Thermal, spectral and antimicrobial study on some Cu(II) complexes with ligands bearing biguanide moieties

Article abstract of DOI:10.1007/s10973-009-0414-8

New complexes of type [Cu(HTBG)₂]Cl₂ (1), [Cu(TBG)₂]?3H₂O (2) and [CuL]?nH₂O (3) L:L¹, n = 2 and (4) L:L², n = 1 (HTBG: 2-tolylbiguanide, L¹ and L²: ligands resulted from 2-tolylbiguanide, ammonia/hydrazine and formaldehyde one pot condensation) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR and UV-Vis data. Redox behaviour was established by cyclic voltammetry. The in vitro qualitative and quantitative antimicrobial activity assays showed that the complexes exhibited variable antimicrobial activity against Gram-negative and Gram-positive strains isolated from the hospital environment. The thermal analyses have evidenced the thermal intervals of stability and also the thermodynamic effects that accompany them. After water elimination, complexes have a similar thermal behaviour. Processes as water elimination, melting, chloride anion removal as well as oxidative degradation of the organic ligands were observed. The final product of decomposition was copper (II) oxide.

Full text of DOI:10.1007/s10973-009-0414-8

J Therm Anal Calorim (2010) 99:815–821
DOI 10.1007/s10973-009-0414-8
Thermal, spectral and antimicrobial study on some Cu(II)
complexes with ligands bearing biguanide moieties
Rodica Olar Æ Mihaela Badea Æ Dana Marinescu Æ
Emilia Elena Iorgulescu Æ Eliza Frunza Æ
Veronica Lazar Æ Carmen Chifiriuc
MEDICTA2009 Conference
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract New complexes of type [Cu(HTBG)2]Cl2 (1),
[Cu(TBG)2]ꢀ3H2O (2) and [CuL]ꢀnH2O (3) L:L1, n = 2
and (4) L:L2, n = 1 (HTBG: 2-tolylbiguanide, L1 and L2:
ligands resulted from 2-tolylbiguanide, ammonia/hydrazine
and formaldehyde one pot condensation) were synthesised
and characterised. The features of complexes have been
assigned from microanalytical, IR and UV–Vis data. Redox
behaviour was established by cyclic voltammetry. The in
vitro qualitative and quantitative antimicrobial activity
assays showed that the complexes exhibited variable anti-
microbial activity against Gram-negative and Gram-posi-
tive strains isolated from the hospital environment. The
thermal analyses have evidenced the thermal intervals of
stability and also the thermodynamic effects that accom-
pany them. After water elimination, complexes have a
similar thermal behaviour. Processes as water elimination,
melting, chloride anion removal as well as oxidative deg-
radation of the organic ligands were observed. The final
product of decomposition was copper (II) oxide.
Keywords Antimicrobial activity ꢀ Copper (II) complex ꢀ
One pot condensation ꢀ Thermal behaviour ꢀ
o-Tolylbiguanide
Introduction
The increasing incidence of bacterial drug resistance
imposes an improvement of the known antimicrobial drugs
and also the development of new ones. In the last years the
attention in this field was oriented to inorganic species
among the organic ones. Although many complexes
showed a good antimicrobial activity so far only a few are
used as metalloantibiotics (antiseptics and antimicrobial) or
disinfectants [1]. So far a good antimicrobial activity was
observed for complexes bearing a biocation [2–9] and a
multidentate ligand and/or having a proved antimicrobial
activity [3, 9].
Among biocations, copper is preferred having in view:
(i) the low human toxicity associated with the both pres-
ence of the albumin in the plasma and the metalotionein in
the cytosol [10]; (ii) the borderline character and the fact
that forms the most stable complexes among the Irving
Williams series of cations; (iii) the stereochemical versa-
tility; (iv) the easiness to change its oxidation state and (v)
the known biological activity including the ability to inhibit
enzyme, one of the mechanisms responsible by the anti-
microbial activity [11].
R. Olar (&) ꢀ M. Badea ꢀ D. Marinescu ꢀ E. Frunza
Faculty of Chemistry, Department of Inorganic Chemistry,
University of Bucharest, 90-92 Panduri Str. Sector 5, 050663
Bucharest, Romania
e-mail: rodica_m_olar@yahoo.com
E. E. Iorgulescu
As for ligands those having the ability to coordinate as
chelate and/or to generate neutral species are preferred in
order to enhance the complex lipophilicity and thus allow
the biological membranes across [12]. The presence of
some supplementary groups able to interact with biomol-
ecules through hydrogen bond formation or week physical
interaction is also important for such ligands. If these
Faculty of Chemistry, Department of Analytical Chemistry,
University of Bucharest, 90-92 Panduri Str. Sector 5, 050663
Bucharest, Romania
V. Lazar ꢀ C. Chifiriuc
Faculty of Biology, Department of Microbiology, University of
Bucharest, 1-3 Aleea Portocalilor St., Sector 6, 060101
Bucharest, Romania
123

816
R. Olar et al.
ligands posses itself an antimicrobial activity then this
could generate the synergism [13]. Some of these com-
plexes that displays an antimicrobial activity were also
thermal characterised [2, 5, 8].
density, represented by Bacillus subtilis, Bacillus cereus,
Salmonella sp. 361, Staphylococcus aureus M., Staphylo-
coccus aureus ATCC 29213, Pseudomonas aeruginosa
1443, recently isolated from clinical samples. The evalu-
ation of the influence of different complex concentrations
on the ability of the tested bacterial strains to colonize the
inert substratum, a very simple microtitre plate method was
used. In this purpose, the microplates used for the M.I.C.
assay were emptied, washed three times by PBS (phosphate
buffered saline). The biofilm formed on the plastic wells
wall was fixed for 5 min with cold methanol, coloured for
15 min by violet crystal solution and resuspended by 33%
acetic acid solution. Cell density was measured by reading
the optical density of the coloured solution at 490 nm using
an ELISA reader (Apollo LB 911).
Hawing in view the antimicrobial activity of both
biguanide derivatives [14] and complexes [15, 16], we
report here the synthesis and characterization of some
Cu(II) complexes with 2-tolylbiguanide as well as the
ligands obtained by its one pot condensation with ammo-
nia/hydrazine and formaldehyde, in order to evaluate the
biological properties and thermal stability of these deriv-
atives. The complexes have been characterized by different
analytical and spectral methods. The antimicrobial activity
of these derivatives was also assayed against planktonic
microbial strains. The thermal behaviour of these deriva-
tives was investigated in synthetic air flow by thermal
analysis (TG, DTA).
The heating curves (TG and DTA) were recorded using a
Labsys 1200 SETARAM instrument, with a sample mass of
5–24 mg over the temperature range of 20–900 °C, using a
heating rate of 10 K/min. The measurements were carried
out in synthetic air atmosphere (flow rate 16.66 cm3/min),
using alumina crucibles.
Experimental
Materials and methods
The melting was evidenced with Automated Melting Point
System (AMPS) MPA 100 OptiMelt Stanford Research
System.
All reagents were of commercial analytical quality and
have been used without further purification. Chemical
analysis of carbon, nitrogen and hydrogen has been per-
formed using a Perkin Elmer PE 2400 analyzer. Chloride
was determined gravimetrically while copper was deter-
mined volumetrically using thiosulfate method.
The X-ray powder diffraction patterns were collected on
a DRON-3 diffractometer with a nickel filtered Cu Ka
˚
radiation (k = 1.5418 A) in a 2h range of 5–70°, a step
width of 0.05° and an acquisition time of 2 s on each step.
IR spectra were recorded in KBr pellets with a Bruker
Tensor 37 spectrometer in the range 400–4,000 cm-1
Synthesis of the complexes
.
Electronic spectra by diffuse reflectance technique, with
MgO as standard, were recorded in the range 300–1,500 nm,
on a Jasco V670 spectrophotometer.
[Cu(HTBG)2]Cl2 (1): To a solution containing 5 mmol
(0.853 g) copper(II) chloride dihydrate in 50 mL acetonitrile
was added drop wise at 50 °C, under continuous stirring, a
solution of 10 mmol (2.365 g) HTBGꢀHClꢀ0.5H2O. The
reaction mixture was magnetically stirred at 50 °C temper-
ature for 24 h, until a sparingly soluble species, pink col-
oured was formed. The precipitate was filtered off, washed
with ethanol and air-dried.
Cyclic voltammograms were recorded by an electro-
chemical system (potentiostat/galvanostat) Autolab
PGSTAT 12. Electrochemical studies were performed at
room temperature under inert atmosphere (Ar 99.9999%) in
DMSO containing tetrabutylammonium perchlorate (Bu4
NClO4) 0.1 M as supporting electrolyte. The reference
electrode was Ag/AgCl (LiCl saturated in ethanol). The
counter electrode was the platinum wire. The working
electrode was a glassy carbon (GC) with the effective aria of
electrode 7.065 mm2.
[Cu(TBG)2]ꢀ3H2O (2): To a solution of copper chloride
dihydrate (0.853 g, 5 mmol) and KOH (0.561 g, 10 mmol)
in water:ethanol, 3:1 (200 mL) was added a solution of
10 mmol (2.365 g) HTBGꢀHClꢀ0.5H2O until the solution
turns magenta. The reaction mixture was then magnetically
stirred at 50 °C for 30 min, until a solution magenta coloured
was formed. After slow evaporation for one month, dark
violet sparingly soluble specie was formed. The precipitate
was filtered off, washed with ethanol and air-dried.
[Cu(L1)]ꢀ2H2O (3): To a solution of chloride dihydrate
(0.853 g, 5 mmol), HTBGꢀHClꢀ0.5H2O (2.365 g, 10 mmol)
in 50 mL methanol was added drop wise 2 mL formalde-
hyde (37%) and 5 mL ammonia. The reaction mixture was
refluxed 80 h until a brown sparingly soluble compound was
The qualitative screening of the susceptibility spectra of
different microbial strains to the complexes was performed
by adapted diffusion techniques, while the quantitative
assay of minimal inhibitory concentration (M.I.C., lg/cm3)
value was based on liquid medium serial microdilutions
[17]. The compounds were solubilised in DMSO to a final
concentration of 1 mg/mL. The in vitro biological screen-
ing effects were tested against a microbial inoculum of
*1.5 9 108 UFC/cm3, corresponding to 0.5 McFarland
123

Thermal, spectral and antimicrobial study on some Cu(II) complexes
817
CH3
formed. The microcrystalline product was filtered off,
washed with MeOH and air-dried.
H
N
N
Cu
N
NH2
N
CH3
H
N
H
N
NH2
[Cu(L2)]ꢀH2O (4): To a solution of chloride dihydrate
(0.853 g, 5 mmol), HTBGꢀHClꢀ0.5H2O (2.365 g, 10 mmol)
in 50 mL methanol was added drop wise 2 mL formalde-
hyde (37%) and 5 mL hydrazine. The reaction mixture was
refluxed 20 h until a dark brown sparingly soluble com-
pound was formed. The microcrystalline product was fil-
tered off, washed with MeOH and air-dried.
N
N
N
N
+ Cu2+ / R-NH / CH O
2
2
2
N
R
R
NH NH
- 4 H2O
H2N
N
H
CH3
1
(3) [Cu(L )]2H2O (R: H)
(4) [Cu(L )]H2O (R: NH2)
2
Scheme 2 Synthesis of complexes (3) and (4)
Table 1 Elemental analysis for complexes
Results and discussions
Compound %Cu
%C
%H
%N
Synthesis and physico-chemical characterisation
of complexes
Exp. Calc. Exp. Calc. Exp. Calc. Exp. Calc.
(1)
(2)
(3)
(4)
12.23 12.29 41.93 41.82 5.06 5.07 27.17 27.10
12.68 12.76 43.38 43.41 6.05 6.07 28.17 28.12
11.19 11.26 46.87 46.84 6.31 6.43 29.85 29.79
9.98 10.03 45.78 45.86 6.28 6.30 34.12 34.04
The complexes [Cu(HTBG)2]Cl2 (1) and [Cu(TBG)2]ꢀ
3H2O (2) were synthesized by the reaction of copper(II)
chloride with 2-tolylbiguanide hydrochloride semihydrate
(HTBGꢀHClꢀ0.5H2O) in neutral and basic condition
respectively (Scheme 1).
Electronic spectra of the complexes (1) and (2) show a
Condensation of [Cu(TBG)2]ꢀ3H2O with ammonia or
hydrazine and formaldehyde resulted in neutral new com-
plexes [CuL]ꢀnH2O (3) L:L1, n = 2 and (4) L:L2, n = 1
(L1 and L2: ligands resulted from ammonia or hydrazine
system) formation (Scheme 2).
single narrow band at high energy, as is usually observed
for Cu(II) complexes with a square planar stereochemistry
[20]. For complex (3) and (4), the broad bands that appear
have a splitting tendency in two or three components.
The absorption maxima is shifted to higher values for
Cu(II) series of complexes as an indicative of the crystal-
line field increasing in the ligand series: HTBG ? TBG ?
L1 ? L2.
The electrochemical investigation of the complexes was
studied using cyclic voltammetry at different scan rates
(10–400 mV s-1) in the potential range from ?1.0 to
-1.0 V (Fig. 1). Cyclic voltammograms for all the com-
plexes show one or two quasireversible redox processes
(Table 2) due to copper ion only, more or less pronounced,
in concordance with both ligand nature and scan rate
[21]. It was observed that 2-tolylbiguanide (HTBG) is
redox silent. In comparison with the reference complex
[Cu(DMSO)4]Cl2 that in the working conditions is reversible
The elemental analyses show 1:2 and 1:1 stoichiometry
respectively for compounds (Table 1).
The IR spectra of complexes reveal the characteristic
bands of biguanide and 2-substituted benzene moieties
respectively. The intense band characteristic to m(C=N)
vibration mode in the 1,650–1,680 cm-1 range, appears
shifted to higher wavenumbers in the complexes spectra as
result of coordination. The new band at about 1,330 cm-1
can be assigned to chelate ring formation by the biguanide
derivatives [18]. For complex (4) in the characteristic range
of d(NH2) vibrations more bands appear in accord with the
supplementary amine groups inserted in the macrocycle
structure by the hydrazine. The water presence in complexes
(2)–(4) generates a broad band around 3,650 cm-1 [19].
-5
0.125×10
[4]
-5
0.083×10
2+ / 0
CH3
H
-5
[3]
0.042×10
N
N
Cu
N
NH2
CH3
H
N
H
N
0
NH2
HN
HN
NH
NH
+ Cu2+
-5
-0.042×10
-0.083×10
-0.125×10
2
NH NH
-5
-5
H2N
N
H
-1.100 -0.838 -0.575 -0.313 -0.050 -0.213 -0.475 -0.738 -1.000
CH3
E/V
(1) [Cu(HTBG)2]Cl2
(2) [Cu(TBG)2]3H2O
Fig. 1 Cyclic voltammograms for (3) and (4) recorded in DMSO at
GC electrode (scan rate 50 mV s-1
,
complex concentration
Scheme 1 Synthesis of complexes (1) and (2)
2 9 10-4 M, supporting electrolyte [Bu4N]ClO4 0.1 M)
123

818
R. Olar et al.
2-tolylbiguanide hydrochloride semihydrate presents the
widest activity spectrum against most of the tested strains,
being active both on Gram positive and Gram negative ones,
being particularly efficient against Staphylococcus aureus
strains. Complex (3) exhibits a 31.25 lg/ml MIC against
Bacillus cereus strains, demonstrating a very good antimi-
crobial activity against these sporulating bacteria.
Table 2 Peak potentials for complexes in DMSO solution containing
0.1 M [Bu4N]ClO4 (scan rate 50 mV s-1
)
Complex
(1)
(2)
(3)
(4)
Epc1 (V)
Epc2 (V)
Epc3 (V)
Epa1 (V)
Epa2 (V)
?0.325
-0.108
-0.541
-0.279
?0.557
–
?0.285
–
?0.295
–
-0.339
–
-0.636
-0.155
?0.520
–
-0.219
?0.739
-0.128
?0.335
It must be mentioned that the used solvent, DMSO, did
not influence the antimicrobial activity of the tested com-
pounds at the working concentrations.
Concerning the influence of different concentrations of the
tested compounds, either MIC or subinhibitory concentra-
tions, on the bacterial adherence to the inert substratum,
the results were different, depending on the tested strains and
complex. The compound (1) inhibits the adherence of
Pseudomonas aeruginosa while HTBG and complexes (1)
and (3) inhibited that of S. aureus strains to the inert substra-
tum, even at very low concentrations. The S. aureus reference
strain was very susceptible to all tested compounds.
reducible on the glassy carbon electrode (GC) (Epc1
=
?0.275 V), the complexes displays more positive values for
the first reduction potential, excepting complex (2) that
follows a single reduction step. This behaviour can be cor-
related with the supplementary stability induced by the
chelate rings formation.
Biological activity
The antimicrobial activity of the tested compounds was
performed against microbial strains, the majority of them
being isolated from different clinical samples and exhib-
iting different resistance patterns.
Thermal behaviour of compounds
The results concerning the thermal decomposition/degra-
dation of the 2-tolylbiguanide hydrochloride semihydrate
and complexes are presented in Table 3.
All tested compound exhibit a good antimicrobial activity
(with MIC values ranging from 1.953 to 1,000 lg/ml). The
Table 3 Thermal behaviour data (in synthetic air flow) for o-tolylbiguanide hydrochloride and complexes
Compound
Step
Thermal effect
Temperature range/°C
Dmexp/%
Dmcalc/%
HTBGꢀHClꢀ0.5H2O
1.
Endothermic
Endothermic
Exothermic
Exothermic
Exothermic
Endothermic
Exothermic
Exothermic
Exothermic
80–110
126a
3.7
0
3.8
0
2.
3.
168–240
240–410
410–790
220a
15.3
39.0
41.9
0
15.4
38.9
41.9
0
4.
5.
[Cu(HTBG)2]Cl2
1.
2.
220–254
254–390
390–810
7.0
7.1
3.
36.0
41.5
15.5
10.7
36.8
36.6
15.9
6.3
35.6
41.9
15.4
10.8
37.0
36.2
16.0
6.4
4.
Residue CuO
[Cu(TBG)2]ꢀ3H2O
[Cu(L1)]ꢀ2H2O
[Cu(L2)]ꢀH2O
1.
Endothermic
Exothermic
Exothermic
60–165
190–410
410–900
2.
3.
Residue CuO
1.
Endothermic
Exothermic
Exothermic
50–125
125–373
373–640
2.
32.2
46.7
14.8
2.9
32.7
46.8
14.1
3.1
3.
Residue CuO
1.
Endothermic
Exothermic
Exothermic
64–110
110–435
435–775
2.
31.6
51.4
14.1
32.0
51.1
13.8
3.
Residue CuO
a
Melting point
123

Thermal, spectral and antimicrobial study on some Cu(II) complexes
819
20
weight corresponding to complex leads to a higher melting
point in comparison with 2-tolylbiguanide hydrochloride
semihydrate.
0
15
-20
-40
10
The first step of compound thermal transformation
consists in an exothermic elimination of hydrochloric acid
(Table 3), moreover the chemical analysis of intermediate
isolated at 270 °C confirm the chloride absence. The sec-
ond step, exothermic also, is not a single one being an
overlapping of at least three processes as DTA curve
indicates. This step corresponds to the partial oxidative
degradation of 2-tolylbiguanide according to the mass lost.
Next step, exothermic also, consists in at least five pro-
cesses (according to DTA curves profile) and leads at CuO
(found/calcd. overall mass loss: 84.5/84.6%). The residue
nature was confirmed with powder X-ray diffraction
(ASTM 5-661).
5
0
-60
-5
-80
-10
-15
-100
0
200
400
600
800
1000
Temperature/°C
Fig. 2 TG and DTA curves of HTBGꢀHClꢀ0.5H2O
The 2-tolylbiguanide hydrochloride decomposition
starts with water elimination (Fig. 2) follows by the
hydrochloride specie melting at 126 °C, process evidenced
with the AMPS also.
Thermal decomposition of [Cu(TBG)2]ꢀ3H2O
The decomposition of complex (2) comprises also three
steps and starts with water elimination, process that occurs
at low temperatures (Fig. 4). This indicates the crystalli-
sation nature of the water molecules, behaviour observed
for other complexes having this type of water in compo-
sition [22–25].
Thermal decomposition follows then in three exother-
mic steps. After melting, the degradation starts with
HCl elimination. The following steps are an overlapping
of at least three processes as DTA indicates and corre-
sponds with the gradually oxidative degradation of the
2-tolylbiguanide.
The anhydrous specie is then stable over a 25 °C tem-
perature range. The thermal degradation of this interme-
diate starts at 170 °C and comprises two steps. The second
step occurs in two exothermic processes as both TG and
DTA profile indicate while at least four processes
(according to both TG and DTA) can be noticed in the last
step. Finally, the oxidative degradation leads to CuO in at
least five processes (overall mass loss found/calcd:
84.1/84.4%). The IR spectrum of the residue displays a band
at 472 cm-1 assigned to m(Cu–O) vibration mode [19].
Thermal decomposition of [Cu(HTBG)2]Cl2
The TG and DTA curves corresponding to the complex (1)
indicate that after melting, decomposition follows also
three steps (Fig. 3).
The compound is anhydrous and it is stable up to
220 °C, where the compound melts, the melting being
confirmed with the AMPS instrument. The higher molar
0
30
20
10
0
-20
15
-20
10
5
-40
-60
-40
0
0
-60
-5
-10
-10
-80
-80
-20
-100
-100
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature/°C
Temperature/°C
Fig. 3 TG and DTA curves of [Cu(HTBG2)]Cl2
Fig. 4 TG and DTA curves of [Cu(TBG)2]ꢀ3H2O
123

820
R. Olar et al.
40
remaining fragment oxidative elimination. The final prod-
uct is CuO (found/calcd. overall mass loss: 85.9/86.2%).
0
-20
-40
-60
-80
30
20
Conclusions
10
0
Complexes of Cu(II) with tolylbiguanide moieties were
characterised in order to obtain new effective antibacterial
agents.
-10
Electronic spectra of complexes are characteristic for a
square planar stereochemistry, while the modifications in
the IR spectra of complexes indicate a chelate coordination
of the biguanide moieties.
-100
-20
1000
0
200
400
600
800
Temperature/°C
The cyclic voltammograms indicates for all complexes
that the quasireversibility of the Cu(II)/Cu(I) and
Cu(I)/Cu(0) reduction steps is influenced by the nature of
ligand.
Fig. 5 TG and DTA curves of [Cu(L1)]ꢀ2H2O
The in vitro antimicrobial activity assays showed that
the complexes exhibit a good antimicrobial activity against
Gram-negative and Gram-positive strains. Moreover, some
compounds inhibit the ability of Pseudomonas aeruginosa
and S. aureus to colonize the inert substratum.
90
80
70
60
50
40
30
20
10
0
-20
Thermal decomposition of complexes allowed us to
establish the number and nature of water molecule, the
composition and also the intervals of thermal stability. The
thermal degradation occurs in four steps for the organic
derivative and the 2-tolyl hydrochloride melting was
observed before decomposition. After water elimination up
to 160 °C, the complexes decompose in two steps leading
to copper(II) oxide as final product. The results are in good
concordance with the complexes composition.
-40
-60
0
-80
-10
-20
1000
-100
0
200
400
600
800
Temperature/°C
Fig. 6 TG and DTA curves of [Cu(L2)]ꢀH2O
References
Thermal decomposition of [Cu(L1)]ꢀ2H2O
1. Bertini I, Grey HB, Stiefel EI, Valentine JS. Biological Inorganic
Chemistry. Structure and reactivity. Sausalito, Califonia: Uni-
versity Science Books; 2007. p. 95.
2. Nomiya K, Yoshizawa A, Kasuga NC, Yokoyama H, Hirakawa
S. Synthesis, solid-state characterization and antimicrobial
activities of three different polymorphs of a copper(II) complex
with 4-isopropyltropolone (hinokitiol). Inorg Chim Acta. 2004;
357:1168–76.
According to the TG profile the decomposition of [Cu(L1)]ꢀ
2H2O (3) occurs in three, well-defined steps (found/calcd.
overall mass loss: 85.2/85.9%) (Fig. 5).
After water loss also at low temperatures (50–125 °C
range), the partial oxidative degradation starts with tolyle
moieties as IR spectrum indicate. In the last step, the pa-
racyanide oxidative degradation leads to CuO.
´
´
´
´
3. Miodragovic DU, Bogdanovic GA, Miodragovic ZM, Radulovic
´
´
M-D, Novakovic SB, Kaluderovic GN, et al. Interesting coordi-
nation abilities of antiulcer drug famotidine and antimicrobial
activity of drug and its cobalt(III) complex. J Inorg Biochem. 2006;
100:1568–74.
Thermal decomposition of [Cu(L2)]ꢀH2O
4. El-Ayaan U, El-Metwally NM, Youssef MM, El Bialy SAA.
Perchlorate mixed–ligand copper(II) complexes of beta-diketone
and ethylene diamine derivatives: thermal, spectroscopic and
biochemical studies. Spectrochim Acta A. 2007;68:1278–86.
5. Singh K, Singh Barwa M, Tyagi P. Synthesis and characterization
of cobalt(II), nickel(II), copper(II) and zinc(II) complexes with
Schiff base derived from 4-amino-3-mercapto-6-methyl-5-oxo-
1,2,4-triazine. Eur J Med Chem. 2007;42:394–402.
The water elimination can be observed for complex (4) also
up to 110 °C (Fig. 6). According with the mass loss and IR
spectrum, the oxidative degradation starts also with o-tolyl
moieties removal in two interfering processes (as both TG
and DTA curves indicate). Next step comprises also at least
two processes (according to DTA) and consists in the
123

Thermal, spectral and antimicrobial study on some Cu(II) complexes
821
6. Efthimiadou EK, Katsaros N, Karaliota A, Psomas G. Mononu-
clear copper(II) complexes with quinolones and nitrogen-donor
heterocyclic ligands: synthesis, characterization, biological
activity and interaction with DNA. Inorg Chim Acta. 2007;360:
4093–102.
7. Sathisha MP, Shetti UN, Revankar VK, Pai KSR. Synthesis and
antitumor studies on novel Co(II), Ni(II) and Cu(II) metal com-
plexes of bis(3-acetylcoumarin)thiocarbohydrazone. Eur J Med
Chem. 2008;43:2338–47.
of cobalt(II), zinc(II), palladium(II) and platinum(II) complexes
with N,N-dimethylbiguanide. J Therm Anal Calorim. 2005;80:
451–5.
16. Olar R, Badea M, Grecu MN, Marinescu D, Lazar V, Balotescu
C. Thermal behavior, spectroscopic and biological characteriza-
tion of copper(II) complexes with N,N-dimethylbiguanide. J
Therm Anal Calorim. 2008;92:239–43.
17. Balotescu M-C, Oprea E, Petrache L-M, Bleotu C, Lazar V.
Antibacterial, antifungal and cytotoxic activity of Salvia offici-
nalis essential oi land tinctures, Roum. Biotech Lett. 2005;10:
2471–9.
8. Gudasi KB, Patil MS, Vadavi RS. Synthesis, characterization of
copper(II), cobalt(II), nickel(II), zinc(II) and cadmium(II) com-
plexes of [7-hydroxy-4-methyl-8-coumarinyl]glycine and
comparitive study of their microbial activities. Eur J Med Chem.
2008;43:2436–41.
a
18. Babykutty PV, Prabhakaran CP, Anantaraman R, Nair CGR.
Electronic and infrared spectra of biguanide complexes of the 3d-
transition metals. J Inorg Nucl Chem. 1974;36:3685–8.
19. Nakamoto K. Infrared and Raman spectra of inorganic and
coordination compounds. New York: Wiley; 1986. p. 228–9.
20. Lever ABP. Inorganic electronic spectroscopy. Amsterdam:
Elsevier; 1986. p. 554.
9. Efthimiadou EK, Katsarou ME, Karaliota A, Psomas G. Copper(II)
complexes with sparfloxacin and nitrogen-donor heterocyclic
ligands: structure–activity relationship. J Inorg Biochem. 2008;
102:910–20.
10. Wang T, Guo Z. Copper in medicine: homeostasis, chelation
therapy and antitumor drug design. Curr Med Chem. 2006;13:
525–37.
21. Zanello P. Inorganic electrochemistry: theory, practice and
application. Cambridge, UK: Royal Society of Chemistry; 2003.
p. 302–313.
11. Louie AY, Meade TJ. Metal complexes as enzyme inhibitors.
Chem Rev. 1999;99:2711–34.
12. Fricker SP. Metal based drugs: from serendipity to design. Dalton
Trans 2007:4903–17.
13. Thompson KH, Orvig C. Metal complexes in medicinal chem-
istry: new vistas and challenges in drug design. Dalton Trans
2006:761–4.
22. Modi CK, Patel MN. Synthetic, spectroscopic and thermal
aspects of some heterochelates. J Therm Anal Calorim. 2008;94:
247–55.
23. Abou El-Enein SA. Polymeric and sandwich Schiff’s bases
complexes derived from 4,40-methylenedianiline. Characteriza-
tion and thermal investigation. J Therm Anal Calorim. 2008;91:
929–36.
14. Olar R, Badea M, Lazar V, Balotescu C, Cristurean E, Marinescu
D. Thermal behaviour of some N,N-dimethylbiguanide deriva-
tives displaying antimicrobial activity. J Therm Anal Calorim.
2007;88:323–7.
15. Olar R, Badea M, Cristurean E, Lazar V, Cernat R, Balotescu C.
Thermal behavior spectroscopic and biological characterization
24. Gaber M, Rehab AF, Badr-Eldeen DF. Spectral and thermal
studies of new Co(II) and Ni(II) hexaaza and octaaza macrocyclic
complexes. J Therm Anal Calorim. 2008;91:957–62.
25. Vikram L, Sivasankar BN. Hydrazinium metal(II) and metal(III)
ethylenediamine tetraacetate hydrates. Spectral, thermal and XRD
studies. J Therm Anal Calorim. 2008;91:963–70.
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