Complexes of adrenaline with some divalent transition-metal ions

Article abstract of DOI:10.1016/S0040-6031(00)00753-X

A thermoanalytical study of different adrenaline coordination compounds with some divalent transition-metal ions such as Co(II), Ni(II) and Cu(II) is reported. The solid precipitated compounds were characterized by elemental analysis and by thermogravimetric analysis also coupled to FTIR spectroscopy to analyze the evolved gases and make consistent the proposed decomposition steps. Several complexes were obtained with the metal/ligand molar ratios of 1:2, 1:4 and 1:6.

Full text of DOI:10.1016/S0040-6031(00)00753-X

Thermochimica Acta 369 (2001) 167±173
Complexes of adrenaline with some divalent transition-metal ions
*
S. Materazzi , C. Nugnes, A. Gentili, R. Curini
Department of Chemistry, University of Roma La Sapienza, p. le A. Moro 5, 00185 Rome, Italy
Received 25 July 2000; received in revised form 3 November 2000; accepted 5 November 2000
Abstract
A thermoanalytical study of different adrenaline coordination compounds with some divalent transition-metal ions such as
Co(II), Ni(II) and Cu(II) is reported. The solid precipitated compounds were characterized by elemental analysis and by
thermogravimetric analysis also coupled to FTIR spectroscopy to analyze the evolved gases and make consistent the proposed
decomposition steps.
Several complexes were obtained with the metal/ligand molar ratios of 1:2, 1:4 and 1:6. # 2001 Elsevier Science B.V. All
rights reserved.
Keywords: Adrenaline; Complexes; TG-FTIR; EGA; Epinephrine; Decomposition
1
. Introduction
after precipitation from aqueous or ethanolic solutions
using several metallic(II) nitrate/adrenaline (M/L)
molar ratios.
The coordination compounds that epinephrine,
commonly also called adrenaline (adr), form with
divalent transition metal-ions, such as Co(II), Ni(II)
and Cu(II), can be useful models to complete the
informations regarding the complexing behaviour of
catecholamines and to ®nd out correlations of the
properties of these compounds in solution with the
properties of them in the solid state.
Different studies of this kind of complexes can be
found in the literature [1±8], but few thermoanalitycal
data are reported for them and there is no information
about the decomposition steps that can be directly
related with the coordination energies of each com-
plex.
The obtained compounds showed M/L molar ratios
of 1:2, 1:4 and 1:6, with successive ligand molecules
being coordinated to a 1:2 base-unit [M(L)2 ]. The
solvent makes the difference, especially in the com-
plexes with more than four coordinated ligand mole-
cules.
The characterization of the solids complexes was
performed by elemental analysis, thermogravi-
metric analysis and coupled TG-FTIR evolved gas
analysis.
2
‡
2. Experimental
The aim of this work is to compare the thermo-
analytical properties of the solid complexes obtained
2.1. Materials
*
Adrenaline and the metallic(II) salts were from
Aldrich and were used without further puri®cation.
All the solvents used were of RPE grade.
Corresponding author. Tel.: ‡39-6-49913616;
fax: ‡39-6-4453616.
E-mail address: smaterazzi@uniromal.it (S. Materazzi).
0040-6031/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 0 0 ) 0 0 7 5 3 - X

1
68
S. Materazzi et al. / Thermochimica Acta 369 (2001) 167±173
2
.2. Syntheses of the complexes
2.2.7. [Cu(adr) ](NO )
6
3 2
To a solution of Adrenaline (6 mmol) in 250 ml of
All the complexes were precipitated from aqueous
solutions at pH ˆ 4 and from ethanolic solutions, with
absolute ethanol, a solution of Cu(NO ) Á5H O
3
2
2
(1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
the same starting Me/adr ratios.
2
.2.1. [Co(adr) ](NO3)2
6
To a solution of Adrenaline (6 mmol) in 250 ml of
absolute ethanol, a solution of Co(NO ) Á3H O
2.2.8. [Cu(adr) ](NO )
4
3 2
To a solution of Adrenaline (3,5 mmol) in 250 ml of
3
2
2
(
1 mmol) in 250 ml of absolute ethanol was added,
absolute ethanol, a solution of Cu(NO ) Á5H O
3
2
2
with heating (508C) and stirring. The solid formed
was washed with absolute ethanol and dried in
vacuo.
(1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
2
.2.2. [Co(adr) ](NO )
4
2.2.9. [Cu(adr) ](NO )
3 2
3 2
2
To a solution of Adrenaline (3.5 mmol) in 250 ml of
absolute ethanol, a solution of Co(NO ) Á3H O
To a solution of Adrenaline (2 mmol) in 250 ml of
absolute ethanol, a solution of Cu(NO ) Á5H O
3
2
2
3 2
2
(
1 mmol) was added in 250 ml of absolute ethanol,
(1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
2
.2.3. [Co(adr) ](NO3)2
2
2.3. Instrumental
To a solution of Adrenaline (2 mmol) in 250 ml of
absolute ethanol, a solution of Co(NO ) Á3H O
The thermoanalytical curves were obtained using a
Perkin-Elmer TGA7 thermobalance (range 20±
10008C); the atmosphere was either pure nitrogen
3
2
2
(
1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
�
1
or air, at a ¯ow rate of 100 ml min ; the heating rate
1
�
was varied between 5 and 408C min , with the best
�
1
2
.2.4. [Ni(adr) ](NO ) .
6
resolution achieved at a rate of 108C min .
3 2
To a solution of Adrenaline (6 mmol) in 250 ml of
absolute ethanol, a solution of Ni(NO ) Á5H O
To obtain the IR spectra of the gases evolved during
the thermogravimetric analysis, the thermobalance is
coupled with a Perkin-Elmer FTIR spectrometer,
model 1760X. The TGA7 is linked to the heated
gas cell of the FTIR instrument by means of a heated
transfer line, and the temperatures of the cell and of
the transfer line are independently selected.
3
2
2
(
1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
2
.2.5. [Ni(adr) ](NO3)2
4
To a solution of Adrenaline (3 mmol) in 250 ml of
absolute ethanol, a solution of Ni(NO ) Á5H O
3. Results
3
2
2
(
1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
3.1. Elemental analysis
In Table 1, the resulting values from the elemental
analysis are listed.
2
.2.6. [Ni(adr) ](NO3)2
2
To a solution of Adrenaline (1,5 mmol) in 250 ml of
absolute ethanol, a solution of Ni(NO ) Á5H O
3.2. Thermal analysis
3
2
2
(
1 mmol) in 250 ml of absolute ethanol was added,
with heating (508C) and stirring. The solid formed was
washed with absolute ethanol and dried in vacuo.
Figs. 1±3 show the thermogravimetric pro®les of
the different complexes.

S. Materazzi et al. / Thermochimica Acta 369 (2001) 167±173
169
Table 1
Elemental analysis of the precipitated complexes: percentage values found (and calculated)
Complex
C
H
O
N
[
[
[
[
[
[
[
[
[
Co(adr)
Co(adr)
Co(adr)
6
4
2
](NO
](NO
](NO
3
3
3
)
)
)
2
2
2
50.7 (50.54)
47.0 (47.17)
39.0 (39.32)
50.7 (50.55)
47.2 (47.18)
39.3 (39.33)
50.5 (50.36)
47.0 (46.94)
39.0 (38.99)
6.4 (6.08)
5.8 (5.67)
4.7 (4.73)
6.1 (6.08)
5.8 (5.68)
4.9 (4.73)
6.1 (6.06)
5.8 (5.65)
4.8 (4.69)
30.0 (29.95)
31.6 (31.45)
34.8 (34.95)
30.1 (29.95)
31.6 (31.45)
35.1 (34.96)
30.1 (29.84)
31.1 (31.29)
34.8 (34.66)
8.9 (8.73)
9.3 (9.17)
10.2 (10.19)
8.6 (8.73)
Ni(adr)
Ni(adr)
Ni(adr)
6
](NO
](NO
](NO
3 2
)
4
2
3
3
)
)
2
9.3 (9.17)
10.3 (10.20)
8.7 (8.70)
2
Cu(adr)
Cu(adr)
Cu(adr)
6
4
2
](NO
](NO
](NO
3
)
2
2
2
3
3
)
)
9.0 (9.12)
10.3 (10.11)
The cobalt(II), nickel(II) and copper(II) complexes
molecules, and the ®nal decomposition to give the
metal oxide. The cobalt complex shows a less marked
process for the second step, while the nickel complex
shows a splitting of the ®nal decomposition in two
well de®ned TG steps.
in the M/L ratio of 1:6 show a different thermal
stability, the Co(II) complex being slightly more stable
than those of Cu(II) and Ni(II) having the lowest
thermal stability of them (Fig. 1).
The decomposition steps of the three complexes (air
ow) show the release of two adrenaline molecules,
Fig. 2 presents the thermogravimetric pro®les
of the complexes with the M/L ratio of 1:4; they
show a very similar thermal stability with air
¯
followed by the release of another two adrenaline
Fig. 1. Thermogravimetric pro®les of the [Me(adr)
�
6
3
](NO )
2
complexes. (Ð) Co(II); (Ð - Ð) Cu(II); (Ð - - Ð) Ni(II). Scanning rate:
1
� 1
1
08C min . Air ¯ow rate: 100 ml min
.

1
70
S. Materazzi et al. / Thermochimica Acta 369 (2001) 167±173
4 3 2
Fig. 2. Thermogravimetric pro®les of the [Me(adr) ](NO ) complexes. (Ð) Co(II); (Ð - Ð) Cu(II); (Ð - - Ð) Ni(II). Scanning rate: 108C
�
1
min . Air ¯ow rate: 100 ml min .
� 1
2 3 2
Fig. 3. Thermogravimetric pro®les of the [Me(adr) ](NO ) complexes. (Ð) Co(II); (Ð - Ð) Cu(II); (Ð - - Ð) Ni(II). Scanning rate: 108C
�
1
min . Air ¯ow rate: 100 ml min .
� 1

S. Materazzi et al. / Thermochimica Acta 369 (2001) 167±173
171
�
1
.
Fig. 4. Infrared spectra of the TG evolved gases for the release of adrenaline molecules. Resolution: 8 cm
¯
ow, with the Co(II) complex more stable than
tion processes. One representative IR spectrum is
shown in Fig. 4.
the Cu(II) complex, both more stable than the
Ni(II) complex.
The thermogravimetric curves of the decomposition
under nitrogen ¯ow (not reported) show a similar
pro®le in the temperature range 20±3008C, with the
®nal decomposition step very broad and often not
reaching a constant weight at 9008C.
The thermal decomposition is characterized by
three main decomposition steps, the ®rst being the
release of two adrenaline molecules, the second being
the loss of the nitrate ions, followed by the ®nal step of
oxidation to obtain the metal oxide.
The complexes with a M/L ratio of 1:2 are again
characterized by three main steps when heated in air
4. Discussion
¯
ow; the ®rst with the release of one adrenaline
molecule, the second with the loss of the nitrate ions
and the third with the ®nal oxidation to give MO. The
Cu(II) complex is more stable than the Co(II) com-
plex, with the Ni(II) complex always being the less
thermally stable.
The evolved gas analysis, performed by coupling
the thermogravimetric analyzer to an infrared spectro-
meter and with the consequent characterization of the
IR bands related to the vapours or gases evolved in the
range 20±3508C, supports the proposed decomposi-
The thermogravimetric pro®les of the solid com-
plexes show an interesting property commonly
observed for other coordination compounds prepared
in our laboratory: TG curves clearly show the pre-
sence of a fundamental 1:2 base-unit for all the 1:4
and 1:6 complexes; this can be deduced from the
releasing temperature and because the step height is
always equivalent to two ligand molecules before the
®nal decomposition process to obtain the metal
oxide.

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72
S. Materazzi et al. / Thermochimica Acta 369 (2001) 167±173
Fig. 5. Thermogravimetric curves of the [Ni(adr) ](NO
6
3
)
2
complexes: (a) precipitated from ethanolic solution; (b) precipitated from water
� 1
�
1
solution. Scanning rate: 108C min . Air ¯ow rate: 100 ml min
.
Thus, it can be proposed the coordination to the 1:2
base-unit of two adrenaline molecules, followed by
the coordination of another two molecules of adrena-
line at a second stage, to form respectively the 1:4 and
the 1:6 complex.
The experimental evidence is that the number of
coordinated molecules increases with the increasing
starting M/L molar ratio.
The analysis of the infrared spectra recorded on the
TG ef¯uent gases or vapours, clearly shows that the
processes related to the loss of two or four adrenaline
molecules are eliminations and not decompositions.
The characteristic IR bands of the TG evolved gases
are typical of adrenaline and can be attributed to the
stretching and bending vibrations of the ±OH, ±CH3
thermogravimetric decomposition in three main steps;
however, the solids precipitated from water solutions
systematically resulted thermally less stable with
respect to those precipitated from ethanolic solutions,
sometimes even 1508C less stable. Fig. 5 presents the
thermogravimetric curves of the [Ni(adr) ](NO )
complexes precipitated from ethanolic (a) or water
(b) solutions. This behaviour could be attributed to the
different polarity of the solvents used in the syntheses,
with a higher stability of the complexes in water
solution than in the ethanolic solution. This means
an opposite trend in the solid state, with the solids
obtained from ethanolic solutions being thermally
more stable than those obtained from aqueous solu-
tions.
6
3 2
and ±NH groups.
2
A possibility of driving the reaction to obtain solids
of different thermal stability was observed by using
different solvents (water and absolute ethanol). The
different solvent used for the syntheses neither chan-
ged the ®nal stoichiometry, nor the characteristic
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