, the persistence of new bands attributed
to υ (M-O) and υ (M-N) supports the formation of the metal complexes. The
authenticity of the prepared o- methoxybenzaldehyde benzoylhydrazone
(MBH)
ligand was proved by 1HNMR spectra as shown in Fig. 3, it was measured in DMSO-
d solvent and showed three signals with integration (1:1:3). The signal at δ= 11.9
6
ppm is assigned to (-NH-, s), the signal at δ= 8.8 ppm is assigned to azomethine (-
CH=N-, s) and at δ= 3.9 ppm (-OCH , s). The multiple (m) signals attributed to the
3
aromatic protons were observed within 6.5-8ppm with slight change in their positions.
3.3. Evaluation of coating film properties
3.3.1. Evaluation of MBH ligand and its metal complexes as a flame retardant
additive incorporated physically into polyurethane coating
It is clear that the incorporation of MBH ligand and its metal complexes into
polyurethane coating, in the ratio’s mentioned in the experimental section, results in
enhanced flame retardancy when compared to blank polyurethane coating. This is as
a result of the fact that, the incorporation of azometine (-CH=N-) linkage in the
polyurethane improved the thermal stability, the introducing of aromatic ring which
has a stabilizing effect against thermal degradation that result in improved flame
retardant and the introducing of nitrogenous compounds provide superior flame
retardant properties. The results obtained from the LOI test are shown in Table 4 and
Fig. 4. It can be observed, that the LOI value of the blank polyurethane coating is 20
and the maximum LOI with Ni-MBH present is 29. Normal atmospheric air (i.e. The
air that we inhale) contains approximately 21% oxygen, so a material with a LOI less
than 21% would burn easily in air. In comparison, a material with a LOI value greater
than 21%, but less than 27%, would be considered to be ‘slow-burning’. However, a
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self-extinguishing material is one that has a LOI greater than 27% and this would stop
burning after the removal of the fire, or the ignition source [32]. An interesting point
associated with the results is that the LOI curves for the MBH ligand and its metal
complexes are more or less linear. A further interesting point is that the LOI values of
metal complex Ni-MBH is higher than the metal complex Cu-MBH, this may be
attributed to the higher melting point of nickel metal and its metal complex than the
corresponding copper metal and its complex. The obtained results also indicated that
the flame retardancy increases with the increase in the metal complex addition level.
3.3.2. Evaluation the antimicrobial activity of MBH ligand and its metal complexes as
a biocide additive incorporated physically into polyurethane coating
The biocide additives are commonly used to prolong the life of surface
coatings. They prevent, or slowdown, the growth of organisms on the coating surface.
Hydrzone ligands have a good potential application as an antimicrobial. The
antimicrobial activities of the prepared MBH ligand and its metal complexes were
evaluated against two Gram- positive bacteria (Staphylococcus aureus and Bacillus
subtilis), two Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli)
and four fungi (Aspergillus fumigates, Penicillium italicum, Syncephalastrum
racemosum and Candida albicans). The activity was tested by a disc-diffusion
method. . The results obtained from the anti-microbial activity are shown in Table 5.
The prepared MBH ligand and its metal complexes exhibited antimicrobial activity,
they are azomethine derivatives, the azomethine (-CH=N-) linkage is essential for
biological activity, several azomethine has been reported to possess remarkable
antibacterial and antifungal activity. In addition the biological activity of this ligand
and its metal complexes are due to the fact that; the aromatic ring present in their
structures is a constituent of many biological systems. The MBH ligand showed little
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better effect on Gram- positive than on Gram- negative bacteria. The results also
indicated that the metal complexes were more effective than the original MBH ligand.
It has been reported that metal complexes have higher antibacterial activity than that
of free ligand. The metal complexes of copper and nickel showed the highest effect on
Gram- positive and negative bacteria and also Fungi. The results also illustrated that
the prepared ligand and its Ni-MBH metal complexes have a lower effect on fungi
than the Cu-MBH metal complex. The obtained results also indicated that the
antimicrobial activity against the target microorganisms increases with the increase in
the metal complex addition level.
3.3.3. Evaluation the effect of MBH ligand and its metal complexes on the physical
and mechanical properties of polyurethane coating
The effect of incorporating MBH ligand and its metal complexes into the
polyurethane coating was evaluated using a variety of standard test methods for gloss,
hardness, adhesion, flexibility and impact strength. These test methods were utilized
to determine any negative aspects that might occur due to the incorporation of MBH
ligand and its metal complexes physically into polyurethane coating. The physical and
the mechanical characteristics of polyurethane coating are presented in Table 6.
Firstly, all films of polyurethane coating compositions gave a very clear, transparent
and homogeneous appearance.
(a) Gloss: This was measured using a Sheen UK glossmeter. On observing the films
◦
using a 60 angle, it could be seen that the MBH ligand and its metal complexes
additives actually increased slightly the gloss level. This is obviously a positive result
which may be attributed to the introduction of aromatic rings, present in the additive
structure. In addition, metals incorporation in the polymer is known to enhance their
gloss [13].
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(b) Scratch hardness test: This was determined by using a Sheen UK hardness tester.
The scratch hardness is observed to vary between 1.4 and 2.0 kg for all coating films.
It is clear from the data that the MBH ligand does not affect on the scratch hardness of
the coating film, while Ni-MBH metal complex showed the highest hardness; this
may be attributed to the fact that, the nickel metal possesses higher hardness than the
copper metal.
(c) Cross hatch adhesion & flexibility test: The cross hatch adhesion and flexibility
(bending) test show that, the film for all the coating compositions passed the adhesion
and Mandrel bend test, with no obvious significant change being observed for the
incorporation of MBH ligand and its metal complexes in polyurethane coating.
(d) Resistance to mechanical damage (impact resistance): This was measured using a
Sheen UK impact tester. The impact resistance of the coating on the steel panels was
tested by means of dropping a 890 g steel ball from a height of 1 m. It is clear from
the data that the MBH ligand does not affect on the impact resistance of the coating
film. The impact strength was shown to increase in the presence of the MBH metal
complexes and Ni-MBH showed the highest results.
3.3.4. Evaluation the effect of MBH ligand and its metal complexes on the chemical
properties of polyurethane coating
The effect of incorporating MBH ligand and its metal complexes into the
polyurethane coating towards the chemical resistance was undertaken using glass
panels (25 mm x 75mm). The coated glass panels were sealed, using paraffin wax at
the edges, and immersed to half their length in each individual test solution: (i) 5.0 wt.
% anhydrous sodium carbonate, (ii) 10.0 wt. % sulphuric acid and (iii) 1:3 by volume
benzene/mineral turpentine solvent mixture. The panels were then removed from the
individual test solution, wiped carefully and then allowed to dry at room temperature,
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prior to assessment of any change. The obtained data indicated that the chemical
resistance of polyurethane coating was not significantly changed by the addition of
MBH ligand and its metal complexes.
3.4. Molecular modeling studies
3.4.1. Geometrical conformation
In trying to achieve better insight into the molecular structure of MBH ligand and
its metal complexes, the conformational analysis of the target compounds has been
performed in (PM3) semi-empirical Hamiltonian molecular orbital calculation using
MOE [30]. The possibility exists of the prepared MBH ligand in two stereoisomer
forms are shown in Fig. 1, the minimal optimal energy at PM3 were calculated to
prefer the most stable stereoisomer is shown in Table 7, which showed that, the most
stable stereoisomer MBH ligand is (Z) form; this may be explained by the presence
the intra-molecular hydrogen bond interaction of H-NH fragment with the O atom of
carbonyl moiety, which owing to slightly reduce its calculated energy. Other evidence
supported this explanation, the NPhC
atom with sp2 hybrid orbital has more s-
N
character, and the maximum of the electron density is closer to the nuclei compared
with the electron density distribution at sp3 hybridized NN N and NN CH atoms, which
leads to lengthening the bonds of PhC N bonds. Furthermore, The geometry
optimization of M-MBH structures were stabilized by arranging four phenyl rings in
coplanar position with each other in all complexes, which arranged at the same time
in perpendicular to the plane of metal rings as shown in Fig. 2. The bond lengths
of all the active groups taking part in coordination are longer than that already exist in
the ligand. All bond angles in complexes are quite near to a tetrahedral geometry
predicting sp3d2 hybridization. The higher HOMO energy values indicate that the
molecule is a good electron donor, yet on the other hand, the lower HOMO energy
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values indicate a weaker ability of the molecules for donating an electron. LUMO
energy is an indication of the ability of a molecule to receive electrons [29].
3.4.2. ADMET factors profiling
The Pharmacokinetic parameters were playing an important role in the
development of bioactive molecules. Many potential bioactive molecules fail to reach
for application trial, because of ADMET (absorption, distribution, metabolism,
elimination and toxic) Factors. Therefore, a computational study was performed for
prediction the ADMET properties of the MBH ligand and its metal complexes by
determination of topological polar surface area (TPSA), a calculated percent
absorption (%ABS) which was estimated by Zhao et al. equation [33], and ‘‘rule of
five’’ formulated by Lipinski [34], which established that, a chemical compound
could be an bioactive, if no more than one violation of the following rule: factor of the
lipophilicity (Log p < 5), number of hydrogen bond donor sites (HBD ≤ 5), number
of hydrogen bond acceptor sites (HBA ≤ 10), molar refractivity (mr, 40-130). In
addition, the total polar surface area (TPSA) is another key property linked bioactive
molecule, the passively absorbed molecules with (TPSA<140) has low oral
bioavailability [35]. All calculated descriptors were performed using MOE Package
[30]. Our results shown in Table 8 revealed that, the factor of the lipophilicity (Log
p) [36] was less than 5.0, number of hydrogen bond donor sites (2-4), number of
hydrogen bond acceptor sites (4-6), molar refractivity (107.75- 116.33) and total polar
surface area (65.1-67.8) which fulfill Lipinski’s rule. In addition the absorbance
percentage of MBH ligand was higher than its metal complexes. The HOMO and
LUMO of a molecule play important roles in intermolecular interactions [37], through
the interaction between the HOMO of the drug with the LUMO of the receptor
and vice versa. The interactions were stabilized inversely with energy gap between
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the interacting orbits. Increasing HOMO energy and decreasing LUMO energy in the
molecule lead to enhancement stabilizing interactions, and hence, binding to the
receptor. The obtained results showed that, Cu-MBH have lowest energy gap (8.84
eV) which explained its highest antimicrobial affinity.
4. Conclusions
In this study Cu and Ni complexes of hydrazone Schiff base ligand, namely o-
methoxybenzaldehyde benzoylhydrazone (MBH) derived from condensation of
benzoylhydrazide and o- methoxybenzaldehyde was synthesized and characterized.
The MBH ligand and its metal complexes were incorporated physically into a
polyurethane coating to study their antimicrobial and flame retardant properties. The
study showed that, the activity order of the synthesized ligand and its metal
complexes against microorganism can be represented as Cu-MBH > Ni-MBH >MBH
ligand. In general the metal complexes show higher activity than the free ligand
against the same organism under identical experimental conditions. This improvement
may be attributed to the presence of azomethine linkage, which possesses biological
activity, in addition to the presence of metal. However, the flame retardant activity
order can be represented as Ni-MBH > Cu-MBH > MBH ligand. This improvement
may be attributed to the introducing of high molecular weight nitrogenous compound,
introducing aromatic ring and introducing of metals with high melting point. The
obtained results also indicated that the antimicrobial activity against the target
microorganisms and the flame retardant properties increases with the increase in the
metal complex addition level. The results obtained, indicate that the mechanical
properties were slightly improved with an increase in the metal complex content
within the polyurethane. However, chemical resistance was not significantly changed
by the addition of MBH ligand and its metal complexes. Also, the molecular
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modeling was studied and this revealed that molecular properties of MBH ligand and
its metal complexes are biologically safe, active and fulfill Lipinski’s rule of five. The
final result may give a promising approach for using such compounds in the future as
a diverse range of applications due to its simple synthesis, high potent antibacterial,
antifungal and flame retardant agent at low concentrations.
Conflict of Interest: The authors declare that they have no conflict of interest.
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Table 1
Polyurethane coating composition.
Component
wt. %
33.42
0.039
0.03
Refined sunflower oil
Glycerol
Litharge (lead oxide catalyst)
Pentaerythritol
4.61
Turpentine
47.30
2.37
Mixed drier
Toluene diisocyanate
UV absorber
11.37
0.26
Anti skinning agent
MBH ligand and its metal complexes
0.32
1.0-2.0
Viscosity: G-I (Gardner), color: 3 (Gardner), solid content: 53±2%

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Table 2
Physico – chemical properties of o- methoxybenzaldehyde benzoylhydrazone (MBH) ligand and its metal complexes.
Characteristics MBH Cu-MBH Ni-MBH
Color
M.p (OC)
White
200
Brown
>220
Green
>280
Calcd. 254.3
Found 254
Mass
Elemental analysis
Calcd. 70.84
63.20
63.51
4.91
4.99
9.83
63.72
63.55
4.96
4.99
9.91
C %
H %
N %
Found 70.61
Calcd. 5.56
Found 5.82
Calcd. 11.02
Found 11.60
9.32
9.26
Calcd.
Found
-
-
10.88
10.40
10.09
10.10
M %
Table 3
IR absorption data of o- methoxybenzaldehyde benzoylhydrazone (MBH) ligand and its metal complexes.
Compound ν(NH) ν(C=O) ν(C=N) ν(CH) aromatic ν(CH) aliphatic δ(NH) νM-O/M-N
MBH
3188
1643
1606
3028
3052
3020
2950
2950
2948
1252
-
Cu-MBH
Ni-MBH
-
-
-
-
1599,1616
1598,1610
-
-
537/447
533/446

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Table 4
Flame retardant characteristics of polyurethane coating incorporated MBH ligand its metal complexes as a flame retardant additives.
Formulation
Additive wt.% Limiting oxygen index (LOI)
Blank polyurethane
-
20
21
22
23
23
25
26
24
27
29
1.0
1.5
2.0
1.0
1.5
2.0
1.0
1.5
2.0
MBH ligand
Cu-MBH
Ni-MBH

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Table 5
The antimicrobial screening activity of polyurethane coating incorporated MBH ligand and its metal complexes as a biocide additive.
MBH wt.%
1.5
Cu-MBH wt.%
1.0 1.5 2.0
Ni-MBH wt.%
1.0 1.5 2.0
Blank
polyurethane
Microorganisms
1.0
2.0
Staphylococcus aureus
Bacillus subtilis
Pseudomonas aeruginosa
Escherichia coli
Aspergillus fumigates
Penicillium italicum
Syncephalastrum racemosum
Candida albicans
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
+ve +ve ++ve ++ve +++ve +++ve
+ve +ve +++ve ++ve +++ve +++ve
+ve
+ve
+ve
+ve
+ve
+ve
++ve ++ve
++ve ++ve
++ve +++ve
++ve ++ve
++ve ++ve
++ve ++ve
-ve
-ve
-ve
-ve
-ve
-ve
+ve ++ve ++ve ++ve +++ve
+ve ++ve ++ve +++ve +++ve
+ve ++ve ++ve ++ve +++ve
+ve ++ve ++ve ++ve +++ve
+ve +++ve ++ve +++ve +++ve ++ve ++ve +++ve
+ve +ve +ve ++ve +++ve +ve +ve ++ve
Where, Inactive = -Ve,
Mildly active: Inhibition values = 0.1–0.6 cm beyond control = +
Moderately active: Inhibition values =0.65–1.0 cm beyond control =++
Highly active: Inhibition values = 1.1–1.5 cm beyond control =+++

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Table 6
Physical and mechanical characteristics of polyurethane coating incorporated MBH ligand and its metal complexes.
◦
Formulation
Additive wt. % Gloss at 60 C Hardness (Kg) Adhesion Flexibility Impact (J)
Blank polyurethane
-
80
82
82
80
84
87
89
87
89
89
1.4
1.4
1.4
1.4
1.6
1.6
1.8
1.6
1.8
2.0
5B
5B
5B
5B
5B
5B
5B
5B
5B
5B
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
Pass
1.6
1.6
1.6
1.6
1.7
1.9
2.0
1.8
2.0
2.2
1.0
1.5
2.0
1.0
1.5
2.0
1.0
1.5
2.0
MHB ligand
Cu-MBH
Ni-MBH
Table 7
The calculated energies at PM3 molecular orbital for compound stereoisomers of MBH ligand and its metal complexes.
Symbol Parameter (unit)
E- MBH
-73844.4
-519760
-9.8148
-9.3471
-0.237
Z- MBH
-80383.5
-526471
-10.362
-8.9961
-0.64
Cu-MBH
-89965.8
-793513
-312.53
-7.97
Ni-MBH
-87590.4
-532050
-280.023
-6.99
E
The total energy (Kcal/mol)
Eele
HF
Electronic energy (Kcal/mol)
Heat of formation (Kcal/mol)
HOMO Highest Occupied Molecular Orbital (eV)
LUMO Lowest Unoccupied Molecular Orbital (eV)
-0.1486
0.37
-0.44
8.781
µ
Dipole moment calculates (Deby)
1.577
8.563

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Table 8
Calculated pharmakinetic parameters of MBH ligand and its metal complexes.
Symbol Lipinski’s rule (limit) Z- isomer Cu-MBH Ni-MBH
Log p (o/w) Factor of the lipophilicity (< 5)
3.974
2
2.721
4
3.974
3
HBD
HBA
mr
TPSA
E gap
% ABS
Log S
Number of hydrogen bond donor sites (≤5)
Number of hydrogen bond acceptor sites (≤ 10)
Molar refractivity (40-130)
Total polar surface area <140
Energy gap (eV)
Absorbance percentage
Solubility parameter
4
6
5
116.33
65.1
-7.33
86.5
-3.0668
107.75
67.8
-8.84
85.4
-2.9525
116.33
67.8
-6.55
85.6
-3.8598

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O
O
O
NH2
NH
N
H
N
H
Ethanol
Acetic acid
+
O
benzoylhydrazide
O- methoxybenzaldehyde
MBH ligand
O
Scheme 1 Synthesis of o- methoxybenzaldeyhde benzoylhydrazone (MBH) ligand.
O
O
O
(a)
NH
N
N
N
H
(E)
(Z)
O
(b)
Fig. 1 (a) The chemical structure of Z- and E-forms of MBH ligand.
(b) The minimum energy of MBH ligand, which represented in ball and stick
model, carbon in magenta, nitrogen in blue, oxygen in red, the hydrogen
atoms removed for clarifying.

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Ni-MBH
Cu-MBH
N
N
N
N
O
Ni
O
Cu
(a)
O
O
O
O
O
O
N
N
N
N
(b)
Fig. 2 (a) The chemical structure, coordination cores of MBH metal complexes.
(b) Minimal energy conformation of MBH ligand, represented in ball and stick
model, which carbon in magenta, nitrogen in blue, oxygen in red, Cu in
green, Ni in white, hydrogen atoms were deleted for clarifying.
1
Fig. 3 HNMR spectra of o- methoxybenzaldeyhde benzoylhydrazone (MBH) ligand.

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Fig.4 Limiting oxygen index (LOI) characteristics of polyurethane coating
incorporated MBH ligand and its metal complexes as flame retardant
additives.