Biological evaluation of a novel amino acid-based macrocyclic Mn(III) and Fe(III) complexes

Article abstract of DOI:10.1002/aoc.4516

A new tetradentate ligand 4-benzylidine-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-bis(2-imino-3-phenylpropanoic acid) of the type N₂O₂ has been synthesized from curcumin derived non-enolisable diketone and L-phenylalanine and complexed with Mn(III) and Fe(III) metal ions. The non-enolisable curcumin was obtained by Knoevenagel condensation. The synthesized ligand and complexes (MnL & FeL) were characterized by various spectral techniques. Using absorption and emission spectral techniques CT-DNA and BSA binding studies has been carried out. The absorption and emission spectral tools reveal the intercalative mode of binding between the CT-DNA and the metal complexes. The fluorescence of BSA was quenched around 340?nm by the metal complexes followed by static quenching mechanism. The emission spectra of BSA were recorded at three different temperatures. The binding sites, mode of binding, binding energy and the donor-acceptor distance on the basis of Forster's resonance energy transfer (FRET) were calculated. The binding site of the metal complexes with CT-DNA and BSA has been discussed by molecular docking studies in order to substantiate the experimental results.

Full text of DOI:10.1002/aoc.4516

Received: 28 March 2018
DOI: 10.1002/aoc.4516
Revised: 11 June 2018
Accepted: 22 June 2018
F U L L P A P E R
Biological evaluation of a novel amino acid‐based
macrocyclic Mn(III) and Fe(III) complexes
1
1
2
3
4
C. Joel
| R. Biju Bennie | S. Daniel Abraham | S. Iyyam Pillai | S. Theodore David
1
PG and Research Department of
A new tetradentate ligand 4‐benzylidine‐1,7‐bis(4‐hydroxy‐3‐methoxyphenyl)
hepta‐1,6‐diene‐3,5‐bis(2‐imino‐3‐phenylpropanoic acid) of the type N O
Chemistry, St. John's College, Tirunelveli‐
627002, Tamilnadu, India
2
2
2
Department of Chemistry, Madras
has been synthesized from curcumin derived non‐enolisable diketone and
L‐phenylalanine and complexed with Mn(III) and Fe(III) metal ions. The
non‐enolisable curcumin was obtained by Knoevenagel condensation. The
synthesized ligand and complexes (MnL & FeL) were characterized by vari-
ous spectral techniques. Using absorption and emission spectral techniques
CT‐DNA and BSA binding studies has been carried out. The absorption and
emission spectral tools reveal the intercalative mode of binding between the
CT‐DNA and the metal complexes. The fluorescence of BSA was quenched
around 340 nm by the metal complexes followed by static quenching
mechanism. The emission spectra of BSA were recorded at three different
temperatures. The binding sites, mode of binding, binding energy and the
donor‐acceptor distance on the basis of Forster's resonance energy
transfer (FRET) were calculated. The binding site of the metal complexes
with CT‐DNA and BSA has been discussed by molecular docking studies in
order to substantiate the experimental results.
Christian College, Chennai‐600059,
Tamilnadu, India
3
PG and Research Department of
Chemistry, Pachaiyappa's College,
Chennai‐600030, Tamilnadu, India
4
Department of Applied Chemistry, PSN
College of Engineering and Technology,
Tirunelveli‐627152, Tamilnadu, India
Correspondence
S. Theodore David, Department of
Applied Chemistry, PSN College of
Engineering and Technology, Tirunelveli‐
627152, Tamilnadu, India.
Email: s.theodore.david@gmail.com
KEYWORDS
BSA,curcumin, docking, intercalation, static quenching
1
| INTRODUCTION
considerable interest due to their application in DNA
molecule probes and chemotherapeutic reagents for the
[
4–6]
Curcumin is one of the most promising candidate for nat-
confrontation against cancer.
Cisplatin, one of the
ural origin having anti‐inflammatory activity with no side
world's most important metal‐based drugs, introduced
in clinical application in the 1970s, acts mainly through
induction of DNA unwinding and DNA‐protein bind-
[1]
effects. Curcumin is a potent anticancer agent and sup-
presses the cancer of the skin, mammary gland, oral
cavity, lung, liver, fore stomach, esophagus, stomach,
[
7–9]
ing.
But the serious side effects such as neuro‐,
[2]
intestine and colon. Curcumin exhibits very effective
wound healing activity. Curcumin bio‐conjugates have
the potential to become useful antibacterial/antifungal
drugs.
hepato‐ and nephrotoxicity, and the insurmountable fre-
quent development of resistance had limited its effective-
ness. As we all know, the nucleic acid is the basic genetic
material of life which is the main target of anti‐cancer
drugs into the human body. Therefore, the study of the
interaction model between drugs and DNA is important
In spite of the rapid development of novel anticancer
drugs, cancer remains as the major cause of death in the
world, due to drug resistance or undesirable side
to make a breakthrough in the mechanism of anti‐cancer
[3]
[10]
effects.
Metal‐based
pharmaceuticals
are
of
drugs cure.
Consequently, numerous attempts have
Appl Organometal Chem. 2018;e4516.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 16
https://doi.org/10.1002/aoc.4516

2
of 16
JOEL ET AL.
been devoted in developing alternative strategies, based
on different metals, with improved pharmacological
properties and aimed at different targets.
The interaction of metal ions has led to our interest in
studying the interaction of transition metal complexes
with proteins. The primary focus has been on the effect
that different ligand systems have on the interaction, par-
ticularly the drug‐binding sites of BSA. Secondly, the pos-
sibility that fluorescence quenching of the protein is due
to FRET (fluorescence resonance energy transfer) from
the protein to the complex will lead to the calculation of
intermolecular distances to help determine the proximity
of the complex to the albumin proteins. In this paper, we
report the association of Mn(III) and Fe(III) complexes of
the curcumin based ligand with Bovine Serum Albumin
utilizing emission, absorption and docking studies.
The structural aspects of these complexes have also
been described. These biological findings from our study
would be helpful in studying the BSA interaction exposed
by metal complexes and may lead to developing novel
metal‐based drug targets.
Since the overall distribution, metabolism, and effi-
cacy of many drugs are correlated with their affinities
[11]
towards serum albumin,
the investigation of drugs
with respect to albumin‐drug binding is imperative and
of fundamental importance. Drug‐plasma‐protein bind-
ing is critically involved in drug pharmacokinetics (i.e.,
absorption, distribution, metabolism and elimination)
[
12]
and pharmacodynamics (pharmacological effects).
It
is hence highly important to estimate drug‐binding
capacity to macromolecules in the beginning periods of
[13]
medication revelation.
BSA is a natural globular protein that is similar to
HSA by 76% in space structure and chemical composi-
[14–16]
tion.
Because of its low cost and ready availability,
BSA has been carefully chosen as our model protein. Sev-
eral different transport proteins exist in blood plasma, but
only the serum albumin is able to bind and transport a
[17–20]
2 | EXPERIMENTAL
wide diversity
affinity.
of ligands with reversibility and high
The chemicals used for the present work were purchased
from commercial sources and the solvents used were of
Albumins can reversibly bind with a number of mole-
cules in the plasma through various interactions. Of the
two major structurally selective binding sites, the binding
affinity offered by the site I are largely through hydropho-
bic interactions, whereas site II involves a combination of
hydrophobic, hydrogen bonding, and electrostatic inter-
99% purity (Merck) and used without further purification.
Curcumin and L‐Phenylalanine were purchased from
Aldrich. CT‐DNA was purchased from Bangalore Genei,
India. Bovine Serum Albumin (BSA) was purchased from
Sigma and Tris Buffer was purchased from HIMEDIA.
The elemental analysis (C, H and N) data were
analysed using Carlo Erba 1108 model elemental
analyser. The metal contents present in the complexes
[21,22]
actions.
Information about the interaction of ions
surrounded by various types of organic ligand with serum
albumin can help reveal the role of albumins in the nor-
mal state and in the diseased state, and thus provide the
basis for the rational design of efficient drugs, sensitizers,
[
30]
13
were estimated as given in the book.
The C NMR
[23]
spectrum was recorded on a Bruker Advance DRX 300
and new therapeutic approaches.
FT‐NMR spectrometer in CDCl solution using TMS as
3
One way to measure the extent and accessibility of
protein binding sites to small molecules involves fluores-
cence quenching. Stern–Volmer kinetics and Forster's
theory is used to investigate the number of binding sites,
standard. Bruker‐Daltonics micro TOF‐Q II mass spec-
trometer is used to record electrospray ionization mass
spectra (ESI). The FT‐IR spectra have been recorded
using JASCO 4100 Spectrometer. The electronic spectra
were recorded from Perkin Elmer Lambda 35 spectropho-
tometer using DMSO as the solvent with the complex
the binding constant K , and the distance between donor
a
[24–27]
and acceptor.
The fluorescence mark of a protein
gets from the aromatic residues.
−
3
concentration of 1x10 M. Magnetic susceptibility mea-
surements of the complexes were computed on a modi-
fied Hertz SG8‐5HJ model gouy magnetic balance using
CuSO .5H O as the calibrant. The molar conductivity of
The fluorescence from the indole group in Trp is
extremely sensitive to its environment and is a conve-
nient spectroscopic probe for the structure and rotational
[28]
4
2
dynamics surrounding the Trp residue.
These Trp res-
the complexes was measured by using Elico model SX
0 conductivity‐bridge in DMF.
idues can undergo electronic excitation in the visible
region, and the emission can be quenched via different
mechanisms depending on the degree of ‘exposure’ to
8
[26,29]
the quencher.
Therefore, changes in the intrinsic
2.1 | Synthesis of Knoevenagel condensate
fluorescence and the bimolecular quenching rate con-
stant can be used to monitor structural changes in a pro-
tein, and reveal information on Trp accessibility and how
Due to possible stabilization by intra‐molecular hydrogen
bonding, curcumin exists rather as an enol. In order to
prevent the enolization and facilitate imine formation,
[25]
deep it is buried in the protein.

JOEL ET AL.
3 of 16
the active methylene group is converted into
a
1,7‐bis(4‐hydroxy‐3‐methoxyphenyl)hepta‐1,6‐diene‐3,5‐
bis(2‐imino‐3‐phenylpropanoic acid (L) obtained
(Scheme 1b) was characterized by FTIR, EI‐MS and C‐
NMR spectroscopy.
benzylidene derivative and is shown in Scheme 1a. The
benzylidene derivative is formed by Knoevenagel conden-
sation between curcumin (4.52 g, 10 mmol) and benzal-
dehyde (10.8 g, 1 mmol) using piperidine as a catalyst in
1
3
Yield: 63%, m.p: 178 °C, Anal. Found.(%): C, 73.58; H,
[31]
the methanolic medium.
5.64; N, 3.73; Calc.: C, 73.51; H, 5.7; N, 3.69; EI‐MS: m/z,
−
1
−1
7
1
50.1041; IR (KBr, cm ): ν
, 1628 cm , νasy(COO‐),
(
C=N)
−1 13
−
1
561 cm , ν
, 1411 cm ; C NMR(δ, ppm in
CDCl ) 158.94(C=N), 183.42 (COO ).
sy(COO‐)
2.2 | Synthesis of ligand
−
3
About 10 mmol of benzylidene derivative (3.68 g) was
taken in a two‐neck flat‐bottomed flask containing
2
.3 | Synthesis of metal complexes
4
0 ml of methanol. To this, 20 mmol of L‐Phenylalanine
3.30 g) dissolved in 20 mmol of sodium hydroxide solu-
tion was added. The reaction mixture was stirred for
0 hrs to give a bright orange coloured precipitate.
(
Finely powdered ligand (1 mmol; 0.66 g) is dissolved in
20 ml methanol. To this, 20 ml methanolic solution of
1 mmol of the metal salt (Mn(OAc) .4H O ‐ 0.27 g/
1
3
2
The precipitate was repeatedly washed with water and
diethyl ether. It was then dried in vacuum over anhy-
drous calcium chloride. The Schiff base 4‐benzylidine‐
FeCl .6H O ‐ 0.40 g) were added drop wise (Scheme 1c).
Then the mixture was stirred and refluxed at 50 °C for
12 hrs. The resulting solution was then slowly evaporated
3
2
SCHEME 1 (a) Synthesis of
Benzylidene derivative (b) Synthesis of
Schiff base ligand (c) Synthesis of Mn(III)
and Fe(III) complexes

4
of 16
JOEL ET AL.
−
1
at room temperature and the product obtained was
washed several times with ethanol and dried in vacuum
pump over anhydrous calcium chloride.
molL NaCl, and the pH are maintained at 7.4 using
con.HCl) are determined from absorption spectroscopy.
The concentration is calculated by dividing absorbance
at 280 nm by molar extinction coefficients of BSA
MnL: Yield: 52%; Brown colour; Anal. Found.(%): C,
−
1
−1 [34]
6
1.95; H, 5.46; N, 3.24 and Mn, 7.54; Calc.: C, 62.3;
(ε280 = 44,300 M cm ).
complexes were prepared by dissolving them in
DMSO and diluting them to a final concentration of 1 x
The stock solutions of metal
−
1
H, 5.3; N, 3.7; ESI‐MS: m/z, 843.26; IR (KBr, cm ):
ν(C=N), 1585 cm , ν
−
1
−1
, 1510 cm , νsy(COO‐),
asy(COO‐)
−
1
−1
2
−5
−1
1
396 cm ;ν(M‐O), 554; ν(M‐N), 452; ʌ (Smol cm ) 52.18;
10 molL .
m
μeff (BM) 4.89; UV–Vis. in DMSO, nm (transition): 250
(
LMCT), 600 and 740 (d‐d).
2.5.2 | Fluorescence spectroscopy
FeL: Yield: 72%; Greencolor; Anal. Found.(%): C,
6
2.19; H, 5.42; N, 3.67 and Fe, 7.4; Calc.: C, 62.2; H, 5.3;
In a run of the fluorescence estimation, 2 ml BSA was
added to quartz cell (1.0 x 1.0 cm). Fluorescence
quenching spectra were recorded at 275–450 nm. The
width of the excitation and emission slit was set to 15
and 4 nm respectively. An excitation wavelength of
−
1
N, 3.7; ESI‐MS: m/z, 844.95; IR (KBr, cm ): ν
,
(
C=N)
−1
−
1
−1
1
593 cm , ν
, 1511 cm , ν
, 1400 cm ;
sy(COO‐)
asy(COO‐)
−
1
2
ν(M‐O), 548; ν
(M‐N)
, 462; ʌ (Smol cm ) 50.76; μ (BM)
m eff
5
6
.93; UV–Vis. in DMSO, nm (transition): 275 (LMCT),
00, 730 (d‐d).
2
85 nm was picked. The BSA was titrated by progressive
−
6
−1
increase of 2 x 10 molL metal complex arrangements.
Titrations were done manually by using micro‐injector.
2.4 | DNA binding experiments
The DNA binding experiments were carried out in double
distilled water with Tris–HCl (5 mM) and NaCl (50 mM)
and the pH adjusted to 7.2. A solution of CT‐DNA in the
buffer gave a ratio of UV absorbance of about 1.89:1 at 260
2
.5.3 | UV–Vis Spectroscopy
The absorption spectra of BSA and BSA‐metal complex
system were recorded in the range of 250–310 nm. The
concentration of BSA and metal complexes were 2 x
[
32]
and 280 nm which shows that the DNA is protein free.
−
6
−1
10
molL .
2.4.1 | Absorption spectral method
2
.6 | Molecular docking study
The electronic absorption spectral titrations were carried
out in 50 mM Tris–HCl buffer, pH 7.5 to scrutinize the
binding affinity between CT‐DNA and complexes.
The concentration of calf thymus DNA was determined
The crystal structure of human DNA–Topo I complex
PDB ID: 1SC7) and BSA protein (PDB ID: 4F5S) were
(
downloaded from Protein Data Bank (PDB) (http://
www.rcsb.org/pdb). The metal complexes were converted
into PDB format using Mercury software. The receptor
and ligand files were generated using auto dock tools.
The default ligand and water present in the biomolecule
were removed. The polar hydrogen atoms and the
kollman charges were added to the receptor. The grid
points were x × y × z directions of 40 × 40 × 40 and a grid
spacing of 0.370 Å. The Docking studies were carried out
using Auto Dock Tools (ADT) version 1.5.6, Auto
Dockvina program and Discovery studio software.
from the absorption intensity at 260 nm with a ε
max
[33]
−1
−1
value
of 6600 M cm . Absorption titration experi-
mentations were carried out by varying the concentration
of the CT‐DNA (0–250 μM) and keeping the complexes
concentration (10 μM) as constant.
2.4.2 | Fluorescence spectral method
The relative binding affinities of complexes to CT‐DNA
was studied with an EB‐DNA solution in Tris–HCl buffer
(pH 7.5). Fluorescence intensities at 612 nm (exited at
5
10 nm) were measured at different complex concentra-
3
| RESULTS AND DISCUSSION
tions. The reduction of emission intensity gives a measure
of the binding propensity of complexes to CT‐DNA.
The ligand L is synthesized by the condensation of
benzylidene derivative produced from curcumin by
Knoevenagel condensation and L‐Phenylalanine, and it
is complexed with Mn(III) and Fe(III) metal ions. The
ligand is stable in air and soluble in common organic sol-
vents like chloroform, ethanol and methanol. The synthe-
sized complexes are stable in air and soluble in DMF &
2
2
.5 | BSA binding experiments
.5.1 | Preparation of stock solutions
The concentrations of the stock solutions of BSA (C
~
BSA
−
6
−1
−1
2
x 10 molL ) in Tris buffer (0.05 molL Tris, 0.15

JOEL ET AL.
5 of 16
DMSO etc., but insoluble in common organic solvents.
Several attempts failed to obtain a single crystal suitable
for X‐ray crystallography. However, the analytical, spec-
troscopic and magnetic data enable us to predict the pos-
sible structure of the synthesized complexes. All the
synthesized compounds give satisfactory elementary ana-
lytical results.
the molecular weight of the ligand with the molecular
formula C H N O . The ion of m/z = 750, undergoes
46
42 2 8
fragmentation to produce a peak at m/z = 662 corre-
sponding to the formula C H N O which is formed
39
36 2 8
by losing the benzylidene moiety. The fragmentation
from m/z = 662 leads to a peak at m/z = 447 with for-
mula C H N O which is formed by losing two mole-
27
30 2 4
cules of 4‐hydroxy‐3‐methoxyphenol from curcumin.
The peak at m/z = 322 is obtained from the fragmenta-
tion of m/z = 447 corresponds to the formula
C H N O is due to the removal of two phenyl groups
3
.1 | Vibrational spectroscopy
The FT‐IR spectra of ligand (L) and the respective metal
complexes (MnL and FeL) are depicted in supplementary
file (Figure S1a, S1b, S1c). The IR spectrum of the ligand
17
26 2 4
from L‐phenylalanine. The peak at m/z = 158 is due to
C H NO of L‐phenylalanine moiety and the peak at
9
9
2
−
1
(Figure S1a) shows an intense peak at 1628 cm which
m/z = 128 is due to the C H O fragment of curcumin
7 7 2
correspond to the imine ν (‐C=N) vibration. The intense
moiety. These fragmentation patterns confirm the struc-
ture of the ligand.
−
1
−
peak at 1561 cm
stretching and the peak at 1411 cm is due to (COO )
symmetric stretching vibration of the carboxylic acid
group. The band at 3424 cm corresponds to ν (‐OH)
stretching vibration. The band at 1027 cm represents
is due to (COO ) asymmetric
−
1
−
In addition, ESI‐MS studies of the complexes were
performed. The molecular ion peak in the spectra of the
complexes MnL and FeL are in expected consistency with
the molecular weight and also the various other peaks are
reliable with the different fragments of the complexes.
The ESI‐mass spectrum of the complex MnL (Figure
S3b) displays the molecular ion peak at m/z = 843.26
which is exactly in accordance with the molecular weight
of the complex. Also for the complex FeL (Figure S3c), a
molecular ion peak at m/z = 844.95 is in correct coher-
ence with its molecular weight. Thus, mass spectral anal-
ysis substantiates well with the proposed chemical
structure of the complexes MnL and FeL.
−
1
−
1
the ν (C‐O) stretching in C‐O‐CH group. The sharp band
3
−
1
appears at 1624 cm is due to ν (C=C) of benzylidine
[35]
moiety.
In the IR spectra of complexes (Figure S1b
and S1c), the imino (C=N) stretching frequency shifts to
−
1
lower frequency regions 1585 and 1593 cm respectively,
−
1
compared to that of the free ligand (1628 cm ). This
indicates the coordination of imino nitrogens to the metal
[
36]
ions.
This is further supported by the presence of M‐N
−
1
bands (452 and 462 cm ). Moreover, the absorption band
due to the asymmetric stretching vibrations of COO
group shifts down to 1510 and 1511 cm , and the sym-
metrical stretching band is also shifted to 1396 and
400 cm , which confirms the bonding of the metal ions
by the carboxylato oxygen atom.
by the formation of M‐O bands at 554 and 548 cm for
−
−
1
3
.4 | Electronic spectra, molar
conductance and magnetic measurements
−
1
1
[37]
This is also confirmed
The electronic spectra of the complexes are given in
Figure 1a and 1b. The UV–Vis spectrum of MnL exhibits
ligand field absorption at 250 nm with molar absorptivity
−
1
MnL and FeL, respectively.
2
−1
value of εmax = 27,50,000 cm mol , which is consistent
with the π‐ π* transition of the ligand. The metal to ligand
charge transfer band is observed at 425 nm and two d‐d
1
3
3
.2 | C NMR spectrum
13
5
5
The C‐NMR spectrum of the ligand L (Figure S2) shows
a signal at δ 56.12 which is assigned to two methyl carbon
atoms. The signals in the range δ 112.06–140.69 are due to
aromatic carbon atoms and the signal at δ 146.93 is
assigned to the hydroxyl carbons. The signal at δ 148.01
is assigned to two C‐O carbons. The signal at δ 158.94 cor-
responds to the azomethine carbon atoms. The presence
of carboxylate carbons is confirmed by the signal at
δ 183.42.
bands at 600 nm and 740 nm corresponds to B → E
1g g
5
5
and B1g → B transitions respectively. These two weak
2g
d‐d transitions are normally expected in the region for
[38]
tetragonally distorted octahedral MnL complex.
The
electronic spectrum of FeL complex exhibits ligand field
absorption at 275 nm with molar absorptivity value of ε
max
2
−1
37,60,000 cm mol , which is consistent with the π‐ π*
=
transition of the ligand. The less intense d‐d bands at
6
4
730nmand600nmcanbeassignedtothe A (S)→ T (G)
1g
1g
6
4
and A (S) → T (G) transitions ascertaining octahedral
structure to FeL complex. The magnetic moment values
1g
2g
[
39]
3.3 | Mass spectra
[
40]
of 4.89 BM and 5.93 BM
for MnL and FeL complexes
The EI mass spectrum (Figure S3a) of ligand shows the
molecular ion (M ) peak at m/z = 750 corresponding to
respectively indicate that both the complexes are in high
spin environment. The molar conductance values of MnL
+

6
of 16
JOEL ET AL.
FIGURE 1 (a) Electronic spectra of MnL complex (b) FeL complex
and FeL are 52.18 and 50.76 which suggests the 1:1 electro-
lytic nature of the complexes.
is consistent with the magnetic moment values. The g⊥
[41]
and g are calculated to be 2.23 and 2.02, respectively.
ll
The gav value can be calculated by the following equation.
1
3
Â
Ã
3
.5 | EPR Spectral Studies
2
av
2
2
⊥
g
¼
2g þ g
ǁ
The solid state X‐band EPR spectrum of the FeL complex
in liquid nitrogen temperature (LNT) is illustrated in
Figure 2. The spectrum exhibiting six hyperfine lines is
an indicative of iron in the high spin state (I = 5/2) which
The gav value is found to be 2.16 which is a character-
istic of octahedral geometry with rhombic distortion.
G = (g – 2)/(g ‐ 2) measures the exchange interaction
ll
⊥
between the iron centre and is found to be 8.64. Since
the G value is greater than 4, the exchange interaction
[
42]
is negligible.
The low intensity forbidden lines in the
spectrum arise due to the mixing of the nuclear hyperfine
levels by the zero field splitting factor of the Hamiltonian.
3.6 | Thermal studies
The thermograms of MnL and FeL complexes are illus-
trated in Figure 3a and 3b. The sample was heated at
−
1
1
atm pressure with a heating rate of 10 °C min and
between the temperature range of 20–700 °C. The decom-
position temperaure, pyrolytic products, percentage mass
loss of the complexes and the ash (per cent) are given in
Table 1. The weight loss of 4.1% at 220–250 °C
FIGURE 2 Solid state X‐band EPR spectrum of FeL complex
FIGURE 3 (a) TG/DTG curve of complex MnL (b) FeL complex

JOEL ET AL.
7 of 16
TABLE 1 Themogravimetric characteristics of metal complexes
Intercalation is caused due to the strong stacking interac-
tion between aromatic chromophores and the base pairs
Mass,%
[
43]
of DNA.
The strength of intercalative binding can be
°
Compound Temp, C Product
found calculated
found from the extent of shift and hypochromism. The
non‐intercalative binding or electrostatic interactions of
metal complexes with DNA may result in hyperchromism
MnL
80–100
Lattice water
2
2OAc and 2H O
Organic moiety
MnO
5.5
11.5
74
4.47
10.45
75.09
10.11
120–240
240–410
410–700
[44]
or hypochromism. The absorption spectrum of the com-
9
plexes MnL and FeL in the absence and presence of CT‐
DNA is shown in Figure 4a and 4b. On adding different
concentrations of CT‐DNA to the complexes, the intensity
of absorption decreases resulting in hypochromism with a
small red shift.
FeL
110–240
2H
2
O and 2Cl
10
82
8
9.63
81.91
8.42
2
4
40–390
00–700
Organic moiety
FeO
In the complexes, MnL and FeL, bands observed in
the region 250 and 270 nm, respectively were assigned
to intra‐ligand charge transfer due to π → π* transition.
Any disturbances in intra‐ligand centred spectral transi-
tions occur as a result of the interaction of metal com-
corresponds to the elimination of coordinated water mol-
ecules. Decomposition of the organic moiety occurs with
a mass loss of 89.2% at 250–350 °C and metal oxides exist
above this temperature.
In FeL complex, the decomposition starts at
[
45]
plexes with DNA.
The binding constant of the
2
00–240 °C with a mass loss of 4.2% which refers to the
complexes with CT‐DNA (K ) was obtained from the
b
removal of two coordinated water molecules. The decom-
position of the organic moiety starts from 250–340 °C
with a major weight loss of 88.1% and the metal oxides
exist above this temperature.
ratio of the slope to intercept by plotting [DNA]/(ε − ε )
a
f
[
46]
versus [DNA] according to the equation:
½
DNAꢀ
½DNAꢀ
ðεb−εf Þ
1
¼
þ
ðεa−εf Þ
Kbðεb−εf Þ
3.7 | DNA binding studies
where [DNA] is the concentration of DNA in base pairs,
εa is the apparent extinction coefficient value found by
In order to find out the feasible binding mode of the com-
plexes with CT‐DNA, various techniques were used and
are discussed below.
calculating A(observed)/[complex], ε is the extinction
f
coefficient for the free compound, and ε is the extinction
b
coefficient for the compound in the fully bound form. The
linear fits of the data gave a straight line with a slope of
3.7.1 | Absorption spectral studies
1
/(ε − ε ) and a y‐intercept of 1/K (ε − ε ), where the
b
f
b
b
f
The binding characteristics of metal complexes with DNA
can be determined by electronic absorption spectroscopy.
Hypochromism along with or without small shifting
arises due to the intercalative mode of binding.
value of K was determined from the ratio of the slope
to intercept.
b
Curcumin is well known in literature for binding with
4
−1
DNA with the binding constant of 4.255 x 10 M which
−
5
FIGURE 4 Absorption spectra of metal complexes with 1 x 10 M concentration in the absence and presence of increasing amounts of
−
5
CT‐DNA (0–25 x 10 M) at room temperature in 50 mM Tris–HCl/NaCl buffer (pH = 7.5). Arrow shows the absorbance changing upon
increasing DNA concentrations. (a) Absorption spectra of MnL complex (b) Absorption spectra of FeL complex

8
of 16
JOEL ET AL.
[
47]
can be tuned upon complexation with transition metals.
I0
¼
1 þ Ksv½Qꢀ:
For example, curcumin derived complexes of metal
ions such as Co(II), Ni(II), Cu(II) & Zn(II) have been
I
reported whose binding constant K ranges from 1.2–2.75
Where I and I are the fluorescence emission intensi-
0
b
4
−1 [48]
(x 10 M )
whereas in the present study Fe(III) and
ties in the absence and presence of quencher (complexes),
respectively; [Q] is the concentration of the quencher; Ksv
is the Stern‐Volmer quenching constant, which is
Mn(III) based complexes of curcumin has been investi-
gated and found to show high binding constant values upto
5
−1
3
.73 x 10 M . This binding constant reported in the study
obtained from the slope of the plot (I /I vs[Q]). The
0
is similar to those reported for typical classical
intercalators (EB‐DNA, 3.3 x 10 M ) and several other
apparent binding constant (Kapp) values were computed
utilizing the condition KEB[EB]/Kapp[complex], where
the complex concentration was the value at a 50% reduc-
tion of the fluorescence intensity of EB and KEB = 1.0 x
10 M ([EB] = 3.3 μM). In the present study, the appar-
ent binding constant Kapp values for Fe(III) and Mn(III)
complexes based on curcumin is observed to be 2.71 x
5
−1
standard intercalators such as proflavin with Escherichia
5
−1
5
coli DNA (4.1 x 10 M ) & phenosafranine (3.81 x 10 M
−
1
[49]
7
−1
).
The magnitudes of intrinsic binding constants
(
K ) are given in Table 2. The observed values of Kb
b
revealed that the MnL and FeL complexes bind to DNA
via intercalative mode. From the electronic absorption
studies, it is inferred that the compounds can bind to
DNA by intercalation, further; the mode of binding should
be proved through some more experiments.
5
−1
5
−1
10 M and 4.19 x 10 M respectively, which is almost
similar to those Cu(II), Ni(II) and Zn(II) curcumin based
5
−1
complexes (3.2–5.3 x 10 M ) reported in the litera-
ture.
[
52]
The apparent binding constant (Kapp) values are
listed in Table 2. The results are consistent with the
absorption spectral studies.
3
.7.2 | EB fluorescence displacement
assay
3.8 | BSA binding studies
The interaction of complexes with CT‐DNA is further
confirmed by performing steady state competitive binding
experiments using complexes MnL and FeL as quenchers,
taking ethidium bromide (EB) as a fluorescent probe. EB
is one of the most sensitive fluorescent probes that bind
3.8.1 | Fluorescence spectroscopy
The process of fluorescence occurs by the emission of a
photon when the electron from the excited state returns
to the ground state. The significance of fluorescence in
biology involves the analysis of biological molecules
which themselves are fluorescent or emit fluorescence
when coupled with some other fluorescent mole-
[50]
to DNA through intercalation.
EB being a planar cat-
ionic dye emits intense strong fluorescence at 612 nm
when it binds to DNA through intercalative mode. When
complexes bind to DNA the probable binding sites for EB
in DNA get decreased resulting in the quenching of EB
fluorescence. As the concentration of the complexes
increases, the fluorescence intensity decreases. This
clearly indicates that the EB molecules are replaced by
[
38,53]
cules.
The intrinsic fluorescence of BSA was due to
the amino acid residues especially tryptophan residues
present in its structure.
Quenching of fluorescence occurs by either dynamic
or static quenching mechanisms. Dynamic quenching
arises due to diffusion and ground state complex forma-
[
51]
the metal complexes in the DNA binding site.
The
[
54]
tion results in static quenching.
At greater tempera-
fluorescence quenching spectra of DNA bound EB by
complexes MnL and FeL are shown in (Figure S4a and
S4b). Both the spectra indicate the displacement of EB
from CT‐DNA as there is an appreciable reduction in
fluorescent intensity is observed.
Fluorescence quenching data were further analyzed
by means of the following Stern‐Volmer equation,
tures, the diffusion coefficients are high. Therefore the
bimolecular quenching constant increases with increas-
ing temperature. But the static quenching constant values
decrease with increasing temperature. The fluorescence
[55]
quenching is described by the Stern‐Volmer relation.
F0= F ¼ 1 þ Ksv½Qꢀ ¼ 1 þ Kqτ0½Qꢀ
TABLE 2 Binding constant (K
b
) andApparent binding constant
Where F and F represent the fluorescence intensities
in the absence and presence of quencher respectively. Ksv
0
(
K
app) calculated for MnL and FeL complexes
is a linear Stern‐Volmer quenching constant, [Q] is the
Binding constant
Apparent binding
constant (Kapp) M
−
1
−1
Complex
(K
b
) M
concentration of quencher, K is the quenching rate con-
q
stant and τ is the fluorescence lifetime of the protein in
the absence of quencher. In the case of fluorescence
5
5
5
0
MnL
FeL
2.04 x 10
3.73 x 10
2.71 x 10
5
4.19 x 10
quenching of BSA, a linear plot of F /F against [Q] was
0

JOEL ET AL.
9 of 16
obtained and from the slope, K was calculated. The unit
τ0 being the average life‐time of BSA is equal to 10 s.
The apparent bimolecular quenching rate constant Kq
TABLE 3
q
Ksv and K values of MnL and FeL complexes
sv
−
8
[56]
4
−1
12
−1 −1
Complex T(K)
K
sv (x 10 Lmol
)
K
q
(x 10 Lmol
s )
MnL
FeL
298
304
2.91
2.76
2.04
2.91
2.76
2.04
which is equal to K /τ0 represents either static or
sv
[57]
dynamic quenching mechanisms.
310
When the different concentration of metal complex
solutions was titrated into a fixed concentration of BSA,
the fluorescence intensity of BSA at around 340 nm
decreased regularly but the emission maximum did not
move to shorter or longer wavelength. The emission spec-
tra of BSA in the presence of complexes MnL & FeL at
298
4.42
4.09
3.18
4.42
4.09
3.18
3
3
04
10
2
98 K is illustrated in Figure 5a and 5b respectively. Also,
3.9 | Analysis of binding constants,
the emission spectra of BSA with the complexes MnL &
FeL at 304 K and 310 K is shown in S5a, S5b and S6a,
S6b, respectively. These results indicated that the metal
complexes could interact with BSA and quench its intrin-
sic fluorescence, but there was no change in the local
dielectric environment of BSA. The K and K values cal-
binding sites and binding energy
For static quenching, when the metal complexes bind
to BSA, the binding constant (K ) and the number of
b
binding sites (n) can be determined from the following
[
59]
equation,
sv
q
ꢀ
ꢁ
culated at different temperatures are given in Table 3.
Since the Stern‐Volmer quenching constants Ksv is
found to decrease with increase in temperature and
F0− F
log
¼ logKb þ n log½Qꢀ
F
1
0
the K values were found to be larger than 2.0 x 10
q
Where F and F are the fluorescence intensities in the
0
−
1 −1
[58]
Lmol s
reported
for the maximum diffusion
absence and presence of quencher, [Q] is the concen-
tration of the quencher. The values of Kb and n are
obtained from the linear fitting plots of log [(F ‐F)/F]
quenching rate constant of various quenchers with bio-
polymers, the quenching of BSA by the metal complexes
could be static and not dynamic quenching.
0
vs. log [Q] is shown in Figure 7a & 7b for MnL and
FeL complexes at 298 K, respectively. The plot for
BSA‐MnL complex at 304 K & 310 K and for BSA‐
FeL complex at 304 K & 310 K are shown in S7a,
S7b and S8a, S8b respectively. The Kb and n values
obtained from the double logarithm plot are shown in
Table 4. The results suggest that there exist a strong
binding force between the BSA and the metal com-
plexes. The BSA contains a hydrophobic cavity in
which the hydrophobic metal complexes can enter into
and interact with it. The number of binding sites for
both the complexes is approximated to unity which
3.8.2 | Absorption spectroscopy
In Figure 6a and 6b explain the quenching mechanism
using the UV–Vis absorption spectra. The absorption
intensity of BSA at 285 nm was slightly shifted to a longer
wavelength upon addition of metal complex solutions.
This confirms that the quenching mechanism of BSA by
metal complexes arises as a result of static quenching
i.e., due to complex formation between the molecules of
BSA and metal complexes.
FIGURE 5 Emission spectra of BSA in the presence of various concentration of metal complexes in DMSO (T = 298 K), c(BSA) = 2.0 x
−
6
−1
−6
−1
1
0
molL , c(Metal complex) = 2, 4, 6, 8, 10 x 10 molL . Insert: Stern‐Volmer plot for quenching of BSA by metal complexes (a)
Emission spectra of BSA with MnL complex (b) Emission spectra of BSA with FeL complex

10 of 16
JOEL ET AL.
−
6
−1
FIGURE 6 UV–Vis absorption spectra of BSA and BSA‐Metal complex solutions: c(BSA) = c(Metal complex) = 2 x 10 molL . (a) BSA‐
MnL solution (b) BSA‐FeL solutions
FIGURE 7 Double logarithm plot for BSA‐metal complexes at 298 K (a) Double logarithm plot for BSA‐MnL (b) Double logarithm plot for
BSA‐FeL
[
60]
TABLE 4 Binding constant (K
b
) and Binding site (n) values of
play in the protein binding process.
The interaction
MnL and FeL complexes
of the complexes with BSA is clarified by the thermody-
namic parameters, Gibbs free energy changes (ΔG),
enthalpy changes (ΔH) and entropy changes (ΔS)
which were obtained from van't Hoff equation. The
signs and magnitudes of the thermodynamic parameters
Binding constant
4
−1
Complex
T (K)
(x 10 Lmol
)
Binding site
MnL
298
4.31
5.87
6.01
1.00
1.19
1.25
3
3
04
10
(ΔH and ΔS) explain the main forces that take place in
the binding process. For this reason, binding constants
were studied at different temperaturesi.e., 298 K,
FeL
298
3.42
3.55
4.39
0.96
0.98
0.99
3
3
04
10
304 K and 310 K. At these temperatures, BSA would
not undergo any structural degradation. The thermody-
namic parameters can be calculated from the van't Hoff
equation:
suggests that there is only one binding site on the pro-
tein where the metal complexes can bind.
[61]
−
ΔH −ΔS
lnK ¼
þ
RT
R
3.9.1 | Thermodynamic parameters
To find the type of binding force between the metal
complexes and BSA, thermodynamic parameters were
evaluated. The electrostatic interactions, hydrogen
bonds, hydrophobic forces and van der Waals interac-
tions are the four types of non‐covalent interactions that
ΔG ¼ −RT lnK
ΔH−ΔG
ΔS ¼
T

JOEL ET AL.
11 of 16
From the above equation, it is evident that there
TABLE 5 Thermodynamic parameters of the binding interaction
of metal complexes with BSA
exists a good linear relationship between lnK and 1/T.
The ΔH and ΔS values are obtained from the slope
and ordinate at the origin of the fitted lines (Figure 8a
and 8b).
The hydrophobic interactions are related to positive
enthalpy change (ΔH) and entropy change (ΔS). The neg-
ative values of ΔH and ΔS are associated with hydrogen
bonding and van der Waals interactions whereas the very
low positive or negative ΔH and positive ΔS values are
characterized by electrostatic interactions.
ΔH
ΔS
(Jmol
ΔG
KJmol )
−1
−1 −1
−1
Complex T (K) (KJmol
)
K
)
MnL
FeL
298
−26.08
−18.82
19.45
−26.44
−27.75
3
3
04
10
−28.36
298
16.72
−25.87
−26.48
3
3
04
10
−27.55
From the results obtained (Table 5), it is evident that
the metal complexes are bound to BSA by electrostatic
interactions and also the negative values of the ΔG show
the spontaneity of BSA‐metal complex interaction.
emission and acceptor absorption spectra using the
[
65]
Forster formula,
3
.9.2 | Energy transfer between the
6
−25
2
−4
R0 ¼ 8:8 x 10 k n ΦJ
complexes and BSA
2
The distance between the fluorophore and the metal
K is the orientation factor related to the geometry of
[62]
2
complex is obtained from Forster's theory.
According
the dipoles of the donor and acceptor and k = 2/3 for
to Forster non‐radiative energy transfer theory, Forster's
resonance energy transfer occurs on account of the over-
lapping of the emission spectrum of the fluorophore
random orientation as in fluid solution; n is the average
refractive index of medium in the wavelength range
where spectral overlap is significant (n = 1.336 ); Φ is
[
66]
(
donor) with the absorption spectrum of another mole-
the fluorescence quantum yield of the donor and for
;
[67]
cule (acceptor). FRET is an important method for study-
ing a wide range of biological process.
acceptor energy transfer efficiency (E) is obtained by the
following equation
BSA it is 0.15
J is the spectral overlap between the
[63]
The donor to
donor emission and the acceptor absorption and is calcu-
lated as follows:
[64]
4
J ¼ ∑
εðλÞ FðλÞλ Δλ
À
Á
6
6
6
E ¼ 1− F=F0 ¼ R0 = R0 þ r
∑ FðλÞ Δλ
Where F is the fluorescent intensity of BSA, F is the
F(λ) = Corrected fluorescence intensity of the donor
in the wavelength range λ
ε(λ) = Molar absorptivity of the acceptor at wave-
length λ.
°
fluorescent intensity of BSA upon addition of the metal
complex when the concentration of which is equal to
BSA, ‘r’ is the distance from the donor to the acceptor
and R is the Forster critical distance where the efficiency
The overlap of the fluorescence emission spectrum of
BSA and the absorption spectrum of MnL and FeL are
0
of energy transfer is 50%. R can be calculated from donor
0
FIGURE 8 (a) Van't Hoff plot for the interaction of BSA with MnL complex (b) FeL complex

12 of 16
JOEL ET AL.
FIGURE 9 Spectral overlap of UV–Vis absorption spectrum of metal complexes with the fluorescence emission spectrum of BSA.
−
6
−1
c(BSA) = c(Metal complex) = 2 x 10 molL , T = 298 K (a) Spectral overlap of MnL (b) Spectral overlap of FeL
TABLE 6 Energy transfer parameters for the interaction of metal
complexes with BSA
It has been observed that the donor to acceptor dis-
[
68]
tance (r) is smaller than 8 nm,
which indicates that
−
15
3
−1
the energy transfer from BSA to metal complexes occurs
with high possibility.
Complex J (10
cm Lmol
)
R
0
(nm)
E
r (nm)
MnL
FeL
2.33
1.19
1.92
1.71
0.06 3.04
0.09 2.52
3
.9.3 | Molecular docking study with
human DNA topoisomerase I
shown in Figure 9a and 9b. The energy transfer parame-
ters for the interaction of metal complexes with BSA are
given in Table 6.
Usually DNA topoisomerase I and II are involved in cell
hereditary procedures such as DNA replication, DNA
FIGURE 10 (a) Molecular docked model of MnL with DNA. (b) specific interaction of MnL with DNA (c) Molecular docked model of FeL
with DNA. (d) specific interaction of FeL with DNA

JOEL ET AL.
13 of 16
TABLE 7 Binding interactions of MnL complex with human DNA and BSA
Dist from best mode
Affinity (kcal/mol)
HDNA
HDNA
BSA
Mode
BSA
rmsdl.b.
rmsdu.b.
rmsdl.b.
rmsdu.b.
1
2
3
4
5
6
7
8
9
−10.8
−10.6
−10.2
−9.9
−9.9
−9.8
−9.7
−9.7
−9.4
−8.9
−8.4
−8.4
−8.3
−8.2
−8
0
0
0
0
14.694
14.223
1.216
14.56
13.437
13.2
19.814
19.805
2.25
13.905
15.199
13.389
16.781
14.064
15.746
16.656
12.197
18.847
18.767
18.519
23.036
18.913
22.09
22.746
14.273
19.32
15.888
15.701
19.2
−8
−8
14.051
14.131
−7.9
18.846
TABLE 8 MnL binds with different amino acid residues and
nucleotide of receptors
recombination and chromosome isolation at mitosis.
Specifically, DNA topoisomerase is a key compound
in metazoans and has been widely utilized as an objective
Ligand
Receptor
Distance A°
Residue
for clinical medications for the treatment of
FeL
HDNA
3.33
DA13‐C28–33
DA14‐C1–6
DA15‐O8
[69,70]
diseases.
Metal complexes MnL and FeL were suc-
4
2
2
3
3
.41
.4
.71
.02
.15
cessively docked with the human DNA–Topo‐I complex
PDB ID: 1SC7). The binding natures of the complexes
MnL and FeL are displayed in Figure 10 (a, b) & 10
c, d). The maximum binding energy values for com-
plexes MnL and FeL are found to be −10.4
(
DT106‐H63
DT106‐H64
DT107‐O40
TRY137‐O27
LYS136‐O27
GLU125‐H61
GLU125‐H41
PHE133‐C26
TYR160‐C26
(
BSA
3.38
−
1
3.42
3.07
4.09
3.49
3.69
and − 10.8 kcal mol , respectively. All the possible bind-
ing modes are given in the Tables 7 and 9. The distance
between the HDNA and the probes are provided in the
Tables 8 and 10. From the coupling energy values, it is
observed that the complexes MnL and FeL have higher
TABLE 9 Binding interactions of FeL complex with human DNA and BSA
Dist from best mode
Affinity (kcal/mol)
HDNA
HDNA
BSA
Mode
BSA
rmsdl.b.
rmsdu.b.
rmsdl.b.
rmsdu.b.
1
2
3
4
5
6
7
8
9
−10.4
−10.4
−9.9
−9.8
−9.8
−9.8
−9.8
−9.7
−9.6
−8.4
−8.3
−8.2
−8.2
−8.1
−8
0
0
0
0
14.905
14.996
16.226
12.625
1.543
14.823
5.528
16.037
18.361
19.832
21.84
19.653
10.704
19.61
13.516
20.171
13.563
13.938
13.711
12.619
12.417
13.922
14.185
14.117
18.397
17.557
16.344
15.525
15.156
18.569
17.284
19.082
−8
−8
−7.9

14 of 16
JOEL ET AL.
TABLE 10 FeL binds with different amino acid residues and
nucleotide of receptors
Figure 11 (a,b) and 11 (c,d) and also the binding of the
complexes with the amino acid residues in the BSA are
given in Tables 8 and 10. The possible binding energy of
the complexes with BSA is displayed in Tables 7 and 9.
These results show that the complexes can be used as
better therapeutic agents.
Ligand
Receptor
Distance A°
Residue
MnL
HDNA
2.74
ARG364‐O7
2
4
3
1
3
.8
.57
.3
.95
.42
TGP11‐O8
HIS266‐O40
HIS266‐O41
AGR316‐O27
DA16‐O25
4
| CONCLUSION
BSA
5.07
LYS132‐C28–33
GLU125‐C28–33
PHE133‐C28–33
LYS132‐C26
LEU122‐C42–48
PRO117‐C42–48
3.46
4.45
4.71
4.83
5.09
A new class of tetradentate Schiff base ligand and its
Mn(III) and Fe(III) metal complexes from curcumin
derived non‐enolisable diketone and L‐Phenylalanine
has been synthesized and characterized using various
analytical and spectroscopic tools. The interaction of
these metal complexes with CT‐DNA and BSA was stud-
ied using emission and absorption spectra. The binding
mode of metal complexes with CT‐DNA was observed
to be intercalative in nature. It was found that the metal
complexes could quench the intrinsic fluorescence of
BSA through static quenching. The enthalpy change and
entropy change reveal that the metal complexes are
bound to BSA by electrostatic interactions into the hydro-
phobic pocket of subdomain II A of BSA which is sup-
ported by the molecular docking studies. The distance
between the BSA and MnL & FeL was found to be 3.04
and 2.52 A°, respectively which indicates that the energy
transfer occurs with high possibility.
binding nature with HDNA. So these complexes can be
taken as a promising candidate for anticancer drugs.
3.9.4 | Molecular docking study with BSA
Metal complexes MnL and FeL were also docked with
BSA protein (PDB ID: 4F5S) using Auto Dockvina
[71]
[72]
tools
and Discovery studio software.
The binding
energy of the complexes MnL and FeL were estimated
−
1
to be −8.9 and − 8.4 kcal mol , respectively. The binding
mode of the complexes MnL and FeL are shown in
FIGURE 11 (a) Molecular docked model of MnL with BSA (b) specific interaction of MnL with BSA (c) Molecular docked model of FeL
with BSA (d) specific interaction of FeL with BSA

JOEL ET AL.
15 of 16
ORCID
[26] M. R. Eftink, C. A. Ghiron, Anal. Biochem. 1981, 114, 199.
[
27] K. M. Sanchez, D. E. Schlamadinger, J. E. Gable, J. E. Kim,
C. Joel http://orcid.org/0000-0002-2680-4395
S. Theodore David http://orcid.org/0000-0001-9873-0754
J. Chem. Educ. 2008, 85, 1253.
[
[
[
28] J. M. Beechem, L. Brand, Annu. Rev. Biochem. 1985, 54, 43.
29] M. R. Eftink, C. A. Ghiron, Biochemistry 1976, 15, 672.
REFERENCES
30] A. Vogel, Text Book of Quantitative Inorganic Analysis, 3rd ed.,
ELBS, Longman, London, 1969.
[
1] R. Motterlini, R. Foresti, R. Bassi, C. J. Green, Free Radic. Biol.
Med. 2000, 28, 1303.
[31] J. Annaraj, S. Srinivasan, K. M. Ponvel, P. R. Athappan,
[
2] B. B. Aggarwal, B. Sung, Trends Pharmacol. Sci. 2009, 30, 85.
J. Inorg. Biochem. 2005, 99, 669.
[
3] M. Alagesan, N. S. P. Bhuvanesh, N. Dharmaraj, Dalton Trans.
[32] P. Krishnamoorthy, P. Sathyadevi, P. T. Muthiah, N.
2
013, 42, 7210.
Dharmaraj, RSC Adv. 2012, 2. 12190
[
[
[
[
4] B. Armitage, Chem. Rev. 1998, 98, 1171.
[33] M. E. Reichmann, S. A. Rice, C. A. Thomas, P. Doty, J. Am.
Chem. Soc. 1954, 76, 3047.
5] H. T. Chifotides, K. R. Dunbar, Acc. Chem. Res. 2005, 38, 146.
6] W. K. Pogozelski, T. D. Tullius, Chem. Rev. 1998, 98, 1089.
7] T. Storr, K. H. Thompson, C. Orvig, Chem. Soc. Rev. 2006,
[
[
[
34] E. Alarcon, A. Aspee, M. Gonzalez‐Bejar, A. M. Edwards, E.
Lissi, J. C. Scaiano, Photochem. Photobiol.Sci. 2010, 9, 861.
35] S. Srinivasan, G. Rajagopal, P. R. Athappan, Trans. Met. Chem.
3
5, 534.
2001, 26, 588.
[
8] G. Giaccone, R. S. Herbst, C. Manegold, G. Scagliotti, R. Rosell,
V. Miller, R. B. Natale, J. H. Schiller, J. von Pawel, A.
Pluzanska, M. Gatzemeier, J. Grous, J. S. Ochs, S. D. Averbuch,
M. K. Wolf, P. Rennie, A. Fandi, D. H. Johnson, J. Clin. Oncol.
36] J. R. Ferraro, Low‐frequency Vibrations of Inorganic and Coordi-
nation Compounds, 3rd ed., Wiley Interscience, New York
1978.
2
004, 22, 777.
[37] S. T. David, R. Antony, K. Saravanan, K. Karuppasamy, S.
Balakumar, Spectrochim. Acta A 2013, 103, 423.
[
9] J. Reedijk, Chem. Commun. 1996, 7, 801.
[
[
[
[
38] J. Xiao, M. Wu, G. Kai, F. Wang, H. Cao, X. Yu, Nanomed.
[
[
[
[
[
[
10] J. Lu, Q. Sun, L. Jun‐Ling, W. G. Jiang, X. Liu, S.‐P. Jin‐Lei
Nanotechnol. Biol. Med. 2011, 7, 850.
Tian, J. Yan, Inorg. Biochem. 2014, 137, 46.
39] G. M. Gehad, M. M. Omar, A. M. Hindy, Turk. J. Chem. 2006,
11] Y. Zhang, H. L. Wu, A. L. Xia, Q. J. Han, H. Cui, R. Q. Yu,
3
0, 361.
40] T. S. Davis, J. P. Fackler, M. J. Weeks, Inorg. Chem. 1968, 7,
994.
41] W. J. Geary, Coord. Chem. Rev. 1971, 7, 81.
Talanta 2007, 72, 926.
12] K. Vuignier, J. Schappler, J. L. Veuthey, P. A. Carrupt, S.
1
Martel, Anal. Bioanal. Chem. 2010, 398, 53.
13] M. L. Howard, J. J. Hill, G. R. Galluppi, M. A. McLean, Comb.
Chem. High T. Scr. 2010, 13, 170.
[42] B. J. Hathaway, D. E. Billing, Coord. Chem. Rev. 1970, 6, 143.
14] X. X. Wang, H. X. Shen, Y. M. Hao, Chin. J. Anal. Chem. 2000,
[
[
[
43] J. S. Guerrero, P. C. Sanchez, E. R. Perez, F. V. Garcia, M. E. B.
2
8, 1388.
Gomez, L. R. Azuara, Toxicol. In Vitro 2011, 25, 1376.
15] C. Y. Guo, X. Wu, J. H. Yang, F. Wang, Z. Jia, D. H. Ran, J. H.
44] T. Topala, A. Bodoki, L. Oprean, R. Oprean, Farmacia 2014, 62,
Zheng, J. Photochem. Photobiol. A 2006, 181, 50.
1049.
[
[
[
16] R. Flores, Anal. Biochem. 1978, 88, 605.
45] M. Das, R. Nasani, M. Saha, S. M. Mobina, S. Mukhopadhyay,
17] H. Vorum, K. Fisker, B. Honore, J. Pept. Res. 1997, 49, 347.
Dalton Trans. 2015, 44, 2299.
18] G. Zolese, G. Falcioni, E. Bertoli, R. Galeazzi, M. Wozniak, Z.
Wypych, E. Gratton, A. Ambrosini, Proteins: Struct., Funct.,
Genet. 2000, 40, 39.
[46] K. Jeyalakshmi, N. Selvakumaran, N. S. P. Bhuvanesh, A.
Sreekanth, R. Karvembu, RSC Adv. 2014, 4, 17179.
[
47] S. Nafisi, M. Adelzadeh, Z. Norouzi, M. N. Sarbolouki, DNA
[
[
19] J. P. Laussac, B. Sarkar, Biochemistry 1984, 23, 2832.
Cell Biol. 2009, 28, 201.
20] W. Bal, J. Christodoulou, P. J. Sadler, A. Tucker, J. Inorg.
Biochem. 1998, 70, 33.
[48] J. Porkodi, N. Raman, Appl. Organomet. Chem. 2017, 32, e4030.
[
[
[
49] N. Shahabadi, M. Falsafi, N. H. Moghadam, J. Photochem.
Photobiol. B 2013, 122, 45.
[
[
[
[
[
21] V. Lhiaubet Vallet, Z. Sarabia, F. Bosca, M. A. Miranda, J. Am.
Chem. Soc. 2004, 126, 9538.
50] L. Li, Q. Guo, J. Dong, T. Xu, J. Li, J. Photochem Photobiol. B:
Biologia 2013, 125, 56.
22] M. C. Jimenez, M. A. Miranda, I. Vaya, J. Am. Chem. Soc. 2005,
1
27, 10134.
51] R. K. Vuradi, K. Dandu, P. K. Yata, V. R. M. R. R. Mallepally,
N. Chintakuntla, R. Ch, S. S. Thakur, C. M. Rao, S.
Satyanarayana, New J. Chem. 2018, 42, 846.
23] H. F. Crouse, J. Potoma, F. Nejrabi, D. L. Snyder, B. S. Chohan,
S. Basu, Dalton Trans. 2012, 41, 2720.
24] Y. J. Hu, Y. Liu, L. X. Zhang, R. ‐M. Zhao, S. S. Qu, J. Mol.
Struct. 2005, 750, 174.
[52] T. K. Muthu, I. S. Pillai, S. Subramanian, P. Venkatesh, Indo
Am. J. Pharm. Sci. 2017, 4, 3357.
25] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Springer
Science, Tirunelveli, Tamil Nadu, India 2004.
[53] X. P. Zhang, Y. H. Hou, L. Wang, Z. Ye‐Zhong, Y. Liu, JOL
2013, 138, 8.

16 of 16
JOEL ET AL.
[
54] J. Liu, Y. He, D. Liu, Y. He, Z. Tang, H. Lou, Y. Huo, X. Cao,
[68] D. J. Li, J. F. Zhu, J. Jin, X. J. Yao, J. Mol. Struct. 2007, 846,
RSC Adv. 2018, 8, 7280.
34.
[
[
[
[
55] O. Stern, M. Volmer, Z. Phys. 1919, 20, 183.
[69] Y. Pommier, Nat. Rev. Cancer 2006, 6, 789.
56] J. R. Lakowicz, G. Weber, Biochemistry 1973, 12, 4161.
57] M. R. Eftink, C. A. Ghiron, J. Phys. Chem. 1976, 80, 486.
[70] D. Lu, X. Zhao, Y. Zhao, B. Zhang, B. Zhang, M. Geng, R. Liu,
Food Chem. Toxicol. 2011, 49, 3158.
[
[
71] C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P.
58] T. A. Wani, A. H. Bakheit, M. A. Abounassif, S. Zargar, Front.
Chem. 2018, 6, 47.
Shields, R. Taylor, M. Towler, J. Streek, J. Appl. Cryst. 2006,
39, 453.
[
59] N. M. R. Martins, S. Anbu, K. T. Mahmudov, R.
Ravishankaran, M. F. C. G. da Silva, L. M. D. R. S. Martins,
A. A. Karande, A. J. L. Pombeiro, New J. Chem. 2017, 41, 4076.
72] O. Trott, A. J. Olson, J. Comput. Chem. 2010, 31, 455.
[
60] V. D. Suryawanshi, L. S. Walekar, A. H. Gore, P. V. Anbhule,
SUPPORTING INFORMATION
G. B. Kolekar, J. Pharm. Anal. 2016, 6, 56.
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[
61] P. D. Ross, S. Subramanian, Biochemistry 1981, 20, 3096.
[
62] L. A. Sklar, B. S. Hudson, R. D. Simoni, Biochemistry 1977, 16,
5
100.
63] Z. J. Yasseen, J. H. Hammad, H. A. Altalla, Spectrochim. Acta A
014, 124, 677.
[
2
How to cite this article: Joel C, Biju Bennie R,
Daniel Abraham S, Iyyam Pillai S, Theodore David
S. Biological evaluation of a novel amino acid‐
based macrocyclic Mn(III) and Fe(III) complexes.
Appl Organometal Chem. 2018;e4516. https://doi.
org/10.1002/aoc.4516
[
[
64] T. Forster, Ann. Phys. 1948, 2, 55.
65] O.‐Y. Yu, Y.‐F. Cheng, S.‐Y. Huang, A.‐M. Bai, Y.‐J. Hu,
J. Solution Chem. 2011, 40, 1711.
[
66] N. Shaklai, J. Yguerabide, H. M. Ranney, Biochemistry 1977,
1
65, 585.
67] L. Cyril, J. K. Earl, W. M. Sperry, in Biochemists' Handbook,
Ed: E. F. N. Spon), London 1961 83.
[
(