Mechanistic investigation of the oxidation of glyoxylic and pyruvic acids by tris(biguanide)manganese(IV) in weakly acidic aqueous media

Article abstract of DOI:10.1002/ejic.200400547

In this study the kinetics of two electron transactions between the reducing substrates glyoxylic and pyruvic acids and the oxidising complex cation, tris(biguanide)manganese(IV) in aqueous acidic media have been examined. Under the experimental conditions (pH = 1.50-3.78) only the fully protonated form of the oxidant reacts with the anions of the substrates whereas the parent acids, viz. glyoxylic and pyruvic acids, were found to be unreactive. The second-order rate constants for the oxidations of glyoxylate and pyruvate by the title Mn^IV species are (2.24 ± 0.10) × 10^-1 and (5.40 ± 0.30) × 10^-2 M^-1S^-1, respectively, at 25.0 °C and at I = 1.0 M (NaNO₃ or NaClO ₄). A rate-liming one-electron change between the redox partners seems justified. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400547

FULL PAPER
Mechanistic Investigation of the Oxidation of Glyoxylic and Pyruvic Acids by
Tris(biguanide)manganese(IV) in Weakly Acidic Aqueous Media
[a]
[a]
[a]
Basab Bijayi Dhar, Ritam Mukherjee, Subrata Mukhopadhyay,* and
Rupendranath Banerjee*[
a]
Keywords: Kinetics / Mechanism / Redox reaction / Manganese() / Glyoxylic acid / Pyruvic acid
In this study the kinetics of two electron transactions be-
tween the reducing substrates glyoxylic and pyruvic acids
and the oxidising complex cation, tris(biguanide)mangane-
se(IV) in aqueous acidic media have been examined. Under
the experimental conditions (pH = 1.50−3.78) only the fully
protonated form of the oxidant reacts with the anions of the
rate constants for the oxidations of glyoxylate and pyruvate
IV
−1
by the title Mn species are (2.24 ± 0.10) × 10 and (5.40 ±
−
2
−1 −1
0.30) × 10
(NaNO
between the redox partners seems justified.
M
s
, respectively, at 25.0 °C and at I = 1.0
M
3
or NaClO ). A rate-liming one-electron change
4
substrates whereas the parent acids, viz. glyoxylic and pyr- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
uvic acids, were found to be unreactive. The second-order
Germany, 2004)
Introduction
4
ϩ
species is noticeably accelerated by chloride ions in what the
authors viewed as the accelerating effect of the polarisable
anion on the redox reaction between two positively charged
metal centres.
Tris(biguanide)manganese() {Figure 1; [Mn(LH ) ]
2
3
(
LH ϭ biguanide, C N H )} is a rare example of a water-
soluble mononuclear Mn complex stable over a wide
range of acidity levels (10 to 2 ). In aqueous solutions
the title Mn complex behaves as a mild dibasic acid
pKa1 ϭ 5.30 Ϯ 0.20, pKa2 ϭ 7.60 Ϯ 0.30) and the depro-
tonations are believed to originate from the protons bound
to the ligand sp nitrogen atoms. Though quite a few di-,
tri- and tetranuclear Mn complexes can be stabilised in
2 2 5 7
IV
Ϫ6
[1]
IV
The present investigation deals with the kinetic and
mechanistic aspects of the oxidation of two small carboxylic
acids of biological relevance, viz. glyoxylic and pyruvic acid.
Detailed kinetic studies of their oxidations are of import-
(
2
[2]
III
IV
ance because Mn species are involved in metabolic pro-
[
6a]
[
3]
cesses such as glycine catabolism
ology,
and plant physi-
whereas the reducing substrate pyruvic acid is in-
volved in a major metabolic sequence (TCA cycle) in living
aqueous solution and have interesting solution chemis-
[
6b]
try,[ the aqueous solution chemistry of mononuclear Mn
4]
IV
[
2]
remained unexplored until recently when we reported the
[
6c]
2
ϩ
IV
systems.
Complete oxidation of these carboxylic acids
oxidation of Fe by Mn . Parallel to our report, Gould
[
5]
2ϩ
IV
with α-carbonyl groups ultimately leads to CO with gener-
et al. observed that the oxidation of Fe by this Mn
2
ation of energy in the metabolic processes. We also note
that examples of oxidations of these substrates by higher
valent oxidising species are only scarce in the literature.[
7]
Results and Discussion
Equilibrium Studies and Preliminary Observations
Using a Metrohm 736 GP Titrino auto-titrator yielded
pK values for glyoxylic and pyruvic acid from the pH-ti-
a
tration curves of 3.20 Ϯ 0.10 and 2.50 Ϯ 0.10, respectively,
at 25.0 °C and at I ϭ 1.0  (NaNO or NaClO ). These
2 3
)
]4ϩ drawn on the basis of its crys-
Figure 1. Structure of [Mn(LH
tal structure
3
4
values are in agreement with those previously reported.[
7h,7i]
Most of the kinetic runs were performed at 433 nm, i.e. the
observed visible absorption maximum of the Mn com-
plex. At this wavelength, all other reaction components ex-
[
a]
Department of Chemistry, Jadavpur University,
Calcutta 700032, India
E-mail: subrataju@vsnl.net
IV
4854
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200400547
Eur. J. Inorg. Chem. 2004, 4854Ϫ4858

Oxidation of Glyoxylic and Pyruvic Acids by Tris(biguanide)manganese(IV)
cept MnIV are transparent. No additional buffer was used Table 1. Some representative first-order rate constants for oxidation
FULL PAPER
4
ϩ
in the kinetic experiments since the pH drift was well within of glyoxylic and pyruvic acid by [Mn(LH
2
)
3
]
at T ϭ 25.0 °C, I ϭ
.05 units during the reaction. We observed no Mn2ϩ ca-
1.0  (NaNO ), λ ϭ 433 nm [concentration of complex used
3
0
0.10 m; the k
o
values calculated using Equation (7a) are given
talysis (studied up to 0.10 ) in the title reaction.
in parentheses]
4
4
pH
RCOCOOH []
10 k
o
(R ϭ H)
o 3
10 k (R ϭ CH )
Ϫ1
Ϫ1
Stoichiometry and Reaction Products
[s
]
[s ]
1
1.70
.46
0.02
0.8 (0.79)
1.4 (1.37)
2.4 (2.43)
4.1 (4.06)[
5.8 (5.76)
0.8 (0.79)
1.4 (1.30)
2.2 (2.16)
3.3 (3.28)
4.3 (4.23)
6.8 (6.85)
8.0 (8.06)
8.2 (8.05)
8.9 (8.96)
9.6 (9.66)
10 (10.2)
2.1 (2.11)
6.3 (6.34)
11 (10.6)
Results of the stoichiometry experiments yielded
[Mn ]/∆[Reductant] ϭ 0.98 Ϯ 0.10 for glyoxylic oxi-
dation and 1.07 Ϯ 0.05 for pyruvic acid oxidation. The
IV
∆
1
2
.96
.20
a]
c]
[b]
[c]
presence of the oxidation product formic acid in the oxi- 2.37
dation of glyoxylic acid was tested for by the addition of 2.80
13 (12.7)[
18 (18.1)[
18 (18.1)
chromotropic acid which gave a violet colour.[8] Acetic acid
3.03
d]
[e]
[d]
[e]
3
3
3
.02
.25
.50
was detected in the pyruvate oxidation by the addition of
lanthanum nitrate and iodine which produced a deep blue
23 (23.7)
30 (30.3)
35 (35.4)
[
8]
2ϩ
precipitate. We verified that the reaction products, Mn
3.78
.37
2
0.01
2.8 (2.88)
8.7 (8.64)
15 (14.4)
or the released biguanide did not interfere with these quali-
0
0
.03
.05
tative experiments. The generation of gaseous CO in both
2
the reactions was confirmed by GC analysis as described
[
9]
[a]
4
Ϫ1
earlier. The overall redox processes for glyoxylic acid and
pyruvic acid are thus described by Equation (1) and (2), (NaNO
o
10 k (R ϭ H) [s ] values are 8.3 and 11 at I ϭ 0.5 and 0.2 
), respectively. [ 10 k
.2 at I ϭ 0.5 and 0.2  (NaNO
are 16 and 8.8 for glyoxylic and pyruvic acid, respectively, at I ϭ
b]
4
(R ϭ CH
), respectively. 10 k
Ϫ1
3
o
3
) [s ] values are 6.5 and
[c]
4
Ϫ1
8
3
o
[s ] values
). [ Reactions carried out in the presence of exter-
4
respectively.
d]
1.0  (LiClO
[e]
4
Ϫ1
nally added 1.00 m  biguanide. 10 k
9
o
[s ] values are 23 and
MnIV ϩ CHOCOOH ϩ H
O Ǟ
2
.0 for glyoxylic and pyruvic acid, respectively, at I ϭ 1.0  (NaCl).
Mn2 ϩ HCO
ϩ
H ϩ CO
ϩ 2 H
ϩ
(1)
(2)
2
2
2
For both the reducing agents, the k values were found
MnIV ϩ CH
o
3
COCOOH ϩ H
2
O Ǟ
Mn2ϩ ϩ CH
ϩ
to increase significantly with the pH of the reaction medium
3
CO
2
H ϩ CO
ϩ 2 H
IV
(Table 1). The title Mn complex is a weak acid (pKa1
ϭ
5.30) and thus its deprotonation may be disregarded,
whereas the concentration of both the neutral and anionic
forms of the reducing agents are substantial under the pH
interval studied (1.46Ϫ3.78).
The small amounts of evolved gas in these reactions did
not interfere with the kinetic measurements. Iodometric de-
termination of copper in the cupric biguanide which pre-
The observed rate constants depend remarkably on the
ionic strength of the reaction medium maintained by
NaNO or NaClO (Table 1). A considerable increase in the
[
10]
cipitated
from the solution indicated release of more
3
4
than 90% biguanide.
reaction rate over the entire pH range for both the reduc-
tants with a decrease in ionic strength indicates a reaction
between oppositely charged ions. The rate constants were
Kinetics
also found to increase substantially when LiClO was used
4
ϩ
instead of Na salts for maintaining the ionic strength of
No immediate spectroscopic change was observed on
IV
the reaction mixture. As the redox partners of the title reac-
tions are oppositely charged, conventional metal ion cataly-
mixing either glyoxylic or pyruvic acid with the Mn com-
plex over the entire range of experimental pH values exam-
ined (1.50Ϫ3.78). The whole reaction course follows first-
order kinetics and the log(A Ϫ A ) versus time plots were
[
11]
sis can be ruled out.
We also verified that the reactions
are not accelerated by addition of chloride. A possible rea-
t
ϱ
ϩ
son for the rate enhancement in the presence of Li may be
found to be linear to more than three half-lives. In all the
explained by the very high approximate hydration number
kinetic runs, A values were less than 0.01. The first-order
ϱ
ϩ
[12]
of Li (25.3), as estimated by transference data,
com-
rate constants, k , as described by Equation (3), were ob-
o
ϩ
pared with that of Na (16.6). This results in a major lower-
ing of the effective concentration of solvent water which in
turn increases the activity of the redox partners.
tained from least-squares slopes of these plots and are pre-
sented in Table 1. Moreover, a tenfold variation in the initial
[
7h]
IV
[
Mn ] value (0.02Ϫ0.20 m) resulted in no change in the
Reactions studied in the presence of 6% (v/v) acrylonitrile
ko values within experimental uncertainty (Ϯ 5%).
showed slow polymerisation after consumption of ca.
IV
4
0Ϫ50% of the initial Mn amount. The log(A Ϫ A ) ver-
t
ϱ
Ϫd[MnIV]/dt ϭ k
[MnIV
]
(3) sus time plots under these conditions showed a definite up-
o
Eur. J. Inorg. Chem. 2004, 4854Ϫ4858
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4855

B. B. Dhar, R. Mukherjee, S. Mukhopadhyay, R. Banerjee
FULL PAPER
ward curvature after ca. 50% completion of the reaction, pyruvic acid, respectively. From the slopes, using such k2
probably due to heterogeneity in the reaction media. Polym- values, K values could be determined. These kinetically
a
erisation of acrylonitrile is more prominent in the case of evaluated K values agree well (within 10%) with the litera-
a
glyoxylic acid than in that of pyruvic acid.
ture values supporting the proposed reaction scheme.
Scheme 1 provides a reasonable explanation for the kine-
tic observations considering the acid dissociation constants
Mechanism
of the complex in aqueous solution (K and Ka2 are 5.01
The reducing anions glyoxylate and pyruvate have been
a1
Ϫ6
Ϫ8
ϫ 10 and 2.50 ϫ 10 , respectively) and K values (i.e. found to be the only reactive species and this result sup-
a
the measured acid dissociation constants of glyoxylic and ports the well-accepted concept that deprotonated reduc-
Ϫ4
pyruvic acid under experimental condition, 6.31 ϫ 10
for glyoxylic and 3.16 ϫ 10  for pyruvic acid).

tants are more effective than their conjugate acids in reduc-
Ϫ3
[2,7h,9,13]
ing higher valent metal centres.
However, we were
astonished at the extent of this behaviour since we recently
observed that both glyoxylic and pyruvic acids are reactive
[
7h,7j]
in reducing ethylenebis(biguanide)silver().
(One of
the referees of this article commented that these reducing
agents have inherent equilibria between the gem-diol and
carbonyl forms in aqueous solution. Literature reports also
[
7c]
support this.
The reactivity of glyoxylate and pyruvate
anions as found in this investigation is thus the combined
reactivities of their gem-diol and carbonyl forms.)
Scheme 1
IV
II
The reduction of Mn to Mn and the oxidation of the
reductants chosen in this study are both net two-electron
transactions. Nevertheless, it is extremely unlikely that the
Scheme 1 leads to the rate law of Equation (7), where
TR ϭ [RCOCOOH] ϩ [RCOCOO ].
Ϫ
IV
Mn reduction proceeds in a single step. Moreover, polym-
ϩ
ϩ
k
o
(K
a
ϩ [H ])/T
R
ϭ k
1
[H ] ϩ k
2
K
a
(7)
erisation experiments also lend support to single-electron
steps which generate polymerisation initiating radicals.
Generation of these substrate radicals by one-electron oxi-
The left-hand-side values of Equation (7) were found to
be nearly a constant within allowable uncertainty in the en-
[14]
dation has been well established by EPR spectroscopy.
IV
Pyruvate oxidation by the Mn complex was found to
be slower than glyoxylate oxidation. The increase in reac-
tion rate may originate from the weaker CϪC bond energy
in glyoxylic acid compared with that in pyruvic acid due to
the presence of an electron-donating methyl group in pyr-
uvic acid which increases the electron density at the car-
bonyl carbon atom. The weakening of the CϪC bond in
glyoxylic acid may be a driving force for a faster initial elec-
tire pH range studied, both for glyoxylic [(1.40 Ϯ 0.02) ϫ
Ϫ4 Ϫ1
Ϫ4 Ϫ1
10
s
] and pyruvic acid [(1.60 Ϯ 0.06) ϫ 10
s ]. We
thus found no contribution from k for both the reducing
agents to the overall rates. Equation (7) can thus be simpli-
fied to Equation (8).
1
ϩ
T
R
/k
o
ϭ 1/k
2
ϩ [H ]/(k
2
K
a
)
(8)
tron transfer leading to a quicker overall oxidation of glyox-
ϩ
Plots of T /k versus [H ] yielded straight lines (Fig-
[7g]
R
o
ylic acid.
A similar explanation was also offered for the
ure 2) with intercepts yielding k values of (2.24 Ϯ 0.10) ϫ
VI [7g]
2
oxidation of these reducing agents by Cr
and ethylene-
Ϫ1
Ϫ2 Ϫ1 Ϫ1
1
0
and (5.40 Ϯ 0.30) ϫ 10

s
for glyoxylic and
[7h,7j]
bis(biguanide)silver().
Moreover, the presence of a
strongly reducing aldehyde function in glyoxylic acid may
also be another explanation, at least in part, for obtaining
a higher rate.
IV
The Mn centre in the title complex is coordinatively
saturated and thus replacement of the strong field chelating
biguanide ligand by the substrate anions seems to be un-
likely. The estimated maximum value for the pre-equilib-
IV
rium formation of a 1:1 adduct between Mn
and
Ϫ
RCOCOO (R ϭ H for glyoxylate and CH for pyruvate)
3
lies between 1 and 10 and this does not confirm a strong
inner-sphere attachment. However, we note that among the
2
IV
three s metal-ion centres studied for the reduction of Mn ,
I
4ϩ
only the reaction of In with [Mn(LH ) ] is subject to
2
3
kinetic saturation for which an association constant of 6 ϫ
3
Ϫ1
1
0  for the formation of this adduct (believed to be due
to strong hydrogen bonding) was estimated by Gould et
[
5]
ϩ
al. The estimated low value for the formation of adducts
in the present study may be due to electrostriction[ or a
Figure 2. Plot of T
R
/k
o
versus [H ]; [complex] ϭ 0.10 m, T
3
R
ϭ
15]
0
.02 , I ϭ 1.0  (NaNO
), T ϭ 25.0 °C
4856
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 4854Ϫ4858

Oxidation of Glyoxylic and Pyruvic Acids by Tris(biguanide)manganese(IV)
FULL PAPER
process aided by hydrogen bonding[16] involving the reduc- The desired concentrations of the complex and the reducing agent
were achieved after mixing. The solution pH values were adjusted
with HNO or NaOH. Solution pH values ranged from 1.52 to
3
tants and the NH or NH fragments of the ligand biguanide
2
moiety of the title complex. The presence of a strong chelat-
IV
3.78 and were measured with an Ag/AgCl combined glass electrode
attached to a Metrohm 736 GP Titrino autotitrator. The electrode
calibration was carried out as reported previously.[ Production of
ing ligand can be expected to stabilise Mn to a great ex-
tent and render the complex a mild oxidant. Cyclic voltam-
metric studies of an aqueous solution (deoxygenated by
20]
2
CO as the gaseous reaction product was qualitatively confirmed
by GC analysis. The gaseous product formed during the reaction
was analysed by gas chromatography using a Chemito (India)
IV
purging with nitrogen) of the Mn complex (0.10 m) in
the presence of 0.1  Et NClO as a supporting electrolyte
4
4
IV
revealed a single irreversible wave corresponding to Mn / GCHT 8610 instrument equipped with TCD (a Porapak Q and
Mn reduction at ca. 0.4 V versus Ag/AgCl (∆E ϭ 400 Ϯ molecular sieves 13X column). A splitless mode of injection of 500
III
p
Ϫ1
5
0 mV depending on scan rate, 50Ϫ300 mV s ). A direct µL of the sample was used. The oven, injector, and detector tem-
IV
peratures were kept at 50, 100 and 150 °C, respectively. The carrier
outer-sphere oxidation by this weakly oxidising Mn may
thus be eliminated. We observed that more than 90% of the
biguanide ligand is released at the end of the reaction
Ϫ1
hydrogen gas flow was adjusted to 30 mL·min . Cyclic voltam-
metric studies were performed with an Electrochemical Analyser
(
Model 600A, CH Instruments, USA) using a three-component
[10]
(tested using an ammoniacal CuSO solution)
and the
encourages the
4
electrode system consisting of Pt wire working and auxiliary elec-
trodes and an Ag/AgCl reference electrode.
[17]
high protonation constants of biguanide
overall reactions to completion.
Stoichiometry and Reaction Products: The stoichiometries were
evaluated by estimating unchanged glyoxylic or pyruvic acid spec-
trophotometrically. Reaction mixtures containing an excess of 4Ϫ6
equiv. of glyoxylic or pyruvic acid relative to the title complex were
allowed to react under nitrogen until the solutions turned colour-
less. To estimate the unspent glyoxylic acid freshly prepared phe-
nylhydrazine hydrochloride (1%) solution was added (3.0 mL) into
the reaction mixture. The resultant solution was incubated at ca.
Experimental Section
Materials: The complex salt [Mn(C
prepared by a known procedure. The crystals obtained were suffic-
iently pure as indicated by satisfactory C, H, N analyses:
2
N
5
H
7
)
3
]
2
SO
4
(NO
3
)
6
·3H
2
O was
[18]
C
12
H
48Mn
2
N
36
O
25S (1238): calcd. C 11.63, H 3.88, N 40.71; found
C 11.3, H 3.9, N 39.9. Biguanide sulfate [C ·H SO ] was pre-
pared by a known method reported previously. An aqueous
1
°
10 °C for 10 min and then cooled to room temperature (ca. 25
C) followed by successive addition of 2.5-mL aliquots of concen-
trated HCl and 1% K Fe(CN) . The reaction mixtures were allowed
2
N
5
H
7
2
10b]
4
[
3
6
solution of glyoxylic acid was prepared by dissolving solid glyoxylic
acid monohydrate (98%, Lancaster) in water and this was standard-
ised either with standard alkali using Weslow’s indicator or by spec-
to stand for ca. 5 min for the quantitative formation of a pink for-
mazan derivative of glyoxylic acid which was analysed at 520 nm
Ϫ1
Ϫ1 [18]
[19]
(
ε ϭ 17990  cm ).
freshly prepared 2,4-dinitrophenylhydrazine solution in MeOH
1 mL, 1%) and 0.1  HCl (1 mL) were added to the reaction mix-
ture along with K-phosphate (K HPO ) buffer (0.1 ) of pH ϭ
.5. The resultant solution was incubated at ca. 80 °C for 10 min
and then cooled in an ice box for 10 min. A 50% KOH solution
5 mL) was then added to the solution which was again incubated
To estimate unchanged pyruvic acid
[
18]
Ϫ1
Ϫ1
trophotometry
us, in agreement with the literature value of 17870  cm
at 520 nm (ε ϭ 17990  cm as estimated by
Ϫ1
Ϫ1 [18]
)
(
after converting glyoxylic acid to 1,5-diphenylformazancarboxylic
acid. Both results agree well with each other (within 4%). We found
that an aqueous solution of ca. 0.5  glyoxylic acid is stable for at
least one weak when kept at low temperature (ca. 5Ϫ10 °C) and in
the dark. Pyruvic acid (98%, Sigma) was used and standardised
2
4
7
(
at room temperature for 10 min. The red colour of the 2,4-dinitro-
phenylhydrazone pyruvate derivative was then analysed at 515 nm
using spectrophotometry[ at 515 nm (ε ϭ 1400  ·cm ). An
19]
Ϫ1
Ϫ1
aqueous solution of NaNO or NaClO (G. R., E. Merck) was
3
4
Ϫ1
Ϫ1 [19]
(
1400  ·cm ). The biguanide ligand in the product solution
standardised by passing through a Dowex 50 W X-8 strong cation
II
2 2 4
was isolated as [Cu(LH ) ]SO by the addition of Cu sulfate. The
amount of Cu thus consumed was determined iodometrically
after decomposing the copper complex.
ϩ
exchange resin in the H from and titrating the liberated acid with
II
standard NaOH to a phenolphthalein end point. All other chemi-
cals were of reagent grade. Most of the kinetic measurements were
[10]
carried out at I ϭ 1.0  (NaNO
same k
been deionised and doubly distilled.
3 4
or NaClO resulted in almost the
values). All solutions were prepared in water which had Acknowledgments
o
The award of a junior research fellowship to B. B. D. by the Univer-
sity Grants Commission, New Delhi is gratefully acknowledged. S.
M. acknowledges the Council of Scientific and Industrial Research,
New Delhi, for funding.
a
Equilibrium Measurements: The acid dissociation constants, K , of
[
7h]
both the glyoxylic
ing several aliquots of different strengths with carbonate-free de-
oxygenated NaOH solution at 1.0  NaNO using a Titrino Auto-
and pyruvic acids were determined by titrat-
3
[1] [1a]
G. Das, P. K. Bharadwaj, D. Ghosh, B. Chaudhuri, R.
titrator (Metrohm, 736 GP) at (25.0 Ϯ 0.1) °C.
Banerjee, Chem. Commun. 2001, 323Ϫ324; see also the Adden-
dum, Chem. Commun. 2002, 2278. [ L.-P. Lu, M.-L. Zhu, P.
Yang, Acta Crystallogr., Sect. B 2004, 60, m18Ϫm20.
B. B. Dhar, R. Mukherjee, S. Mukhopadhyay, R. Banerjee, Eur.
J. Inorg. Chem. 2004, 2950Ϫ2955.
1b]
Physical Measurements and Kinetics: All absorbance versus time
data were recorded with a Shimadzu (1601 PC) spectrophotometer
using 1.00-cm quartz cells. The kinetics were monitored in situ in
the ‘‘kinetic mode’’ of the instrument at 433 nm which is one of the
[
[
2]
3] [3a]
K. R. Reddy, M. V. Rajasekharan, S. Padhye, F. Dahan, J.
IV
absorption peaks of the Mn complex. An electrically controlled
[3b]
P. Tuchagues, Inorg. Chem. 1994, 33, 428Ϫ433.
K. R.
thermostat (25 Ϯ 0.1) °C cell housing (CPS-240) was employed.
For faster reactions, the reductant solution (adjusted to the desired
pH) was injected directly into the spectrophotometer cell contain-
ing other components of the reaction mixture kept at the same pH.
Reddy, M. V. Rajasekharan, N. Arulsamy, D. J. Hodgson, In-
[3c]
org. Chem. 1996, 35, 2283Ϫ2286.
K. Wieghardt, Angew.
Chem. Int. Ed. Engl. 1994, 33, 725Ϫ728. [ H. J. Mok, J. A.
3d]
Davis, S. Pal, S. K. Mandal, W. H. Armstrong, Inorg. Chim.
Eur. J. Inorg. Chem. 2004, 4854Ϫ4858
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4857

B. B. Dhar, R. Mukherjee, S. Mukhopadhyay, R. Banerjee
FULL PAPER
Acta 1997, 263, 385Ϫ394. [3e] C. E. Dube, D. W. Wright, S. Pal,
[8]
[9]
F. Feigl, Spot Tests in Organic Analysis, 5th ed., Elsevier, Lon-
don, 1956, p. 331, 332.
P. J. Bonitatebus, Jr., W. H. Armstrong, J. Am. Chem. Soc.
998, 120, 3704Ϫ3716. [ S. Mukhopadhyay, R. J. Staples, W.
3f]
P. Bandopadhyay, B. B. Dhar, J. Bhattacharyya, S. Mukho-
padhyay, Eur. J. Inorg. Chem. 2003, 4308Ϫ4312.
1
H. Armstrong, Chem. Commun. 2002, 864Ϫ865.
[
4] [4a]
[10] [10a]
[10b]
A. K. Bhattyacharya, A. B. Mondal, R. Banerjee, J. Chem.
B. Rathke, Ber. Dtsch. Chem. Ges. 1879, 12, 774.
P.
[4b]
[10c]
Soc., Dalton Trans. 1997, 2351Ϫ2355.
Kundu, R. Banerjee, J. Chem. Soc., Dalton Trans. 1997,
B. Mondal, S.
Ray, Chem. Rev. 1961, 61, 314Ϫ359.
R. Banerjee, K. Das,
A. Das, S. Dasgupta, Inorg. Chem. 1989, 28, 585Ϫ588.
M. Gupta, S. K. Saha, P. Banerjee, J. Chem. Soc., Perkin Trans.
2. 1988, 1781Ϫ1785.
12]
[
4c]
[11]
4
341Ϫ4344.
S. Mukhopadhyay, Dalton Trans. 2002, 2047Ϫ2052.
Mondal, A. K. Bhattyacharya, R. Banerjee, Polyhedron 2000,
S. Banerjee, U. Roy Choudhury, R. Banerjee,
[4d]
B.
[
F. A. Cotton, G. Wilkinson, C. A. Murillo, M. Bochmann,
Advanced Inorganic Chemistry, 6th ed., Wiley, New York, 1999,
chapter 3, p. 102.
[
4e]
1
9, 1213Ϫ1218.
Met. Chem. 2002, 27, 80Ϫ84.
R. Banerjee, Transition Met. Chem. 2002, 27, 42Ϫ46.
Maji, R. Banerjee, Transition Met. Chem. 2001, 26, 544Ϫ550.
D. Maji, P. K. Das, R. Banerjee, Transition
[4f]
U. R. Choudhury, S. Banerjee,
[4g]
[13]
[14]
D.
P. Bandopadhyay, S. Mukhopadhyay, Polyhedron 2002, 21,
1893Ϫ1898.
[
4h]
U. R. Choudhury, S. Banerjee, R. Banerjee, J. Chem. Soc.,
B. Neumann, O. Steinbock, S. C. Muller, N. S. Dalal, J. Phys.
Chem. 1996, 100, 12342Ϫ12348.
Dalton Trans. 2000, 589Ϫ592.
[
[
5]
[15] [15a]
O. A. Babich, E. S. Gould, Inorg. Chem. 2004, 43, 1779Ϫ1783.
M. G. Evans, G. H. Nancollas, Trans. Farad. Soc. 1953,
6] [6a]
[15b]
A. White, Principles of Biochemistry, 2nd ed., McGraw-Hill,
49, 363Ϫ366.
59, 1208Ϫ1211.
C. Postmus, E. L. King, J. Phys. Chem. 1955,
[15c]
New York, 1954, p. 548. [ E. H. Rodd, Chemistry of Carbon
6b]
F. Basolo, R. G. Pearson, Mechanisms of
Compounds, Elsevier, Amsterdam, 1952, part B, vol. 1, p. 850.
Inorganic Reactions, 2nd ed., Wiley, New York, 1967, p. 34.
[
6c]
[15d]
E. S. G. Barron, Trends in physiology and Biochemistry, Aca-
demic Press, New York, 1952, p. 471.
M. Grant, R. B. Jordan, Inorg. Chem. 1981, 20, 55Ϫ59.
16] [16a]
[
C. D. Hubbard, A. Gerhard, R. van Eldik, J. Chem. Soc.,
[
7] [7a]
[16b]
W. J. Albery, R. P. Bell, A. L. Powel, Trans. Farad. Soc.
Dalton Trans. 2001, 1069Ϫ1073.
M. C. Ghosh, J. W. Reed,
[
7b]
1
965, 61, 1194.
P. Manikyamba, React. Kinet. Catal. Lett.
R. N. Bose, E. S. Gould, Inorg. Chem. 1994, 33, 73Ϫ78.
L. Fabbrizzi, M. Micheloni, P. Paoletti, G. Schwarzenbach, J.
Am. Chem. Soc. 1977, 99, 5574Ϫ5579.
D. N. Kramer, N. Klein, R. A. Baselice, Anal. Chem. 1959,
30, 250Ϫ252.
S. Takenaka, S. Murakami, R. Shinke, K. Aoki, Arch. Micro-
biol. 1998, 170, 132Ϫ137.
S. Banerjee, U. R. Choudhury, B. C. Ray, R. Banerjee, S. Mu-
khopadhyay, Anal. Lett. 2001, 34, 2797Ϫ2815.
Received June 22, 2004
2
003, 78, 169Ϫ173. [ L. Maros, I. Molnar-Perl, L. Kover, J.
7c]
[17]
[18]
[19]
[20]
[7d]
Chem. Soc., Perkin Trans. 2. 1976, 1337Ϫ1342.
K. K. Seng-
upta, J. Indian Chem. Soc. 1964, 41, 423. [ R. Banerjee, R.
7e]
Das, A. K. Chakraborty, J. Chem. Soc., Dalton Trans. 1990,
3
[
7f]
277Ϫ3281.
K. K. Sengupta, H. R. Chatterjee, Inorg. Chem.
978, 17, 2429Ϫ2431. [ K. K. Sengupta, T. Sarkar, Tetra-
7g]
1
[
7h]
hedron 1975, 31, 123Ϫ127.
A. Das, S. Mukhopadhyay, Poly-
hedron 2004, 23, 895Ϫ901. [ A. E. Martel, R. Smith, Critical
Stability Constants, Plenum Press, New York, 1977, vol. 3,
7i]
[
7j]
p. 66.
in press.
A. Das, S. Mukhopadhyay, Transition Met. Chem.,
Early View Article
Published Online October 21, 2004
4858
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