Synthesis of new oxido-vanadium complexes: Catalytic properties and cytotoxicity

Article abstract of DOI:10.3184/174751918X15168821806597

Reaction of 2,3-dihydroxy benzaldehyde with 2-({2-amino phenyl}diazenyl)phenol afforded the ligand 3-(2-(2-hydroxyphenyl)diazenyl)- 4-alkylphenyliminomethyl)benzene-1,2-diol. Reaction of H₂L with VOSO₄. 5H₂O gave the oxido-vanadium(IV) complexes [(L)VO], which exhibited a quasi-reversible oxidative cyclic voltammetric response in a V(IV)/V(V) oxidative process. The complexes act as catalysts in the oxidation of organic thioethers and bromination of phenol. Their cytotoxic properties were examined for three cancer cell lines.

Full text of DOI:10.3184/174751918X15168821806597

JOURNAL OF CHEMICAL RESEARCH 2018
VOL. 42 JANUARY, 57–62
RESEARCH PAPER 57
Synthesis of new oxido-vanadium complexes: catalytic properties and
cytotoxicity
a,b
a
c
a
Uttam Das , Poulami Pattanayak , Manas Kumar Santra and Surajit Chattopadhyay *
a
Department of Chemistry, University of Kalyani, Kalyani 741235, India
Department of Chemistry, Kalyani Government Engineering College, Kalyani 741235, India
Cancer Biology and Epigenetics Lab, National Center for Cell Science, Ganeshkhind, Pune 411007, India
b
c
Reaction of 2,3-dihydroxy benzaldehyde with 2-({2-amino phenyl}diazenyl)phenol afforded the ligand 3-(2-(2-hydroxyphenyl)diazenyl)-
4
-alkylphenyliminomethyl)benzene-1,2-diol. Reaction of H L with VOSO . 5H O gave the oxido-vanadium(IV) complexes [(L)VO], which
2 4 2
exhibited a quasi-reversible oxidative cyclic voltammetric response in a V(IV)/V(V) oxidative process. The complexes act as catalysts in
the oxidation of organic thioethers and bromination of phenol. Their cytotoxic properties were examined for three cancer cell lines.
Keywords: oxido-vanadium, sulfide oxidation, phenol bromination, cytotoxic properties
Oxido-vanadium(IV) complexes have been recognised to
occur in the active sites of several vanadium-containing
Results and discussion
The ligands 1a, 1b and 1c were prepared by refluxing
1–6
enzymes. Vanadium haloperoxidase is one of the important
2
,3-dihydroxybenzaldehyde with 2-({2-aminophenyl}diazenyl)
7–14
vanadium-containing proteins.
Amavadine contains oxido-
phenol in diethyl ether (Scheme 1).
vanadium(IV) complexes having good electron transfer
Slow evaporation of solvent afforded the crystalline (E)-2-({2-
aminophenyl}diazenyl)-5-alkylphenols, which were collected
and used without further purification. In this paper, for ease of
15–17
properties and stability against hydrolysis.
In mushrooms,
amavadine acts as an electron transfer centre mediating thiol
oxidation in the absence of peroxide. A number of vanadium(IV)
and vanadium(V) complexes with N,O donor ligands have been
1
representation, 1a, 1b and 1c have been abbreviated as H L ,
2
2
3
H L and H L , respectively, where H represents the ionisable
2
2
18–32
examined for potential medicinal applications.
The anticancer
phenolic protons upon complexation. Reaction of VOSO with
4
activity of a few oxido-vanadium(IV) complexes encouraged us
to prepare new oxido-vanadium(IV) complexes incorporating
N,O donor ligands with reversible electron transfer properties.
This work stems from our interest in the vanadium chemistry
of azosalen ligands. It is worthwhile mentioning that the oxido-
vanadium(IV) complexes of such ligands exhibit interesting
electron transfer, catalytic and cytotoxic properties. Therefore,
we report here several new analogues of azosalen ligands as well
as the chemistry of the derived oxido-vanadium(IV) complexes.
The new ligands were designed in such a way that the free
uncoordinated phenolic group in the ligand backbone could act
either to form polynuclear V(IV) complexes or to enhance the
possibility of hydrogen bond formation with polar biomolecules
for suitable interactions.
H L in refluxing methanol afforded brown-coloured crystalline
2
complexes 2a, 2b and 2c, which for clarity will be abbreviated
1
2
3
as [(L )VO], [(L )VO] and [(L )VO], respectively (Scheme 2).
The UV-Vis spectra of the H L ligands exhibited a broad
2
absorption within the range 300–500 nm, with absorbance
33
maxima near 315 nm and a shoulder near 400 nm. The
corresponding [(L)VO] complexes exhibited three absorption
maxima, near 345, 375 and 485 nm.
The IR spectra of the H L ligands displayed two distinct
2
−1
absorptions near 1618 and 1466 cm for νCN of azomethine
(–CH=N–) and νN=N of diazo (–N=N–), respectively, which
−
1
−1
shifted to lower frequencies (1611 cm and 1432 cm ,
respectively) upon complexation.
3
4–38
Although there are
three phenolic OH groups in the ligands, only one absorption
−1
The activity of the new complexes in the oxidation of organic
thioethers and bromination of phenol was studied, and their
cytotoxic properties against a breast cancer cell (MCF7) line
were also examined.
near 3470 cm could be observed. In the case of the (L)
VO complexes, ν of the free phenolic group was near
OH
−
1
−1
1–3
3450 cm . The ν was near 978 cm for all of the [(L )
VO
3
3
VO] complexes.
R
R
HO
CHO
OH
OH HO
OH
N
Et O
2
N
+
N
N
N
Reflux
NH2
OH
HL
Compound
R
Abbreviation
1
1
a
H
H L
2
1
b
c
CH3
Cl
H
L2
3
2
1
H L
2
Scheme 1 Synthesis of H L ligands.
2
*
Correspondent. E-mail: scha8@rediffmail.com

58 JOURNAL OF CHEMICAL RESEARCH 2018
R
HO
R
HO
O
V
VOSO . 5H O
4
2
OH HO
O
N
O
N
Reflux in MeOH
N
N
N
N
Compound
R
Abbreviation
1
2
a
H
(L )VO
2
2
b
c
CH3
Cl
(
L )VO
(L)VO
3
2
(
L )VO
Scheme 2 Preparation of vanadium complexes.
1
Fig. 1 Ortep plot of [(L )VO] with atom numbering scheme. The hydrogen
atoms have been omitted for clarity.
Table 1 Selected bond lengths and angles for compound 2a
Bond lengths (Å)
V(1)–O(1)
V(1)–O(2)
V(1)–O(4)
V(1)–N(2)
V(1)–N(3)
O(2)–C(19)
Bond angles (°)
O1–V1–O2
O1–V1–O4
O1–V1–N3
O2–V1–N3
O4–V1–N3
1
Fig. 2 Cyclic voltammogram of [(L )VO] in CH CN–CH Cl mixed solvent.
3
2
2
1.9211(13)
1.9277(13)
1.5990(14)
2.0628(16)
2.0514(16)
1.330(2)
O(1)–C(1)
N(1)–N(2)
N(1)–C(6)
N(2)–C(7)
N(3)–C(12)
N(3)–C(13)
1.324(2)
1.281(2)
1.385(2)
1.423(2)
1.424(2)
1.307(2)
1
Table 2 Oxidation of sulfides catalysed by [(L )VO] in methanol–
dichloromethane (9:1)
H2O2
equiv.)
Yield (%)
Entry
Time (h)
2.5
(
Sulfoxide
Sulfone
S
5
45
60
35
55
Ph
Ph
Ph
CH3
88.11(6)
109.14(6)
144.53(6)
88.71(6)
105.22(7)
127.11(12)
114.76(16)
O1–V1–N2
O2–V1–O4
O2–V1–N2
O4–V1–N2
N2–V1–N3
85.45(6)
109.33(6)
148.10(6)
102.28(7)
78.89(6)
S
5
5
2.5
30
45
50
CH Ph
2
S
-
=
2.5
2.5
CH CH CH
2
2
V1–O2–C19
N2–C7–C12
122.63(11)
V1–O1–C1
S
5
40
Ph
Ph
1
The H NMR spectra of the ligands displayed three resonances
in the range of δ values 12.87–13.09, 11.54–11.64 and 9.21–9.38
The vanadium ion is displaced towards the oxido-ligand with a
deviation of 0.454 Å from the square plane (0.0241 Å) formed by
38
for the three free phenolic protons. The azomethine proton (–
38
CH=N–) signal appeared within the range 8.90–9.05. The spectra
for other aromatic protons appeared within the range 6.74–7.99, and
the number of protons and their patterns were consistent with the
1
2−
the four NNOO donors of the (L ) ligand. The bond lengths and
angles are presented in Table 1.
1
The [(L )VO] complex exhibited a quasi-reversible oxidative
1
proposed composition. UV-Vis, IR and H NMR data are collected
cyclic voltammetric response at E1/2 = 0.67 V vs SCE, which was
1
together in the experimental section. Figures showing the H NMR
33
assigned to a V(IV)/V(V) oxidative process. It is worthwhile
spectra are given in the electronic supplementary material (ESI).
mentioning that there was no reversible reductive response, unlike
1
The crystal structure of [(L )VO] was determined as
33
the similar complex reported earlier.
representative for unequivocal characterisation. The molecular
structure contains the V(IV) metal ion in a distorted square
pyramidal ligand field, where the square plane is constituted by
All of the complexes displayed magnetic moments of one
equivalent electron, which is consistent with the V(IV) oxidation
state.
1
2−
the NNOO donors of the (L ) ligand and the axial position is
occupied by the oxido-ligand.
1
A few organic sulfides have been oxidised by H O using [(L )
2
2
VO] as catalyst, and the results are given in Table 2. Formation of
mono-oxygenated sulfoxides and dioxygenated sufones occurred,
but selective oxidation to form only sulfoxides did not take place.
The V–O bond length (1.5999 Å) is shorter than the V–O single
33
bond (1.9277 Å), indicating a higher VO bond order as expected.

JOURNAL OF CHEMICAL RESEARCH 2018 59
1
Scheme 3 Oxidation of sulfides catalysed by [(L )VO].
1
Scheme 4 Bromination of phenolic compounds using [(L )VO] as catalyst.
1
Table 3 Bromination of phenolic compounds by bromide and peroxide
Table 4 IC50 determination of [(L )VO]
1
using [(L )VO] as catalyst
Sr no.
Cell line
MCF7
Compound
[(L )VO]
[(L )VO]
[(L )VO]
IC50 (µM)
64.67 ± 9.01
49.33 ± 6.1
39.03 ± 1.1
Yield (%)
1
H O
1
2
3
Entry
2
2
Time (h)
(
equiv.)
1
Mono-bromo Di-bromo Tri-bromo
MDA-MB-231
HCT-116
1
Phenol
5
5
20
20
13
30
27
40
41
–
p-Cresol
1
Fig. 3 Effect of [(L )VO] on growth of breast cancer cell line MCF7.
1
Fig. 4 Effect of [(L )VO] on growth of breast cancer cell line MDA-MB-231.
Products were isolated to calculate the yields and for
characterisation. The characterisations of the sulfoxides and
sulfones were carried out by matching the IR spectra.
Bromination of aromatic moieties in vivo by bromide
and peroxide in the presence of the vanadium-containing
bromoperoxidase enzyme is well documented in the
7,39–42
literature.
Thus, brominations of phenolic compounds in
vitro by bromide and peroxide in the presence of vanadium
complexes have been examined in the search for a potential
1
catalyst for such bromination. In this context, the complex [(L )
VO] has been used as catalyst for bromination of phenol and
p-cresol. Both phenolic compounds were brominated up to 70%
and 80% extent. The yields were calculated after isolating the
products (Scheme 4 and Table 3).
1
Fig. 5 Effect of [(L )VO] on growth of breast cancer cell line HCT116.
IC50 determination
1
(Figs. 2, 3 and 4, respectively). The IC50 values were found to
be 64.67 ± 9.01, 49.33 ± 6 and 39.03 ± 1.1 for the MCF7, MDA-
MB-231 and HCT116 cell lines, respectively.
The complex [(L )VO] was found to be effective in suppressing
the growth of human breast cancer cells (MCF7 and MDA-
MB-231 cell lines) and human colon cancer cells (HCT116)

6
0 JOURNAL OF CHEMICAL RESEARCH 2018
Experimental
and then methanol (5 mL) was added. The solution of VOSO was then
4
1
added to a solution of H L (0.165 g, 0.5 mmol) in methanol (20 mL)
The solvents used in the reactions were of reagent grade (E. Merck,
Kolkata, India) and were purified and dried using previously reported
2
and the mixture was refluxed for 15 min. The dark brown-coloured
solid product was separated by filtration and the solid mass was
dissolved in dichloromethane. Single crystals were obtained by slow
evaporation of the solvent. Isolated yield: 0.19 g (65%); Anal. calcd
for C H N O V (398.27): C, 57.30; H, 3.29; N, 10.55; found: C, 57.34;
43
procedures. VOSO .5H O was purchased from E. Merck (Kolkata,
4
2
India) and was used as received. The ligands 2-({2-aminoaryl}
diazenyl) phenol were prepared following previously reported
3
8
procedures. Microanalyses (C, H, N) were performed using a Perkin-
Elmer 2400 C, H, N, S/O series II elemental analyser. IR spectra
were recorded as KBr pellets on a Perkin-Elmer L120-00A FT-IR
19 13
3
4
−1
−1
H, 3.18; N, 10.68%; UV-Vis spectrum (CH Cl ): l (ε, M cm ) 486
8413), 375 (16329), 343 (20760), 240 (23299); IR (KBr) (ν /cm ):
2
2
max
sh
−1
(
max
1
438 (N=N), 1618 (C=N), 3450 (O−Η), 978 (V=O).
spectrometer. Electronic spectra were recorded on a Shimadzu UV-
2
3
2
1
[(L )VO] (2b) and [(L )VO] (2c): Complexes [(L )VO] (2b) and
1800 PC spectrophotometer. H NMR spectra were obtained on a
3
2
3
1
[(L )VO] (2c) were prepared using H L and H L in place of H L ,
Bruker 400 NMR spectrometer in CDCl3 using tetramethylsilane
TMS) as internal standard. Electrochemical measurements
2
2
2
respectively.
(
[
(2-Hydroxy-6-(2-(2-oxido-4-methyl-phenyl)diazenylphenylimino)
were made under dinitrogen using a CH instruments model 600D
potentiostat. A platinum disc working electrode, a platinum wire
auxiliary electrode and an aqueous saturated calomel reference
electrode (SCE) were used in a three-electrode configuration. All
electrochemical data were collected at 298 K and are uncorrected for
junction potentials. 2,3-Dihydroxybenzaldehyde, the human breast
cancer cells (MCF7 and MDA-MB-231), DMEM medium and HCT116
colon cancer cells, RPMI-1650 medium, penicillin (100 μg mL ) and
streptomycin sulfate (100 μg mL ) were all purchased from Sigma-
Aldrich (USA), as was 10% foetal bovine serum (FBS).
2
methylphenolate)oxidovanadium(IV)-N,N,O,O] [(L )VO] (2b): Isolated
yield: 0.18 g (61%); Anal. calcd for C20 V (412.32): C, 58.26; H,
3.67; N, 10.19; found: C, 58.12; H, 3.63; N, 10.23%; UV-Vis spectrum
(CH Cl ): l (ε, M cm ) 489 (12664), 378 (21382), 348 (25093), 243
(26094); IR (KBr) (νmax/cm ): 1432 (N=N), 1611 (C=N), 3446 (O−Η),
978 (V=O).
H N O
15 3 4
−1
−1
sh
2
2
max
−1
−1
[(2-Hydroxy-6-(2-(2-oxido-4-chloro-phenyl)diazenylphenylimino)
−1
3
methylphenolate)oxidovanadium(IV)-N,N,O,O] [(L )VO] (2c): Isolated
yield: 0.19 mg (62%); Anal. calcd for C H N O ClV (432.73): C, 52.73;
19
12
3
4
All of the ligands 1a, 1b and 1c were prepared following similar
procedures. A representative procedure for 1a is given below.
H, 2.80; N, 9.71; found: C, 52.71; H, 2.77; N, 9.75%: UV-Vis spectrum
−1
−1
sh
(CH Cl ): l (ε, M cm ) 481 (31849), 370 (52966), 347 (60755), 264
2
2
max
1
−1
Synthesis of H L (1a): A mixture of 2-({2-aminophenyl}diazenyl)
(45783), 239 (64563); IR (KBr) (νmax/cm ): 1430 (N=N), 1615 (C=N),
3443 (O−Η), 977 (V=O).
2
phenol (2.13 g, 10 mmol) and 2,3-dihydroxybenzaldehyde (1.38g,
1
0 mmol) in dry diethyl ether (100 mL) was refluxed for 12 h. Reddish-
Catalytic oxygenation of thioethers
brown crystalline solid 1a was obtained on slow evaporation of the
solvent.
To
dichloromethane (10:90 v/v), the catalyst [(L )VO] (6.0 mg,
.015 mmol) and 50% H O (1 mL) were added at 0 °C. The mixture
a solution of PhSMe (465 mg, 3.75 mmol) in methanol–
1
3
-(2-(2-Hydroxyphenyl)diazenyl)phenyliminomethyl)benzene-1,2-
0
diol (1a): Isolated yield: 3.3 g (94%); Anal. calcd for C H N O (333):
C, 68.46; H, 4.54; N, 12.61; found: C, 68.48; H, 4.51; N, 12.68%; UV-
2
2
19
15
3
3
was stirred for 2.5 h keeping the temperature at 0–4 °C. The solution
was then dried in a vacuum. The products were isolated by thin layer
chromatography (TLC). The solid PhSOMe and PhSO Me were
−1
−1
sh
Vis spectrum (CH Cl ): l (ε, M cm ) 402 (5894), 312 (13420);
2
2
max
−
1
IR (KBr) (ν /cm ): 1466 (N=N), 1618.75 (CH=N), 3468.43 (OΗ);
2
max
1
isolated as the third and second fractions, respectively, with yields of
H NMR (DMSO-d ): δ 13.09 (s, OH), 11.54 (s, OH), 9.38(s, OH ),
6
187 mg and 222 mg, respectively. The products were characterised by
9
7
6
.05(s, CH=N), 7.99 (d, 1H), 7.87 (d, 1H), 7.72(t, 1H), 7.66 (d, 1H),
.54–7.47 (m, 2H), 7.23 (d, 1H), 7.13 (d, 1H), 7.11 (t, 1H), 7.04 (d, 1H),
.87 (t, 1H).
-(2-(2-Hydroxyphenyl)diazenyl)-4-methyl-phenyliminomethyl)
IR spectroscopy. The results of the conversions of other thioethers to
sulfoxides and sulfones are given in Table 2.
3
Bromination of aromatic alcohols
2
benzene-1,2-diol H2L (1b) and 3-(2-(2-hydroxyphenyl)diazenyl)-
4
Complex 2a (6 mg, 0.015 mmol) and p-cresol (198 mg, 1.8 mmol) were
3
-chloro-phenyliminomethyl)benzene-1,2-diol H L (1c): 1b and 1c
2
dissolved in CH CN (10 mL). To this mixture, KBr (440mg, 3.7 mmol)
3
were prepared following the same procedure as described for 1a, using
-({2-aminophenyl}diazenyl)-5-methylphenol and 2-({2-aminophenyl}
dissolved in water (2 mL) was added, followed by 30% H O (1 mL)
2
2
2
added dropwise with constant stirring. The pH of the solution was
adjusted to approximately 3 by dropwise addition of 2N HCl solution.
The reaction mixture was stirred for 20 h at room temperature. The
product was extracted with diethyl ether and concentrated to about
diazenyl)-5-chlorophenol in place of 2-({2-aminophenyl}diazenyl)phenol,
respectively.
(
1b): Isolated yield: 3.32 g (91%); Anal. calcd for C H N O (347.4):
20 17 3 3
C, 69.14; H, 4.94; N, 12.1; found: C, 69.02; H, 4.88; N, 12.18%; UV-
1
4
mL. Two products, 2-bromo-4-methylphenol and 2,6-dibromo-
-methylphenol, were separated by TLC and characterised by
−1
−1
sh
Vis spectrum (CH Cl ): l (ε, M cm ) 321 (15020), 400 (7876);
2
2
max
−
1
IR (KBr) (ν /cm ): 1466.99 (N=N), 1618.47 (C=N), 3475.40 (O−Η);
max
spectroscopic techniques. The isolated yields were 79 mg and 60 mg,
respectively. The results of the conversions are given in Table 3. The
same reaction was carried out keeping all other components and
conditions the same but not adding the catalyst.
1
H NMR (DMSO-d ): δ 12.87 (s, OH), 11.64 (s, OH), 9.26(s, OH ),
6
8
7
1
.90 (s, CH=N), 7.84 (d, 1H), 7.66 (d, 1H), 7.55 (t, 1H), 7.51 (d, 1H),
.38 (t, 1H), 7.10 (d, 1H), 6.91 (d, 1H), 6.81 (s, 2H), 6.79 (d, 1H), 6.74 (t,
H), 2.43 (t, 3H).
1c): Isolated yield: 3.28 g (85%); Anal. calcd for C H N O Cl
(
Biological activity
19
14
3
3
(
367.8): C, 62.04; H, 3.84; N, 11.43; found: C, 61.96; H, 3.79; N,
Cell lines: Human breast cancer cells (MCF7 and MDA-MB-231) were
grown in DMEM medium, and HCT116 colon cancer cell cells were
grown as a monolayer in RPMI-1650 medium fortified with antibiotics
−1
−1
1
3
3
1.55%; UV-Vis spectrum (CH Cl ): l (ε, M cm ) 319 (10014),
2
2
max
sh
−1
92 (5911); IR (KBr) (ν /cm ): 1467.80 (N=N), 1618.82 (C=N),
max
1
474.99 (O−Η); H NMR (DMSO-d ): δ 13.20 (s, OH), 11.57 (s, OH),
−1
−1
6
(penicillin 100 μg mL , streptomycin sulfate (100 μg mL ) and 10%
9
.21 (s, OH ), 8.93 (s, CH=N), 7.86 (d, 2H), 7.71 (d, 1H), 7.58 (t, 1H),
foetal bovine serum (FBS) at 37 °C, 5% CO atmosphere in humid
2
7
(
.56 (d, 1H), 7.40 (t, 1H), 7.10 (s, 1H), 7.08 (d, 1H), 7.00 (d, 1H), 6.91
d, 1H), 6.72 (t, 1H).
Synthesis of [(L)VO]: The complexes [(L )VO] (2a), [(L )VO] (2b)
conditions (Table 4).
1
2
Determination of 50% inhibitory concentration (IC50)
3
1
and [(L )VO] (2c) were prepared following similar procedures. A
representative procedure for 2a is given below.
The cytotoxic effect of [(L )VO] on MCF7, MDA-MB-231 and
HCT116 was evaluated by MTT (3-{4,5-dimethylthiazol-2-yl}-2,5-
4
4–47
[
(2-Hydroxy-6-(2-(2-oxido-4-alkyl-phenyl)diazenylphenylimino)
diphenyltetrazolium bromide) assay.
Cells of the required cell
1
3
methylphenolate)oxidovanadium(IV)-N,N,O,O] [(L )VO] (2a):
drop of water was added to dissolve VOSO .5H O (0.125 g, 0.5 mmol)
A
line were seeded in a 96-well plate (5 × 10 cells/well) and allowed
to adhere for the next 24 h. The cells were then treated with different
4
2

JOURNAL OF CHEMICAL RESEARCH 2018 61
1
Table 5 Crystallographic data for [(L )VO]
Received 1 December 2017; accepted 19 January 2018
Paper 1705131
https://doi.org/10.3184/174751918X15168821806597
Published online: 31 January 2018
Empirical formula
Formula weight
Crystal system
Space group
a/Å
C H N O V
398.26
Monoclinic
P2 /n (No. 14)
10.2000(4)
9.3314(4)
17.7691(7)
90
19 13 3 4
1
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wR [I > 2σ(I)]
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2
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013, 38, 43.
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2
0
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4
8,49
2
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8,49
All non-hydrogen atoms were refined
2
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CCDC 1572035 contains the supplementary crystallographic data
for compound 2a. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2
2
2
6
7
8
Electronic supplementary information (ESI)
2
3
9
0
Figs S1–S6 show the UV-Vis spectra of the ligands and
complexes, Figs S7–S12 show the IR spectra of the ligands and
complexes, and Figs S13–S15 show the H NMR spectra of the
ligands. The ESI is available through http://ingentaconnect.
com/content/stl/jcr/2018/00000042/00000001/art00014
1
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Acknowledgements
The necessary laboratory and infrastructural facilities were
provided by the Department of Chemistry, University of
Kalyani. The support of DST under FIST and Purse Program
of the Department of Chemistry, University of Kalyani is
acknowledged.
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