Synthesis, structure and catalytic promiscuity of a napthyl-pyrazole Mn(II) complex and structure–activity relationships

Article abstract of DOI:10.1080/00958972.2019.1658192

The napthyl/pyridine-pyrazole-derived complexes, [Mn(L¹)Cl₂] (1), [Co(L¹)Cl₂] (2), [Cu(μ-Cl)(Cl)(L)]₂ (3), [Cu₂(L)₂(N₃)₃(μ2-N₃)] (4), and [Co(L²)Cl₂] (5) (where L¹ = bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-napthalen-1-ylmethyl-amine (L¹), L = 5-methyl-pyrazol-1-ylmethyl) -napthalen-1-ylmethyl-amine (L) and L² = 2-[2-(3,5-dimethyl-pyrazol-1-yl)-1-methyl-ethyl]-pyridine), exhibited phenoxazinone synthase activity in methanol in the range 5–54 h^?1. Binuclear copper(II) derivatives 3 and 4 show better catalytic activities than manganese(II) and cobalt(II) derivatives. The kinetic studies reveal that phenoxazinone chromophore is produced via a complex-substrate intermediate. Further, 3 and 4 show catecholase activity in methanol in the presence of oxygen. All the complexes showed potent antimicrobial activity against the tested strains of bacteria and fungi. Complex 1 was synthesized for the first time by mixing L¹ and MnCl₂ (1:1) and characterized by single-crystal X-ray crystallography, cyclic voltammetry, density functional theory, and thermogravimetry analysis. The present study suggests that napthyl/pyridyl-anchored pyrazole metal complexes are interesting scaffolds for the development of novel model compounds for biochemical reaction and efficient antimicrobial agents.

Full text of DOI:10.1080/00958972.2019.1658192

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, structure and catalytic promiscuity
of a napthyl-pyrazole Mn(II) complex and
structure–activity relationships
Abhimanyu Jana, Paula Brandão, Harekrishna Jana, Atish Dipankar
Jana, Gopinath Mondal, Pradip Bera, Ananyakumari Santra, Ajit Kumar
Mahapatra & Pulakesh Bera
To cite this article: Abhimanyu Jana, Paula Brandão, Harekrishna Jana, Atish Dipankar
Jana, Gopinath Mondal, Pradip Bera, Ananyakumari Santra, Ajit Kumar Mahapatra &
Pulakesh Bera (2019): Synthesis, structure and catalytic promiscuity of a napthyl-pyrazole
Mn(II) complex and structure–activity relationships, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2019.1658192
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2019.1658192
Synthesis, structure and catalytic promiscuity of a
napthyl-pyrazole Mn(II) complex and structure–activity
relationships
a
b
c
d
Abhimanyu Jana , Paula Brand ~a o
, Harekrishna Jana , Atish Dipankar Jana ,
a
a,e
a
f
Gopinath Mondal , Pradip Bera , Ananyakumari Santra , Ajit Kumar Mahapatra
a
and Pulakesh Bera
a
Post Graduate Department of Chemistry, Panskura Banamali College (Vidyasagar University),
b
Midnapore (East), India; Department of Chemistry, CICECO, University of Aveiro, Aveiro, Portugal;
c
Department of Microbiology, Panskura Banamali College (Vidyasagar University), Midnapore (East),
d
e
India; Department of Physics, Behala College, Kolkata, India; Department of Chemistry, Kandi Raj
College, Murshidabad, India; Department of Chemistry, Indian Institute of Engineering Science and
f
Technology, Howrah, India
ABSTRACT
ARTICLE HISTORY
Received 20 May 2019
Accepted 8 August 2019
1
The napthyl/pyridine-pyrazole-derived complexes, [Mn(L )Cl
2
] (1),
1
[
[
Co(L )Cl ] (2), [Cu(m-Cl)(Cl)(L)] (3), [Cu (L) (N ) (m2-N )] (4), and
2
2
2
2
3 3
3
2
1
Co(L )Cl ] (5) (where L ¼ bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-
2
1
KEYWORDS
Napthyl/pyridine-pyrazole
complexes; X-ray
crystallography; phenoxazi-
none synthase; catechol
oxidase; antimicro-
bial activity
napthalen-1-ylmethyl-amine (L ), L ¼ 5-methyl-pyrazol-1-ylmethyl)
2
-
napthalen-1-ylmethyl-amine (L) and L ¼ 2-[2-(3,5-dimethyl-pyra-
zol-1-yl)-1-methyl-ethyl]-pyridine), exhibited phenoxazinone syn-
ꢀ
1
thase activity in methanol in the range 5–54 h . Binuclear
copper(II) derivatives 3 and 4 show better catalytic activities than
manganese(II) and cobalt(II) derivatives. The kinetic studies reveal
that phenoxazinone chromophore is produced via a complex-sub-
strate intermediate. Further, 3 and 4 show catecholase activity in
methanol in the presence of oxygen. All the complexes showed
potent antimicrobial activity against the tested strains of bacteria
and fungi. Complex 1 was synthesized for the first time by mixing
1
L and MnCl (1:1) and characterized by single-crystal X-ray crystal-
2
lography, cyclic voltammetry, density functional theory, and ther-
mogravimetry analysis. The present study suggests that napthyl/
pyridyl-anchored pyrazole metal complexes are interesting scaf-
folds for the development of novel model compounds for biochem-
ical reaction and efficient antimicrobial agents.
CONTACT Pulakesh Bera
pbera.pbc.chem@gmail.com
Post Graduate Department of Chemistry, Panskura
Banamali College (Vidyasagar University), Panskura R.S., Midnapore (East), West Bengal 721152, India.
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2019.1658192.
ß 2019 Informa UK Limited, trading as Taylor & Francis Group

2
A. JANA ET AL.
1. Introduction
Pyrazole (1,2-diazole) which is isomeric to imidazole (1,3-diazole), an integral part of
histidine unit of several proteins, has great interest due to its wide range of applica-
tions in catalysis, medicine, and agro-chemicals [1–4]. The attractiveness of pyrazole
and its derivatives is their versatility that allows for the synthesis of a series of analog
building blocks with different moieties which affect the electronic properties of the
resultant compounds [5]. Biological applications of pyrazole derivatives such as anti-
fungal, antitubercular, antibacterial, antiviral [6–8], antioxidant [1, 9–11], anti-inflamma-
tory [12], antipyretic, antimicrobial [13], anticonvulsant [14], antihistaminic [15],
antidepressant [16], insecticides, and fungicides [17] were well documented.
The event of biocatalysts and catalytic promiscuity has been focused by bioinor-
ganic chemists in recent years [18–20]. Generally, enzymes have high efficiency and
specificity but in many cases, a single catalytic site can activate more than one bio-
chemical transformation. This phenomenon is known as catalytic promiscuity. The lit-
erature on biomimetic studies has shown several examples of such catalytic
promiscuity over the last two decades [21]. Attempts have been made for modeling
the active site of several metalloenzymes like hydrolase, phosphodiesterase, super-
oxide dismutase (SOD), nuclease, phenoxazinone synthase (PHS), and catecholase oxi-
dase (CO) activities with rationally synthesized model complexes [22]. The enzyme-
donor sites are rationally designed with small molecule ligands which are then incor-
II
I
III
II
II
II
porated with metals to form metal complexes. Generally, Cu /Cu , Co /Co , Ni , Fe /
III
II
II
Fe , Mn , and Zn ions are used for bio-mimetic functional models and mechanistic
studies [23]. It has been noticed that the strongly coordinated multiple N-donors
enhance the rate of enzymatic reaction [23]. Several multiple N-donors and N,O-donors
are modeled for enzymatic study. Several pyrazole-derived multipodal copper(II) com-
plexes showing CO activity were reported [24, 25]. Earlier, Malachowski and
Davison reported CO activity of some pyrazole-derived ligands [26]. In view of poten-
tial biological activity of pyrazolyl derivatives, we explore the various pyrazole-based
compounds annexed with napthalene/pyridine for biomimicking activities. Herein, we

JOURNAL OF COORDINATION CHEMISTRY
3
report the PHS activity of 1–5 and CO mimicking activities of 3 and 4 with detailed
kinetic studies. The antimicrobial activities of the napthyl/pyridyl-pyrazole derivatives
1
–5 have been screened with eight bacteria, Escherichia coli, Staphylococcus aureus,
Streptococcus faecalis, Salmonella typhi, Proteus vulgaris, Pseudomonas aeruginosa,
Klebsiella pneumonia, and Bacillus subtilis, and two fungi Aspergillus flavus and Candida
albicans. The synthesis and structural characterization of 1 is reported for the
first time.
2. Experimental
2.1. Materials and reagents
The starting materials for the synthesis of the ligands like acetylacetone, hydrazine
hydrate, formalin, 2-methylamino-pyridine, 1-methyl-napthyl-amine, 2-amino-phenol,
and 3,5-ditertiary-butyl-catechol were purchased from Aldrich Chemical Company and
used as procured. Copper(II) chloride dihydrate, copper(II) nitrate hexahydrate,
manganese(II) chloride trihydrate, cobalt(II) chloride hexahydrate, and sodium azide
were purchased from Merck, India, and used for the preparation of complexes.
Solvents like methanol, ethanol, chloroform, diethyl ether, and acetonitrile were of
reagent grade and dried before use.
2.1.1. Synthesis of ligands
The present ligands were synthesized by the condensation of 3,5-dimethyl-pyrazole-1-car-
binol and amine at ambient conditions. The preparation of 3,5-dimethyl-pyrazole-1-carbi-
1
2
nol is carried out following a known literature procedure [26, 27]. The details of L and L
preparation and characterization were reported earlier by one of the authors (A
Jana) [28].
1
2
.1.2. Preparation of [Mn(L )Cl ] (1)
2
1
MnCl ꢁ3H O (1 mmol, 0.241 g) was added to a solution of L (1 mmol, 0.373 g) in 20-
2
2
mL acetonitrile at room temperature. The mixture was stirred for 0.5 h. The resultant
solid was filtered off and dried over silica gel. Colorless crystals suitable for X-ray crys-
tallography were obtained from the acetonitrile solution of L . Yield: 62% (based on
1
metal salt). CHN Analysis found (calcd) for C H Cl MnN : C, 55.31 (55.27); H, 5.37
23
27
2
5
ꢀ
1
(
(
5.40); N, 13.96 (14.01). IR assignments (KBr pellet) (in cm ); m(C ¼ C)pyrazole 1571
strong(s)); m(C ¼ N) 1465 (s); m(C ꢀ N) 1304 (s).
pyrazole
aliphatic amine
Complexes 2–5 were synthesized once again following the procedures [28, 29] to
investigate and compare their catalytic efficiency with 1. The isolation of 3 and 4 was
1
obtained prior to dissociation of L , where one pyrazole unit was lost during complex-
1
ation. The details of the fragmentation of L and the formation of 3 and 5 were
1
described earlier and are not included in the present study. We recrystallized 1–5, L
and L before in vitro biological experiments.
2

4
A. JANA ET AL.
2.2. Physical measurements
Elemental analysis (C, H, and N) were carried out using a FISONS EA-1108 CHN ana-
lyzer. The FTIR analyses were performed by using a Perkin Elmer Spectrum Two
ꢀ
1
Spectrophotometer (400–4000 cm ). The samples were prepared as KBr pellets using
anhydrous KBr salt. The UV-vis spectra of the complex were measured using a Perkin
Elmer Lamda-35 spectrophotometer with a 1-cm path length quartz-cell. TGA analysis
of 1 is performed using an instrument from Perkin Elmer, model TGA 4000, at a heat-
ꢂ
ing rate of 20 C/min under nitrogen. The ground-state electronic structure calculations
have been carried out using the X-ray coordinates of the complex with the help of
DFT [30] methods with the Orca 2.7 program [31]. Becke’s hybrid function [30] with
the Lee-Yang-Parr (LYP) correlation function [32] was used throughout the study.
LANL2DZ valence and effective core potential functions were used. All energy calcula-
tions were performed using the self-consistent field “tight” option of the Orca 2.7 pro-
gram to ensure sufficiently well-converged values for the state energies. Cyclic
voltammetry studies were performed at room temperature in methanol solvent using
tetrabutylammonium perchlorate as a supporting electrolyte on a CH Instrument elec-
trochemical workstation model no CHI630E. The conventional three-electrode assem-
bly is comprised of a platinum working electrode, a platinum wire auxiliary electrode,
and Ag/AgCl reference electrode.
2.3. X-ray crystallography
The single-crystal X-ray diffraction (XRD) of 1 was carried out on a Bruker SMART APEX
II X-ray diffractometer equipped with graphite-monochromated Mo-Ka radiation (k ¼
0.71073 Å) and 16 CCD area detector. The intensity data were collected in the p and
x scan mode, operating at 50 kV, 30 mA at 296 K [33]. The data reduction was per-
formed using SAINT and SADABS [34]. All calculations in the structural solution and
refinement were performed using the Bruker SHELXTL program [35]. The structure was
solved by the heavy atom method and refined by full-matrix least-squares methods.
All the non-hydrogen atoms were refined anisotropically; hydrogens were geometric-
ally positioned and fixed with isotropic thermal parameters. The final electron density
maps showed no significant difference.
2.4. Kinetics of catalytic activity
The PHS mimicking activity of 1–5 was studied by monitoring the oxidation of O-ami-
ꢂ
nophenol (OAPH) spectrophotometrically in dioxygenated methanol at 25 C. Auto-oxi-
dation of substrate is strictly prohibited by not adding any base. All the complexes in
ꢀ
5
the concentration 1 ꢃ 10 M catalyze the formation of phenoxazinone from OAPH in
oxygenated methanol showing progressive increase of peak intensity at 435 nm, which
is characteristic of phenoxazinone chromophore. It is to be noted that blank experi-
ment without complex (catalyst) does not give any peak at 435 nm in an identical
reaction condition. To examine the catalyst dependency on the rate of the reaction,
ꢀ
5
the amounts of the catalyst (10–200 ꢃ 10 M) were mixed with a fixed concentration
of substrate (1 ꢃ 10ꢀ M) in methanol (2.0 mL) saturated with dioxygen. Same
3

JOURNAL OF COORDINATION CHEMISTRY
5
concentration of substrate and catalysts (3 and 4) was also maintained for catecholase
activity and kinetic study.
2.5. Determination of the logP by using the shake-flask method
Lipophilicity of the ligands and complexes are determined by calculating logP values
according to the shake-flask method [36]. Compounds under investigation were
weighted out accurately and partitioned between equal volumes of water and 1-octa-
nol (5 mL each) by shaking for 30 h at room temperature to assure full partitioning of
the analyzed compounds between two water and 1-octanol phases. Then, the solution
was centrifuged at 3500 rpm for 10 min to separate two layers. The concentration of
the compounds in different layers was measured by the optical density values
obtained from UV-Vis spectroscopy.
2.6. Antibacterial assays
1
2
Antibacterial sensitivity of the five metal complexes along with free L and L was
tested by the agar well diffusion method using Mueller–Hilton agar media. The agar
diffusion method was employed for the determination of antibacterial activities
according to the method described by van den Berghe and Vlietinck in 1991 [37]. The
compounds under investigation were dissolved in methanol and acetonitrile to a final
concentration of 1000 lg/mL. Eight species of pathogenic bacteria, Escherichia coli,
Staphylococcus aureus, Streptococcus faecalis, Salmonella typhi, Proteus vulgaris,
Klebsiella pneumonia, Pseudomonas aeruginosa, and Bacillus subtilis, were used to
screen the antibacterial activity of the metal complex [38]. Pathogenic bacterial strains
ꢂ
were incubated in sterile nutrient broth and incubated at 37 C for 24 h. The patho-
gens were swabbed (inoculum size was adjusted so as to deliver a final inoculums of
6
approximately 10 CFU/mL) on the surface of Mueller–Hilton agar media and petri
dishes containing 20 mL of Mueller–Hinton agar with 100 lL inoculums of bacterial
strain and media were allowed to solidify. Wells were cut into solidified agar media
with the help of sterilized cup-borer; 100 lL of each sample solution was poured in
the respective wells and the plates including control were incubated overnight at
ꢂ
3
7 C for bacteria. The experiment was performed in triplicate under strict aseptic con-
ditions and the antibacterial activity of each compound was expressed in terms of the
mean diameter of zone of inhibition (cm) produced by the respective compound.
Similarly, antifungal sensitivity is tested by the agar well diffusion method using PD
agar media [38]. Two species of pathogenic fungi, Aspergillus flavus and Candida albi-
cans, are used to screen the antifungal activity of the pyrazolyl compounds.
Pathogenic fungal strain is inoculated in sterile potato dextrose broth and incubated
ꢂ
at 25 C for 48–72 h. Petri dishes containing 25 mL of potato dextrose agar with 100 lL
inoculums of fungal strain and media are allowed to solidify. The remaining work-up
process is similar to that of antibacterial sensitivity test. The stock solution (5000 mg/
mL) was made by dissolving the antibiotic in sterile distilled water. From this stock
solution, 1000 mg/mL was prepared for determination of the sensitivity of fungi.

6
A. JANA ET AL.
1
2
Scheme 1. Schematic presentation of preparation of 1–5 with L and L .
2.7. Determination of MIC value
Minimum inhibitory concentration (MIC) was determined using inhibitory concentra-
tion in diffusion (ICD) method [23]. The MIC values, which represent the lowest con-
centration of the compound that completely inhibits the growth of microorganisms,
were determined by a micro-well dilution method [24]. The inoculums of each bacter-
6
ium were prepared and the suspensions were adjusted to 10 CFU/mL. For making
these dilutions, metal complexes were dissolved at a required concentrations and
diluted with methanol to obtain concentration 1000 lg/mL, 800 lg/mL, 600 lg/mL,
4
00 lg/mL, 200 lg/mL and 100 lg/mL in the respective wells and the plates were incu-
ꢂ
bated for 24 h at 37 C. The experiment was performed in triplicate under strict asep-
tic conditions.
3. Results and discussion
3.1. Chemistry
Primarily dioxygen activation and oxygenation occur at the active site(s) of an enzyme
in the process of phenoxazinone and quinone synthesis. This fundamental idea should
be considered in designing mimics of metallo-enzymes. The present work includes
1
2
two pyrazole-based ligands, L and L , with varying substitutions in pyrazolyl-

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 1. Surface plots of 1.
methylamine with napthalene and pyridine group, respectively. Anchoring with
napthyl/pyridyl group with pyrazole-core unit eventually increases steric crowding in
1
the resultant molecules (Scheme 1). To relieve the steric repulsion, L dissociates
1
before the formation of 3 and 4 as explained earlier by us [27]. However, L forms sta-
ble mononuclear complexes of manganese(II) (1) and cobalt(II) (2) with undissociated
ligand form (Supplementary Figures S3 and S4) [39]. The reasons are by no means cer-
tain but several factors are involved. The size of the ligand is probably a major one.
1
Fragmented L less by one methylpyrazole unit prefers to stabilize the bridged
1
copper(II) complex rather than a mononuclear Cu(II)–L complex. There is a delicate
balance between the formation of chelate with undissociated ligand and the forma-
tion of polynuclear chain with dissociated fragment [29, 40]. The inherent electronic as
well as steric factors of the ligands and their metal complexes bearing pyrazolyl-scaf-
fold might be potential showing biological functions. The chemistry and details of
characterization of complexes, except 1, are reported earlier by us [28].
3
.2. Structural characterization of 1
FTIR characterization is done comparing the spectrum of 1 and that of L
Supplementary Figure S1). The peaks in the spectrum of complexes are less in num-
1
(
1
ber and quite sharper than the spectrum of L , clearly providing strong binding of lig-
and with Mn(II) ion. The presence of a strong band at 1548 cm
ꢀ
1
1
for L due to
ꢀ
1
m(C ¼ N) is shifted to lower frequency at 1465 cm in 1, indicating the involvement of
tertiary N atom in coordination with manganese atom. The positive shift of m(N-N) at
pz
ꢀ
1
1
ꢀ1
1240 cm for L to 64 cm on complexation with Mn(II) indicates the involvement of
pyrazolyl tertiary N atom in bonding.
Analysis of single-point DFT of 1 reveals the contribution of chloride ions in HOMO
and HOMO–1 function where the pyrazole and napthalene moieties contribute more
in the formation of LUMO and LUMO þ 1 function (Figure 1). These theoretical data
suggest that the complex is labile with respect to chloride substitution.
Thermal decomposition of 1 has been performed to study the decomposition pat-
tern of the complex (Figure 2 and Scheme 2). The decomposition of 1 occurs in four
ꢂ
ꢂ
steps. The first step of decomposition of 1 starts at 80 C and continues up to 150 C,
giving a sharp loss of 33.46% of total mass. This mass loss can be assigned to the loss
of 1-methyl napthylamine group (ca. 31.16%). The second step of decomposition
accounts for 5.6% of the total mass which referred to the loss of two CH2 units
attached to the N atom of pyrazole. About 14.3% weight loss occurred in the third

8
A. JANA ET AL.
Figure 2. TG of 1 in nitrogen atmosphere with sample of amount 1 mg at a heating rate
ꢂ
1
0 C/min.
Scheme 2. Plausible mechanism of decomposition of 1.
ꢂ
step of decomposition of 1 at 180–240 C, which can be attributed to the loss of coor-
dinated chlorine as Cl2(g). At the fourth step of decomposition, weight loss of 38%
occurred due to the loss of two 3,5-dimethylpyrazolyl units. The last step of decom-
ꢂ
position (estimated 8%) comprises the loss of remaining organics from 210 to 800 C,
giving residual metallic manganese (i.e. 11%).
3.3. X-ray crystallography of 1
1
The molecular structure of 1 consists of one tridentate N,N,N-donor ligand L with two
chlorido ligands, resulting in a five-coordinate manganese(II) center with the MnN Cl2
3
chromophore. The geometry of the five-coordinate metal center can be ascertained by
the Addison parameter (s) [41]. The s value is 0.38 for 1 (s ¼ (a ꢀ b)/60, where a and
b are the two largest ligand-metal-ligand angles of the coordination sphere), suggest-
ing a distorted square pyramid (s ¼ 0 for a perfect square pyramid and s ¼ 1 for a

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. ORTEP diagram (30% ellipsoidal probability) with atom numbering scheme of 1.
Table 1. Crystal data and refinement parameters of the structure of 1.
Crystal data
Formula
23 2 5
C H27Cl MnN
Formula weight
CCDC No.
499.34
1865481
Orthorhombic
P212121 (No. 19)
Crystal system
Space group
a, b, c [Å]
8.5764(3), 10.3057(4), 26.5632(10)
3
V [Å ]
2347.81(15)
Z
4
1.413
3
D(calc) [g/cm ]
m(MoKa) [/mm ]
F(000)
0.810
1036
Crystal size [mm]
Data collection
Temperature (K)
Radiation [Å] MoKa
0.10 ꢃ 0.20 ꢃ 0.30
150
0.71073
1.5, 29.2
h
min-max [Deg]
Data set
ꢀ11: 10; ꢀ14: 9; ꢀ36: 36
22803, 6212, 0.039
5293
Tot., Uniq. data, R(int)
Observed data [I > 2.0 r(I)]
Refinement
Nref, Npar
R, wR2, S
Max. and av. shift/error
6212, 284
0.0341, 0.0696, 1.02
0.00, 0.00
Flack x
0.025(9)
ꢀ0.26, 0.25
3
Min. and max. resd. dens. [e/Å ]
1
2
0
2
C
w ¼ ½
2
where P ¼ ðF þ 2F Þ=3.
2
2
0
r ðF Þþð0:0267PÞ þ0:2598Pꢄ
1
perfect trigonal bipyramid). The ORTEP diagram of [MnL Cl ] (1) is given in Figure 3.
2
Complex 1 crystallized in the orthorhombic system with space group P2 2 2 with
1
1 1
manganese in þ2 oxidation state. The Mn-N bonds are shorter than Mn-Cl bonds,
Mn–N2 ¼ 2.171 Å, Mn–N4 ¼ 2.198 Å, Mn–Cl1 ¼ 2.3443 Å, and Mn–Cl2 ¼ 2.4076 Å,
except for the tertiary-N atom where Mn–N1 ¼ 2.572 Å. The long bond Mn-N1 is due

1
0
A. JANA ET AL.
ꢂ
Table 2. Selected bond distances (Å) and angles ( ) of 1.
Bond distances (Å)
Mn-Cl1
Mn-Cl2
Mn-N1
Mn-N2
Mn-N4
N1-C1
Bond angles ( )
Cl1-Mn-Cl2
Cl1-Mn-N1
Cl1-Mn-N2
Cl1-Mn-N4
Cl2-Mn-N1
Cl2-Mn-N2
Cl2-Mn-N4
N1-Mn-N2
N1-Mn-N4
2.3445(9)
2.4069(8)
2.571(2)
2.170(2)
2.197(3)
1.454(3)
N1-C7
N1-C13
N2-N3
N2-C4
N4-N5
N4-C8
1.471(3)
1.494(4)
1.375(3)
1.337(4)
1.375(3)
1.339(4)
ꢂ
108.64(3)
161.24(5)
108.55(6)
103.05(6)
89.94(5)
96.95(6)
97.78(6)
70.53(8)
70.88(8)
N2-Mn-N4
Mn-N1-C1
Mn-N1-C7
Mn-N1-C13
Mn-N2-N3
Mn-N2-C4
Mn-N4-N5
Mn-N4-C8
138.47(9)
98.89(15)
95.03(13)
126.70(16)
117.06(17)
137.74(19)
113.83(17)
141.30(18)
Figure 4. Cyclic voltammogram of 1 in methanol containing tetrabutylammonium perchlorate as
ꢀ
1
the supporting electrolyte at a scan rate of 100 mV s
.
to relieving some of the steric stains arising out of the bulky napthyl group and two
methyl groups in the 3- and 5-position of pyrazole ring. Similar results in bond param-
eters were also observed in literature [42–46]. The weak interaction between Mn and
N1 gives lability in the structure of coordination, which may impart the property to
bind with molecular oxygen. Selected bond distances and angles of complex are given
in Table 2. The remaining bond lengths and angles of 1 are listed in Supplementary
Table S1. The ORTEP diagrams of 2–5 are given in Supplementary Figures S2–S5 to
know the appropriate structure of the molecules.
3.4. Electrochemical study
Electrochemical study of 1 is performed using methanol as solution and tetrabutylam-
monium perchlorate as supporting electrolyte at scan rate 100 mV/sec in the potential

JOURNAL OF COORDINATION CHEMISTRY
11
range þ1.0 V to ꢀ1.0 V. As shown in Figure 4, 1 shows only the reductive response at
ꢀ
0.89 V in cathodic scan while two oxidative waves appear at þ0.95 V and þ0.087 V.
The reductive wave at ꢀ0.89 V corresponds to oxidative wave þ0.087 V; this oxidation
and reduction couple corresponds to a quasi-reversible redox process of Mn(III)/Mn(II)
couple [43, 44]. The average formal potential E1/2 ¼ ꢀ0.48 V. The other oxidation
wave at þ0.95 V has no corresponding counterpart in the cathodic wave, practically
I ¼ 0 for the potential range to þ0.75 V, indicating the absence of electroactive spe-
P
ꢀ
4
cies in forward scan. The (I ) value ꢀ2 3 10 A at þ0.95 V may be due to the for-
P a
mation of manganese(II) oxide. The sequence of redox process can be presented as:
III
II
Mn ꢀ Mn ꢀ Mn
The details of peak potential values and E1/2 values for the complex are listed in
Table 3.
3.5. Phenoxazinone synthase (PHS) and catechol oxidase (CO) activity
Phenoxazinone synthase is a multicopper oxidase enzyme which catalyzes the biosyn-
thesis of the actinomycin D by streptomycin antibiotics. The catalysis reaction is con-
cerned with the oxidative condensation of two molecules of 3-hydroxo-4-methyl-
anthranilic acid pentapeptide lactone to form phenoxazinone chromophore. In bio-
mimetic chemistry, enzymes PHS and CO have been widely attempted for modeling
the active sites not only using copper(II) complexes [47] but also with several manga-
nese [43, 44, 46] and cobalt [42, 45] complexes with redox behavior. Manganese might
be the best alternative metal for performing PHS and CO activity other than nature’s
II
choice copper [23]. Comparison showed that Mn complexes of N,O-donors showed
II
II
better PHS and CO activity than Co and Cu analogues [23]. In the present report, we
model manganese, copper, and cobalt complexes to compare their kcat values. Figure
ꢀ
2
5
shows the UV-vis spectra for the oxidation OAPH (concentration 1 ꢃ 10 M) cata-
ꢀ
5
lyzed by 1, 3, and 4 (1 ꢃ 10
M) and oxidation of 3,5-ditertiary-butylcatechol
ꢀ
2
(
2
1.0 ꢃ 10 M) catalyzed by 3 and 4 up to 2 h of reaction in oxygenated methanol at
ꢂ
5 C. Supplementary Figure S6 shows the UV-vis spectra for the oxidation of OAPH
by 2 and 5 at similar conditions.
To know the extent of the catalytic efficiency of the complexes, kinetic studies are
ꢀ
5
performed. For this purpose, a 1 ꢃ 10 M solution of 1–5 is allowed to react with
about 10-fold concentrated OAPH solution to meet a pseudo-first-order rate law. All
ꢂ
the experiments are performed at 25 C under aerobic conditions. The initial rate of
reaction of 1–5 shows rate saturation kinetics as shown in Supplementary Figure S7.
This observation indicates the formation of substrate-catalyst intermediate and the
rate-determining step is the decomposition step of the intermediate.
Michaelis–Menten enzymatic kinetics is used to understand the kinetics of PHS [48].
The observed and simulated initial rates versus substrate concentrations of the non-lin-
ear plot and the Lineweaver–Burk plot for 1–5 are shown in Supplementary Figure S8.
The value of Michaelis binding constant (K ) and Vmax, and the turnover number (Kcat
)
m
of the complexes, are listed in Table 4. A linear relationship for the initial rates is
obtained varying the complex concentration which gives first-order reaction kinetics.

1
2
A. JANA ET AL.
Table 3. Cyclic voltammetry data for 1–5.
Complex
E
pa1
E
pc1
(E1/2
)
1
E
pa2
E
pc2
(E1/2)
2
1
2
3
4
5
ꢀ0.89
1.36
0.38
0.38
0.79
ꢀ0.08
1.71
0.55
0.49
0.91
–0.48
1.536
0.46
0.43
0.90
0.76
–
0.75
0.77
–
0.95
–
0.93
0.93
–
0.85
–
0.84
0.85
–
ꢀ
2
Figure 5. The time resolved spectral profile showing oxidation of o-aminophenol (1.0 ꢃ 10 M)
ꢀ2
catalyzed by 1, 3 and 4 and 3,5-ditertiary-butylcatechol (1.0 ꢃ 10 M) catalyzed by 3 and 4 in
dioxygen-saturated methanol. The spectra were recorded at 5 min intervals under aerobic condi-
tions at room temperature.
As shown in Table 4, the turnover number (Kcat) for the oxidation of OAPH follows the
order 3 > 4 > 5 > 1 > 2. The higher reactivity of 3 and 4 is due to the dinuclearity
in the molecule, which confirms stable binding with molecular O in the labile copper
2
centers of the complex. Relatively lower Kcat values of mononuclear complexes 1, 2,
and 5 than dinuclear 3 and 4 are probably due to steric crowding arising from the
napthyl/pyridine group around the metal center of 1, 2, and 5 (ORTEP of 2 and 5 in
Supplementary Figures S4 and S5). The steric effect resists the oxygen binding to the
metal center. However, the same steric effect somehow is less in the dinuclear com-
plex (ORTEP of 3 and 4 in Supplementary Figures S2 and S3) as the metal centers are
sufficiently separated by bridged bonds. The greater the steric repulsion in the system,
the lesser is the formation of substrate binding property.
Complexes 3 and 4 show higher catecholase activity than recently reported com-
pounds bearing similar scaffolds [24, 25]. A tentative catalytic cycle can be proposed
based on the kinetics. The OAPH forms an adduct with the metal complex in the first
step. The adduct yields aminophenol radical in the reaction with dioxygen, which is
rate-determining step for the process. The OAP radical generates ortho-benzoquinone

JOURNAL OF COORDINATION CHEMISTRY
13
Table 4. Kinetic parameters of phenoxazinone synthase activity of 1–5 and catecholase activity of
and 4.
3
ꢀ
1
ꢀ1
Substrate
OAPH
Catalyst
V
max (Ms
)
K
M
(M)
k
cat (h
)
ꢀ
ꢀ
8
ꢀ3
ꢀ3
1
2
3
4
5
3
4
4.211 ꢃ 10
1.68 ꢃ 10
1.56 ꢃ 10
15.15
5.45
53.28
37.80
20.36
28.40
40.24
8
1.51 ꢃ 10
ꢀ
ꢀ
7
7
ꢀ3
ꢀ3
(1.48 ± 0.01) ꢃ 10
(1.05 ± 0.06) ꢃ 10
(1.55 ± 0.6) ꢃ 10
(5.58 ± 0.6) ꢃ 10
ꢀ
ꢀ
8
8
7
ꢀ3
ꢀ3
ꢀ3
5.65 ꢃ 10
7.89 ꢃ 10
1.01 ꢃ 10
3,5-DTBC
6.35 ꢃ 10
1.12 ꢃ 10ꢀ
1.33 ꢃ 10
monoamine [48–51]. Representative CO activities of 3 and 4 are also performed using
substrate 3,5-ditert-butyl catechol (3,5-DTBC). 3,5-DTBC has two bulky methyl groups
in the ring with low reduction value for quinone-catechol transformation. Upon treat-
ment of methanolic solution of 3 and 4 into 100 equivalents of 3,5-DTBC in aerobic
condition, repetitive spectra were recorded (Figure 5). The colorless 3,5-DTBC solution
turns into deep brown, indicating the conversion of 3,5-DTBC to correspond-
ing quinone.
The smooth increases of quinone band around 390 nm which shifts ultimately to
ꢀ
5
4
01 nm. The same reaction is carried out at a substrate catalyst concentration 1 ꢃ 10
M. The time-dependent change in absorption at a wavelength of 401 nm was meas-
ured for 25-min interval to find out the reaction rate. The difference of absorption
(DA) at 401 nm is plotted against time to get the rate/velocity for that particular cata-
lyst to substrate concentration ratio. The reaction kinetics were studied by observing
the time-dependent change in absorption at a wavelength of 401 nm for catalysis in
methanol. The DA versus time plot gives the rate of the reaction. First-order reaction
ꢀ
3
ꢀ1
ꢀ3
ꢀ1
kinetics with rate 6.35 ꢃ 10 min and 1.33 ꢃ 10 min in methanol are observed
for 3 and 4, respectively (Supplementary Figure S7). The rate of each concentration of
the substrate was determined by the initial rate method. The rate versus concentration
of the substrate plots are analyzed on the basis of Michaelis–Menten approach of
enzymatic kinetics to obtain the Lineweaver–Burke (double reciprocal) plot as well as
the values of the various kinetic parameters (Vmax, K , and Kcat). The observed rate ver-
m
sus substrate concentration plot as well as Lineweaver–Burke plot in methanol are
given in Supplementary Figures S7 and S8, respectively. The kinetic parameters are
listed in Table 4. From the results of kinetic study, a mechanism is proposed for CO.
The process may follow two step mechanistic pathways. The first step is the rate-
determining step where probably 1:1 adduct of catalyst-substrate is formed [52–57].
3.6. Antimicrobial activities
The ability to penetrate the cell wall of a foreign compound determines the extent of
antimicrobial activity. The antibacterial/antifungal agents target the structures and
functions or both which are relevant to the inhibitory activity of the organisms. The
structural types with the combination of pyridyl/napthalene group in the pyrazole
moiety might have high effect on biological potency by regulating the lipid-water par-
tition coefficient and binding affinity to target enzymes. The results in the present in
1
2
vitro antimicrobial activities and MIC values of L , L and 1–5 are presented in Table 5

1
4
A. JANA ET AL.

JOURNAL OF COORDINATION CHEMISTRY
15
Figure 6. Graphical presentation of sensitivity of the compounds against different bacteria
and fungi.
Table 6. The lipophilicity values of ligands and their corresponding metal complexes in loga-
rithm form.
Water
Concentration (M)
1-Octanol
Concentration (M)
Sample ID
Absorbance
Absorbance
P
logP
–
–
–
–
–
4
–3
–3
–3
–3
–3
–3
–3
1
2
3
4
5
4.509 ꢃ 10
1.751 ꢃ 10
1.735 ꢃ 10
1.687 ꢃ 10
4.983 ꢃ 10
2.073 ꢃ 10
1.84 ꢃ 10
0.19952
0.3335
1.2423
1.238
2.6140
0.8484
0.2215
2.296 ꢃ 10
7.59 ꢃ 10
1.0159
1.5159
2.5399
2.4996
3.1179
1.7539
0.49833
5.092
4.334
2.0443
2.0195
1.1929
2.067
2.250
0.7068
0.6369
0.3105
0.3052
0.0766
0.315
3
3
3
3
3.547 ꢃ 10
3.407 ꢃ 10
5.9445 ꢃ 10
4.285 ꢃ 10
4.141 ꢃ 10
1
–3
–3
L
2
L
0.352
and Supplementary Table S2, respectively. The sensitivity of these compounds against
different bacteria and fungi is graphically represented in Figure 6. The sensitivity and
MIC values of some standard antibiotics are given in Supplementary Tables S3–S6 to
compare the activity that is shown by the compounds under investigation. The camera
views of the sensitivity of tested bacteria and fungi against the present compounds
1
are shown in Supplementary Figures S9 and S10. The present study reveals that L
2
and L show better antibacterial activity than their metal complexes. This may be
1
2
explained in terms of high structural strain in L and L (Figure 1) arising from the
presence of two and one bulky group of N-(methyl-3,5-dimethyl-pyrazole), respect-
ively. The presence of three bulky groups in the aliphatic tertiary N-atom registers
high strain to the ligand structures which can disrupt the cell division/DNA replication
1
of the bacteria (prokaryotes). The general order of antibacterial activity is found as L
2
>
L > 1 > 3 > 2 > 4 > 5. Among the complexes, 1 shows excellent antibacterial
activity against E. coli, S. aureus, S. faecalis and Bacillus sp with MIC values 300, 200,
00 and 300 mg/mL, respectively, whereas 3 also has comparable antibacterial activities
against P. aeruginosa, S. faecalis and P. vulgaris with MIC values of 400, 600 and
4
1
2
3
00 mg/mL, respectively. Therefore, L , L , 1 and 3 can be regarded as significant

1
6
A. JANA ET AL.
antibacterial agents for environmental cleanup and also can be used as drug. The pre-
sent order of antibacterial activity of the metal complexes may be attributed to the
inhibition of the synthesis of the peptidoglycan layer of bacterial cell walls.
All the ligands and the complexes show good antifungal activities against eukar-
yotes A. flavus and C. albicans. The antifungal screening data typically show the
reverse order of antibacterial activity, i.e. the metal complexes have a greater inhibi-
tory tendency than the free ligands. Among the complexes, the antifungal activity
5
5
0
9
order is found as manganese(II)-complex, d (t
e ) (1) > copper(II)-complex, d
2
g
g
1
6
3
7
6
(
t2g e ) (3 and 4) > cobalt(II)-complex, d (t
e ) (2 and 5). In this context, the
g
2g
g
increased activity of the metal complexes can be explained in terms of lability and lip-
5
9
ophilicity. The d to d systems are generally labile with e filling of electron(s) with
g
respect to ligand substitution reaction leading to formation of metal-DNA adduct.
Metal ions having unpaired electron (one unpaired electron in each case) are highly
polar in nature. The chelation phenomenon minimizes the polarity of the metal ion
due to potential charge sharing between metal and donors, and subsequently
increases the lipophilic character of the metal complex. The logP values are presented
in Table 6. The higher lipophilicity of the compounds accelerates the cell permeation,
leading to cell damage. It can be concluded that the antifungal activity of the complex
increases with the increased lipophilicity.
4. Conclusion
Napthyl-anchored pyrazole ligand with multiple nitrogen donor atoms produce mono-
meric complexes of manganese(II) (1) with distorted square pyramidal structure. The
monomeric complexes of napthyl/pyridyl-anchored pyrazole ligand are moderately
II
reactive towards the catalytic oxidation of o-amino-phenol whereas dimeric Cu com-
plexes are very effective models of phenoxazinone synthase and catecholase activities.
The catalytic efficiency mainly arises from the structural aspects of the crowded pyra-
zole derived compounds. The highly-crowded complexes (1, 2 and 5) show less cata-
lytic promiscuity than less-crowded bridged copper(II) complexes (3 and 4). Most of
the reported compounds have the property to destroy the cell of pathogen bacteria
and fungi. Ligands are good antibacterial agents where metal complexes are capable
in showing better antifungal activity than the ligands. There is a scope to explore in
the structure-activity relationship with pyrazole-based lead compounds for biological
applications.
Disclosure statement
There is no conflict of interest to declare.
Funding
We gratefully acknowledge the grant from Council for Scientific and Industrial Research (CSIR),
Government of India through the project [No. 1(2858)/16/EMR ꢀ II]. Panskura Banamali College
acknowledges the grants received from Department of Science and Technology (DST), Govt. of
India through FIST program (Sanction no. SR/FST/College ꢀ 295 dated 18/11/2015).

JOURNAL OF COORDINATION CHEMISTRY
17
ORCID
Paula Brand ~a o
Pulakesh Bera
http://orcid.org/0000-0002-4746-6073
http://orcid.org/0000-0001-8566-0742
References
[
[
[
1] N.M. Abunada, H.M. Hassaneen, N.G. Kandile, O.A. Miqdad. Molecules, 13, 1501 (2008).
2] A.B. Adnan, T.A. Aziem. Bioorg. Med. Chem., 12, 1935 (2004).
3] E. Aiello, S. Aiello, F. Mingoia, A. Bacchi, G. Pelizzi, C. Musiu, M.G. Setzu, A. Pani, P.L. Colla,
M.E. Marongiu. Bioorg. Med. Chem., 8, 2719 (2000).
[
[
[
[
4] E. Akbas, I. Berber. Eur. J. Med. Chem., 40, 401 (2005).
5] J. Parez, L. Liera. Eur. J. Inorg. Chem., 33, 4913 (2009).
6] J.S. Larsen, M.A. Zahran, E.B. Pedersen, C. Nielsen. Monatsh. Chem., 130, 1167 (1999).
7] I. Bouabdallah, L.A. M’Barek, A. Zyad, A. Ramdani, I. Zidane, A. Melhaoui. Nat. Prod. Res.,
2
0, 1024 (2006).
8] H.J. Park, K. Lee, S. Park, B. Ahn, J.C. Lee, H.Y. Cho, K.I. Lee. Bioorg. Med. Chem. Lett., 15,
307 (2005).
9] A.H. Abadi, A.A.H. Eissa, G.S. Hassan. Chem. Pharm. Bull., 51, 838 (2003).
[
3
[
[
[
10] M.K. Sharma, P.R. Murumkar, A.M. Kanhed, R. Giridha, M.R. Yadav. Eur. J. Med. Chem., 79,
98 (2014).
2
11] M. Ezawa, D.S. Garvey, D.R. Janero, S.P. Khanapure, L.G. Letts, A. Martino, R.R. Ranatunge,
D.J. Schwalb, D.V. Young. Lett. Drug Des. Discov., 2, 40 (2005).
12] A. Mishra, A.K. Tewari. Bioorg. Med. Chem., 9, 715 (2001).
13] I.V. Mashevskaya, S.V. Kol’tsova, E.V. Voronina, T.F. Odegova, A.N. Maslivets. Pharm. Chem.
J., 35, 18 (2001).
[
[
[14] V. Michon, C.H. Du Penhoat, F. Tombret, J.M. Gillardin, F. Lepage, L. Berthon. Eur. J. Med.
Chem., 30, 147 (1995).
€
[
[
15] I. Yildirim, N. Ozdemir, Y. Ak c¸ amur, M. Din c¸ er, O. Anda c¸ . Acta Cryst. E, 61, 256 (2005).
16] D.M. Bailey, P.E. Hansen, A.G. Hlavac, E.R. Baizman, J. Pearl, A.F. Defelice, M.E. Feigenson.
J. Med. Chem., 28, 256 (1985).
[
[
17] C.K. Chu, J. Cutler. J. Heterocycl. Chem., 23, 289 (1986).
18] E.I. Solomon, D.E. Heppner, E.M. Johnston, J.W. Ginsbach, J. Cirera, M. Qayyum, M.T.
Kieber-Emmons, C.H. Kjaergaard, R.G. Hadt, L. Tian. Chem. Rev., 114, 3659 (2014).
19] J. Kaizer, G. Barath, R. Csonka, G. Speier, L. Korecz, A. Rockenbauer, L. Parkanyi. J. Inorg.
Biochem., 102, 773 (2008).
[
[
20] G. Blay, I. Fern ꢀa ndez, J.R. Pedro, R. Ruiz-Garc ꢀı a, T. Temporal-S ꢀa nchez, E. Pardo, F. Lloret,
M.C. Mu n~ oz. J. Mol. Catal. A: Chem., 250, 20 (2006).
[
[
[
[
[
21] S.D. Copley. Curr. Opin. Chem. Biol., 7, 265 (2003).
22] I.A. Koval, P. Gamez, C. Belle, K. Selmeczi, J. Reedijk. Chem. Soc. Rev., 35, 814 (2006).
23] S.K. Dey, A. Mukherjee. Coord. Chem. Rev., 310, 80 (2016).
24] I. Bouabdallah, R. Touzani, I. Zidane, A. Ramdani. Catal. Commun., 8, 707 (2007).
25] N. Boussalah, R. Touzani, I. Bouabdallah, S. El Kadiri, S. Ghalem. J. Mol. Catal. A: Chem.,
3
06, 113 (2009).
[
[
[
26] M.R. Malachowski, M.G. Davidson. Inorg. Chim. Acta, 162, 199 (1989).
27] I. Banerjee, J. Marek, R. Herchel, M. Ali. Polyhedron, 29, 1201 (2010).
28] A. Jana, P. Brand ~a o, G. Mondal, P. Bera, A. Santra, A.D. Jana, R.B. Mokhamatam, S.K.
Manna, N. Bhattacharyya, P. Bera. Inorg. Chim. Acta, 482, 621 (2018).
29] A. Santra, G. Mondal, M. Acharjya, P. Bera, A. Panja, T.K. Mandal, P. Mitra, P. Bera.
Polyhedron, 113, 5 (2016).
[
[30] A.D. Becke. J. Chem. Phys., 98, 5648 (1993).
[31] R.G. Parr, W. Yang. Density Functional Theory of Atoms and Molecules, Oxford University
Press, Oxford (1989).

1
8
A. JANA ET AL.
[
[
32] C. Lee, W. Yang, R.G. Parr. Phys. Rev. B Condens. Matter, 37, 785 (1988).
33] Bruker. SAINT (Version 6.28a) and SADABS (Version 2.03): Data Reduction and Absorption
Correction Program, Bruker AXS Inc., Madison, WI (2001).
[
[
[
[
[
34] Bruker. SMART (Version 5.625): Data Collection Program, Bruker AXS Inc., Madison, WI
(2001).
35] G.M. Sheldrick. SHELXL-97, Crystal Structure Refinement Program, University of G o€ ttingen,
Germany (1997).
36] B. Kupcewicz, M. Ciolkowski, B.T. Karwowski, M. Rozalski, U. Krajewska, I.P. Lorenz, P.
Mayer, E. Budzisz. J. Mol. Struct., 1052, 32 (2013).
37] D.A. van den Berghe, A.J. Vlietinck. In Methods in Plant Biochemistry, P.M. Dey, J.B.
Harbone (Eds.), p. 47, Academic Press, London (1991).
38] A. Nostro, M.P. German oꢁ , V. D’Angelo, A. Marino, M.A. Cannatelli. Lett. Appl. Microbiol., 30,
379 (2000).
[
[
[
39] A. Jana, M. Dolai, B.K. Shaw, S.K. Saha, M. Ali. Transition Met. Chem., 3, 347 (2016).
40] A. Solanki, M. Monfort, S.B. Kumar. J. Mol. Struct., 1050, 197 (2013).
41] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor. J. Chem. Soc., Dalton Trans.,
1349 (1984).
[
[
[
[
[
[
[
[
[
[
[
42] A. Panja. Dalton Trans., 43, 7760 (2014).
43] A. Panja. RSC Adv., 4, 37085 (2014).
44] A. Panja. Polyhedron, 79, 258 (2014).
45] A. Panja, M. Shyamal, A. Saha, T.K. Mandal. Dalton Trans., 43, 5443 (2014).
46] A. Panja, N.C. Jana, S. Adak, K. Pramanik. Inorg. Chim. Acta, 459, 113 (2017).
47] M.R. Maurya, S. Sikarwar, T. Joseph, S.B. Halligudi. J. Mol. Catal. A: Chem., 236, 132 (2005).
48] A.J. Kenneth, S.G. Roger. Biochemistry, 50, 8264 (2011).
49] T. Horvath, J. Kaizer, G. Speier. J. Mol. Catal. A: Chem., 215, 9 (2004).
50] L.I. Simandi, T. Barna, S. Nemeth. J. Chem. Soc., Dalton Trans., 473 (1996).
51] T.M. Simandi, Z. May, I.C. Szigyarto, L.I. Simandi. Dalton Trans., 365 (2005).
52] A. Mart ꢀı nez, I. Membrillo, V.M. Ugalde-Sald ꢀı var, L. Gasque. J. Phys. Chem. B, 116, 8038
(2012).
[
[
53] A. Banerjee, R. Singh, E. Colacio, K.K. Rajak. Eur. J. Inorg. Chem., 2009, 277 (2009).
54] L. Gasque, V.M. Ugalde-Sald ꢀı var, I. Membrillo, J. Olgu ꢀı n, E. Mijangos, S. Bern ꢁe s, I. Gonz ꢀa lez.
J. Inorg. Biochem., 102, 1227 (2008).
[
[
[
55] M. Merkel, N. M o€ ller, M. Piacenza, S. Grimme, A. Rompel, B. Krebs. Chemistry, 11, 1201
(2005).
56] I.A. Koval, C. Belle, K. Selmeczi, C. Philouze, E. Saint-Aman, A.M. Schuitema, P. Gamez, J.-L.
Pierre, J. Reedijk. J. Biol. Inorg. Chem., 10, 739 (2005).
57] T. Mallat, A. Baiker. Chem. Rev., 104, 3037 (2004).