Synthesis, characterization, and prohibitive action on free radical O 2 -? Of β-phenylalanine schiff base binuclear complexes

Article abstract of DOI:10.1134/S1070328408100114

A new Schiff base ligand as salt (KL) was synthesized using potassium salt of DL-β-phenylalanine and 2-hydroxy-1-naphthaldehyde. Two binuclear complexes of this ligand, [M₂L₂(CH₃COO) ₂] (M = Cu(II), Ni(II)) have been synthesized and characterized by elemental analyses, IR, UV spectra, and molar conductance. Their prohibitive action on the superoxide anion free radical (O ₂ ^-? ) was estimated by the NBT illumination deoxidizing method (Methionine- lactoflavin illumination method). The results suggested that the ligand and its complexes had the prohibitive action on O ₂ ^-? .

Full text of DOI:10.1134/S1070328408100114

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2008, Vol. 34, No. 10, pp. 772–774. © Pleiades Publishing, Ltd., 2008.
Synthesis, Characterization, and Prohibitive Action on Free
Radical O–2• of b-Phenylalanine Schiff Base Binuclear Complexes1
Y. H. Fana, S. Y. Bib, Y. Y. Lia, C. F. Bia, and S. T. Xiea
aCollege of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China
bCollege of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China
E-mail: fyh1959@163.com; fanyh@ouc.edu.cn
Received August 2, 2007
Abstract—A new Schiff base ligand as salt (KL) was synthesized using potassium salt of DL-β-phenylalanine
and 2-hydroxy-1-naphthaldehyde. Two binuclear complexes of this ligand, [M2L2(CH3COO)2] (M = Cu(II),
Ni(II)) have been synthesized and characterized by elemental analyses, IR, UV spectra, and molar conductance.
Their prohibitive action on the superoxide anion free radical (O–2• ) was estimated by the NBT illumination
deoxidizing method (Methionine-lactoflavin illumination method). The results suggested that the ligand and its
complexes had the prohibitive action on O–2•.
DOI: 10.1134/S1070328408100114
INTRODUCTION
(0.826 g, 5.0 mmol) dissolved in 10 ml of ethanol. The
reaction proceeded for 1 h at 40°C, and then the reac-
tion mixture was filtered. 2-Hydroxy-1-naphthalde-
hyde (0.861 g, 5.0 mmol) dissolved in 15 ml of ethanol
was added dropwise to the above filtered solution and
the mixture stirred for 6 h at 50–55°C to give a precip-
itate. The light yellow precipitate was collected by fil-
tration, washed with ethanol, and dried in vacuum. The
yield was 1.40 g (78%).
Some Schiff base complexes derived from amino
acids are particularly active in biology. Recently, stud-
ies of some metal complexes with α-amino acid Schiff
bases have been reported [1–5]. To continue the inves-
tigation in this area, a new Schiff base ligand as salt
(KL) was synthesized using potassium salt of
DL-β-phenylalanine and 2-hydroxy-1-naphthaldehyde,
and two binuclear complexes [M2L2(CH3COO)2] (M =
Cu(II) (I), Ni(II) (II); HL—β-phenylalanine-2-
hydroxy-1-naphthaldehyde Schiff base) were synthe-
sized in 95% ethanol. The prohibitive action on the
For C20H16NO3K (M = 357.4)
anal. calcd, %: C, 67.20;
Found, %: C, 67.03;
H, 4.51;
H, 4.41;
N, 3.92.
N, 3.85.
superoxide anion free radical (O–2• ) of the ligand and its
complexes was also studied.
The synthesis reactions of the KL are shown below:
EXPERIMENTAL
NH2
NH2
All reagents used in this work were of analytical
grade or biological grade.
Preparation of potassium salt of the ligand. Po-
tassium hydroxide (0.281 g, 5.0 mmol) was dissolved
in 20 ml ethanol and mixed with DL-β-phenylalanine
COOH
+ KOH
COOK
COOK
CHO
NH2
HO
COOK
N
+
HO
1
The text was submitted by the authors in English.
772

SYNTHESIS, CHARACTERIZATION, AND PROHIBITIVE ACTION
UV spectra for the ligand and complexes
773
ε1 × 10–4,
ε2 × 10–4,
ε3 × 10–4,
Compound
λmax1, nm
λmax2, nm
λmax3, nm
mol–1 l cm–1
mol–1 l cm–1
mol–1 l cm–1
KL
255
255
258
6.16
10.5
12.9
308
318
1.15
1.82
[Cu2L2(CH3COO)2]
[Ni2L2(CH3COO)2]
388
413
1.44
1.78
Preparation of the complexes I and II. The potas- of the ligand occurs at 1210.5 cm–1. The shift of the
sium salt of the Schiff base ligand (1.07 g, 3.0 mmol) band to a higher frequency by about 34 cm–1 in the
dissolved in 30 ml of 95% ethanol was mixed with met- metal complexes indicates the coordination of hydroxyl
al acetate (3.0 mmol) dissolved in 10 ml of anhydrous oxygen to the metal ion. The shifts of νas(COO–) and
ethanol, and the mixture stirred for 12 h at 65°C to give νs(COO–) from 1636.4 and 1451.0 cm–1 in the ligand to
precipitates, which were cooled and filtered off. The 1644.6 and 1434.4, 1633.5 and 1442.8 cm–1 in the Cu(I)
precipitates were collected, washed with ethanol, and and Ni(II) complexes, respectively, suggest the coordina-
dried in vacuo. The purity of the complexes was higher tion of the oxygen in the carboxylate group to the metal
than 99%.
ions. The value of νas(COO–) – νs(COO–)] > 180 cm–1
indicates that the –COO– group in the ligand is coordi-
nated to the metal ions by the monodentate mode [7, 8].
The bands at about 1574 and 1434 cm–1 are assigned to
the coordinated –COO– group by the bridged mode [8].
The spectra of the Cu(II) and Ni(II) complexes exhibit
a broad band at 3411.6 and 3420.4 cm–1, respectively,
which are attributed to ν(O−H) of phenol.
For C44H38N2O10Cu2 (I) (M = 881.9)
anal. calcd, %: C, 59.93; H, 4.34; N, 3.18; Cu, 14.41.
Found, (%):
C, 59.39; H, 4.14; N, 3.21; Cu, 14.36.
For C44H38N2O10Ni2 (II) (M = 872.1)
anal. calcd, %: C, 60.59; H, 4.39; N, 3.21; Ni, 13.46.
Found, %:
C, 60.23; H, 4.52; N, 3.35; Ni, 13.57.
The spectral data are shown in the table. The elec-
tronic spectra of the Cu(II), Ni(II) complexes in DMSO
exhibit three bands (at 255, 318, and 388 nm) and two
bands(at 258 and 413 nm), respectively. Two bands
occur at 255 and 308 nm in the spectrum of the ligand.
Compared with the electronic spectrum of the ligand,
there are some changes in the numbers of wave and the
molar extinction coefficients, which further indicates
the formation of the complexes.
The synthesis reaction of the complexes may be rep-
resented in the following way:
2M(CH3COO)2 · nH2O + 2KL
[M2 L2(CH3COO)2] + 2CH3COOK + 2nH2O.
Physical measurement of the complexes I and
II. Elemental analyses were carried out with a model
240C Perkin Elmer analyzer. The metal content was
determined by gravimetry. The UV spectra were
The prohibitive action on the superoxide anion free
radical (O–2• ) of the Schiff base ligand and its com-
recorded on a TU-1901 spectrophotometer in plexes was studied by the NBT illumination deoxidiz-
DMSO. The molar conductance was measured with ing method (Methionine-lactoflavin illumination
a Shanghai DDSJ-308A conductivity meter. IR spec- method) [9]. The phosphate buffer solutions (pH 7.8)
containing 3.3 × 10–6 mol l–1 lactoflavin, 0.01 mol l–1
tra of the ligand and complexes were recorded in
DL-methionine, 4.6 × 10–5 mol l–1 NBT, and 0–10 mg l–1
KBr pellets using a AVATAR 360 FT-IR spectropho-
tometer. Visible spectra were measured with a
723 spectrophotometer.
of the ligand or complexes were made up. This solution
was kept at a constant temperature (30 0.2°C) for
10 min and illuminated with a 72-W daylight lamp with
invariable intension. Its absorbance was measured with
a 723 spectrophotometer at 560 nm per 1 min. The
inhibitive percent of compounds (b, %) at some con-
centration was calculated by the formula:
RESULTS AND DISCUSSION
The molar conductance values of Cu(II) and Ni(II)
complexes are 14.3 and 1.41 Ohm–1 cm2 mol–1, respec-
tively, indicating their nonelectrolytic nature [6]. This
suggests that two acetate ions are within the coordina-
tion sphere. The complexes are stable in air and insolu-
ble in water and ethanol; however, they are soluble in when the concentrations of the ligand or complexes
DMF and DMSO.
β (%) = [(∆A/∆t)0 – (∆A/∆t)m]/(∆A/∆t)0 × 100%,
where (∆A/∆t)0 is the variety of absorbance in unit time
were zero, (∆A/∆t)m is the variety of absorbance in unit
time when the concentrations of the ligand or com-
plexes were measured.
The shift of the band with ν(C=N) from 1636.4 cm−1
in the ligand to 1644.6 and 1633.5 cm–1 in the Cu(II)
and Ni(II) complexes, respectively, suggests the forma-
As seen from the figure, the Schiff base and com-
tion of a C=N–M bond system. The vibration ν(Ar–O) plexes have a certain inhibitive effect to the free radical
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 34 No. 10 2008

774
FAN et al.
Inhibition rate
80
2
60
40
20
0
3
1
2
4
6
8
10
12
Concentration, mg/l
Percent curve of the complex and Schiff base inhibition to the free radical O–•: (1) Schiff base KL, (2) [Cu L (CH COO) ], and
2
2
3
2
2
(3) [Ni L (CH COO) ].
2
2
3
2
O–2•. The inhibitive rate of the complexes was higher its complexes to the free radical O–2• is to be studied in
the future.
than that of the Schiff base ligand in summary. The
inhibitive rate of the ligand increases with the concen-
tration increasing. The inhibitive rate of the
[Cu2L2(Ac)2] complex reduces with the concentration
increasing; however, the inhibitive percent of the
[Ni2L2(Ac)2] complex has a nadir at a concentration of
8 mg/l and is lower than that of the ligand at this con-
Thus, the results presented here clearly indicate that
copper acetate and nickel acetate can form stable solid
binuclear complexes with Schiff base DL-β-phenylala-
nine-2-hydroxy-1-naphthaldehyde. The compositions
of the complexes are confirmed to be
[M2L2(CH3COO)2] (M = Cu(II), Ni(II)). The structures
centration. The inhibitive mechanism of the ligand and proposed for the complexes I and II are shown below:
O
CH3
C
O
CH2 CH
N
CH CH2
N
O
O
O
O
O
CH
CH
M
M
O
O
H
O
H
C
CH3
M = Cu, Ni.
4. Singh, N.K. and Misseema Agrawal, R.C., Synth. React.
Inorg. Met.-Org. Chem., 1985, vol. 15, p. 75.
The ligand and its two complexes have prohibitive
action on superoxide anion free radical O–2•.
5. Fan, Y.H., Bi, C.F., and Li, J.Y., Chin. J. Appl. Chem.,
2003, vol. 20, p. 262.
6. Geary, W.J., Coord. Chem. Rev., 1971, vol. 7, no. 1,
REFERENCES
p. 81.
7. Xu, Q.L., Sun, L.J., Li, H., et al., Appl. Organomet.
Chem., 1994, vol. 8, p. 57.
1. Fan, Y.H., Bi, C.F., and Li, J.Y., Synth. React. Inorg.
Met.-Org. Chem., 2003, vol. 33, p. 137.
8. Kazuo, N. and Wang, Q.R., Infrared and Raman Spectra
of Inorganic and Coordination Compounds, Beijing:
Chemical Industry, 1988, vol. 10, p. 235.
2. Si, W.L., Chen, D.Y., Chen, S.M., and Yan, X.M., Chin.
J. Inorg. Chem., 2001, vol. 17, p. 239.
3. Liu, D.J., Fan, Y.H., and Bi, C.F., Chin. J. Nucl. Radio-
chem., 2003, vol. 25, p. 210.
9. Wang, J.H., Lei, W., and Wang, Y.L., Chin. J. Synth.
Chem., 2002, vol. 10, p. 314.
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