The physicochemical and biological properties of zinc(II) complexes

Article abstract of DOI:10.1007/s10973-006-8115-z

Spectroscopic (IR), thermoanalytical (TG/DTG, DTA) and biological methods were applied to investigate physicochemical and biological properties of seven zinc(II) complex compounds of the following formula Zn(HCOO)₂? 2H₂O (I), Zn(HCOO

Full text of DOI:10.1007/s10973-006-8115-z

Journal of Thermal Analysis and Calorimetry, Vol. 88 (2007) 2, 355–361
THE PHYSICOCHEMICAL AND BIOLOGICAL PROPERTIES OF
ZINC(II) COMPLEXES
Erika Szunyogová1, Dagmar Mudro×ová2, Katarína Györyová3*, Radomíra Nemcová2,
Jana Kováéová4 and Lenka Piknová-Findoráková3
1Department of Biophysics, Slovak Academy of Science, Bulharská 6, 040 01 Košice, Slovak Republic
2Research Institute of Gnotobiology and Prevention of Diseases in Young, University of Veterinary Medicine, Komenského 73
041 81 Košice, Slovak Republic
3Department of Inorganic Chemistry, P. J. Šafarik University, Moyzesova 11, 041 54 Košice, Slovak Republic
4Institute of Macromolecular Chemistry AV ‡R, Heyrovského nám. 2, 162 06 Praha 6, Czech Republic
Spectroscopic (IR), thermoanalytical (TG/DTG, DTA) and biological methods were applied to investigate physicochemical and bi-
ological properties of seven zinc(II) complex compounds of the following formula Zn(HCOO)2·2H2O (I), Zn(HCOO)2·tph (II),
Zn(CH3COO)2·2H2O (III), Zn(CH3COO)2·tph (IV), Zn(CH3COO)2·2phen (V), Zn(CH3CH2COO)2·2H2O (VI),
Zn(CH3CH2CH2COO)2·2H2O (VII), where tph=theophylline, phen=phenazone. The formation of various intermediates during ther-
mal decomposition suggests the dependence on the length of aliphatic carboxylic chain and type of N-donor ligand (tph, phen). The
final product of the thermal decomposition was ZnO. The antimicrobial activity of these complexes were tested against G+ and G–
bacteria. Strong inhibitive effect was observed towards E. coli, salmonellae and Staph. aureus.
Keywords: antimicrobial activity, complexes, IR spectra, thermal properties, Zn(II)
Introduction
This paper presents results in thermoanalytical
study and biological activity of further zinc(II)
carboxylate compounds.
Zinc is an essential microelement for all living systems
including also microorganisms. Zinc is required to
maintain normal physiological and biochemical func-
tions in cells. It is a structural and catalytic cofactor in
many bacterial metalloproteins, e.g. zinc-dependent
proteinase in the cell wall of Lactobacillus delbrueckii
subsp. bulgaricus, phospholipase C in Bacillus cereus,
alcohol dehydrogenase isolated from Mycobacterium
bovis, Bacillus subtilis and Helicobacter pylori [1–3].
On the other hand zinc inhibits the growth of a lot of
bacteria, e.g. Escherichia coli, Streptococcus faecalis
and some strains of soil bacteria [4]. This inhibiting ef-
fect of zinc has been used successfully in the treatment
of E. coli diarrhoe in post-weaning piglets [5]. More-
over, zinc is used in prevention and therapy of many
illnesses itself or as a component of drugs (e.g. zinc
bacitracin) and biopreparations. Despite its antimicro-
bial effect, influence of zinc on the probiotic lacto-
bacilli is poorly known.
Materials and methods
The following chemicals of A.R. grade were used for
the synthesis of the compounds: ZnCO3 (Lachema),
HCOOH 86% (Lachema), CH3COOH 98%
(Lachema), CH3CH2COOH 99% (Lachema),
CH3CH2CH2COOH 98% (Merck), theophylline
(Aldrich), phenazone (Aldrich).
Preparation of the complexes
Compounds (I, III, VI, VII) were prepared by the
gradual addition of 0.01 mole appropriate carboxylic
acid to a water solution of 0.005 mole zinc carbonate.
Compounds (II, IV, V) were prepared by dissolving
phenazone or theophylline in hot water, followed by
addition of a water solution 0.01 mole appropriate
carboxylato Zn(II) complexes in a molar ratio 4:1. Af-
ter stirring, the solutions were reduced in volume at
70°C in a water bath and left to crystallize at room
temperature. The complexes which formed were fil-
Zinc(II) carboxylates form a part of coordination
compounds that are studied from chemical and bio-
logical viewpoints. Our scientific research has been
focused on the study of syntheses, spectral, thermal,
structural, chromatographic and biological properties
of zinc(II) carboxylate complex compounds [6–9].
*
Author for correspondence: gyoryova@upjs.sk
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2007 Akadémiai Kiadó, Budapest

SZUNYOGOVÁ et al.
Table 1 The results of chemical analysis of the synthesized compounds
C/%
H/%
N/%
Zn/%
Compound
theor.
exp.
theor.
exp.
theor.
exp.
theor.
exp.
Zn(HCOO)2·2H2O
15.44
32.18
21.87
36.30
55.80
29.11
34.90
15.01
31.97
21.73
36.25
55.54
29.01
34.76
3.81
3.00
4.59
3.88
5.40
5.70
6.59
3.05
2.98
4.40
3.71
5.22
5.65
6.42
0.00
16.69
0.00
0.00
16.52
0.00
15.38
9.92
0.00
0.00
34.15
19.48
29.79
17.98
11.68
26.43
23.70
33.92
18.50
29.20
16.60
10.70
26.25
23.58
Zn(HCOO)2·tph
Zn(CH3COO)2·2H2O
Zn(CH3COO)2·tph
15.41
10.01
0.00
Zn(CH3COO)2·2phen
Zn(CH3CH2COO)2·2H2O
Zn(CH3CH2CH2COO)2·2H2O
0.00
tered off, washed with diethyl ether and dried at room
temperature.
powder diffraction analyser MIKROMETA 2 (Czech
Republic).
Instrumental measurements
Antimicrobial activity
The content of C, H and N was determined by CHN
analyser PERKIN ELMER 2400 and zinc content was
determined complexometrically using Complexone
III as an agent and eriochrome black T as an indicator.
IR spectra were recorded with EXCALIBUR
FTS 3000 MX FTIR spectrophotometer in the region
4000–400 cm–1 using the diffusive reflection method.
Thermal decomposition studies were carried out
on Paulik–Paulik–Erdey Derivatograph (OD 102,
MOM Budapest) in the air atmosphere under dynamic
conditions (heating rate 9°C min–1) using platinum
crucibles with a sample mass of 100 mg in the temper-
ature range 20–900°C.
The antibacterial activity of Zn(II) complexes (I–VII)
and ZnSO4·7H2O in concentration 0.01 mol dm–3
were tested against G– bacteria – Escherichia coli
K88+ent+, Salmonella enterica Serovar Düsseldorf,
Salmonella enterica and G+ bacteria – Staphylococ-
cus aureus, Lactobacillus plantarum CCM 7102 and
Lactobacillus fermentum CCM 7158. Pathogenic
bacteria were cultivated in PYG broth medium (5 g
peptone for bacteriology, 5 g enzymatic caseine
hydrolyzate, 10 g yeast extract, 10 g D(+)glu-
cose/1000 mL, pH 7) and counts of cfu (colony form-
ing units) were evaluated on PYG agar (composition
as PYG broth+18 g agar/1000 mL, pH 7) after 24 h
cultivation at 37°C. Lactobacilli were grown under
anaerobic conditions in MRS broth resp. agar (Merck,
Germany) at 37°C for 18–24 h resp. 48 h. The strains
were also tested in the presence of sodium(I) formate,
acetate, propionate and butyrate in a concentration
The presence of gaseous intermediates was con-
firmed by IR spectra measured in gaseous cells on
SPECORD spectrophotometer and final solid prod-
ucts were identified by X-ray analysis using X-ray
Table 2 IR spectroscopic data of the prepared compounds/cm–1
Assigment/Compound
(I)
(II)
(III)
(IV)
(V)
(VI)
(VII)
3500
1650
–
n(O–H)H
3500
1650
–
–
–
3550
1680
–
–
–
–
–
3500
1650
–
2O
d(O–H)H
2O
n(C=O)
1660
1620
1380
240
–
1700
1650
1410
240
–
1700
1600
1400
200
nas(COO–)
ns(COO–)
DCOO
1590
1330
70
–
1580
1320
150
–
1540
1400
220
–
1530
1380
310
–
n(C–H)ph
d(C–H)ph
g(C–H)ph
n(N–CH3)
n(N–H)pyr
3080
1400–1000
720–580
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1150
3200
–
–
–
–
–
–
–
–
ph = phenyl, pyr = pyridine
(I) Zn(HCOO)2·2H2O; (II) Zn(HCOO)2·tph; (III) Zn(CH3COO)2·2H2O; (IV) Zn(CH3COO)2·tph; (V) Zn(CH3COO)2·2phen;
(VI) Zn(CH3CH2COO)2·2H2O; (VII) Zn(CH3CH2CH2COO)2·2H2O
356
J. Therm. Anal. Cal., 88, 2007

THE PHYSICOCHEMICAL AND BIOLOGICAL PROPERTIES OF ZINC(II) COMPLEXES
0.002 mol dm–3. The viable counts of bacteria are ex-
Thermal behaviour was studied on the serie of
zinc(II) formiate, acetate, propionate, butyrate and
thermal decomposition data are reported in Table 3.
The TG/DTG and DTA curves of complex (I) are
given in Fig. 1. The compound is stable up to 70°C
pressed as the log 10 of cfu mL–1 of growth media.
Results and discussion
The results of chemical analysis are reported in Ta-
ble 1. The analytical data reveal a good agreement
with calculated data.
Characteristic vibrations of the prepared com-
pounds are collected in Table 2 and are in a good ac-
cordance with literature data [10].
The presence of water in compounds (I, III, VI,
VII) was confirmed by stretching vibration n(O–H)
occurred in the range 3500–3000 cm–1 and deforma-
tion vibration d(O–H) occured in the range
1680–1650 cm–1. The parameter DCOO was determined
by analysis of COO– group band frequencies, where
DCOO=nas(COO–)–ns(COO–) and was used as a crite-
rion of carboxylate anion coordination to metal ions.
Values of DCOO were calculated from IR spectra and
are less than 200 cm–1 for compounds (I, III) that
shows bidentately bounded formiate and acetate
group and for compounds (II, IV–VII) are in the range
200–310 cm–1 that is in a good agreement with litera-
ture data for unidentately bounded carboxylate struc-
tures [11] along with the three absorption bands of
COO deformation at 920–720 cm–1 and a strong ab-
sorption near 540 cm–1.
Fig. 1 TG/DTG and DTA curves of Zn(HCOO)2·2H2O
Table 3 Intermediates and final products of the thermal decomposition of the prepared compounds
Mass loss/mg mmol–1
DTA peak
Products of the thermal
decomposition
Compound
T/°C
exp.
theor.
Zn(HCOO)2·2H2O
120 / endo
280 / endo
600
2H2O
CH2O, CO2
ZnO
36.39
72.79
82.37
36.02
74.03
81.38
Zn(HCOO)2·tph
170 / endo
280 / endo
600
tph
CH2O, CO2
ZnO
182.48
72.99
82.40
180.17
74.03
81.38
Zn(CH3COO)2·2H2O
Zn(CH3COO)2·tph
90 / endo
130 / endo
600
2H2O
(CH3)2CO, CO2
ZnO
35.16
105.50
79.12
36.02
102.00
81.38
180 / endo
300 / endo
600
tph
(CH3)2CO, CO2
ZnO
179.50
103.40
78.80
180.17
102.00
81.38
Zn(CH3COO)2·2phen
Zn(CH3CH2COO)2·2H2O
230 / endo
310 / endo
600
2phen
(CH3)2CO, CO2
ZnO
375.40
104.80
78.20
376.46
102.00
81.38
220 / endo
380, 620 / endo
900
H2O
H2O, (C2H5)2CO, CO2
ZnO
19.80
143.50
84.16
18.01
148.00
81.38
Zn(CH3CH2CH2COO)2·2H2O
endo=endothermic effect
220, 470 / endo
900
2H2O, (C3H7)2CO, CO2
ZnO
192.84
82.64
194.00
81.38
J. Therm. Anal. Cal., 88, 2007
357

SZUNYOGOVÁ et al.
Fig. 3 TG/DTG and DTA curves of Zn(CH3COO)2·2H2O
Fig. 2 TG/DTG and DTA curves of Zn(HCOO)2·tph
where the process of dehydration begins. This is fol-
lowed by one mass loss step attributed to the release
of formaldehyde and carbon dioxide, while the final
solid product was ZnO. The following mechanism of
the thermal decomposition was proposed:
Zn(HCOO)2·2H2O ® 2H2O+CH2O+CO2+ZnO
The thermal decomposition of compound (II)
starts with the release of theophylline with minimum
on the DTA curve at 170°C (Fig. 2). In the next step
of the thermal decomposition molecules of formalde-
hyde and carbon dioxide are released. ZnO was found
as a final product. The following reaction was pro-
posed for the mechanism of thermal decomposition:
Zn(HCOO)2·tph ® tph+CH2O+CO2+ZnO
By the release of two mol of water as depicted in
Fig. 3 the thermal decomposition of compound (III)
starts. Then, the next step corresponds to the mass
loss of acetone and carbon dioxide, on the DTA curve
at 120°C. The final product was ZnO. The thermal de-
composition can be expressed by the following equa-
tion:
Fig. 4 TG/DTG and DTA curves of Zn(CH3COO)2·tph
Zn(CH3COO)2·2H2O ®
2H2O+(CH3)2CO+CO2+ZnO
found as a final product. The following mechanism of
the thermal decomposotion was proposed:
Compound (IV) starts to decompose with the elim-
ination of theophylline in one step with minimum on the
DTA curve at 180°C (Fig. 4). In next step the release of
acetone and carbon dioxide took place and ZnO was
Zn(CH3COO)2·tph ® tph+(CH3)2CO+CO2+ZnO
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J. Therm. Anal. Cal., 88, 2007

THE PHYSICOCHEMICAL AND BIOLOGICAL PROPERTIES OF ZINC(II) COMPLEXES
The TG curve of compound (V) indicates that the
complex is stable up to 160°C as given in Fig. 5. Then
two molecules of phenazone are released in one step fol-
lowed by elimination of acetone and carbon dioxide in
next step. The final product was ZnO. The most proba-
ble scheme of the thermal decomposition is here:
Zn(CH3COO)2·2phen ®
2phen+(CH3)2CO+CO2+ZnO
The TG/DTG and DTA curves of compound
(VI) are depicted in Fig. 6. The first step of the ther-
mal decompostion begins with the release of water
(DTA curve 220°C). Afterwards the DTA curve dis-
plays two endothermic peaks with minima at 380 and
620°C that corresponds to the elimination of the sec-
ond water molecule, diethyl ketone and carbon diox-
ide. ZnO was found as a final product. The following
reaction was proposed for the mechanism of the
thermal decomposition:
Zn(CH3CH2COO)2·2H2O ®
2H2O+(C2H5)2CO+CO2+ZnO
As it is displayed on the DTA curve of com-
pound (VII) (Fig. 7) in two endothermic effects with
minima at 220 and 470°C two mol of water, dipropyl
ketone and carbon dioxide are released in one step
and ZnO was the final product. The mechanism of the
thermal decomposition can be expressed by the fol-
lowing equation:
Zn(CH3CH2CH2COO)2·2H2O ®
2H2O+(C3H7)2CO+CO2+ZnO
Fig. 5 TG/DTG and DTA curves of Zn(CH3COO)2·2phen
Fig. 6 TG/DTG and DTA curves of
Fig. 7 TG/DTG and DTA curves of
Zn(CH3CH2COO)2·2H2O
Zn(CH3CH2CH2COO)2·2H2O
J. Therm. Anal. Cal., 88, 2007
359

SZUNYOGOVÁ et al.
Table 4 Antibacterial activity of Zn(II) complexes vs. G– bacteria
E. coli
S. Düsseldorf
S. enterica
log cfu
Compound
log cfu
D log
log cfu
D log
D log
Control
8.79
5.81
2.90
6.20
3.38
5.62
5.91
5.57
5.85
–
8.83
5.76
0.00
6.20
4.18
4.90
6.20
6.08
6.46
–
8.87
4.85
3.81
7.00
4.04
6.00
5.92
–
Zn(HCOO)2·2H2O
Zn(HCOO)2·tph
3.0
5.9
2.6
5.4
3.2
2.9
3.2
2.9
3.2
8.8
2.6
4.7
3.9
2.6
2.8
2.4
4.0
5.1
1.9
4.8
2.9
2.9
–
Zn(CH3COO)2·2H2O
Zn(CH3COO)2·tph
Zn(CH3COO)2·2phen
Zn(CH3CH2COO)2·2H2O
Zn(CH3CH2CH2COO)2·2H2O
ZnSO4
6.96
2.2
Table 5 Antibacterial and probiotic activity of Zn(II) complexes to G+ bacteria
Staph. aureus L. plantarum
L. fermentum
Compound
log cfu
D log
log cfu
D log
log cfu
D log
Control
8.57
8.28
6.67
8.63
6.63
5.72
7.94
7.28
8.54
–
8.82
8.43
6.20
8.86
8.28
8.76
8.61
8.28
8.57
–
9.35
9.56
8.32
9.67
9.04
9.13
9.37
9.13
9.35
–
Zn(HCOO)2·2H2O
Zn(HCOO)2·tph
0.3
1.9
–0.1
1.9
2.8
0.6
1.3
0.0
0.4
2.6
0.0
0.5
0.1
0.2
0.5
0.3
–0.2
1.0
–0.3
0.3
0.2
0.0
0.2
0.0
Zn(CH3COO)2·2H2O
Zn(CH3COO)2·tph
Zn(CH3COO)2·2phen
Zn(CH3CH2COO)2·2H2O
Zn(CH3CH2CH2COO)2·2H2O
ZnSO4
The results of antimicrobial activity are listed in
Tables 4–5. Microbiological studies confirmed a
strong antibacterial activity of Zn(II) complexes
(I–VII) against G– pathogens. If Zn2+ ion in
alkylcarboxylates (I, III, VI, VII) was substituted by
Na+ ion, no antimicrobial activity was found as it is
known from literature [12]. Based on these results, it is
supposed that zinc is a ‘carrier’ of an antibacterial ac-
tivity in the tested zinc compounds without ligands.
Compound (II) is the strongest inhibitor of G– bacteria.
This compound absolutely inhibited the growth of
S. enterica Serovar Düsseldorf (cfu=0) and suppressed
the growth of S. enterica and E. coli by 5–6 log. Simi-
lar results were achieved by testing compound (IV)
that made counts of G– strains lower by cca 5 log.
In comparison to compounds (I, III, VI, VII) which in-
hibited the growth of G– bacteria by 2–4 log, it was
confirmed that the main antibacterial component of all
compounds was theophylline and G– bacteria were
sensitive to this heterocyclic ligand. The antibacterial
activity of theophylline is well known, especially as
one of alkaloids contained in the tea leaves [13]. Com-
pound (V) was more active vs. pathogens by 3–4 log
than compound (III) that inhibited the growth of G–
strains by 2–2.5 log. This confirms that antibacterial
effect of zinc is enhanced also by phenazone.
The sensitivity of G+ bacteria to the tested com-
pounds (I–VII) was higher than that of G– ones that
corresponds with literature data [12]. The counts of
Staph. aureus were mostly inhibited by com-
pound (V) (2.9 log) and compounds (II, IV) contain-
ing theophylline (cca 2 log). It can be supposed that
the growth of Staph. aureus was inhibited especially
by theophylline and phenazone.
The counts of L. plantarum that is used as a
probioticum for piglets was the most strongly inhib-
ited by compound (II) (2.6 log). The other com-
pounds (I, III–VII) inhibited its growth more weakly
or nowise. The counts were lowered in the range
0.1–0.5 log and compound (III) had no effect on the
growth of bacteria. The most resistant to the tested
zinc compounds was L. fermentum. This strain is used
in the probiotic preparations for poultry and rabbits.
Its growth was inhibited only by compound (II) and
weakly by compounds (IV, V, VII). Compound (VI)
and ZnSO4 have not influenced the numbers of this
strain. On the other hand, the compounds (I, III) had
weak stimulative effect on its growth.
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THE PHYSICOCHEMICAL AND BIOLOGICAL PROPERTIES OF ZINC(II) COMPLEXES
Conclusions
Acknowledgements
The thermal behaviour of studied compounds de-
pends on the length of aliphatic chain. Thermal de-
composition of hydrated compounds starts with the
release of water in the temperature range 70–220°C.
After dehydration, organic ligand take place and
carboxylate anion decomposes and CO2 and ketone
are liberated. Volatile intermediates and solid final
product were confirmed by X-ray diffraction method
and methods of qualitative chemical analysis.
Microbiological studies confirmed a strong anti-
bacterial activity of tested complexes. The strongest
antagonistic activity against G+ and G– bacteria was
found in compound (II). Compounds (II, IV, V)
showed a stronger antibacterial activity than basic
compounds (I, III, VI, VII). It confirms that theophyl-
line and phenazone enhance inhibitory activity of
zinc. The weakest compound of all tested complexes
was compound (III). The most resistant to the tested
zinc carboxylate complexes were both probiotic
strains of lactobacilli. These strains can be used in the
feedstuffs containing higher amount of zinc without
inhibition of their growth activity.
This work was supported by the Slovak Ministry of Education
VEGA project No.1/2474/05. This financial support is grate-
fully acknowledged.
References
1 D. Stefanitsi and J. R. Garel, Lett. Appl. Microbiol.,
24 (1997) 180.
2 J. E. Coleman, Ann. Rev. Biophys. Biomol. Struct.,
21 (1992) 441.
3 I. Fridovich, Science, 201 (1978) 875.
4 T. J. Beveridge and R. J. Doyle, Metal Ions and Bacteria,
Wiley, New York 1989.
5 A. Holm and H. D. Poulsen, Compend. Cont. Educ. Prac.
Vet., 18 (1996) 26.
6 K. GyÞryová, J. Kováéová and J. Chomi¹, J. Therm. Anal.
Cal., 80 (2005) 375.
7 K. GyÞryová , J. Chomi¹, E. Szunyogová, L. Piknová,
V. Zele×ák and Z. Vargová, J. Therm. Anal. Cal.,
84 (2006) 727.
8 Z. Vargová, V. Zele×ák, I. Císaéová and K. GyÞryová,
Thermochim. Acta, 423 (2004) 149.
9 K. Král’ová, E. Masarovi¹ová and K. GyÞryová, Fresenius
Environ. Bull., 12 (2003) 857.
The achieved results can be used in selective in-
hibition of the growth of G– and G+ bacteria and in de-
velopment of new preparations that can suppress the
growth of some pathogenic bacteria in a digestive
tract and at the same time it can be a zinc source for a
macroorganism.
10 M. Bellamy, The Infra-Red Spectra of Complex
Molecules, Wiley, New York 1954.
11 K. Nakamoto, Infrared and Raman Spectra of Inorganic
Compounds, John Wiley, New York 1986.
12 M. Melník, M. Anderová and M. Hol’ko, Inorg. Chim.
Acta, 67 (1982) 117.
13 I. E. Dreosti, Nutr. Rev., 54 (1996) S51.
DOI: 10.1007/s10973-006-8115-z
J. Therm. Anal. Cal., 88, 2007
361