Study of the syntheses and antioxidative actions of (η-C5H5)2Ti(IV)(Asp)2 and (η-C5H5)2Ti(IV)(Sal)2

Article abstract of DOI:10.1081/SIM-100106864

In this paper two metalorganic complexes of dicyclopentadienyltitanium(IV) with aspirin and dicyclopentadienyltitanium(IV) with salicylic acid have been synthesized. Their chemical compositions and structures have been studied by elemental analyses, XPS, IR, ¹H NMR. The formulas of the complexes were confirmed as (Cp)₂Ti(Asp)₂ and (Cp)₂Ti(Sal)₂ [Cp = cyclopentadienyl ion (η⁵-C₅H₅), Asp = anion of aspirin (acetylsalicylate ion, CH₃CO₂C₆H₄COO^-), Sal = salicylate anion, C₆H₄(OH)COO^-], in which the carboxyl oxygen atoms of Asp and Sal are coordinated to Ti(IV) in a monodentate manner. It was found that the complexes of Sal or Asp and cyclopentadienyl ion have a synergistic action on the elimination of superoxide radicals (O^-?₂) and hydroxyl radicals (OH^?). The possible mechanism of these reactions has been discussed.

Full text of DOI:10.1081/SIM-100106864

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STUDY OF THE SYNTHESES AND ANTIOXIDATIVE
ACTIONS OF (η-C5H5)2Ti(IV)(Asp)2 AND (η-C5H5)2Ti(IV)
(Sal)2
Zhengzhi Zeng a
a Department of Chemistry , Lanzhou University , Lanzhou, 730000, China
Published online: 15 Feb 2007.
To cite this article: Zhengzhi Zeng (2001) STUDY OF THE SYNTHESES AND ANTIOXIDATIVE ACTIONS OF (η-C5H5)2Ti(IV)(Asp)2
AND (η-C5H5)2Ti(IV)(Sal)2 , Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 31:7, 1285-1296, DOI: 10.1081/
SIM-100106864
To link to this article: http://dx.doi.org/10.1081/SIM-100106864
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(7), 1285–1296 (2001)
STUDY OF THE SYNTHESES AND
ANTIOXIDATIVE ACTIONS OF
(g-C5H5)2Ti(IV)(Asp)2 AND
(g-C5H5)2Ti(IV)(Sal)2
Zhengzhi Zeng
Department of Chemistry, Lanzhou University,
Lanzhou 730000, China
E-mail: fangjian@china.com
ABSTRACT
In this paper two metalorganic complexes of dicyclopenta-
dienyltitanium(IV) with aspirin and dicyclopentadienyltita-
nium(IV) with salicylic acid have been synthesized. Their
chemical compositions and structures have been studied by
1
elemental analyses, XPS, IR, H NMR. The formulas of the
complexes were confirmed as (Cp)2Ti(Asp)2 and (Cp)2Ti(Sal)2
[Cp ¼ cyclopentadienyl ion (Z5-C5H5), Asp ¼ anion of aspirin
(acetylsalicylate ion, CH3CO2C6H4COOÀ), Sal ¼ salicylate
anion, C6H4(OH)COOÀ], in which the carboxyl oxygen atoms
of Asp and Sal are coordinated to Ti(IV) in a monodentate
manner. It was found that the complexes of Sal or Asp and
cyclopentadienyl ion have a ‘‘synergistic action’’ on the
elimination of superoxide radicals (OÀ2 ꢀ) and hydroxyl radi-
cals (OHꢀ). The possible mechanism of these reactions has
been discussed.
1285
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1286
ZENG
INTRODUCTION
In the 1990s, Qian1 studied the elimination effect of salicylic acid on
the lipid peroxidation in phosphatidylcholine liposomes. Experimental
results show that salicylic acid can scavenge the hydroxyl free radicals (OHꢀ)
and superoxide free radicals (OÀ2 ꢀ). We2 reported the antioxidative action of
rare earth complexes with b-diketoisonicotinoyl hydrazone in 1998. It has
been shown that complexes of rare earth(III) cations and ligands have an
enhancement or synergistic effect, and that the antioxidative action of the
ligand and complexes containing ferrocenyl groups far exceeds other ligands
and complexes. It is not known whether the antioxidative action is caused by
the iron(II) cation or cyclopentadienyl ion. This mechanism has not been
resolved. In this paper two new complexes of dicyclopentadienyl-titanium-
(IV) diaspirin and dicylcopentadienyltitanium(IV) disalicylate have been
synthesized, and their composition and structure have been studied by ele-
1
mental analyses, XPS, IR and H NMR. The formulas of the complexes
were comfirmed as (Cp)2Ti(Asp)2 and (Cp)2Ti(Sal)2 [in which Cp ¼ cyclo-
pentadienyl ion (Z5-C5H5), Asp ¼ anion of aspirin (acetylsalicylate ion),
Sal ¼ salicylate anion]. The IR and XPS data show that the carboxy oxygen
atoms of Asp and Sal are coordinated to Ti(IV) in a monodentate manner.
We also have determined the inhibition rates (Ih and Ih*) of seven com-
pounds [(Cp)2Ti(Asp)2, (Cp)2Ti(Sal)2, (Cp)2TiCl2, HAsp, HSal, Ti(OH)2-
(Asp)2 and Ti(OH)2(Sal)2 to superoxide free radicals (OÀ2 ꢀ) and hydroxyl
free radicals (OHꢀ). The experimental data indicated that the complexes of
Sal or Asp and cyclopentadienyl ion have an ‘‘synergistic action’’ for the
elimination of the above radicals.
EXPERIMENTAL
Reagents and Apparatus
Reduced coenzyme I (NADH), phenazine metasulfate (PMS), nitro-
blue tetrazolium (NBT) and methional (3-methionpropionaldehyde) were
purchased from Sigma. Tris-HCl (0.01 mol=L, pH ¼ 8.0) and NaH2PO4-
Na2HPO4(0.01 mol=L, pH ¼ 7.4) buffers were prepared with twice distilled
water. Ascorbic acid, aspirin (2-acetoxybenzoic acid, HAsp or H3CCO2-
C6H4COOH), salicylic acid (o-hydroxybenzoicaicd, HSal or HOC 6H4-
COOH), NaAsp, NaSal, TiCl4, Ti(OH)2SO4, EDTA, FeSO4 etc. were of
analytical grade. Benzene and petroleum ether (60790 ꢁC) were dried over
anhydrous calcium chloride for 30 h and THF was dried with potassium
hydroxide for 24 h. Then these compounds were refluxed with sodium sand

(g-C5H5)2Ti(IV)(Asp)2 AND (g-C5H5)2Ti(IV)(Sal)2
1287
and diphenyl ketone (benzophenone) until the color stabilized. Triethyla-
mine was distilled after drying for 24 h with potassium hydroxide. Dicy-
clopentadienyltitanium dichloride was synthesized according to the
literature3. Ti(OH)2(Asp)2 or Ti(OH)2(Sal)2 were prepared by the reactions
of Ti(OH)2SO4 with NaAsp or NaSal.
A Bruker AM-400 NMR spectrometer (using CDCl3 as solvent and
TMS as internal reference), a Nicolet 170SX IR spectrometer, 4000-
200 cmÀ1 (using KBr pellets), a DDS-11A electric conductivity apparatus
and 721 UV-Vis spectrophotometer were used. The experiments of XPS
were performed in an ESCALAB 2201-XL X-ray photoelectron spectro-
meter using Al Ka radiation, with the pressure of the residual gases better
than 5 Â 10À10 Torr. The working power (P) of the X-ray gun was 300 W
using the C1s spectrum (284.60 eV) as internal reference. A GC-9A gas
chromatograph with a Paropark Q chromatographic column (3 m  3 mm)
was used.
Syntheses of Complexes
In an anhydrous alcohol solution (200 mL) 0.05 mol aspirin (9 g) or
salicylic acid (6.9 g) was reacted with 0.05 mol sodium (1.2 g) to form white
NaAsp (or NaSal) as precipitate. The precipitate was filtered and dried in a
vacuum desiccator over phosphorus pentoxide. Then 8 mmol NaAsp
(1.62 g) or NaSal (1.28 g) were refluxed with 2 mmol (Cp)2TiCl2 (0.5 g) in
60 mL benzene for 15 h. After cooling to room temperature, the insoluble
residue was filtered. The filtrate was evaporated under vacuum to 1=6 of its
original volume. On adding 20 mL dried petroleum ether and placing the
mixture in a refrigerator overnight, orange crystals were obtained. After
filtration, the precipitates of (Cp)2Ti(Asp)2 [or (Cp)2Ti(Sal)2] were dried in a
vacuum desiccator over phosphorus pentoxide for 30 h. The carbon,
hydrogen, nitrogen and chlorine contents of the above compounds were
determined by an Elementar Vario EL elemental analyser. Titanium was
determined by a gravimetricmethod.
Elimination Effect to Biological Free Radicals (OÀ2 ꢀ and OHꢀ)
The inhibition rates (or elimination rates) of different compounds
toward superoxide anion free radical (OÀ2 ꢀ) and hydroxyl free radical (OHꢀ)
were determined according to the literature2,4,5
.
The compounds (Cp)2Ti(Asp)2, (Cp)2Ti(Sal)2, HAsp, HSal, Ti(OH)2-
(Asp)2, Ti(OH)2(Sal)2 and (Cp)2TiCl2 were dissolved in acetone-DMF

1288
ZENG
(1:2 V=V) to give a respective solution Z of 0.5 mg=mL for determination.
Where Z is a solution one of the aforesaid seven compounds.
OÀ2 ꢀ released from the reaction of NADH and PMS can react quan-
titatively with NBT to give a blue solution, and the absorbance of the
solution has a linear relationship with the concentration of OÀ2 ꢀ in the range
of 0À1 Â 10À4 mol=L, which can be used to detect OÀ2 ꢀ. The capability of a
biological free radical scavenger on OÀ2 ꢀ can be expressed by the inhibition
rate, Ih,
A0 À A
Ih ¼
 100%
A0
where A0 is the absorbance of a blank solution and A is the absorbance of a
solution containing a free radical scavenger at different doses.
NADH, PMS and NBT were dissolved in tris-HCl buffer, respectively,
to give a solution of 3:0 Â 10À5 mol=L for use. The solutions of NADH
(1.0 mL), PMS (1.0 mL) and NBT (1.0 mL) were added to the solution of
0.00, 0.25, 0.50, 0.75, 1.00 ml of Z, respectively (doses of 0.000, 0.125, 0.250,
0.375, 0.500 mg, respectively). After diluting them to 5.0 mL with tris-HCl
buffer and keeping them below 37 Æ 1 ꢁC for 5 min the absorbance of the
solutions was determined at the wave length of 560 nm with a reference
solution of acetone-DMF (1:2 V=V).
The hydroxyl radical OHꢀ generated by the reaction of H2O2 with
ascorbic acid using Fe2þ-EDTA as catalyst reacts with methional to release
ethylene that can be detected by gas chromatography. The inhibition rate
Ih* of a free radical scavenger may be calculated as follows
a0 À a
Ihà ¼
 100%
a0
where a0 is the yield of ethylene without free radical scavenger and a is the
yield of ethylene with free radical scavenger.
8.4 mg FeSO4Á7H2O (3 mmol) and an equimolar (11.1 mg) quantity
of EDTA disodium (C10H14N2O8Na2Á2H2O) were dissolved in 1000 mL
NaH2PO4-Na2HPO4 buffer to give a solution of 3:0 Â 10À5 mol=L.
Methional and ascorbic acid were dissolved in this buffer solution,
respectively, to give a 3:0 Â 10À5 mol=L solution for use. The solutions of
Fe2þ-EDTA (1.0 mL), methional (1.0 mL) and ascorbic acid (2.0 mL) were
added to the solution of 0.00, 0.25, 0.50, 0.75, 1.00 mL of Z, respectively
(doses of 0.000, 0.125, 0.250, 0.375, 0.500 mg, respectively). After diluting
them to 5.0 mL with NaH2PO4-Na2HPO4 buffer, and keeping them below
37 Æ 1 ꢁC for 30 min the yields of ethylene were determined by gas
chromatography.

(g-C5H5)2Ti(IV)(Asp)2 AND (g-C5H5)2Ti(IV)(Sal)2
RESULTS AND DISCUSSION
1289
Properties and Composition of the Complexes
Elemental analyses, molar conductances (LM, 1:0 Â 10À4 mol=L in
acetone, 10 ꢁC), melting points etc. of the complexes are presented in Table I.
The chemical compositions of the complexes examined by elemental
analyses correspond to the calculated values. The low conductance of the
two complexes indicate that they are non-electrolytes. They are soluble in
acetone, benzene, chloroform and THF, but insoluble in water, petroleum
ether and diethyl ether. In acetone=benzene (1:1) the complexes were eluted
on GF254 silica gel. The Rf (relative band speed) values are also presented in
Table I. The LM values of the two complexes are higher, and the Rf values
are lower than those of (Cp)2TiCl2, which showed that their polarities are
higher than that of (Cp)2TiCl2.
IR Spectra
The characteristic IR absorption peaks of the complexes and ligands are
listed in Table II. In the complexes the stretching vibration band nðC¼OÞ
(1700, 1670 cmÀ1) ascribed to the carboxylic groups (COOH) of HAsp and
HSal has disappeared, and the characteristic absorption band of the carbox-
ylate group has appeared. The differences D of the unsymmetrical stretching
vibration bands, nas (1636, 1600 cmÀ1), and the symmetrical vibration bands,
ns (1340, 1342 cmÀ1), are 296 and 258 cmÀ1, respectively, which indicate that
the oxygen atoms of the carboxylate groups are coordinated to Ti(IV) in a
monodentate manner6. The absorption bands of n(O-H) of HSal and its
complex are seen at 250073200 and 260073300 cmÀ1, which show that the
oxygen atom of the carboxy group forms an intramolecular hydrogen bond
with the o-hydroxyl group. However, HAsp and its complex do not show the
above absorption band. Compared to (Cp)2TiCl2, the characteristic absorp-
tion band of the cyclopentadienyl ion (Z5-C5H5) in the complexes shifts to
higher wave numbers; the characteristic band of n(Ti-O) appeared and the
absorption band of n(Ti-Cl) of (Cp)2TiCl2 disappeared which indicated still
further that Asp or Sal take part in the coordination to the Ti(IV) ion.
1H NMR Spectra
The 1H NMR spectra of the ligand and complex are listed in Table III.
The integrated areas of the various protons correspond to the proton

1290
ZENG

(g-C5H5)2Ti(IV)(Asp)2 AND (g-C5H5)2Ti(IV)(Sal)2
1291

1292
ZENG
Table III. 1H NMR Chemical Shifts (d, ppm)
Compound
Z5-C5H5
C6H4
H3CCO2
OH
(Cp)2Ti(Asp)2
Hasp
(Cp)2Ti(Sal)2
Hsal
(Cp)2TiCl2
6.68 (s, 10H)
—
6.67 (s, 10H)
—
6.60 (s, 10H)
6.878.0 (m, 8H)
7.078.5 (m, 4H)
6.878.0 (m, 8H)
7.078.5 (m, 4H)
—
1.25 (s, 6H)
2.35 (s, 3H)
—
—
—
—
—
11.92 (s, 2H)
—
—
numbers in the structure of the complexes. The NMR signals of the sub-
stituted benzene ring (-C6H4) and acetyl group (OCCH3) at 7.078.5 ppm
and 2.35 ppm move to higher field at 6.878.0 ppm and 1.25 ppm, respec-
tively. The NMR signals of the cyclopentadienyl protons (Z5-C5H5) move
slightly to lower field and the NMR signals of the carboxy group disappear
which verifies that the ligand coordinates to the metal cation in forming the
complex. The structures of the complexes are shown in Fig. 1.
XPS Spectra7
To obtain further insight into the nature of bonding, the XPS spectra
of the complexes were measured at room temperature. It was found that the
data of atomic molar percent of the complexes are very close to those of the
elemental analyses given above. The electron binding energy (BE) data of
C1s and O1s for the complexes are listed in Table IV.
Figure 1. Suggested structure of the complexes (R¼OH or OOCCH3).

(g-C5H5)2Ti(IV)(Asp)2 AND (g-C5H5)2Ti(IV)(Sal)2
Table IV. XPS Spectra Data of the Complexes (eV)
1293
A%a
Binding Energy (BE) (peak area)
CBls CCls CDls OAls
Compound
C=O=Ti
CAls
OBls
(Cp)2Ti(Sal)2
24.2=5.8=1 283.02 287.97
(10.35) (1.22)
531.24 533.50
(22.95) (12.12)
(Cp)2Ti(Asp)2 28.4=8.1=1 283.12 289.22 287.24 286.30 531.33 527.66
(21.68) (2.09) (2.19) (2.11) (26.48) (27.02)
aAtomicmolar ratio in the complexes.
In (Cp)2Ti(Sal)2, the O1s electron spectra are asymmetric and their
deconvolution yields two components (OA1s and O1Bs) which revealed the
chemical shifts for oxygen. The weak intense component (OA1s) with the
lower BE at 531.24 eV remains almost unchanged and belongs to the oxygen
of the carbonyl (-COOÀ) group. The strong intense component (O1Bs) with
the higher BE (533.50 eV) value belongs to the oxygen of the hydroxy group
(-OH). The assignment is supported not only by IR spectra but also by their
peak area ratio 22.95=12.12 (OA1s=O1Bs), which is close to the atomic ratio
(2=1) of two different types of oxygens in (Cp)2Ti(Sal)2 (Fig. 2). The same
reason explains the different values for (Cp)2Ti(Asp)2. In (Cp)2Ti(Asp)2, the
weak intensity component (OA1s) with the higher BE at 531.33 eV is assigned
to the oxygen of the carbonyl (-COOÀ) group and the strong intensity one
((OB1s) with the lower BE (527.66 eV) value is assigned to the oxygen of the
acetyl group (-OOCCH3). Their peak area ratio (OA1s=O1Bs) is 26.48=27.02
which is also close to the atomic ratio (1=1) of two types of oxygens in
(Cp)2Ti(Asp)2.
C1s in (Cp)2Ti(Sal)2 is split into two peaks (CA1s and C1Bs). C1As belongs
to the carbons of the cyclopentadieny radical (-C5H5) and benzene ring
Figure 2. Schematic representation of assignment of C1s and O1s for the complexes.

1294
ZENG
(-C6H4), and CB1s is assigned to the carbons of carbonyl (-COOÀ).
The assignment is verified by their peak area ratio 10.35=1.22 (CA1s=C1Bs)
which is consistent with the atomic ratio (11=1) of two types of carbons in
the complex. Unlike (Cp)2Ti(Sal)2, C1s in (Cp)2Ti(Asp)2 is split into four
peaks with the peak area ratios being 21.68=2.09=2.19=2.11
(CA1s=CB1s=C1Cs=CD1s). The ratio is identical to the atomic ratio (11=1=1=1) of
four types of carbons. C1As, C1Bs, C1Cs and C1Ds are assigned to the carbon of the
cyclopentadieny radical (-C5H5) and benzene ring (-C6H4), carbonyl
(-COOÀ), acetyl group (-OOCCH3) and methyl group (-CH3), respectively7.
Elimination of OÀ2 ꢀ and OHꢀ
The inhibition rates Ih (%) and Ih* (%) of the ligand and the complex to
superoxide free radicals (OÀ2 ꢀ) and hydroxyl free radicals (OHꢀ) are pre-
sented in Table V. These data reveal that the inhibition rates of HAsp (or
HSal) and Ti(OH)2(Asp)2 [or Ti(OH)2(Sal)2] to superoxide anion free
radicals (OÀ2 ꢀ) and hydroxyl free radicals (OHꢀ) are close, but the elimina-
tion actions of (Cp)2Ti(Asp)2 [or (Cp)2Ti(Sal)2] are greater than those of the
corresponding ligands and compounds such as (Cp)2TiCl2, HAsp (or HSal),
Ti(OH)2(Asp)2 [or Ti(OH)2(Sal)2] etc. It is shown that Ti(IV) does not
produce an enhancement action to Asp or Sal, however, after formation of
complexes with Sal (or Asp), larger inhibition rates are seen. It is possible
that the ‘‘synergistic action’’ was produced by the mixed ligands (Cp and
Table V. Inhibition Rate of Seven Compounds to OÀ2 ꢀ and OHꢀ Radicals (%)
Ih (%)a
IhÃ(%)b
Dose=mg Dose=mg
0.00 0.125 0.25 0.375 0.50 0.00 0.125 0.25 0.375 0.50
Compounds
(Cp)2Ti(Asp)2
HAsp
Ti(OH)2(Asp)2
(Cp)2Ti(Sal)2
HSal
0
0
0
0
0
0
0
2.24 11.48 22.88 24.76
2.12 10.60 18.05 21.45
2.02 11.87 17.65 19.94
6.45 23.64 38.22 42.76
6.66 22.13 33.35 37.62
6.21 21.53 31.78 33.23
7.13 17.88 24.67 29.81
0
0
0
0
0
0
0
38.84 43.55 48.87 55.24
38.26 41.11 45.45 52.20
34.90 40.08 43.19 50.68
58.77 70.32 77.87 81.34
56.80 67.65 73.82 78.14
54.11 63.55 67.60 71.08
31.32 34.65 41.76 50.58
Ti(OH)2(Sal)2
(Cp)2TiCl2
aIh (%): Inhibition rate of OÀ2 ꢀ radical (%), p < 0:05, p ¼ probability of null
hypothesis.
bIhà (%): Inhibition rate of OHꢀ radical (%), p < 0:05.

(g-C5H5)2Ti(IV)(Asp)2 AND (g-C5H5)2Ti(IV)(Sal)2
1295
Figure 3. Reaction mechanism of elimination of hydroxyl free radical (OHꢀ) by
salicylic acid.
Asp or Sal). From the data in Table V it is indicated that the elimination
capabilities of the compounds containing phenolic hydroxyl groups, such
as (Cp)2Ti(Sal)2, Ti(OH)2(Sal)2, HSal etc. are all higher than those of
compounds without phenolic hydroxyl groups such as (Cp)2Ti(Asp)2,
Ti(OH)2(Asp)2 and HAsp. In fact, the reaction mechanism of the phenolic
hydroxyl group to eliminate hydroxyl free radicals is probably that the
hydrogen atom of the phenolic hydroxyl group of salicylic acid is substituted
by a hydroxyl free radical to form a free radical at the benzene ring, which
then forms dihydroxy benzoic acid with a hydroxyl free radical again1.
The reactions are shown in Fig. 3.
REFERENCES
1. Qian, Y.M.; Li, X.P.X.; Liang F.; Huang, F. Inhibition of Liped Per-
oxidation in Artificial Membranes by Salicylic Acid. Acta Biophysica
Sinica 1990, 6 (3), 3327337. (In Chinese with English summary).
2. Jing, H.W.; Chen, B.H.; Zeng, Z.Z.; Huo, W.M. Synthesis and Char-
acterization of b-Diketone Isonicotinoylhydrazone-Rare Earth Com-
plexes and their Elimination Effect on Biological Free Radicals. Chem.
Papers 1998, 52 (3), 1637166.
3. Gorsich, R.D. Preparation and Properties of Cyclopentadienyltitanium
Trichloride. J. Am. Chem. Soc. 1960, 82, 421174214.
4. Winterbourn, C.C. Comparison of Superoxide with Other Reducing
Agents in the Biological Production of Hydroxyl Radicals. Biochem.
J. 1979, 182, 6257628.
5. Winterbourn, C.C. Hydroxyl Radical Production in Body Fluids.
Biochem. J. 1981, 198, 1257131.

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ZENG
6. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordi-
nation Compounds; 4th Edn.; John Wiley & Sons, Ltd.: New York,
1986; 232.
7. Briggs, D.; Seah, M.P. Practical Surface Analysis by Auger and X-ray
Photoelectron Spectroscopy; John Wiley & Sons, Ltd.: New York,
1983; 5157526.
Received September 6, 1999
Accepted June 10, 2001
Referee I: D. W. Stephan
Referee II: R. F. Jordan