Thermal investigations of cefadroxil complexes with transition metals coupled TG-DSC and TG-FTIR techniques

Article abstract of DOI:10.1023/B:JTAN.0000046112.27166.91

The cefadroxil (Cet) complexes with transition divalent metals of the formula MCef·nH₂O (where n=2 for M=Cu²⁺, Ni ²⁺, Zn²⁺ and n=3 for Co²⁺) and CdCe _1.5·4H₂O were prepared and c

Full text of DOI:10.1023/B:JTAN.0000046112.27166.91

Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 473–486
THERMAL INVESTIGATIONS OF CEFADROXIL
COMPLEXES WITH TRANSITION METALS
Coupled TG-DSC and TG-FTIR techniques
*
Renata Mrozek-˜yszczek
Department of General Chemistry, Faculty of Chemistry, Maria Curie-SkÓodowska University
M. C. SkÓodowskiej Sq. 2, 20-031 Lublin, Poland
Abstract
The cefadroxil (Cef) complexes with transition divalent metals of the formula MCef·nH
2
O (where n=2
2+
2+
2+
2+
2
for M=Cu , Ni , Zn and n=3 for Co ) and CdCef1.5·4H O were prepared and characterized by ele-
mental and infrared spectra. The thermal analysis of the investigated complexes in air atmosphere was
carried out by means of simultaneous TG-DSC technique. During heating in air they lose bound water
molecules and then decompose to oxides: Co
plex forms probably an intermediate product Cd
ployed to study of decomposition pathway of the investigated complexes. The first mass loss step is the
water loss of the complexes. Next, decomposition of cefadroxil ligand occurs with evolution of CO
and NH . At slightly higher temperature COS is observed according to decomposition of cephem ring.
Additionally, as decomposition gaseous products: HCN, HNCO (HOCN), H CNH, CO, SO , hydro-
3 4
O
, NiO, CuO, ZnO and CdO. The CdCef1.5·4H
2
O com-
2
OSO . The combined TG-FTIR technique was em-
4
2
3
2
2
carbons and carbonyl compounds were observed. The formation of metal sulfates is postulated as solid
intermediate product of decomposition in the argon atmosphere.
Keywords: cefadroxil, gaseous products, metal complexes, TG-DSC, TG-FTIR analysis
Introduction
An interaction between metal ions and pharmaceutics is an attractive field of study.
Metal ions are easily available for pharmaceutics ligands because they appear in liv-
ing system as free ions and they are bound to proteins, enzymes, nucleic acids and
other bioligands [1, 2]. The metal complex formation is a simple way of modifying
the properties of a drug. The adriamycin complex with Pt(II) is more active against
certain tumor cells in comparison to parent drug while complex with Pd(II) has re-
duced antitumor activity [3]. The metal (II) complexes of cephalexin show better an-
tibacterial activity than the antibiotics themselves [4]. In some cases metal ions are
necessary for therapeutical activity of pharmaceutics [5].
The most important class of drugs against infectious diseases caused by bacteria
is β-lactamic antibiotics. The great families of such antibiotics form cephalosporins,
*
Author for correspondence: E-mail: reniam@hermes.umcs.lublin.pl
1
388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
©
2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

4
74
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
which contain β-lactam moiety fused with a six-member ring. Cefadroxil Scheme 1
belongs to the first generation of cephalosporin antibiotics. The cefadroxil form in
solution complexes of molar ratio 1:1 with following ions: Ca(II), Cu(II), Zn(II),
Pb(II) and La(III) [6]. In the solid-state cefadroxil forms complexes with Cu(II) and
Co(II) with molar ratio also 1:1 [7].
Scheme 1
This paper presents results from spectroscopic and thermal investigations of
2
+
cefadroxil complexes with some divalent metals. The following metal ions: Cu ,
2
+
2+
2+
2+
Ni , Zn , Co and Cd have been chosen because they appear in human body. As
can be seen from above mentioned literature, the metal complexes of cefadroxil may
have better therapeutic activity in comparison to uncoordinated by metals antibiotic.
In the future, the antibacterial activity of the studied complexes will be tested.
The TG-DSC method was used in order to determine the thermal behavior of the
studied compounds in the air. The major goal of the application of coupled TG-FTIR
technique was to give a possible decomposition path of metal complexes based on
the composition of evolved gases. This method is widely used in the investigation of
many drugs as well as substances of pharmacological interest [8–11].
Experimental
All chemicals were of analytical grade. Cefadroxil was obtained from Sigma. The
metal nitrates and chlorides were obtained from P.O.CH. Gliwice.
The complexes have been obtained in the reaction of aqueous solution of so-
3
dium cefadroxil (pH=9; 2.744 mmol; 10 cm ) with solution of corresponding metal
3
nitrate or chloride (2.744 mmol; 10 cm ) in a molar ratio 1:1. The solution of metal
salt was added dropwise to solution of sodium salt at room temperature. After mixed,
compounds precipitated immediately. The complexes have been washed with a little
amount of water and acetone and dried at room temperature.
The percentage of C, H and N were obtained by means of elemental analysis using a
PerkinElmer CHN 2400 apparatus. The transition metal contents were estimated by
spectrometry of atomic absorption by using Spectrophotometer AA-880 (Varian).
The IR spectra of free cefadroxil and the studied compounds were recorded in
–
1
the range 4000–400 cm on a Specord M80 spectrophotometer.
Thermal analysis of prepared compounds was carried out by the TG-DSC method
using a Setsys 16/18 analyzer (Setaram). Samples about 7 mg were heated in ceramic
J. Therm. Anal. Cal., 78, 2004

MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
475
–1
crucibles up to 1000°C at heating rate of 10°C min in dynamic air atmosphere
3
–1
(
v=0.75 dm h ).
The TG-FTIR coupled measurements have been carried out using a
Netzsch TG 209 apparatus coupled with a Bruker FTIR IFS66 spectrophotometer.
The sample of about 5 mg were heated in ceramic crucibles up to 600°C at a heating
–
1
rate of 10°C min in flowing argon atmosphere.
X-ray powder diffraction patterns for the studied complexes and final solid
product of thermal decomposition were recorded on a HZG 4 diffractometer. Mea-
surements were taken over the range of 2θ=2–70° using Ni filtered CuK radiation.
α
Results
The complexes of the formulae: CoCef·3H O, NiCef·2H O, CuCef·2H O, ZnCef·2H O
2
2
2
2
and CdCef ·4H O (where Cef-cefadroxil) were obtained. The cefadroxil ligand coordi-
1.5
2
nates metal ions in the stoichiometric ratio 1:1. The analytical data of the investigated
complexes are shown in Table 1. The powder patterns of the investigated complexes
(with exception of cadmium complex) indicate that they are amorphous.
Table 1 Elemental analysis data
C/%
H/%
N/%
M/%
found
Complex
calc.
40.30
41.88
41.47
41.34
39.48
found
calc.
4.83
4.58
4.53
4.52
4.59
found
4.62
4.94
4.52
4.57
4.61
calc.
8.73
9.16
9.07
9.04
8.64
found
8.82
9.04
9.13
9.17
8.73
calc.
12.37
12.80
13.74
14.08
15.41
CoCef·3H
2
O
40.03
41.26
41.55
41.92
40.22
11.83
13.05
13.99
13.82
15.62
NiCef·2H
2
O
CuCef·2H
2
O
ZnCef·2H
2
O
CdCef1.5·4H
Cef=C16
2
O
17 3 5
H N O S
Spectroscopic description
Evidence for complex formation was obtained by comparing the infrared spectra of
–
1
the free cefadroxil and complexes in the region of 4000–400 cm . The most charac-
teristic bands and their assignments are given in Table 2. The spectra of cobalt,
nickel, copper and zinc complexes are very similar to each other. The IR spectrum of
cadmium complex looks entirely different. The IR spectrum of cefadroxil shows in
–
1
the wavenumber region 3600–2400 cm broad band with many submaxima. The
–
1
sharp band at 3505 cm is due to stretching vibrations of ‘free’ OH group of
hydroxyphenyl from cefadroxil [7]. This band disappeared in spectra of metal com-
plexes that may point to ionization of the hydroxyl group. In the spectrum of
–
1
cefadroxil, the band at 3273 cm is assigned to stretching vibration of N–H of hydro-
gen bound amide group [12]. In the investigated complexes in this wavenumber re-
–
1
gion only a very broad band with a maximum at about 3200 cm appears. This band
J. Therm. Anal. Cal., 78, 2004

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76
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
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MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
477
is assigned to stretching vibrations of OH group from hydrogen bonded water mole-
+
3
–1
cules [13]. The band of NH group at 2600 cm in cefadroxil spectrum disappeared
in spectra of metal complexes.
The infrared spectra of β-lactam antibiotics exhibit the characteristic band arising
from stretching vibrations of the carbonyl group of β-lactam ring [14]. In the free
–1
cefadroxil spectrum vibration of this mode appears at 1758 cm . This band appears also in
all studied complexes almost at the same wavenumber. It may suggest that the carbonyl ox-
ygen atom from β-lactam ring is not engaged in metal binding. Disappearing of such band
is indicative for the participation of β-lactam in metal coordination or hydrolysis of
β-lactam ring [15]. Another characteristic group from cefadroxil ligand is an amide group
–1
from side chain. The band observed at 1686 cm is coming from stretching vibrations of
amide carbonyl group [16]. This band vanished in metal complexes with the exception of
CdCef ·4H O. Because of zwitterionic character of cefadroxil the spectrum of free ligand
1.5
2
shows bands of antisymmetric (ν ) and symmetric (ν ) vibrations of carboxylate group at
as
s
–1
1
563 and 1399 cm , respectively [4]. The bands assigned to ν COO overlapped with II
as
amide band (βNH, νCN). In spectra of metal complexes ν COO band is shifted towards
as
higher wavenumber than ν COO towards lower wavenumber. This fact suggests interac-
sym
tion between metal ions and carboxylate group of cefadroxil [17]. Based on the analysis of
infrared spectra coordination through amide group and carboxylate group is proposed.
Probably, the studied complexes have polymeric structure. For cadmium complex entirely
different mode of coordination is observed. The principle difference in comparison to re-
–1
maining spectra is present of stretching vibration of carbonyl group at 1664 cm . The
antisymmetric and symmetric stretching vibrations of carboxylate group are shifted to-
–1
wards frequencies 1568 and 1420 cm , respectively. It may point to coordination only by
carboxylate group while carbonyl group from amide group is not engaged in coordination.
Thermal description
Thermal behavior of metal complexes has been studied by using TG-DSC method
and coupled TG-FTIR system in order to investigate evolved gases. For understand-
ing the decomposition pathway of metal complexes better the degradation of free
cefadroxil has been studied.
Description of cefadroxil decomposition
The TG and DSC curves of cefadroxil obtained during heating in air are shown in
Fig. 1. The first mass loss on the thermogravimetric curve occurring in the 70–180°C
range corresponds to the loss of 1 mol water molecule. The dehydration is accompa-
nied by a broad endothermic peak according to the loss of an adsorbed water mole-
cule. In interval 200–600°C decomposition with burning of cefadroxil is observed.
At 207°C on the DSC curve very sharp exothermic peak is observed. At the same
temperature on the TG curve a rapid loss of mass is recorded that can be attributed to
releasing of 1 mol of NH and 1 mol of CO (16.8%). The second exothermic effect is
3 2
superimposition of processes connected with degradation and oxidation.
J. Therm. Anal. Cal., 78, 2004

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78
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
Stacked plot of the infrared spectra of the evolved gases for cefadroxil is given
in Fig. 2. In the coupled TG-FTIR experiment water molecules were detected as the
first product of cefadroxil thermal decomposition. FTIR spectra recorded to 200°C
–
1
show bands in the wavenumber ranges 3750–3500 and 1900–1300 cm correspond-
ing to stretching and deformation vibrations of H O molecules, respectively [18, 19].
2
Next complex degradation process occurs with releasing many gaseous products.
Carbon dioxide is evolved at all temperature from 200 to 600°C. It gives characteris-
–
1
tic absorption bands in frequencies ranges: 2300–2250 and 750–600 cm due to va-
lence and deformation vibrations, respectively. On the carbon dioxide bands over-
–
1
lapped vibrations from cyanic acid, which give band at 2280 cm . In the temperature
range 200–440°C besides CO and weak band H O there are observed evolution of
2
2
–
1
COS, NH and SO . The double-band at 2071 and 2040 cm has been assigned to
3
2
stretching vibrations of COS molecules [20, 21]. Ammonia gives easy detectable
–
1
double-peak bands with maxima at 966 and 932 cm arising from deformation vibra-
Fig. 1 TG and DSC curves of cefadroxil (in air)
Fig. 2 Stacked plot of the FTIR spectra of the evolved gases for the cefadroxil
J. Therm. Anal. Cal., 78, 2004

MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
479
–
1
tions. The bands at 1374, 1361, 1339 cm have been recognized as arising from SO
2
molecule [22]. The TG-FTIR spectra collected in the temperature range 440–500°C
near bands raised from CO , NH , HCN, HOCN and COS show presence of absorp-
2
3
–
1
tion peaks at 2926, 1626, 1516, 1542 and 1533 cm . These bands were attributed to
aromatic species of degradation products. The band at 2926 cm corresponds to
stretching vibrations of C–H group [23]. The peaks at 1516, 1542 and 1533 cm
–
1
–
1
were assigned to stretching vibration C C in aromatic ring [24].
Ar Ar
The thermal decomposition (in air) of metal complexes
The TG and DSC curves are shown in Figs 3–7. All the investigated complexes are sta-
ble up to about 50°C. Further heating of complexes in air atmosphere as well as in argon
resulting in dehydration process, which occurs in about 50–150°C temperature range.
Mass loss on the TG curve is accompanied by weak endothermic effect on the DSC
curve. This fact may point to only weak bonding of water molecules in structures of com-
plexes. Further heating of unstable anhydrous complexes causes decomposition. As con-
trasted with remaining compounds only anhydrous CdCef1.5 is stable (up to 191°C). The
experimental and expected mass losses are given in Table 3.
Table 3 Thermogravimetric data obtained during heating complexes in air atmosphere
Mass loss/%
Mass loss/%
Compound
CoCef·3H
T
i
/°C
T
2
/°C
Residue
Co
found
calc.
11.34
7.85
7.78
7.75
9.87
found
calc.
83.15
85.05
82.83
74.81
82.40
2
O
50–150
40–145
48–160
51–140
48–148
11.22
8.05
8.15
7.68
9.35
150–530
145–555
160–428
140–630
191–623
84.38
84.31
81.23
75.10
81.18
3
O
4
NiCef·2H
2
O
NiO
CuO
ZnO
CdO
CuCef·2H
2
O
ZnCef·2H
2
O
2
CdCef1.5·4H O
In oxidative air atmosphere degradation of organic ligand is accompanied by
strong exothermic effect connected with burning of organic ligand. The degradation
process is intricate and is not possible to distinguish intermediate solid products.
Only in the case of CdCef ·4H O compound, the TG curve shows distinct mass loss
1
.5
2
(
46.17%), which may be attributed to Cd OSO formation (Fig. 7). The solid residues
2 4
obtained during thermal decomposition of complexes are suitable metal oxides:
Co O , NiO, CuO, ZnO and CdO. Their compositions have been confirmed by X-ray
3
4
diffraction measurement. The diffraction patterns of obtained residues have been
compared with reference patterns.
The thermal decomposition of the studied complexes in argon atmosphere has been
investigated using coupled TG-FTIR technique. The data obtained from analysis of gas-
eous products of thermal decomposition point to some differences in decomposition way
of complexes. Therefore TG-FTIR spectra will be described apparently for cefadroxil
and its metal complexes. Gaseous products observed during decomposition of metal
J. Therm. Anal. Cal., 78, 2004

4
80
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
2
Fig. 3 TG and DSC curves of CoCef·3H O (in air)
2
Fig. 4 TG and DSC curves of NiCef·2H O (in air)
complexes and cefadroxil are given in Table 4. The figure of FTIR spectra of evolved gas
products is given only for CoCef·3H O as the most representative among metal com-
2
plexes, which behave relatively similar during thermal decomposition.
TG-FTIR spectra of CoCef·3H O
2
The FTIR spectra recorded to 170°C range show only weak bands from water mole-
cules. At a slightly higher temperature characteristic bands from stretching and de-
formation vibrations of carbon dioxide are observed according to decomposition of
J. Therm. Anal. Cal., 78, 2004

MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
481
2
Fig. 5 TG and DSC curves of CuCef·2H O (in air)
2
Fig. 6 TG and DSC curves of ZnCef·2H O (in air)
organic ligand. At the same temperature as the product of decomposition ammonia is
produced. Upon further heating the opening of cephem ring appears. The FTIR spec-
–
1
tra show bands with maxima at 2070; 2050 cm which are attributed to vibrations of
–
1
COS and additionally are present absorption peaks at 1375, 1359, 1341 cm recog-
–
1
nized as asymmetric stretching vibrations of SO . Additionally, a band at 2280 cm
2
appears attributed to stretching C≡ N vibrations from cyanic acid [25]. The highest
intensity of evolution of these gases is observed at 320°C. Moreover, at the same time
J. Therm. Anal. Cal., 78, 2004

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82
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
2
Fig. 7 TG and DSC curves of CdCef1.5·4H O (in air)
Table 4 Indentification of FTIR peaks observed in various temperature ranges during heating of
free ligand and metal complexes
Compound
Cefadroxil
T/°C
Gases (or groups)
to 200
200–440
2
H O
H
2
O, NH
3 2 2
, CO , COS, SO , HOCN
4
40–500
CO
2
, NH , HCN, HOCN, COS, –CH, CArC
3
Ar
to 170
2
H O
1
70–320
CO
2
, NH
C=O, –C=N–, CAr
, NH , SO , HOCN, CO
3 2
, COS, SO , HOCN, –CH,
2
CoCef·3H O
–
2
C
Ar
>320
CO
3
2
to 180
2
H O
1
80–400
CO
2
, COS, HCN, HNCO, NH
–C=O, –C=N–, SO2
3 Ar
, CArC
NiCef·2H
2
O
4
00–600
CO
2
, CO, NH
3
, HNCO, SO
, –SH
2
6
00
CO , SO , NH
2
2
3
to 200
2
H O
2
00–490
H
2
O, CO
2 3
, NH , COS, HNCO, HCN, –CH–
CuCef·2H
2
O
Ar 4
C CAr, CH
>
490
to 180
180–370
CO , CO, SO , HNCO, NH
2 2 3
2
H O
ZnCef·2H
2
O
H O, CO , NH , COS, HCN, SO , HOCN
2
2
3
2
3
70–420
3 2 2
CO, NH , CO , SO
to 120
2
H O
CdCef1.5·4H
2
O
230–460
60
CO
2
, HOCN, NH
3
, –C=N–, HCOOH, –CH
, COS, SO
4
CO
2
, NH
3
2
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MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
483
–
1
bands at 2974, 1734, 1626 and 1508 cm were recorded. The absorption peak at
–
1
2
974 cm was assigned to stretching vibrations of C–H due to evolution of hydrocar-
–
1
bons or theirs derivatives. The band at 1505 cm was recognized as aromatic ring vi-
brations. The band at 1626 cm was attributed to stretching vibrations of –C=N–
from methanimine [26]. Probably also some carbonyl compounds are evaluated due
to stretching vibration of –C=O group observed at 1734 cm [27]. Upon 320°C the
absorption bands from COS and hydrocarbons disappeared. On the contrary beside
HOCN, CO and NH gases evolution are present very indicative and strong bands
–
1
–
1
2
3
from SO and CO. Carbon monoxide give easily detectable double-bands in the
2
–
1
2
250–2050 cm region (Fig. 8).
2
Fig. 8 FTIR spectra of evolved gas products of CoCef·3H O
TG-FTIR spectra of NiCef·2H O
2
Based on the analysis of TG-FTIR spectra of evolved gases formed during complex
heating, a four-step decomposition process can be proposed. At first, at 180°C only
water molecules have been detected. In the 180–400°C temperature range strong
bands from CO , HCN, HONC, COS, SO and NH were recorded. At the same tem-
2
2
3
perature, aromatic hydrocarbons, methaneimine and carbonyl compounds are re-
–
1
leased due to the appearance of bands at 2947, 1736, 1626, 1533 cm , respectively.
Upon 400°C bands from COS disappear and the produced gases are: SO , CO ,
2
2
HONC, CO and NH . The FTIR spectrum recorded at 600°C shows weak absorption
3
–
1
band at 2500 cm assigned to S–H vibration [28], medium bands from NH and CO
3
2
and very intense bands from stretching asymmetric and symmetric vibrations of SO
in ranges 1370, 1350 and 1150, 1140 cm , respectively.
2
–
1
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MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
The TG-FTIR spectra of CuCef·2H O
2
Similarly as in other complexes the first step of decomposition is dehydration. After
that degradation of complex with evolution of gaseous products appears. The FTIR
spectra collected in the 200–490°C temperature range show evolution of H O,
2
–
1
HOCN, CO , NH and COS. Beside them there are bands at 3211 and 713 cm as-
2
3
signed to vibrations from HCN [29]. At the same time methane is evolved due to
–
1
presence of very diagnostic band at 3016 cm [13]. Appearance of absorption bands
–
1
at 2931 and 1510 cm is connected with stretching vibrations of C–H group and aro-
matic ring vibrations C C , respectively. It points to the evolution of some aromatic
Ar Ar
hydrocarbons. Spectra of evolved gases recorded upon 490°C show bands attributed
to CO , CO, HOCN, SO and traces of NH .
2
2
3
The TG-FTIR spectra of ZnCef·2H O
2
During heating to 180°C, the stretching and deformation vibrations of water molecules
are only observed. In the temperature interval 180–370°C the following gaseous prod-
ucts of decomposition appear: H O, CO , NH , COS, SO and HCN. Additionally,
2
2
3
2
cyanic acid (HOCN) was recognized according to the appearance of stretching vibrations
–1
–1
of C≡N group at 2253 cm and vibrations from OH group at 3560 and 1261 cm . The
–1
–1
stretching vibrations C–H at 3250 cm and deformation vibrations at 712 cm were at-
tributed to HCN. The most intensity of releasing the above mention gases (except ammo-
nia) is observed at 370°C. At 420°C the double peak arisen from vibrations of COS dis-
appeared whereas very diagnostic bands of CO molecule are emerged. Additionally, at
the same temperature the highest intensity of ammonia emission is observed. Further
heating causes further NH , CO and SO evolution.
3 2 2
The TG-FTIR spectra of CdCef ·4H O
2
1.5
According to the dehydration process up to 120°C water molecules are observed on the
FTIR spectra. Above 230°C decomposition of anhydrous complex appears. At first, car-
bon dioxide and ammonia are observed as a product of decomposition. Next, decomposi-
tion of cephem ring appears that is reflected in releasing of COS molecules. Releasing
carbonyl sulfide coincide with formation of HOCN. Cyanic acid gives characteristic
–1
bands: at 3597 and 1261 cm due to stretching and deformations vibrations of OH
–1
group, respectively and stretching vibrations of C≡N group at 2284 cm [25]. Addition-
–1
ally, on the FTIR spectra bands are shown at: 3580, 1797, 1780 and 1170 cm assigned
to: stretching vibrations of OH group, stretching vibrations of –C=O group and stretch-
ing vibrations of –C–O group, respectively. Such vibrations can be produced by evolved
–1
formic acid [30]. Also absorption peak at 1626 cm is observed as driving from –C=N–
vibrations. Traces of some hydrocarbons can be observed according to weak band at
–1
2
927 cm . At slightly higher temperature bands from formic acid disappeared and in-
crease of evolution of CO , NH and COS are observed. Upon 460°C carbonyl sulfide is
2
3
not released. Among the gaseous products of decomposition only absorption bands from
NH , CO , CO and SO are observed as can be seen from Fig. 9.
3
2
2
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MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
485
2
Fig. 9 Stacked plot of FTIR spectra of evolved gas products of CdCef1.5·4H O
Conclusions
•
•
The investigated complexes are stable up to 50°C in air as well as in argon atmo-
sphere.
From TG data obtained in air atmosphere two main stages of decomposition can be
distinguished. In the first step, water molecules are evolved. When temperature in-
creased to about 150°C immediately burning of organic ligand appears. The metal
oxides (MO or M O ) are formed as final stable product of decomposition.
3
4
•
The CdCef bands H O complex shows different thermal behavior. In comparison to
1.5 2
other compounds during heating, the stable anhydrous complex is formed. Addition-
ally, formation of intermediate product of decomposition (Cd OSO ) is postulated.
2
4
•
•
The TG-FTIR spectra of free cefadroxil as well as complexes point to multi-stage
decomposition in argon atmosphere.
Cefadroxil decomposes in three stages: a) evolution of weakly bound water mole-
cule; b) releasing of CO and NH with opening of cephem ring (evolution of car-
2
3
bonyl sulfide and sulfur dioxide); c) further decomposition with releasing of aro-
matic species and HCN, HOCN and methanimine.
•
Based on the nature of evolved gaseous products, the way of the decomposition of
complexes has been proposed. During heating three main stages can be distin-
guished: a) dehydration process (evolution of water molecules); b) evolution of
gaseous products as: CO , NH , HCN, HNCO (HOCN), COS, SO (connected
2
3
2
with degradation of dihydrothiazine ring), hydrocarbons, carbonyl compounds; c)
evolution of CO and SO . In comparison to free cefadroxil carbon monoxide is
2
produced during complexes heating. Additionally, in the high temperature the in-
creasing of intensity of SO evolution is observed. It may be explained by the fact
2
of metal sulfate formation during the decomposition process, which at higher tem-
perature (argon atmosphere) is reduced by carbon to SO2.
•
The temperature of evolution of hydrocarbons and aromatic compounds in metal
complexes is relatively lower in comparison to free ligand.
J. Therm. Anal. Cal., 78, 2004

4
86
MROZEK-˜YSZCZEK: CEFADROXIL COMPLEXES
•
The decomposition pathway confirms also differences in mode of bonding metal
by cefadroxil. Only in the case of CdCef ·4H O among gaseous products formic
1
.5
2
acid is observed as driving probably from decomposition of side chain.
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