Novel triazine centred manganese based complex: A photophysical and biological studies

Article abstract of DOI:10.14233/ajchem.2020.22302

In this work, Mn(II) complex of triazine based ligand has been synthesized and characterized using various physico-chemical methods including C,H,N elemental analysis, FT-IR,¹H NMR and EI-mass analysis. The synthesized compounds serve as potential photoactive material as indicated from its characteristic fluorescent properties. The ligand and its metal complex were assayed for in vitro antimicrobial activity on four bacterial strains (S. aureus, B. subtilis, E. coli and K. pneumoniae) using well-diffusion method and it was observed that metal complex showed enhanced antimicrobial activity against all tested strains as compared to ligand.

Full text of DOI:10.14233/ajchem.2020.22302

Asian Journal of Chemistry; Vol. 32, No. 1 (2020), 91-94
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22302
Novel Triazine Centred Manganese Based Complex: A Photophysical and Biological Studies
1
1
2
2,*
L. ALPHONSE , P. THARMARAJ , B. AVILA JOSEPHINE and V. MARY TERESITA
1
2
Department of Chemistry, Thiagarajar College, Madurai-625009, India
Department of Chemistry, Stella Maris College, Chennai-600086, India
*Corresponding author: E-mail: alfosdb@gmail.com
Received: 1 July 2019; Accepted: 22 August 2019;
Published online: 18 November 2019;
AJC-19678
In this work, Mn(II) complex of triazine based ligand has been synthesized and characterized using various physico-chemical methods
1
including C,H,N elemental analysis, FT-IR, H NMR and EI-mass analysis. The synthesized compounds serve as potential photoactive
material as indicated from its characteristic fluorescent properties. The ligand and its metal complex were assayed for in vitro antimicrobial
activity on four bacterial strains (S. aureus, B. subtilis, E. coli and K. pneumoniae) using well-diffusion method and it was observed that
metal complex showed enhanced antimicrobial activity against all tested strains as compared to ligand.
Keywords: Triazine, Mn(II) complex, Fluorescent properties, Antimicrobial activity.
accelerate the drug action and the efficacy of the organic
therapeutic agents. The pharmacological efficiencies of metal
complexes depend on nature of the metal ions and the ligands.
Manganese complex of nitrogen-oxygen chelating agents
derived from Schiff bases have been studied extensively due
to their pronounced applications in biological, clinical, analy-
tical and pharmacological areas [10]. So, there is an increasing
requirement for the discovery of new compounds having
antimicrobial, antioxidant and antitubercular activities [11].
In an attempt to find a new class of agents, a novel Mn based
chalcone bearing 1,3,5- triazine complex is synthesized using
Claisen-Schmidt condensation with appropriate chemical
reagents. The presence of α,β-unsaturated carbonyl moiety as
well as of substituted aromatic rings renders the chalcones to
possess a wide range of pharmacological activities such as
cytotoxic, antiretroviral, antimalarial, antiplatelet, antituber-
cular, antimicrobial, etc. [6].
Manganese is an essential trace element for living crea-
tures and its trace amount range is 16.00 - 443 ppb which is
within the proper level according to the WHO guide [12]. It is
widely distributed in soil, sediment, water and in biological
materials. Manganese is used as a benign catalyst under mild
conditions [13] and manganese sulfate is used to make a fungicide.
Mn(III) complexes have been proposed as mimetics of anti-
oxidant enzymes such as catalase and superoxide dismutase.
INTRODUCTION
1
,3,5-Triazine (s-triazine) derivatives are salient class of
heterocyclic compounds [1] that have an excellent potential
for the formation in coordination chemistry, supramolecular
chemistry and in material chemistry due to their π-interaction
abilities and H-bond networks [2]. Triazines are heterocyclic
analogue of benzene containing three nitrogen atoms with
molecular formula C
3
H
3
3
N . Molecules containing triazine
skeletons show considerable biological activities and used as
precursors for the synthesis of various biologically active
compounds [3-5]. The s-triazine scaffold provides the basis
for the design of compounds with a variety of properties useful
in medicinal and agricultural applications [6] having anti-
malarial, antiviral, antibacterial, antifungal [7], antineoplastic
[
8], fungicides, insecticides, herbicides, anti-oxidant [9], anti-
cancer, estrogen receptor modulators, anti-tubercular and anti-
inflammatory activities [7] besides increased efficiency for
the corrosion protection of steel in acidic solution in electro-
chemical process [1].
Since there is a rapid development of pathogen resistance
to most of the known antibiotics is becoming a serious health
problem, to synthesis a new derivative of chalcone [6] based
s-triazine to enhance the pharmacological activities is a requi-
rement. It is well known that metal ions present in complexes
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9
2 Alphonse et al.
Asian J. Chem.
Mn(III)-citrate is believed to be the main Mn species to assess
the brain in humans, leading to a cascade of redox-active based
neurotoxic events [14]. Herein, we report the synthesis, spectral
characterization, bioscreening and fluorescence study of Mn
based metal complex derived from ligand which is formed
from salicylaldehyde and acetophenone in combination with
A solution of PTAPP ligand (0.59968 g, 1 mmol) in DCM-ethanol
(50 %) was added to equimolar quantity of MnCl (anhydrous).
2
and stirred for 1 h. A spatula of sodium hexafluorophosphate
was then added and then mixture was stirred magnetically for
3 h (Scheme-III). The product formed was filtered and recrystal-
lized in hot ethanol and finally dried in vacuum at room temper-
ature.
6-phenyl-1,3,5-triazine [15-17]. The chemical structures of the
ligand and complex are established on the basis of their FT-IR,
1
H NMR, UV, mass as well as elemental analysis. The newly
designed compound is assayed for its in vitro antimicrobial
activity against selected pathogens by well diffusion method.
N
N
N
N
N
N
N
MCl2·xH2O
N
O
N
N
O
EXPERIMENTAL
DCM, NaF6PO4,
Magnetic stirring,
3 h
Mn
OH
HO
PTAPP
2
,4-Diamino-6-phenyl-1,3,5-triazine, 3-formylchromone,
sodium hexafluorophosphate, salicylaldehyde were procured
OH2
from Sigma-Aldrich. The other chemicals viz. acetophenone,
Scheme-III: Formation of [Mn-PTAPP] complex
NaOH, ethanol, dichloromethane and MnCl
from various reliable sources.
2
·4H O were obtaind
2
RESULTS AND DISCUSSION
Synthesis of ligand
Infrared analysis: IR spectral analysis of free ligand and
its metal complexes revealed the involvement of coordination
sites in chelation [18,19]. The infrared spectral data of complex
Mn-PTAPP is given in Table-1. The broad band observed in
Synthesis of chalcone [((E)-3-(2-hydroxyphenyl)-1-
phenylprop-2-en-1-one)]:A solution of acetophenone (6 mL,
51 mmol) and salicylaldehyde (5.77 mL, 54 mmol) was disso-
lved at 0 ºC in mixture of NaOH (3M, 20 mL) and ethanol (15
mL). It was stirred for 0.5 h and then heated in microwave
oven at 360 ºC for 30 s (4 times). It was cooled and the reddish
black precipitate formed was filtered and recrystallized using
ethanol (Scheme-I). The product was finally dried at room temp-
erature.
-
1
3
443-3394 cm region is assigned to the -OH stretching
-1
vibration of hydrate molecules.The band at 3216 cm corresponds
2
-1
to the sp C-H stretch. The band exhibited at 1617 cm refers
to stretching frequency of ν(C-O) of the ring. The band located
at 2095 cm is attributed to stretching frequency νasy(N ).
-
1
−
-1
Further, the two bands observed at 1389 and 1323 cm are
assigned to νasy(C-O) and νsy(C-O) [10]. The bands at 1389 and
-1
O
O
1
8
323 cm are referred to the presence of ν(C-N). The band at
OH
-1
17 cm refers to (C-N, s-triazine) and the same is reaffirmed
NaOH + Ethanol
. 5 h stirr ing
O
+
-1
by the band at 826 cm [6]. Two bands in the region (482-439
cm ) correspond to ν(Mn-N) and ν(Mn-O) as new bands [10].
The peak at 1537 cm corresponds to C=N stretch, which
confirms the condensation reaction between chalcone and 6-
phenyl-2,4-diaminotriazine. A peak at 1389 cm is due to C-N
0
OH
Ch alcone
-1
Salicylaldehyde
Ace toph enone
-1
Scheme-I: Synthesis of chalcone
-1
Synthesis of 2,2′-(6-phenyl-1,3,5-triazine-2,4-diyl)bis-
azanylylidene))bis(3-phenylprop-1-en-1-yl-3-ylidene))-
-1
bending vibration. The three peaks observed at 1323 cm can
(
be attributed to the C-O bending vibration of phenolic moiety.
diphenol (PTAPP):A solution of chalcone (4.4816 g, 20 mmol)
and 6-phenyl-1,3,5-triazine-2,4-diamine (2 g, 1 mmol) was
dissolved in minimum amount of ethanol and stirred under
reflux for 6 h. The dark brown powder formed was filtered and
recrystallized from ethanol and finally dried the product in
vacuum at room temperature (Scheme-II).
-1
The band at 985 cm is due to 1,2-disubstituted trans-alkene.
-1
The peak at 817 cm arises due to C-H out of plane bending.
A peak due to o-substitution of phenyl ring is observed at 746
TABLE-1
IR VIBRATION DETAILS OF Mn-PTAPP LIGAND
Band position
System
Vibration mode
–1
(cm )
O
Metal
Metal
Phenyl substitution
on s-triazine
Alkene
Mn-O
Mn-N
o-substitution
439
482
746
N
N
Ethanol
N
N
N
+
N
N
OH
Chalcone
Re flux, 6 h
2
H N
N
NH2
OH
HO
PTAPP
C-H out of plane bending
1,2-disubstuted trans alkene
C-O-H bending
C-O bending
C-N bending
C=N
826
985
1237
1323
1389
1537
2
,4-Diamino-6-phenyl-
,3,5-triazine
1
Alkene
Phenolic
Phenolic
Imine
Scheme-II: Synthetic scheme of ligand 2,2′-(6-phenyl-1,3,5-triazine-2,4-
diyl)bis-(azanylylidene))bis(3-phenylprop-1-en-1-yl-3-
ylidene))-diphenol (PTAPP) ligand
Imine
Aromatic
Alkene
Phenolic
Overtones
C=C-H stretching
-OH
1899, 2095
3186
Synthesis Mn-PTAPP complex: MnCl
in a hot air oven for 2 h to remove the hydrated water molecules.
2
·4H
2
O was heated
3394

Vol. 32, No. 1 (2020)
Novel Triazine Centred Manganese Based Complex: A Photophysical and Biological Studies 93
-
1
-1
cm . The bands correspond to 439 and 482 cm are due to
ν(Mn-O) and ν(Mn-N) stretching, respectively, which confirms
the coordination of manganese ion to PTAPP ligand. This suggests
that imino nitrogen is coordinated to manganese metal ion.
UV absorption analyses: The UV-Vis absorption spectrum
of the metal and ligand mixture was recorded in DMF solution.
The spectrum of complex is dominated by intense intra-ligand
charge transfer bands. The geometries are supported by their
electronic spectra [20]. Absorption spectrum of the ligand is
characterized by three strong absorption bands with major
maxima at 211, 253 and 325 nm (Fig. 1). The absorption spectrum
of metal complex is characterized by three strong absorption
bands with major maxima at 239, 293 and 360 nm [21] (Fig.
peak due to the two phenolic protons at 5.32 ppm. Two doublet
peaks at 5.81 and 7.14 ppm are due to four alkene protons of
chalcone.A multiplet peak in the range 7.32-7.72 ppm corres-
ponding to thirteen protons, doublets at 7.75, 7.82, 8.12 and
8.37 ppm corresponding to two protons each are attributed to
the aromatic protons (Table-2).
TABLE-2
1
H NMR SPECTRAL DETAILS OF LIGAND PTAPP
Signal
position
Relative no
of protons
Multiplicity
Inference
5
5
7
.32
.81
.14
2H
2H
2H
10H
2H
2H
3H
br
d
d
m
d
d
OH
-C=CH
-C=CH
Ar-H
Ar-H (phenolic moiety)
Ar-H (phenolic moiety)
Ar-H (phenyl substituted
on triazine)
2
). For the metal complex the first two peaks lie at range 239
and 293 nm refer to 41841 and 34,129 cm , respectively indic-
ating n → π* transitions, the third peak lies at 360 nm range
refers to 27,777 cm indicating n-π* transition. The different
transitions exhibit bathochromic shift or hypsochromic shift
when compared with that of free ligand (HL) leading to a square
pyramidal structure [10,22].
7
.32-7.51
.75
7.82
7.85-7.98
-1
7
-1
m
8
.12
.37
4H
2H
d
d
Ar-H (phenyl substituted
on alkene)
Ar-H (phenyl substituted
on triazine)
8
1
1
H NMR analysis: H NMR spectral analysis of the ligand
PTAPP was carried out using Bruker 500 MHz and the solvent
1
used was DMSO. The H NMR spectra for PTAPP shows a broad
Mass analysis: The molecular ion peak in mass spectrum
of Mn-PTAPP complex is observed at m/z 672.63, which is in
2.0
agreement with the calculated mass, corresponding to the mole-
+
cular ion formula MnC39
H
29
N O
5 2
. The base peak is observed
at 183 which correspond to a triazine mass fragment. The spec-
trum records the presence of fragments with m/z values 75, 101,
1.5
1
44, 183, 203 and 654. The possible fragmentation pattern is
211 nm
shown in Fig. 3.
PTAPP
1.0
NH
253 nm
0.5
OH
N
N
N
N
325 nm
m/z = 77
N
N
N
N
N
CH
m/ z = 148
0.0
m/ z = 209.7
m/ z = 183
250
300
Wavelength (nm)
350
400
Fig. 1. UV spectrum of ligand PTAPP
39 nm
0
0
0
0
0
.6
2
.5
.4
.3
.2
Mn-PTAPP
N
N
N
N
N
Mn
293 nm
O
O
360 nm
OH2
m/ z = 645.17
0
.1
.0
0.1
0
Fig. 3. Fragmentation pattern of Mn-PTAPP complex
-
Fluorescence studies: The fluorescent studies were carried
out for ligand (PTAPP) and its metal complex in DMSO. The
fluorescent spectrum of the metal complex is presented in Fig.
3
00
400
Wavelength (nm)
Fig. 2. UV spectrum of complex Mn-PTAPP
500

9
4 Alphonse et al.
Asian J. Chem.
4
. The spectral studies showed that the ligand (PTAPP) and its
ciable antimicrobial activity against all tested strains in comp-
arison to its ligand.
metal complex were highly fluorescent in nature. The ligand
exhibits a broad emission band with a maximum wavelength
of 270 nm upon photo excitation at 300 nm. Similarly, Mn(II)
complex was characterized by the emission band around 451 nm.
Significant differences in positions of emission maximum of
ligand and its complex establish the complexation process.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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In this work, triazine based ligand PTAPP was synthesized
in two steps. In the first step, chalcone was synthesized by
condensation of salicylaldehyde with acetophenone. In second
step, chalcone was made to undergo a condensation reaction
with 2,4-diamino-6-phenyl triazine. Then the ligand success-
fully reacted with Mn(II) to form Mn-PTAPP complex, which
has a square pyramidal geometry. The newly designed ligand
and its Mn complex were assayed for its in vitro antimicrobial
activity against selected pathogens. The complex showed appre-
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