Spectral, magnetic, thermal, and DNA interaction of Ni(II) complexes of glutamic acid schiff bases

Article abstract of DOI:10.1080/15533174.2012.684260

Ni(II) complexes with Schiff bases obtained by condensation of glutamic acid with salicylaldehyde; 2,3-; 2,4-; and 2,5-dihydroxybenzaldehyde; and o-hydroxynaphthaldehyde have been synthesized using the template method in ethanol or ammonia media. They were characterized by elemental analyses, conductivity measurements, magnetic moment, UV, IR, and ¹H NMR spectra as well as thermal analysis (TG, DTG, DTA). The Schiff bases are dibasic tridentate or tetradentate donors and the complexes have square planar and octahedral structures. The complexes decompose in two or three steps where kinetic and thermodynamic parameters of the decomposition steps were computed. The interactions of the formed complexes with FM-DNA were monitored by UV and fluorescence spectroscopy. Copyright Taylor & Francis Group, LLC 2013.

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Spectral, Magnetic, Thermal, and DNA Interaction of
Ni(II) Complexes of Glutamic Acid Schiff Bases
A. S. Orabi a , A. M. Abbas a & S. A. Sallam a
a Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
Accepted author version posted online: 07 Aug 2012.Version of record first published: 03 Dec
2012.
To cite this article: A. S. Orabi , A. M. Abbas & S. A. Sallam (2013): Spectral, Magnetic, Thermal, and DNA Interaction of Ni(II)
Complexes of Glutamic Acid Schiff Bases, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
43:1, 63-75
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:63–75, 2013
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.684260
Spectral, Magnetic, Thermal, and DNA Interaction of Ni(II)
Complexes of Glutamic Acid Schiff Bases
A. S. Orabi, A. M. Abbas, and S. A. Sallam
Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt
the coordination chemistry of Cu(II), Ni(II), Co(II), UO22+
,
[9,10]
and lanthanide[11–13] complexes containing Schiff base ligands
derived from glycylglycine and D-penicillamine and its methyl
ester.
Ni(II) complexes with Schiff bases obtained by condensa-
tion of glutamic acid with salicylaldehyde; 2,3-; 2,4-; and 2,5-
dihydroxybenzaldehyde; and o-hydroxynaphthaldehyde have been
synthesized using the template method in ethanol or ammonia me-
dia. They were characterized by elemental analyses, conductivity
In order to contribute to these studies, we have prepared—in
solution—Schiff bases of glutamic acid (glu) with salicylalde-
hyde (sal); 2,3-dihydroxybenzaldehyde (2,3-diOHbenz); 2,4-
dihydroxybenzaldehyde (2,4-diOHbenz); 2,5-dihydroxybenzal
dehyde (2,5-diOHbenz); and o-hydroxynaphthaldehyde (o-
OHnaph). Ni(II) complexes of the Schiff bases were synthesized
by template reaction using alcohol or ammonia as solvents.
They were characterized using elemental analysis, magnetic
1
measurements, magnetic moment, UV, IR, and H NMR spectra
as well as thermal analysis (TG, DTG, DTA). The Schiff bases
are dibasic tridentate or tetradentate donors and the complexes
have square planar and octahedral structures. The complexes de-
compose in two or three steps where kinetic and thermodynamic
parameters of the decomposition steps were computed. The inter-
actions of the formed complexes with FM-DNA were monitored by
UV and fluorescence spectroscopy.
1
properties, spectral (IR, UV-vis. and H NMR), and thermal
Keywords FM-DNA interaction, glutamic acid Schiff bases, mag-
methods (TG, DTG, and DTA). The interaction between
the Ni(II) complexes of the Schiff bases and fish melt DNA
(FM-DNA) under physiological conditions was investigated by
UV and fluorescence spectroscopy.
netic, Ni(II) complexes, spectral and thermal properties
INTRODUCTION
Several structural studies have been carried out on transition
metal complexes of the Schiff bases derived from condensa-
tion of salicylaldehyde and hydroxynaphthaldehyde with amino
acids in view of the fact that these complexes can be used as
non-enzymatic models analogous to the key intermediates in
many metabolic reactions of amino acids such as transamina-
tion, decarboxylation, α- and β-elimination, racimization, and
intermediate products in biologically important reactions.[1–5]
Derivatives of amino acids and pyridoxal or salicylaldehyde
Schiff bases have been widely studied as a model systems for
studying enzymatic processes.[6]
A series of N-salicylaldeneglutamatocopper(II) complexes
of composition Cu(sal-glu)X, where sal-glu represents Schiff
bases derived from salicylaldehyde with L- and DL-glutamic
acid and X = pyridine, 2-, 3-, and 4-methylpyridine, were pre-
pared and characterized.[7] Recently, manganese complexes of
the Schiff base derived from 2-hydroxy-1-naphthaldehyde and
glutamic acid have been prepared.[8] We have been interested in
EXPERIMENTAL
Glutamic acid; salicylaldehyde; 2,3-diOH-; 2,4-diOH-; 2,5-
diOH-benzaldehyde, and o-hydroxynaphthaldehyde were pur-
chased from Fluka, Aldrich, and Merck. All solvents were of
analytical-grade reagents.
Preparation of Sodium Salt of the Schiff Bases
Glutamic acid (2 mmol, 0.294 g) and NaOH (4 mmol, 0.16 g)
were suspended in EtOH (10 mL), and H2O was added drop
wise with stirring tell complete dissolution. 2 mmol of the cor-
responding aldehyde was dissolved in 10 mL of EtOH and was
added to the sodium glutamate solution dropwise. The mixture
was refluxed with stirring and pubbling of purified N2 gas for 2 h.
The solution turns to yellow color indicating the formation of
the Schiff bases. We succeeded to precipitate salicylaldeneglu-
tamic acid Schiff base by reduction of solvent volume followed
by acidification using CH3COOH, but trials to precipitate the
other Schiff bases by acidification, evaporation of the solvent,
or using solvents mixture were unsuccessful.
Template Synthesis of the Ni(II) Complexes
Received 12 December 2011; accepted 1 April 2012.
Address correspondence to S. A. Sallam, Chemistry Department,
Faculty of Science, Suez Canal University, Ismailia, Egypt. E-mail:
shehabsallam@yahoo.com
To the obtained Schiff bases solutions in EtOH/H2O medium,
a solution of NiCl2.6H2O (2 mmol, 0.5 g) in 10 mL EtOH was
added with stirring and the mixture was refluxed for 1 h. After
63

64
A. S. ORABI ET AL.
cooling, the solid complexes were precipitated and washed with ambient temperature to 750◦C. Electrical conductivity measure-
EtOH and Et2O and dried under vacuum. If we added ammonia ments were carried out at room temperature on freshly prepared
solution (5 mL 28%) before reflux of the mixture, we obtain 10−3M DMSO solutions using a WTW conductivity meter (Mul-
another series of Ni(II) complexes in which NH3 is the coligand tiline, Germany) fitted with L100 conductivity cell. Metal con-
instead of H2O.
tent was obtained by EDTA titration using murexide indicator
and ammonia buffer.
Physical Measurements
DNA Interaction
C, H, and N were estimated using a Heraus CHN-rapid an-
alyzer. The H NMR spectra were traced on Varian-Gemini
1
Experiments were carried out in Tris–HCl buffer at pH 7.0.
200MHz spectrometer in DMSO-d6 using TMS as internal A solution of fish melt DNA gave a ratio of UV absorbance
standard. The IR spectra were recorded (KBr disc) in the more than 1.8 at 260 and 280 nm, indicating that DNA was suf-
400–4000 cm−1 range on a Bruker Vector 22 spectrometer. ficiently free from protein.[15] The stock solution of FM-DNA
The electronic absorption spectra were obtained by nujol mull was prepared by dissolving DNA in 10 mM of the Tris–HCl
and 10−3M DMF solution in 1 cm quartz cell using UV- buffer at pH 7.0. The DNA concentration of the stock so-
1601PC Shimadzu spectrophotometer. Magnetic susceptibil- lution was determined by UV spectrophotometery—in prop-
ity measurements were carried out using the modified Gouy erly diluted samples—using the molar absorption coefficient
method[14] on MSB-MK1 balance at room temperature using 6600 M−1.cm−1 at 260 nm.[16] The stock solution was stored at
mercury(II)tetrathiocyanatecobaltate(II) as standard. The effec- 4◦C and used over no more than 4 days.
tive magnetic moment, μeff, per metal atom was calculated from
Absorption titration experiments were performed with fixed
√
the expression μeff = 2.83 χ.T B.M., where χ is the molar concentration of the complexes (10−3M) while gradually in-
susceptibility corrected using Pascal’s constant for the diamag- creasing the concentration of DNA (0.5–8×10−4M) at 25◦C.
netism of all atoms in the complexes. TGA, DTG, and DTA were While measuring the absorption spectra, an equal amount of
recorded on Shimadzu 60 thermal analyzer under a dynamic DNA was added to both the compound solution and the refer-
flow of nitrogen (30 mL/min) and heating rate 10◦C/min from ence. To compare quantitatively the affinity of the compound
TABLE 1
Analytical data, conductivity, and magnetic moments of the nickel(II) complexes of the glutamic acid Schiff bases
Elemental analysis
Found Calcd (%)
Melting and
Complex
Color
Mol. Wt. Dec. point oC
C
H
N
M
Ωa μeff B.M.
[Ni(HL1)(H2O)].3H2O
Light olive
379.75
324.75
431.75
349.75
413.75
412.75
431.75
448.75
429.79
374.79
>390
366
31.9 2.8 3.7 15.8 24
37.9 2.9 3.7 15.5
44.6 3.1 4.4 18.2 15
44.3 3.4 4.3 18.1
33.0 2.7 3.1 13.4 17
33.3 2.8 3.2 13.6
41.1 3.4 3.8 16.3 14
41.2 3.4 4.0 16.8
34.5 2.8 3.2 13.9 17
34.8 2.9 3.4 14.2
34.6 2.8 3.5 13.8 14
34.9 2.9 3.4 14.2
33.1 2.7 3.1 13.3 17
33.4 2.8 3.2 13.6
Dia
Dia
[Ni(HL1)(NH3)]
Shining brown
Light brown
Brown
[Ni(H2L2)(H2O)2].4H2O
[Ni(H2L2)(NH3)].1/2H2O
[Ni(H2L3)(H2O)2].3H2O
[Ni(H2L3)(NH3)(H2O)].3H2O
[Ni(H2L4)(H2O)2].4H2O
[Ni(H2L4)(NH3)(H2O)].5H2O
[Ni(HL5)(H2O)].3H2O
[Ni(HL5)(NH3)]
>388
>395
>380
>390
>375
>370
>385
>390
3.1
Dia
Light olive
Greenish brown
Greenish brown
Deep brown
Light olive
Brown
3.17
3.23
3.25
2.97
Dia
32.3 2.6 3.2 12.9
32.2 2.4 3.1 13.0
2
44.3 3.2 3.4 13.9 12
44.7 3.0 3.3 13.7
51.4 3.2 3.4 15.6 15
51.2 3.5 3.7 15.7
1.66
a10−3 M in DMSO, ohm−1.cm2.mol−1
.

INORGANIC CHEMISTRY
65
[Ni(H2L2)(NH3)].21 H2O and [Ni(H2L3,4)(NH3)(H2O)].nH2O
where n = 3, 5; and L = Schiff base (H3L1 = glu-sal, H4L2 =
glu-2,3-diOHbenz, H4L3 = glu-2,4-diOHbenz, H4L4 = glu-2,5-
diOHbenz, H3L5 = glu-o-OHnaph). The prepared complexes
were found to be air stable and they decomposed at tempera-
ture greater than 380◦C (Table 1) except [Ni(HL1)(NH3)], which
melts at 334–336◦C. They are insoluble in water and most or-
ganic solvents but soluble in Lewis bases such as DMF and
DMSO. The molar conductance values for 10−3 M DMSO solu-
bound to DNA by the luminescence titration method, fixed
amounts of the complexes (10−4 M) were titrated with increasing
amounts of DNA at 25◦C, over a range of DNA concentrations
from 5 to 80 μM.
RESULTS AND DISCUSSION
Salicylaldeneglutamic Acid Schiff Base
Salicylaldeneglutamic acid was the only isolated Schiff base,
which is soluble in ethanol and polar organic solvents. It is stable
for about 24 h after which it changed to black sticky material
indicating its atmospheric decomposition.
tions of the prepared complexes at 25◦C (2–24 ohm−1cm2mol−1
indicate the non-electrolytic nature of these complexes.[17]
)
Infrared Spectra
Table 2 gives assignments of the most important IR bands
for the synthesized nickel(II) complexes.
In order to study the binding mode of the Schiff bases to
the nickel(II) ion in the complexes, the IR spectrum of the
salicylaldeneglutamic acid Schiff base ligand was compared
with the spectra of the nickel(II) complexes. On coordina-
tion, due to possible drift of the lone pair density toward the
nickel ion, the azomethine (–C N) bond is expected to ab-
The IR spectrum of the salicylaldeneglutamic acid Schiff
base ligand show a broad medium band assigned to the pheno-
lic υ(OH) vibration at 3425 cm−1. The azomethine stretching
band is observed at 1635 cm−1. The strong absorptions at 1585
and 1457 cm−1 are attributed to the asymmetric and symmetric
υ(COO−) stretch.
Nickel(II) Complexes
The results of microanalyses of the prepared nickel(II) com- sorb at lower frequency in the complexes. The band observed at
plexes suggest the molecular formulas: [Ni(HL1,5)X].nH2O ≈ 1644–1612 cm−1 indicates the coordination of the azome-
where X = H2O and n = 3 or X = NH3 and n = 0; thine nitrogen to the nickel(II) ion.[18] In all the complexes, a
[Ni(H2L2,3,4)(H2O)2].nH2O where n = 4, 3, 4, respectively; new band was shown at 422–560 cm−1 region, which is probably
TABLE 2
IR spectral data of the Ni(II) complexes of the glutamic acid Schiff bases
υ(H2O)
υ(C N)
and/or
+
υ(Ph-C- υsym
Complex
υ(OH) υ(OH) υ(NH) υas (COO−) C N) (COO−) ꢀ υ υ(C-O) υ(M-O) υ(M-N)
[Ni(HL1)(H2O)].3H2O
3381b
3446b
—
—
—
3302s
—
1634s
1596s
1618sh
1578m
1644s
1566s 1334m 262 1298m 558m
1528(s) 1349m 229 1219m 593m
1569s 1392m 233 1253m 660m
457m
465m
531m
456m
560m
[Ni(HL1)(NH3)]
[Ni(H2L2)(H2O)2].4H2O
[Ni(H2L2)(NH3)].21 H2O
[Ni(H2L3)(H2O)2].3H2O
3402b 3306b
1625s
3360m 3324m 3281sh
3348b 3282b
3411b 3274b 3185b
3389b 3242b
3403b 3314b 3217b
1622sh.
1551m
1507m 1393s 158 1226s
541m
ꢀ
—
1630 S
1578s 1342m 255 1218m 676m
1597
[Ni(H2L3)(NH3)(H2O)].3H2O
[Ni(H2L4)(H2O)2].4H2O
[Ni(H2L4)(NH3)(H2O)].5H2O
[Ni(HL5)(H2O)].3H2O
[Ni(HL5)(NH3)]
1625 S
1557s 1408m 194 1221m 643m
1566s 1346m 230 1226m 676m
1550s 1400m 161 1266m 671m
1550m 1401m 184 1248m 571m
1533s 1396m 204 1242m 550m
540m
560m
422m
502m
438m
ꢀ
1602
ꢀ
—
1625 S
1576
ꢀ
1625 S
1561
ꢀ
3395b 3282b
3423b
—
1623 S
1585
—
3319sh.
1612
ꢀ
1600 S
Note. sh = sharp; s = strong; b = broad; m = medium.

66
A. S. ORABI ET AL.
due to the formation of Ni–N bond.[19] The complexes exhibit
Magnetic and UV-Vis Spectral Properties
a broad band in the region 3348–3446 cm−1 due to υ(O–H) of
Electronic spectral data and magnetic moments of the
the coordinated water.[20] The two absorption bands occurring nickel(II) complexes are summarized in Table 3.
near 1561–1625 cm−1 and 1342–1408 cm−1 corresponding to
The recorded visible spectra of the complexes [Ni(HL1)
the asymmetric and symmetric stretching vibration bands of the (H2O)].3H2O and [Ni(H2L2)(NH3)].21 H2O show two bands at
ionic carboxylic group υ(COO−) which is shifted toward lower 558, 468 and 559, 448 nm (nujol) of A2g← A1g(υ1) and
1
1
1
frequency compared with the free Schiff bases. The value of 1B1g← A1g(υ2) transitions in square planar structure.[26] In the
|υas(COO−) – υsym(COO−)| indicates the monodentate nature same time, the square planar complexes [Ni(HL1)(NH3)] and
of the carboxylate group (ꢀυ = 161–262 cm−1).[21] The ap- [Ni(HL5)(NH3)] show only υ2 transition at 440 and 443 nm
pearance of a new band at 541–676 cm−1 due to Ni–O, further (nujol) but in the electronic spectrum of [Ni(HL5)(H2O)].3H2O,
confirms the coordination nature of the carboxylate group.[22] A the d→d transitions were not observed because the peaks over-
medium strong band at 1507–1587 cm−1, always present, may lapped with the charge transfer bands.[27] Diamagnetic behavior
be originated from the vibration of the Ph–C–C–( N) moi- of these complexes is also in accordance with the proposed
ety and typifies complexes derived from salicylaldehyde.[23–25] square planar structure.[28] A lack of any absorption bands at
Medium strong bands in the range 1218–1298 cm−1 are proba- wavelength longer than 600 nm indicates a large crystal field
bly due to the υ(Ph–O).
splitting and is consistent with the square planar geometry.[29]
Besides these general features in nickel(II) complexes, H4L2- Anomalous magnetic moment of the complex [Ni(HL5)(NH3)]
H4L4 Schiff bases complexes show υ(O–H) of the second free (1.66 B.M.) may result from either spin-spin coupling[30] or
OH group as a medium broad band at 3242–3324 cm−1. A strong configurational equilibria.[31]
sharp band appear in the 3185–3319 cm−1 is due to υ(N–H) of
the coordinated ammonia.
Rest of the nickel(II) complexes have magnetic mo-
ments in the 2.97–3.25 B.M. range, indicating two unpaired
TABLE 3
Electronic spectra of the nickel(II) complexes of the glutamic acid Schiff bases
Nujol mull DMSO
Complex
π→π∗
263
n→π∗
CT
d→d
558
468
440
π→π∗
258
295
257
n→π∗
CT
d→d
—
μeff B.M.
[Ni(HL1)(H2O)].3H2O
318
342
318
339
334
366
318
342
320
348
368
326
337
321
338
304
366
Dia.
[Ni(HL1)(NH3)]
260
275
264
250
431
358
431
384
365
406
—
—
Dia.
3.1
[Ni(H2L2)(H2O)2].4H2O
[Ni(H2L2)(NH3)].21 H2O
[Ni(H2L3)(H2O)2].3H2O
—
251
256
294
725
662
—
559
448
—
341
344
420
—
Dia.
3.17
430
362
257
282
294
260
293
728
662
Ni(H2L3)(NH3)(H2O)].3H2O
[Ni(H2L4)(H2O)2].4H2O
263
275
263
318
342
369
325
350
439
369
—
—
—
339
304
394
411
418
724
660
555
730
666
3.23
3.25
2.97
430
385
365
440
357
254
257
[Ni(H2L4)(NH3)(H2O)].5H2O
317
344
255
274
313
351
735
670
558
[Ni(HL5)(H2O)].3H2O
[Ni(HL5)(NH3)]
318
345
323
357
391
366
423
367
259
267
273
394
414
419
275
265
—
443
313
313
332
351
—
—
Dia.
1.66

INORGANIC CHEMISTRY
67
electrons per Ni(II) ion and suggesting an octahedral ge-
Structure of the Nickel(II) Complexes
ometry for the Ni(II) complexes.[32] The electronic spec-
tra of these complexes show d→d bands in the region
735–724 and 670–660 nm. These are assigned to the spin
In the studied complexes, nickel(II) ion is coordinated to
the Schiff base as (O–N–O) donor sites through o-OH phenolic
or naphtholic group, azomethine nitrogen, and α-carboxylate
oxygen in addition to one aqua or ammonia ligand (square
planar structure).[7,38,39] Octahedral nickel(II) complexes have
the same coordination sites as the square planar in addition
to ε-carboxylate oxygen (ONOO donor) and coordination is
completed by two water molecules or one water and one am-
monia molecule as a coligand. This structure is similar to
that found in the manganese(III) complexes of 2-hydroxy-1-
naphthyldeneaspartic acid Schiff bases.[8]
3
3
3
allowed transitions T1g(P) ← A2g(F) and T1g(F) ←
3A2g(F) consistent with their well-defined octahedral configu-
ration. Only the complexes [Ni(H2L3)(NH3)(H2O)2].3H2O and
[Ni(H2L4)(NH3)(H2O)2].5H2O show T2g(P) ← A2g(F) tran-
sition of Ni(II) ion in an octahedral geometry at 555 and
558 nm.
3
3
1H NMR Spectra
Evidences for the proposed structure are the following:
1H NMR spectra of the complexes [Ni(HL1)(NH3)] and
[Ni(HL2)(NH3)].21 H2O recorded in DMSO-d6 are shown in
Figure 1.
• In the square planar Ni(II) complexes, the phenolic
oxygen is bonded to the Ni(II) ion through protonated
OH group, its frequency is overlapped with υ(H2O) of
the hydrated and coordinated water. The IR spectra of
the complexes [Ni(HL1)(NH3)] and [Ni(HL5)(NH3)]
show υ(OH) of the coordinated hydroxyl group as
broad band at 3446 and 3423 cm−1. The γ -carboxyl
group of the glutamic acid Schiff bases does not share
in coordination process may be due to steric hindrance.
In the same time, the υ(C O) band (1720 cm−1),
which is characteristic to the uncoordinated carboxylic
group is not observed in the IR spectra of the com-
plexes, which prove the ionization of this group.
• The pKa values for the carboxylic groups of the
free glutamic acid are 2.19 (α-COOH) and 4.25
(γ -COOH),[40] and of the free salicylaldehyde is 8.2
in water[41] and 10.17 in dioxan-water medium.[42]
The pKa values of the salicylglycine are 3.44 for
the carboxylic acid group and 8.24 for the phenolic
group.[43] Recently, Schiff bases of sal-Cl-gly, sal-Cl-
ala, sal-Br-gly, and sal-Br-ala were synthesized and
the protonation constants of the carboxylate anion
are 9.6–10.74 and that of the phenolate anion are
1.86–2.22.[44] These figures show that the carboxylic
groups of the salcylidene- and naphthyldeneglutamic
The multisignals at δ 6.47–7.35 and 6.35–6.81 ppm are as-
signed to aromatic-H protons.[3] Doublet signals at δ 7.74–7.80
and 7.81–7.85 ppm (JHC N = 12 and 7.6 Hz) are due to H atom
of the azomethine group for the two complexes. This suggests
the presence of proton transfer equilibrium and the existence of
NH tautomer in the studied complexes.[33–35] Deutration of the
DMSO solution of the complexes show the azomethine proton
as a singlet at δ 7.77 and 7.78 ppm. The value of J(NH, H) for pure
NH form was found to be ≈ 13 Hz.[36] The calculations show
that, the complex [Ni(HL1)(NH3)] exists mainly or even exclu-
sively as NH tautomer. On the other hand, the fraction of NH
tautomer for the complex [Ni(H2L2)(NH3)].21 H2O is close to
58%. The high field shift of the azomethine proton is assigned
to the increase of the shielding effect due to decrease of the
electronic cloud density of H atom at α-CH group after coordi-
nation with nickel(II) ion.[37] The signal observed at 8.57–8.63
and 9.25–9.28 ppm (exchangeable with D2O) may be assigned
to NH of the coordinated ammonia or the bonded OH of the
phenolic or naphtholic moiety.
FIG. 1. 1H NMR spectra of some Ni(II) complexes.
FIG. 2. TG, DTG, and DTA analysis of [Ni(H2L5)(NH3)].

68
A. S. ORABI ET AL.
acid Schiff bases are ionized before the phenolic and
decomposition stage. It takes place in the temperature range
32–192◦C with DTG peaks at 80, 81, 57, 85, 73, 83, 74, and
78◦C, giving endothermic DTA peaks in the 28–210◦C range
with maxima at 80, 88, 59, 91, 81, 89, 82, and 84◦C, respectively.
The complexes [Ni(HL1(NH3)] and [Ni(HL5)(NH3)] have no
hydrated water.
naphtholic OH. This result indicates that H3L1–H3L5
Schiff bases are dibasic tridentate in square planar
stereochemistry or tetradentate in octahedral geome-
try (Scheme 1).
The anhydrous nickel(II) complexes decompose in the sec-
ond decomposition stage mainly in the coordination sphere.
All the complexes lose the coligand (H2O or NH3) associated
with Schiff base dissociation. The complex [NiL1(H2O)].3H2O
gives H2O associated with the fragment C2H5COOH at 366◦C
with recorded mass loss 25.12% (calcd. 24.15%) accompa-
nied with exothermic DTA peak at 366◦C. Water or ammo-
nia along with the species C3H8(COOH)2 are evolved in the
second decomposition step for the complexes [Ni(HL1)(NH3)],
[Ni(H2L2)(H2O)2].4H2O, [Ni(H2L3)(H2O)2].3H2O, [Ni(H2L4)
(H2O)2].4H2O, [Ni(HL5)(H2O)].3H2O, and [Ni(HL5)(NH3)],
with DTG peaks at 333, 377, 390, 361, 380, and 362◦C, re-
spectively. Weight loss observed is (Found/Anal. Calcd. [%])
45.33/46.49, 39.2/39.37, 41.45/41.1, 39.4/39.4, 35.9/35.26, and
41.86/41.77 accompanied with exothermic DTA peaks at 334,
367, 398, 350, 374, and 351◦C, respectively. [Ni(HL1)(NH3)]
is the only complex which has a melting point (336◦C) that is
confirmed by sharp endothermic DTA peak at 334◦C. In a dif-
ferent manner for the second decomposition stage, [Ni(H2L2)
O
C
CH2
O
CH2
H
CH
C
N
C
O
Ni
O
O
H
R
X
R= H or o-OH
X=H2O or NH3
(NH3)].1 H2O loses NH3 and CO2, while both [Ni(H2L3)
2
(NH3)(H2O)].3H2O and [Ni(H2L4)(NH3)(H2O)].5H2O lose
NH3, H2O, and CH3COOH with reduced masses of 17.15%,
22.85%, and 21.1% (calcd. 17.44%, 23.02%, and 21.16%) at
353, 327, and 391◦C associated with exothermic DTA maxima at
355, 329, and 359◦C, respectively. Final decomposition includes
dissociation of the remaining part of the Schiff bases with the
formation of NiO residue except [Ni(HL1)(H2O)].3H2O, which
gives NiCO3 as a final product.
Square planar structure
O
O
O
N
To speculate the probable decomposition mechanism
of the complexes [Ni(H2L2)(H2O)2].4H2O and [Ni(H2L2)
Ni
O
(NH3)].1 H2O, IR spectra of heated samples of the complexes
O
2
are recorded at 200, 430, 510, 600◦C and 170, 350, 450, 530◦C,
(an example is given in Figure 3).
R
X
H
OH2
The IR spectra of the heated [NiL2(H2O)2].4H2O and
Ni(H2L2)(NH3)].21 H2O at 200 and 170◦C, respectively, show
no difference when compared with that obtained at room tem-
perature, indicating dehydration. [44] Heated samples at 430 and
350◦C show IR spectra as a sharp medium band at 2358 and
2362 cm−1, respectively, which may be ascribed to the formation
of (–C≡N) group.[21] Also, the vibrations due to the carboxy-
late group, υ(NH) of the ammonia which act as coligand and
υ(C N) were disappeared. New medium broad bands at 3434,
3435 cm−1; medium to weak bands at 2930, 2923 cm−1; 2865,
2872 cm−1; and 1645, 1643 cm−1 may be assigned to υ(OH),
υ(CH2), and ꢀ(OH), respectively, of aqua-hydroxo species.[45]
NiO is the final product as shown by the strong υ(Ni–O) band
at 417 and 420 cm−1 in the IR spectra of the complexes heated
at 600 and 530◦C. The mechanism of thermal decomposition of
[Ni(H2L2)(H2O)2].4H2O is shown as follows:
R= o-OH , m-OH or p-OH
X=H2O or NH3
Octahedral structure
SCH. 1. Ni(II) complexes of the glutamic acid Schiff bases.
Thermal Analysis
TG/DTG and DTA curves of the nickel(II) complexes are
shown in Figure 2 (as an example). The phenomenological as-
pects are illustrated in Tables 4 and 5.
The dehydration process for all complexes is very similar,
they lose crystallization water in a single step, which is the first

INORGANIC CHEMISTRY
69
O
O
O
N
200oC
[Ni(H2L2)(H2O)2].4H2O
4H2O
Ni
X
O
O
H
R
OH2
430oC
O
C
N
C
2H2O
C3H8COOH
Ni O
OH
O
H
OH
510oC
C
O
N
OH2
OH
CH3COOH
Ni
OH
600oC
NiO
Kinetic Parameters
All the well-defined stages were selected for the study of the
kinetics of the decomposition of the nickel(II) complexes. The
order of the decomposition process (n), the activation energy
ꢀEa and the pre-exponential factor (Z) were calculated using
the Coats-Redfern equation.[46] Thermodynamic parameters of
the decomposition process ꢀG◦, ꢀH◦, and ꢀS◦ were also eval-
uated. The kinetic parameters are listed in Table 6.
The activation energy ꢀEa in the first decomposition step are
in the 45–64 kJ.mol−1 range and in the 47–192 kJ.mol−1 range
for the second decomposition step. The respective values of the
pre-exponential factor (Z) vary from 1.5 × 105 to 5.2 × 108 s−1
.
The corresponding values of the entropy of activation ꢀS◦ are
in the range –85 to –167 J.mol−1.K−1. The negative values of
the entropy of activation indicate that the activated complexes
have a more ordered structure than the reactants.[47]
DNA Interaction
Assuming that DNA forms a 1:1 systems with Ni(II)-
complexes, the binding constant of the formed complexes (Kb)
FIG. 3. IR spectra of [Ni(H2L2)(NH3)]. 21 H2O at different temperatures.

70

INORGANIC CHEMISTRY
71
TABLE 5
DTA of the nickel(II) complexes of the glutamic acid Schiff bases complexes
Complex
Temp. range ◦C
DTA temp. ◦C
ꢀH (J/g)
Process
Dehydration
Coordination sphere
Ligand decomposition
Final decomposition
Melting
Coordination sphere
Dehydration
Coordination sphere
Final decomposition
Solid state reaction.
Dehydration
Coordination sphere
Ligand decomposition
Final decomposition
Dehydration
Coordination sphere
Final decomposition
Solid state reaction
Dehydration
Coordination sphere
Ligand decomposition
Final decomposition
Dehydration
Coordination sphere
Final decomposition
Dehydration
[Ni(HL1)(H2O)].3H2O
28–221
262–400
80 endo.
366 exo.
383
480 exo.
334 endo.
559 exo.
88 endo.
367
486 exo.
537
59 endo.
355
396 exo.
577
91 endo.
398
450 exo.
536
81 endo.
329 exo.
404 exo.
447
89 endo.
350 exo.
491
82 endo.
359 exo.
553 exo
84 endo
374 exo.
485
722
−6180
410–541
271–394
394–700
30–193
[Ni(HL1)(NH3)]
−5870
[Ni(H2L2)(H2O)2].4H2O
799
225–576
−5840
59
[Ni(H2L2)(NH3)].21 H2O
[Ni(H2L3)(H2O)2].3H2O
[Ni(H2L3)(NH3)(H2O)].3H2O
28–101
206–632
−9300
676
36–182
284–525
−6060
691
32–174
205–340
350–520
33–210
232–468
–10510
819
−7960
[Ni(H2L4)(H2O)2].4H2O
[Ni(H2L4)(NH3)(H2O)].5H2O
[Ni(HL5)(H2O)].3H2O
[Ni(HL5)(NH3)]
27–198
328–400
420–600
33–182
916
−65
Coordination sphere
Final decomposition
Dehydration
Coordination sphere
Final decomposition
Coordination sphere
Ligand decomposition
Solid state reaction
−11
517
231–550
−7280
296–380
420–600
617–677
351 exo.
440 exo.
652 exo.
−3880
−2000
−246
is given by Benesi–Hildebrand plot[48]
:
The changes of emission intensity in emission titrations en-
sured the availability of the association constants (K) of the com-
plexes with DNA from the analysis of the relationship between
the fluorescence intensity and [DNA] by Benesi–Hildebrand
plot.[48] The association constants of the formed complexes (K)
are given by
[Ni − complex]0
1
1
=
+
ꢀA
ꢀε K[DNA]0ꢀε
Where ꢀA is the difference between the absorbance of Ni(II)-
complex in the presence and absence of DNA and ꢀε is the
difference between the molar absorption coefficients of Ni(II)-
complex and Ni(II)-complex-DNA system. [Ni(II)-complex]0
and [DNA]0 are the initial concentration of the Ni(II)-complex
and DNA. Linear relationship of [Ni(II)-complex]/ꢀA versus
IF0
α
1
= α +
,
α =
IF − IF0
K ꢁDNAꢂ 0
IFL − IF0
1/[DNA] confirms the formation of a 1:1 Ni(II)-complexes- Where [DNA]0 represents the analytical concentration of DNA,
DNA system. From its intercept and slope values, Kb is evaluated IF0 and IF are the fluorescence intensities in the absence and
at room temperature (25◦C).
presence of DNA, IFL is the limiting intensity of fluorescence

72
A. S. ORABI ET AL.
TABLE 6
Kinetic parameters for the decomposition steps of the nickel(II) complexes of the glutamic acid Schiff-bases
Complex
Order n
Ts Ko
bꢀEa
cZ
dꢀS◦
bꢀH◦
bꢀG◦
[Ni(HL1)(H2O)].3H2O
I
II
II
I
II
II
I
II
I
II
I
II
I
I
II
II
2
0.5
0
2
2
2
2
2
0.5
0
2
2
2
2
2
2
354
657
607
356
648
625
357
661
348
600
356
636
347
350
653
635
57
128
153
61
53
163
61
87
45
47
59
29
5.2
62
490
2.7
660
390
56x
150
39
240
1.9
230
26
2.3
65
−103
−85
54
123
148
58
48
158
58
82
42
43
56
37
56
62
42
58
75
43
68
58
63
44
59
56
37
60
65
[Ni(HL1)(NH3)]
−102
−118
−90
[Ni(H2L2)(H2O)2].4H2O
[Ni(H2L2)(NH3)].21 H2O
[Ni(H2L3)(H2O)2].3H2O
−121
−120
−103
−167
−106
−124
−93
[Ni(H2L3)(NH3)(H2O)].3H2O
[Ni(H2L4)(H2O)2].4H2O
91
58
64
91
86
55
66
86
[Ni(H2L4)(NH3)(H2O)].5H2O
[Ni(HL5)(H2O)].3H2O
−123
−104
−91
[Ni(HL5)(NH3)]
bkJ/mol.
392
−102
387
cvalues x 108; s−1
dkJ/mol.K.
.
and α is 1/(IFL −IF0). A plot of IF0/(IF −IF0) vs. 1/[DNA]0 should 3–9 nm. Therefore, the observed hyperchromism reflect strong
give a straight line with a good linear relationship.
structural damage, which is probably due to strong binding of
the complexes to the DNA base moieties through covalent-bond
formation.[50] The intrinsic binding constants Kb of the com-
plexes were in the 1.1×104–6.4×104M−1 range. The obtained
values indicate that the nickel(II) complexes are moderately
bind to FM-DNA with almost the same affinity. However, these
values are smaller than those of classical intercalators whose
Electronic Absorption Titration
The absorption spectra of the complexes of Ni(II)-glut. Schiff
bases in presence of FM-DNA (at a constant concentration of
the complexes) are given in Figure 4 and Table 7.
The potential FM-DNA binding ability of the complexes
was studied by following the intensity changes of the intraligand
π–π∗ transition bands in the UV spectra.[49] In presence of DNA,
the absorption bands of the complexes at about 223–270 nm ex-
hibited hyperchromism of about 3–84% and blue shift of about
Kb values are in order of 107 M−1 [51]
Therefore, it is likely
.
that the proposed covalent binding of the complexes is more
feasible although electrostatic interactions can not be ruled
out.
TABLE 7
Binding constants (K M−1) of the interaction between the Ni(II) complexes of the glutamic acid Schiff bases and FM-DNA
UV.
Fluorescence
Hyper. %
Complex
Kb M−1
Hyper.%
ꢀ/λ
K M−1
ꢀ/λ
[Ni(HL1)(H2O)].3H2O
[Ni(HL1)(NH3)]
2.0 × 104
5.9 × 104
1.1 × 104
5.2 × 104
1.5 × 104
7.2 × 104
6.2 × 104
4.2 × 104
6.4 × 104
3.2 × 104
10
69
9
—
–3
–4
—
—
—
–5
–9
—
–5
3.5 × 104
3.2 × 104
1.6 × 104
3.3 × 104
7.4 × 104
3.1 × 104
9.7 × 104
2.3 × 104
6.1 × 104
2.8 × 104
71
63
47
58
76
55
76
44
65
57
—
—
–15
—
—
-8
—
—
—
—
[Ni(H2L2)(H2O)2].4H2O
[Ni(H2L2)(NH3)].1/2H2O
[Ni(H2L3)(H2O)2].3H2O
[Ni(H2L3)(NH3)(H2O)].3H2O
[Ni(H2L4)(H2O)2].4H2O
[Ni(H2L4)(NH3)(H2O)].5H2O
[Ni(HL5)(H2O)].3H2O
[Ni(HL5)(NH3)]
3
13
55
68
84
43
60

INORGANIC CHEMISTRY
73
Fluorescence Titration Studies
The nickel(II) complexes under study can emit fluorescence
in Tris-HCl buffer at ambient temperature with maxima appear-
ing at about 425–500 nm. As shown in Figure 5, the fluores-
cence intensities of the complexes are increased steadily with
increasing concentration of FM-DNA, which agrees with those
observed for other intercalators[52] and pronouncing their in-
teraction with FM-DNA. This implies that the complexes can
insert between DNA base pairs deeply and that they can bind to
DNA. The binding of the complexes to DNA leads to a marked
increase in emission intensity which is also observed with com-
plexes containing ligands bearing NH and OH groups.[53,54] The
association constant (K) evaluated using Bensi-Hildebrand plot
is 1.6–7.4 × 104 M−1
.
CONCLUSION
Schiff bases of glutamic acid with salicylaldehyde, 2,3-;
2,4-; and 2,5-dihydroxybenzaldehyde; and o-hydroxy-
naphthaldehyde and their nickel(II) complexes have been
synthesized by template method in ethanol or ammonia media.
Magnetic and spectral properties show that three types of
the complexes were obtained. Diamagnetic square planar,
octahedral with μ = 2.97–3.25 B.M. and a complex with μ =
1.66 B.M.—indicating spin-spin interaction or configurational
equilibrium—were obtained. The complexes decompose
starting by evolution of crystallization water followed by
decomposition of the coordination sphere. Interactions of the
complexes with FM-DNA show hyperchromism and blue shift
of their UV and florescence spectra, which reflect structural
damage probably due to binding of the complexes to DNA.
The intrinsic binding constants Kb of the complexes were in
the 1.1×104–6.4×104M−1 range, which are smaller than those
of classical intercalators.
FIG. 4. Electronic spectra of 10−3 M [Ni(HL1(NH3)] in the presence of in-
creasing amounts of FM-DNA, 0–8 × 10−5 M (color figure available online).
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