Copper(II) complexes with derivatives of pyrazole as potential antioxidant enzyme mimics

Article abstract of DOI:10.1007/s00044-012-0233-5

A series of six mononuclear Cu(II) complexes with pyrazole-based ligands: 5-(2-hydroxybenzoyl)-3-methyl-1-(2-pyridinyl)-1H-pyrazol-4-phosphonic acid dimethyl ester (1a), 5-(2-hydroxyphenyl)-3-methyl-1-(2-pyridylo)-1H-pyrazole-4- carboxylic acid methyl ester (1b) and 1-benzothiazol-2-yl-5-(2-hydroxyphenyl)-3- methyl-1H-pyrazole-4-carboxylic acid methyl ester (1c) were characterized regarding to electrochemical and antioxidant properties. All complexes exhibit suitable Cu(II)/Cu(I) redox potential (E _1/2) to act as antioxidant enzymes mimic. The five of these complexes were found to be trifunctional enzyme mimics possessing SOD, CAT and GPx-like catalytic activities. Moreover, Cu(II) complexes were capable to decrease ROS level in melanoma cells and observed effects were not merely a reflection of cytotoxicity.

Full text of DOI:10.1007/s00044-012-0233-5

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2395–2402
DOI 10.1007/s00044-012-0233-5
ORIGINAL RESEARCH
Copper(II) complexes with derivatives of pyrazole as potential
antioxidant enzyme mimics
•
Bogumiła Kupcewicz Krzysztof Sobiesiak Katarzyna Malinowska
•
•
•
Kamila Koprowska Malgorzata Czyz Bernhard Keppler Elzbieta Budzisz
•
•
_
Received: 21 December 2011 / Accepted: 13 September 2012 / Published online: 26 September 2012
ꢀ The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract A series of six mononuclear Cu(II) complexes
with pyrazole-based ligands: 5-(2-hydroxybenzoyl)-3-methyl-
1-(2-pyridinyl)-1H-pyrazol-4-phosphonic acid dimethyl ester
(1a), 5-(2-hydroxyphenyl)-3-methyl-1-(2-pyridylo)-1H-pyra-
zole-4-carboxylic acid methyl ester (1b) and 1-benzothiazol
-2-yl-5-(2-hydroxyphenyl)-3-methyl-1H-pyrazole-4-car-
boxylic acid methyl ester (1c) were characterized regard-
ing to electrochemical and antioxidant properties. All
complexes exhibit suitable Cu(II)/Cu(I) redox potential
(E1/2) to act as antioxidant enzymes mimic. The five of
these complexes were found to be trifunctional enzyme
mimics possessing SOD, CAT and GPx-like catalytic
activities. Moreover, Cu(II) complexes were capable to
decrease ROS level in melanoma cells and observed effects
were not merely a reflection of cytotoxicity.
Keywords Enzyme mimic ꢀ Copper(II) complexes ꢀ
Pyrazoles ꢀ Reactive oxygen species ꢀ Cyclic voltammetry
Introduction
Reactive oxygen species (ROS) such as O2-, H2O2 and
•OH are generated in cells through aerobic metabolic
processes or as a result of interaction with exogenous
agents. Low levels are essential for proper cell function,
but excess levels of ROS are responsible for ‘oxidative
stress’ which has been linked with the progression of
ageing and many human diseases, e.g. neurogenerative,
cardiovascular and cancer. Superoxide dismutases (SODs),
catalase (CAT) and glutathione peroxidase (GPx) are
enzymes which act as a primary cellular defence system
against oxidative damage in living organisms.
B. Kupcewicz (&) ꢀ K. Sobiesiak ꢀ E. Budzisz
Department of Inorganic and Analytical Chemistry,
Faculty of Pharmacy, Collegium Medicum in Bydgoszcz,
Nicolaus Copernicus University in Torun, Curie-Sklodowskiej 9,
85-094 Bydgoszcz, Poland
Copper(II) has an important biological role in all living
systems as an essential trace element (Linder and Hazegh-
Azam, 1996). The Cu(II) complexes with organic ligands
have been used as analgesic, antipyretic, antiinflammatory
and a platelet anti-aggregating agents. Due to the redox
behaviour of the Cu(II)/Cu(I) system and the interaction of
copper complexes with O2 biomimetic complexes of cop-
per ions with biologically interesting ligand have been
investigated in detail. They have antioxidant, antitumor
activity and protect against some injuries being conse-
quences of UV exposure (Zheng et al., 2006). Recently,
several reports have appeared in the literature describing
the anticancer activity of Cu(II) derivatives of many classes
of nitrogen donors including thiosemicarbazone, imidazole
(Huang et al., 2005). Among them, pyrazole-containing
complexes have been reported to possess antitumor activity
which is comparable to that of cisplatin (Sakai et al., 2000;
Wheate et al., 2001; Al-Allaf and Rashan, 2001).
e-mail: kupcewicz@cm.umk.pl
K. Malinowska
Department of Chemistry and Clinical Biochemistry, Medical
University of Lodz, Haller Square 1, 90-647 Lodz, Poland
K. Koprowska ꢀ M. Czyz
Department of Molecular Biology of Cancer, Medical University
of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland
B. Keppler
Institute of Inorganic Chemistry, University of Vienna,
¨
Wahringerstr. 42, 1090 Vienna, Austria
E. Budzisz
Department of Cosmetic Raw Materials Chemistry,
Faculty of Pharmacy, Medical University of Lodz,
Muszynskiego 1, 90-151 Lodz, Poland
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Med Chem Res (2013) 22:2395–2402
Blood sample preparation and enzymes activity
In addition, considerable interest in the pyrazole moiety
has been stimulated by promising pharmacological, agro-
chemical and analytical applications of pyrazole-contain-
ing derivatives (Eicher and Hauptmann, 1995; Eliguero
et al., 1997; Onoa et al., 1999, 2002; Duivenvoorden et al.,
2005). Recently, substituted pyrazoles have been used as
analytical reagents in the complexation of transition metal
ions (Wisniewski et al., 1994; Majsterek et al., 2011).
In our previous articles, we have investigated the syn-
thesis, X-ray structures, physicochemical properties and
preliminary cytotoxic effect for Cu(II) complexes with
pyrazole derivatives as ligands (Miernicka et al., 2008;
Budzisz et al., 2009, 2010).
measurement
Examinated group comprise 50 individuals (aged 27–45 years).
Blood was taken from cubital vain on heparinized sample
(5 mL). Blood was centrifuged 10 min at 3,000 rpm in room
temperature. Obtained erythrocytes were three times washed
0.9 % sol NaCl at the same condition of centrifugation. After
centrifugation and removal of the supernatant 920 lL of sample
and 80 lL of Cu(II) complex solution were mixed. Next it was
added to 1 mL glucose and incubated at 37 ꢁC, after which the
hemolysate were prepared and then frozen at -70 ꢁC. Thus,
prepared hemolysate was used for further experiments. The
concentration of compounds 2a–c and 3a–c in experiment was
25 lg/mL of blood.
Activity of CAT, GPx, SOD enzymes and TAS value
were determined in blood samples (erythrocytes) treated by
Cu(II) complexes and in control samples using spectro-
photometric methods. All absorbance measurements were
performed with a UV/Vis Spectrometer Lambda 14P
(Perkin Elmer, USA).
Here, we present evaluation of the antioxidant activity
of six Cu(II) complexes with three ligands: 5-substituted-
3-methyl/phenyl-1-(2-pyridinyl)-1H-pyrazol-4-carboxylic
acid methyl ester (1a) or phosphonic acid dimethyl ester
(1b) and 1-benzothiazol-2-yl-5-(2-hydroxyphenyl)-3-methyl-
1H-pyrazole-4-carboxylic acid methyl ester (1c). We assessed
the ability to act these complexes as SOD, CAT and GPx
enzyme mimics and to scavenge ROS.
CAT activity in erythrocytes was determined according
to spectrophotometric procedure by Beers and Sizer (1952)
and expressed in Bergmeyer units (BU/g Hb). CAT activ-
ity was measured at 25 ꢁC by recording H2O2 decompo-
sition at 240 nm. One BU of CAT activity is defined as the
amount of enzyme decomposing 1 g of H2O2/min.
GPx activity in erythrocytes was measured according to
Little and O’Brien (1968) methods and expressed in
enzymatic units (U/g Hb). The difference in the rate of
GPx reaction with glutathione and lumen in the sample is
used for its activity determination by absorbance mea-
surement at 412 nm. One unit of GPx activity is calculated
as an amount of enzyme which causes 10 % decrease of
the level of reduced glutathione within 1 min at 25 ꢁC, pH
7.0.
Experimental
Materials and methods
The ligands and complexes with Cu(II) ions were prepared
as described elsewhere (Miernicka et al., 2008; Budzisz
et al., 2009, 2010). All substances were reagent grade or
better and were used without further purification.
Trolox equivalent antioxidant capacity (TEAC) assay
with ABTS and K2 S2O8
SOD activity in erythrocytes was measured according to
Misra and Fridovich (1972) methods. The activity was
determined at 37 ꢁC by the absorbance increase at 480 nm.
Activity of SOD was expressed in adrenaline units
(U/g Hb/100 mL). Haemoglobin concentrations were car-
ried out according to Van Kempen and Zijlstra (1961).
The main mechanism of this test is the reduction of the ABTS
(2,20-azino-bis[3-ethylbenzothiazoline-6-sulphonate]) radical
cation by antioxidants. The ABTS radical cation was obtained
as a result of reaction of ABTS stock solution (7 mM in
water) with 2.45 mM potassium persulfate. For measure-
ments, the ABTS•? solution was diluted with ethanol to an
absorbance of 0.700 0.020 at 754 nm. Stock solutions of
the all compounds were diluted with DMSO. For the photo-
metric assay 1,350 lL of the ABTS•? solution and 150 lL of
antioxidant solution were mixed for 45 s and absorbance was
measured immediately after 1 min at 754 nm. The concen-
tration of Cu(II) complexes was varied in the range
2–400 lM. The antioxidant activity of the tested compounds
was calculated by determining the decrease in absorbance at
Total antioxidant status determination
Determination of the total antioxidant status in blood
plasma was performed by spectrophotometric method
according to procedure no. NX2332 by Randox (Randox
Laboratories Ltd., United Kingdom,). In brief, ABTS
(2,20-azino-di-[3-ethylbenzthiazoline sulphonate]) was
incubated with peroxide (metmyoglobin) and H2O2 to
produce the radical cation ABTS with a relatively stable
blue-green colour. Antioxidants when added in examined
different concentrations by using the following equation
•?
(Schlesier et al., 2002): %antioxidant activity = ((E
Standard)/E•A?BTS) 9 100.
-
ABTS
E
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Med Chem Res (2013) 22:2395–2402
2397
Measurement of intracellular ROS
sample caused suppression of this colour production mea-
sured as decrease of absorbance with a spectrometer (UV/
Vis Spectrometer Lambda 14P, Perkin Elmer, USA) at
600 nm. The total antioxidant status was calculated as
concentration of antioxidants (mM).
ROS levels were evaluated by flow cytometry using the
probe 20,70-dichlorodihydrofluorescein diacetate (H2DCF-
DA; Sigma-Aldrich, St. Louis, MO, USA) as described
previously (Lesiak et al., 2010). In brief, A375 melanoma
cells (a gift from Prof. Piotr Laidler, Jagiellonian University,
Poland) were seeded into a 12-well plate and cultured for
18 h in RPMI-1640 medium with 5 % foetal bovine serum.
On the day of experiment, the cells were treated with
complexes at indicated concentrations for 1 h. An equivalent
concentration of DMSO was used in the control culture. In
all experiments, incubation with 2 mM N-acetylcysteine
(NAC) for 1 h was used as a reference control. After
treatment, cells were collected, washed with PBS and
incubated with the 5 lM H2DCF-DA at 37 ꢁC for 30 min in
the dark. Immediately after staining cells were collected and
analyzed by flow cytometry (FACSCalibur; Becton–Dick-
inson, Mountain View, CA, USA). All results were pro-
cessed by using CellQuest software (Becton–Dickinson).
The electrochemical properties
The electrochemical properties of ligands and metal ion
complexes have been studied by cyclic voltammetry in
DMF solution. Voltammetric measurements were made
with the aid PGSTAT12 AUTOLAB electrochemical
analyzer. Three electrodes were utilized in this system, a
glassy carbon working electrode (GCE), a platinum wire
auxiliary electrode and silver wire in contact with 0.1 M
AgNO3 in ACN reference electrode. The GCE with 3.0-
mm diameter was manually cleaned with 1 lm alumina
polish prior each scan. All solutions were deareated for
10 min prior to measurements with pure argon and then a
blanket atmosphere of argon was maintained over the
solution during measurements. The potentials were mea-
sured in 0.2 M [nBu4N][BF4]/DMF as supporting electro-
lyte, using the [Fe(g5-(C5H5)2] in DMF (E1/2 = ?0.72 V)
as internal standard.
Results and discussion
Chemistry
Cell viability
We have prepared a two series of Cu(II) complexes with a
substituted pyrazoles (1a–c), as depicted in Fig. 1. Com-
plexes 2a–c of the general formula (CuLCl2) were
obtained in reaction of ligands with CuCl2ꢀ2H2O (in a 1:1
molar ratio) in ethyl acetate. The complexes 3a–c were
synthesized in molar ratio 2:1 giving ionic complexes of
general formula [CuL2](ClO4)2 (Fig. 2). The details of
synthesis, results of elemental analysis and characteriza-
tion of complexes using IR, NMR and MS spectroscopy
were described in our previous articles (Miernicka et al.,
2008; Budzisz et al., 2009, 2010). All complexes were
recrystallized from DMF, but only compounds 2a–c
yielded crystals suitable for X-ray diffraction. The com-
plexes exhibit trigonal bipyramidal configuration at Cu(II)
centre.
Cell viability was determined after 44 h of culturing of
A375 cells in the presence of tested compounds at indi-
cated concentrations. An acid phosphatase activity (APA)
assay was used to assess viable cell numbers in cultures. In
brief, the plates were centrifuged at the indicated time
points, the medium was discarded and replaced with
100 lL assay buffer containing 0.1 M sodium acetate (pH
5), 0.1 % Triton X-100 and 5 mM p-nitrophenyl phosphate
(pNPP; Sigma-Aldrich, St. Louis, MO) and incubated for
additional 2 h at 37 ꢁC. The reaction was stopped with
10 lL of 1 M NaOH, and the absorbance values were
measured at the wavelength of 405 nm using a microplate
reader (Infinite M200Pro, Tecan, Austria).
Fig. 1 Structure of the ligands
OH
COOCH3
OH
COOCH3
OH
P(O)(OCH3)2
N
N
N
S
CH3
CH3
CH3
N
N
N
N
N
N
1a
1b
1c
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Med Chem Res (2013) 22:2395–2402
OH
P(O)(OCH3)2
OH
COOCH3
OH
COOCH3
N
N
N
S
CH3
Cl
N
CH3
Cl
CH3
N
N
N
N
N
Cu
Cu
Cu
Cl
Cl
Cl
2b
Cl
2a
2c
2
2+
2+
OH
COOCH3
OH
P(O)(OCH3)2
OH
COOCH3
N
N
S
N
CH3
CH3
N
N
N
CH3
N
-
N
N
2
N
-
2 x ClO4
Cu
N
Cu
N
Cu
N
2 x ClO4
N
N
H3C
H3C
H3C
N
N
S
N
CH3OOC
HO
(CH3O)2(O)P
HO
CH3OOC
HO
3a
3b
3c
Fig. 2 Proposed structures of the 2a–c and 3a–c complexes
½2Oꢁ2ꢂ þ 2Hþ ! H2O2 þ O2:ꢃ
SOD/CAT/GPx-like activity
The mechanism proposed for the dismutation of
superoxide anions by both SOD and metal complexes is
thought to involve redox reactions with Cu(II) and
Cu(I) ions (Ercal et al., 2001; Patel et al., 2009):
Complexes 2a–c and 3a–c were investigated on their
antioxidant activity. The SOD (SOD-1), GPx and CAT
activities and moreover total antioxidative status (TAS)
have been determined. The results were expressed as
enhancement (in %) of antioxidant enzymes activity and
TAS value in blood samples treated with Cu(II) complexes
in comparison to antioxidant activity in control samples
and are presented in Fig. 3.
½Cu2þ þ O2ꢁꢂ ! Cuþ þ O2ꢃ
½Cuþ þ O2ꢁꢂ þ 2Hþ ! Cu2þ þ H2O2:ꢃ
The addition of Cu(II) complexes to blood samples result in
statistically significant increase of SOD activity (p\0.01) in
case of all compounds. The level of SOD was increased in order
a \b \c in both series of complexes, 16.00 \28.00
\38.42 % and 3.85 \33.03 \59.16 % for series 2 and 3,
respectively. The comparison of complexes with the same
ligands revealed statistically significant difference only
between 2a and 3a complexes (p\0.001).
Our data underline that addition of compounds in blood
lead to statistically significant increase in enzymes activi-
ties in comparison to control samples. The differences
between two groups (samples with synthesized compounds
and control group) were calculated using t test for depen-
dent samples. T test results indicate that activity of CAT,
SOD, GPx and TAS value in all samples with metal
complexes was statistically significant (p \ 0.01) greater
than in control samples.
CAT and GPx are enzymes which disproportionate
H2O2 by converting it into the H2O and O2 (CAT) or only
into the water (GPx) (Day, 2009).
SOD-1 is metalloprotein that catalyze ‘dismutation’
reaction which detoxify superoxide radicals (O•2-) (Ercal
et al., 2001):
½H2O2 ! O2 þ H2Oꢃ
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Med Chem Res (2013) 22:2395–2402
2399
Fig. 3 The enhancement (in %,
mean value ? SEM) of
antioxidant activity of catalase,
superoxide dismutase (SOD),
glutathione peroxidase (GPx)
and total antioxidant status
(TAS) value in blood samples
treated with Cu(II) complexes
(20 lg/mL of blood) in
comparison with antioxidant
activity in control samples
complexes themselves. Trolox used as a standard is a deriv-
ative of vitamin E, strong natural antioxidant. The TEAC
value reveal the relative ability of hydrogen- or electron-
donating antioxidants to scavenge the ABTS•? radical cation
compared with that of Trolox. The results obtained for
complexes with Cu(II) ions are summarized in Table 1.
ROS levels were also evaluated by flow cytometry using
the probe H2DCF-DA. This non-polar compound diffuses
into cells, where undergoes deacetylation by cytosolic
esterases to form the non-fluorescent polar derivative
DCFH and thereby is trapped within the cells. In the
presence of intracellular H2O2, DCFH is oxidized to the
highly fluorescent DCF. Cells were untreated or exposed to
selected concentrations (1 or 20 lM) of Cu(II) complexes
for 1 h and then stained with 5 lM H2DCF-DA for 30 min.
The test was carried out in duplicate.
½2GSH þ H2O2 ! GS-SG þ 2H2O:ꢃ
In the present findings, all six Cu(II) complexes induced
a significant (p \ 0.01) increase (from 45 to 126 % more
than in control samples) in antioxidant enzymes levels of
GPx and CAT.
When SOD activity is high, the conversion of super-
oxide anion (O2•-) to hydrogen peroxide (H2O2) is facil-
itated. High SOD activity in conjunction with low GPx
activity will lead to increased levels of H2O2 and H2O2-
derived reactive species such as hydroxyl radical (•OH).
Relationship between SOD and CAT ? GPx can affect
more on cell sensitivity to a free radical attack than abso-
lute amounts of the individual antioxidant enzymes. Low
ratio of SOD/CAT ? GPx demonstrates high cell resis-
tance to oxidative damage.
The ratio between SOD activity and the activities of
CAT ? GPx that remove the H2O2 formed by SOD was
from 6.06 to 37.55 % lower in samples treated by Cu(II)
complexes than in control samples. These results indicated
that all complexes are more efficient in reduction of H2O2
than scavenging of superoxide radicals. In the series 3 of
complexes SOD/(CAT ? GPx) ratio decreased in order:
a [ b [ c and is very good correlated with Cu(II)/
Cu(I) redox potential.
Table 1 Antioxidant activity of complexes based on ABTS•? assay
(absorbance was measured at 734 nm, 5 min after initial mixing)
Compounds
IC50 (mM)
TEAC (mM)
2a
5.88 0.59
0.11 0.00
1.56 0.12
9.62 2.13
[100
0.12
0.27
2b
2c
0.14
3a
0.11
3b
\0.06
0.13
Free radical and ROS scavenging ability
of the complexes
3c
10.04 0.26
0.136 0.05
Trolox
The antioxidant activity of Cu(II) complexes can also be
expressed as TEAC, which means the concentration (mM) of
Trolox whose antioxidant activity are identical to 1 mg of the
Data expressed as mean value SD of triplicate measurements
TEAC Trolox equivalent antioxidant capacity, expressed as mmol
Trolox/mg of complex
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Med Chem Res (2013) 22:2395–2402
When A375, a highly aggressive melanoma cell line
were treated with Cu(II) complexes, a marked reduction of
H2O2 levels was observed, irrespective of the structure of
tested compounds. Measurements of fluorescence revealed
that Cu(II) complexes reduced intracellular H2O2 in mel-
anoma cells to the level similar as obtained in the presence
of NAC, well known for its high antioxidant activity. NAC
(2 mM) which was used as a reference control induced
50 % decline in fluorescence intensity in comparison to
untreated cells, whereas Cu(II) complexes at 20 lM caused
40–49.5 % decrease in fluorescence intensity (Fig. 4). At
that concentration Cu(II) complexes were not highly toxic
to melanoma cells as they reduced the viable cell number
to 70–85 % of that observed in control culture even when
incubation was prolonged to 44 h (Fig. 5). Thus, the
observed effects were not mainly due to cytotoxicity of
Cu(II) complexes.
Fig. 6 TAS–TEAC, TAS–ROS and TEAC–ROS relationships
The ROS-scavenging potential, TAS and TEAC values
of five Cu(II) complexes were compared each other and the
very good linear correlation were obtained (3b complex
was excluded due to inconsistent results of Trolox assay).
Correlation coefficient (r) values were: 0.9932, 0.9431 and
0.9588 for TAS–TEAC, TAS–ROS and TEAC–ROS rela-
tionships, respectively (Fig. 6).
Fig. 4 Effects of Cu(II) complexes on intracellular ROS level in
A375 melanoma cells
Cyclic voltammetry
Electrochemical properties of the complex series were
investigated with cyclic voltammetry in DMF solution. The
results obtained in the electrochemical studies are sum-
marized in Table 2. The complexes were also studied under
the same conditions for a direct comparison of the results.
All complexes show one-electron redox wave in the plotted
potential range, attributed to the Cu(II)/Cu(I) redox couple.
Second pair of peaks was only observed in the case of 1c
compound. For four of them (1a, 1b, 2b and 3b) only
single reduction waves were present additionally. The E1/2
values are within the range of -0.538 V (1b) to 0.076 V
(2c). A considerable dispersion of E values was observed.
It is possible to observe that E values are increasing in the
Fig. 5 Cu(II) complexes decreased the number of viable cells in
melanoma cultures. An APA assay was used to assess changes in
viable cell numbers. Melanoma cell line A375 was cultured with
complexes at the indicated concentrations for 44 h. Viable cell
numbers in drug-treated cultures were expressed as the percentages of
cell number in the control culture. Data represent the mean SD of
three measurements
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Med Chem Res (2013) 22:2395–2402
2401
found to be trifunctional enzyme mimics possessing SOD,
CAT and GPx-like catalytic activities. They may react with
superoxide as well as with product of superoxide dismu-
tation, H2O2. The only 3a complex showed negligible
SOD-like activity but moderate ability to reduction H2O2.
Moreover, Cu(II) complexes were capable to decrease
ROS level in melanoma cells. Those cells constantly
exposed to oxidative stress induced by UV radiation and
quinone toxicity from melanin synthesis are very efficient in
scavenging ROS. Thus, the capacity of tested compounds to
neutralize hydrogen peroxide was shown to substantially
support natural mechanisms existing in those cells.
Table 2 Cyclic voltammetry data (V)
No of
compounds
E1pa
E1pc
E11/2
E2pa
E2pc
E21/2
1a
1b
1c
2a
2b
2c
3a
3b
3c
a
0.081 -0.344 -0.131
-0.400 -0.675 -0.538 -0.287a
–
–
–
–
–
0.097 -0.014 0.042 -0.034 -0.380 -0.207
-0.216 -0.264 -0.250
-0.219 -0.349 -0.284 0.043a
–
–
–
–
–
–
–
–
–
–
–
–
–
0.158 -0.005 0.076
0.123 -0.082 0.021
-0.148 -0.339 -0.244 0.225a
–
–
-0.229 -0.400 -0.315
–
Acknowledgments We sincerely thank Dr. Roman Modranka and
´ ´
Only anodic peak
Dr. Magdalena Miernicka from Medical University in Łodz for pro-
viding Trolox assay and synthesis of ligands, respectively. Financial
support from Collegium Medicum of Nicolaus Copernicus University
following row: a \ b \ c for ligands and 2 series of
complexes. However, for 3 series of complexes there is an
inverse relationship: c \ b \ a. In case of complexes with
1a ligand (2a and 3a), one observes peak separation of
roughly 45 mV, in contrast to complexes with ligands 1b
and 1c which exhibit three times greater peak separation
(130–190 mV). The peak-to-peak separation (DEp) and
proportion of the anodic peak current and the cathodic peak
current mostly indicates a quasireversible process. How-
ever, in the case of 1a, 2a and 3a compounds, there is a
reversible process.
´ ´
(Grant No. 411) and Medical University of Łodz (Grant Nos. 507-13-
041 and 503/3-066-02/503-01 to E. Budzisz, 502-17-664 to K.
Malinowska, and 503/1-156-01/503-01 to M. Czyz) are gratefully
acknowledged.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
It is known that an adequate Cu(II)/Cu(I) redox potential
for effective catalysis of superoxide radical must be
required between -0.405 V for O2/O•2- and ?0.645 V for
O•2-/H2O2 versus SCE (at pH 7) or between -0.762 and
?0.29 V versus Ag/AgNO3/ACN, respectively. The
Cu(II)/Cu(I) redox couples of both series of complexes
(2a–c, 3a–c) are within this potential range; therefore,
these complexes are expected to exhibit SOD-like activity.
The highest enhancement of SOD activity exhibits com-
plexes with ligand 1c (2c, 3c).
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