Periasamy Dharmalingam et al. / Journal of Pharmacy Research 2012,5(8),4526-4529
Research Article
ISSN: 0974-6943
Available online through
http://jprsolutions.info
Synthesis, characterization and dioxygenase activity of
tri- and tetradentate ligands containing manganese(II) complexes
Periasamy Dharmalingam* and Ramasamy Elayaperumal1
Department of Chemistry, Urumu Dhanalakshmi College, Tiruchirappalli , TamilNadu, India.
1
Department of Chemistry, J. J. College of Engineering and Technology, Tiruchirappalli, TamilNadu, India.
*
Received on:09-05-2012; Revised on: 14-06-2012; Accepted on:22-07-2012
ABSTRACT
In the present work mononuclear manganese(II) complexes [Mn(L1)Cl2] (where L1= N,N-bis(pyrid-2-ylmethyl)propylamine) and [Mn(L2)Cl2] (where
L2=N,N’-dimethyl-N,N’-bis(pyrid-2-ylmethyl)ethylenediamine) of tri- and tetradentate ligands have been isolated and characterized by elemental analysis,
1
H NMR and UV–Vis spectroscopy. The electrochemical properties of the Mn(II) complexes has been studied in methanol solution using cyclic and
differential pulse voltammetric techniques with a view to relate the electrochemical behavior to the structural aspects and reactivity of the model complexes.
The electronic spectral properties of the complexes have been studied. The cleavage products were analysed by gas chromatography and their percentage of
conversion of catechols to organic products were shown.
KEYWORDS: Manganese(II), catechols, ethylenediamine, propylamine, tetradentate
1.INTRODUCTION
Manganese is an essential trace element for all forms of life. It accumulates in
mitochondria and is essential for their function. The manganese transport
protein, transmanganin, is thought to contain Mn(III). It activates a wide
range of enzymes for example arginase, pyruvate carboxylase and one family
of superoxide dismutases. Mn-containing redox enzymes are omnipresent in
nature and execute a number of vital functions.[1] It is well known that manganese plays a vital role in many biological systems including photosystemII, catalase, manganese-dependent dioxygenases and superoxide dismutase.[2]
Catechol metabolism is an important process both in biologically and environmentally. Two major enzymes play key role in these reaction, catechol
oxidase[3] and catechol dioxygenase. Catechol oxidase is inferred to be involved in plant defense as highly reactive o-quinones[4] auto polymerises to
brown polyphenolic catechol melanins, a process that is thought to protect
the damaged plant from pathogens or insects. Like hemocyanin and tyrosinase, catechol oxidase is a type three copper enzyme.[5] Therefore, most
functional mimics of catechol oxidase are Cu(II) complexes, although catalytically active complex containing other transition metal ion such as Mn, Co
or Ni [6] are also known. Manganese(II) nitrogen species, and especially
Mntrienaq2+, show strong catalytic activity towards the decomposition of
hydrogenperoxide and are used to accelerate the polymerization of vinyl
polymers in the presence of CCl4. Catechol dioxygenases are a part of Nature’s
strategy for degrading aromatic molecules. They are found in soil bacteria and
act in the last step of transforming aromatic precursors into aliphatic products.
Though the active site of these enzymes contains mononuclear iron(II) or
manganese(II) center, various types of mononuclear iron(II) and iron(III)
complexes have been designed and their reactivity with catechol and dioxygen
have been studied. In the last decade, a variety of iron(II)/III) complexes of
*Corresponding author.
Dr. P. Dharmalingam,
Associate Professor,
Department of Chemistry,
Urumu Dhanalakshmi College,
Tiruchirappalli-620019,
Tamilnadu, India.
tri- and tetradentate ligands as models for iron containing enzymes have been
isolated and studied in detail. The design of synthetic models for active site of
extradiol-cleaving enzyme containing manganese is still in a rudimentary stage
due to the paucity of information on the manganese coordination sites. So far,
only a few manganese(II) complexes of tetradentate ligands have been studied as models for manganese-dependant catechol dioxygenase enzymes. Also,
the manganese(II) complexes reported already show only oxidation products, that is, quinone as the final product with small amounts of cleavage
products. In this paper we report the synthesis and structural and spectroscopic characterization of two mononuclear manganese(II) complexes of triand tetradentate ligands such as N,N-bis(pyrid-2-ylmethyl)propylamine (L1)
and N,N’-dimethyl-N,N’-bis(pyrid-2-ylmethyl)ethylenediamine (L2) that
serve to model the chemistry of metal-catalyzed catechol degradation.The
aim of the present work will be to study the interaction of various substituted catechols with the Mn(II) complexes synthesized to establish the nature of enzyme-substrate interaction and also to obtain an insight into the
mechanism of cleavage of catechols by these enzymes. The present linear triand tetradentate ligands are expected to offer different coordination geometry
around the metal center during oxygenation reaction. Also, it would be interesting to make a correlation between the coordination geometry and reactivity of model complexes.
2.MATERIALS AND METHODS
The chemicals used include pyridine-2-carboxaldehyde, n-propylamine N,N‘dimethylethylenediamine, 2-chloromethylpyridine hydrochloride,
manganese(II) chloride tetrahydrate, (Aldrich), sodium triacetoxyborohydride,
4-methylcatechol, sodium borohydride, 3,5-di-tert-butylcatechol (Aldrich),
3-methylcatechol (Acros), catechol (Loba, India), tetrahydrofuran,
dichloromethane, ethylacetate and triethylamine (Merck, India) were used as
received. Microanalyses were performed at Sophisticated Test and Instrumentation Centre (STIC), Cochin University, Kerala. The electronic spectra
were recorded on an Agilent 8453 diode array spectrophotometer. 1H NMR
spectra were recorded on a Bruker 200 MHz NMR spectrometer. Cyclic
voltammetry (CV) and differential pulse voltammetry (DPV) were performed
in a single compartment cell with a three electrode system using a EG & G
PAR273 potentiostat/Galvanostat equipped with Pentium-IV computer.
EG&GM270 software was used to acquire the data. The working electrode
Journal of Pharmacy Research Vol.5 Issue 8.August 2012
4526-4529
Periasamy Dharmalingam et al. / Journal of Pharmacy Research 2012,5(8),4526-4529
was Pt sphere (0.2866 cm2), counter electrode was Pt plate and the reference
electrode was a Ag/AgNO3 electrode. The supporting electrolyte was 0.1 M
TBAP. The catechol cleavage activity of the complexes toward H2DBC was
examined by exposing a solution of manganese(II)-DBC2− adduct generated
in situ in methanol to molecular oxygen. Kinetic analyses of the catechol
cleavage reactions were carried out by time dependent measurement of the
disappearance of the DBC2−-to-manganese(II) LMCT band in presence and
absence of chloride ions. The oxygenated products of H2DBC were identified by GC-MS, quantified by GC using Hewlett-Packed HP 6890 series gas
chromatograph.
over an anhydrous sodium sulphate, followed by rotaevaporation to yield
L2 as a yellowish brown liquid. Yield: 5.34 g ( 81 % ). 1H NMR (200 MHz,
CDCl3): δ 8.54-7.36 (m, 8H), 3.91 (s, 4H), 2.28 (s, 4H), 2.10 (s, 6H).
2.2
Synthesis of Manganese(II) Complexes
[Mn(L1)Cl2] (1)
[Mn(L1)Cl2] was prepared by adding MnCl2.4H2O (0.198 g, 1 mmol) in
methanol (10 mL) to a solution of L1 (0.24 g, 1 mmol) in methanol, stirred for
30 minutes, and then cooled. The white colored complex was filtered off,
washed with cold methanol and diethylether, and then dried under vacuum.
Yield: 0.19 g (80 %).
2.1 Synthesis of Ligands
Synthesis of N,N-bis(pyrid-2-ylmethyl)-n-propylamine (L1)
This was prepared by a procedure reported previously.[7] To a mixture of
alkylamine (4.5 mmol) and sodium triacetoxyborohydride (3.75 g, 17.7 mmol)
in dichloromethane (100 mL) was added pyridine-2-carboxaldehyde (1.45 g,
13.5 mmol) and stirred for 18 h. The reaction was quenched with sodium
hydrogencarbonate and extracted with ethylacetate (3×150 mL). The organic
fractions were combined, dried (Na2SO4), and the solvent was removed under
reduced pressure. The residue was redissolved in tetrahydrofuran (50 mL)
and treated with NaH (0.22 g, 9.1 mmol). After the mixture was stirred for 2
h, the solvent was removed and the residue was extracted with
dichloromethane. The extracts were combined, and the solvent was evaporated
under reduced pressure to obtain L1 as a yellow oil, which is used without
further purification. Yield: 2.97 g (91 %). 1H NMR (200 MHz, CDCl3): δ
8.54-7.36 (m, 8H), 3.91 (s, 4H), 2.28 (t, 2H), 1.32 (m,2H), 1.11 (t,3H).
[Mn(L2)Cl2] (2)
This was synthesized by using same procedure as described for the
[Mn(L1)Cl2] by reacting MnCl2.4H2O (0.20 g, 1 mmol) with L2 (0.27 g, 1
mmol). Yield: 0.29 g (72 %).
N
N
N
MeOH
N
N
+
N
Mn
MnCl2.4H2O
Cl
H3C
N
H3C
O
N
H3C
H3C
N
N
+
H3C
CH3
MeOH
N
N
-
Cl
N
Cl
Mn
Cl
-
N
CH3
N
MnCl2. 4 H2O
+
H2N
N
CH3 Na(CH3COO)3BH
N
THF, 24 h
1.RESULTS AND DISCUSSION
L1
Cl
Cl
H3C N N CH3
N + H H
+
N
Scheme 2.2. Synthesis of manganese(II) complexes
N
H3C
2 TEA
EtOH: EtOAc
Stirred 5 days
N
CH3
N
N
N
L2
Scheme 2.1. Synthesis of ligands
Synthesis of N,N’-dimethyl-N,N’-bis(pyrid-2-ylmethyl)
ethylene diamine (L2)
This was prepared by a modified procedure reported already.[8]
To a solution of N,N’-dimethylethylenediamine 2.15 g (24.4
mmol) and triethylamine 2.5 g ( 24.7 mmol) in 90mL of
ethylacetate was added 10 mL of an ethanolic solution of 2chloromethylpyridine (obtained by the neutralization of
monohydrochloride using potassium carbonate solution with
vigorous shaking). The mixture was allowed to stir at room
temperature for 5 days. After filtration, the solvent was removed
under reduced pressure to give yellowish oil. To this was added
20 mL of ethylacetate; the mixture was filtered and the volume
of the filtrate was reduced to ~5 mL by rotary evaporation.
The remaining solution was extracted with chloroform and dried
3.1 Synthesis of the ligands and the complexes
The ligands were reacted with equimolar amount of MnCl2⋅4H2O in methanol to give mononuclear manganese(II) complexes in good yield. The tripodal/linear tri- and tetradentate ligands L1 and L2 are expected to impose
either distorted square pyramidal or trigonalbipyramidal and distorted octahedral geometry around the manganese(II) center respectively. Since the
manganese ion is in +2 oxidation state, the metal complexes of pyridinebased ligands (L1 and L2) offered high-spin d5 system as reported in the
literature. Conductivity studies in methanol solution (ΛM, 80-105 Ω-1 cm2
mol-1) suggest that one of the chloride ions is not coordinated to the metal
center.
Table 3.1. Microanalytical data of ligands and Mn(II) complexes
Ligands &
Colour
complexes
Empirical
Molecular
formula
weight
C
Elemental analysis Calculated (found) (%)
H
N
L1
L2
yellow
yellow
C 15H 19N 3
C 16H 22N 4
241.157
270.373
74.65(74.62)
71.08(71.06)
7.94(7.92)
8.20(8.16)
17.41(17.38)
20.72(20.70)
[Mn(L1)Cl2]
White
MnC 15H19N 3Cl2
366.033
49.07(49.04)
5.22(5.18)
11.48(11.46)
[Mn(L2)Cl2]
White
MnC 16H22N 4Cl2
396.217
48.50(48.48)
5.59(5.56)
14.14(14.10)
3.2 Electronic Spectra
The complexes show two bands around 250 and 215 nm, which are assigned
as the inter -electronic transitions between π→π* and n→π*. A new
visible band (650-770 nm) appears on adding one equivalent of catechols
Journal of Pharmacy Research Vol.5 Issue 8.August 2012
4526-4529
Periasamy Dharmalingam et al. / Journal of Pharmacy Research 2012,5(8),4526-4529
pretreated with two equivalents of triethylamine to the present complexes in
methanol solution. This is attributed to catecholate-to-Mn(II) charge-transfer transition[9-10] involving catecholate orbital and dπ* orbital of manganese(II).
The position of the band strongly depends on the nature of the substituents
on the catechol ring. The band position is shifted to higher energies when the
substituents are varied from electron-donating to electron-withdrawing.[11-15]
The energy of the LMCT band decreases in the order: H2CAT > 3MeH2CAT > 4Me-H2CAT > H2DBC (Table 3.2, Scheme 3.3). Upon increasing the electron density on the catecholate oxygen atom, the energy of the
catecholate orbitals increases and hence the DBC2- adducts of the manganese(II)
complexes show bands at lower energies than the other catecholate adducts.
obtain 2, the redox potential of the Mn(II)/Mn(III) couple is shifted to lower
negative region leading to decrease the Lewis acidity of Mn(II) center. This is
caused by the steric crowd of the tridentate ligand which removes one of the
coordinated chloride ions from the coordination sphere and hence the high
Lewis acidity.
Table 3.3. Electrochemical dataa of mononuclear manganese(II) complexes in methanol solution at 25 ± 0.2 °C
Complex
Epa(mV)
Epc(mV)
∆E (mV)
E1/2
Redox
p
CV(mV)
DPV(mV)
process
553.5
MnII®MnIII
OH
OH
OH
OH
[Mn(L1)Cl2]
612.5
494.5
118
553.5
928.5
MnIII®MnIV
OH
OH
OH
OH
[Mn(L2)Cl2]
412.5
328.5
84
370.5
373.5
MnII®MnIII
776.5
688.5
88
732.5
751.5
MnIII®MnIV
4Me-H2CAT
3Me-H 2CAT
H2 CAT
Scheme 3.3. Differently substituted catechols used in this study
Also the catecholate adducts show a remarkable dependence on the type of
ligand and the LMCT band energy shifted to higher energy when replacing
the tridentate ligand by tetradentate one. A similar trend in shift is observed
for all the catecholate adducts except H 2DBC. Upon replacing the tridentate
ligand in 1 by tetradentate ligand to obtain 2 causes a negative charge built on
manganese(II) center to increase, and as a result the dπ* orbital of the
manganese(II) is destabilized leading to increase in energy gap between the
dπ* orbital and catecholate orbitals and hence the observed increase in LMCT
band energy.
Table 3.2. Electronic spectral dataa (λ max in nm; εmax in M-1 cm-1 in
paranthesis) for manganese(II)-catecholate adductsb in methanol solution
Complex
[Mn(L1)Cl2]
[Mn(L2)Cl2]
H2DBC c
4Me-H2CAT c
760 (440)
721 (480)
765 (340)
698 (160)
3Me-H2CAT c
H2CAT c
678 (680)
663 (480)
660 (300)
654 (100)
a
Concentration of manganese(II)-catecholate adducts: 1 × 10-3 M. b The ratio
of added ligands to manganese was 1:1; the anions were generated by adding
two equivalents of triethylamine. c H2DBC = 3,5-di-tert-butylcatechol, 4MeH2CAT = 4-methylcatechol, 3Me-H2CAT = 3-metylcatechol, H2CAT = catechol
3.3 Electrochemical Behavior of the Manganese(II) Complexes
The electrochemical features of the manganese(II) complexes were investigated in methanol solution by employing cyclic (CV) and differential pulse
voltammetry (DPV) on a stationary platinum-sphere electrode. The redox
potentials are summarized in Table 3.3. By comparison to the electrochemical data given in the literature for similar type of manganese(II) complexes,
the following assignments can be made for the present system. All the present
complexes display one electron redox process around E1/2 = 370-590 mV
with ∆Ep = 80-120 mV, corresponding to Mn(II)/Mn(III) redox couple.
Another one around 700-980 mV originating from the Mn(III)/Mn(IV) redox
couple. The E1/2 values of the potentials follow the trend 1 > 2, reflecting a
decrease in Lewis acidity of the Mn(II) center. Upon replacing tridentate
ligand in 1 by tetradentate ligand to obtain 2, the negative charge built on the
metal center increases causing a shift in redox potential to lower negative
region and expected to exhibit lower interaction with catechols. This trend is
in good agreement with the results of the electronic spectral data (cf. above).
Upon replacing the tridentate ligand in 1 by linear tetradentate ligand to
a
Potential measured vs Ag(s)/Ag+ (0.01 M, 0.10 M TBAP)
3.4 Kinetic Investigations of Manganese(II) Complexes
The kinetics of oxygenation of the DBC2- adducts of the present complex
generated in situ by treating them with one equivalent of H2DBC and two
equivalents of Et3N in methanol solution, were investigated by monitoring
the disappearance of the DBC2-→Mn(II) ligand to metal charge-transfer
band (Figure 3.1) under 1 atm of O2 at room temperature. The products of
the cleavage of H2DBC in methanol (Table 3.3) are identified 3,5-di-tertbutyl-2-hydroxyhexa-2,4-dienedioic acid and 3,5-di-tert-butyl-[1,2]benzoquinone, by GC-MS and quantified by GC analysis.The electronic
absorption spectrum of the product solution showed an intense absorption
at 400 nm indicating the production of 3,5-di-tert-butylquinone. It is clear
that the presence of a vacant or solvent-coordinated site on the iron(III)
center of the catecholate adducts is essential for dioxygen attack to achieve
cleavage of catechols instead of oxidised products.[18-19] All the present
complexes also afford major amount of quinone (25-75%) as the oxidised
products and small amount of intradiol cleavage products (1-16%). It is
remarkable that the catecholate adducts derived from the manganese(II)
complexes of tridentate ligands show intradiol cleavage products 7-15 % in
addition to the oxidised product quinone. This illustrates that the vacant
coordination site in these complexes may be used to form peroxo type
intermediate as observed in the iron dependent catechol-cleaving enzymes as
well as in their model complexes. Interestingly, complex 2 also showed the
formation of intradiol cleavage products on exposure to molecular oxygen
but with poor yield.
0.3
0.25
0.2
Absorbance
H 2 DBC
0.15
0.1
0.05
0
400
500
600
700
800
900
1000
1100
Wavelength (nm)
Figure 3.1. Progress of the reaction of adduct [Mn(L1)(DBC)] derived
from [Mn(L1)Cl2] with O2 in methanol solution. The disappearance of
the DBC2−-to-Mn(II) charge-transfer band is monitored.
Journal of Pharmacy Research Vol.5 Issue 8.August 2012
4526-4529
Periasamy Dharmalingam et al. / Journal of Pharmacy Research 2012,5(8),4526-4529
The second order rate constant (kO2 = 3 - 10 M -1 s-1) for the adducts
[Mn(L)(DBC)] derived from complexes of the type [Mn(L)(Sol)2]2+ is two
fold higher than those (kO2 = 1.0 - 4.0 M-1 s-1) for the adducts derived from
complexes 1 & 2. This is expected of higher Lewis acidity of the solvated
manganese(II) complexes, which favors the binding of catechols and dioxygen.
The reactivity of the present complexes follow the trend: [Mn(L1)(DBC)] >
[Mn(L2)(DBC)], reflecting a decrease in reaction rate along the series. This
trend is in good agreement with the spectral and electrochemical behavior of
the complexes. Interestingly, on replacing the tridentate ligand by tetradentate
ligand, the reactivity increases illustrating that the weak interaction of DBC2to the manganese(II) complexes of tetradentate ligand.
Table 3.3. Kinetic dataa oxygenation reaction of H2DBC catalysed by
manganese(II) complexes and the cleavage products
Complex
kobs, s-1
t1/2, s
kO2 M-1s-1
Conversion
3.
4.
5.
6.
7.
8.
Cleavage products in %
Intradiol
Quinone
[Mn(L1)Cl2]
0.0076
091.2
3.59
88.3
15.5
24.8
[Mn(L2)Cl2]
0.0022
314.6
1.04
97.4
1.3
67.5
a
ko2 = kobs/[O2]. The solubility of O2 in methanol is accepted to be 2.12 mM at
25°C. The kinetic data were obtained by monitoring the disappearance of the
DBC2−-to-Mn(II) LMCT band.
CONCLUSIONS
Two new mononuclear manganese(II) complexes for tri- and tetradentate
ligands have been isolated and studied as models for manganese(II) dependent catechol dioxygenase enzymes. Complexes derived from tri- and
tetradentate ligands are expected to have trigonal bipyramidal and octahedral
geometry respectively. The conductivity studies of the present complexes
showed that one of the chloride ions is not coordinated to the metal center in
methanol solution. Upon interaction of the present complexes with various
catechols, the catecholate dianion binds to the metal center by replacing the
coordinated chloride ions. The catecholate-to-manganese(II) LMCT band
are observed at longer wavelengths (650-770 nm) as a broad band, which is
typical of bidentate coordination of catechols. When the catecholate adducts
of the complexes are exposed to dioxygen, molecular oxygen is activated to
give cleavage products and oxidised products of catechols. The rate of oxygenation increases with increasing the Lewis acidity of the manganese(II)
center whereas the product yield increases with a decrease in Lewis acidity.
Very interestingly, we have observed the cleavage instead of simple oxidation
of catechols by the manganese(II) complex of tridentate ligand indicating that
a vacant coordination site on the metal center plays a vital role in the oxygenation and oxidation chemistry of manganese(II) complexes.
ACKNOWLEDGEMENTS
The authors thank almighty God for their immaculate genesis in this world to
lead the right path in their career. Thanks are also due to the Head, Department of Chemistry, UDC, Trichy for providing Laboratory facilities.
9.
10.
11.
12.
13.
14.
15.
16.
17.
REFERENCES
1. Sigel A, Sigel H, Manganese and Its Role in Biological Processes.
Metal Ions in Biological Systems; Vol. 37, Marcel Dekker: New
York, 2000.
2. (a) Penner-Hahn TE, Pecoraro VL, Ed. In Manganese Redox Enzymes, VCH: New York, 29, 1992. (b) Wieghardt K, The Active
Sites in Manganese-Containing Metalloproteins and Inorganic
Model Complexes, Angew. Chem., Int. Ed. Engl., 28, 1989, 1153
(c) Pecoraro VL, Baldwin MJ, Gelasco A, Chem. Rev., 94, 1994,
807.
18.
19.
Karlin KD Tyeklar Z, Eds. Bioinorganic Chemistry of Copper,
Chapman & Hall, New York, 1993.
Solomon EI, Chen P, Metz M, Lee SK, Palmer AE, Oxygen Binding,
Activation, and Reduction to Water by Copper Proteins, Angew.
Chem., Int. Ed.Engl., 40, 2001, 4570.
Kaim W, Ral J, Copper—A “Modern” Bioelement, Angew. Chem.,
Int. Ed. Engl., 108,1996,47.
Klabunde T, Eicken C, Sacchettini JC, Krebs B, Crystal structure
of a plant catechol oxidase containing a dicopper center, Nat. Struct.
Biol., 5, 1998, 1084.
Britovsek GJP, England J, White AJP, Non-heme Iron(II) Complexes Containing Tripodal Tetradentate Nitrogen Ligands and Their
Application in Alkane Oxidation Catalysis, Inorg. Chem., 44, 2005,
8125.
Gupta N, Mukerjee S, Mahapatra S, Ray M, Mukherjee R, Triply
bridged diruthenium complexes with [RuIII2(.mu.-O)(.mu.O2CCH3)2]2+ and [RuIVRuIII(.mu.-O)(.mu.-O2CCH3)2]3+
cores: synthesis, spectra, and electrochemistry, Inorg. Chem., 31,
1992, 139.
Hitomi Y, Ando A, Matsui H, Ito T, Tanaka T, Ogo S, Funabiki T,
Aerobic Catechol Oxidation Catalyzed by a Bis(µ-oxo)
dimanganese(III,III) Complex via a Manganese(II)? Semiquinonate
Complex, Inorg. Chem., 44, 2005, 3473.
Triller MU, Pursche D, Hsieh WY, Pecoraro VL, Rompel A,
Krebs B, Catalytic Oxidation of 3,5-Di-tert-butylcatechol by a
Series of Mononuclear Manganese Complexes:? Synthesis,
Structure, and Kinetic Investigation, Inorg. Chem., 42, 2003, 6274.
Viswanathan R, Palaniandavar M, Balasubramanian T and Muthiah
P T, Synthesis, structure, spectra and redox chemistry of iron(III)
complexes of tridentate pyridyl and benzimidazolyl ligands, J.
Chem. Soc., Dalton Trans., 12, 1999, 2519.
Viswanathan R, Palaniandavar M, Balasubramanian T and Muthiah
T P, Functional Models for Catechol 1,2-Dioxygenase. Synthesis,
Structure, Spectra, and Catalytic Activity of Certain Tripodal
Iron(III) Complexes, Inorg. Chem., 37,1998, 2943.
Velusamy M, Palaniandavar M, Gopalan R S and Kulkarni G U,
Novel Iron(III) Complexes of Tripodal and Linear Tetradentate
Bis(phenolate) Ligands: Close Relevance to Intradiol-Cleaving
Catechol Dioxygenases, Inorg. Chem., 4, 2003, 8283.
Velusamy M, Mayilmurugan R and Palaniandavar M, Iron(III)
Complexes of Sterically Hindered Tetradentate Monophenolate
Ligands as Functional Models for Catechol 1,2-Dioxygenases: The
Role of Ligand Stereoelectronic Properties, Inorg. Chem.,43, 2004,
6284.
Velusamy M, Mayilmurugan R and Palaniandavar M, Functional
Models for Catechol Dioxygenases: Iron(III) Complexes of Certain
cis-facially coordinating linear 3N Ligands, J. Inorg. Biochem., 99,
2005, 1032.
Mialane P, Tehertanov L, Banse F, Sainton J, Girerd J,
Aminopyridine Iron Catecholate Complexes as Models for Intradiol
Catechol Dioxygenases. Synthesis, Structure, Reactivity, and
Spectroscopic Studies, Inorg. Chem., 39, 2000, 2440.
Yamahara R, Ogo S, Watanabe Y, Funabiki T, (Catecholato)iron(III)
complexes with tetradentate tripodal ligands containing substituted
phenol and pyridine units as structural and functional model
complexes for the catechol-bound intermediate of intradiol-cleaving
catechol dioxygenases, Inorg. Chim. Acta, 300, 2000, 587.
Ito M, Que L, Biomimetic Extradiol Cleavage of Catechols: Insights
into the Enzyme Mechanism, Angew. Chem., Int. Ed. Engl.,
36,1997, 1342.
Bugg TDH, Lin G, Solving the riddle of the intradiol and extradiol
catechol dioxygenases: how do enzymes control hydroperoxide
rearrangements?, Chem. Commun., 11, 2001, 941.
Source of support: Nil, Conflict of interest: None Declared
Journal of Pharmacy Research Vol.5 Issue 8.August 2012
4526-4529