Metal complexes of ONO donor Schiff base ligand as a new class of bioactive compounds; Synthesis, characterization and biological evolution

Article abstract of DOI:10.1016/j.saa.2014.03.038

Present work reviews that, the synthesis of (E)-N′-((7-hydroxy-4- methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide [L] ligand and their metal complexes. The colored complexes were prepared of type [M²⁺L]X ₂, where M²⁺ = Mn, Co, Ni, Cu, Sr and Cd, L = (7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide, X = Cl ^-. Ligand derived from the condensation of 8-formyl-7-hydroxy-4- methylcoumarin and benzohydrazide in the molar ratio 1:1 and in the molar ratio 1:2 for metal complexes have been prepared. The chelation of the ligand to metal ions occurs through the both oxygen groups, as well as the nitrogen atoms of the azomethine group of the ligand. Reactions of the Schiff base ligand with Manganese(II), Cobalt(II), Nickel(II), Copper(II), Strontium(II), and Cadmium(II) afforded the corresponding metal complexes. The structures of the obtained ligand and their respective metal complexes were elucidated by infra-red, elemental analysis, Double beam UV-visible spectra, conductometric measurements, magnetic susceptibility measurements and also thermochemical studies. The metal complex exhibits octahedral coordination geometrical arrangement. Schiff base ligand and their metal complexes were tested against antioxidants, antidiabetic and antimicrobial activities have been studied. The Schiff base metal complexes emerges effective α-glucosidase inhibitory activity than free Schiff base ligand.

Full text of DOI:10.1016/j.saa.2014.03.038

Accepted Manuscript
Metal complexes of ONO donor Schiff base ligand as a new class of bioactive
compounds; Synthesis, characterization and biological evolution
K.H. Kumar Naik, Selva Raj, Nagaraja Naik
PII:
S1386-1425(14)00449-1
http://dx.doi.org/10.1016/j.saa.2014.03.038
SAA 11871
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
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Revised Date:
Accepted Date:
17 December 2013
12 March 2014
20 March 2014
Please cite this article as: K.H. Kumar Naik, S. Raj, N. Naik, Metal complexes of ONO donor Schiff base ligand as
a new class of bioactive compounds; Synthesis, characterization and biological evolution, Spectrochimica Acta Part
A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.03.038
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Metal complexes of ONO donor Schiff base ligand as a new class of bioactive compounds;
Synthesis, characterization and biological evolution
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K. H. Kumar Naik a, Selva Rajb, Nagaraja Naika*
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aDepartment of Studies in Chemistry, University of Mysore, Manasagangotri,Mysore-06
bDepartment of Studies in Zoology, University of Mysore, Manasagangotri, Mysore-06,
Karnataka, India.
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Email: drnaik_chem@yahoo.co.in
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*Corresponds addresses
Dr. NAGARAJA NAIK M.Sc., Ph.D.,
Professor of Chemistry
Department of Studies in Chemistry
Manasagangotri, Mysore-570006
Karnataka state, India
Phone: (Off) +91-821-2419655
Mob: +91-9842959088
Email Id: drnaik_chem@yahoo.co.in
drnaikchem@gmail.com
kumarnaikinorg@gmail.com
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ABSTRACT
Present work reviews that, the synthesis of (E)-N'-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-
yl)methylene)benzohydrazide [L] ligand and their metal complexes. The colored complexes
were prepared of type [M2+L]X2, where M2+=Mn, Co, Ni, Cu, Sr and Cd, L=(7-hydroxy-4-
methyl-2-oxo-2H-chromen-8-yl)methylene)benzohydrazide, X=Cl-. Ligand derived from the
condensation of 8-formyl-7-hydroxy-4-methylcoumarin and benzohydrazide in the molar ratio
1:1 and in the molar ratio 1:2 for metal complexes have been prepared. The chelation of the
ligand to metal ions occurs through the both oxygen groups, as well as the nitrogen atoms of the
azomethine group of the ligand. Reactions of the Schiff base ligand with Manganese(II),
Cobalt(II), Nickel(II), Copper(II), Strontium(II), and Cadmium(II) afforded the corresponding
metal complexes. The structures of the obtained ligand and their respective metal complexes
were elucidated by infra-red, elemental analysis, Double beam ultraviolet–visible spectra,
conductometric measurements, magnetic susceptibility measurements and also thermochemical
studies. The metal complex exhibits octahedral coordination geometrical arrangement. Schiff
base ligand and their metal complexes were tested against antioxidants, antidiabetic and
antimicrobial activities have been studied. The Schiff base metal complexes emerges effective α-
glucosidase inhibitory activity than free Schiff base ligand.
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Key words; Schiff base ligand, Metal complexes, α-Glucosidase inhibitory activity, Antioxidant
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activity, Antimicrobial activity.
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Introduction
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Schiff bases are popular ligands in coordination chemistry due to their ease of synthesis
and their ability to be readily modified both electronically and sterically. Many complexes of
Schiff-base ligands with metal ions have been investigated as models for active sites of enzymes
[1, 2] including DNA-cleavage systems [3, 4] and as antibacterial [5, 7] and anticancer [8] drugs.
They also provide useful magnetic materials and have a wide range of catalytic applications,
such as in polymerization [7], olefin oxidation [6] and Suzuki-Miyaura coupling [7, 8]. In
particular, complexes of metal ions with tetrahedral (e.g. Ag(I)) or octahedral (e.g. Cu(II), Co(II),
Fe(II) and Zn(II)) coordination preferences have been found to display important
physicochemical properties as well as biological activity. Mixed donor Schiff bases have been
used extensively in catalysis [9]. Most of the mixed-donor Schiff base ligands developed to date
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have nitrogen with phosphorous [10] or oxygen [11-14] atoms as the other donor unit. Several
metal ions and their complexes exhibit antidiabetic effects [15-18]. Recently, Chakravarty and
co-workers have utilized O, N, and S-Schiff bases as ligands for models of copper-containing
enzymes [18-20].
In view of these facts, we have synthesized a novel Schiff base ligand and their
coordination behaviour with different metals for which antidiabetic, antioxidant and
antimicrobial activities have been discussed.
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Materials and methods
Materials
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All the reagents were of AR grade and used as received from BDH, England, Merck
reagent, Germany and Sigma-Aldrich chemical company, USA. The partial dehydration of the
salts was carried out by drying the hydrated salts in a vacuum oven for several hours at 100-
110oC.
Apparatus and methods
Melting point of the complexes were determined using Thomas Hoover apparatus and
uncorrected. Molar conductance of the complexes were determined using systronics conductivity
metre 304 conductivity bridge provided with a dip-type conductivity cell having platinised
platinum electrodes. IR spectra were recorded using Shimadzu 8201 PCFT-IR spectrometer by
KBr technique. Electronic spectra of DMF solutions of the metal complexes were carried out by
using Double beam UV-VIS Spectrophotometer Perkin–Elmer Model Lamda 900. Magnetic
susceptibility measurements were done using Gouy balance consisting of the type NP-53
electrometer with DC power supply type NP-1053 and Keroy semi microbalance supplied by
Universal scientific company, Mumbai, India. Thermogravimetric analysis of complexes was
carried out in oxygen atmosphere using Perkin- Elmer TGA-7. Elemental analysis were done
using Vario-EL III CHN and S elemental analyzer.
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Scheme
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Scheme. Reagents and conditions: (a) Ethanol, reflux, 2-3 h; (b) Ethanol, reflux, 2 h (c) Metal
chlorides.
Result and discussion
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Chemistry
The synthetic strategies adopted for the synthesis of the intermediate and target
compounds are depicted in above Scheme. A mixture of 8-formyl-7-hydroxy-4-methylcoumarin
and benzohydrazide in 1:1 ratio in alcoholic medium containing 5-6 drops of concentrated HCl
was refluxed for 3-4 h to form Schiff base. When alcoholic solution of Schiff base (2 m mol) was
refluxed with metal chlorides which forms Schiff base metal complexes [21, 22]. This was
characterized by IR Spectra, Double beam UV-VIS Spectrophotometer, elemental analysis,
conductometry measurements, magnetic susceptibility measurements and thermal behaviour.
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Conductivity studies.
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Conductivity measurements of the complexes in HPLC grade DMF solutions were made
to verify the ionic formulation of the complexes. The molar conductivity of a solution was
obtained from a following relation. The measurements were made by using an systronics
conductivity metre 304 conductivity bridge provided with a dip-type conductivity cell having
platinised platinum electrodes. The cell constant was determined by measuring the resistance of
aqueous KCl solutions, the specific conductivities of which were known accurately from
literature [23]. The conductivity measurements of the complexes were carried out at 10-3 M is
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HPLC grade DMF solvent. The molar conductance values are too low to account for any
dissociation of the complexes in DMF, indicating the non-electrolytic nature of the complexes in
DMSO shown in table-1.
The magnetic susceptibility measurements of the complexes were obtained at room
temperature using Gouy balance. Pure Hg[Co(SCN)4] was synthesized and used as calibration
standard [24]. The effective magnetic moment values of the complexes are in table-1. The
complexes are paramagnetic in nature. The magnetic moment values of complexes are in the
range 1.29-5.85 BM, which suggests that the complexes have high spin octahedral geometry [25,
26]. The Mn(II), Co(II), Ni(II), Cu(II), Sr(II), and Cd(II) complexes are colored, stable and non-
hygroscopic in nature. The complexes are insoluble in common organic solvents like chloroform,
ethanol and methanol but soluble in DMF and DMSO. The elemental analyses shows that, the
above complexes have 1:2 stoichiometry of the type [M2+L]X2, where L stands for a tridentate
ligands.
UV-VIS absorption Spectral studies
The Electronic Absorption Spectral Studies of Schiff base and some of metal complexes
had carried out in the region 200-1100 nm were measured by double beam spectrophotometer.
Weighed samples were dissolved in appropriate DMF of HPLC grade at a concentration of 10-6
and 10-7 M. were measured and carried out at room temperature. The electronic absorption
spectrum of the Schiff base is depicted in figure-2, exhibited two absorption bands around 340
nm and 420 nm respectively.
The first band around 340 nm corresponds to Π→Π* of the azomethine group and second
band at 420 nm corresponds to n→ Π* transitions. The typical electronic absorption spectrum of
the Co2+ complex assented in figures-3. This spectra exhibit absorption bands in the region 8100-
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10500 cm-1 and 18100-20100 cm-1 corresponding to the transitions T1g (F) → T2g (F) (ν1) and
4T1g (F)→4T1g (P) (ν3) respectively [27]. In the present investigation, brownish Co2+ complexes
shows the absorption bands around 240 nm and 384 nm corresponding to ν1 and ν3 transitions
respectively. The ν2 band is not observed due to strong proximity to ν3 transition. These bands
are characteristic of high spin octahedral Co2+ complexes. The spectrum is depicted in the figure-
3. The Ni2+ complex exhibited three bands at 246, 261 and 266 nm attributed to the 3A2g →3T2g
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(ν1), A2g → T1g (F) (ν2) and A2g → T1g (P) (ν3) transitions respectively, which indicate
octahedral geometry around Ni2+ ion and the spectra shown in figure-4. And also for remain
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complexes of Cu2+, Mn2+, Sr2+ and Cd2+ complexes results comparable with other reported
complexes [28-30]. The electronic spectra of Cu2+ complexes display two prominent bands; a
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low-intensity broad band around 16,253 cm−1 is assignable to Eg → T2g transition and another
high-intensity band at 26,466 cm−1 is due to ligand→ metal charge transfer. On the basis of
electronic spectra, the distorted octahedral geometry around the Cu2+ ion is suggested [31]. The
Cu2+ complexes showed magnetic moment of 1.80–1.86 BM, which is slightly higher than the
spin-only value (1.73 BM) expected for one unpaired electron, which offers the possibility of an
octahedral geometry [32].
Table-1 and Figure-2, 3, and 4; should be here.
Infrared spectral studies
The IR Spectra of ligand and few of its metal complexes were obtained on a Shimadzu
8400-S, Japan, in the region 4000-350 cm-1. The typical infrared spectrum of the Schiff base
have been represented in figure-4. The most important IR bands of Schiff base exhibited a broad
band at 3425-3450 cm-1, strong band at 1720, 1597 and 1475 cm-1 assigned to ν(C=O) lactonic
carbonyl, amide ν(C=O) carbonyl and ν(C=N) vibrations respectively. A broad band in the
range 3450 cm-1 is ascribed to the stretching vibration of ν(NH) [33] The medium intensity bands
at 1050 and 1150 cm-1 are attributed to ν(N-N) and ν(C-O) vibrations, respectively [34]. The IR
spectra of the metal complexes clearly indicate the bonding mode of Schiff base with the metal
ions.
In comparison with the spectra of the Schiff base, the metal complexes exhibited the
band of ν(C=N) in the region 1612 cm-1, showing the shift of band to lower wave numbers
indicating that, the azomethine nitrogen is coordinated to the metal ion. The disappearance of the
broad band due to H-bonded –OH stretching in the spectra of the metal complexes gives
evidence for the formation M-O bonds via deprotonation. The new bands in the region of 400-
420 cm-1 and 600-650 cm-1 in the metal complexes are assigned to stretching frequencies of (M-
O) and (M-N) bonds respectively [35]. The unaltered position due to lactonyl ν(C=O) in all the
metal complexes confirms its non involvement in coordination. Thus, the IR spectral data
provide strong evidence for the complexation of the potentially tridentate Schiff base [36]. The
prominent infrared spectral data are presented in the table-2 and the IR spectra of the
representative Co2+, Ni2+ complexes are shown in supplementary file.
Table- 2; should be here
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Thermogravimetric studies
The thermal behavior of Co2+, Ni2+ complexes have been studied, as a function of
temperature. The thermal decomposition of [Co(C18H14N2O4)2] and [Ni(C18H14N2O4)2]
O
O
complexes took place in one step as indicated by DTG peaks around 383 C and 380 C
respectively as predicted in figure-5 and figure-6 respectively, corresponding to the mass loss of
organic moiety. Hence, finally the metal complexes decompose gradually with the formation of
metal oxide above 400ºC [37].
Figure-5 and 6; should be here
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Biological evolutions
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In-vitro α-glucosidase inhibition activity
The inhibitory effects of acarbose (positive control) and metal complexes of [Mn2+L]X2,
[Co2+L]X2, [Cu2+L]X2 [Sr2+L]X2 and [Cd2+L]X2 on α-glucosidase activity were concentration
dependent. α-Glucosidase inhibition data (percentage inhibition at 50, 100 and 200 µM and IC50
values) for complexes and ligand are presented in table-3. The results of inhibition of α-
glucosidase by newly synthesized ligand and their complexes at various concentrations are also
presented graphically in figure-7. A perusal of the data reveals that all complexes show much
better α-glucosidase inhibition [38] compared to the corresponding Schiff base ligands, except
[Sr2+L]X2 that shows almost same inhibitory potential as Schiff base ligand and [Cd2+L]X2
shows less inhibitory potential than that of Schiff base ligand [39]. Finally we concluded that, the
apparent IC50 values of the test compounds with respect to the α-glucosidase activity were
estimated table-3. In comparison with acarbose, all test compounds except for [Sr2+L]X2 and
[Cd2+L]X2 showed better α-glucosidase inhibitory effect.
Table-3 and figure-7; should be here
Antioxidant Activity
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The antioxidant activity of ligand as well as metal complexes is presented in table-4 and
figure-8. At the different concentration of 10, 25, 50, 100, 200 and 500 µM, few complexes
showed a much stronger DPPH scavenging (>80%) than free Ascorbic acid. The Ascorbic acid
showed 59% of DPPH scavenging property. The marked antioxidant activity of ligand [L] and
metal complexes 1 and 4 in comparison to free Ascorbic acid, could be due to the coordination of
metal after complexation of the system, increasing its capacity to stabilize unpaired electrons and
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Thereby, to scavenge free radicals. And remain complexes 2, 3, 5 and 6 shows moderate activity
of scavenging property [40].
Table-4 and figure-8; should be here
Antimicrobial activity
The minimum inhibitory concentration (MIC) values of the compounds against the
respective strains are summarized in table-5, table-6 and graphically represented in figure-9,
figure-10. The antimicrobial screening results of all the synthesized ligand and their metal
complexes exhibited antimicrobial properties. It is important to note that the metal complexes
exhibited a more inhibitory effect compared to their respective parent ligands. The enhanced
activity of the complexes over the ligand can be explained on the basis of chelation theory [36].
It is known that chelation makes the ligand a more powerful and potent bactericidal agent, thus
killing more of the bacteria than the ligand. The enhancement in the activity may be rationalized
on the basis that ligands mainly possess an azomethine (C = N) bond. It has been suggested that
ligands with hetero donor atoms (nitrogen and oxygen) inhibit enzyme activity, since the
enzymes that require these groups for their activity appear to be especially more susceptible to
deactivation by metal ions on coordination. It is observed that, in a complex, the positive charge
of the metal ion is partially shared with the hetero donor atoms (nitrogen and oxygen) present in
the ligand, and there may be π-electron delocalization over the whole chelating system [41].
Table-5 & 6 and figure-9 & 10; should be here
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Conclusion
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In summary, the metal complexes of Mn2+, Co2+, Ni2+, Cu2+, Sr2+ and Cd2+ of Schiff base
ligand
derived
from
7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde
and
benzohydrazide were synthesized and characterized. The Schiff bases are tridentate, coordinated
through the azomethine nitrogen, phenolic oxygen and benzohydrazide oxygen, confirmed by
analytical, spectral, magnetic, and thermal studies. On the basis of different techniques, it is
tentatively proposed that, the metal complexes have octahedral geometries and the Schiff base
act as a versatile tridentate ligand. The newly synthesized complexes were evaluated for their in
vitro α-glucosidase inhibition activity, antioxidant and antimicrobial activity. Among the
complexes 2, 3 and 4 demonstrated potent α-glucosidase inhibition activity. The complexes 1
and 4 exhibited maximum antioxidant activity. Whereas in antifungal studies all complexes
exhibits moderate activity in comparison with their corresponding parent ligand and standard
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drug. All these observations put together lead us to propose the structure for the Mn2+, Co2+,
Ni2+, Cu2+, Sr2+ and Cd2+ complexes as depicted in figure-1.
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Figure Captions
Figure-1; Proposed structure of metal complexes, [M2+L]X2=Mn, Co, Ni, Cu, Sr, Cd. X=Cl-
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Figure-2; UV-VIS spectra of Schiff base ligand [L]
Figure-3; Electronic Absorption Spectrum of Co(II) Complex
Figure-4; Electronic Absorption Spectrum of Ni(II) Complex
Figure-5; DTG Curve of [Co(C18H14N2O4)2] X2
Figure-6; DTG Curve of [Ni(C18H14N2O4)2] X2
Figure-7; α-Glucosidase activity of the Schiff base ligand and its metal complexes
Figure-8; Antioxidant activity of the Schiff base ligand and its metal complexes
Figure-9; Antibacterial activity of the Schiff base ligand and its metal complexes
Figure-10; Antifungal activity of the Schiff base ligand and its metal complexes
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
12

341
342
343
Figure-1; Proposed structure of metal complexes,
344
345
[M2+L]X2=Mn, Co, Ni, Cu, Sr, Cd. X=Cl-
346
347
348
349
Figure-2; UV-VIS spectra of Schiff base ligand [L]
13

350
351
352
353
354
Figure-3; Electronic Absorption Spectrum of Co(II) Complex
14

355
356
357
358
359
360
Figure-4; Electronic Absorption Spectrum of Ni(II) Complex
361
362
Figure-8; Antioxidant activity of the Schiff base ligand and its metal complexes
15

363
364
365
366
367
368
369
370
371
372
373
374
16

375
376
377
17

378
379
18

380
381
19

382
383
384
385
Table caption
Table-1; Molecular formulae, color, yield, melting point, elemental analysis, magnetic
susceptibility and molar conductance data of the Schiff base ligand and its metal complexes
386
387
388
Table-2; The Important Infrared Frequencies (in cm-1) of the Schiff base ligand and its metal
complexes
Table-3; α-Glucosidase activity of the Schiff base ligand and its metal complexes
389 Table-4; Antioxidant activity (IC50) of the Schiff base ligand and its metal complexes
390
391
392
393
Table-5; Antibacterial activity of the Schiff base ligand and its metal complexes (minimum
inhibitory concentration × 10-2 M).
Table-6; Antifungal activity of the Schiff base ligand and its metal complexes (minimum
inhibitory concentration × 10-2 M).
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
20

414
415
416
Table-1; Molecular formulae, color, yield, melting point, elemental analysis, magnetic
susceptibility and molar conductance data of the Schiff base ligand and its metal complexes
Elemental analysis
Calc. (found) (%)
Molar
conduct.(O
hm-1cm-
2mol-1)
µ eff
Mol. For.
color Yiel Mel.poin
Com
pds
(BM)
d
t (oC)
(%)
C
H
N
O
M
--
C18H14N2O4
Yello
w
56
51
65
186-188 66.89(6 4.25(4. 8.51(8. 19.74(1
6.91) 31) 57) 9.78)
195-198 61.01(6 3.16(3. 7.85(7. 18.08(1 7.51(
1.05) 20) 91) 8.12) 7.57)
201-205 61.23(6 3.44(3. 7.84(7. 18.11(1 8.20(
1.27) 48) 89) 8.17) 8.24)
197-198 61.41(6 3.42(3. 7.74(7. 18.14(1 8.28(
1.47) 46) 82) 8.23) 8.31)
208-210 61.23(6 3.71(3. 7.93(8. 18.13(1 9.00(
1.26) 77) 01) 8.20) 9.05)
181-183 59.13(5 3.46(3. 7.58(7. 17.49(1 11.91
--
--
[L]
[1]
[2]
[3]
[4]
[5]
[Mn(C36H26N4O8)2]X2
[Co(C36H26N4O8)2] X2
Viole
nt
86.25
91.04
79.12
84.15
89.17
5.81
Brow
nish
3.75
2.45
1.29
--
[Ni(C36H26N4O8)2] X2 Green 58
[Cu(C36H26N4O8)2] X2 Green 70
[Sr(C36H26N4O8)2] X2
White 53
9.17)
49)
62)
7.57)
(12.0
4)
[Cd(C36H26N4O8)2] X2 White 48
193-195 57.16(5 3.31(3. 7.41(7. 16.71(1 14.74
76.51
diama
gnetic
[6]
7.19)
34)
48)
6.84)
(14.7
8)
417
418
419
420
421
422
423
424
425
426
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427
428
429
Table-2; The Important Infrared Frequencies (in cm-1) of the Schiff base ligand and its metal
complexes
Lactonyl
ν(C=O)
cm-1
ν(C=N)
ν(O-H)
Phenolic
ν(C–O)
cm-1
ν(M–N)
ν(M–O)
Compound ν(N-H) cm-1
cm-1
cm-1
cm-1
cm-1
3450
3421
3435
3430
3445
3430
3431
1720
1695
1701
1710
1690
1660
1685
1622
1608
1594
1582
1610
1584
1598
1720
1650
1645
1630
1668
1675
1680
1282
1281
1306
1307
1302
1304
1036
--
--
[L]
[1]
[2]
[3]
[4]
[5]
[6]
605
612
614
612
608
615
405
410
412
415
408
420
430
431
432
433
Table-3; α-Glucosidase activity of the Schiff base ligand and its metal complexes
IC50(µM)
Compounds
50 µM
100 µM
150 µM
200 µM
C18H14N2O4 [L]
0.289
0.231
0.132
0.213
0.102
0.814
0.341
0.091
0.314
0.222
0.198
0.245
0.125
0.971
0.409
0.091
0.391
0.286
0.221
0.301
0.181
1.05
0.421
0.419
0.308
0.379
0.204
1.21
[Mn(C36H26N4O8)2]X2 [1]
[Co(C36H26N4O8)2] X2 [2]
[Ni(C36H26N4O8)2] X2 [3]
[Cu(C36H26N4O8)2] X2 [4]
[Sr(C36H26N4O8)2] X2 [5]
[Cd(C36H26N4O8)2] X2 [6]
Acarbose
0.457
0.091
0.498
0.091
434
22

435
436
437
438
Table-4; Antioxidant activity (IC50) of the Schiff base ligand and its metal complexes
Compounds
IC50 (µM)
C18H14N2O4 [L]
>214
[Mn(C36H26N4O8)2]X2 [1]
187 0.13
[Co(C36H26N4O8)2] X2 [2]
[Ni(C36H26N4O8)2] X2 [3]
[Cu(C36H26N4O8)2] X2 [4]
[Sr(C36H26N4O8)2] X2 [5]
[Cd(C36H26N4O8)2] X2 [6]
Ascorbic acid
121 0.09
142 0.53
122 0.21
84 0.04
95 0.31
59 0.05
439
440
441
442
443
Table-5; Antibacterial activity of the Schiff base ligand and its metal complexes (minimum
inhibitory concentration × 10-2 M).
444
Compounds
E. coli
B. subtilis R. solanacearum
4.9
11.3
05.9
C18H14N2O4 [L]
[Mn(C36H26N4O8)2]X2 [1]
[Co(C36H26N4O8)2] X2 [2]
[Ni(C36H26N4O8)2] X2 [3]
[Cu(C36H26N4O8)2] X2 [4]
[Sr(C36H26N4O8)2] X2 [5]
[Cd(C36H26N4O8)2] X2 [6]
Chloramphenicol
4.2
4.1
4.1
4.0
6.1
6.4
5.9
10.3
11.0
8.0
04.6
05.0
06.8
06.2
6.4
10.2
11.2
12.0
07.1
5.9
04.3
23

445
446
447
448
449
450
451
452
453
454
Table-6; Antifungal activity of the Schiff base ligand and its metal complexes (minimum
inhibitory concentration × 10-2 M).
Compounds
A. niger
A. flavus
R. bataicola
6.1
4.8
5.3
C18H14N2O4 [L]
[Mn(C36H26N4O8)2]X2 [1]
[Co(C36H26N4O8)2] X2 [2]
[Ni(C36H26N4O8)2] X2 [3]
[Cu(C36H26N4O8)2] X2 [4]
[Sr(C36H26N4O8)2] X2 [5]
[Cd(C36H26N4O8)2] X2 [6]
Nystatin
3.1
4.9
5.1
5.0
6.1
6.8
7.0
3.5
4.2
5.4
4.4
5.4
6.1
6.5
4.5
5.1
6.0
3.8
2.9
3.7
5.2
455
456
457
24

458
459
460
461
462
463
464
465
466
467
468
Research Highlights
• We are synthesized novel Organic ligands and their metal complexes.
• Characterization of ligands and metal complexes were carried out by various spectral
techniques, i. e., IR spectral studies, elemental analysis, magnetic properties, and Double
beam UV-visible Spectral studies.
•
α-Glucosidase inhibitory activity, Antioxidant activity, Antimicrobial activity were
carried out for our novel ligands and metal complexes.
25

469
470
471
472
473
Graphical abstract
Metal complexes of ONO donor Schiff base ligand as a new class of Bioactive compounds;
Synthesis, characterization and Biological evolution
474
475
476
477
478
479
480
481
482
483
484
485
486
26