Synthesis, potentiometric and antimicrobial activity studies on DL-amino acids-Schiff bases and their complexes

Article abstract of DOI:10.1134/S1070328406070086

A relationship between antimicrobial activities and the formation constants of amino acid-Schiff bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared from DL-amino acids (DL-glycine, DL-alanine)

Full text of DOI:10.1134/S1070328406070086

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2006, Vol. 32, No. 7, pp. 511–517. © Pleiades Publishing, Inc., 2006.
Synthesis, Potentiometric and Antimicrobial Activity Studies
on DL-Amino Acids–Schiff Bases and Their Complexes1
‘N. Saria, P. Gürkana, S. etea, and I. S¸akiyanb,2
C¸
a Department of Chemistry, Faculty of Arts and Science, Gazi University, 06500, Teknikokullar, Ankara, Turkey
b
s
Department of Chemistry, Faculty of Science, Ankara University, 14280, Be ¸evler, Ankara, Turkey
Received July 11, 2005
Abstract—A relationship between antimicrobial activities and the formation constants of amino acid–Schiff
bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared
from DL-amino acids (DL-glycine, DL-alanine) and halo aldehydes (5-chloro-2-hydroxybenzaldehyde,
5-bromo-2-hydroxybenzaldehyde). Schiff bases and their Cu(II) and Ni(II) complexes were characterized by
the elemental analysis, spectral analysis, magnetic moment (at ca. 25°C), molar conductivity, and thermal anal-
ysis data. The complexes were found to have general compositions [ML(H2O)]. The protonation constants of
the Schiff bases and stability constants of the complexes were determined potentiometrically in a dioxane–
water (1 : 1) solution at 25°C and 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and their
complexes were estimated for six bacteria, such as Bacillus cereus RSKK 863, Staphylococcus aureus ATCC
259231, Micrococcus luteus NRLL B-4375, Escherichia coli ATCC 11230, Aeromonas hydrophila 106,
Pseudomonas aeroginosaATCC 29212, and the yeast Candida albicansATCC 10239. The role of halogen sub-
stitution on the ligands, effect of the metal ion, and stabilities of the complexes are discussed on antimicrobial
activities.
DOI: 10.1134/S1070328406070086
INTRODUCTION
plexes, whose structure agrees with the above men-
tioned structural and coordinative patterns for biologi-
cal activity [7–8]. The N- and O-containing ligands and
their complexes have become important due to their
wide biological activity [9], such as anti-HIV activities
[10]. It is known that the existence of metal ions bond-
ed to biologically active materials can enhance their ac-
tivities [11].
In this study, four Schiff bases prepared from
DL-glycine and DL-alanine with 5-chloro and 5-bromo
derivatives of 2-hydroxybenzaldehyde and their Ni(II)
and Cu(II) complexes were synthesized and character-
ized. The relations between the stability concerned with
Schiff bases and their complexes exhibit a wide range
of biological activities and applications as a marker in
the study of biological processes [1–3]: decarboxylation,
transamination, electron transfer, etc. Over the recent de-
cade there has been a growing interest in a correlation
between biological activities and molecule structures
[4]. This has been partially the result of reports concern-
ing with the interaction of various chemicals including
molecules and their some properties [5–6]. These prop-
erties can be of importance to understand biological ac-
tivities on the molecular structure.
In order to contribute to these studies, we have pre- the existence of the halogen in the ligand molecule
pared amino acid–Schiff bases and their metal(II) com- were also investigated.
OH
Cl
Br
CH N CH2 COOH
OH
5-chloro-2-hidroxybenzylidene-DL-glicine, [SalCl-Gly];
5-bromo-2-hidroxybenzylidene-DL-glicine, [SalBr-Gly];
CH N CH2 COOH
1
2
The text was submitted by the authors in English.
E-mail: nursens@gazi.edu.tr
511

512
SARI et al.
OH
5-chloro-2-hidroxybenzylidene-DL-alanin, [SalCl-Ala];
Cl
Br
CH N CH COOH
CH3
OH
CH N CH COOH
CH3
5-bromo-2-hidroxybenzylidene-DL-alanin, [SalBr-Ala].
EXPERIMENTAL
(Escherichia coli ATCC 11230, Aeromonas hydrophi-
la 106, Pseudomonas aeroginosa ATCC 29212), and
Synthesis of ligands. A solution of 5-Cl or 5-Br deriv-
atives of 2-hydroxybenzaldehyde (0.001 mol) in MeOH
(20 ml) was added dropwise to a hot aqueous solution
(10 ml) of the DL-amino acid (0.001 mol), and the mix-
ture was heated under reflux for 2 h. After cooling, the
mixture was filtered, and evaporated under reduced
pressure to produce an oily syrup. This was dissolved
in a dioxin–MeOH (9 : 1, v/v) mixture then stirred mag-
netically for 2 h at 15°C, filtered, and allowed to stand.
A yellow solid formed was collected by filtration,
washed with a small volume of ethanol and dioxane,
and then dried over anhydrous CaCl2. The yields were
78–81%.
Synthesis of complexes. A hot aqueous solution
(25 ml) of DL-amino acid (0.005 mol) was added to
5-Cl or 5-Br derivatives of 2-hydroxybenzaldehyde
(0.005 mol) dissolved in MeOH (25 ml). The solution
was stirred magnetically and heated at 50°C for 3 h.
Metal(II) chloride (0.005 mol) dissolved in MeOH
(10 ml) was added to a solution of the Schiff base. The
mixture was kept for two days at room temperature.
The solid product was filtered, washed with H2O and
Me2CO–H2O (1 : 1) solutions, and dried in vacuo (over
P4O10). The yields were 78–82%.
A dioxane–water (1 : 1) solution was used as solvent
for potentiometric studies. All metal ion solutions were
prepared from their chlorides (analytical grade) and
standardized by the atomic absorption spectroscopic
method. A standard 0.064 M KOH solution (Merck)
was used for titrations. Potassium chloride and concen-
trated HCl (Merck, extrapure grade) were used for the
preparation of 1.0 M KCl and 0.062 M HCl solutions.
An HCl solution was standardized against standard
KOH solutions. Alkali solutions were stored under ni-
trogen atmosphere. The system used for potentiometric
measurements and calculations has been described pre-
viously [12], and pH-meter readings in an aqueous−or-
ganic system were corrected [13, 14].
the yeast (Candida albicans ATCC 10239). The bacte-
rial and yeast cultures were incubated at 37°C for 18 h.
The ligands and the complexes were stored dry at room
temperature and dissolved (250 µg/ml) in DMSO. Mol-
ten nutrient agar (15 ml) kept at ca. 45°C was then
poured in the petri-dishes and allowed to solidify. Then
holes of 6 mm diameter were punched carefully using a
sterile cork borer and these were completely filled with
the test solutions. The plates were incubated for 24 h at
37°C. The mean value obtained for the two holes was
used to calculate the zone of growth inhibition of each
sample.
Carbon, hydrogen, and nitrogen contents were ob-
1
13
tained using a LECO-9320 analyzer. H and C NMR
spectra of the ligands were recorded with a Bruker Spec-
trospin Avance DPX-400 instrument using TMS as in-
ternal standard and CD3OD as solvent. IR spectra in the
4000–400 cm–1 range were measured using KBr discs on
a Mattson 1000 FTIR spectophotometer. Conductivity
measurements were carried out at 20°C in 10–3
M
DMSO using a Siemens WPA CM 35 apparatus. The
TGA curves were performed on a General V4.1C Du
Pont 2000 instrument between 30–500°C at a heating
rate of 10 K min–1 in N2 atmosphere. The room-temper-
ature magnetic moments were measured with MK-1
model Gouy Balance of Christison Scientific Equip-
ment Ltd. Metals were determined with Philips PU
9285 model AAS spectrophotometer.
RESULTS AND DISCUSSION
The molar conductance values of the Schiff bases and
the complexes are found to be 12–31 Ω–1 cm2 mol–1 in
10–3 M DMF solutions. This fact indicates the nonelec-
trolytic nature of the compounds [15].
The Schiff bases are yellow and soluble in metha-
nol, acetone and other polar solvents. However, the
complexes are only soluble in DMF and DMSO. Ana-
lytical, physical electronic, and characteristic IR spec-
tral data of the Schiff bases and complexes are given in
Tables 1 and 2, respectively.
In vitro antibacterial activities of the Schiff bases
and the complexes were studied using the well-diffu-
sion method in the bactericidal and fungicidal testing
screening. The strains chosen were G(+) (Bacilus
cereus RSKK 863, Staphylococcus aureus ATCC
The 1H and 13C NMR data of the Schiff bases and
259231 and Micrococcus luteus NRLL B-4375), G(–) Ni(II) complexes are collected in Tables 3 and 4, re-
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SYNTHESIS, POTENTIOMETRIC AND ANTIMICROBIAL ACTIVITY
Table 1. Analytical and physical data of the compounds
513
Empirical formu-
Contents (found/calcd), %
Λ,
Compound
[SalCl-Gly]
la (decomp.
Color (µB)
Ω–1cm–1 cm2
C
H
N
M
temp., °C)
C9H8NO3Cl
(130–131)
C10H10NO3Cl
[95–97]
C9H8NO3Br
[79–81]
Yellow
50.46/50.59 3.58/3.75
53.47/47.47 3.93/4.40
41.59/41.86 3.67/3.10
44.34/44.11 3.34/3.68
36.49/36.86 2.70/2.73
39.56/39.09 2.67/2.61
6.56/6.56
[SalCl-Ala]
[SalBr-Gly]
[SalBr-Ala]
6.51/6.15
5.03/5.43
5.18/5.15
Yellow
Yellow
Yellow
C10H10NO3Br
[84–86]
[Cu(SalCl-Gly)H2O] C9H8NO4ClCu
4.73/4.78 21.45*/21.67
4.67/4.56 21.07/20.68
26
12
Light green
(1.80)
> 225*
[Cu(SalCl-Ala)H2O] C10H10NO4ClCu
> 225*
Light green
(1.81)
[Cu(SalBr-Gly)H2O] C9H8NO4BrCu
31.26/32.00 2.32/2.37
33.38/34.14 2.78/2.84
37.09/37.47 2.74/2.76
39.30/39.71 2.92/3.31
31.70/32.46 2.35/2.40
33.83/34.61 2.82/2.88
4.05/4.15 18.38/18.81
3.89/3.98 17.66/18.07
4.81/4.86 20.08/22.03
4.58/4.63 19.77/21.01
4.11/4.21 17.23/17.64
3.95/4.04 16.58/18.32
31
18
21
17
24
12
Light green
(1.84)
> 225*
[Cu(SalBr-Ala)H2O] C10H10NO4BrCu
Light green
(1.82)
> 225*
[Ni(SalCl-Gly)H2O] C9H8NO4ClNi
Green
diamagnetic
> 225*
[Ni(SalCl-Ala)H2O] C10H10NO4ClNi
Green
diamagnetic
> 225*
[Ni(SalBr-Gly)H2O] C9H8NO4BrNi
Green
diamagnetic
> 225*
[Ni(SalBr-Ala)H2O] C10H10NO4BrNi
Green
diamagnetic
> 225*
* M.p.
spectively. In general, the multiplets observed at
In the IR spectra of the Schiff bases, the strong ab-
6.55–7.54 ppm and the singlets at 7.14–8.40 ppm are as- sorptions at 1516–1518 and 1425–1428 cm–1 are attrib-
signed to ring protons, and imine protons, respectively. uted to the asymmetric and symmetric ν(COO) bands
The imine proton signal showed a downfield shift of about [16]. The imine stretching bands were observed in the
0.75 ppm in the Ni(II) complexes [16]. Methyl protons of 1653–1656 cm–1 range. The observation of bands at
alanine residues were observed at 1.56 and 1.44 ppm for 3081–3086, 2920–2928, and 2889–2897 cm–1 can be
the ligands and 1.52 ppm for the Ni(II) complexes (posi- attributed to the νarom and νalif stretching vibrations [16].
tion 11). In the 1H NMR spectra of the Schiff bases, the The bands in the 3416–3429 cm–1 region in the spectra
peaks at 10.12–11.06 and 12.03–12.73 ppm are protons of the Schiff bases are ascribed to ν(OH) vibrations,
attributed to the phenolic OH and COOH protons [16], re- which can be due to the hydroxyl of carboxyl group. The
spectively. The absence of these two peaks in the spectra characteristic vibrations of the free ligand were shifted
of the Ni(II) complexes favor the loss of OH protons due upon complex formation. A shift to a lower frequency,
to complexation.
relative to the free Shiff bases, of about 29–25 cm–1 for
the –CH=N– stretching vibration in the complexes
showed that coordination occurs through the nitrogen at-
oms of the azomethine groups. The IR spectra of the com-
plexes showed a strong band in the regions 1448–1487
and 1389–1394 cm–1, which can be attributed to the car-
boxyl group [17].
More detailed information about the structure, of
the ligands and their Ni(II) complexes were provided
by the 13C NMR spectral data. Aromatic, imine, and
carboxyl C atoms are observed at 108.97–165.06,
158.40–165.06, and 174.93–168.54 ppm, respectively.
In the C2, C4, and C10 carbon atoms of the free Schiff
bases, a significant shift after complexation was shown.
This bands shifted to lower frequency values upon
This shift appears due to the coordination of the ligand complexation indicating that the azomethine nitrogen
to the metal atom by the azomethine nitrogen, phenolic and the oxygen atom of the carboxylate group are coor-
oxygen and carboxyl oxygen.
dinated to the metal ion [18, 19]. The IR spectra of the
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514
SARI et al.
Table 2. Major IR absorption bands and electronic spectral data (nm) (εmax, mol–1 l–1 cm–1) of the compounds
IR spectrum, cm–1
ν(COO–1)
Electronic absorption spectrum
max(ε)
Compound
ν(CH)arom
ν(OH) ν(CH = N)
ν(M–O) ν(M–N)
λ
ν(CH)alif
(asym) (sym)
[SalCl-Gly]
3429* 1656
1518 1428
3085
2928, 2892
215 (2.3 × 104), 237 (6.4 × 103)
216 (1.7 × 104), 238 (6.3 × 103)
213 (1.5 × 104), 236 (6.4 × 103)
214 (1.2 × 104), 237 (6.3 × 103)
[SalCl-Ala]
[SalBr-Gly]
[SalBr-Ala]
3420* 1657
3416* 1653
3418* 1653
1516 1425
1517 1426
1516 1428
1487 1391
1462 1393
1448 1390
1491 1394
1483 1391
1462 1389
1456 1392
1469 1393
3089
2924, 2897
3081
2920, 2889
3086
2920, 2889
532 462
535 464
517 464
523 461
538 464
531 468
547 461
542 460
[Cu(SalCl-Gly)H2O] 3467
[Cu(SalCl-Ala)H2O] 3471
[Cu(SalBr-Gly)H2O] 3471
[Cu(SalBr-Ala)H2O] 3479
[Ni(SalCl-Gly)H2O] 3459
[Ni(SalCl-Ala)H2O] 3467
[Ni(SalBr-Gly)H2O] 3477
[Ni(SalBr-Ala)H2O] 3482
1634
1638
1632
1628
1636
1631
1629
1630
3087
2926, 2894
216 (1.2 × 104), 238 (6.31 × 103)
370 (106), 699 (82)
216 (2.2 × 104), 237 (5.31 × 103)
370 (706), 696 (71)
216 (2.8 × 104), 247(5.21 × 103)
378 (306), 697 (34)
216 (2.8 × 104), 247 (5.21 × 103)
380 (310), 698 (52)
3086
2923, 2892
3085
2925, 2890
3087
2924, 2890
3083
2926, 2893
216 (1.2 × 104), 238 (6.31 × 103),
362(106)
3085
2924, 2890
212 (2.1 × 104), 244 (5.32 × 103),
383(306)
3086
2928, 2888
216 (1.5 × 104), 238 (6.31 × 103),
371(136)
3085
362(113)
2927, 2891
216 (1.2 × 104), 238 (6.31 × 103),
362(113)
*OH due to COOH.
Cu(II) and Ni(II) complexes exhibit characteristic bands
of coordinated water at ca. 3400, 880, and 770 cm–1 as-
signed as ν(OH), ρr(OH), and ρw(OH2), vibrations, re-
spectively [19]. The appearance of new bands in the
517–547 and 460–468 cm–1 regions are due to ν(M–O)
and ν(M–N), respectively [20]. Furthermore, the ap-
pearance of new two bands at ca. 430, 421, and 308 cm–1
regions are due to δ(M–C–N) for D4h Ni(II) and Cu(II)
complexes, respectively [17]. In addition, the Schiff
bases exhibit sharp bands at ca. 690, 650 and 607,
770 cm–1 due to ρw(COO–) and δ(COO–) stretching vi-
brations in the carboxyl group of amino acid, respec-
tively. The bands appear in somewhat lower regions
than those for the free ligands due to coordination of the
amino acid group with the metal ion [20, 21]. The struc-
ture of the Ni(II) complexes is the following:
9
OH
M
2
5
O
O
C
6
4
M: Ni;
7
N
O
X: Cl, Br;
C1H
11Y
3
2
10
X
8
C
H
Y: H, CH .
3
On the basis of the IR spectral results, it can be de-
duced that the anion of the amino acid Schiff base is co-
ordinated to the metal ion as a binegative tridentate
ligand where the five-membered chelated ring is
formed.
The electronic spectra of the Schiff bases in MeOH
show two bands at 213–216 and 236–238 nm assign-
able to the σ–σ* and π–π* transitions of the imine
group. The electronic spectra of the Cu(II) complexes
show two d–d bands at ca. 710 and 375 nm, respective-
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SYNTHESIS, POTENTIOMETRIC AND ANTIMICROBIAL ACTIVITY
Table 3. H and 13C NMR chemical shifts (ppm) of the Shiff bases
Compound
515
1
Position
[SalCl-Gly]
1H
[SalCl-Ala]
1H
[SalBr-Gly]
1H
[SalBr-Ala]
1H 13C
13C
13C
13C
1
2
3.97 (s.), 2 H
8.21 (s.), 1 H
60.30
167.08
133.68
165.06
131.56
121.95
119.04
118.76
3.57 (q.), 3 H
7.96 (t.), 1 H
54.78
158.87
132.27
164.82
129.45
127.73
124.48
121.56
3.87 (s.), 2 H
8.40 (s.), 1 H
60.00
165.10
133.05
158.40
131.60
122.57
119.47
108.97
3.31 (q.), 3 H
8.05 (s.), 1 H
48.57
162.23
131.67
162.46
124.32
123.52
121.03
125.08
3
4
5
6.72 (d.), 1 H
7.24 (d.), 1 H
6.67 (d.), 1 H
7.24 (d.), 1 H
6.77 (s.), 1 H
7.20 (s.), 1 H
6.61 (d.), 1 H
7.21 (d.), 1 H
6
7
8
7.38 (d.), 1 H
10.12 (s.), H
12.46 (s.), H
7.42 (s.), 1 H
7.41 (s.), 1 H
10.87 (s.), 1 H
7.54 (s.), 1 H
11.06 (s.), 1 H
9
10.31
10
11
170.34 12.03 (s.), 1 H
1.56 (d.), 1 H
168.54 12.32 (s.), 1 H
174.93 12.73 (s.), 1 H
1.44 (d.), 1 H
172.12
21.14
23.41
OH9
OH9
5
5
6
7
6
7
4
4
1
1
3
3
X
CH N CH2 COOH
X
CH N CH COOH
8
8
10
2
2
CH3
11
X: Cl, Br
ly, the positions of which are consistent with the ly. Figure in Table 3 shows the potentiometric titration
square-planar environment [22]. The observed high
magnetic moment values of the Cu(II) complexes indi-
cate that these complexes have the square-planar geom-
etry. The Ni(II) complexes show the low-intensity
bands in a range of 360–370 nm consistent with the
square-planar structure [22]. The magnetic behavior of
the Ni(II) complexes is also in accord with the proposed
structure [23].
The TGA curves of the copper(II) and nickel(II)
complexes are similar in the 130–450°C temperature
range; the weight loss is equivalent to the degradation
of the complexes. For all the complexes, the first
weight loss (ca. 5–6%) in the 110–135°C range can be
accounted for in terms of the loss of coordinated water
[24]. The residues at the end of the decomposition for
all of the complexes were found to be NiO/CuO.
curves of [SalCl-Gly] and its Cu(II) and Ni(II) com-
plexes. Methyl groups of [SalCl-Ala] and [SalBr-Ala]
Schiff bases are capable of releasing electrons, and the
1
Table 4. H and 13C NMR chemical shifts (ppm) of the nick-
el(II) complexes
Compound
Position [Ni(SalCl-Gly)H2O]
1H 13C
3.94 (s.), 2 H 60.04 3.56 (q.), 2 H
[Ni(SalCl-Ala)H2O]
1H
13C
1
2
54.4
7.38 (s.), 1 H 148.91 7.14 (t.), 1 H 150.87
3
128.21
142.86
132.27
164.82
It is evident from the above spectroscopic, analyti-
cal, and the other data that the Schiff bases behave as
binegative tridentate ligands, and coordinating sites are
the Ar–O, C=N, and COO groups. The other coordina-
tion sites in the complexes are occupied by H2O (see
the figure in Table 3).
4
5
6.55 (d.), 1 H 126.12 6.58 (d.), 1 H 129.41
6.85 (d.), 1 H 122.08 7.18 (d.), 1 H 127.73
6
7
118.98
124.08
The constants of the ligands and complexes are giv-
en in Table 5. The Schiff bases have three protonation
constants as expected. The first constant refers to the
protonation of the phenolate anion. The second and
third constants correspond to the protonation of the
imine nitrogen atom and carboxylate anion, respective-
8
7.24 (d.), 1 H 116.49 7.41 (s.), 1 H 120.56
9
10
11
12.46 (s.), 1 H 156.36
155.54
54.78
1.52 (d.), 3 H
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 7 2006

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SARI et al.
Table 5. Protonation constants of the Schiff bases (logK1,logK2 andlogK3) and stability constants of the complexes (logKML
)
at 25 0.1°C, µ = 0.1 M KCl, and biological activity (zone of inhibition, mm)
logK1, logK2, and
Compound
logKML
logK3
[SalCl-Gly]
[SalCl-Ala]
[SalBr-Gly]
[SalBr-Ala]
1.86 0.02, 7.58 0.02,
9.60 0.03
2.20 0.03, 7.76 0.03,
9.69 0.01
1.97 0.04, 7.85 0.04,
10.74 0.04
2.22 0.02, 8.09 0.01,
10.25 0.01
–
–
–
–
[Cu(SalCl-Gly)H2O]
[Cu(SalCl-Ala)H2O]
[Cu(SalBr-Gly)H2O]
[Cu(SalBr-Ala)H2O]
[Ni(SalCl-Gly)H2O]
[Ni(SalCl-Ala)H2O]
[Ni(SalBr-Gly)H2O]
[Ni(SalBr-Ala)H2O]
10.72 0.03
10.53 0.03
11.48 0.03
11.98 0.03
9.41 0.03
9.88 0.02
9.78 0.02
10.71 0.03
8
10
10
10
6
12
19
22
7
9
8
10
14
6
11
8
8
8
4
6
8
6
5
8
8
6
8
8
13
14
6
14
11
10
13
11
16
14
9
9
8
8
12
8
19
20
17
18
21
19
22
35
8
12
14
14
electron densities of the carboxylate anion and imine of these complexes. The lipophilicity of complexes in-
nitrogen increase. Therefore, the second and third pro- creases due to the delocalization of π-electrons in the
chelate ring with an increase in the stability constants.
In some cases, an increased lipophilicity leads to a
breakdown of the permeability barrier of the cell [26].
The stability constants of the [Ni(SalBr-Gly)H2O] and
[Ni(SalBr-Ala)H2O] complexes are higher than those
of [Ni(SalCl-Gly)H2O] and [Ni(SalCl-Ala)H2O].
tonation constants of these ligands are higher than for
their Gly derivatives. The first protonation constants of
the chlorine-substituted Schiff bases are lower than
those of the bromine-substituted ones. It can be attrib-
uted to the higher-inductive electron-withdrawing ef-
fect of chlorine. The stability constants of the complex-
es with the ligands containing the alanine residue are
higher than those of the glycine derivatives. In addi-
The antifungal activity against C. albicans of all the
complexes is higher than their anitibacterial activities
against all the bacteria tested. Compared with our previ-
tion, the logK values of the bromine-substituted com-
plexes are higher than the others. This is an expected ous work, all of the presented complexes show 4–6-fold
result, because more stable complexes are formed with higher activities than the former. This result can be due
to the higher stability constants of the present complex-
es than the former [12].
stronger bases. The order of the stability constants for
the same ligand with different metal ions are found to
be Ni(II)≤Cu(II), which is confirmed by the Irving–
Williams order for bivalent ions [25].
In general, the activity of the complexes depended
on the chain length of the amino acid–Schiff bases
ligand. For example, the [Cu(SalCl-Ala)H2O] complex
is more active than the [Cu(SalCl-Gly)H2O] complex
due to the chain length. Similar results have previously
been reported for other works [26, 27].
The results of antimicrobial activity tests of the
newly prepared compounds summarized in Table 5
could be determined due to the solubility (DMSO) of
the compounds in the testing medium. The antimicrobi-
al activity assessment revealed that the amino acid–
Schiff bases possess no activity. The Ni(II) complexes
are found to be more biologically active than the Cu(II)
complexes, except for [Ni(SalCl-Ala)H2O] and
[Ni(SalBr-Ala)H2O] against S. aureus and M. luteus.
The biological activity increases due to the fairly
easy attachment of substrates to the metal ion center in
the square-planar complexes [28]. The molecular struc-
ture determined herein suggests that the Ni(II) com-
plexes (D4h) showed more antibacterial activities than
On the contrary, the stability constants of the Ni(II) the Cu(II) complexes (D4h). That is why activity of
complexes are lower than those of the Cu(II) complex- Ni(II) complexes is higher than that of the Cu(II) com-
es. The bromine-substituted complexes of the Ni2+ ion plexes, perhaps, because the oxygen atoms in the phe-
are generally more active than their chlorine-contain- nol and carboxyl group have high polarity in weak
ing analogs. This result is in accord with the stabilities complexes [28, 29].
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SYNTHESIS, POTENTIOMETRIC AND ANTIMICROBIAL ACTIVITY
517
14. Martell, A.E. and Moteakits, R., Determination and Use
of the Stability Constants, New York: VCH Publishers,
1988.
15. Geary, W.S., Coord. Chem. Rev., 1971, vol. 7, no. 1,
p. 81.
ACKNOWLEDGMENTS
The authors are grateful to the Research Foundation
(F.E.F. 05/2002-59) of Gazi University for supporting
this study.
16. Silverstein, R.M., Bassler, G.C., and Morrill, T.C., Spec-
trophotometric Identification of Organic Compounds,
New York: J. Wiley & Sons, 1981.
17. Nakamoto, K., Infrared and Raman Spectra of Inorganic
and Coordination Compounds, New York: J. Wiley &
Sons, 1986.
18. Ibrahim, G., Chebli, E., Kahan, M.A., and Bouet, G.M.,
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19. Ki-Yung Choi, Yong-Man Jeon, Haiil Ryu, et al., Poly-
hedron, 2004, vol. 23, no. 6, p. 903.
20. El-Sayed, B.A., Abo-Aly, M.M., and Attia, G.M., Synt.
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