Manganese(III) complexes of some amino acid (L-serine, L-methionine, L-cystein) Schiff bases derived from 2-hydroxy-1-naphthaldehyde

Article abstract of DOI:10.1081/SIM-120021931

A new series of manganese(III) complexes of amino acid Schiff bases synthesized from 2-hydroxy-1-naphthaldehyde and L-serine, L-methionine and L-cystein. The structure of their metal complexes was investigated by elemental analyses, IR, TGA, magnetic susceptibility, and mass spectra. The structure of the N-naphthylidene amino acid Schiff bases were determined by IR, UV, ¹H NMR and mass spectra for a comparison with those of the complexes.

Full text of DOI:10.1081/SIM-120021931

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Manganese(III) Complexes of Some Amino Acid
(L‐Serine, L‐Methionine, L‐Cystein) Schiff Bases
Derived From 2‐Hydroxy‐1‐Naphthaldehyde
ıffet Şakıyan a & Hamza Yılmaz a
a Ankara University, Science Faculty, Department of Chemistry, 06100, Ankara, Turkey
Published online: 15 Feb 2007.
To cite this article: ffet akyan & Hamza Ylmaz (2003) Manganese(III) Complexes of Some Amino Acid (L‐Serine, L‐Methionine,
L‐Cystein) Schiff Bases Derived From 2‐Hydroxy‐1‐Naphthaldehyde, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 33:6, 971-983
To link to this article: http://dx.doi.org/10.1081/SIM-120021931
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 6, pp. 971–983, 2003
Manganese(III) Complexes of Some Amino Acid
(L-Serine, L-Methionine, L-Cystein) Schiff Bases
Derived from 2-Hydroxy-1-naphthaldehyde
*
˙
Iffet S¸akıyan and Hamza Yılmaz
Ankara University, Science Faculty, Department of Chemistry,
Ankara, Turkey
ABSTRACT
A new series of manganese(III) complexes of amino acid Schiff bases
synthesized from 2-hydroxy-1-naphthaldehyde and L-serine, L-methio-
nine and L-cystein. The structure of their metal complexes was
investigated by elemental analyses, IR, TGA, magnetic susceptibility,
and mass spectra. The structure of the N-naphthylidene amino acid
Schiff bases were determined by IR, UV, 1H NMR and mass spectra for a
comparison with those of the complexes.
Key Words: Manganese complexes; Schiff bases of amino acids;
Hydroxynaphthaldehyde.
*
˙
Correspondence: Iffet S¸akıyan, Ankara University, Science Faculty, Department of
Chemistry, 06100, Ankara, Turkey; E-mail: sakiyan@science.ankara.edu.tr.
971
DOI: 10.1081/SIM-120021931
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

972
S¸akıyan and Yılmaz
INTRODUCTION
Manganese is an essential element in many biological processes where
manganese-containing enzymes exhibit two distinguished functions as
Lewis acids and redox catalysts. On account of the strong affinity of
manganese ion to oxygen atom coupled with its redox process manganese
containing enzymes catalyze the oxidation of water in photosystem II (PS
II) and disproportination of the superoxide ion and hydrogen peroxide.[1–9]
A multinuclear manganese center is known to play an integral role in the
water-oxidizing complex of photosystem II. This manganese center is
capable of cycling between five oxidation levels (S0–S4) during the
catalytic water oxidation cycle.[10] The Sn states contain manganese ions in
various combinations of oxidation states, including Mn(II), Mn(III) and
Mn(IV) and ligation is provided by O and N atoms from amino acid
moieties. It was, therefore, of interest to determine some of the chemical
properties of the manganese ion in the presence of natural compounds
which are known to be acted upon by enzymes activated by small amounts
of this metal. Many of the proposed models containing simple nitrogen
donor and acetate ligands have been employed as alternatives for the amino
acid side groups in proteins. Manganese(III) Schiff base complexes also
provide a rich series of structural types that can be used as models for the
magnetic and structural properties of mangano enzymes.[11–14]
In this paper we report on the preparation and characterization of new
manganese(III) complexes of Schiff bases derived from 2-hydroxy-1-
naphthaldehyde and L-serine, L-methionine and L-cysteine (Figure. 1). The
structures of the new complexes were characterized by elemental analyses,
Figure 1. Tautomeric forms of amino acid Schiff bases.

Manganese(III) Complexes
973
IR, TGA, magnetic susceptibilities and mass spectra. The Schiff bases were
1
also synthesized and their structures investigated by elemental analyses, H
NMR, IR, UV, mass spectra and compared with those of the complexes.
RESULTS AND DISCUSSION
Synthesis of Schiff Bases and Their
Manganese(III) Complexes
New manganese(III) complexes of amino acid Schiff bases were syn-
thesized in this work. The Schiff bases of L-serine, L-methionine and L-
cysteine with 2-hydroxy-1-naphthaldehyde were also obtained [Eq. 1]. In this
work we used a method for the synthesis of the Schiff bases which is different
from that in our previous work.[15] While using NaOH in previous work we
didn’t use it here and observed that the Schiff bases are more stable than other
Schiff bases described in previous work. Manganese(III) complexes were
synthesized by the template method [Eq. 2]. In addition to 1:2 complexes
Na[MnL2]ꢀxH2O, we obtained also 1:1 [MnL] complexes in the same media.
Spectroscopic analyses showed that in the 1:2 complexes carboxylate, the
nitrogen of imine and oxygen of the hydroxy naphtylidene group of the the
Schiff bases coordinate to manganese(III) ion as a tridentate ligand. But in the
cysteine Schiff base complex SH also coordinates to Mn(III) ion as fourth
donor group. Thus, it preferred to give 1:1 complexes. Both serine and
methionine Schiff bases form 1:2 and 1:1 complexes. Although the 1:2
complexes are soluble in methanol, the 1:1 complexes are not. Therefore, we
washed them with methanol a few times. For this reason only the structure of
the 1:2 complexes are discussed in more detail.

974
S¸akıyan and Yılmaz

Manganese(III) Complexes
Table 2. Significant IR bands of the manganese(III) complexes.
975
1:2 Complexes
v(OH)
v(C=N) v(COO) v(C=C) v(COO)
Na[Mn(L1)2]ꢀ3H2O
Na[Mn(L2)2]ꢀ3H2O
Na[Mn(L3)2]ꢀ6H2O
1:1 Complexes
3381 s 1620 vs
3402 s 1617 vs
3364 s 1618 vs
1572 sh
1579 sh
1580 sh
1537 s
1537 s
1458 s
1392 m
1389 m
1389 m
[Mn(L1)(OOCCH3)]ꢀ2H2O
3387 s 1617 vs
[Mn(L2)(OOCCH3)]ꢀ0.5H2O 3405 s 1620 vs
1571 sh
1573 sh
1537 sh
1540 s
1541 s
1537 s
1388 m
1395 m
1389 m
[Mn(L3)]ꢀ2.5H2O
3348 s 1613 vs
Elemental Analyses
The general characteristic properties of the manganese(III) complexes
and the Schiff bases are shown in Tables 1.
The elemental analysis results agree with the calculated values
showing that the manganese(III) complexes have 1:2 and 1:1 metal/ligand
ratios. While the 1:2 complexes exist as Na salts, the 1:1 complexes do
not. All of the Schiff bases are yellow crystalline solids which appear to
be stable in air for a long time. The complexes are brown and are not
stable in air.
Magnetic Susceptibility
The molar magnetic moments of the complexes are presented in
Table 1. The magnetic susceptibility measurements show that the meff
values of the manganese(III) complexes range from 4.68 to 5.01 B.M.
These results are consistent with the presence of four unpaired electrons
per Mn(III) ion.[16] These results are in agreement with mononuclear
manganese(III) complexes and also show that they exist in an octahedral
configuration (Figure 3).
Table 3. IR spectra (cm–1) of amino acid Schiff bases.
v(COO)
(non-ionized)
Schiff bases
v(O–H)
v(S–H)
v(C=O)
v(C=C)
H2L1
H2L2
H2L3
3306 s
3444 m
3385 s
–
1684 m
1719 s
1717 m
1634 vs
1646 vs
1627 vs
1558 m
1537 m
1560 m
–
2590 m

976
S¸akıyan and Yılmaz

Manganese(III) Complexes
977
Figure 2. The structure of methionine Schiff base (* denotes asymmetric carbon).
IR Spectra
The IR spectra of the manganese(III) complexes and Schiff bases are
summarized in Tables 2 and 3, respectively. In the IR spectra of the serine
Schiff base, the band at 3306 cm–1 is assigned to v(OH) of the serine
moiety. A broad band at around 3300 cm–1 in the methionine and cysteine
Schiff bases is ascribed to v(OH) of water molecules. Since these amino
acid Schiff bases do not exist as their salts, ionized COO asymetric and
symetric stretching bands are not observed. Only the non-ionized COO
stretching frequency at 1684–1718 cm–1 is observed.[17] Very strong bands
at 1646–1627 cm–1 may be attributed to v(C=O) in the keto form because
the amino acid Schiff bases exist in keto and imine tautomeric forms as
solids[18–21] (Figure 1). In the IR spectra of the manganese complexes, the
presence of coordinated water is observed as broad absorption bands around
3300 cm–1. The strong band observed at about 1630 cm–1 is due to
v(C=N), the imine group of the ligands. Generally, amino acid Schiff base
ligands in complexes exist only in the imine form[15] (Figure 3). Peaks at
around 1540 cm–1 are assigned to v(C=C) stretching. Asymmetric and
symmetric strectching frequencies of ionized COOꢁ groups are observed at
1580–1571 and 1382–1395 cm–1, respectively.
NMR Spectra
1H NMR spectra of the Schiff bases were studied and the d values are
given in Table 4. Integration of the multiplet peaks between d 6.76 and 8.80
Table 5. UV spectra of amino acid Schiff bases.
Schiff bases
Bands lmax (nm),
304 (9,380)
(e in cm2mol–1
)
H2L1
H2L2
H2L3
400 (9,473)
402 (9,802)
402 (8,680)
418 (9,670)
420 10,150)
422 (9,050)
308 (10,800)
312 (9,140)
296 (11,570)

978
S¸akıyan and Yılmaz
Figure 3. Suggested structure of manganese(III) complexes.
accounted for the six aromatic protons of the naphthylidene group. The
COOH peaks of free amino acid Schiff bases are observed at 10.96–10.89
ppm. The azomethine proton peaks of the Schiff bases are seen at 9.06–8.8
ppm. Because the amino acid Schiff bases have an asymmetric carbon, the
CH2 protons are near the asymetric carbon show different chemical shift
values because of diastereotopic.
These protons are an ABX system and are coupled to each other and
the CH proton. In the methionine Schiff base there are two methylene
groups and one of them is neighbouring to CH (Figure 2). Since they are
diastereotopic, both of the methylene protons are coupled to each other.
Therefore, they show up as multiplet peaks.
UV Spectra
The UV spectral data of the Schiff bases are summarized in Table 5.
As expected, there are two strong broad bands at ꢂ300 and ꢂ400–420 in
the UV spectra of the amino acid Schiff bases. The existence of two
absorbtion bands for the amino acid Schiff bases is attributed to the two
Table 6. Characteristic ions observed in mass spectra of the cysteine Schiff base and
the Mn(III) complexes.
Ion observed
H2L3
Moleculer weight
Ion
275
569
356
275 (M+ )
569 (M+ )
356
MnL1 (Molecular ion)
2
MnL2 (fragment)
2

Manganese(III) Complexes
979
Table 7. Thermogravimetric analyses of manganese(III) complexes.a
xH2Oc 2CO2
(100–250 °C)b
Residue Mn3O4 /MnO2 (1:2)
(250–1099 °C)b
Complexes
Na[Mn(L1)2]ꢀ3H2O
Na[Mn(L2)2]ꢀ3H2O
Na[Mn(L3)2]ꢀ6H2O
21.50 (21.97)
18.01 (19.32)
26.33 (26.75)
30.80 (31.19)
27.55 (27.42)
27.60 (27.50)
aCalculated values in parentheses.
bTemperature ranges.
cx = 3, 3 or 6, respectively.
tautomeric (keto and imine) forms.[18–21] The strong broad band at ꢂ300
nm is indicating the imine form, and the strong broad bands at ꢂ400–420
nm is assigned to the p! p* transition in the keto form[15] (Figure 3).
Mass Spectra
The mass spectra of the cysteine Schiff base and the manganese(III)
complexes support their structures (Table 6). The moleculer ion peak of
H2L3 at m/z 284 indicates the formula weight of the cysteine Schiff base.
The mass spectrum of the cysteine complex is different from those of the
serine and methionine complexes. Although the moleculer ion peak of
serine and methionine complex was observed, we couldn’t observed mole-
culer ion peak for the cysteine Schiff base manganese complex Table 7.
Thermogravimetry
Thermogravimetric analyses of the manganese(III) complexes indicate
the presence of various levels of water molecules per manganese atom,
which are lost at around 100–250 °C.[13,22] In the temperature range 250–
1099 °C the complexes probably are converted to Mn3O4/MnO2 (1:2).
EXPERIMENTAL
Chemicals
The amino acids (L-serine, L-methionine, L-cysteine) were purchased
from Fluka. Manganese(III) acetate was prepared by the method of Gu¨ndu¨z
at al.[23] 2-Hydroxy-1-naphthaldehyde and methanol were purchased from
Aldrich or Merck, respectively.

980
S¸akıyan and Yılmaz
Physical Measurements
Infrared spectra of the complexes and Schiff bases were obtained from
4000 to 350 cm–1 in KBr pellet using a Mattson FT-IR 1020 spec-
trophotometer. Magnetic susceptibilities of the complexes were measured at
room temperature using a model MKI, Sherwood Scientific, Cambridge-
England, Magnetic Susceptibility Balance. HgCo(SCN)4 was used as a
standard. C, H, N, S were determined by microanalyses on a Leco 932
elemental analyser. Electronic spectra of the Schiff bases were recorded on
1
an Unicam UV2-100 UV/Visible spectrophotometer. H NMR spectra of
the Schiff bases were obtained on a Bruker GmbH DPX-400 400 MHz
High Performance Digital FT-NMR spectrometer (SiMe4 as standard). TGA
of the complexes were carried out with a Rigaku Thermoflux TG 8110
system. Mass spectra of H2L3 and the manganese complexes were recorded
on a Micromass UK Platform II LC-MS spectrometer.
Preparation of Schiff Bases
2-Hydroxy-1-naphthaldehyde (5 mmol, 061 g) in methanol (50 mL)
was added to the amino acid (5 mmol) (L-serine, L-methionine, L-cystein)
in methanol solution (50 mL). The mixture was refluxed 3 hours at 100 °C,
the solvent removed by a rotary evaporator and the residue let stand at
room temperature. The resulting yellow crystals were recrystallized from
methanol/n-heptane (2:1).
Preparation of Complexes
The amino acid (L-serine, L-methionine, L-cysteine) (10 mmol) was
added to a methanol solution (50 mL) containing NaOH (20 mmol, 0.8 g).
A methanol solution (50 mL) of 2-hydroxy-1-napthaldehyde (10 mmol,
2.44 g) was then added to this mixture and stirred magnetically. After 2
minutes, solid Mn(OOCCH3)3ꢀ2H2O (5 mmol, 1.34 g) was added and
mixture stirred for 3 h at room temperature. The dark brown solution was
evaporated to one-fifth of its initial volume and was left to stand overnight
at room temperature. After one day, a dark brown microcrytalline solid was
obtained which was filtered by suction and dried under vacuum. The solid
was recrystallized from a methanol/ethanol (50 %) mixture.
ACKNOWLEDGMENTS
We express our sincere thanks to the Ankara University Research
Foundation (No: 2001 070 50 47) for financial support and TUBITAK (The

Manganese(III) Complexes
981
Scientific and Technical Research Council of Turkey) for providing
spectroscopy laboratory facilities. We also thank Dr. Hamide enyuva for
a special effort in obtaining mass spectra at TUBITAK.
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Received June 27, 2002
Accepted February 24, 2003
Referee I: G. C. Dismukes
Referee II: K. Moedritzer