Synthesis, crystal structure, properties, and nuclease activity of a new Cu(II) complex [Cu(L)2(Py)2(H2O)] (HL = N-(5-(4-methylphenyl)-[1,3,4]-thiadiazole-2-yl)toluenesulfonamide)

Article abstract of DOI:10.1134/S1070328415050024

A new N-sulfonamide ligand, N-(5-(4-methylphenyl)-[1,3,4]-thiadiazole-2-yl)toluenesulfonamide (HL) and its Cu(II) complex [Cu(L)₂(Py)₂(H₂O)] (I), have been synthesized. The X-ray crystal structure of the ligand and of comp

Full text of DOI:10.1134/S1070328415050024

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2015, Vol. 41, No. 6, pp. 395–404. © Pleiades Publishing, Ltd., 2015.
Synthesis, Crystal Structure, Properties, and Nuclease Activity
of a New Cu(II) Complex [Cu(L)2(Py)2(H2O)] (HL = Nꢀ(5ꢀ(4ꢀ
Methylphenyl)ꢀ[1,3,4]ꢀThiadiazoleꢀ2ꢀyl)toluenesulfonamide)1
A. C. Hangana, A. Turzab, R. L. Stana, *, R. Stefanc, and L. S. Opreana
a Faculty of Pharmacy, University of Medicine and Pharmacy, ClujꢀNapoca, 400010 Romania
b National Institute for R&D of Isotopic and Molecular Technologies, Cluj, 400293 Romania
c Preclinics Department, University of Agricultural Science and Veterinary Medicine, ClujꢀNapoca,400372 Romania
*eꢀmail: roxanaluc@yahoo.com
Received October 24, 2014
Abstract—A new
mide (HL) and its Cu(II) complex [Cu(L)2(Py)2(H2O)] (
structure of the ligand and of complex have been determined (CIF files CCDC nos. 975153 (HL), 851790 (
In
, the Cu2+ ion is fiveꢀcoordinated, forming a CuN4O chromophore. The ligand acts as monodentate,
coordinating the metal ion through a single Nthiadiazole atom. The molecules from the reaction medium (pyriꢀ
dine and water) are also involved in the coordination of the Cu2+ ion. Complex
has a slightly distorted square
N
ꢀsulfonamide ligand,
N
ꢀ(5ꢀ(4ꢀmethylphenyl)ꢀ[1,3,4]ꢀthiadiazoleꢀ2ꢀyl)toluenesulfonaꢀ
), have been synthesized. The Xꢀray crystal
)).
I
I
I
I
I
pyramidal geometry. The complex was characterized by FTꢀIR, electronic, EPR spectroscopic and magnetic
methods. The nuclease activity studies of the synthesized complex confirm his capacity to cleavage the DNA
molecule. The ligand has two important roles in the nuclease activity of I: it influence the reactivity of the
Cu2+ ion and interact with DNA molecule. The complex interacts with the DNA molecule. Immediately, the
Cu2+ ion is reduced to Cu(I), and in the presence of molecular oxygen the formed Cu(I) complex produces
reactive oxygen species in close proximity to the double helix.
DOI: 10.1134/S1070328415050024
1
INTRODUCTION
the structure of the complexes) results in degradation
of the DNA molecule through an oxidative mechaꢀ
nism [9, 10].
Transitionꢀmetal complexes endowed with redox
properties and DNA affinity have been developed as
chemical cleavers of nucleic acids over the last two deꢀ
cades. Their ability to cleave DNA has several possible
applications that include probing structural variations
in nucleic acids, identification of binding sites of DNA
ligands, design of artificial DNA cleavers and potential
chemotherapeutic agents [1–3].
For the past several years, our group has worked on
the synthesis of copperꢀsulfonamide complexes in orꢀ
der to obtain novel antitumor agents. These complexes
are especially attractive as anticancer agents because
several substituted sulfonamides have been found to arꢀ
rest the cell cycle, causing apoptosis in the M phase [11].
In this context, we have described the nuclease activity of
several copperꢀsulfonamide complexes [12–15]. In the
present paper, we report the synthesis, the crystal
structure and the physicoꢀchemical characterization of a
The synthesis of Cu(II) complexes with Nꢀsubstiꢀ
tuted heterocyclic sulfonamides greatly increased in
the past twenty years due to the diversity of biological
activity of the resulting compounds: antimicrobial,
antiꢀinflammatory, the mimetic superoxide dismutase
(SOD) or nuclease activity. Studies have shown that
Cu(II) complexes with different types of ligands can
be used as potential “chemical nucleases” [4–8].
new
Nꢀsubstituted heterocyclic sulfonamide: HL =
Nꢀ(5ꢀ(4ꢀmethylphenyl)ꢀ[1, 3, 4]ꢀthiadiazoleꢀ2ꢀyl)ꢀtoluꢀ
enesulfonamide
2
2
3
3
As reported in literature, the ligands commonly
used to form complexes with “nuclease activity” are
quinolones, sulfonamides and flavonoides. The aroꢀ
N
S
4
N
N
S
CH3
H O2
5
1
matic rings in the structure of Nꢀsubstituted sulfonaꢀ
6
5
mides can be intercalated between the bases of the
DNA chain. This interaction, followed by reactive oxꢀ
ygen species (ROS) formation (due to this Cu2+ ion in
6
H3C
7
(HL)
1
The article is published in the original.
395

396
HANGAN et al.
One complex of this ligand with Cu(II), 7.73–7.71 (4H, d.,
[Cu(L)2(Py)2(H2O)] (I), was prepared and its strucꢀ
J
= 7.8, Hꢀ6, Hꢀ3), 8.52 (1H, s.,
Hꢀ1). MS (
m/z):
346 [M + H+].
ture was determined by Xꢀray diffraction. Its IR, EPR,
electronic spectra and its magnetic susceptibility were
investigated and discussed, along with the structural
and spectral comparison with those of the analogous
complexes. The study of nuclease activity shows his
capacity to intercalate in the DNA molecule and the
Synthesis of complex I. A solution of CuSO4
⋅
5H2O
(4 mmol) in 20 mL of pyridine–H2O (V : V = 1 : 1) was
added dropwise under continuous stirring to a solution
of HL ligand (1 mmol) dissolved in 25 mL pyridine–
H2O (V : V = 2 : 3). The resulting solution was stirred
at room temperature for 2 h and left to stand at room
temperature. After two months by the slow evaporation
of the solvent, greenꢀblue crystals suitable for Xꢀray difꢀ
fraction were obtained. The yield was ~58%.
OH• radicals and the O–2 anion radical are the speꢀ
•
cies involved in the cleavage of the DNA molecule.
EXPERIMENTAL
For C42H40N8O5S4Cu (M = 928.61)
Materials and physical measurements. Copper sulꢀ
fate pentahydrate, methanol, toluenesulfonylchloꢀ
ride, 2ꢀaminoꢀ5ꢀ(4ꢀmethylphenyl)ꢀ[1,3,4]ꢀthiadiazꢀ
ole and pyridine were purchased from Fluka and Merꢀ
ck chemical companies and were used without further
purification.
Elemental analyses (C, N, H, and S) were perꢀ
formed with Vario EL analyser. IR spectra were reꢀ
corded with a Jasco FT/IRꢀ4100 spectrophotometer
using diffuse reflectance of incident radiation focused
on a sample in the 4000–450 cm–1 range. All melting
points were determined in open capillaries with an
Electrothermal IA 9100 apparatus and were uncorꢀ
rected. 1H NMR spectrum of the ligand was recorded at
room temperature using DMSO as solvent in 5 mm
tubes on Bruker AM 300 NMR spectrometer equipped
with a dual, 1H (multinuclear) head operating at 300 MHz
for protons. Fast ion bombardment (FAB) mass specꢀ
trum of the ligand was obtained on a VG Autospec
anal. calcd., %: C, 54.31; H, 4.31; N, 12.06; S, 13.79.
Found, %:
C, 54.20; H, 4.22; N, 12.21; S, 13.85.
IR (KBr;
ν
, cm–1): 1488 (thiadiazole); 1296 (S=Oas),
1125 (S=Os), 927 (S–N). UVꢀVis (solid; λmax , nm):
314 (π → π∗), 401(LMCT), 583 (d–d).
Xꢀray crystallography
(HL), size 0.25 0.21
glass fiber and used for data collection. Crystal data
were collected at 293(2) K using a dual microsourse
Supervova Diffractometer and MoKα radiation (
0.71073 ). A blue crystal of was mounted on a glass
fiber and used for data collection. Crystal data
were collected at 293(2) K using a dual microsourse
Supervova Diffractometer and CuKα radiation (
1.54184 ).
.
A white crystal of the ligand
×
× 0.15 mm was mounted on a
λ
=
Å
I
λ
=
Å
The data were processed with CrysAlisPro [16] and
corrected for absorbtion using ABSPACK [17]. The
structure was solved by direct methods using the program
SHELXSꢀ97 [18] and refined by fullꢀmatrix leastꢀsquares
techniques against F 2 using SHELXLꢀ97 [19]. Both
SHELXSꢀ97 and SHELXLꢀ97 are incorporated in
Olex2 [20] software package. Positional and anisoꢀ
tropic atomic displacement parameters were refined
for all nonhydrogen atoms. Hydrogen atoms were loꢀ
cated in difference maps and included as fixed contriꢀ
butions riding on attached atoms with isotropic therꢀ
mal parameters. Atomic scattering factors were from
International Tables for Crystallography [21]. Molecꢀ
ular graphics were from PLATON [22] and
SCHAKAL [23]. A summary of the crystal data, experiꢀ
mental details and refinement results is listed in Table 1.
spectrometer in mꢀnitrobenzene as a solvent. Diffuse
reflectance spectrum of the complex was carried out
on a Jasco Vꢀ550 spectrophotometer. Magnetic susꢀ
ceptibilitie was measured at room temperature with
the Faraday MSBꢀMKI balance. Hg[Co(NCS)4] was
used as susceptibility standard. Electronic paramagꢀ
netic resonance (EPR) spectrum was performed at
room temperature with a Bruker ELEXSYS spectromꢀ
eter operating at the Xꢀband frequency.
Synthesis of HL. A solution containing 1 mmol of
2ꢀaminoꢀ5ꢀ(4ꢀmethylphenyl)ꢀ[1,3,4]ꢀthiadiazole and
0.9 mmol of toluenesulfonylchloride in 18 mL of pyriꢀ
dine was heated at reflux for 1 h, at 60
was added to 30 mL of cold water and stirred for severꢀ
al minutes. The resulting solid was recrystallized from
ethanol. The yield was 87%; m.p. = 232–234 C.
°C. The mixture
Supplementary material has been deposited with
the Cambridge Crystallographic Data Centre
°
(nos. 975153 (HL), 851790
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
(I); deposit@
For C16H15N3O2S2 (
M = 345)
anal calcd., %: C, 55.63; H, 4.38; N, 12.16; S, 18.56.
.
DNA cleavage Reactions were performed by mixꢀ
ing 7 L of cacodylate buffer 0.1 M, pH 6 (cacodylic
acid/sodium cacodylate), 6 L of complex solution
(final concentrations: 3, 6, 9, 12 and 15 M), 1 L of
pUC18 DNA solution (0.25 g/ L, 750 M in base
pairs), and 6 L of activating agent solution (H2O2–
= 7.8, Hꢀ5, Hꢀ2), ascorbic acid) in a threefold molar excess relative to
.
Found, %:
C, 55.47; H, 4.26; N, 12.25; S, 18.72.
μ
μ
IR (KBr;
ν
, cm–1): 3260 (N–H), 1544 (C=Car), 1551
μ
μ
(thiadiazole), 1315 (S=Oas), 1154 (S=Os); 903 (S–N).
1H NMR (DMSOꢀd6;
, ppm ( , Hz)): 2.37–2.36 (6H, s.,
Hꢀ4, Hꢀ7), 7.38–7.34 4H, d.,
μ
μ
μ
μ
δ
J
J
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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SYNTHESIS, CRYSTAL STRUCTURE, PROPERTIES, AND NUCLEASE ACTIVITY
Table 1. Crystal data, experimental details and refinement results for HL and complex
397
I
Parameter
Formula weight
Value
345.44
293(2)
928.61
293(2)
Temperature, K
Crystal system
Triclinic
Monoclinic
Space group
P/n2
P
1
a
, Å
, Å
6.5667(4)
10.6561(10)
13.5350(16)
67.598(10)
88.551(8)
72.139(7)
828.91(13)
2
15.0977(3)
21.7903(4)
13.1399(2)
90
b
c
, Å
, deg
, deg
, deg
α
β
103.3750(17)
90
γ
Volume, Å3
4205.56(8)
4
Z
ρcalcd, mg/m3
1.432
1.468
Absorption coefficient, mm–1
0.336
3.049
F
(000)
Crystal size, mm
Range for data collection, deg
372
1928
0.25
6.28–58.14
8, –14 14, –17
×
0.21
×
0.15
0.37
3.46–74.78
18, –26 22, –16
8243
× 0.14 × 0.07
θ
Limiting indices
–8
≤
h
≤
≤
k
≤
≤
l
≤
18 –14
≤
h
≤
≤
k
≤
≤ l ≤ 11
Collected reflections
Independent reflections (Rint
6166
)
3755 (0.0444)
99.90
3998 (0.0575)
99.92
Completeness to θ = 27.48, %
Data/restraints/parameters
3755/0/210
1.152
5127/6/552
1.019
Goodnessꢀofꢀfit on F 2
Final
indices (all data)
Δρmax Δρmin
Å–3
R
indices (
I
> 2
σ
(I
))
R
1 = 0.0732, wR2 = 0.1934
1 = 0.1119, wR2 = 0.2329
0.44/–0.42
R
1 = 0.0523, wR2 = 0.1314
1 = 0.1125, wR2 = 0.1748
0.183/–0.191
R
R
R
/
, e
the concentration of the complex. The resulting soluꢀ ium bromide (10 mg/mL) at 100 V for 2 h. The bands
were photographed on a capturing system (Gelprinter
Plus TDI).
tions were incubated for 1 h at 37°C, after which a
quench buffer solution (3 L) consisting of broꢀ
µ
mophenol blue (0.25%), xylene cyanole (0.25%) and
glycerol (30%) was added. The solution was then subꢀ
To test for the presence of ROS generated during
strand scission and for possible complexꢀDNA interaction
sites, various reactive oxygen intermediate scavengers and
groove binders were added to the reaction mixtures. The
jected to electrophoresis on 0.8% agarose gel in 0.5
TBE buffer (0.045 M Tris, 0.045 M boric acid, and 1 mM
EDTA) containing 5
×
µ
L/100 mL of a solution of ethidꢀ scavengers used were 2,2,6,6ꢀtetramethylꢀ4ꢀpiperidone
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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398
HANGAN et al.
H(1)
N(2)
N(1)
H(6)
C(6)
O(1)
C(5)
H(7)
H(1c)
C(2)
N(3)
H(15)
C(15)
C(1)
C(8)
C(7)
C(9)
S(2)
S(1)
C(4)
H(1a)
H(14)
O(2)
H(1b)
C(3)
H(4)
H(3)
C(10)
C(11)
C(14)
C(13)
C(16)
H(11)
C(12)
H(12)
H(16c)
H(16b)
H(16a)
Fig. 1. ORTEP drawing of ligand HL.
(0.5 M), DMSO (14 M),
(400 mM), superoxide dismutase (SOD; 15 units). In
addition, a chelating agent of copper(I), neocuproine
t
ꢀbutyl alcohol (10.5 M), NaN3 typical for double bonds. The N(1)–S(1) length of
1.612 , is consonant with data obtained for other sulꢀ
Å
fonamides with similar structure [27]. The geometry of
the N(1) atom of the sulfonamide group is trigonal plaꢀ
nar, as shown by the values of the angles between neighꢀ
(36
(80
µ
µ
M), along with the groove binder distamycin
M) were also assayed. Samples were treated as
boring atoms: H(1)N(1)S(1) (120
(119 ) and C(8)N(1)S(1) (121 ).
The S(1)–C(5) bond (1.766
bonds in the molecule and indicates the of
°), H(1)N(1)C(8)
described above.
°
°
Å
) is the largest of all
interacꢀ
RESULTS AND DISCUSSION
π
Relevant bond distances and angles for the molecule
HL are collected in Table 2. The molecular structure
and crystallographic numbering scheme are illustrated in
Fig. 1. Interpretation of the crystallographic data is
carried out by comparison with data available from methꢀ
azolamide ligands and 5ꢀaminoꢀ1,3,4ꢀthiadiazoleꢀ2ꢀsulꢀ
fonamide [24, 25].
tions between the sulfonamide group and the toluene’s
ring.
The C–C bond lengths of the two toluene rings in
the sulfonamidic molecule are between 1.362 and
1.394
ble bond. The distances C(13)–C(16) and C(1)–C(2),
1.517 and 1.518 , respectively, indicate the existence
of bond between these atoms.
Relevant bond distances and angles for complex
Å and are intermediate between a single and a douꢀ
Å
The resulting structure for the thiadiazole ring is
planar. The bond distance between the C(9)–N(3) atoms
σ
I
is 1.296
bond length is larger (1.345
tion of charge on these atoms and the adjacent N(1)
atom in the sulphonamidic group. Nevertheless, the
C(8)–N(2) and C(8)–N(1) bonds, the latter of 1.319
Å
, typical for a double bond. The C(8)–N(2)
are collected in Table 2. The molecular structure and
crystallographic numbering scheme are illustrated in
Fig. 2.
Å
), due to the delocalizaꢀ
Complex
I contains a CuN4O entity in a slightly
Å,
are shorter than a C–N single bond (1.416
Å for
distorted square pyramidal geometry. In the basal
(equatorial) plane Cu2+ ion is coordinated by two niꢀ
trogen atoms of the two thiadiazole rings (N(2a) and
N(2b)) from the sulfonamidate ligands and two nitroꢀ
gen atoms from each pyridine molecules (N(1) and
N(2)). The Cu(1)–Nthiadiazole lengths (Cu(1)–N(2a)
N(sp3). Also, due to the delocalization of charge in the thiꢀ
adiazole ring and sulfanilamido group, the N(2)–N(3)
bond of 1.369
On the other hand, the C–S bonds of the thiadiazꢀ
ole ring, C(9)–S(2) (1.746 ) and C(8)–S(2) (1.729 ),
are essentially equal and similar to the thiophene ring [26].
This indicated a marked character of the bonds, reꢀ
sulting as a delocalization of the negative charge denꢀ
sity through the thiadiazole ring.
Å is lower than N–N single bond (1.420 Å).
Å
Å
2.004(3) and Cu(1)–N(2b) 2.026(3) Å) are similar to
π
those corresponding to the other complexes with sulꢀ
phonamide ligands containing a thiadiazole ring [8,
28, 29]. Cu(1)–Npyridine lengths (Cu(1)–N(1) 2.025(4)
The sulfur atom (S(1)) of the sulfonamide group and Cu(1)–N(2) 2.023(3)
shows a distorted tetrahedral geometry, the largest deꢀ measured for similar compounds [8]. One water O atꢀ
viation occurs at the O(1)S(1)O(2) angle of 118.7 om occupies the axial position with a bond length of
while the other angles have values between 104 –111 2.316(3) . The angles between the atoms in the ecuaꢀ
The distances between the sulfur and oxygen atoms in torial plane are of about 90 (88.2(1) –91.2(1)
S(1)–O(1) and S(1)–O(2) bonds are 1.424 and 1.441 and those between the atoms on the axial plane and
Å) are consonant with those
°
,
°
°.
Å
°
°
°)
Å,
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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SYNTHESIS, CRYSTAL STRUCTURE, PROPERTIES, AND NUCLEASE ACTIVITY
399
Table 2. Selected bond lengths (Å) and angles (deg) for HL and complex
Bond , Å
I
d
Bond
d, Å
HL
C(8)–N(2)
C(9)–N(3)
N(1)–S(1)
N(1)–C(8)
S(1)–O(1)
S(1)–O(2)
S(1)–C(5)
1.612(5)
1.319(5)
1.424(3)
1.441(4)
1.766(3)
1.345(6)
1.296(7)
1.369(5)
1.746(4)
1.729(5)
N(3)–N(2)
C(9)–S(2)
C(8)–S(2)
I
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(2a)
2.025(3)
2.023(3)
2.004(3)
Cu(1)–N(2b)
Cu(1)–O
2.026(3)
2.316(3)
Angle
ω
, deg
Angle
ω, deg
HL
N(1)C(8)S(2)
N(1)S(1)O(1)
N(1)S(1)O(2)
N(1)S(1)C(5)
O(1)S(1)O(2)
N(1)C(8)N(2)
107.1(2)
111.1(2)
104.1(2)
118.7(2)
120.5(4)
130.6(3)
121.1(3)
107.5(2)
107.3(2)
S(1)N(1)C(8)
C(5)S(1)O(2)
C(5)S(1)O(1)
I
N(1)Cu(1)N(2)
N(1)Cu(1)N(2a)
N(1)Cu(1)N(2b)
N(2)Cu(1)N(2a)
N(2)Cu(1)N(2b)
166.4(1)
91.1(1)
88.6(1)
88.2(1)
91.2(1)
N(2a)Cu(1)N(2b)
N(1)Cu(1)O
176.3(1)
96.3(1)
97.3(1)
90.5(1)
93.2(1)
N(2)Cu(1)O
N(2a)Cu(1)O
N(2b)Cu(1)O
the ecuatorial plane are similar (90.5(1)°–97.3(1)°). ture for the complex [Cu(L)2(Py)2(H2O)]. The bond
length change is described by the tetragonality (T
5).
The tetragonality values, 0.87 for the compound, fit
into the range expected for square pyramidal complex
[26]. The inꢀplane angular distorsions described by the
The distances almost equal between Cu(1) and N atꢀ
oms in the ecuatorial plane, the distance significantly
bigger between Cu(1) and O atom in the axial plane
and the angles forming the coordination polyhedron
confirm the slightly distorted square pyramidal strucꢀ ratio τ represent a percentage of trigonal distortion of
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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400
HANGAN et al.
C(1b)
C(2b)
C(3b)
C(7b)
C(6b)
C(5b)
C(4b)
C(3)
O(1b)
S(1b)
C(16a)
C(13a)
O(2b)
C(4)
C(14a)
C(15a)
C(2)
C(1)
N(1b)
C(8b)
S(2b)
C(5)
N(1)
Cu(1)
N(2b)
N(3a)
O
C(12a)
C(11a)
N(2a)
C(11b)
C(12b)
C(10a)
C(9a)
C(9b)
N(3b)
N(1a)
N(2)
C(6)
S(2a)
C(10b)
C(8a)
O(1a)
C(15b)
C(14b)
C(10)
O(2a)
C(13b)
C(16b)
C(9)
C(7)
C(8)
S(1a)
C(4a)
C(3a)
C(6a)
C(5a)
C(2a)
C(7a)
C(1a)
Fig. 2. ORTEP drawing of the [Cu(L) (Py) (H O)] complex.
2
2
2
a squareꢀpyramidal geometry [30]. The
τ value of
3083, 3055, 3030 (
(C–C), (CCH)); 1292, 1226 (
1145, 1081, 1067 ( (CCH)); 991 ( (N–C)); 973, 940,
883, 748 ( (N–C)); 704 ( (C–H)); 653 ( (NCC));
604 cm–1
(NCC)) [31].
q
(C–H)); 1581, 1573, 1481, 1437
0.165 for indicates a very slight distortion. It is noteꢀ
I
(q
β
β(NCH)); 1216,
worthy that the coordination of Cu2+ ion takes place
through the Nthiadiazole (N(2a) and N(2b)) atom instead
through the deprotonated Nsulfonamido (N(1a) and
N(1b)) atom. This is a consequence of the charge delꢀ
localization between the sulfonamido and the thiadiaꢀ
zole ring. The sulfonamidate ligand (L–) acts as monꢀ
odentate as it coordinates through a nitrogen atom of
the thiadiazole heterocycle. The sulfonamide moleꢀ
cules of this type can behave as bidentate ligands as
well through the N atom from the thiadiazole moiety
and through one of the O atoms and even through the
Nsulfonamido atom from the sulfonamido moiety [27]. As
it is expected the pyridine and the water molecules
participate in the coordination as monodentate
ligands.
β
q
χ
γ
ρ
γ
(
In spectrum of , the bands related to pyridine only
I
exist; they appear at the same wavenumber ~994 and
~1070 cm–1, but at the same time there are bands with
different spectral position than in intial compound
spectrum situated at 1043, 1446 1488 cm–1. The shift
of the bands assigned to ν(C–C) in pyridine from
1034, 1039, 1483 cm–1 to the above mentioned posiꢀ
tion ilustrated that external environment influence
upon that ring.
The most remarkable difference between the IR
spectrum of the ligand and the IR spectrum of I occurs
in the band corresponding to the stretching vibration of
the thiadiazole ring, which is shifted from 1550 cm–1
The experimentally observed Fourier transform inꢀ
frared (FTꢀIR) peaks of the complex are compared
with the obtained spectra for the starting materials: pyꢀ
ridine and HL. Infrared bands, related to ligand and
pyridine molecules, are present in the obtained crystal
spectrum and prove the raw materials presence in the
final structure as described through XRD analysis.
(HL) in the free ligand to 1488 cm–1 in
I
. The characꢀ
teristic band corresponding to the
ν
(S–N) (927 cm–1)
in the complex shifted to higher frequencies with reꢀ
spect to those of the uncoordinated HL (920 cm–1).
The characteristic band corresponding to the ν(N–N)
Literature indicates that the bands corresponding (1181 cm–1) in the complex shifted to higher frequenꢀ
to the uncoordinated pyridine molecules appear at cies with respect to those of the uncoordinated ligand
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SYNTHESIS, CRYSTAL STRUCTURE, PROPERTIES, AND NUCLEASE ACTIVITY
401
HL (1152 cm–1). These modifications in the thiadiazꢀ
ole heterocycle and in the sulfonamide group are atꢀ
tributed to the involvement to the Nthiadiazole atom in
coodination of Cu(II) and to the deprotonation of the
sulfonamido moiety for the complex [32]. Bands due
to the antisymmetric and symmetric vibration modes
of the S=O bond appear at 1296 and 1128 cm–1 in the
IR spectrum of I
, that is lower (~15 cm–1) than those
Experimental
Simulated
corresponding to the free ligand; such a decrease can
be related to the electron transfer from the deprotoꢀ
nated, negatively charged N atom to the sulfonyl oxyꢀ
gen atoms, which results in partial singleꢀbond charꢀ
acter for the S–O bonds [33–35]. The lack of bands
close to 3200 cm–1, which were originally present in
the spectra of the free ligands confirms the deprotonaꢀ
tion of the N–H bonds. This deprotonation of the
Nsulfonamido atom causes a weak conjugation effect
among the three N, S, O atoms of the moiety.
2600 2800 3000 3200 3400 3600 3800
, G
H
In final complex spectrum, there are bands related to
the ligand only which changed their spectral position
because of the new environment where the atoms are
bonded. For instance, bands at 1274, 1296, 1306 cm–1
in I are shifted to lower wave number when compared
with the ligand and their relative intensity has been
changed after crystallization.
Fig. 3. FTꢀIR spectrum of complex I.
mid DNA, the fastest migration will be observed for
DNA of the closed circular conformation (Form I), if
one strand is cleaved, the supercoiled conformation
will relax to produce a slowerꢀmoving nicked conforꢀ
mation (Form II). If both strands are cleaved, a linear
conformation (Form III) will be generated that miꢀ
grates in between.
The other bands can be attributed to pyridine, as
they sometimes overlap the frequencies corresponding
to moieties of the ligand. The features of the IR specꢀ
trum of the complex are similar to those reported for
the other copper Nꢀsulfonamide derivatives [10, 34,
36] and demonstrate the existence of new linkages
within the complex.
The ability of the complexes to cleave DNA was asꢀ
sayed with the aid of gel electrophoresis on supercoiled
pUC18 DNA in DMF: cacodylate buffer (0.1 M, pH 6.0)
a molar proportion (1 : 39) in the presence of
H2O2/ascorbic acid, 3.0ꢀfold excess relative to the
complex concentration. Control experiments with
CuSO4 were also carried out under the same experiꢀ
mental conditions. The obtained results are presented
The solid electronic spectrum of I displays a band
at 401 nm assigned to a LMCT transition. The comꢀ
plex exhibits a d–d band at 583 nm. This pattern,
characteristic for a distorted squareꢀpyramidal geomꢀ
etry, agrees well with the crystallographic data [37].
in Fig. 4
mid in cacodilate buffer) or of the control with reducꢀ
ing agents, there is no nuclease activity (lanes 2 and 3).
. In the presence of the control (pUC18 plasꢀ
The polycrystalline Xꢀband EPR spectrum of the
complex is axial. The EPR parameters, obtained by simꢀ
g|| = 2.31, g⊥ = 2.076 and A|| = 159 ×
10–4 cm–1
It appears that complex can destroy the DNA
molecule in stages, forming the circular form at a conꢀ
centration of 18 M and then the linear form of the
DNA molecule at the concentration of 24 and 30 M.
In the case of the last two concentrations, the circular and
linear form coexist (lane 12 and 13), while at 18 M the
I
ulation are
for complex (Fig. 3) [38]. According to the Bertini
classification, the value of || can be correlated with the
geometry of the complex [39]. Thus, values between
μ
A
μ
A
160 and 200 ×
10–4 cm–1 correspond to a squareꢀplanar
μ
geometry and the values between 130 and 160 cm–1 corꢀ
respond to a square pyramidal or distorted trigonal biꢀ
circular and the helicoidal form coexist (lane 11). Iniꢀ
tially, the cleavage is realized in a single point of a
DNA chain, leading to the circular form. Later, a secꢀ
ond cleavage occurs in another point of the chain,
leading to the linear form.
pyramidal geometry. As g||
unpaired electron must be in the
[40].
>
g
⊥ in the complexes, the
dx2 −y2
(or dxy) orbital
The room temperature mesurements of the magꢀ
netic moments of complex μeff = 1.83 μB) are conꢀ
sistent with the presence of a single unpaired electron.
The copper salt, CuSO4
stroy the DNA chain, leading to the circular form, which
also appears at higher concentrations (24 and 30 M).
Comparing the nuclease activity of CuSO4 5H2O(lanes 7
⋅ 5H2O, 18 μM, starts to deꢀ
I
(
μ
⋅
It is known that the DNA cleavage is controlled by
relaxation of the supercoiled circular conformation of and 8) at the same concentrations with those of the
pUC18 DNA to the nicked circular and/or linear conꢀ complex (lanes 12 and 13), it can be observed that the
formations. When electrophoresis is applied to plasꢀ latter has a superior nuclease activity. According to the
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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402
HANGAN et al.
1
2
3
4
5
6
7
8
9
10 11 12 13
Fig. 4. Electrophoregram in agarose gel of the pUC18 plasmid treated with the [Cu(L) (Py) (H O)] complex: base marker (1);
2
2
2
control (2); control with reducing agents (3); CuSO
⋅
5H O 6
μ
M (4), 12 (5), 18 (6), 24 (7), 30
μ
M (8); complex 6
μ
M (9),
4
2
12 (10), 18 (11), 24 (12), 30
μ
M (13).
1
2
3
4
5
6
7
8
9
10
11
Fig. 5. Electrophoregram in agarose gel of the pUC18 plasmid treated with the [Cu(L) (Py) (H O)] complex and various inhibꢀ
2
2
2
iting agents: base marker (1); control (2); control with reducing agents (3); complex 30
μM without inhibitors (4); complex
30 M with: NaN (5); piperidone (6); DMSO (7); tꢀbutyl alcohol (8); distamycin (9); SOD (10); neocuproine (11).
μ
3
analysis of the same electrophoresis, it can be deduced to complex concentration) as an activating agent. The
that the nuclease activity of the complex depends on results for are shown in Fig. 5.
its concentrations. Thus, its capacity to degrade DNA
I
The influence of the inhibitors on the nuclease acꢀ
tivity of the complex can be observed in the fact that
sodium azide and 2,2,6,6ꢀtetramethylꢀ4ꢀpiperidone
(lanes 5 and 6) do not greatly modify the nuclease acꢀ
tivity of the complex. This proves the fact that the sinꢀ
glet oxygen 1O2 does not participate in the destruction
of the DNA.
rises with the increase of complex concentration.
The coordination of the Cu2+ ion with the sulfonaꢀ
mide deprotonated ligand HL facilitates the destrucꢀ
tion of the DNA molecule. Due to the plane aromatic
rings from its structure, the sulfonamide allows that
the complex molecule be intercalated between base
pairs in the DNA chains. This phenomenon is folꢀ
lowed by the destruction of the nucleic acid, caused by
the production of reactive species of oxygen in its close
vicinity [33, 41]. The direct influence of the nuclearity
of the copper(II) complexes on their nuclease activity
has previously been showed in [41, 42].
The involvement of ROS, such as hydroxyl, superꢀ
oxide, singlet oxygenꢀlike species and hydrogen perꢀ
oxide in the nuclease mechanism, was determined by
monitoring the quenching of the DNA cleavage in the
presence of ROS scavengers. To clarify other aspects of
the mechanism, the copper(I)–chelator (neocuꢀ
proine) and the minor groove binder distamycin were
also used. The assays were performed with
H2O2/ascorbic acid (in a 3.0ꢀfold molar excess relative
In the presence of DMSO and of
(lanes 7 and 8), we can observe a decrease in the degꢀ
radation of the DNA molecule. This can be explained
by the presence of the OH radicals in the destruction
tꢀbutyl alcohol
·
process of the nucleic acid, as the two inhibitors act by
capturing these radicals, thus decreasing their concenꢀ
tration and consequently the nuclease activity of the
complex.
By adding distamycin (lane 9), the nuclease activity
of I is slightly increased. This proves that its activity is
not similar with that of distamycin – a binder of the
minor groove of DNA.
The SOD enzyme leads to a significant increase of
the nuclease activity of the complex (line 10). This can
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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SYNTHESIS, CRYSTAL STRUCTURE, PROPERTIES, AND NUCLEASE ACTIVITY
403
10. Thomas, A.M., Nethaji, M., Chakravarty, A.R.,
J. Inorg. Biochem., 2004, vol. 98, p. 1087.
11. Owa, T., Yoshino, H., Okauchi, T., et al., J. Med.
Chem., 1999, vol. 42, p. 3789.
12. Cedujo, R., Alzuet, G., GonzalezꢀAlvarez, M., et al.,
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13. GonzalezꢀAlvarez, M., Alzuet, G., CastilloꢀAgudo, L.,
et al., Eur. J. Inorg. Chem., 2006, vol. 19, p. 3823.
14. Marcias, B., Villa, M.J., Gomez, B., et al., J. Inorg.
Biochem., 2006, vol. 101, p. 444.
15. GarciaꢀGimenez, J.L., Alzuet, G., GonzalezꢀAlvarez, M.,
et al., J. Inorg. Biochem., 2009, vol. 103, p. 243.
16. CrysAlis PRO CCD and CrysAlis PRO RED, Oxford Difꢀ
fraction Ltd., Abingdon, 2006.
be noticed from an increase of the amount of linear
DNA in this sample as compared to the complex samꢀ
ple without SOD (lane 4). This enzyme catalyzes the
−i
dismutation of the superoxide anion radical
leadꢀ
O2 ,
ing to H2O2 and O2, which can further produce active
species which participate in the destruction of DNA.
In the presence of neocuproine (lane 11), the caꢀ
pacity of the complex to destroy DNA is much reꢀ
duced (the helicoidal and circular form coexist). In
the case of the studied complex, this can be explained
by the reduction of the Cu2+ ion to Cu(I) as intermeꢀ
diate step in the DNA degradation process. By adding
neocuproine, a stable complex of Cu(I) is formed
(Cu(I)ꢀneocuproine), thus inhibiting the subsequent
reactions of the degradation mechanism of the DNA
molecule.
17. SCALE3 ABSPACK, Empirical Absorption Correction,
CrysAlis–Software Package, Oxford Diffraction Ltd.,
2006.
Hydroxyl radicals are generated by a variety of
chemical and physical processes. Transitionꢀmetal
mediated OH production is known to occur by a
18. Sheldrick G.M., SHELXSꢀ97
Structure Solution, G ttingen (Germany): Univ. of
ttingen, 1997.
19. Sheldrick G.M., SHELXLꢀ97
ment of Crystal Structures, G ttingen (Germany): Univ.
of G ttingen, 1997.
20. Dolomanov, O.V., Bourhis, L.J., Gildea, et al., J. Appl.
Cryst., 2009, vol. 42, p. 339.
21. Wilson A.J.C., International Tables for Crystallography
vol. C, Dordrecht (The Netherlands): Kluwer Acaꢀ
demic Publishers, 1995.
22. Spek A.L., PLATON A Multipurpose Crystallographic
Tool, Utrecht (The Netherlands): Utrecht Univ., 2000.
23. Keller E., SCHAKALꢀ97 A Computer Program for the
, Program for Crystal
ö
•
G
ö
,
Program for the Refineꢀ
number of routes; two well known pathways are the
Fenton [43] and the Haber–Weiss [44] mechanisms.
The complex interacts with the DNA molecule. Imꢀ
mediately, the Cu2+ ion is reduced to Cu(I), and in the
presence of the molecular oxygen, the formed Cu(I)
complex produces reactive oxygen species in close
proximity to the double helix. These species finally atꢀ
tack the 2ꢀdeoxyribose moiety, leading to the cleavage
of the DNA chain. If the reactive species are not
formed close to DNA, they are likely to be dispersed
and neutralized.
ö
ö
,
,
,
Graphic Representation of Molecular Crystallographic
Models, Freiburg (Germany): Univ. of Freiburg, 1997.
ACKNOWLEDGMENTS
24. Alzuet, G., Ferrer, S., and Borras, J., Acta Crystallogr.,
C
, 1991, vol. 47, p. 2377.
25. Pedregosa, J.C., Alzuet, G., and Borras, J., Acta Crysꢀ
tallogr., , 1993, vol. 49, p. 630.
26. Allen, А.M., Kennard, O., Watson, D.G., et. al. Trans.
Perkin 2, 1987, p. S1.
27. Borras, E., Alzuet, G., Borras, J., et al., Polyhedron
2000, vol. 19, p. 1859.
Adriana Hangan is thankful for the financial supꢀ
port offered by research grant Resurse Umane PNIIꢀ
PD 474/2010.
C
,
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