Antibacterial activity of macrocyclic complexes of Cu(II), Ni(II) and VO(II) derived from o-aminobenzaldehyde

Article abstract of DOI:10.1155/2012/953727

Novel Cu(II), Ni(II) and VO(II) complexes are synthesized with N ¹,N⁴-bis(2-aminobenzylidene)benzene-1,4-diamine (L). Complexes were characterized by elemental analysis, molar conductance, IR, UV and EPR. Spectral studies reveals a s

Full text of DOI:10.1155/2012/953727

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2012, 9(1), 481-486
http://www.e-journals.net
Antibacterial Activity of Macrocyclic
Complexes of Cu(II), Ni(II) and VO(II)
Derived from o-Aminobenzaldehyde
K. ANURADHA and R. RAJAVEL*
Department of Chemistry
Periyar University, Salem-11, Tamilnadu, India
anuradhakaliappan@gmail.com
Received 24 July 2011; Accepted 22 September 2011
Abstract: Novel Cu(II), Ni(II) and VO(II) complexes are synthesized with
N1,N4-bis(2-aminobenzylidene)benzene-1,4-diamine (L). Complexes were
characterized by elemental analysis, molar conductance, IR, UV and EPR.
Spectral studies reveals a square planner geomentry for Cu(II), Ni(II)
complexes and square pyramidal for VO(II) complex. The ligand and its
complexes were also evaluated against the growth of gram positive bacteria and
gram negative bacteria.
Keywords: Macrocyclic, Electrolytic, Cu(II), Ni(II), VO(II), o-Aminobenzaldehyde
Introduction
Metal complexes containing synthetic macrocyclic ligands have attracted a great deal of
attention because they can be used as models for more intricate biological macrocyclic
systems like metalloporphyrins (hemoglobin, myoglobin, cytochromes, chlorophylls),
corrins (vitamin B12) and antibiotics (valinomycin, nonactin). So it attracted the attention of
both inorganic and bioinorganic chemists1. These discoveries have created supramolecular
chemistry and its enormous diversity. The formation of macrocyclic complexes mainly
depends on size of the internal cavity and rigidity of the macrocycle formed2. Schiff bases
having donor atoms such as N2O2 and N4 around the metal ion have received more attention,
mainly because of their extensive applications as catalysts for carbonylation, hydrogenation
hydroformylation, epoxidation, nucleicacid modification, electrochemical reduction,
alkanehydroxylation, Diels–Alder transformations, carboxylic acid decarboxylation, amines
oxidation and medicinal studies as models for mimicking the superoxide dismutase3–8. The
chemistry of macrocyclic complexes is also important due to its use as dyes, pigments and
NMR shift reagents9.
Metal condensation reaction with the ligand often provides selective routes towards
product that are not obtainable in absence of metal ions. A rational control of the nuclearity
of transition metal complexes is important to design systems with the desired properties,

482
R. RAJAVEL et al.
as some of these applications require the presence of more than one metal center in the
particular complex. Indeed, binuclear complexes may have very different reactivity than
mononuclear counterparts, thereby enabling transformations inaccessible to single metal
ions10. For instance, nucleic acid hydrolysis is postulated to be facilitated by the cooperative
action of two metal ions11. Furthermore, bi or oligo nuclear complexes containing transition
metals may be formed by bridging ligands that can mediate magnetic interactions between
paramagnetic metal ions12.
Experimental
Materials
o-Phthalaldehyde and p-phenylenediamine were purchased from Aldrich. Ethanol, methanol,
DMSO and DMF were used as solvents. The solvents metals and reagents with analytical
grade were obtained commercially and used without further purification.
Physical measurement
The elemental analysis was performed using Carlo-Eraba 1106 instrument. Molar
conductance of the complexes in DMF solution was measured with ELICO CM 185
Conductivity Bridge. The Infrared spectra were recorded on the Perkin Elmer FT-IR-8300
model spectrometer using KBr disc. Electronic absorption spectra in the UV-Visible range
were recorded on Perkin Elmer Lambda-25 between 200-800 nm by using DMSO as the
solvent. ESR spectra of the complexes were recorderd as powder samples at room
temperature on an E4-EPR spectrometer using DPPH as the g-marks. Magnetic
susceptibility data were collected on powdered sample of the compounds at the room
temperature with PAR155 vibrating sample magnetometer.
Synthesis of Schiff base ligand
The starting material o-aminobenzaldehyde was prepared according to the literature
procedure13. An ethanolic solution of freshly prepared o-aminobenzaldehyde was mixed
slowly with stirring ethanolic solution of p-phenylenediamine. The mixture was refluxed at
≈ 70°C for 2 h. On cooling yellow colored precipitate was separated out, filtered, washed
with ethanol, diethylether and dried in vaccum14. The binucleating Schiff base ligand is
shown in Figure 1. Yield 71%. Elemental analysis: C20H18N4, calculated C, 76.43, H, 5.73,
N, 17.83%, Found C, 75.96, H, 5.54, N,17.89% ν(C=N), 1622 cm-1, ν(NH2), 3442 cm-1, UV-
vis (λmax) DMSO: π-π*-228 nm, 280 nm, n-π*-390 nm.
CHO
CHO
FeSO4 HCl
NH2
H2N
+
NH4OH, H2O
90 oC
NO2
NH2
p-Phenlenediamine
o-Nitrobenzaldehyde
o-Aminobenzaldehyde
2 h
70 oC
NH2
H2N
N
N
N1,N4-bis(2-aminobenzylidene)benzene-1,4-diamine
Figure 1. Synthesis of the ligand (L)

Antibacterial Activity of Macrocyclic Complexes
483
Synthesis of Cu(II) complex
The Cu(II) complex was prepared by methanolic solution of Cu(ClO4)2.6H2O salt. This was
slowly added with stirred hot methanolic solution of binucleating Schiff base ligand. After
half an hour phthalaldehyde was added drop wise to the same solution. The strring was
continued for 1 h, after it undergoes reflux for 10-12 h at ≈70 °C. A dark blue colored
precipitate formed was filtered, washed several times with methanol, diethylether and dried
in vaccum15. Yield 64%. Elemental analysis: C56H40N8Cu2Cl4O16 Calcd; C, 49.88, H, 2.96,
N, 8.31, Cu, 9.43%. Found: C, 50.18, H, 309, N, 8.38, Cu, 9.29% Λm, 265 (Ω-1cm2m-1),
ν(C=N), 1609 cm-1, ν(M-N), 510 cm-1, ν(ClO4) 1110 cm-1 and 620 cm-1 , UV-vis (λmax
DMSO: d↔d, 580 nm.
)
Synthesis of Ni(II) complex
The same procedure was adopted for Ni(ClO4)2.6H2O complex. It undergone reflux until
dark green color precipitate was formed. Yield 66%. Elemental analysis:
C56H40N8Ni2Cl4O16, Calcd: C, 50.24, H, 2.99, N,8.37, Ni, 8.77%, Found: C, 50.43, H, 2.89,
N, 8.25, Ni, 8.80% Λm 223 (Ω-1cm2m-1), IR (KBr pellet) ν(C=N),1617 cm-1, ν(M-N), 538 cm-1,
ν(ClO4) 1086, cm-1and 626 cm-1, UV-vis (λmax) DMSO: d↔d, 520 nm.
Synthesis of vanadyl complex
The same procedure was adopted for VOSO4.4H2O complex. It gave steel blue color
precipitate. Yield 62%, C56H40N8V2S2O10, Calcd: C, 58.44, H, 3.47, N, 9.74,V2, 8.86%,
Found: C,57.98, H, 3.29, N, 9.30, V2, 9.92% Λm, 139 (Ω-1cm2m-1), ν(C=N), 1599 cm-1,
ν(M-N), 515 cm-1, ν(SO4) 1084 cm-1, ν(V=O) 943 cm-1 , UV-vis (λmax) DMSO: d↔d, 531 nm.
Antibacterial studies
The antibacterial activity of the macrocyclic binuclear Cu(II), Ni(II) and VO(II) complexes
were checked by the disc diffusion technique16. This was done on gram negative bacterial
like Klebsiella pneumoniae, Escherichia coli and gram positive bacterial like
Staphylococcus aureus at 37°C. The disc of Whatman no. 4 filter paper having the diameter
8.00 mm were soaked in the solution of compounds in DMSO (1.0 mg cm-1). After drying it
was placed on nutrient agar plates. The inhibition areas were observed after 36 hours.
DMSO was used as a control and Stremptomycin as a standard.
Results and Discussion
A novel macrocyclic binuclear Cu(II), Ni(II) and VO(II) Schiff base complexes have been
synthesized by template condensation of binucleating schiff base ligand with metal salt and
o-phthalaldehyde. All the complexes were crystalline in nature, dark colored solid, stable at
room temperature and soluble in DMF or DMSO. The ligand can be confirmed by 1H NMR.
All the complexes gave satisfactory elemental analysis results with the proposed structure of
the complexes. The formation and their geometry were further confirmed by IR, UV Vis,
magnetic, EPR spectral studies. The ligand and complexes were also screened for
antibacterial activity against bacteria species.
1H NMR spectra of Schiff base ligand
The formation of Schiff base ligand was observed by peak ratios in the 1H NMR spectra. 1H-
NMR spectra of the ligand was taken using DMSO d6 solvent (Figure 2). The aromatic
region was a set of multiplets in the range of 6–7.5 ppm, while the azomethine proton was
observed in the range 8.25 ppm.

484
R. RAJAVEL et al.
Figure 2. 1H NMR Spectra of ligand in DMSO-d6
Magnetic and electronic studies
The electronic spectra of the Schiff base ligand and its complexes were recorded in DMSO
solution. The absorption spectrum of free ligand consist of an intense bands centered at 265
nm and 370 nm attributed to π–π* and n– π* transition within the Schiff base ligand. These
transitions are also found in spectra of the complexes, but they shifted, confirming the
coordination of ligand to metal ions17. Further, the d-d transition showed a strong band at 580 nm
2
2
for Cu(II) complex, this is due to B1g → A1g. This transition shows the square plannar
geometry around the metal18. In room temperature magnetic moment values for Cu(II) is 1.65
B.M. In general, the low magnetic moment values of binuclear copper complex are attributed
to the antiferromagnetic interaction between two central Cu(II) metal ions19.
The spectra of Ni(II) complex in the visible region at about 520 nm and 480 nm is
assigned to 1A1g → 1A2g, 1A1g → 1B1g, transitions, suggesting an approximate square planar
geometry of the ligand around the metal ions20. The magnetic moment data of VO(II)
complex was 1.75 B.M., which confirms the binuclear structure of the complex. The intense
2
charge transfer band at 531 nm in VO(II) complex assigned to B2 →2E transition. This is
due to electron delocalization over whole molecule on complexation. Based on these data, a
square pyramidal geometry has been assigned to the complex VO(II)21,22
EPR spectral studies
The X-band EPR spectrum of the Cu(II) and VO(IV) complexes were recorded at room
temperature. Cu(II) complex consists of an axial symmetrical signal with gll= 2.12 and g┴ = 2.05.
2
The unpaired electron lies in the (dx2–y2) orbital giving B1g as the ground state with the
gll > g⊥ > ge (2.0023 free spin value)23. The observed gll value for square planner geometry
Cu(II) complex is less than 2.3, which is in agreement with the covalent character of metal
ligand bond24. G value less than 4 indicates a considerable metal - metal interaction in a
complex25. Vanadyl complexes show peaks with gll= 2.08 and g┴ = 2.01 which indicates
that the unpaired electron is present in the dxy orbital with square pyramidal geometry
around the VO(II) chelates26.

Antibacterial Activity of Macrocyclic Complexes
485
Antibacterial activity
The Schiff base ligand and their macrocyclic binuclear Schiff base complexes were tested in
vitro to assess their growth inhibitory activity against Gram negative bacterial like Klebsiella
pneumoniae, Escherichia coli and gram positive bacterial like Staphylococcus aureus are
given in Table 1. The antibacterial activity of complexes arises due presence of several
azomethine groups which coordinate with metal ions. Cu(II) has more activity than ligand
and other complexes. Difference in the effectiveness was depends on the impermeability of
microbial cells or on the difference in ribosome of microbial cells27. The increase in
antibacterial activity of metal chelates with increase in concentration is due to the effect of
metal ion on normal cell processes. Such increases in activity of metal chelates can be
explained on the basis of chelation theory28. On chelating, the polarity of the metal ion will
be reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of
positive charge of metal ion with donor groups. Further, it increases the delocalization of π-
electrons, enhances liphophilicity and penetration of the complexes which blocks metal binding
sites on enzymes of microorganism. These complexes also disturb the respiration process of cell
and thus block the synthesis of proteins, which restricts further growth of organism29,30
.
Table 1. Antibacterial activity of the ligand and complexes
Bacterial inhibition, %
Compound
S.aureus
+++
++
K. pneumoniae
E.coli
+++
++
C20H18N4
+++
++
C56H40N8Cu2Cl4O16
C56H40N8Ni2Cl4O16
C56H40N8V2S2O10
+++
+++
++
+++
+++
++
*50% growth by ++, less than 50% growth by +++
Conclusion
A novel macrocyclic binuclear schiff base ligand and complexes have been synthesized by
using freshly prepared o-aminobenzaldehyde with p-phenylenediamine, and o-phthalaldehyde
with respective metal salts. The metal-ligand ratio of 1:1 has been arrived at by estimating
the elemental contents. The presence of counter ions has been confirmed from the IR and
high molar conductance values. 1H NMR confirms the complete condensation of the ligand.
ESR shows a covalent bonding nature of the complexes and also the geometry of the
complexes. The antibacterial activity for Cu(II) complexes was more pronounced because of
the chelation theory.
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