Copper(II) complexes of tridentate N,N,N′,N″,N″-pentamethyldiethylenetriamine: Superoxide dismutase and inhibitory activity against bacteria and fungi

Article abstract of DOI:10.1016/j.saa.2006.04.017

A series of ternary copper(II) complexes containing same coordination sphere but difference in the counter ions, viz., [Cu(PMDT)(OAc)]PF₆ (1); [Cu(PMDT)(OAc)]ClO₄ (2); [Cu(PMDT)(OAc)]BF₄ (3) and [Cu(PMDT)(OAc)]BPh₄

Full text of DOI:10.1016/j.saa.2006.04.017

Spectrochimica Acta Part A 66 (2007) 726–731
Copper(II) complexes of tridentate
N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine:
Superoxide dismutase and inhibitory activity
against bacteria and fungi
R.N. Patela,∗, Nripendra Singha, V.L.N. Gundlaa, U.K. Chauhanb
a Department of Chemistry, A.P.S. University, Rewa (M.P.) 486003, India
b School of Environmental Biology, A.P.S. University, Rewa (M.P.) 486 003, India
Received 17 February 2006; received in revised form 22 April 2006; accepted 25 April 2006
Abstract
A series of ternary copper(II) complexes containing same coordination sphere but difference in the counter ions, viz., [Cu(PMDT)(OAc)]PF6
(1); [Cu(PMDT)(OAc)]ClO4 (2); [Cu(PMDT)(OAc)]BF4 (3) and [Cu(PMDT)(OAc)]BPh4 (4) where PMDT = N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-
pentamethyldiethylenetriamine, OAc = Acetate ion were synthesized and characterized by means of spectroscopic, magnetic and cyclic
voltammetric measurements. In frozen solution e.p.r. spectra, an interesting relation g > g has been observed which is a typical of the axially
||
⊥
symmetric d9 CuII (SCu = 1/2) having an unpaired electron in a dx −y
orbital. Single crystal X-ray analysis of (1) has revealed the presence
2
2
of distorted square planar geometry. The influence of the counter ion on the complexes has been examined by performing some biological
experiments like superoxide dismutase and anti-microbial activity.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Copper(II) complexes; Electron paramagnetic resonance (e.p.r.); Superoxide dismutase (SOD); Crystal structure; Anti-microbial activity
1. Introduction
(PMDT) is a potentially tridentate ligand capable of bonding
through two amino groups and one imino group. Our interest
in these complexes was associated with the structural, mag-
netic, spectroscopic and redox properties as well as catalytic
(superoxide dismutase activity) and inhibitory activity against
bacteria and fungi of [(PMDT)Cu(II)(OAc)]+ chelates bearing
different anions. In this communication, we report the syn-
thesis, characterization and biological activity of some Cu(II)
complexes containing same coordination sphere but different
in counter ions.
Copper is a bioessential element with relevant oxidation
states +1 and +2 and its coordination geometries are square
planar or square pyramidal. Tridentate ligands have been exten-
sively used in coordination chemistry in recent years [1]. Beside
other reasons, the interest in these systems are concerned to
the possibility of obtaining low symmetry four, five or six
coordinated complexes, especially if significant steric ligand
restrictions are present [2,3]. The presence of unsymmetrical
metal environments in several biological systems (e.g. in copper
enzymes) has been linked to their redox properties [4,5].
In our previous communications [6,7], we have reported a
series of copper(II) complexes having diethylenetriamine and
N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine as tridentate lig-
ands and some bidentate (2,2ꢀ-bipyridine, 1,10-phenanthroline)
ligands. The N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine
2. Experimental
2.1. Materials and methods
N,N,Nꢀ,Nꢀꢀ,Nꢀꢀ-pentamethyldiethylenetriamine,
NaPF6,
NaClO4, NH4BF4 (Aldrich), copper(II) acetate monohydrate,
NaBPh4 (s.d. fine Chemicals) were used as purchased. Ele-
mental analyses were performed on elemental analyzer. FAB
mass spectra were recorded on a JEOL SX 102/DA 6000 mass
∗
Corresponding author. Tel.: +91 07662 231373; fax: +91 07662 230819.
E-mail address: rnp64@yahoo.co.uk (R.N. Patel).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.04.017

R.N. Patel et al. / Spectrochimica Acta Part A 66 (2007) 726–731
727
spectrometer using Xenon (6 kV, 10 mA) as the FAB gas. The
magnetic susceptibility data were recorded on a Gouy balance
at room temperature using mercury(II) tetrathiocyanato cobal-
tate(II) (χg = 16.44 × 10−6 c.g.s. unit) as calibrant. e.p.r. spectra
were recorded at RT and LNT (77 K) on a Varian E-line Century
Series e.p.r. Spectrometer operating at 9.4 GHz with TCNE
as a calibrant. UV–vis spectra were recorded on a Shimadzu
UV–vis 160 spectrophotometer with quartz cells. The SOD
activities were evaluated using alkaline DMSO as a source of
superoxide radicals (O2−) and nitro blue tetrazolium (NBT)
as scavanger [8,9]. The in vitro anti-microbial (antibacterial
and antifungal) activities of these complexes were tested using
paper disc diffusion method and agar plate technique [10,11]. A
BAS-100 Epsilon electrochemical analyzer was used for cyclic
voltammetric experiment on DMSO solution of the complex
containing tetrabutylammonium perchlorate (TBAP) as the
supporting electrolyte. The three-electrode measurement was
carried out at 298 K under nitrogen atmosphere with a platinum
working electrode, a platinum wire auxiliary electrode and a
silver/silver chloride reference electrode (Ag/AgCl).
Fig. 1. ORTEP diagram of the complex [Cu(PMDT)(OAc)]PF6.
mary of crystal data and structure refinement parameters for
[Cu(PMDT)(OAc)]+ are given in Table 1. Selected bond angle
and bond distances are listed in Table 2. In this complex,
PMDT is coordinated to copper(II) through two amino and one
imino nitrogen and one oxygen (hydroxyl) from the acetate.
The copper center in the complex has a distorted square planar
environment.
2.2. Synthesis of the complexes
2.2.1. Preparation of [Cu(PMDT)(OAc)]PF6 (1);
[Cu(PMDT)(OAc)]ClO4 (2); [Cu(PMDT)(OAc)]BF4 (3)
and [Cu(PMDT)(OAc)]BPh4 (4)
Bond angles show that the coordination geometry around the
copper atom is a distorted square planar, were N(3)Cu(1)N(2)
Allthepresentcomplexeswerepreparedbyageneralmethod.
To an aqueous methanolic solution (15 ml 1:3, v/v) of copper
acetate monohydrate (1 mmol, 0.199 g) a methanolic solution
(10 ml) of PMDT (1 mmol, 0.137 g) was reacted under stirring
for 0.5 h at 25 ◦C. After completion of the reaction, a saturated
methanolic solution (5 ml) of NaPF6 was added to the above
reaction mixture and left for slow evaporation. After 3–4 days
dark blue crystals of complex (1) were obtained. They were
washed with diethyl ether and dried on air at room temperature,
Yield 80%. Anal. Found: C, 30.00; H, 5.85; N, 9.52%. Calc. for
C11H26N3CuO2PF6: C, 29.94; H, 5.89; N, 9.52%. FAB Ms; m/z
obs. (cal.) 295 (295.84).
Complexes (2), (3) and (4) were prepared as described above
by employing NaClO4, NH4BF4 and NaBPh4, respectively in
place of NaPF6. Anal. Found: C, 33.75; H, 7.01; N, 10.55%.
Calc. for C11H26N3CuO6Cl (2): C, 33.43; H, 6.58; N, 10.63%.
FAB Ms; m/z obs. (cal.) 295 (295.84). Anal. Found: C, 34.60; H,
6.90; N, 11.02%. Calc. for C11H26N3CuO2BF4 (3): C, 34.47; H,
6.79; N, 10.97%. FAB Ms; m/z obs. (cal.) 295 (295.84). Anal.
Found: C, 21.45; H, 4.60; N, 7.11%. Calc. for C35H46N3CuO2B
(4): C, 21.46; H, 4.22; N, 6.82%. FAB Ms; m/z obs. (cal.) 295
(295.84).
Table 1
Crystal data and structure refinement for [(PMDT)Cu(OAc)](PF)6 (1)
Empirical formula
Formula weight
Temperature (K)
C11H26CuF6N3O2P
440.86
293 (2)
0.70930
Monoclinic
P21
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
˚
˚
˚
a (A)
6.4310 (7)
b (A)
17.7140(10)
c (A)
7.9960(5)
90
92.082 (7)
90
910.29 (13)
2, 1.608
1.355
454
α (◦)
β (◦)
γ (◦)
3
˚
Volume (A )
Z, calculated density (mg/m3)
Absorption coefficient (mm−1
F (000)
)
Crystal size (mm)
θ range for data collection
Index ranges
0.40 × 0.35 × 0.35
2.29◦–24.94◦
0 ≤ h ≤ 7, −21 ≤ k ≤ 0, −9 ≤ l ≤ 9
1802/1652 [Rint = 0.0581]
99.6%
Reflections collected/unique
Completeness to 2θ = 24.94◦
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R indices (all data)
Ψ-scan
3. Results and discussion
0.6485 and 0.6133
Full-matrix least-squares on F2
1652/1/223
3.1. Crystal structure
1.022
R1 = 0.0372, wR2 = 0.0889
R1 = 0.0650, wR2 = 0.0986
−0.02 (5)
The crystal structure of the mononuclear copper(II) com-
plex consists of cationic unit of [Cu(PMDT)(OAc)]+ and
un-coordinated one hexafluorophate ion. A perspective view
of [Cu(PMDT)(OAc)]PF6 (1) is shown in Fig. 1. Sum-
Absolute structure parameter
Largest diff. peak and hole (e, A
−3
˚
)
0.484 and −0.490

728
R.N. Patel et al. / Spectrochimica Acta Part A 66 (2007) 726–731
Table 2
3.2. Magnetic moment
◦
˚
Selected bond lengths (A) and angles ( ) for [(PMDT)Cu(OAc)](PF)6 (1)
The magnetic susceptibility measurements in the polycrys-
talline state show that the complexes are paramagnetic at ambi-
ent temperature. The observed magnetic moment values of the
present complexes are quiet close to the values expected for cop-
per(II) complexes without interaction. The magnetic moment
values of the complexes are with in the range of 1.80–1.82 B.M.
Incaseofcomplex(4)thevalueisfoundtobe1.78B.M. Thislow
value is due to magnetic interaction between two copper metal
centres (intermolecular). Such type of magnetic interaction has
been proved by our e.p.r. observations of the same complex.
The magnetic moment value (μeff.) for remaining complexes as
indicated above lie within the range normally found for other
copper(II) complexes [14,15].
Cu(1) O(2)
Cu(1) N(3)
Cu(1) N(2)
Cu(1) N(1)
N(1) C(3)
N(1) C(1)
N(1) C(2)
N(2) C(4)
N(2) C(5)
N(2) C(6)
N(3) C(9)
N(3) C(7)
1.940(3)
1.990(13)
1.993(4)
2.117(12)
1.458(19)
1.47(2)
1.575(18)
1.476(19)
1.488(7)
1.49(2)
1.410(19)
1.49(2)
1.49(2)
91.8(5)
178.9(5)
88.8(6)
N(3) C(8)
O(2) Cu(1) N(3)
O(2) Cu(1) N(2)
N(3) Cu(1) N(2)
O(2) Cu(1) N(1)
N(3) Cu(1) N(1)
N(2) Cu(1) N(1)
C(3) N(1) Cu(1)
C(1) N(1) Cu(1)
C(2) N(1) Cu(1)
C(4) N(2) Cu(1)
C(5) N(2) Cu(1)
C(6) N(2) Cu(1)
C(9) N(3) Cu(1)
C(7) N(3) Cu(1)
C(8) N(3) Cu(1)
95.2(5)
162.6(2)
84.0(6)
3.3. e.p.r. Spectra
107.2(9)
105.9(10)
108.9(9)
106.9(8)
109.5(4)
104.9(9)
120.0(10)
107.6(9)
106.1(9)
e.p.r. Spectra of the present complexes were recorded in
polycrystalline and in glassy state at room temperature (r.t.)
and liquid nitrogen temperature (l.n.t.), respectively. Derived
e.p.r. spectral parameters are given in Table 3. Representative
e.p.r. spectra are shown in Figs. 3 and 4. Polycrystalline spec-
tra of the present complexes show a single broad line at room
temperatures. The basic spectral features at both temperatures
are same with slight better resolution at l.n.t. These broad line
e.p.r. spectra are due to Ms = 1 at g = ∼2.08. Ms = signal
(half-field signal) is observed in (4) only which is characteris-
tic of a magnetic triplet [16,17]. However, when dissolved in
coordinating solvents such as dimethyl sulphoxide, the samples
provided a four line spectra typical of monomeric copper(II)
species. The frozen solution e.p.r. spectra of these complexes in
DMSO shows g > g . It is interesting that the relation g > g
is 88.8(6); N(3)Cu(1)N(1) and O(2)Cu(1)N(2) angles are
162.6(2) and 178.9(5), respectively. Above observation is
in agreement with other four coordinated copper(II) sys-
tems [12]. Cu O and Cu N bond lengths are 1.940(3) and
1.990(13)–2.117(12), respectively and are in general agreement
with similar complexes [6,7,13]. The elongation of the Cu N
bonds in the present complex with comparison to Cu N bonds
(1.990(13)–2.117(12)) containing diethylenetriamine (Cu N
2.005(4)–2.186(4)) [7] clearly indicates the strong electron-
withdrawing effect of the methyl substituents. All distances and
angles in PF6− anion appear normal.
||
⊥
||
⊥
is typical of the axially symmetric d9 CuII (SCu = 1/2) hav-
ing one unpaired electron in a dx2−y2 orbital [18]. The spectra
showed well resolved e.p.r. features arising out of MI = +3/2
component of copper giving a A value 175 1 G. No nitrogen
||
A stereoscopic view of the unit cell −can be seen in
Fig. 2 and this shows how the large PF6 ion isolate the
[Cu(PMDT)(OAc)]+ cation.
Fig. 3. e.p.r. Spectrum (liquid nitrogen temperature) in 100% DMSO of
[Cu(PMDT)(OAc)]ClO4.
Fig. 2. Unit cell diagram of the complex [Cu(PMDT)(OAc)]PF6.

R.N. Patel et al. / Spectrochimica Acta Part A 66 (2007) 726–731
729
Table 3
e.p.r. Parameters of copper(II) complexes
Complexes
g
g
⊥
A (G)
||
g1
g2
f (cm−1
)
||
[Cu(PMDT)(OAc)]PF6 (1)
[Cu(PMDT)(OAc)]ClO4 (2)
[Cu(PMDT)(OAc)]BF4 (3)
[Cu(PMDT)(OAc)]BPh4 (4)
2.20
2.20
2.20
2.20
2.046
2.042
2.046
2.046
176
174
178
177
2.053
2.148
2.148
–
2.031
2.074
2.076
–
134
135
132
133
superhyperfine splitting have been observed. The spectral fea-
tures are similar to those reported for copper(II) – polyamines
complexes[19,20].
The g and A values of the complexes are found to be almost
||
||
the same, which indicate that the bonding is dominated by the
PMDT moiety. The empirical factor f = g /A cm−1 is an index
|| ||
of tetragonal distortion and its value may vary from 105 to 135
for small to extreme distortion in square planar complexes and
depends on the nature of the coordinated atoms [21]. The f values
ofthecomplexes are found to bein therange132–135, indicating
significant distortion from planarity.
Fig. 5. The UV–vis spectra (0.003 mol−1 dm−3
) of complexes (1)
As follows 135 (2) > 134 (1) > 133 (4) > 132 (3).
The above spectral observations are in agreement with X-ray
diffraction studies for the complex [Cu(PMDT)(OAc)](PF6).
[Cu(PMDT)(OAc)]PF6, (2) [Cu(PMDT)(OAc)]ClO4, (3) [Cu(PMDT)(OAc)]
BF4 and (4) [Cu(PMDT)(OAc)]BPh4.
3.5. Cyclic voltammetry
3.4. UV–vis spectra
Theredoxbehaviourofthepresentcomplexeshasbeenexam-
ined by cyclic voltammetry (CV) under nitrogen atmosphere
in dimethylsulphoxide, in the potential range +0.9 V to −0.8 V
versus Ag/AgCl. Cyclic voltammetric data for the copper(II)
complexes in 0.1 M TBAP-DMSO solution are listed in Table 4.
The complexes show two quasireversible redox waves (Fig. 6)
of an one-electron transfer corresponding to Cu(II)/Cu(I) and
Cu(I)/Cu(0) redox couples. Complex (2) and (3) exhibit ill-
defined anodic waves.
The UV–vis spectra of the present complexes were recorded
in 100% DMSO. The visible spectra of the present com-
plexes in solutions show that the absorption bands occurs at
650 1 nm (Fig. 5), characteristic of a copper(II) dx2−y2
→
dxz, dyz (2B1g → Eg) [22,23] transition in a tetragonal ligand
field, in which the copper(II) has a distorted square planar geom-
etry environment. The above observations are in agreement with
those found from the X-ray data.
3.6. Biological activities
3.6.1. Anti-microbial activity
All complexes were tested for anti-microbial activity. The
activity of the complexes were evaluated against different
species of bacteria and fungi [11,24–26]. The susceptibility of
the certain strains of bacteria and fungi towards the present metal
complexeswerejudgedbymeasuringthesizeofinhibitiondiam-
eter.
In the present experiment, we have tested all the four
complexes (1), (2), (3), and (4) against five bacterial cultures
and four fungal cultures. These complexes showed significant
Table 4
Cyclic voltammetric data of copper(II) complexes
Complex
CuII/I couple
CuI/0 couple
Epa(Epc), V
Epa(Epc), V
[Cu(PMDT)(OAc)]PF6 (1)
[Cu(PMDT)(OAc)]ClO4 (2)
[Cu(PMDT)(OAc)]BF4 (3)
[Cu(PMDT)(OAc)]BPh4 (4)
0.212(−0.380)
(−0.208)
−0.215(−0.532)
(−0.322)
Fig. 4. Polycrystalline e.p.r. spectrum (room temperature) of (a)
[Cu(PMDT)(OAc)]PF6, (b) [Cu(PMDT)(OAc)]ClO4 and (c) [Cu(PMDT)
(OAc)]BPh4.
(−0.223)
(0.293)
0.191(−0.216)
−0.142(−0.365)

730
R.N. Patel et al. / Spectrochimica Acta Part A 66 (2007) 726–731
Table 5
Anti-microbial activity of the title complexes against human pathogens
S. No.
Test organisms
Zone of inhibition (nm)
Complex (1)
Complex (2)
Complex (3)
Complex (4)
Bacterial species
1
2
3
4
5
Proteus vulgaris
Streptococus sp.
E. coli
Pseudomonas pyocyanea
Salmonella sp.
2.1
2.6
R
3.5
R
3.5
4.9
2.6
1.9
2.1
R
R
3.6
2.8
1.9
1.0
3.5
R
2.6
3.9
Fungal species
6
7
8
9
Aspergillas nigar
Alternaria
Penicillium sp.
Fusarium sp.
6.5
7.1
R
6.3
4.1
2.1
6.5
R
R
3.6
2.5
5.8
3.6
R
8.7
6.0
R: resistant.
activity against Aspergillas vigan, Alterneria altemata, Peni-
cillium sp. and Fusarium sp. a plant pathogen. It was noticed
that complex (1) was the best antifungal agent in comparison to
others. Showed least activity in comparison to other complexes.
It was observed that bacterial species were more susceptible
than fungi. Complex (2) was comparatively more effective
than (1), (3) and (4) against all tested bacteria, but (3) was not
effective against P. vulgaris and Streptococcus bacteria. This
also showed least effectiveness against Salmonella sp. Complex
(1) was effective against Pseudomonas bacteria and (4) showed
good activity against Salmonella sp. only. Complex (3) was
only complex which showed anti-microbial activity for E. coli.
and Pseudomonas. Results of anti-microbial assessment of
complexes are shown in Table 5.
Fig. 7. Superoxide dismutase activity of [Cu(PMDT)(OAc)]PF6.
distorted geometry of complexes may favor the geometrical
change, which is essential for the catalysis of copper in the
Cu–Zn SOD that also changes distorted square pyramidal geom-
etry [28,29].
3.6.2. Superoxide dismutase activity
The SOD activity of the present complexes were investigated
by NBT assay and catalytic activity towards the dismutation of
superoxide anion was measured. IC50 value of the complex (1)
is 68 ␮mol dm−3 (Fig. 7), and the remaining complexes (2), (3)
and (4) are 66, 70 and 73 ␮mol dm−3, respectively these are in
the same order of magnitude as the best SOD model complexes
[27,28] but higher than the native SOD (0.04 ␮mol dm−3). The
4. Supplementary material
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 294244 for complex [Cu(PMDT)(OAc)]PF6 (1).
Copies of this information be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge, CB 21 EZ,
UK (fax: +44 1223 336033; e-mail: deposit@ccdc-cam.ac.uk or
http://www.ccdc.cam.ac.uk/.
Acknowledgements
Our grateful thanks are due to National Diffraction Facility,
X-ray Division and RSIC (SAIF), IIT Mumbai for single crys-
tal data collection and e.p.r. measurements, respectively. The
Head RSIC, Central Drug Research Institute, Lucknow is also
thankfully acknowledged for providing analytical and spectral
facilities. Financial assistance from CSIR New Delhi is also
thankfully acknowledged. One of the authors (N.S.) is thankful
to CSIR New Delhi for the award of Research Associateship.
Fig. 6. Cyclic voltammogram of [Cu(PMDT)(OAc)]BPh4 in 0.1 M TBAP [scan
rate: 100(mV/s)].

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