Spectroscopic studies of some copper(II) complexes with amino acids

Article abstract of DOI:10.1016/j.molstruc.2006.11.048

Copper-amino acids complexes in aqueous solution: [Cu-(L₁)₂]·H₂O (1), (L₁ = methionine), [Cu-(L₂)₂]·H₂O (2), (L₂ = phenylalanine) and [Cu(L₃)₂] (

Full text of DOI:10.1016/j.molstruc.2006.11.048

Journal of Molecular Structure 834–836 (2007) 364–368
www.elsevier.com/locate/molstruc
Spectroscopic studies of some copper(II) complexes with amino acids
A. Stanila a, A. Marcu b, D. Rusu c, M. Rusu d,¤, L. David b
a Agricultural Sciences and Veterinary Med. University, 400018 Cluj-Napoca, Romania
b Babes-Bolyai University, Faculty of Physics, 400084 Cluj-Napoca, Romania
c Iuliu Hatieganu University, Faculty of Pharmacy, 400023 Cluj-Napoca, Romania
d Babes-Bolyai University, Faculty of Chemistry, 400028 Cluj Napoca, Romania
Received 8 September 2006; received in revised form 7 November 2006; accepted 18 November 2006
Available online 28 December 2006
Abstract
Copper-amino acids complexes in aqueous solution: [Cu-(L1)2]·H2O (1), (L1 D methionine), [Cu-(L2)2]·H2O (2), (L2 D phenylalanine)
and [Cu(L3)2] (3), (L3 D triptophan) were synthesized and characterized by means of elemental, thermal and IR, UV–Vis and EPR spec-
troscopic investigations.
The IR spectra show that amino acids act as bidentate ligands with coordination involving the carboxylic oxygen and the nitrogen
atom of the amino group. The ꢀ(CBO) and ꢁ(N–H) vibrations are shifted toward higher (for 1 and 2) and lower-wave numbers for 3.
Visible electronic and Powder EPR spectra at room temperature are typical for monomeric species with square-planar local symmetry
around the metal ion.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Amino acids; Cu(II) complexes; FT-IR spectroscopy; UV–Vis spectroscopy; EPR spectroscopy
1. Introduction
which is very speciWc, forms complexes with divalent metal
ions [3].
In recent years Cu(II) amino acids complexes have
received much attention because they proved to be useful
antibacterial agents applied against Staphylococcus aureus,
Escherichia coli, nutritive supplies for humans and animals,
etc. [1].
Methionine is one of the amino acids containing sulphur,
it helps to prevent disorders of the hair, skin and nails, in
lowering the cholesterol levels by increasing the liver’s pro-
duction of lecithin and reduces fat build-up in the liver and
body [4].
Twenty natural amino acids comprise the building
blocks of proteins, which are chemical species indispensable
to perform a large number of biological functions [2]. From
these 20 amino acids, eight are essential and cannot be pro-
duced by the human body. Methionine, phenylalanine and
tryptophan are three of these essential amino acids.
Complexes of transition metals with amino acids in pro-
teins and peptides are utilized in numerous biological pro-
cesses, such as oxygen conveyer, electron transfer and
oxidation. In these processes, the enzymatic active site,
Phenylalanine is essential to many functions and is one
of the few amino acids that can directly aVect brain chemis-
try by crossing the blood–brain barrier [5].
Tryptophan is a precursor of the vital neurotransmitter,
serotonin, tryptophan levels in the body regulate moods
and sleep [6].
2. Experimental
2.1. Methods
The Vario El device allows the quantitative determination
of the carbon, nitrogen, hydrogen, sulfur, and oxygen in vari-
ous operating modes. Atomic absorption measurements of
*
Corresponding author.
E-mail address: mrusu@chem.ubbcluj.ro (M. Rusu).
0022-2860/$ - see front matter © 2006 Elsevier B.V. All rigts reserved.
doi:10.1016/j.molstruc.2006.11.048

A. Stanila et al. / Journal of Molecular Structure 834–836 (2007) 364–368
365
copper were realized with an AAS-1 device at ꢂD320nm
wavelength. Melting points were recorded on an Electrother-
mal Analyser working in the temperature range of 20°C and
370°C and checked by thermal analysis and are uncorrected.
The thermogravimetric analysis (TG) were carried out
using a Q-1500 D derivatograph, in the temperature
range of 20–800 °C, at a heating rate of 10 °C min¡1. The
analyses were carried out over samples varying from 100
to 300 mg.
FT-IR spectra were taken with a Perkin-Elmer FT-IR
1730 spectrophotometer over KBr solid samples in
4000–400cm¡1 range.
UV and visible electronic spectra were recorded in the
ꢂ D190–800 nm range in aqueous and DMF solutions using
a standard Jasco V-530 spectrophotometer.
tion measurements of the copper conWrm the 1:2 copper ion
to ligand composition for the synthesised complexes.
Data of the elemental analysis results for copper amino
acids complexes are illustrated in Table 1.
3.2. Thermogravimetric diVerential analysis
The weight loss proWles are analyzed the amount or per-
cent of weight loss at any given temperature, and the tem-
perature ranges of the degradation processes were
determined [8].
Thermal stability domains, melting points, decomposi-
tion phenomena and their assignments for the copper
amino acids complexes are summarized in Table 2.
The analysis of thermal curves of the complexes clearly
indicates that the weight loss between 20 and 105 °C corre-
sponds to one water molecule for Wrst two complexes.
Because of the low temperatures, this water molecule may
be considered as crystal water [9].
Powder EPR measurements were performed at room
temperature at 9.4 GHz (X band) using a standard JEOL-
JES-3B equipment.
2.2. Synthesis of copper amino acids complexes
The sharp endothermic peak occurring between 230 and
260°C may be due to melting of the complexes without
weight loss.
In the temperature range 200–500°C the exothermic
peaks in the DTA curves indicated the successive two
decompositions steps.
The exothermic peak at »320 °C may be due to loss of
two molecule of organic radicals (C3H7SO-S-metyl-thio-
ethyl, C7H7-phenyl or C9H8N-indolyl) from two molecules
of the ligand. The second exothermic peak at »470 °C, cor-
respond to the pyrolysis of the amino acid rest. The com-
plexes are stable up to ca. 350 beyond which they start
decomposing and decomposition continues up to 500 as
shown by a horizontal plateau on the TG curves. The Wnal
weight of the residues correspond to the corresponding
metal oxides as end product [10].
The purpose of the study was to obtain neutral com-
plexes of CuL2·nH2O type at pH 8–10, in the presence of a
strong basis (NaOH) to obtain the ionization conditions of
the amino acid (methionine, phenylalanine and triptophan).
The complexes were prepared following the procedure
described in the literature [7]: 2mmol of L1 (0.286 g), L2
(0.320 g) or L3 (0.408 g) were dissolved in distilled water
(5ml for L1 and 20 ml for L2 and L3). For L1 dissolution
took place only with slow heating. For deprotonation of
the amino acids 0.33 ml 30% NaOH was added.
Then 1 mmol of the metal salt (0.241g of
Cu(NO3)2·3H2O) was dissolved in 2ml of distilled water,
and was added to the deprotonated amino acid solution
under stirring for several minutes. The precipitate was
Wltered oV, washed with water several times, and dried in
air.
Based on the above arguments, the proposed structures
of the complexes are shown in Fig. 7.
For all amino acids precipitation was instantaneous, and
were grey-blue for Cu(L1)2 (ꢃ D 85.8%), blue-green for
Cu(L2)2 (ꢃ D 88.6%) and light-blue for Cu(L3)2 (ꢃ D84.4%).
The compounds were found to be soluble in methaol, etha-
nol, DMSO or DMF.
3.3. FT-IR spectroscopy
Information about the copper ion coordination was
obtained by comparing the IR frequencies of the ligands
with those of the copper complexes with amino acids as
ligands.
3. Results and discussions
In the Wgures (Figs. 1–3) the main parts of the IR spectra
are presented and the most important absorption bands
and their assignments are shown in Table 3.
3.1. Elemental analysis
The elemental analysis measurements of the carbon,
nitrogen, hydrogen, sulfur, and oxygen and atomic absorp-
In the spectra of the ligands, the ꢀ(N–H) stretching
vibrations appear at t3146 cm¡1 for L1, t3070 cm¡1,
Table 1
Elemental analysis data for copper amino acids complexes
Compound
Formula
weight
Colour
Yield %
Melting
point (°C)
% Found (Calc.)
C
H
N
S
Cu
[Cu(L1)2]·H2O
[Cu(L2)2]·H2O
[Cu(L3)2]
377.96
407.92
469.96
Grey-blue
Blue-green
Light-blue
85.80
88.60
84.40
230
255
260
31.54 (31.77)
53.40 (53.00)
55.80 (56.22)
5.72 (5.86)
4.72 (4.94)
7.89 (7.71)
7.27 (7.41)
7.00 (6.86)
11.65 (11.92)
8.56 (8.73)
–
–
16.44 (16.81)
15.82 (15.57)
13.56 (13.52)

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A. Stanila et al. / Journal of Molecular Structure 834–836 (2007) 364–368
Table 2
Thermal data of the copper (II)–amino acids complexes
Compound
Temperature range (°C)
DTG peak (°C)
Endo
TG weight loss (%)
Assignment
Exo
Calc.
Found
[Cu(L1)2]·H2O
20–200
200–350
100
230
–
–
–
310
465
4.76
–
4.83
One mole of crystal water
Melting point
Organic rest 2C3H7SO
2C2H3NO2
–
39.77
38.65
16.81
4.39
–
44.46
35.64
15.50
–
39.82
37.20
17.04
4.45
–
44.52
35.15
15.86
–
350–500
–
CuO residue
[Cu(L2)2]·H2O
[Cu(L3)2]
20–200
200–350
105
255
–
–
–
320
470
One mole of crystal water
Melting point
Organic rest 2C7H7
2C2H3NO2
CuO residue
–
350–500
–
20–200
–
–
200–350
260
–
–
–
320
475
–
–
Melting point
Organic rest 2C9H8N
2C2H3NO2
55.39
31.08
13.52
55.60
30.20
13.68
350–500
CuO residue
Fig. 1. IR spectra of L1 and 1.
3030cm¡1 for L2 and at 3076cm¡1, 3012 cm¡1 for L3. These
bands appear to be shifted toward higher frequencies in the
spectra of the complexes with 83cm¡1 for (1), 250 cm¡1 and
226cm¡1 for (2), and 190 cm¡1 for (3) proving the involve-
ment of the –NH2 group in the complex formation [11].
The absorption band at 1610 cm¡1 was attributed to the
ꢀ(CBO) stretching vibration in the L1 spectrum and
appears to be shifted to 1648cm¡1 for complex (1). The
same vibration appears in the L3 spectrum at 1660cm¡1
which is shifted with 35cm¡1 toward lower frequencies in
the spectrum of complex (3) displaying a well-resolved and
high-intensity signal, which involves the carboxylic group
in covalent bonding to the copper ion [12].
Fig. 2. IR spectra of L2 and 2.
symmetric and asymmetric bending vibrations of N–H
bond. In the spectrum of the complex (1) these bands
appear at 1616 cm¡1 and at 1568 cm¡1, shifted compared to
those of the ligand, which means that –NH2 group is
involved in metal–ligand formation. These vibrations in the
L2 and L3 spectra appear at 1557 cm¡1, 1581 cm¡1, respec-
tively and are shifted to 1567 cm¡1 and 1568 cm¡1 in the
corresponding spectra of the complexes (2) and (3), which
The consecutive bands at 1580 cm¡1, 1563 cm¡1,
1508cm¡1 in the spectrum of the L1 were assigned to the

A. Stanila et al. / Journal of Molecular Structure 834–836 (2007) 364–368
367
Fig. 4. Visible spectra of (2) in DMSO.
spectrum of L3 was attributed to the ꢀ(O–H) vibration and
appears to be shifted in the spectrum of the complex (3) to
3389 cm¡1 meaning that the O–H band is not involves in
hydrogen bonding.
The band at 2909cm¡1 the spectrum of complex (1) was
attributed to the CH2–S and CH3–S symmetric and asym-
metric bonds and is slightly shifted compared to that of the
ligand (2915 cm¡1) which means that these groups were not
involved in the coordination. The narrow peak at
1243 cm¡1 in the spectrum of L1 is due to the wagging
vibration of the CH2–S bond [13].
Fig. 3. IR spectra of L3 and 3.
The stretching vibration of the benzene ring appears at
745cm¡1 and 1495 cm¡1 in the spectrum of L2 and is
slightly shifted in the spectrum of complex (2).
The stretching vibration of the indol ring has similar
value for the L3 ligand and (3) which means that there was
no involvement in the coordination [14].
Table 3
Some IR bands (cm¡1) of the ligands and the copper–amino acids com-
plexes
Band
L1
1
L2
2
L3
3
ꢀ(N–H)
3146
3229
3070
3030
1623
3320
3256
1627
3076
3012
2851
2733
1660
–
3269
ꢀ(C–H)
2574
2737
1610
1352
1316
1580
1563
1508
1406
–
–
–
ꢀ(CBO)
ꢀ(C–C)
1648
1334
–
–
–
–
1625
–
ꢁs(N–H)
1616
1568
1557
1567
1581
1568
ꢁ(C–H)
ꢀ(O–H)
ꢀ(benzene)
1403
3449
–
1409
–
745
1495
–
1377
3500
750
1498
–
1411
3401
752
1387
3389
–
–
ꢀ(indolinic)
–
–
740
1456
–
742
1456
–
Wagging(CH2S)
ꢀ(CH2S–CH3S)
1243
2915
–
–
–
–
–
2909
–
–
also indicates the involvement of this group in the metal–
ligand bond formation.
The ꢀ(O–H) stretching vibration does not appear in the
spectra of the Wrst two ligands, but they do in spectra of
their complexes (1) and (2) at 3449 cm¡1 and 3500 cm¡1,
respectively, suggesting the presence of the crystal water in
these compounds. The shoulder at 3377cm¡1 in the
Fig. 5. Powder EPR spectra of 1 (a), 2 (b) and 3 (c) at room temperature.

368
A. Stanila et al. / Journal of Molecular Structure 834–836 (2007) 364–368
O
C
NH2
O
R
CH
Cu
HC
R
C
H2N
O
S
O
H3C
(CH )
2 2
for Cu-L1
for Cu-L2
R =
Fig. 6. EPR spectrum of Cu-phenylalanine in DMF solution at room tem-
perature.
CH2
R =
R =
for Cu-L3
CH2
NH
3.4. UV–Vis spectroscopy
Fig. 7. Structural formula proposed for the copper amino acid complexes.
The bands in the range 200–370 nm can be assigned to
n ! ꢀ¤/ꢀ! ꢀ¤ intraligand transitions associated to amino
acid. Free ligands and complexes exhibit similar spectra in
UV region in relation to the number the absorption bands.
A common feature of these spectra is the presence of three
absorption peaks. The two located at lower frequencies
have been ascribe to ꢀ! ꢀ¤(338 nm) and ꢀ! ꢀ¤(260 nm)
transition and the additional peak found at higher frequen-
cies correspond to the ꢀ! ꢀ¤(210 nm) transition in a
sequence of increasing energy. These bands are shifted to
lower energy in the copper complexes at 384nm, 275 nm
and 225 nm, respectively [15].
The visible spectra of the copper complexes exhibit a d–d
broad band whose max. 650–550nm and two lower-intensity
shoulders at »540 and »720nm, respectively. Such a feature
should be expected for a square planar CuO2N2 chromo-
phore. (Fig. 4) Moreover, the variation of the position of the
above absorption band can be ascribed to perturbation ener-
gies arising from the inductive and delocalization eVects of the
substituents on the amino acids fragments.
phenylalanine) and [Cu(L3)2] (L3 D triptophan) were syn-
thesized and analyzed by means of elemental analysis, ther-
mogravimetric and diVerential analysis, atomic absorption,
IR, UV–Vis and EPR spectroscopies.
The composition corresponded to a metal–ligand ratio
in all the Cu(II) complexes was found to be 1:2.
The IR spectra show that the amino acids act as biden-
tate ligands with coordination involving the carboxyl oxy-
gen and the nitrogen atom of amino group.
The electronic and EPR spectra conWrm square-planar
local symmetry for the copper ion.
The obtained structural data allow us to propose struc-
tural formula for the studied copper complexes as shown in
Fig. 7.
References
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3.5. EPR spectroscopy
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tion Metal Compounds, Elsevier, Amsterdam, 1992, p. 102.
Powder EPR spectra (Fig. 5) at room temperature are typ-
ical for monomeric species with square-planar local symme-
try around the metal ion. The principal values of the g tensor
are: gII D2.197, gr D2.136 (1), gII D2.202, gr D2.128 (2) and
gII D2.212, gr D2.120 (3). The ordering of g values indicates
2
2
the presence of an unpaired electron in a dx ¡y orbital. The
calculated gav values (gav t2.15) show a considerable cova-
lent character of the complexes. Fig. 6 show the EPR spec-
trum of the Cu(II)-phenylalanine in DMF solution at room
temperature display the copper hyperWne structure. The iso-
tropic EPR parameters for investigated complexes are:
g0 D2.135, A0 D82G for (1), g0 D2.122, A0 D80G for (2) and
g0 D2.132, A0 D81G for (3) [16].
4. Conclusions
The copper amino acids complexes in aqueous solution:
[Cu(L1)2]·H2O (L1 D methionine), [Cu(L2)2]·H2O (L2 D