Pt(II), Pd(II) and UO2(II) complexes of N,N′-bis(2- pyridyl)thiourea; Structural, thermal and biological studies

Article abstract of DOI:10.1016/j.molstruc.2011.04.024

Novel complexes of Pt²⁺, Pd²⁺ and UO₂ ²⁺ with N,N′-bis(2-pyridyl)thiourea (H₂BPT) 1 were synthesized. These complexes namely [Pt(HBPT)₂] 2, [Pd(HBPT) ₂] 3 and [UO₂(HBPT)(OAc)(H₂O)] 4 , were characterized by elemental analysis and spectral measurements. Suggested structures (square-planar for both 2 and 3 complexes and pentagonal-bipyramidal geometry for 4) were confirmed by applying geometry optimization and conformational analysis. Thermal properties and decomposition kinetics of all compounds are investigated. The interpretation, mathematical analysis and evaluation of kinetic parameters (E, A, ΔH, ΔS and ΔG) of all thermal decomposition stages have been evaluated using Coats-Redfern, Horowitz-Metzger and MKN Methods: The biochemical studies showed that, complex 2 has powerful and complete degradation effect on DNA. The antibacterial screening demonstrated that, complex 2 has the maximum and broad range activities against Gram-positive and Gram-negative bacterial strains.

Full text of DOI:10.1016/j.molstruc.2011.04.024

Journal of Molecular Structure 998 (2011) 11–19
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
0
Pt(II), Pd(II) and UO (II) complexes of N,N -bis(2-pyridyl)thiourea; structural,
2
thermal and biological studies
⇑
Usama El-Ayaan
Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt
Department of Chemistry, College of Science, King Faisal University, P.O. Box 380, Hofuf 31982, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Novel complexes of Pt2+, Pd2+ and UO22+ with N,N -bis(2-pyridyl)thiourea (H BPT) 1 were synthesized.
0
Article history:
Received 3 March 2011
Received in revised form 29 March 2011
Accepted 16 April 2011
Available online 22 April 2011
2
2 2 2 2
These complexes namely [Pt(HBPT) ] 2, [Pd(HBPT) ] 3 and [UO (HBPT)(OAc)(H O)] 4 , were characterized
by elemental analysis and spectral measurements. Suggested structures (square-planar for both 2 and 3
complexes and pentagonal-bipyramidal geometry for 4) were confirmed by applying geometry optimiza-
tion and conformational analysis.
Thermal properties and decomposition kinetics of all compounds are investigated. The interpretation,
Keywords:
Thiourea complexes
Spectroscopy
Thermal analysis
Antibacterial
mathematical analysis and evaluation of kinetic parameters (E, A,
DH, DS and DG) of all thermal decom-
position stages have been evaluated using Coats–Redfern, Horowitz–Metzger and MKN methods. The bio-
chemical studies showed that, complex 2 has powerful and complete degradation effect on DNA. The
antibacterial screening demonstrated that, complex 2 has the maximum and broad range activities
against Gram-positive and Gram-negative bacterial strains.
Ó 2011 Elsevier B.V. All rights reserved.
1
. Introduction
The interpretation, mathematical analysis and evaluation of
kinetic parameters (E, A,
DH, DS and DG) of all thermal decompo-
Thioureas are recognized for their inter- and intra-molecular
sition stages have been evaluated using Coats–Redfern, Horowitz–
Metzger and MKN methods.
hydrogen-bonding. In addition, they can act as ligands in coordina-
tion complexes. This combination has led to their increasing use in
an array as self-assembled network materials [1]. Thiourea com-
plexes with transition metal atoms are also subject of interest
because of the special roles played by these kinds of compounds
in biological processes [2–4]. Recently, extensive studies [5–7] on
2
. Theoretical
2.1. Thermal degradation kinetics
0
the structures of N,N -bis(substituted 2-pyridyl)thioureas and their
Non-isothermal methods have been extensively used for the
intra-molecular and inter-molecular hydrogen bonding interac-
tions have been published. The ligational behavior and the X-ray
single crystal structures of copper(I) and zinc(II) complexes with
evaluation of kinetic parameters of decomposition reactions. The
rate of degradation or conversion, d /dt, is a linear function of
temperature-dependant rate constant k, and temperature-
a
a
0
N,N -bis(2-pyridyl) thiourea, have been reported [8] .
independent function of conversion
follow [9] :
a, and can be described as
In this paper we prepared new complexes of Pt2+, Pd2+ and
2
+
0
UO
2
2
with N,N -bis(2-pyridyl) thiourea (H BPT) (Fig. 1). Very pure
d
dt
a
solid complexes were obtained but unfortunately crystals suitable
for X-ray measurements were not available. We apply geometry
optimization and conformational analysis to the free ligand and
all studied complexes as a further tool to confirm the proposed
structures.
¼
kðTÞfð
aÞ
ð1Þ
The reaction rate constant, k, has been described by the Arrhe-
nius expression
k ¼ A eꢀ
E=RT
ð2Þ
ꢀ
1
ꢀ1
⇑
Present address: Department of Chemistry, College of Science, King Faisal
University, P.O. Box 380, Hofuf 31982, Saudi Arabia. Tel.: +996 553901011; fax:
where R is the gas constant in (J mol
K
). Substituting Eq. (2) into
Eq. (1), we get
+966 35886437.
E=RT
da
=dt ¼ Aðeꢀ
Þfð
aÞ
ð3Þ
E-mail address: uelayaan@kfu.edu.sa
0
022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.04.024

1
2
U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
2
Fig. 1. Structure of the free ligand (H BPT).
If the temperature of the sample is changed by a controlled and
constant heating rate, = dT/dt, the variation of the degree of
conversion can be analyzed as a function of temperature, this tem-
perature being dependant on the time of heating. Therefore, the
rearrangement of Eq. (3) gives
2.1.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approx-
imation methods. These authors derived the relation:
u
1ꢀnꢁ=ð1 ꢀ nÞg ¼ Eh=2:303RT
2
s
for n – 1
ð9Þ
logf½1 ꢀ ð1 ꢀ
aÞ
A
u
When n = 1, the LHS of Eq. (9) would be log[ꢀlog(1ꢀ
a
)]. For
=dt ¼ ðeꢀ Þfð
E=RT
a
Þ
ð4Þ
d
a
first-order kinetics process the Horowitz–Metzger equation maybe
written in the form:
The integrated form of Eq. (4) is generally expressed as
2
s
log½logðw
a
=w
c
Þꢁ ¼ Eh=2:303RT ꢀ log 2:303
ð10Þ
Z
ꢀ
ꢁ Z
a
T
d
a
a
A
u
ꢀ
E=RT
gð
a
Þ ¼
¼
e
dT
ð5Þ
fð
Þ
where h = T ꢀ T
s
, w
c
= w
a
ꢀ w, w
a
is the mass loss at the completion
0
0
of the reaction, and w is the mass loss up time t. the plot of log[log(
w /w )] versus h was drawn and found to be linear from the slope of
where g(
a) is the integrated form of the conversion dependence
a
c
function. The integral on the right-hand side of Eq. (5) is known
as temperature integral and has no closed form solution. Several
techniques have been used for the evaluation of temperature inte-
gral. Most commonly used methods for this purpose are integral
method of Coats–Redfern [10], the approximation method of Horo-
witz–Metzger [11] and MKN equation [12].
which E was calculated. The pre-exponential factor, Z, is calculated
from the equation [14].
E
z
h
ꢀE=RT
s
¼
e
ð11Þ
2
RTs
In the present investigation, kinetic parameters have been eval-
uated using the following three methods and the results obtained
by these methods are compared with one another. The following
three methods are discussed in brief.
2
.1.3. MKN equation
Evaluation of the temperature integral (the right-hand side of
Eq. (5)) have been evaluated using the numerical solution method.
In this method, the rate equation, Eq. (4), was integrated as:
ꢂ
Z
ꢃ
x
ex
x
AE
a
ꢀe
AE
a
2
.1.1. Coats–Redfern equation
The Coats–Redfern equation, which is a typical integral method,
gð/Þ ¼
þ
dx
¼ pðxÞ
uR
ð12Þ
uR
x
1
can be represented as
a
where x = E /RT
Madhusudanan et al. [12] have proposed a new simple approx-
imation Eq. (13) for solving the p(x) function.
Z
Z
1
T
2
n
ꢀE=RT
da
ð1 ꢀ
a
Þ ¼ ðA=
u
Þ
e
dt
ð6Þ
0
T
1
ꢂ
ꢃ
ꢀ
x
e
ðx þ 1Þ
ðx þ 3Þ
pðxÞ ¼ x
ð13Þ
For convenience of integration the lower term T
1
is usually ta-
2
ken as zero. This equation on integration gives,
It has been shown that ln p(x) is a linear function of x and the
slope and intercept of ln p(x) versus x curves are linear function
of 1/x and ln(x), respectively. On combining these, the Eq. (14)
was obtained
2
ln½ꢀ lnð1 ꢀ
a
Þ=T ꢁ ¼ ꢀE=RT þ ln½AR=
u
Eꢁ
ð7Þ
A plot of left-hand side (LHS) against 1/T was drawn. E was
calculated from the slope and A from the intercept value. The en-
tropy of activation
S ¼ R½lnðAh=kT Þꢁ
where k is the Boltzmann’s constant and h is the Planck’s constant
DS was calculated by using the equation:
LnpðxÞ ¼ a þ bx þ c ln x
ð14Þ
D
s
ð8Þ
On substituting the numerical values of a, b, and c, values of p(x)
were determined which was substituted in Eq. (11) and rearranged
to get Madhusudanan Krishnan–Ninan (MKN) Eq. (15).
and T is the DTG peak temperature [13].
s

U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
13
ꢀ
ꢁ
gðxÞ
AE
collected and washed with water, m.p. 158 °C, yield 18 g (78.3%),
S (230.3) calcd: C 57.37, H 4.38, N 24.33, S 13.92; found
Ln
¼ ln
þ 3:7721 ꢀ 1:9215 ln E
1
:9215
T
uR
11 10 4
C H N
ꢀ
ꢁ
1
C 57.60, H 4.30, N 24.50, S 13.75 – H NMR (DMSO-d6, 500 MHz)
= 7.14 (s, 2H, Hpy), 7.81–7.84 (m, 3H, Hpy), 8.34 (s, 3H, Hpy),
1.15 (br s, 1H, NH), 14.21 (br s, 1H, SH).
E
T
ꢀ
0:120394
ð15Þ
D
1
The plot of the left-hand side of Eq. (14) against 1/T gives a
straight line (the slope is equal to ꢀ0.120394E and the intercept
equals lnðAE= RÞ þ 3:7721 ꢀ 1:9215 ln E which on simplification
gives intercept =lnðA= Þ þ 0:9215 ln E þ ꢀ1:654, E and A can be
calculated from the slope and intercept, respectively.
In all complexes, the enthalpy ( H) and the free energy of acti-
vation G) were calculated using the following relations,
respectively:
3
.3. Synthesis of metal complexes
u
u
Complexes were prepared by refluxing
H
2
BPT (0.23 g,
PtCl , 0.32 g of
2
O in 20 ml ethanol for 6 h.
1
K
.0 mmol) and 1.0 mmol of metal salt; 0.42 g of K
PdCl or 0.42 of UO (CH COO) .2H
2
4
D
2
4
2
3
2
(D
The resulting metal complexes were filtered off while hot, washed
with ethanol followed by diethyl ether and dried in vacuo over
CaCl
1
2
.
H NMR (DMSO-d6, 500 MHz) for complex 2 (Fig. 3);
D
D
H ¼ E ꢀ RT
G ¼ H ꢀ T
d = 12.3 (br s, 1H, NH), 12.7 (br s, 1H, NH), 7.2–8.5 (pyridyl protons,
6H), for complex 3 (Fig. 4), d = 12.0 (br s, 1H, NH), 12.6 (br s, 1H,
1
D
DS
NH), 7.1-8.4 (pyridyl protons, 16H) and for complex 4 (Fig. 5);
d = 10.3 (br s, 1H, NH), 7.0-8.6 (pyridyl protons, 8H), 2.86 (s, 3H,
CH3).
2.2. Molecular modeling
An attempt to gain a better insight on the molecular structure of
2
BPT ligand and its complexes, geometry optimization and
3.4. Biological studies
H
conformational analysis has been performed by the use of
MM+[15] force field as implemented in hyperchem 7.5 [16].
3
3
UO
.4.1. DNA electrophoreses
.4.1.1. Agarose gel. The free (H
2
BPT) ligand or its Pt(II), Pd(II) and
g of
2
(II) complexes (100
l
M) were added individually to 1
l
3
. Experimental
the DNA isolated from Escherichia coli. These samples were incu-
bated for 1 h at 37 °C. The DNA was analyzed by using horizontal
agarose gels electrophoresis. The electrophoresis was performed
3.1. Instrumentation and materials
using 0.7% (w/v) agarose gels in TAE buffer (5
M EDTA and 0.04 M Tris-HCl pH 7.9). The agarose gels were
stained with ethidium bromide (0.5 g/mL) and the DNA was
lM sodium acetate,
All starting materials were purchased from Fluka, Riedel and
1 l
Merck and used as received. Elemental analyses (C, H and N) were
performed on a Perkin-Elmer 2400 Series II Analyzer. Infrared
spectra were recorded on a Perkin-Elmer FTIR Spectrometer 2000
l
visualized on a UV transilluminator [17].
ꢀ
1
as KBr pellets and as Nujol mulls in the 4000–200 cm spectral
3.4.2. Protein gel electrophoresis
1
range. H NMR measurements at room temperature were obtained
Bovine serum albumin (BSA) (3 mg) was treated with the free
BPT) ligand or its Pt(II), Pd(II) and UO (II) complexes
(100 M) individually. The reaction mixture was incubated for
on a Jeol JNM LA 300 WB spectrometer at 250 MHz, using a 5 mm
(H
2
2
probe head in CDCl
3
. Electronic spectra were recorded on a
l
UV-UNICAM 2001 spectrophotometer using 10 mm pass length
quartz cells at room temperature. Thermogravimetric (TG) and dif-
ferential (DTG) thermogravimetric analysis were performed on a
DTG-50 Shimazu instrument at heating rate of 10 °C/min.
1 h at 37 °C. The protein samples were analyzed using vertical
one dimensional SDS-polyacrylamide gel electrophoresis according
to the method of Laemmli [18].
The samples were prepared by adding 15
ing buffer (100 mM Tris-HCl pH 6.8, 4% (w/v) SDS, 0.2% (w/v)
bromophenol blue, 20% (v/v) glycerol, 200 mM DTT) and 15 lL
lL 2 ꢂ SDS-gel load-
0
3
.2. Preparation of the free ligand, N,N -bis(2-pyridyl)thiourea (H
2
BPT)
protein samples and boiled in water bath for 3 min, 20
lL of dena-
2
-aminopyridine (0.2 mol, 19 g), carbon disulfide (0.1 mol,
tured protein samples were loaded into the gel.
6
mL) and triethylamine (0.1 mol, 15 mL) were refluxed for 48 h.
Excess of carbon disulfide was removed by rotary evaporator
3.4.3. Antibacterial effect
(
Fig. 2). It was then diluted with water 100 mL and cooled. Then
2
The antibacterial investigation of the free (H BPT) ligand or its
0
the solid off-white needles of N,N -bis(2-pyridyl) thiourea was
2
Pt(II), Pd(II) and UO (II) complexes was carried our using cup
H
N
SH
NH
2
+
CS
2
N
N
S
2
-H S
NH
2
H
N
N
H
N
H
N
N
C
C
N
C
S
N
SH
N
N
S
N
N
Fig. 2. Synthesis of H
2
BPT ligand.

1
4
U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
2
Fig. 3. Structure of [Pt(HBPT) ].
2
Fig. 4. Structure of [Pd(HBPT) ].
2 2
Fig. 5. Structure of [UO (HBPT)(OAc)(H O)].
diffusion technique [19]. The test was done against the Gram-
negative Escherichia coli (E. coli) and Pseudomonas aeruginosa
(S. aureus) and Bacillus thuringiensis (B. thuringiensis). The tested
free (H BPT) ligand or its complexes were dissolved in DMSO at
concentration 1 mg/mL. The Luria-Bertani Agar (LBA) medium
2
(
P. aeruginosa) and the Gram-positive Staphylococcus aureus

U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
15
Table 1
Analytical and physical data and main IR spectral bands of H
2
BPT ligand and its metal complexes.
Compound
%Calc. (Found)
m
(C@N)py
m
(C@S)
m(SAC@N)
m(CAS)
Empirical formula
(F. Wt)
Color
C
H
N
(
[
[
[
H
2
BPT), C11
Pt(HBPT) ], C22
Pd(HBPT) ] ,C22
UO (HBPT)(OAc)(H
H
10
N
H
H
4
S
(230.3)
(653.6)
(564.98)
(576.4)
Off-white
Yellow
Orange
57.37 (57.60)
40.40 (40.10)
46.77 (45.67)
27.10 (27.50)
4.38 (4.30)
2.77 (2.69)
3.21 (3.25)
2.45 (2.50)
24.33 (24.50)
17.10 (16.85)
19.83 (19.77)
9.72 (10.20)
1603
787
–
–
–
–
2
18
N
8
PtS
PdS
O)], C13
2
1610, 1630
1608, 1642
1616, 1652
1553
1549
1555
1150
1151
1150
2
18
N
8
2
2
2
H
14
4
N O
5
SU
Pale-yellow
–
2
Fig. 6. Possible conformers (A, B and C) of the free ligand H BPT.
First Stage
Second stage
a
b
c
2
Fig. 7. Coats–Redfern (a), MKN (b), and Horowitz–Metzger (c) plots for [Pd(HBPT) ].
was used. An aliquot of the solution of the tested complexes equiv-
alent to 100 g was placed separately in each cup. The LBA plates
were incubated for 24 h at 37 °C and the resulting inhibition zones
were measured. Ampicillin 1 mg/mL was used as a positive control
while DMSO, which exhibited no antibacterial activity, was used as
a negative control.
l

1
6
U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
First stage
1.94 1.96
Second Stage
Third Stage
1
1-
1
12.4-
.92
1.98
2
1.65
1.7
1.75
1.8
1.85
1
1.5-
2-
12.5-
3-
3.5-
4-
12.8-
13.2-
13.6-
1
a
b
1
14-
1
1
14.4-
1
1
1
1
0.5-
12-
0.00165 0.0017 0.00175 0.0018 0.00185
2.4-
0.00192 0.00194 0.00196 0.00198 0.002
1
1-
1.5-
2-
2.5-
3-
3.5-
1
1
1
2.8-
3.2-
1
1
13.6-
4-
1
0.4
0
0
5
10
15
20
30- 20- 10-
.2-
0
10
20
30
0
0
0
0
0
.4-
.6-
.8-
0.4-
0.8-
1.2-
c
1
-
1
.2-
2
Fig. 8. Coats–Redfern (a), MKN (b), and Horowitz–Metzger (c) plots for [Pt(HBPT) ].
4
. Results and discussion
[20]. The force constant (F) for the bonding sites of m(U@O) is
calculated by the method of McGlynn et al. [21].
4
.1. IR and NMR spectra of H
2
BPT and its metal complexes
2
2
ð
m
3
Þ ¼ ð1307Þ ðFUAOÞ=14:1
The FUAO value is 7.01 m dynes A° , the UAO bond distance is
Important IR bands for the ligand and complexes with their
tentative assignments are presented in Table 1.
Conformational performance of H BPT ligand was examined by
the rotation and orientation in the space of the flexible thiourea and
pyridyl groups. For such compound the MM calculations led to
three minimum energy conformations (Fig. 6) within energy differ-
ences of less than 4 Kcal/mol.
The arrangement around the N1AS1 and N2AS1 bonds mainly
determine the geometry of the N-substituent groups. So it is clear
from the calculation that the conformer A is more stable than B and
C with energy content of 19.075, 19.093 and 22.78 Kcal/mol,
ꢀ1
calculated with the help of the equation [22] shown below.
2
1=3
R
UAO ¼ 1:08ꢀ þ 1:17
The UAO bond distance (1.74 A°) falls in the usual region as
reported earlier [23,24].
Acetate chelates show two bands at 1541 and 1456 cm 1
ꢀ
assignable to
ence exhibit
masym(COO) and
msym(COO), respectively. This differ-
ꢀ
1
D
value [
masym(COO) ꢀ
msym(COO)] equal to 85 cm
that is significantly smaller than the ionic value indicating biden-
tate chelating acetate group[25,26]. NMR spectrum of this complex
shows new signal at d = 2.86 ppm assigned to the methyl protons
indicating the presence of acetate group in the coordination sphere
of uranium.
1
respectively. Experimentally, H NMR spectra of the ligand confirm
the presence of the H
4.21 ppm assigned to SH proton.
BPT behaves as mononegative bidentate ligand coordinating
2
BPT ligand as conformer A with a signal at
1
H
2
via the nitrogen of the pyridyl group and the CS group in the thiol
form. This behavior which is found in all studied complexes is
4.2. Electronic spectra of complexes
py
ꢀ1
revealed by (i) the
m(C@N) vibration is observed at 1603 cm
ꢀ1
for BPT and at 1610, 1630 cm
H
2
for complex 2, 1608,
The electronic spectra of complexes 2 and 3 are indicative of
square-planar geometry. In the visible region of the square-planar
complexes of Pt(II) and Pd(II), three spin-allowed singlet-singlet
ꢀ1
ꢀ1
1
642 cm for complex 3 and at 1616, 1652 cm for complex 4.
py
All complexes exhibit two
one pyridine ring participating in coordination. (ii) The disappear-
ance of (C@S) peak with the appearance of new bands due to
(SAC@N) and (CAS).
In complex 4, a peak is observed at 921.9 cm assigned to the
asymmetric stretching frequency ( ) of the dioxouranium ion
m(C@N) peaks, indicating that only
1
1
d-d transitions are predicted. The ground state is A1g
, B1g and
1
m
Eg in order of increasing energy. Strong charge transfer transition
m
m
interferes and prevents the observation of all expected bands. The
very intense band observed at 22,000–23,000 cm in the elec-
tronic spectra of complexes 2 and 3 is assignable to a combination
ꢀ1
ꢀ1
m
3

U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
17
First stage
Second Stage
Third Stage
1
3-
1
1
2.7-
12.8-
13-
.76 1.8 1.84 1.88 1.92 1.96
1
.35
1.4
1.45
1.5
1.05
1.1
1.15
1.2
1
1
1
1
1
3.1-
3.2-
3.3-
3.4-
3.5-
12.8-
12.9-
13-
13.2-
13.4-
13.6-
13.8-
a
b
13.1-
13.2-
1
1
1
2.4-
12.2-
12.2-
0
.00175 0.0018 0.00185 0.0019 0.00195
0.00136 0.0014 0.00144 0.00148
0.00104 0.00108 0.00112 0.00116 0.0012
2.4-
1
1
1
1
1
2.3-
1
1
1
2.6-
2.4-
2.5-
2.6-
2.7-
2.6-
2.8-
2.8-
1
3-
1
3-
13.2-
0
0
0
1
0
30
50
70
30-
20-
10-
0
10
20
20-
0
20
40
60
0
.2-
0.1-
0.2-
0.3-
0.4-
0.5-
0.1-
0.2-
0.3-
0.4-
0.5-
0.4-
c
0.6-
.8-
0
1-
Fig. 9. Coats–Redfern (a), MKN (b), and Horowitz–Metzger (c) plots for [UO
2 2
(HBPT)(OAc)(H O)].
of sulfur ? M(II), nitrogen(pyridyl) ? M(II) charge transfer (L(
P) ?
CH/P interaction of methyl group with pyridine ring (2.6 Å). This
MCT) and M(II) d–d bands. The strong bands at 25,000–
nonbonded interaction may be the reason for the coplanarity of
the dipyridyl groups and this factor may be strong enough to
compensate the steric repulsion. On the other hand, the calculation
on complex 4, dipyridyl groups were arranged itself coplanar. This
coplanar orientation of is caused by the presence of strong SAN
interaction (1.42 Å), which prevents rotation of pyridyl moiety in
the plane formed by the complex core.
ꢀ
1
2
7,000 cm
are assignable to a combination of metal-ligand
charge transfer (M ? LCT) and d–d bands. The band at
ꢀ1
ꢃ
3
2,000–33,000 cm is assignable to the n ? P transition of the
pyridine ring and the thiourea moiety (L() ? MCT).
The electronic spectra of complex 4 exhibit several bands in the
ꢀ1
range of 50,000–14,000 cm . The bands in the region 50,000–
ꢀ
1
3
2,000 cm coincide with the bands observed in the free ligand.
Some of these bands are slightly shifted towards lower energy
region compared to the free ligand transitions because of the coor-
dination with the U(VI) ion. Since these are essentially the intrali-
4
.4. Thermal behavior and the decomposition kinetics
TG/DTG curves of the complexes showed that complex 3
gand transitions they are allowed and occur with high intensity.
decomposes in two steps, while complexes 2 and 4 are decomposes
in three steps.
In studying the decomposition kinetics, three methods namely,
Coats–Redfern (CR), Horowitz–Metzger (HM) and MKN were used.
In these methods (CR, HM and MKN) the left-hand side of equations
6, 9 and 11 is plotted against 1000/T, h and 1/T, respectively (Figs.
Two relatively less intense bands occur at 22,000–27,000 cm -
1
.
These can be assigned to uranyl oxygen to uranium and pyridyl
nitrogen to uranium charge transfer transitions, respectively.
4.3. Molecular modeling studies
7
–9). From the results obtained, the following remarks can be
An attempt to gain a better insight on the molecular structures
pointed out: (i) the kinetic parameters (E, A, H, S and G) of
D
D
D
of the (2–4) complexes, conformational analysis of the target com-
pounds have been performed by MM + force field as implemented
in HyperChem 7.5. The results show that the lowest energy con-
former as calculated by PM3 semiempirical method of both
all studied complexes have been determined (Table 2) using CR,
HM and MKN methods. The values obtained from the three meth-
ods are quite comparable. (ii) All complexes decomposition stages
show a best fit for (n = 1) indicating a first-order decomposition in
all cases. Other n values (e.g. 0, 0.33 and 0.66) did not lead to better
(2 and 3) complexes have approximate atomic coordinates. The
calculations performed indicate that the pyridyl groups, showing
highly free rotations, were spatially arranged itself approximately
coplanar and perpendicular to the plane of core complex. This
unique arrangement may be stabilized by nonbonded interaction;
correlations. (iii) The value of
sequently decomposition stages of a given complex. This is due to
increasing the value of T S significantly from one stage to another
which overrides the value of H. Increasing the value of G of a
DG increases significantly for the sub-
D
D
D

1
8
U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
Table 2
2
Kinetic parameters of H BPT ligand and its metal complexes.
A (Sꢀ1)
E (KJmol
ꢀ1
)
D
H (KJmol
ꢀ1
)
D
S (KJmol
ꢀ1
)
DG (KJmol )
ꢀ1
Complex
Stage
T (K)
Coats–Redfern method
3
5
[
Pd(HBPT)
2
]
1st
560
840
6.2 ꢂ 10
6.0 ꢂ 10
65.7
134.2
61.0
127.2
ꢀ0.186
ꢀ0.151
165.1
254.3
2
nd
2
8
[
Pt(HBPT)
2
]
1st
500
570
700
5.8 ꢂ 10
3.3 ꢂ 10
18.39
297.3
78.0
52.8
293.2
73.2
47.0
0.293
146.6
171.4
212.3
4
2
3
nd
rd
ꢀ0.172
ꢀ0.236
[
UO
2
(HBPT)(OAc)(H
2
O)]
1st
500
700
870
0.20
1.13
19.0
24.5
37.4
67.3
20.4
31.5
60.1
ꢀ0.271
ꢀ0.259
ꢀ0.238
155.7
213.1
266.9
2
3
nd
rd
Horowitz–Metzger method
3
5
[
Pd(HBPT)
2
]
1st
560
840
7.4 ꢂ 10
6.9 ꢂ 10
65.9
134.7
61.3
127.7
ꢀ0.184
ꢀ0.150
164.6
253.7
2
nd
2
8
[
Pt(HBPT)
2
]
1st
500
570
700
6.0 ꢂ 10
3.8 ꢂ 10
22.66
297.4
78.2
53.2
293.2
73.2
47.4
0.293
146.5
170.9
211.5
4
2
3
nd
rd
ꢀ0.171
ꢀ0.234
[
UO
2
(HBPT)(OAc)(H
2
O)]
1st
500
700
870
0.29
1.43
23.42
24.9
37.8
67.9
20.7
31.9
60.6
ꢀ0.268
ꢀ0.257
ꢀ0.236
155.0
212.1
265.9
2
3
nd
rd
MKN Method
4
5
[
Pd(HBPT)
2
]
1st
560
840
2.4 ꢂ 10
9.9 ꢂ 10
72.0
135.1
67.4
128.1
ꢀ0.174
ꢀ0.147
165.1
251.7
2
nd
2
8
[
Pt(HBPT)
2
]
1st
500
570
700
7.6 ꢂ 10
5.2 ꢂ 10
37.3
292.0
87.1
56.3
287.9
82.4
50.4
0.295
140.1
167.4
211.6
5
2
3
nd
rd
ꢀ0.149
ꢀ0.230
[
UO
2
(HBPT)(OAc)(H
2
O)]
1st
500
700
870
2.35
6.20
43.90
28.7
46.9
72.5
24.6
41.1
65.2
ꢀ0.250
ꢀ0.245
ꢀ0.231
149.8
212.7
265.9
2
3
nd
rd
given complex on going from one decomposition step subsequently
to another reflects that the rate of removal of the subsequent ligand
will be lower than that the precedent ligand [27,28]. This may be
attributed to the structure rigidity of the remaining complex after
the explosion of one and more ligands, as compared with the prec-
1
2
3
4
5
6
edent complex, which require more energy, T
ment before undergoing any compositional change. (iv) The
negative value of activation entropies S indicates a more ordered
activated complex than the reactants and/or the reactions are slow
29]. (v) The positive value of H means that the decomposition
DS, for its rearrange-
D
[
D
processes are endothermic. (vi) The energy of activation values E
for the second step of decomposition of complex 3 and complex 4
are found to be higher than that of the first stage indicating that
the rate of decomposition for this stage is lower than that for the
first stage. In case of complex 2, the energy of activation for the sec-
ond stage is lower than the first step. This confirms that the rate of
decomposition is higher in the second step [30].
It is generally observed that stepwise stability constants
decrease with an increase in the number of ligands attached to
the metal ion [31,32]. During the decomposition reaction a reverse
effect may occur. Hence the rate of removal of the remaining
ligands will be smaller after the explosion of one or two ligands.
Fig. 10. Effect of 100
in vitro.
2
lM of H BPT free ligand and its metal complexes on the DNA
nic radius of 87 pm and initial decomposition temperature of
0 °C).
7
4.5. Ionic radius/thermal stability
2
4.6. Biochemical effect of H BPT ligand and its metal complexes on the
From the data obtained in this work, it was possible to show the
DNA in vitro
relation between thermal stability of complexes and their metal
ion radii. The higher the ionic radius of the metal ion in the com-
plex, the lower was the initial decomposition temperature of the
complex as measured by TG, in the following order of thermal
stability complex 2 (ionic radius of 74 pm and initial decomposi-
tion temperature of 200 °C) > complex 3 (ionic radius of 78 pm
and initial decomposition temperature of 100 °C) > complex 4(io-
2
The degradation effect of 100 lM of the free (H BPT) ligand 1,
and its (2–4) complexes on the DNA in vitro illustrated in Fig. 10.
Both the ꢀve control (only DNA) and +ve control (DNA in DMSO)
does not exhibit any degradation through the incubation period
as illustrated in Fig. 10 lanes 1 and 2, respectively. The Pt(II)
complex 2 has a powerful and complete degradation effect on

U. El-Ayaan / Journal of Molecular Structure 998 (2011) 11–19
19
1
2
3
4
5
6
5. Conclusion
Novel complexes of Pt2+, Pd2+ and U6+ with N,N -bis(2-pyri-
0
dyl)thiourea (H BPT) 1 were synthesized. Geometry optimization
2
and conformational analysis have been performed and a perfect
agreement with spectral studies and analytical measurements
allow for suggesting the exact structure of all studied complexes.
The stability of complexes was explained and the kinetic parame-
ters (E, A, DH, DS and DG) of all thermal decomposition stages have
been evaluated using Coats–Redfern, Horowitz–Metzger and MKN
methods. The results shows that the kinetic parameters (Table 2)
evaluated by all three methods are in a very good agreement.
The biological studies showed that Pt(II) complex has a powerful
and complete degradation effect on DNA ‘‘which maybe a sign
for anti-tumor activity’’. Moreover, the antibacterial screening
demonstrated that, Pt(II) complex has the maximum and broad
range activities against Gram-positive and Gram-negative bacterial
strains.
Fig. 11. Effect of 100
protein in vitro.
l
2
M of H BPT free ligand and its metal complexes on the BSA
Table 3
The antimicrobial effect of
microorganisms. The results are expressed as zone inhibition in millimeter diameter.
2
H BPT legand and its metal complexes on some
Compound
Ampicillin
E. coli P. aeruginosa S. aureus B. thuringiensis
16
13
12
14
H
2
BPT, 1
Pt(HBPT)
Pd(HBPT)
UO (HBPT)(OAc)(H
7
9
6
12
6
12
ꢀve
[
[
[
2
], 2
], 3
11
2
ꢀve
ꢀve
ꢀve
ꢀve
ꢀve
Acknowledgements
2
2
O)], 4 ꢀve
ꢀve
ꢀve
The financial support by the Deanship of Scientific Research
(
Project Number 10080) King Faisal University, Saudi Arabia, is
gratefully acknowledged. Thanks are due to Dr. Magdy M. Youssef,
Chemistry department, Faculty of Science, for the help with
biological studies.
the DNA as illustrated in Fig. 10 lane 4. Therefore complex 2 can be
used as a promising anti-tumor agent in vivo to inhibit the DNA
replication in the cancer cells and not allow the tumor for further
growth. The Pd(II) complex 3 has a strong degradation effect on the
DNA as represented in lane 5 compared with the free ligand lane 3.
References
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2
The UO (II) complex 4 has a partial degradation effect on the DNA
as observed in lane 6.
Further biochemical studies to illustrate the exact role of the
promising degradation effect by complexes 2 and 3 on tumor cells
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compounds on the protein as another important macromolecule.
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[
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[
2
ate degradation effect on BSA while the free (H BPT) ligand 1, has
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represented in Fig. 11 lane 4.
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[
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Pseudomonas aeruginosa (P. aeruginosa) as listed in Table 3. Com-
plex 2 give a strong antimicrobial activity against all studied
bacterial strains compared with ampicillin as antimicrobial drug.
Complexes 3 and 4 do not show any antimicrobial activity against
all tested bacterial strains.
<
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[
[
[
[
[
Cisplatin has been used in the treatment of many cancers. Upon
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[
[
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