SYNTHESIS, SPECTROSCOPIC AND
MOLECULAR MODELLING STUDIES
ON LANTHANUM(III)-CHRYSIN
COMPLEX
CHAPTER-I
INTRODUCTION
POLYHYDROXY PHENOLS
Polyphenols are basically one of the most important oxygen
donor compounds, which have been used as complexing agents
for metal ions. These are characterized by the presence of multi
hydroxyl groups in them, which offers a ready coordination site.
Polyphenolic compounds found in fruits, vegetables and certain
beverages that have diverse beneficial biochemical and
antioxidant effects [1]. Antioxidant activity is due to metal ion
chelation and scavenging active free radicals . They have been
reported to have antiviral, antiallergic, anti-inflammatory,
antitumor and antioxidant activities [2-4].
ANTIOXIDANTS
Antioxidants are chemical substances that donate an electron to
the free radical and convert it to a harmless molecule. Free
radicals are highly reactive chemicals that attack molecules by
capturing electrons and thus modifying chemical structures.
Antioxidant play important role in biological system, such as
suppressing the formation of active species by reducing
hydrogen peroxide and by scavenging active free radicals [5].
What are free radicals?
Any molecule or atom that possesses one unpaired electron is
called “free radical”. These are unstable, short lived and will
react with other compounds, which results in the stabilization
of the free radical.
Free radicals can be divided into different categories e.g.,
reactive oxygen species (ROS), reactive nitrogen species
(RNS), reactive chlorine species (RCS) etc., The prominent
member of such categories include superoxide (O2.-), hydroxyl
(OH.), peroxyl (ROO.) and nitric oxide (NO.) radicals [6]
Generation of free radicals
Free radicals generated in so many ways such as Fenton type
reaction, where metal ions in biological system (eg. Fe3+/2+)
involved and therefore a chain of oxidation and reduction
reaction occurs which results in more free radicals [7]. Some
of important sources of free radicals in biosystems are
metabolism of drugs, inflammation, enzymatic activity,
smoking and radiation [8,9].
Types of Antioxidant
There are two mechanistic groups of antioxidants, those,
which are interrupting the radical chain reaction, are called
“chain breaking” (CB) antioxidants and those which inhibit or
retard the formation of free radicals from their unstable
precursors are called “preventive antioxidants”.
Naturally occurring antioxidants
Both chain breaking and preventive antioxidants are naturally
occurring in living bodies e.g., Vitamin E, Vitamin C,
Polyphenols etc. Some important preventive antioxidants are
catalase (CAT), glutathione peroxidase (GSHPX) and
superoxide dismutase.
FLAVONOIDS
Flavonoids are polyphenolic compounds, which constitute one
of the most characteristic classes of compounds in higher
plants. The flavonoids have aroused considerable interest
recently because of their potential beneficial effects on human
health. They have been reported to have antitumor and
antioxidant activities [2-4].
The chemical structure of flavonoid
Antioxidant activity of flavonoids
Flavonoids are powerful antioxidant, and their activity is
related to their chemical structures. Plant polyphenols are
multifunctional and can act as reducing agents, as hydrogen
atom-donor and as singlet oxygen quencher.
AIM OF PRESENT WORK
In present study, we have chosen chrysin (5,7-dihydroxy
flavone) which shows interesting antioxidant activities and
remarkable chelation with metal ions [10-13]. In order to
investigate the interaction of chrysin with metal ion,
spectroscopic (IR, UV-Visible, 1H NMR spectras and
Thermal analysis) and molecular modeling studies were
carried out.
chrysin (5,7-dihydroxy flavone)
1.
2.
Biometals, 18; 143-154, 2005.
Bioorganic Chemistry, 33; 67-81, 2005.
CHAPTER-II
MATERIALS AND THEORY OF METHODS
USED
Theory of Methods Used
Although almost all parts of the electromagnetic spectrum are used
for studying matter but energy absorption from four regions such as
ultraviolet and visible, infrared, microwave and radio frequency
absorption are of main concern.
UV-Vis, IR and 1H NMR Spectroscopy
Radiation absorbed
Effect of the molecule
UV-Visible
Change in electronic energy
(λ=200-800 nm)
levels with in the molecules.
Infrared
Changes in vibrational and
(=400-4000cm-1)
rotational movements of the
molecule
Radio-frequency
Changes in the magnetic
(ν =60-600 MHz)
properties of certain atomic
nuclei (Hydrogen)
Thermogravimetric Analysis
Thermal methods of investigation generally referred to as thermal
or thermo- analytical techniques. These may be defined as
experimental methods for characterizing a system (element,
compound or mixture) by measuring changes in physico-chemical
properties at elevated temperatures as a function of increasing
temperature [14,15]. The two chief methods are


Differential thermal analysis (DTA) [16], in which changes in
“heat content” are measured as a function of increasing
temperature and
Thermogravimetric analysis (TGA), in which changes in weight
are measured as a function of increasing temperature.
Computational Chemistry
Computational chemistry is a new discipline. Its advent and
popularity have paralleled improvements in computing power
during the last several decades. As with other disciplines in
chemistry, computational chemistry uses tools to understand
chemical reactions and processes.
Calculation Methods
There are two types of methods in calculations: molecular
mechanics and quantum mechanics. The quantum mechanics
methods include semi-empirical, abinitio, and density
functional quantum mechanics methods.
CHAPTER-III
EXPERIMENTAL
Materials
Lanthanum oxide (Lieco Chemicals, USA) is converted to the
corresponding chloride. Chrysin (Sigma-Aldrich, USA) and
methanol (SD Fine) were used as such in this study.
Preparation of La (chrysin)3 complex
Hot solution of chrysin (3 m mol) in 50 ml methanol was added
drop wise to the hot solution of hepta-hydrated lanthanum chloride
(1m mol) in 50 ml methanol with constant stirring and kept the
solution at 80oC temperature. After 1 hour stirring, yellow color
needle shaped crystalline precipitate formed. The precipitate was
filtered and washed with methanol and dried in vaccuo over
P4 O10.
Methods or Physical Measurements
Microanalysis (Carbon and Hydrogen) was carried out with a FISONS EA-1108 elemental analyzer. The metal content of the
complex was estimated by complexometric titration. The
thermogram was recorded on du Pont TA 2000 TGA machine
under nitrogen atmosphere at a heating rate of 10oC min-1. Melting
point (mp) was measured with a Gallen kamp MBF-595 apparatus.
A Shimadzu UV-2501PC spectrophotometer was used to obtain
the electronic spectra in the region 200-700 nm in methanol, DMF
and DMSO solvents. FTIR spectra in the 4000-400 cm-1 regions
were recorded from KBr pellets on a shimadzu-250
spectrophotometer. 1H NMR chemical shift was measured in
DMSO-d6 solvent on Bruker 300 MHz spectrophotometer.
Molecular modeling calculations were carried out using
Hyperchem (Version 7.5)[17].
Results and Discussion
The chrysin complex of lanthanum (III) has been isolated in
methanol under normal conditions. The complex is pale yellow
color polycrystalline solid and having sharp melting point between
the range 289-290oC. The complex was hygroscopic in nature and
soluble in common organic solvents but slightly soluble in water,
ether, chloroform and CCl4. On the basis of elemental analysis,
UV-Vis, IR, TGA/DTA and NMR spectral studies we assumed that
chrysin acted as a bidentate ligand and formed a mononuclear
complex where one La(III) ion is bound to three chrysin
molecules. These results suggest that the composition of the
complex is La(chrysin)3.
Table 1. Physical properties of lanthanum-chrysin complex
Complex
Color MP oC
% Metal Calculated (Observed)
C
H
M
La(chrysin)3 Yellow 289-90
51.84(50.96) 2.61(2.70) 13.32(12.72)
UV-VIS Spectral analysis
The absorption spectra of the chrysin and its lanthanum complex
were recorded in methanol, DMF and DMSO solvents within the
spectral range 200-700 nm. The absorption spectra of free chrysin
molecule revealed two major intense absorption bands in DMF,
DMSO and methanol solutions in the ultraviolet part of the
spectrum. The absorption in 260-326 nm range correspond to the
B ring portion (phenolic system band I) and related to the П- П
transitions with in the aromatic ring of the ligand molecules. The
second absorption transition was observed between the spectral
range 200-293 nm is correspond to the A ring portion (quinonolic
system band II) which is due to П- П, n- П and n- transitions
with in the quinonolic ring of the chrysin molecule.
The absorption spectrum of chrysin metal complex was shifted
towards higher wavelength in comparison with free chrysin
ligand spectrum. Such bathochromic shift can be explained by
the extension of the conjugated system with the complexation.
The absorption band II was shifted more than band I it
indicates that band II (ring A, quinonolic system) is involved
in coordination to the metal ion [18,19]. These observed
results were suggested that 4-oxo and 5-OH groups of chrysin
ligand are involve in coordination to the metal ion.
Ligand/
Complex
Chrysin
La(Chrysin)3
Band I
DMSO
DMF
MeOH
…..
315(31746.03)
314(31847.13)
316(31645.56)
315(31746.03)
315(31746.03
Band II
DMSO
DMF
MeOH
269(37174.72)
….
268(37313.43)
272(36764.70)
277(36101.08)
266(37593.98
Band III
DMSO
DMF
MeOH
…..
…..
218(45871.55)
…..
217(46082.94)
219(45662.10)
UV-Visible spectra of La(chrysin)3complex in DMSO solution
UV-Visible spectra of La(chrysin)3complex in MeOH solution
UV-Visible spectra of La(chrysin)3complex in DMF solution
IR Spectra
Infrared absorption spectra are found to be the most useful
physical method for investigation & identifying functional
groups. The characteristic IR absorption frequencies in the
spectral range 4000-400 cm-1 were measured for free chrysin
and its metal complex. The IR absorption spectrum of lanthanum
metal complex clearly indicates that the free chrysin molecule
loses their original characteristics and participate in coordination
to the metal ion. The complex exhibited (M-O) band at 500-400
cm-1 while ligand exhibited no such band and suggests the
metal-oxygen coordination. On the other hand, a diffused band
in the region 3500-3000 cm-1 was appeared in the spectrum of
ligand, which is attributed to the symmetrical and antisymmetrical stretching modes of (O-H), which undergo change
in the spectra of the complex. The appearance of this frequency
suggests the presence of hydroxyl group and shift of the ligand
frequency due to the loss of OH group during the coordination to
the lanthanum ion.
The (C-O-C) and (C=C) frequencies changed slightly upon
complexation indicates the ring oxygen does not form metaloxygen bond. However, a strong band at about 1653 cm-1,
detected in the spectra of the ligand is assigned to (C=O), which
was shifted in the spectrum of the metal complex, which
indicates that the coordination occurs through the C=O oxygen
atom [20-22].
Table 3. IR absorption frequencies of lanthanum-chrysin complexe.
Functional Groups
Chrysin
La(Chrysin)3
(O-H)
3500-3000
3090
(C-H)
2926
2886
(C=O)
1653
1621
 C=C)
1611
1576
1553
1610
1577
1554
(O-H)
C-O-H
1450
1453
(C-O)
C-O-C
C-C-O
1356
1313
1356
 C-C) C - C - C
1245
1168
1164
 (O-H)in-planedeformation
1029
1026
(C-H)in-plane-deformation
907
905
(C-C)in-plane-deformation
841
840
(O-H)out-of-plane
deformation
806
803
(C-H)out-of-plane
deformation
782
731
778
734
(C-C)out-of-plane
deformation
692
641
509
639
504
M-O
…..
429
O
IR Spectra of Chrysin
IR Spectra of La(chrysin)3 complex
Thermal Analysis
Thermogravimetric analysis of the complex was carried out to
examine the thermal stability, number and nature of water
molecule(s) present in the complex. The thermogram was
recorded in the temperature range 30-600oC in nitrogen
atmosphere with heating rate 10 oC per minute. Thermal
spectra of the complex revealed that the complex is stable up
to 300oC and does not show any weight loss below this
temperature. This is strong evidence that the complex is
devoid of lattice water as well as coordinated water in the
coordination sphere. The TGA curve shows that the first
weight loss of the complex was observed between the range
56.31-51.86 %, which occurs between the temperature 327289 oC, corresponds to the two molecule of chrysin. After
elimination of first and second molecule, decomposition of
third molecule of chrysin was started simultaneously between
the temperature 534-505 oC. The observed weight loss 28.1527.23 %, which is equivalent to one molecule of chrysin.
Table 4. Thermal analysis data of lanthanum-chrysin complex.
Complex
La(chrysin)3
Temp oC
% Weight loss
Constituents eliminated
Calc.
Obs
314
56.31
51.86
2 molecule of chrysin
526
28.15
27.23
1 molecules of chrysin
Thermal Spectra of La(chrysin)3 complex
1H
NMR Spectra
1H
NMR spectral studies have been carried out to investigate the
solution structure of the lanthanum chrysin complex and its
stability in the solution medium. The 1H NMR spectra of ligand
and its lanthanum metal complex were measured in DMSO-d6
solvent. 1H NMR resonance signals with their tentative
assignments are based on the reports available in the literature.
The resonance signals of coordinated chrysin are found to have
shifted downfield as well as up field as compared to the free
chrysin molecule. The 5-OH proton resonance signal was not
observed in the spectrum of complex. Disappearance of this
resonance signal in the complex spectrum indicates that 5-OH
proton loses during the complexation process and this phenolic
group participates in coordination to the metal ion. These proton
NMR spectrum results suggest that, DMSO is a strongly
coordinating solvent, which coordinate to the metal ion and may
replace the ligand from the coordination sphere and form the
complex. The Uv-Vis spectral results also suggest that DMSO is
strongly coordinating solvent. [23-28].
Table 5.1H NMR chemical shift data of lanthanum-chrysin complexe in
DMSO-d6 on 300 MHz.
Compo
und
7-OH
5-OH
H2’&6’
H-3’,
4’&5’
H-4’
H-3
H-8
H-6
Chrysin 12.83s
10.91s
8.08
7.62m
7.55
6.97s
6.52s
6.22s
La(chrys 12.82
in)3
……
8.05d
7.64m
7.56s
6.96s
6.53s
6.23s
/Ligand
S= singlet, d= doublet and m= multiplet
1H
NMR Spectra of chrysin in DMSO-d6 at 300 MHz.
1H
NMR Spectra of La(chrysin)3 complex in DMSO-d6 at 300 MHz.
Computational details
Molecular modeling studies on chrysin and its complex were
carried out using molecular mechanics (MM+) methods. The
minimized energy of chrysin and La(chrysin)3 complex are
17.1360 and 70.7312 k.cal respectively.
Geometry optimization of chrysin was also carried out via
semiempirical (PM3) and ab initio methods to obtain charge
density on atoms and geometrical parameters. Hydroxyl group
(-OH) at 5th position and oxo group (-C=O) at 4th position
have higher charge density; it suggests these two positions are
most possible chelating sites.
Table 6. Optimized geometrical parameters of chrysin
Bond length
Value (Ǻ)
C(1)-C(2)
C(2)-H(20)
C(2)-C(3)
C(3)-O(4)
C(3)-C(5)
C(5)-C(12)
C(12)-O(13)
O(13)-C(1)
C(5)-C(6)
C(6)-C(8)
C(6)-O(7)
O(7)-H(21)
C(8)-H(22)
1.3562
1.08
1.4382
1.2138
1.4934
1.4165
1.3866
1.3933
1.4893
1.4315
1.2285
0.96
1.08
C(8)-H(9)
1.4325
Bond angle
C(2)-C(3)-O(4)
C(5)-C(3)-O(4)
C(5)-C(6)-O(7)
H(21)-O(7)-C(6)
C(8)-C(6)-O(7)
C(8)-C(9)-O(10)
C(9)-O(10)-H(23)
C(11)-C(9)-O(10)
Value (Ǻ)
126.041
126.073
123.761
109.471
122.798
127.599
109.471
127.5
Bond length
Value (Ǻ)
C(9)-O(10)
O(10)-H(23)
C(9)-C(11)
C(11)-H(24)
C(11)-C(12)
C(1)-C(14)
C(14)-C(15)
C(15)-H(25)
C(15)-C(16)
C(16)-H(26)
C(16)-C(17)
C(17)-H(27)
C(17)-C(18)
C(18)-H(28)
C(18)-H(19)
C(19)-H(29)
C(19)-C(14)
1.2256
0.96
1.4470
1.08
1.3909
1.4318
1.4226
1.08
1.3476
1.08
1.3225
1.08
1.4145
1.08
1.3933
1.08
1.3895
Energy minimized structure of chrysin obtained by using semiemprical (PM3) and
ab initio methods.
Energy minimized structure of chrysin and La(chrysin)3 complex
obtained.[Cyan represents carbon and white and red represent hydrogen and
oxygen]
charge density diagram of chrysin obtained by using semiemprical (PM3) and
ab initio methods.
Conclusion
UV-Visible, IR and 1H NMR studies on lanthanum complex
and chrysin indicate that the metal ion coordinated through 5(OH) and 4-(C=O) groups. Thermogravimetric study shows
that the complex losses three molecules of chrysin. Molecular
Modeling study also supports the above studies.
Proposed structure of La(chrysin)3
Reference
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
J. R. Corbett, The Biochemical Mode of Action of Pesticides. Academic Press, New
York. 1974.
F. Matsumura, Toxicity of Insecticides. Plenum Press, New York. 1985.
R. D. O'Brien, Insecticides, Action and Metabolism. Academic Press, New York.
1967.
M. B. Shimkim, and N. N. Anderson, Proc. Soc. Exp. Biol. Med. 34(1936)135.
N. Noguchi, E. Niki, Radical Biolilgy & Medicine, 28(10)(2000)1538.
B. Halliwell, Biochemical pharmacol., 49(1995)1341
H.J.H. Fenton, J. Chem. Soc.,65(1984)899.
J.J. Van Hammen, Nature (London), 231(1971)79.
P. Wardman, “Atmospheric oxidation and antioxidants” vol.III(Scott,G.Ed.),
Elsevier, Amsterdam, 1993, chapter 4.
V. Cody, E. Middleton and J.B. Harborne, Plant Flovonoids in Biology and
Medicine: Biochemical, Pharmacological and Structure Activity Relationships,
Alan R.Liss, NY, (1986).
V. Cody, E. Middleton and J.B. Harborne and A. Beretz, Plant Flovonoids in Biology
and Medicine II: Biochemical, Cellular and Medicinal properties, Alan R.Liss, NY,
(1988).
J. Wilska-Jeszka, Wlad. Chem., 13(1959)289.
J. Pusz, B. Nitka and S. Wolowiec, Polish J. Chem., 75(2001)795.
14)
15)
16)
17)
18)
19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
J.P. Redfern, Editor,”Thermal Analysis Review”, Santon Instruments, London.
S. Gordon, “Encyclopedia of Sciences and Technology”, MecGraw-Hill Book Co.Inc.,
New York, Toronto and London, (1960)556.
R.C. Mackenzie and B.P. Mitchell, Analyst, 87(1962)420.
Hyperchem. Release 7.51 professional version, Hypercube Inc., Canada.
J. Kang, L. Zhou, X. Lu, H. Liu, M. Zhang and H. Wu, J. Inorg. Biochemistry, 98(2004)
79.
L.J. Porter and K. R. Markham, J. Chem. Soc.,(C), (1970)1309.
K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds,
3rd Edit., John Wiley Interscience, New York, 1978, 264p.
J. R. Ferraro and W.R. Walker, Inorg. Chem. ,4(1965)1382.
V.T. Kasumov, E. Taş, F. Köksal and Ş. Ö.-Yaman, Polyhedron, 24(2005)319.
S. Quici, M. Cavazzini, G. Marzzani, G. Accorsi, N. Armaroli, B. Ventura and F.
Barigelleti, Inorg. Chem., 44(2005) 529.
V. Gutmann, Coord. Chem. Rev., 18(1976) 225.
V. Monga, B.O. Patrick and C. Orving; Inorg. Chem., 44(2005) 2666.
U. Casellato, S. Tamburini, P. Tomasin, P.A. Vigato, S. Aime and M. Botta,
Inorg.Chem.,38(1999)2906.
X.P. Yang, B.-S. Kang, W.K. Wong, C. Y. Su and H.Q. Liu, Inorg. Chem., 42(2003)169.
B. Bleaney, J. Mag. Resonance,8(1972) 91.
THANK YOU