1. INTRODUCTION:
In recent years, the chemistry of coordination
compounds has shown a rapid development in diverse disciplines as a result of
the possible use of these new compounds in biological applications. Transition
metal complexes with potential biological activity are the focus of extensive
investigations. Oximes and azo dyes have often been used as chelating ligands
in the field of coordination chemistry and their metal complexes have been of
great interest for many years. The biological importance of oximes and their
complexes is very well known.1 Different oximes and their metal
complexes have shown notable bioactivity as chelating therapeutics, as drugs,
as inhibitors of enzymes and as intermediates in the biosynthesis of nitrogen
oxides.2,3
Transition metal complexes with o-hydroxy aromatic
oximes have attracted much attention as they exist as cis and trans geometrical
isomers. Copper complexes are known to assume trans structures while cobalt
complexes have cis structures.4 The presence of mildly acidic
hydroxyl groups and slightly basic nitrogen atoms makes vic-dioximes amphoteric
ligands, which form square-planar, square-pyramidal or octahedral complexes
with transition metal ions such as Ni(II), Co(II) and Cu(II) as the central
atom.5
Salicylaldoxime and its derivatives have been the
focus of comprehensive research in coordination chemistry6-10.
Because of their richly painted complexes with a wide structural variety
developed with the majority of transition metals11-15. Due to the
importance of oxime compounds and in continuance of interest in the synthesis,
spectral properties of salicylaldoxime compound and its Mn(II) complexes are
reported herein.
2. METERIALS AND METHODS:
2.1 Chemicals:
All chemicals used in this work were reagent grade
(BDH/ Aldrich), including the metal salts i.e. MnSO4.6H2O,
Ethanol, salicylaldehyde, hydroxylamine hydrochloride, chloroform, DMSO, CaCl2,
NH4OH. Double distilled water was used.
2.2 Instruments:
The percentage compositions of C, H, and N of
complexes were determined by using micro analytical methods on Perkin Elmer
240C (USA) elemental analyzer. Infrared spectra of the ligand and its complexes
were carried out by using KBr pellets in the range (4000-400 cm-1)
on Bruker Infra red model 337. The electronic absorption was carried out by
using a Shimadzu UV-1601 using DMSO as solvent. The mass spectrum was recorded
by ESI technique on VG AUTOSPEC mass spectrometer instrument. The 1H
spectrum was recorded on Varian Gemini Unity Spectrometer by employing TMS as
internal standard. Melting points of the ligand and decomposition temperature
of complexes were determined on Polmon instrument (model No.MP-96). The Molar
conductance measurements were carried out in DMSO (10-3 M) using
Digisun Electronic Digital conductivity meter of model: DI-909 having a
dip-type cell calibrated with KCl.
2.3 Biological activity:
The antimicrobial tests were performed by the standard
disc diffusion method. The antibacterial activity of the complexes was studied
against E. coli, S.aureus and Klebsiella pneumonia. Each
of the metal complex compounds dissolved in ethanol at a concentration of 1
mg/ml was prepared. Paper discs of Whatman filter paper no. 1 were cut and
sterilized in an autoclave. The paper discs were saturated with 10μl of
the metal complex compounds dissolved in ethanol solution or ethanol as
negative control and were placed aseptically in the Petri dishes containing
Nutrient agar media inoculated with the above mentioned two bacteria
separately. The petridishes were incubated at 370C and the
inhibition zones were recorded after 24 h of incubation.
3. RESULTS AND DISCUSSION:
3.1 Synthesis of Salicylaldoxime (SAOX):
Dissolve 3g (0.164mol) of salicyladehyde was dissolved
in 10ml rectified spirit, add a solution of 1.5g (0.216mol) of hydroxylamine
hydrochloride in 10ml of water and render the mixture just alkaline with 10
percent, sodium carbonate solution while cooling in ice. The reaction mixture
was allowed to stand overnight. The solution was acidified with acetic acid,
distill off the alcohol under reduced pressure on a rotary evaporator, dilute
with twice the volume of water and extract with two 50ml portions of ether. The
ether extract was dried with sodium sulphate or magnesium sulphate, distill off
most of the ether and allow the residue to crystallise. The Reaction equation
of synthesis of the SAOX is shown in fig.1. The yield of salicylaldoxime (m.pt:
1570C) is 1.2g.
Figure.1 Reaction equation of synthesis of the SAOX
3.2 Preparation of [Mn(SAOX)2]
A solution of salicylaldoxime (Salox) (0.378gm, 2.000
mmole) in EtOH (10 mL) with some drops of Et3N was added with
stirring to an aqueous solution of MnSO4 (0.134gm, 1.00mmole) in (10
mL). A dark yellow ppt. was produced directly. The mixture was stirred for
three hours then filtered off and dried in vacuum oven. The reaction equation
of synthesis of the [Mn(SAOX)2] is shown in fig.2 (Yellow, 0.348 g,
78% yield, m.p (2690C).
Figure. 2 Reaction equation of synthesis of the
[Mn(SAOX)2]
3.3 Physical properties:
The physical data for SAOX and [Mn(SAOX)2]
are shown in table.1. The yield of SAOX and [Mn(SAOX)2] are 72% and
78% respectively. The melting point of [Mn(SAOX)2] is greater than
3600C which indicates the formation of chelated complex. The
elemental analytical datas of carbon, hydrogen and nitrogen are similar to the
calculated values. The molar conductance of the [Mn(SAOX)2] is
greater than the SAOX because of the presence of d-d transition in manganese
ion.
3.5 1H NMR Spectral characterization:
The 1H NMR spectrum of SAOX is shown in
Fig.4 (a,b). The 1H-NMR data recorded in DMSO-d6 provided
further evidence for the structural characteristics of the oxime ligand. The 1H-NMR
spectrum of the SAOX compound displayed the presence of a broad singlet signal
due to the hydrogen of aldehyde group at 9.95 ppm, which is lower field shifted
to 8.55ppm in the spectrum of the aldoxime ligand through the oximation
reaction.[16] The spectrum of the SAOX ligand exhibited multiplet signals at
7.45–7.60ppm due to aromatic protons.[17] The strong signals appearing in the
chemical shift ranges 6.42–6.45 ppm can be attributed to the hydrogen of the
–NH of the hydroxyimino group. In addition, the spectrum of the ligand SAOX
showed a singlet signal at 10.20 ppm due to the hydrogen of the –OH group. The 1H-NMR
spectrum of the ligand exhibited a signal at 14.20 ppm, which can be attributed
to the hydrogen bonded OH proton of the hydroxyimino group.
(a)
(b)
Fig.4 (a) 1H NMR spectrum of SAOX in the
region of -2 to 15 ppm (a) and 6 to 8 ppm (b).
Figure.5 EIS-Mass spectrum of SAOX
3.6 EIS-Mass spectrum analysis of SAOX:
The EIS mass spectra of the ligand recorded at room
temperature is shown in fig.5. The ligand [L] shows a molecular ion peak at m/z
207.1, which corresponds to [L+H] peak as the calculated m/z being
206.
3.7 Electronic Spectra:
The electronic spectra of the complexes in 10–3
M DMF solutions at room temperature were recorded and shown in fig.6. The
electronic spectra can often provide quick and reliable information about the
ligand arrangement in transition metal complexes. The electronic spectra of the
SAOX and [Mn(SAOX)2] in DMF showed 3–5 absorption bands between 275
and 661 nm. The ligand showed absorption bands at 421, 348 and 287 nm. These
bands are assigned to the 
and
transitions,
respectively.[18] The electronic absorption spectrum of the [Mn(SAOX)2]
complex showed weak bands at 647 and 440 nm, which are assigned to the 
and
transitions,
respectively. A d5 metal ion, Mn(II) exhibits a preference for
octahedral geometry with oxime complexes. The decrease in the intensities of
the transitions indicated coordination to the nitrogen atoms. The band at 340
nm is due to the charge-transfer transition and that at 275 nm is due to transitions
19.
Figure.6 The electronic spectra of [Mn(SAOX)2]
3.8 Antimicrobial Activity:
The antibacterial activity of SAOX and its [Mn(SAOX)2]
were tested in vitro against bacteria such as E.Coli, S.aureus and Klebsiella
pneumonia by agar disc method. From table.3, it is clear that the
inhibition by metal chelates is higher than that of a ligand and results are in
good agreement with previous findings with respect to comparative activity of
SAOX ligand and [Mn(SAOX)2]. Such enhanced activity of metal
chelates is due to lipophilic nature of the metal ions in complexes. The
increase in activity with concentration is due to the effect of metal ions on
the normal process. The action of compounds may involve the formation of
hydrogen bond with the active center of cell constituents, resulting in
interference with the normal cell process.
4. CONCLUSIONS:
The SAOX and [Mn(SAOX)2] have been
structurally characterized. The spectral data show that the ligand act as
neutral and bidentate coordinating through nitrogen atom of the hydrazine and
oxygen atom of the hydroxyl group of salicylaldehyde. Based on analytical,
molar conductance and spectral data, the complex is assigned to be in
octahedral geometry. Biological studies of the complex reveal that they show
better activity when compared to that of the SAOX.
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