Complexing properties of nucleic-acid constituents adenine and guanine complexes

Article abstract of DOI:10.1016/j.saa.2003.09.025

Cobalt, nickel and copper complexes of adenine and guanine, as nucleic-acid constituents, were prepared. The adenine and guanine complexes are of tetrahedral and octahedral geometries, respectively. All are of high spin nature. The nickel complexes are of

Full text of DOI:10.1016/j.saa.2003.09.025

Spectrochimica Acta Part A 60 (2004) 1907–1915
Complexing properties of nucleic-acid constituents
adenine and guanine complexes
a,∗
a
b
Mamdouh S. Masoud , Amina A. Soayed , Alaa E. Ali
a
Chemisty Department, Faculty of Science, Alexandria University, Alexandria, Egypt
b
Physics and Chemistry Department, Faculty of Education, Damanhour, Alexandria University, Alexandria, Egypt
Received 19 August 2003; received in revised form 14 September 2003; accepted 30 September 2003
Abstract
Cobalt, nickel and copper complexes of adenine and guanine, as nucleic-acid constituents, were prepared. The adenine and guanine
complexes are of tetrahedral and octahedral geometries, respectively. All are of high spin nature. The nickel complexes are of 2:1 metal:ligand
ratio with Ni · · · Ni direct interaction in the guanine complex. The coordination bonds of adenine metal complexes are calculated and follow
II
II
I
II
the order: Cu -adenine < Ni -adenine < Co -adenine. The Cu -adenine complex is the stronger following the softness of the copper, while
that of guanine is less covalent. The copper complexes are with stronger axial field. The differential thermal analysis (DTA) and TGA of
the complexes pointed to their stability. The mechanism of the thermal decomposition is detected. The thermodynamic parameters of the
dissociation steps are evaluated. The complexes are of semi-conducting behaviour for their technical applications. Empirical equations are
deduced between the electrical conducting and the energy of activation of the complexes.
©
2003 Elsevier B.V. All rights reserved.
Keywords: Nucleic acid complexes; Magnetism; Spectroscopy; Thermal; Electrical conductivity
1
. Introduction
Nucleic acids and their derivatives are natural multisided
ligands. The interaction of these molecules with both nat-
ural and foreign metal species has stimulated great interest
for many reasons [1–4]: (1) enzyme reactions that require
nucleic-acid constituents; (2) enzyme reactions that act on
these compounds; (3) the structures of nucleic acids in vivo;
and (4) the structures of nucleic acid–protein complexes.
The key of studying these important aspects is to study the
complexing properties of the nucleic-acid constituents with
different metal ions in a sequel of continuation. Masoud and
others [5–14] reported the complexing properties of some
biologically active pyrimidine compounds. In continuation,
purines (adenine and guanine) complexes of cobalt, nickel
and copper ions are the major goal of the present work. The
study includes spectral (UV-Vis, IR, ESR), magnetic sus-
ceptibility, thermal and electrical properties to shed light on
their structural chemistry.
2
. Experimental
2.1. Preparation of the complexes
Ammoniacal solutions of 0.01 mol cobalt(II), nickel(II)
and copper(II) chlorides were mixed with 0.02 mol of ade-
nine or guanine previously dissolved in ammonia solution.
The reaction mixture was refluxed for two hours and then
left overnight where the complexes were precipitated, then
filtered, washed with distilled water and dried in a vacuum
∗
4 10
desicator over P O . The melting points of the complexes
Corresponding author.
◦
are over 300 C.
E-mail address: drmsmasoud@yahoo.com (M.S. Masoud).
1
386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2003.09.025

1
908
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
2
.2. Analysis of metal ion content
The complexes were digested and decomposed with
2.6. Magnetic susceptibility measurements
Molar magnetic susceptibility corrected for diamagnetic
using Pascal’s constant were determined at room temper-
ature (298 K) using Faraday’s method. The apparatus was
calibrated with Hg [Co(SCN)4] [18].
aquaregia. The metal ion contents were determined by usual
complexmetric procedures [15].
2
.3. Carbon, hydrogen and nitrogen analyses
2.7. Thermal analysis
These were done at the Micro Analytical Laboratory, Fac-
ulty of Science, Alexandria University, Egypt.
Differential thermal analysis (DTA) was carried out using
◦
−1
.
a Schimatzu DTA-50. The rate of heating was 10 C min
.8. Electrical conductivity
The dc electrical conductivity measurements of the solid
2
.4. Halogen analysis
2
It was determined by titration with standard Hg(NO3)2
solution using diphenylcarbazone indicator [15]. The ana-
lytical data, colours of the prepared complexes are collected
in Table 1.
complexes were taken in air on keithley multimeter with
applied voltage 200 V using two probe method. The discs
−2
were pressed under 5 t cm to a thickness of 0.1–0.3 cm.
The tablets were covered on both sites with sliver paste to
improve the contact with the electrodes. The conductivity
was measured in the temperature range 298–643 K with a
2
2
.5. Instruments and working procedures
◦
stability and accuracy of ± 0.1 K. The dc electrical conduc-
.5.1. UV-Vis spectra
The spectral studies were measured using PYE-Unicam
tivity was calculated using the general equation:
spectrophotometer model 1750 covering the wavelength
range 190–900 mm. The complexes were measured in Nujol
mull following the method described by Lee et al. [16].
I d
σ =
Vc a
where I is the current in ampere and Vc is the potential drop
across the sample of the cross-section area a and thickness d.
2
.5.2. IR spectra
The KBr IR spectra were recorded using Perkin-Elmer
spectrophotometer model 1430 covering the frequency range
−
1
2
00–4000 cm . Calibration of the frequency readings was
3. Results and discussion
made with polystyrene film.
3.1. Spectral and magnetic identification of adenine
2
.5.3. ESR spectra
complexes
ESR spectra were recorded at 100 kHz modulation and
0 G modulation amplitude on Varian E-9 Spectrophotome-
1
The IR spectra of adenine and its metal complexes have
been studied by several research groups [19–22]. Cer-
tain band assignments, especially those concerning with
ter. Incident power of 10 mV was used and resonance con-
ditions were at ca 9.75 GHz (X-band) at room tempera-
ture. Spectra were obtained with an air products LTD-3-110
Heli-Trans liquid helium transfer refrigerator. The field was
calibrated with a powder sample of 2,2-diphenyl pyridylhy-
drazone (DPPH) g = 2.0037 [17].
−
1
NH2 modes at 1260–1020 cm , differ from work to work
−1
[19–22]. The NH2 bands of adenine at 3286 and 3114 cm
(Table 2) are slightly shifted on complexation. The δNH2
−1
mode of the free adenine at 1668 cm undergoes shifts
Table 1
Analytical data and colour of the purine complexes
Complex
Colour
Calculated (found) (%)
C
H
N
M
Cl
Co-adenine
Ni-adenine
Cu-adenine
Co-guanine
Ni-guanine
Cu-guanine
Black
Pale green
Green
Beige
Pale green
Green
24.36 (24.21)
15.98 (15.80)
23.91 (23.95)
30.30 (30.37)
29.20 (29.18)
31.40 (31.41)
2.45 (2.36)
1.61 (1.61)
2.41 (2.40)
3.80 (3.76)
3.40 (3.42)
3.09 (3.09)
28.41 (28.32)
18.63 (18.60)
27.89 (27.95)
32.80 (32.58)
30.01 (29.07)
33.31 (33.31)
23.91 (23.87)
31.23 (31.22)
25.30 (25.29)
12.40 (12.39)
16.80 (16.80)
15.10 (15.09)
14.38 (14.27)
28.29 (28.31)
14.12 (14.10)
7.50 (7.49)
–
–
◦
All of the complexes have melting points over 300 C.

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
1909
Table 2
Fundamental infrared bands (cm 1) of adenine and its complexes
−
Adenine
CoII complex
NiII complex
CuII complex
Assignment
3
2
2
1
1
1
1
286, 3114
976
3340
2970
2629
1638
1603, 1544, 1460
1392, 1339, 1308
1200
3362
2971
2921, 2627
1638
1545, 1462
1391
3327, 3180
–
3630
1637
1603, 1544
1460, 1392, 1339, 1308
1199
νNH2
νC–H
νN–H
δNH2
790, 2688, 2596
668
601, 1502, 1446
451, 1365, 1331, 1307
250
νC=N, νC=C + ring
Vibrations
1212
νC–NH , or δN–H
2
1
025
1045
1048
341
231
1043
341
231
ρNH2
νM–O
νM–N
3
2
41.3
31
as large as those corresponding to N-bonded complexes of
this ligand. So, the NH2 group (exocylic NH2 nitrogen),
is coordinated to the metal ion in the complexes. Adenine
presumably coordinates through ring nitrogen with appre-
ciable shifts and occasional splitting of νC=C, νC=N and
Table 3
Nujol mull electronic absorption spectra δmax (nm) and effective magnetic
moment values (νeff , BM at 298 K) for the adenine complexes
CoII complex
NiII complex
CuII complex
δmax
νeff
500, 655
4.49
655, 850
3.67
560
1.19
−
1
ring vibrations of the ligand (1605–1300 cm ) [19–25].
The νNH region, 2900–2500 cm 1, suffered considerable
−
II
II
II
changes in the Co , Ni and Cu complexes resulting of
−
1
two weak maxima in this region. The 1250 cm of ade-
nine due to νC–NH2 or δN–H ring mode shifts to lower
wavelength upon complexation. The bands at 1045, 1048
sponding to νM–O and νM–N, respectively. The electronic
absorption spectra of the separated solid complexes showed
characteristic bands at (500, 665), (655, 850) and 560 nm
−
1
II
II
II
II
and 1043 cm in Co , Ni and Cu complexes (Table 2),
with magnetic moments of 4.49, 3.67 and 1.19 BM for Co ,
II
II
respectively, are due to νNH . This facilitates that adenine is
Ni and Cu complexes, respectively (Table 3), depicting
their existence in tetrahedral geometries [28].
2
binding exclusively through ring nitrogen [19]. The copper
atom in the Cu-adenine complex lies on a crystallographic
two fold axis, the four coordination sites being accepted by
two chlorides and the N(9) atoms of two adenine cations
[26]. The reported Cu–Cl and Cu–N distances of 2.228 and
2
.012 Å, respectively are normal. The Cl–Cu–Cl, Cl–Cu–N,
N–Cu–N and two independent bond angles subtended at
copper by coordinated ligands are 97.78, 93.80, 94.74 and
◦
1
44.66 , respectively [26]. There is no close approach of
any atom to the copper centre. There are weak Cl · · · Cl
interactions of length 3.755 Å which link one copper centre
to those above and below it from infinite zigzag polymeric
◦
chains with Cu–Cl · · · Cl bond angle of 169.33 , while these
Cl · · · Cl separations might normally be considered large.
3.2. Spectral and magnetic identification of guanine
complexes
The [Cu(H2L)Cl2]2 monomers would also be expected to
provide pathway for magnetic exchange. The Cu(L)2·4H2O
complex contains the diameric unit Cu2(L)4(H2O)2 [27],
with a structure similar to that of copper acetate with four
binding adenine anions coordinated through N and water
occupying axial sites.
+
The IR spectra of the free guanine and its complexes are
collected in Table 4. Guanine exhibits bands at 3320, 1630,
−
1
780, 735 and 500 cm which are due to the different modes
of vibrations of the NH, ν, δ and ρ. On complexation, these
bands are not affected indicating that the amino group is
not involved on complexation. The ligand gave strong split-
The complex Cu(HL)Cl2 prepared in solutions which are
only slightly acidic contains neutral adenine as a ligand
−
1
[28]. The magnetic susceptibility of this complex exhibits
ted carbonyl bands at 1695, 1670 cm corresponding to
a maximum at 55 K and the complex is diamagnetic be-
low 10 K [38]. The magnetic results clearly demonstrate
the presence of exchange coupled copper dimers and thus
a ligand-bridged structure is required. However, the studied
the νC=O of the amide. However, these two bands and the
−
1
γ = band of the ligand at 580 cm are shifted towards
C
O
−1
lower wave number by about 10 and 30 cm , respectively,
on complexation indicating that the C=O group is either in-
volved on the structural configuration of the complex or the
−
1
complexes gave new IR bands at 341 and 231 cm corre-

1
910
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
Table 4
Fundamental infrared bands (cm 1) of guanine and its complexes
−
Ligand
Cobalt(II) complex
Nickel(II) complex
Copper(II) complex
Assignment
3
3
3
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
8
8
8
7
7
7
6
6
6
5
5
4
440(b)
320(s)
120(s)
980(sh)
910(m)
840(sh)
690(m.b)
450(sh.w)
695(sp.s)
670
630(sh.w)
565(s)
505(v.w)
475
460(sp.m)
415(m)
375(v.s)
260(v.s)
215(s)
175(s)
150(w)
120(s)
050(w)
55(v.s)
85(s)
55(s)
45(sh)
80(s)
3440(w.sh)
3320(s)
3120(s)
2990(sh)
2910(m.b)
2840(w)
2690(m)
2450(sh.w)
1680(sp.s)
1655
1630(v.sh)
1560(s.b)
–
1470(sp.m)
1455
1400(m)
1370(v.s)
1260(s)
1215(s)
1170(s)
1145(w)
1110(s)
1040(w)
955(v.s)
880(s)
850(b.s)
840(b.s)
780(s)
735(sh.w)
705(m.sp)
670(m)
3440(w.sh)
3320(s)
3120(s)
2980(sh)
2910(m.sp)
2840(sh)
2690(m)
2450(sh)
1685(sp.s)
1655
1630(w.sh)
1560(b.s)
1505(v.w)
1470(sp.m)
1460
1400(m)
1370(v.s)
1260(v.s)
1215(s)
1170(s)
1145(w)
1110(s)
1040(w)
955(v.s)
880(s)
850(s)
840(w.sh)
780(s)
735(w.b)
700(m.sp)
670(m)
645(m)
605(m)
550(b.m)
500(m)
400(m)
3440(w)
3320(s)
3120(s)
2980(sh)
2910(m.sp)
2840(sh)
2690(m)
2450(sh)
1685(sp.s)
1655
1630(w.sh)
1560(b.s)
1505(v.w)
1470(sp.m)
1460
ν OH
ν NH of amino
ν NH of amide
}
ν C–H
}
N(9)–H stretching vibration
ν C=O
δ N–H of amide
ν N–H of amide
ν C–N of amide
1400(m)
1370(v.s)
1260(v.s)
1215(s)
1170(s)
ν C–NH of amino
1145(w)
}
1110(s)
1040(w)
955(v.s)
ν C–OH
Ring vibration
}
880(s)
850(s)
840(w.sh)
γ
OH
}
780(s)
γ NH of amino
}
35(v.w.sh)
05(m.sp)
90(m)
50(m)
05(m)
80(sh.b)
00(w)
00(s)
735(w.b)
700(m.sp)
670(m)
γ C–OH
γ C–OH
}
645(m)
605(w)
550(sh.b)
505(b.w)
400(s)
645(m)
605(m)
γ C=O
}
550(b.m)
500(m)
400(s)
–
ρ NH of amide
ρ NH of amino
M–Cl
–
345(s)
–
phenomenon of tautomerism is assigned. The ligand and
the complexes showed νOH bands at 3440 cm , indicating
that the ligand existed in a keto-enol form. The band corre-
gathered with that of effective magnetic moment values
(Table 5) indicated the high-spin octahedral geometry of all
complexes [39]. So the following structures are postulated
for the prepared complexes:
−
1
−
1
sponding to νC–N (amide) in the free ligand, at 1415 cm
7
is shifted on complexation, i.e. the C–N of the five mem-
bered ring in guanine is involved on the complexation. This
indicates that N(7) is more donating than N(3), because of
the resonance stabilization of N(7).
The Nujol mull electronic absorption spectra of the gua-
II
II
II
nine complexes for Co , Ni and Cu complexes (Table 5)
Table 5
Nujol mull electronic absorption spectra δmax (nm) and effective magnetic
moment values (νeff , BM at 298 K) of the guanine complexes
Complex
δmax (nm)
νeff
Co-guanine
Ni-guanine
Cu-guanine
696(sh), 587(sh), 413(s), 312(s)
853(sh), 743(w.b), 416(s), 286(s), 262(sh)
683(v.b), 423(sh), 409(s), 355(w), 313(s)
5.2
2.1
2.52

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
1911
Table 6
Coordination bond lengths of pyrimidine–metal complexes
Compound
r (A)
Co[adenine ] Cl·H2O
Ni2[adenine] Cl3·H2O
Cu[adenine] Cl·H2O
2.25
2.23
2.18
3.4. ESR of copper complexes
It is possible to measure the covalent band character α2,
where α is the coefficient of the ground state of d
bital, from the expression [26–37]:
x2−y2
or-
A11
3
2
α =
+ (g11 − 2.0023) + (g⊥ − 2.0023) + 0.04
7
0
.036
−
1
2
A11 is the parallel coupling constant (cm ). The α value for
II
Cu complexes with tetragonal distortion lies in the range
of 0.63–0.84 for nitrogen donor ligands [38] and 0.84–0.94
for oxygen donor ligands [39]. Axial ligands cause changes
in equatorial bond length and hence g and A values [40].
II
Bonding between ligands and Cu ion occurs through the
II
4
s and 4p orbitals of the Cu ion with the ligand orbitals.
The presence of apical ligands introduces 4s character in
the ground state which decreases the contact hyperfine in-
teraction. Therefore, if the 4s character in the ground state is
known, it is possible to know the axial field strength in the
presence of small percentage of 4s character in the ground
state, the fraction of the 3d character in the CuII 3d–4s
2
ground state, f , can be determined from the following equa-
tion [36]:
ꢁ
ꢂ
3
.3. Bonding in adenine complexes
7
4
A11
A
2
3
5
6
7
2
2
α f =
−
+
g11 −
g⊥ −
0.036 0.036
21
The coordination bond length r can be determined from
The room temperature poly crystalline X-band ESR spec-
tral pattern of the Cu-adenine and Cu-guanine complexes
Table 7) gave similar pattern. Both are of anisotropic na-
ture. The spectral analysis of these complexes gave two
values g11 2.11 and 2.23 and g⊥ 2.03 and 2.05 for both
adenine and guanine complexes, respectively. The calcu-
lated <g> values = (g11 + 2g⊥)/3 are 2.06 and 2.11, re-
spectively. The lowest g value was more than 2.00 conse-
quently, to assign the tetragonal distorted symmetry associ-
the relation [30,31]:
ꢀ
3
2πα νx=y − νx−y
2
(
ꢀ
ν =
exp(−2π (2r/a)
a
I
where α is the bond polarisability, ꢀν the shift in the oscil-
lator frequency, a the lattice constant of the metal salt (a =
3
.5, 3.524 and 3.614) for cobalt, nickel and copper, respec-
tively [32], νx−y the frequency of the oscillator with single
bond, νx=y the frequency of the oscillator with double bond
and I is the length of the oscillator coordinated to the metal
ion (I = 1.905 and 1.993 for cobalt [33], nickel [30] and
copper [30], respectively. The values were computed based
on a published data [34]. These are 48.61, 46.59 and 42.50
for cobalt, nickel and copper, receptively. From such data,
the r values between the metal and the nitrogen atom of
the C=N group are computed (Table 6). It seems that the
ated with d
2
ground state rather than dz
2 2
[41]. The G
x −y
values were 3.66 and 4.60 for adenine and guanine com-
plexes, indicating weak Cu–Cu interaction in the adenine
complex and no Cu–Cu interaction in the guanine complex.
The A11 values for the two complexes were 185 and 88, indi-
cating the probability of the pseudo T structure around Cu
d
copper complexes are with shorter coordination bond length
than those of cobalt and nickel complexes. This could be
attributed to the increase in the strength of the electrostatic
field of the copper ion as a result of the smaller ionic radius
of the Cu ion compared to that of Ni or Co ions, i.e. the
electronic configuration of the element affects such trend.
Table 7
ESR parameters for copper-adenine and guanine complexes
2
f2
Complex
g11
g⊥
<g>
G
A11
A⊥
α
II
II
II
Cu-guanine 2.23 2.05 2.11
Cu-adenine 2.11 2.03 2.06
4.60
88 38
0.52 0.80
3.66 185 18.5 0.67 0.98

1
912
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
Table 8
DTA parameters of the adenine complexes
ꢀEa (kJ mol 1)
−
n
αm
ꢀS# (kJ mol
−1
)
ꢀH# (kJ mol
−1
)
Z
Assignment
Compound
Type
Tm (K)
Co[adenine]Cl·H2O
Ni2[adenine ]Cl3·H2O
Cu[adenine]Cl·H2O
Endo
Endo
Endo
660
508
603
121.94
323.08
231.35
1.16
0.59
2.52
0.60
0.72
0.46
−0.24
−0.22
−0.23
−156.41
−113.57
−138.57
5.746
22.23
12.45
Formation of CoO
Formation of NiO
Formation of CuO
ion in the guanine complex; where the value of A11 < 100
signed to the desolvation of 1C2H OH and 1NH3 molecules,
respectively. This is strongly supported by the TG mea-
surements, which gave weight loss exactly equivalent to
5
2
2
[35]. The calculated α and f values (Table 7) indicated the
stronger axial field in the adenine complex. From the values
2
of α one can say that the metal–ligand bond in the guanine
1C2H OH and 1NH3 molecule. The TGA curve displays
5
complex is less covalent than that of adenine. Generally,
the difference in the ESR spectral data of the Cu-adenine
and Cu-guanine complexes may attribute to the difference
in the geometry of the two complexes, i.e. Td and Oh,
respectively.
the observed weight loss 7.5% in the temperature range
(491.8–704.3 K), which is probably due to replacement of
HCl molecule (calcd. 7.7%). The DTA and TGA curves de-
picted that as the HCl is removed, the complex is decom-
posed. The third strong endothermic peak in the temperature
range (704.3–798.6 K) could be argued to the first step of
the decomposition. This is confirmed by the observed TG
weight loss 43.5% equivalent to 3N2, 2CH2=C=CH2 and
H2O (calcd. 44.1%). The fourth endothermic peak in the
temperature range (98.6–843.0 K) is due to the second de-
composition step, as evident from the observed TG weight
loss 10.9% equivalent to 2C=N (calcd. 10.9%). On the other
hand, the fifth endothermic peak in the temperature range
3
3
.5. Thermal analysis
.5.1. Adenine complexes
Differential thermal analysis of these complexes (Table 8)
gave the following features.
1
. The DTA pattern of Co-, Ni- and Cu-adenine complexes
indicated that there is a great similarity in their ther-
mal behaviour. Each complex gave one exothermic broad
(843.0–925.0 K) and the TG measurements illustrated the
following processes.
◦
band at a temperature higher than 250 C indicating the
(i) The observed weight loss (14.6%) is equivalent to 2N,
higher stability of these complexes up to this temperature.
. The activation energy changes of the decomposition
step for the complexes were in the order Co-adenine <
Cu-adenine < Ni-adenine complexes. Such order is
reversed to the maximum temperature of the decomposi-
tion step, i.e. the decomposition steps of these complexes
are thermodynamically controlled.
2C and H2O at 843.0–885.0 K (calcd. 14.7%).
2
(ii) The decomposition process with 15.8% is equivalent to
CoO at 885.0 K (calcd. 15.7%).
(
iii) The formed metal oxide started to lose oxygen temper-
ature ranges (885.0–935.0 K). The DTA endothermic
peak in the temperature range (935.0–976.0 K) is due
to the formation of Co + 0.4 (᭺) as evident from TGA
curve, where the observed value becomes 13.8 % com-
pared to the calculated value 13.7%.
3
4
. The fractions appeared in the calculated order of the
thermal decomposition steps indicated that these thermal
steps are not kinetically simple.
. The narrow range of the entropy changes (−0.22 to
In summary, the mechanism of the cobalt guanine com-
plex could be given in the following steps:
−
0.24) illustrated the similarity of the thermal behaviour.
The negative sign indicated that the transition states of
the thermal reaction are more ordered.
5
6
. The values of the enthalpy changes have a similar trend
as that of the entropy changes.
. The thermal gravimetric analysis indicated that the prod-
ucts of the residual decomposition complexes are the
metal oxides.
3
.6. Guanine complexes
The DTA curve of octahedral cobalt guanine complex,
ꢀ
ꢀ
[
Co(H2L )HL H2O]·NH3·C2H OH, exhibits six endother-
5
mic peaks in the temperature range 310.0–976.0 K (Table 9).
The first and the second weak endothermic peaks in the
temperature range (310.0–404.5 and 404.5–491.8 K) are as-

Table 9
DTA and TGA analysis of guanine complexes, guanine = HL
ꢀS#
(kJ mol
ꢀH#
−1
(kJ mol )
10 Z (s
3
−1
)
Temperature Loss (wt.%)
range
Assignment
Complex
Type Tm (K) ꢀE
n
αm
kJ mol 1)
−
−1
)
(
Calculated Found
Co(HL)2·OC2
Endo 350.55
25.27
1.35 0.58 −0.320
−112.1
1.45
310.0–404.5
04.5–491.8
3.9
4.0
Dehydration of C2H5OH
H5Cl·H2O·NH3
4
3.6
3.6
7.5
Dehydration of NH3
Replacement of HCl
7.7
Endo 781.99 119.72
Endo 817.46 34.67
0.69 0.7
−0.320
−250.38
3.07
491.8–704.3 44.1
704.3–798.6
43.5
Decomposition of 3N2, H2O, 2CH2=C=CH2
1
.63 0.54 −0.331
−276.76
−270.4
0.85
9.88
798.6–843.0 10.9
843.0–925.0 14.7
10.9
14.6
15.8
13.8
Decomposition of 2C=N
Decomposition of 2N, 2C, H2O
Formation of CoO
Formation of Co + 0.4(O)
Endo 868.51 428.17
2.08 0.49 −0.311
15.7
Endo 945.1
Endo 354.63
599.77
25.86
2.34 0.47 −0.310
−292.91
0.013
935.0–976.0 13.7
Ni2L3·OC2H5·5H2O
1.59 0.54 −0.320
0.99 0.63 −0.315
0.73 0.69 −0.319
−113.4
1.46
4.31
3.73
3.99
4.47
323.0–398.0
398.0–635.5
704.3–791.0
1.25
3.75
1.38
Dehydration of H2O + C2H5OH
Endo 619.05 133.02
Endo 777.88 144.66
Endo 814.66 162.12
Endo 895.35 199.54
−195.26
−274.78
−259.34
−284.89
3.75 Dehydration of H2O
1.21 0.6
−0.318
791.0–841.0 22.5
841.0–938.0
22.4
Formation of 2NiO + 0.5(O) as a final product
Loss of 0.25C2H5OH
Loss of 2H2O and 0.25C2H5OH
1.17 0.60 −0.318
2.78 0.44 0.309
CuL2·2H2O·0.25C2H5OH Endo 307.33
Endo 367.33 138.59
Exo 531.1 236.95
70.67
−94.98
−112.55
−163.62
4.61
7.56
8.94
303.0–438.0
2.72
2.75
11.24
1.26 0.59 −0.306
1.52 0.55 −0.308
438.0–663.0 11.10

1
914
M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
Then the dissociation of A:
perature ranges (303.0–438.0 K), corresponding to the ob-
served TG weight loss (2.75%), equivalent to 0.25 ethanol
molecule (calcd. 2.72%) exists as crystal voids. Follow-
ing the process of the decomposition in the temperature
ranges (438.0–703.0 K). The DTA curve exhibits an exother-
mic peak. The TGA data pointed to that the observed TG
weight loss (11.24%) is equivalent to the weight loss of
2
H2O and 0.25C2H OH molecules (calcd. 11.1%) in the
5
temperature range (438.0–663.0 K). The solvent molecules
0.25C2H OH and 2H2O) are in the lattice structure and in
(
5
the coordinated sphere of the complex, respectively. The fi-
nal product of the thermal decomposition of the complex
#
is copper metal. The change of entropy, ꢀS , values for all
complexes (Table 9) are nearly of the same magnitude and
−
1
−1
lie within the range −0.305 to −0.331 kJ K mol . So,
the transition states are more ordered, i.e. in a less random
molecular configuration, than the reacting complex
(
185)
. The
fraction appeared in the calculated order of the thermal re-
action, n (Table 9) confirmed that the reactions proceeded in
complicated mechanisms. The calculated values of the col-
lision number, Z, showed a direct relation to the activation
energy ꢀE. The peak temperature, Tm, at which the peak is
maximum or minimum, defines the position of the peak. The
values of the decomposed substance fraction, αm, at maxi-
mum development of the reaction were calculated (Table 9).
It is nearly of the same magnitude and lies within the range
#
The order of reaction and the activation energy of different
(0.44–0.71). The change of the heat of transformation, ꢀH ,
#
kinetic steps were calculated and the data are collected in
Table 9. The first step of the decomposition reaction is of
a pseudo first order kinetics while the second step proceeds
in second order conditions.
can be calculated from the DTA curves. In general, the ꢀH
for any phase transformation taking place at any peak tem-
perature, Tm, can be given by the following equation:
#
ꢀ
H
The DTA curve of the octahedral nickel guanine com-
#
ꢀ
S =
ꢀ
ꢀ
plex, [Ni(HL )2L (H2O)4]·H2O·C2H OH exhibits five en-
T
m
5
dothermic peaks in the temperature range (323–929 K). The
first two weak endothermic peaks in the temperature ranges
#
where ꢀS is the entropy of activation.
(323.0–398.0 and 398.0–635.5 K) are assigned to be the loss
of crystallization molecules as evident from the TG observed
weight loss (5.13%) equivalent to one water and one alco-
hol molecules (calcd. 5.01%) where the solvents are trapped
in the crystal voids. The activation energies and the order
3.7. Electrical conductivity measurements
The dependence of the electrical conductivity on tempera-
ture is expressed by the following equation σ = σ e
◦
ꢀE/KT
,
−
1
◦
of the desolvation reaction are 25.86 kJ mol , n = 1.59
where ꢀE is the activation energy for the conduction, σ is a
constant for the conductivity independent of the temperature
and K is the Boltzmann constant. The electrical conductiv-
ity data are collected in Table 10. The data depict that all
complexes are of semi-conductor behaviour. The magnitude
of ꢀE can be affected by the ambient atmosphere, the pres-
ence of impurities and pressure. The discontinuation in the
complexes in the conducting curves can be argued to be a
molecular rearrangement or crystallographic transition due
to traps formation or delocalization. Such case is familiar
for complexes with semi-conductor behaviour.
−
1
and 133.02 kJ mol , n = 0.996 for the first and second
peaks, respectively (Table 9). The DTA curve shows loss
in energy in the temperature range (636.5–704.3 K), corre-
sponding to the observed TG weight loss 4.9% equivalent to
the loss of the coordinated water molecules (calcd. 5.1%).
This is confirmed from the TGA curve. The third, fourth
and fifth endothermic DTA peaks in the temperature ranges
7
04.3–791, 791–841 and 841–938 K, respectively, are due
to vigorous decomposition process. The TGA curves proved
such view: 2NiO + 0.5O as final products. The orders of
the reactions for these peaks are 0.73, 1.21, 1.17, respec-
tively, i.e. the decomposition of the complex follows the first
order reaction mechanism. The DTA and TGA curves of
The electrical conductivity pattern of the Co-, Ni- and
Cu-adenine complexes showed five, four and five regions,
respectively, with transition temperatures 571.43, 526.32,
473.93, 425.35, 571.43, 476.19, 369.00 and 529.1, 483.09,
37.37, 331.13 K, respectively. The activation energies are
ꢀ
the octahedral copper guanine complex, [Cu(HL )2(H2O)2]
0
.5C2H OH, gave two weak endothermic peaks in the tem-
5

M.S. Masoud et al. / Spectrochimica Acta Part A 60 (2004) 1907–1915
[3] S. Ljungquist, T. Lindahl, J. Biol. Chem. 249 (1974) 1530.
1915
Table 10
Electrical conductivity parameters of adenine and guanine complexes
[4] G.L. Eichhorn, in: G. L. Eichhorn (Ed.), Inorganic Biochemistry,
vol. 2, Elsevier, New York, 1973, p. 1191, 1210.
◦
Complex
Region
ꢀE (eV)
log σ
Transition
temperatures
[
[
5] M.S. Masoud, S.S. Haggag, Thermochim. Acta 196 (1922) 221.
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(1992) 1365.
−
1
−1
(ꢁ
cm )
Co-adenine
A
B
C
D
E
1.464
0.475
0.043
7.8
8.7
9.6
10.1
9.35
571.43
526.32
473.93
425.35
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[8] M.S. Masoud, O.H.A. El-Hamid, Z.M. Zaki, Trans. Met. Chem. 19
(1994) 21.
−0.119
−0.277
[9] M.S. Masoud, S.S. Haggag, Z.M. Zaki, M. El-Shabasy, Spectrosc.
Ni-adenine
Cu-adenine
A
B
C
D
1.765
0.232
7.6
9.6
11.0
8.7
571.43
476.19
369.00
Lett. 27 (1994) 775.
10] M.S. Masoud, A.A. Hasanein, A.K. Ghonaim, E.A. Khalil, A.A.
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Phys. Chem. 211 (1999) 13.
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Ali, Z. Fur Phys. Chem. 513 (2000) 215.
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A.A. Mohamed, J. Coord. Chem. 55 (2002) 79.
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ed., Longmann, London, 1978, p. 116, 452.
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17] D. Reinen, G. Friebel, Inorg. Chem. 23 (1984) 791.
[
−0.269
0.102
[
A
B
C
D
E
1.492
0.250
0.011
6.8
9.4
10.2
11.5
9.4
529.10
438.09
370.37
331.13
−0.179
0.073
Co-guanine
Ni-guanine
A
B
C
D
0.604
−0.198
−0.784
−1.112
1.279
0.083
−0.851
−0.239
0.031
8.75
480.77
711.52
334.45
[
10.3
12.6
8.1
[
[
A
B
C
D
E
8.4
9.9
12.6
9.24
7.4
578.03
483.09
392.16
322.58
[18] N.B. Figgs, J. Lewis, Modern Coordination Chemistry, Interscience,
New York, 1967, p. 403.
[19] S. Shirotake, Chem. Pharm. Bull. 28 (1980) 1673.
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Acta 38 (1982) 561.
[
21] J. Brigando, D. Colitis, M. Morel, Bull. Soc. Chem. Fr. 3445 (1969)
Cu-guanine
A
B
C
2.104
0.462
−0.159
5
7.3
10.3
496.89
371.75
3449.
[
22] T. Fujita, T. Sakaguchi, Chem. Pharm. Bull. 25 (1977) 1055.
23] A.N. Speca, C.M. Mikulski, F.J. Iaconianni, L.L. Pytlewski, N.M.
Karayannies, J. Inorg. Nucl. Chem. 43 (1981) 2771.
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[
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within the range of −0.269 to 1.464 eV. The data revealed the
semi-conducting behaviour of these complexes. The ꢀE −
[25] A. Lautie, A. Novak, J. Chem. Biol. 65 (1968) 1359.
◦
log σ relation for the adenine complexes gave the following
[26] D.B. Brawn, J.W. Hall, H.M. Helis, E.G. Walton, D.J. Hodgson,
◦
empirical equation: ꢀE = −1.579 log σ + 0.984.
W.E. Halfield, Inorg. Chem. 16 (1977) 2675.
[
[
[
[
27] E. Sletten, Acta Crystallogr. B 25 (1969) 1480.
The electrical conductivity patterns of (1:2) cobalt, (2:3)
nickel and (1:1) copper complexes of guanine showed four,
five and three regions, respectively, with transition tempera-
tures of 480.77, 411.52 and 334.45, 578.03, 483.09, 392.16
and 322.58, and 496.89 and 371.75 K, respectively, and ac-
tivation energies ranged from −0.112 to 2.164 eV. Regions
B–D, and B and C of Co and Cu complexes, respectively,
are due to the desolvation process of the complexes and re-
gion A is due to the partial decomposition of the complexes.
Whereas, in case of nickel complex, all the five regions are
due to the desolvation process of the complex (Table 10).
28] R. Weiss, H. Venner, H. Seyler, Z. Physiol. Chem. 33 (1963) 169.
29] W. Levason, C.M. MacAulife, Inorg. Chim. Acta 14 (1975) 127.
30] S.C. Bhtia, J.M. Bindlish, A.R. Saini, P.C. Jain, J. Chem. Soc.,
Dalton Trams. (1981) 1773.
[31] G. Karagonins, O. Peter, Z. ElectroChem. Ber. Eunsenges Phys.
Chem. 63 (1959) 1170.
[
32] C.H. Macgillavery, G.D. Rieckin, in: K. Lonsdale (Ed.), International
Tables for X-ray Crystallography: Physical and Chemical Tables,
vol. 3, 1962.
[33] I. Saski, D. Pujol, A. Gauderner, A. Chiaroni, C. Riche, Polyhedron
6 (1987) 2103.
[34] R.K. Parasher, R.C. Sharma, A. kumar, G. Hohan, Iinorg. Chim.
◦
Acta 72 (1988) 201.
The ꢀE − log σ curve gave the following empirical equa-
[
[
35] D. Kirelson, R. Neiman, J. Chem. Phys. 35 (1961) 149.
36] H.A. Kuska, M.T. Rogers, R.E. Drullinger, J. Phys. Chem. 71 (1967)
109.
tion for the conduction of the studied guanidine complexes:
◦
ꢀ
E = −2.172 log σ + 9.559.
[
[
37] J.I. Zink, R.S. Drago, J. Am. Chem. Soc. 94 (1972) 44550.
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