12
M.H. Soliman, G.G. Mohamed / Spectrochimica Acta Part A 91 (2012) 11–17
2.4.2. Sabouraud’s dextrose agar medium (pH 5.6)
It consists of peptone (10 g), dextrose (20 g), agar (15 g), and
distilled water (100 mL).
O
O
O
N
N
S
N
H
H
3. Results and discussion
2
OMe
The formation of metal complexes with drug compounds has
long been recognized. However, the binary complexes of the cited
drug with metal ions have not been studied yet, although they
may be an area of interest. This is because these complexes
may affect the bioavailability of this drug as certain metal ions
were present in relatively appreciable concentration in biological
fluids [8].
OMe
Fig. 1. Structural formula of VER drug.
2.2. Instruments
The molar conductance of the solid complexes in DMF was
measured using Sybron–Barnstead conductometer (Meter-PM.6,
E = 3406). Elemental microanalyses of the separated solid chelates
for C, H, N, and S were performed at the Microanalytical Center,
Cairo University. Infrared spectra were recorded on a Perkin-
Elmer FT-IR type 1650 spectrophotometer in wave number region
4000–400 cm−1. The spectra were recorded as KBr pellets. The
1H NMR spectra were recorded using 300 MHz Varian-Oxford
Mercury. The molar magnetic susceptibility was measured on
powdered samples using the Faraday method. The diamagnetic cor-
rections were made by Pascal’s constant and Hg[Co(SCN)4] was
used as a calibrant. The thermogravimetric (TG and DTG) analy-
3.1. Mass spectrum of VER
The electron impact mass spectrum of VER is recorded and
investigated at 70 eV of electron energy. The mass spectrum of
the studied drug (Supplementary Fig. 1) is characterized by mod-
erate to high relative intensity molecular ion peaks at 70 eV. The
The mass spectrum of VER shows a well-defined parent peak at
m/z = 383.5 (M+) with a relative intensity = 5%. The parent ion and
the fragments obtained by cleavage in different positions in VER
molecule are shown in Scheme 1.
sis was carried out in dynamic nitrogen atmosphere (20 mL min−1
)
with a heating rate of 10 ◦C min−1 using Shimadzu TG-60H thermal
analyzers.
3.2. Composition and structures of metal complexes
The aim of this work is to prepare the solid complexes of the
drug under investigation and carrying out complete characteriza-
tion using different physicochemical techniques. Many attempts
have proven to be the most suitable technique to give enough
information’s to elucidate the nature of bonding of the ligand to
the metal ion. The present works deals specifically the coordina-
tion properties of VER drug (Fig. 1) concerning its interactions with
Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. The bioefficacy of
these complexes has also been examined against the growth of bac-
teria and pathogenic fungi in vitro to evaluate their anti-microbial
potential and in order to throw more light on the effect of chelation
on the drug activity.
2.3. Synthesis of metal complexes
The metal complexes were prepared by the addition of hot solu-
tion (60 ◦C) of the appropriate metal chloride salts (0.278, 0.168,
0.277, 0.248, 0.225, and 0.217 g of Cr(III), Mn(II), Co(II), Ni(II), Cu(II)
and Zn(II), respectively, 1 mmol) in an ethanol–water mixture (1:1,
25 mL) to the hot solution (60 ◦C) of VER (0.4 g, 2 mmol) in the
same solvent (25 mL). The resulting mixture was stirred under
reflux for 1 h whereupon the complexes precipitated. They were
collected by filtration, washed with a 1:1 ethanol:water mixture
and diethylether.
2.4. Biological activity
The isolated solid complexes of Cr(III), Mn(II), Co(II), Ni(II), Cu(II)
yses (C, H, N, S, Cl and metal content), IR, 1H NMR, magnetic moment
studies, molar conductance, and thermal analysis (TG), to identify
their tentative formulae in a trial to elucidate their molecular struc-
tures. The results of elemental analyses listed in Table 1 suggest that
the complexes are formed in 1:2 [Metal]:[VER] ratio and they pro-
posed to have the general formulae [MCl2(VER)2(H2O)2]·yH2O and
[CrCl2(VER)2(H2O)2]Cl·H2O (where M = Mn(II) (y = 2), Co(II) (y = 2),
Ni(II) (y = 2), Cu(II) (y = 1) and Zn(II) (y = 0)).
The antimicrobial activities were carried out by disc diffusion
technique as described in British pharmacopoeia (2003). Nutrient
agar was melted at 45 ◦C and inoculated by the cell suspension
(1 mL/100 mL) bacteria or yeast. The flask was shaken well and
poured into a petri-dish (15 cm in diameter). Filter paper discs
(6 mm) Whatman No. 2 were thoroughly moistened by antibiotics
(50 g), the treated discs were aseptically transferred and placed
and kept in a refrigerator for 1 h to permit diffusion of antimicro-
bial substances. The plates were incubated at 37 ◦C for 24 h in case
of bacteria and at 28 ◦C for 48 h in case of yeast. The zones of inhi-
bition were measured in mm the mean values of inhibitions were
calculated from triple reading in each test [7].
3.3. Molar conductivity measurements
The following media were used in studying the antimicrobial
properties of VER drug and its complexes. The weights are given in
gram per 1-L medium.
Table 1 summarizes the molar conductance values of the com-
plexes (10−3 M) in DMF solvent at 25 ◦C. It is concluded from
the results that, the divalent metal chelates are found to have
molar conductance values of 15.40–24.50 ꢀ−1 mol−1 cm2 indicat-
ing that all the divalent metal chelates are non-electrolytes. The
Cr(III) complex is found to have a molar conductance value of
68 ꢀ−1 mol−1 cm2 indicating its electrolytic nature and of the type
1:1 electrolyte.
2.4.1. Nutrient agar medium (pH 7.4)
It consists of beef extract (1.0 g), yeast extract (2.0 g), peptone
(5.0 g), sodium chloride (5.0 g), agar (15.0 g), and distilled water
(100 mL).