Structurally characterized mononuclear Mn(II) complex: Functional model for catecholase and phenoxazinone synthase activities

Article abstract of DOI:10.1016/j.ica.2017.04.043

Structurally characterized [Mn(L)₂(OH₂)₂] (1) [L?=?3-methoxy-4-hydroxy benzaldehyde] with C2/c space group and distorted octahedral molecular geometry is found to show catecholase as well as phenoxazinone synthase activities in MeOH at room temperature. Each of the reactions with 1 as catalyst is found to be of first order with turn over numbers 5.98?×?10² and 3.15?×?10²?h^?1, respectively. Catalyst-substrate adduct as intermediate is trapped by mass spectrometry for both the activities.

Full text of DOI:10.1016/j.ica.2017.04.043

Accepted Manuscript
Research paper
Structurally characterized mononuclear Mn(II) complex: functional models for
catecholase and phenoxazinone synthase activities
Sarat Chandra Kumar, Ayon Kanti Ghosh, Jhy-Der Chen, Rajarshi Ghosh
PII:
S0020-1693(16)31067-2
http://dx.doi.org/10.1016/j.ica.2017.04.043
ICA 17548
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
28 December 2016
13 April 2017
17 April 2017
Please cite this article as: S.C. Kumar, A.K. Ghosh, J-D. Chen, R. Ghosh, Structurally characterized mononuclear
Mn(II) complex: functional models for catecholase and phenoxazinone synthase activities, Inorganica Chimica
Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.04.043
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1
1
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Structurally characterized mononuclear Mn(II) complex: functional models for
catecholase and phenoxazinone synthase activities
a
a
b
a,*
3
4
5
6
7
Sarat Chandra Kumar , Ayon Kanti Ghosh , Jhy-Der Chen , Rajarshi Ghosh
a
Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b
Department of Chemistry, Chung Yuan Christian University, Chung Li, Taiwan 32023
Abstract
8
9
0
1
2
3
Structurally characterized [Mn(L)
2
(OH
2
) ] (1) [L = 3-methoxy-4-hydroxy benzaldehyde] with
2
C2/c space group and distorted octahedral molecular geometry is found to show catecholase as
well as phenoxazinone synthase activities in MeOH at room temperature. Each of the reactions
1
1
1
1
2
2 -
with 1 as catalyst is found to be of first order with turn over numbers 5.98 × 10 and 3.15 × 10 h
1
, respectively. Catalyst-substrate adduct as intermediate is trapped by mass spectrometry for
both the activities.
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19
Keyword: Manganese, Schiff base, catecholase activity, phenoxazinone synthase activity
____________
*Corresponding author, E. mail: rghosh@chem.buruniv.ac.in

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1. Introduction
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Design and synthesis of transition metal complexes as structural and/or functional model for
the active site structures of a number of metalloenzymes are area of growing research interest [1-
3]. Catechol-quinone aerial oxidation (Scheme 1) reaction catalysed by the enzyme catecholase
is of importance because the quinone formed generally autopolymerizes to generate brown
pigments which protect the plant systems from pathogens, pests, etc. Just after the publication of
active site structure of catecholase as antiferromagnetically coupled dinuclear Cu(II) system [4] a
number of researchers round the globe started to synthesize different dinuclear Cu(II)
compounds to mimic the catecholase [5-7]. Not only dinuclear Cu(II), but also other transition
metal compounds which include Mn, Ni, Fe, Co, Zn, V of different nuclerities [8-10] respond in
catalyzing this very oxidation reaction. Phenoxazinone synthase, another copper containing
protein, produced by Streptomyces antibioticus oxidises 2-aminophenol to phenoxazinone
chromophore (Scheme 2). Modelling phenoxazinone chromophore [11, 12] is important as the
antineoplastic agent actinomycin D, which contains this chromophore, is used as an important
antitumour agent [13].
35
36
37
38
In this present context, we have designed and synthesized one mononuclear diaquo Mn(II)
complex [Mn(L)
2
(OH
2
2
) ] (1) [L = 3-methoxy-4-hydroxy benzaldehyde] [14] which is catalyzing
the aerial oxidation of o-phenol and o-aminophenol, to o-quinone and 2-aminophenoxazine-3-
one, respectively.
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41

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45
46
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48
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50
51
52
Scheme 1. Catecholase activity
Scheme 2. Phenoxazinone synthase activity
2. Experimental
2.1. Materials
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54
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High purity 3-methoxy-4-hydroxy-benzaldehyde (Lancaster,UK), manganese bromide
tetrahydrate (E. Merck, India) were purchased from respective concerns and used as
received.MeOH-H O (3:1) mixture was used as solvent in this reaction conditions.
2
56
2.2. Physical measurements
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58
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60
61
62
63
Elemental analyses (carbon, hydrogen and nitrogen) were performed on a PerkinElmer
-
1
2400 CHNS/O elemental analyser. IR spectrum was recorded (KBr discs, 4000-300 cm )
using a PerkinElmer RX1 FTIR spectrometer. Ground state absorption was measured
with a JASCO V-530 UV-Vis spectrophotometer.
susceptibilities were determined on a PAR 155 vibrating sample magnetometer with
Hg[Co(SCN) ] as reference. Diamagnetic corrections were made using Pascal’s constants.
Thermal analysis was done on PerkinElmer Diamond TG/DTA system.
Room temperature magnetic
4

4
64
2.3. Preparation of 1
6
6
6
5
6
7
The golden coloured mononuclear
1
was initially synthesized by reaction of
MnBr
solvent mixture. Typical synthesis is described below:
A methanol-water solution (5 ml) of L (0.1521 g, 1 mmol) was added dropwise to a
solution of MnBr .4H O (0.2147 g, 1 mmol) in the same solvent (10 ml) and addition was
2
.4H
2
O with L in 1:2 molar ratio at room temperature (298 K) in MeOH-H
2
O
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72
73
74
75
76
77
2
2
done keeping the solution on magnetic stirrer. The very pale pink solution of manganese
was turned to yellow, to brown, to dark brown clear solution during the course of
reaction. The dark brown solution was filtered and the supernatant liquid was kept in air
for slow evaporation. After a few days
dried in vacuo over silica gel indicator. Yield, 0.1863 g (87% based on metal salt). Anal
cal. for C16 Mn (1): C, 48.86; H, 4.61; O, 32.55 Found: C, 48.82; H, 4.60; O, 32.53.
1 that separated out was washed in hexane and
H
18
O
8
-
1
IR cm (KBr): 3300 (s), 2980-2900(w). UV-Vis (MeOH, nm): λmax (ε) at 230 (12550),
278 (8560), 308 (8460).
78
2.4. X-ray diffraction study
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A summary of the crystallographic data and structure refinement parameters is given
3
in Table 1. Single crystals [size: 0.2 × 0.3 × 0.4 mm ] of
1 were obtained by slow
evaporation of MeOH-H O solution of the reaction mixture. Light orange crystals suitable
2
for X-ray crystallographic analysis were selected following examination under a
microscope. Diffraction data 295(2) K were collected on a Bruker AXS P4
diffractometer using Mo-K radiation (λ = 0.71073 Å). Systematic absence led to the
α
identification of space group C2/c. The structure was solved by direct methods, and the
2
structure solution and refinement were based on |F| . All non-hydrogen atoms were

5
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90
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92
refined with anisotropic displacement parameters whereas hydrogen atoms were placed in
calculated positions when possible and given isotropic
to which they are bonded. At convergence the final residuals were R1 = 0.0292; wR2 =
0.0752 with I (I), goodness-of-fit = 1.048. The final differences Fourier map showed
U values 1.2 times that of the atom
>2σ
-
3
the maximum and minimum peak heights at 0.197 and -0.186 eÅ . All calculations were
carried out using SHELXTL 5.10. [15].
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3
4
3. Results and discussion
9
3.1. Synthesis and formation
95
96
97
98
Light orange coloured crystalline hexacoordinated mononuclear complex [Mn(L)
2
(OH
2
) ] (1)
2
resulted in good yield through single pot reaction of 1:2 molar ratio of the manganesel(II)
bromide tetrahydrate and 3-methoxy-4-hydroxy benzaldehyde (L) in methanol-water solution.
The synthetic procedure is summarized in Scheme 3.
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Scheme 3
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103
104
105
The air-stable moisture-insensitive complex is moderately soluble in
dimethylformamide. Analytical data for all the complexes are consistent with the
calculated values.
3.2. Spectroscopic studies and magnetic measurement
-
1
106
107
108
In IR, one well resolved peak is observed at 3300 cm attributed to the ν(OH)
-
1
stretching mode [16]. Weak bands in the range 2980-2900 cm are assignable to the
aliphatic C-H stretching vibration [16]. The complex displays intense absorption bands in

6
5
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110
111
112
113
114
solid state at 280 and 308 nm which is assignable to a π-π* transition [17]. The d
hexacoordinated high-spin manganese(II) complex does not contain any excited state with
same spin multiplicity as in the ground state which vitiates bands in the visible region
[17]. The room-temperature solid-phase magnetic susceptibility measurement shows that
the manganese(II) complex have moments close to their spin-only value (S = 5/2): 5.88
BM.
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3.3. X-ray structure
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121
122
123
124
125
126
127
128
129
130
131
Crystals of
cell. The asymmetric unit contains a half Mn(II) cation, one L and one H
the Mn(II) cation is located on a C2 axis. The ORTEP diagram is shown in Fig. 1. The
coordination geometry around manganese(II) center in [Mn(L) (H O) ] ( ) is best
described as distorted octahedron with MnO chromophore. Among the six coordinating
1
conform (Table 1) to the space group C2/c with four molecules in a unit
2
O molecule and
2
2
2
1
6
oxygen atoms two are from phenolic oxygens (O1 and O1A), other two from methoxy
groups (O2 and O2A) and the rest two are from the coordinated water molecules (O4 and
O4A). The Mn-O bond distances range from 2.3473(14) to 2.0914(13) Å and the
difference
∆ between the longest and shortest Mn-O bonds amounts 0.2559 Å. The
geometric distortion of an octahedron can be characterized by the asymmetry parameter
namely, axial distortion D [18]. The axial distortion can result in either a compression or
elongation (four short and two long bonds) of the octahedron along the z axis. Positive
value of D indicates elongation while negative values denote the occurance of
compression. Assuming the two phenolic oxygen atoms [O(1) and O(1A)] in the axial
[consideration from bond distance values, each of Mn-O(1) and Mn-O(1A) distance is
2.0914(13) (Table 2)] and the methoxy- [O(2) and O(2A)] and water oxygen atoms [O(4)

7
1
32
33
and O(4A)] in the equatorial plane in
1
, the negative D value [19] indicates axial
1
compression of the octahedron which is also relevant from the bond distances (Table 2).
3.4. Thermogravimetric analysis
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The important role of water molecules in the crystal packing provoked us to study the
thermal behavior of the complex. The thermal behavior of
1 was followed up to about
800°C in a static nitrogen atmosphere with a heating rate of 5°C per minute.
1
decomposes in three steps (Fig. 2). The first step between 97.20 and 221.43°C
corresponds to the endothermic process with the loss of two coordinated water molecules
with the mass loss of 7.02% (calcd. 9.15%). The release of branchings (here two aldehyde
and two methyl groups) take place in the second step (221.43°C-375.63°C). The
experimental mass loss 22.80% agrees well with the calculated mass loss 22.38%. In the
last step (375.63°C-804.85°C), the analysis results in the formation of MnO
(experimental mass loss = 33.78%, calculated mass loss = 46.28%). The formation of
MnO is also confirmed from infrared spectral analysis of the end ash. A band in the
2
2
-
1
range 850-980 cm confirms the band for oxomanganese.
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3.5. Catecholase activity
3.5.1. Spectrophotometric studies
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The catechol-quinone oxidation reaction was carried out using 3,5-di-tert-butyl
catechol (3,5-DTBC) as substrate. The oxidized product 3,5-di-tert-butyl quinone (3,5-
DTBQ) is highly stable and shows a maximum absorption at 401 nm in methanol [20].
Spectral bands at 230, 278 and 308 nm appear in the electronic spectrum of
3,5-DTBC shows a single band at 282 nm. Methanolic solution of was added in 100
equivalents of 3,5-DTBC under aerobic conditions and the repetitive UV-Vis spectral
1, whereas
1

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scan was recorded (Fig. 3). Conversion of 3,5-DTBC to 3,5-DTBQ was indicated by slow
colour change from light yellow to deep brown. In UV-Vis spectrophotometry, after this
addition, the spectral scan shows very smooth increase of a quinone band at around ~390
nm which shifts ultimately to 401 nm as reported by Krebs et al [21]. 3,5-DTBQ
produced in the reaction was purified by column chromatography. It was then isolated
1
1
and identified by HNMR spectroscopy (Fig. S1; Supporting information). HNMR
(CDCl , 400 MHz): δ = 1.16 (s, 9H), 1.20 (s, 9H), 6.15 (d, J = 2.4 Hz, 1H), 6.86 (d, J =
3
H
2.4 Hz, 1H). Chromatographically pure 3,5-DTBQ was also characterized by determining
its melting point (~110°C) which agreed well with that reported in literature [22].
164
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The time dependent change in absorbance at a wavelength of 401 nm, characteristic of
3,5-DTBQ in methanol, was observed for 25 min to comprehend the reaction kinetics and
find out the reaction rate between 3,5-DTBC and 1. The difference in absorbance ∆A at
401 nm, was plotted against time to obtain the rate/velocity for that particular catalyst to
substrate concentration ratio (Fig. 4). A first-order catalytic reaction is observed, with rate
-
3
-1
5.59 × 10 min .
170
3.5.2. Enzyme kinetics study
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Kinetic experiments were performed spectrophotometrically with 1 and the substrate
3,5-DTBC in methanol, thermostated at 20°C. 0.04 ml of the complex solution, with a
-
4
constant concentration of 1 × 10 M, was added to 2 ml of 3,5-DTBC of a particular
-
3
-2
concentration (varying its concentration from 1 × 10 M to 1 × 10 M) to achieve the
-
4
final concentration of the complex as 1 × 10 M. The conversion of 3,-5-DTBC to 3,5-
DTBQ was monitored with time at a wavelength of 401 nm for solutions in MeOH. The
rate for each concentration of the substrate was determined by the initial rate method.

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The rate versus concentration of substrate data were analyzed on the basis of
Michaelis-Menten approach of enzymatic kinetics to get the Lineweaver-Burk (double
reciprocal) plot as well as the values of the various kinetic parameters Vmax, K
M
and Kcat.
The observed rate vs. [substrate] plot as well as Lineweaver-Burk plot in methanol is
given in Fig. 5 and inset to Fig. 5, respectively. The kinetic parameters are listed in Table
2
-1
3. The turnover numbers (Kcat) are 5.98 × 10 h .
184 3.5.3. Reaction Mechanism
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193
194
195
196
197
198
199
The catalytic process follows a two-step mechanistic pathway. The first step is the rate
determining step. Probably, in this step, the 1:1 adduct of catechol and the manganese
complex is formed. To obtain a mechanistic inference of the catecholase activity and to
get an idea about the complex-substrate intermediate, we recorded an ESI-MS spectrum
of
of
1
in methanol (Figs. S2(a) and S2(b); Supporting information) and of a 1:100 mixture
and 3,5-DTBC of mixing them together (Figs. S2(c) and S2(d); Supporting
1
information). The signal at m/z = 152.97 (Fig. S2(a); Supporting information) is due to
the formation of the ligand 3-methoxy-4-hydroxy benzaldehyde. The peak at m/z = 243
+
can be assigned to sodium aggregate of quinone [3,5-DTBQ]-Na (Fig. S2(c); Supporting
information). The
1 exhibits a peak at m/z = 395.94 (Fig. S2(b); Supporting information).
The formation of a complex-substrate adduct intermediate species is identified by the
peak at m/z = 684 (Fig. S2(d); Supporting information). The catechol derivative, 3,5-
DTBC gets oxidised to quinone in presence of oxygen. The aerial oxygen that oxidises
3,5-DTBC to 3,5-DTBQ in this process is converted to H
2
O
2
. H
2
2
O thus liberated was
identified and characterized spectrophotometrically (S1; Supporting information) [23].
200

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2
01
02
3.6. Phenoxazinone synthesis
2
3.6.1. Spectrophotometric studies
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The phenoxazinone synthase activity study was carried out using the substrate o-
aminophenol (OAPH). OAPH shows bands at 286 and 232 nm in pure methanol. Upon
treatment of methanolic solution of into 100 equivalents of OAPH under aerobic
1
conditions, the repetitive UV-Vis spectral scan was recorded (Fig. 6). The colourless
solution gradually turned deep brown which indicates conversion of OAPH to 2-
aminophenoxazine-3-one (APX). The spectral scan shows very smooth growing of APX
band at 427 nm [11]. APX was identified by HRMS with m/z = 212.93 (Fig. S3;
Supporting information). The time dependent change in absorbance at a wavelength of
427 nm, characteristic of APX in methanol, was observed for 25 min to comprehend the
reaction kinetics and find out the reaction rate between OAPH and 1. The difference in
absorbance ∆A at 427 nm, was plotted against time to obtain the initial rate for that
particular catalyst to substrate concentration ratio (Fig. 7). A first-order catalytic reaction
-
2
-1
is observed, with initial rate 1.20 × 10 min .
216
3.6.2. Enzyme kinetics study
217
218
219
220
221
222
223
Enzymatic kinetic experiments were performed UV-Vis spectrophotometrically
thermostated at 25°C with
1 and the substrate OAPH in MeOH. 0.04 ml of the complex
-
4
solution, with a constant concentration of 1 × 10 M, was added to 2 ml of OAPH of a
-
3
-2
particular concentration (varying its concentration from 1 × 10 M to 1 × 10 M) to
-
4
achieve the final concentration of the complex as 1 × 10 M. The conversion of OAPH to
APX was monitored with time at a wavelength of 427 nm for solutions in MeOH. The
rate for each concentration of the substrate was determined by the initial rate method. The

11
224
225
226
227
228
229
rate versus concentration of substrate data were analyzed on the basis of Michaelis-
Menten approach of enzymatic kinetics to get the Lineweaver-Burk (double reciprocal)
plot as well as the values of the various kinetic parameters Vmax, K
M
and Kcat. The
observed rate vs. [substrate] plot in methanol solution as well as Lineweaver-Burk plot is
given in Fig. 8. The kinetic parameters are listed in Table 4. The turnover number (Kcat) is
2
-1
3.15 × 10 h in methanol.
230
3.6.3. Reaction Mechanism
231
232
233
234
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236
To elucidate mechanistic pathway of the reaction it is found that initially OAPH forms
an adduct with
1
which is trapped by mass spectrometry at m/z = 503.99 (OAPH-1) and
+
527.04 (OAPH-
1
-Na ) (Fig. S4; Supporting information). This adduct generates 2-
amoinophenoxazine-3-one through some intermediate reaction with molecular oxygen
[11d]. Reduced molecular oxygen in the form of
spectrophotometrically (S1; Supporting information).
H
2
O
2
was detected
237
4. Conclusions
238
239
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In this present work, we have synthesized and X-ray crystallographically characterized one
mononuclear Mn(II) complex (1) which is found to show catecholase as well as phenoxazinone
synthase activities in methanol. The turn over number for the catecholase activity is better than
some recent reports [6a, 6c, 7b, 19b]. For phenoxazinone synthase activity also, the turn over
number with our compound is better than few molecules available in literature [11a, 11b]. The
manganese(II) complexes as phenoxazinone synthase mimics reported in literature also have
smaller turn over number than ours [12]. Comparing all these it can be concluded that our

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compound is a better catalyst than some of the reports towards aerial oxidation of 2-5-
2
ditertiarycatechol and 2-aminophenol.
247
5. Acknowledgements
248
249
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RG sincerely thanks Department of Science & Technology, Government of West Bengal
[No. 781(Sanc.)/ST/P/S&T/4G-4/2013 dated 04-12-2014], India for financial assistance. AKG
thanks CSIR, New Delhi, India for his fellowship.
2
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2
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A. Panja, Dalton Trans., 43 (2014) 7760; (c) C. Mukherjee, T. Weyhermüller, E.
Bothe, P. Chaudhuri, C R Chimie., 10 (2007) 313; (d) M. Mitra, T. Kundu, G. Kaur, G.
Sharma, A. R. Choudhury, Y. Singh, R. Ghosh, RSC Adv 6 (2016) 58831; (e) M.
Mitra, R. Ghosh, Indian J. Chem., 55A (2016) 681.
[12] (a) A. Panja, RSC Adv. 4 (2014) 37085; (b) A. Panja, Polyhedron 79 (2014) 258.
[13] A. W. Smith, A. Camara-Artigas, M. Wang, J. P. Allen, W. A. Francisco, Biochem.,
45 (2006) 4378.
[14] J. Gao, Y. Liu, Acta Cryst., 61 (2005) p1692.
[15] G. M. Sheldrick, Acta Cryst, A64 (2008) 112.
[16] K. Nakamoto Infrared and Raman Spectra of Inorganic and Coordination
Compounds, part B: Applications in Coordination, Organometallic, and Bioinorganic
Chemistry (John Wiley & Sons Inc, New York), (1997) p116.
[17] J. G. Sole, L. E. Bausa, D. Jaque An Introduction to Optical Spectroscopy of
Inorganic Solids (John Wiley & Sons Ltd). (2005).
[18] R. Boca, Theoretical Foundations of Molecular Magnetism, Elsevier, Amsterdam,
1999; D is calculated as D = d
z
– (d
x
+ d )/2.
y
[19] D = 2.0928 – (2.3473 + 2.1120)/2; D = -0.13685.
[20] (a) K. S. Banu, T. Chattopadhyay, A. Banerjee, S. Bhattacharya, E. Suresh, M.
Nethaji, E. Zangrando, D. Das, Inorg Chem., 47 (2008) 7083; (b) S. Majumder, S.
Sarkar, S. Sasmal, E. Carolina Sãnudo, S. Mohanta, Inorg Chem., 50 (2011) 7540;
(c) A. Banerjee, S. Sarkar, D. Chopra, E. Colacio, K. K. Rajak, Inorg Chem., 47

15
312
313
314
315
316
317
318
319
320
321
322
(2008) 4023; (d) A. Banerjee, R. Singh, E. Colacio, K. K. Rajak, Eur J Inorg Chem.,
(2009) 277.
[21] F. Zippel, F. Ahlers, R. Werner, W. Haase, H. -F. Nolting, B. Krebs, Inorg Chem., 35
(1996) 3409.
[22] S. Tsuruya, S. -I. Yanai, M. Masai, Inorg Chem., 25 (1986) 141.
rd
[23] (a) A. I. Vogel, Textbook of quantitative inorganic analysis, (Ed.: 3 ) Longmans,
Green, Co. Ltd., London (1961) p.366; (b) A. Neves, L. M. Rossi, A. J. Bortoluzzi,
B. Szpoganicz, C. Wiezbicki, E. Schwingel, Inorg Chem., 41 (2002) 1788; (c) E.
Monzani, L. Quinti, A. Perotti, L. Casella, M. Gullotti, L. Randaccio, S. Geremia, G.
Nardin, P. Faleschini, G. Tabbi, Inorg Chem., 37 (1998) 553.
323
324
325
326
327
328
329
330
331

16
332
Table 1. Crystallographic data of 1
Crystal parameters
Empirical formula
Formula weight
Temperature
1
C
16
H
18
8
O Mn
393.24
295(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Monoclinic
C2/c
Unit cell dimensions
a = 22.453(3) Å, b = 10.5800(12) Å, c =
7
.8576(7)Å
o
β( )= 106.460(11)°
Volume
3
1
4
790.1(4) Å
Z
Density (calculated)
3
1
0
.459 Mg/m
Absorption coefficient
-1
.777 mm
F(000)
812
3
Crystal size
0.35 × 0.35 × 0.15 mm
-26, 1/-1, 12/-9, 9
1918
h/k/l
Reflections collected
Max. and min. transmission
Refinement method
0.9821 and 0.8542
2
Full-matrix least-squares on F
Data / restraints / parameters
1586/0/123
1.048
2
Goodness-of-fit on F
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0.0292, wR2 = 0.0752
R1 = 0.0348, wR2 = 0.0780
Largest diff. peak and hole
-3
.197 and -0.186 e.Å
0

17
3
3
33
34
Table 2. Selected bond distances (Å) and angles (°) for 1
Bond distances
Mn-O(1)
2.0914(13)
2.3473(14)
Mn-O(4)
2.1111(16)
Mn-O(2)
Bond angles
O(1)-Mn-O(2)
O(1)-Mn-O(4)
O(1)-Mn- O(1A)
O(1)-Mn-O(2A)
O(1)-Mn-O(4A)
71.90(5)
96.40(6)
156.97(8)
91.89(5)
99.27(6)
O(2)-Mn-O(4)
168.30(6)
91.90(8)
88.26(6)
93.93(10)
168.30(6)
O(2)-Mn-O(2A)
O(2)-Mn-O(4A)
O(4)-Mn-O(4A)
O(2A)-Mn-O(4A)
3
35
36
3
Table 3. Kinetic parameters for the oxidation of 3,5-DTBC catalyzed by 1
-
1
-1
Solvent
MeOH
V
max (M s )
Std. error
1.04 × 10
K
M
(M)
Std. error
K
cat (h )
-5
-5
-3
-3
2
1.66 × 10
1.89 × 10
1.08 × 10 5.98 × 10
3
37
38
3
Table 4. Kinetic parameters for the oxidative coupling of OAPH catalyzed by 1
-
1
-1
Solvent
MeOH
V
max (M s )
Std. error
1.64 × 10
K
M
(M)
Std. error
K
cat (h )
-6
-6
-3
-4
2
8.76 × 10
1.57 × 10
2.08 × 10 3.15 × 10
339
340
341

18
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
Fig. 1. ORTEP diagram of
1 with 20% ellipsoid probability. Symmetry transformation used
to generate equivalent atoms: (A) -x, y, -z + 3/2.
End product of burnt 1
MnO
1
7
2
16
1
1
1
1
1
1
5
4
3
2
1
0
9
1
000
2000
3000
4000
-1
Cm
Fig. 2. Thermal spectrum of 1 (inset: IR spectrum of final ash of 1 and standard MnO )
2

19
3
62
63
Fig. 3. Change in spectral pattern of 1 after reaction with 3,5-DTBC, observing the reaction for 6
3
h in methanol; inset: spectrum of pure 3,5-DTBC in methanol.

20
3
64
65
Fig. 4. A plot of the difference in absorbance (∆A) vs time to evaluate the rate of catalysis of
3,5-DTBC by 1 in methanol
3
366
3
67
68
Fig. 5. Plot of rate vs. [substrate] (3,5-DTBC) in presence of 1 in MeOH; inset: Lineweaver-
3
Burk plot

21
3
69
70
3
371
372
373
374
375
376
377
378
Fig. 6. Change in spectral pattern of 1 in MeOH after reaction with OAPH, observing the
reaction for 6 h; inset: spectrum of pure OAPH in methanol
379
380
381
382
383
384
385
3
86
87
Fig. 7. A plot of the change in absorbance with time to evaluate the initial rate of the catalytic
oxidation of OAPH by 1
3

22
388
389
390
391
392
393
394
395
396
397
398
Fig. 8. Plot of rate vs. [substrate] (OAPH) in presence of 1 in MeOH; inset: Lineweaver-Burk
plot.
3
99
00
4

23
4
01
02
4
4
03
04
4
405
4
06
07
Structurally characterized mononuclear Mn(II) complex: functional models for
catecholase and phenoxazinone synthase activities
4
a
a
b
a,*
408
409
410
411
412
Sarat Chandra Kumar , Ayon Kanti Ghosh , Jhy -Der Chen , Rajarshi Ghosh
a
Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b
Department of Chemistry, Chung Yuan Christian University, Chung Li, Taiwan 32023
413
414
415
416
A catecholase as well as phenoxazinone synthase-active Mn(II) complex is isolated in MeOH
at room temperature. Each of the catalytic reactions with the Mn(II) complex as catalyst is found
2
2
-1
to be of first order with turn over numbers 5.98 × 10 and 3.15 × 10 h . Catalyst-substrate
adduct as intermediate is trapped by mass spectrometry for both the activities.

24
4
17
18
4

25
419
420
421
• Manganese(II) complex
• Functional models for catecholase and phenoxazinone synthase
422