- Email: [email protected]
Reduction of methylene blue by hydrazine catalyzed by manganese(III)-hematoporphyrin
131
Journal of &foiecufar Catalysis, 5 (1979) 131 - 138 @ EXsevier Sequoia S-A., Iausanne -Printed in the Netherlands
REDUCTION OF METHYLENE &DE BY EIYDRAZINE BY MANGANESE(III)-IIEMATOPORPHYRIN
ICHIRO
OKURA.
NGUYEN
D
April
KIM THUAN
and TOMINAGA
Tdqm
CATALYZED
KElI
x%zs~stc ofS!'ebSu~,
Si---&
17-1978)
Summary The reduction of methylene blue is catalyzed by manganese (III)-hematoporphyrin_ From kinetic studies of the reaction, a reaction mechanism is proposed in which the catalyst is reduced first by hydrazine, and then methylene blue is reduced by the reduced catalyst_ The effect of additives, such as imidazole, pyrrole, cyanide, and pyridine, on the reaction has been studied- Differences in the stimulation of the catalytic activity are explained by differing abilities of the additives tcr,Zorm enrn$3exes -6%n rnim~7m~3~>1%>herna%~q++in-
Introduction Since manganese(III)-hematoporphyrin (Mn(III)-Hm) was synthesized by Calvin et al.[l] as a model complex in the photosynthetic process, few examples of catalysis by Mn(III)-Hm have been reported except for the autoxidation of hydrazine [2] _ In the autoxidation, the-oxidation state of the central ion has not changed during the reaction_ At higher concentrations of hydrazine, however, the oxidation state of manganese ion changed, evidently, from trivalent to divalent. This raised interest in utilizing the complex for methylene blue reduction due to the redox -z&ion of Mr&I)-Km in -the course of -&tierea-&.io~_ In this paper, the reduction of methylene blue by hydrazine with Mn(III)-Hm is described and the reaction mechanism is discussed on the basis of kinetic data_
Pyrrole (obtained from Yoneyama Yakuhin Co-), imidazole (Tokyo Kasei Co.), potassium cyanide and pyridine (Wako Pure Chemical Ind.), are used without further purification.
1T-
Ail I
A
B
C
Fig_ 1, Apparatus for the reduction ofmethykme (25 “C);33.Reactor; C. MagneZic skirter; D. RoIler off visib‘le @‘3f!CctNR.
blue by hydrazine. A- Tberrnosta~ E_ Spectrophotometer; F. Cell
pump;
Other chemicals used are the same as those described elsewhere [2] _ The reduction of methylene blue was carried out in a recirculating system, as outlined in Fig_ 1, Mn(III)-Hm (0.625mM) and hydrazine (33.3mM) were introduced into a reactor and methylene blue (217mM) added t-3 start the reaction_ The total volume of the reaction mixture was kept constant at 30 ml by adding O-IN sodium hydroxide_ In the studies of the effect of the axial ligands of Mn(III)-Hm, the third component was added just before the introduction of hydrazineThe rate of decolorization of methylene blue was followed by a Sltimadzu sgectro~hotom~, SEiXIel SWS-SMM, us&g a cell of 5.0 mm width, The concentration of methylene blue solution was followed automatically by measuring the absorbance change at 660 nm. The ionic strength was maintained at 0-U for all runs. As the maximum ionic strength of Mn(III)-Hm is 9.37 X lo%%, the Mn(III)-Hm concentration change has no effect on the total ionic strength_ Results and discussion Spectrum studies Mn(III)-Hm is known as a very stable complex in alkaline solution, even kcZti 11) _ ocr BXe &&Sorr oe cancetr~~‘, ‘erawever, [email protected]>-S&n is reduced, as shown in Fig_ 2. Mn(IS‘l-I-Irn wi%h absorption bands at 355,462 and 560 nm is changed by the addition of concentrated hydrazineThe new spectra represented the formation of Mn(II)-Hm [l] _ The introduction of methylene blue into the system caused the regeneration of Mn(III)-Hm, as shown in Fig_ 2. The results gave evidence of the reduction of methy?ene blue by hydrazine catalyzed by Mn(III)-Hm_ Kinetic studies At high concentrations of hydrazine, a zero-order rate law with respect ty methylene blue is obtained in low conversions. As the reduction rate of
133
/-
/
/
.’
_-2;
/“\ / i i i
I i
‘\ ‘\ -\ -\--_
Fig. 2. Effect of hydrazine and methylene blue on the visible spectrum of Mn(III)_Hm. Reaction conditions: [Mn(III)-JSm] 2.1 x 10ezmM; [hydrazine] 33_3mM; [methylene bIue J 3.63 X 10~%nM; reaction temperature, 25 ‘C; -_ catalyst; - - - - - -, catalyst + + methyIene blue. hydrazine; ---I -, catalyst + hydrazine
P
20
40 N2H4
f
dl
Fig, 3_ ReIation between u and the concentration blue] [Mn(III)-Hm] 1.05 X 10%; [ methylene
of hydrazine. Reaction conditions: 1.45 x 10~%nM at 25 “CL
Fig_ 4. Relation between u, and the concentration tions: [Mn(III)-Hin] 1.05 X lo-%M; [hydrazine]
of methylene blue. 33.3mM at 25 “C.
Reaction
condi-
methylene blue was the same in air as in nitrogen atmosphere, the following studies were carried out in air. As methylene blue is reduced by hydrazine, even in the absence of catalyst, the activities of Mn(III)-Hm were expressed by subtracting the noncatalyzed activities. The experiments were carried out at pH 13.1 because the rate was independent of pH between pH 12.5 and 13-Z The reduction rate was proportional to the concentration of catalyst, but showed Langmuir adsorption type dependence on the concentration of
134
hydrazine as well as on the concentration of methylene blue, as shown in Figs. 3 and 4. The conversion of methylene blue to the leuko form is described 133 by two univalent reduction steps, the first of which is considered slow and subject to ca*?alysis. MB + N2H4 v MB- + NaH,
slow
fast H20
MB- + NzH, LMB + NaHa
where MB and LMB represent methylene blue and its leuko form, respectively. The formation of N,H, radical has been proposed in the autoxidation of hydrazine by Wagnerova et aZ_ [4] _ The foIlowing scheme can be considered for the catalytic methylene blue reduction on the basis of the above results and Schrauzer’s mechanism [ 51 with respect to the cobalamin catalyzed reduction of methylene blue by thfol.
-
Mn(III)-Hm
+ N2H4
Mn(III)-Hm-N2H, Mn(II)-Hm
+ MB
Mn(II)-Hm-MB
6.x
,2 K, C
Mn( III)-Hm - NaH, Mn(II)-Hm
KB
k,
Mn( II)-Hm Mn(III)-Hm
(A)
+ N2H3
(B) s
-MB + MB
_
(0 (D)
The above reactions describe a process equivalent to a sequential enzyme-catalyzed reaction with two substrates for which rate expressions have been derived [S] . The rate of methylene blue decolorization is described by eqn_ (I)_
%
=
_W’W dt
or
1 -= v,
1
1
kl[Mn(III)-Hm],
KACN~H& 1 k2[Mn(III)-Hm]0
The validity of the mechanism
(2), as shown in Figs. 5 and 6.
is verified from the linear plot of eqn.
(2)
135
1c 0
8
-ik . In
‘0
0
“x 5
o”
/-
O
0 100 (1 / rf&?[s’i
200 -L n
Fig. 5. Relation between uo and hydrazine concentration_ J!im] 1.05 X lo-‘mM, [methylene blue] l-45 X lo-ImM Fig. 6_ Relation between u,, and the concentration tions: [Mn(iII)-EIm] l-05 x lo-‘mM, [hydrazine]
0
40
20 N2H4 /
Reaction conditions: at 25 “C_
of methylene blue- Reaction 33.3mM at 25 “C_
fMn(III)condi-
60
nM
Fig_ 7. Relation between the reduction rate of Mn(III)-Iim and the concentration hydrazine. Reaction conditions: [Mn(III)-Hm] 1.05 X lo-‘mM at 25 “C_
of
In order to determine these equilibrium and rate constants, it is necessary to obtain more detailed kinetic data- Under these experimental conditions, hydrazine in high concentration could reduce the central manganese ion from the trivalent oxidation state to divalent, as evidenced by the observed spectrum in Fig. 2, In the absence of methylene blue, the reduction of the central metal ion by hydrazine is observed, and the relation between the reduction rate, u, and the concentration of hydrazine is shown in Fig. 7. On the basis of the proposed mechanisms (A) and (B), the reduction rate is expressed as follows_
136
0
LOO
200
600
Fig. 8. Relation between the reduction rate of Mn(III)-Hm hydrazineReaction conditions: similar to the conditions
U=
and the concentration in Fig. 7.
k,~IMn(III)-~ml,CN,H~l,
of
(3)
I+ KJ%Wo
or 1 -= iJ
1
1
WLCMnUWHml,
+
IN2H4lo
1 hr[Mn(III)-Hm],
(4)
.
From the slope and the intercept of the straight line of eqn_ (4) in Fig. 8, KA and k, are calculated. Furthermore, from the linear plot in Figs. 5 and 6, the other rate constants are obtained as follows. KA = 6.25~1 fir
= 1.09
KB = 455 ks
x 10-2s-= X 104M-r
= 4.90
x 10-s s-l.
In this study, nitrogen was the only reaction product_ In addition to the scheme (A) - (D), the following process of the formation of molecular nitrogen from hydrazine was considered, like the alternate reaction schemes proposed by Wagnerova et aZ. [7]
=%J&
K& Effect
Mn(III)-Hm, -2e-
MI?
+
2N2H3
-
N,Hs
-
NzHz
+ N2H4
-N2.
of additives Extensive studies of the reactions of metallo-porphyrins with further ligands have been stimulated by their obvious relevance to the understanding
137
1.
IRIDIZOLE
I t. CYANIDE 8.
PYRWLF
I).
PWDIWE
Fig. 9. Effects of the axial ligands of Mn(III)Hm hydrazine. Reaction conditions: [Mn(III)-Hm] [methylene blue] l-45 X lo-‘mM at 25 “C.
on the reduction l-05 x lO@mM,
of methylene blue by [hydrazine] 33.3mM.
of haemoprotein [S - 111 _Limited comparisons are available of the relative affinities of ligands for ferriporphyrin, for example, cyanide > imidazole > pyridine. As with iron complexes, the manganese chelate in the trivalent state can combine with two more ligands to form pure- or mixed further complexes [ Xl]_ In the case of Mn(III)-Hm, the reduction of methylene blue was initiated by one electron transfer from hydrazine which was present in the axial Mn(III)-Hm coordination site of the catalystThe addition of a third component such as imidazole, pyridine, pyrrole, or cyanide into the reaction system influenced the rate of decolorization of methylene blue, as shown in Fig. 9_ The rate increased with the addition of the third component and then decreased through the maximum in the case of imidazole, pyrcoIe, and cyanide. The maximum was observed at the equimolar addition of the third component to the catalyst. Similar results are reported in the autoxidation of acetaldehyde catalyzed by cobalt-@-methyl)-tetraphenylporphyrin [12] _ A different phenomenon was observed in the case of pyridine, As shown in the Figure, the rate was independent of the amount of pyridine, even in excess concentration. Though no change in the spectrum was observed by the equimolar addition of pyrrole to Mn(III)-Hm, the spectrum of Mn(III)-Hm appeared upon the addition of hydrazine, and the peak decreased in the presence of
138
a further concentration of pyrrole. Similar spectra were also found in the case of imidazole and cyanide, By contrast, Mn(II)-Hm was produced in the same amount regardless of the ratio of pyridine to catalyst. Differences in the stimulation of cataIytic activity are explained by differences in the ability of the third components to complex with Mn(II)-Hm_ Therefore, the effect of the extra Iigand on the reduction rate may be expkined by the concept that an appropriate amount of l&and would coordinate to the central manganese ion of the planar porphyrin molecule as a fifth Iigand. This would facilitate electron transfer from a hydrazine moIecuIe as the sixth ligand to manganese ion. Excess ligand will prevent hydrazine coordination because of the occupation of the sixth position by the third component.
References 361. 1 P. A_ Loach and M. Calvin, Biochemistry, 2 (1963) 125. 2 I. Okura, N. Kim Thuan and T_ Keii, J. Mol. Catal., 5 (1979) 3 L_ Michaelis, in J_ B_ Summer and K_ Myrbach (eds.), The Enzymes, Vol. II, Part 2, Academic Press, New York, Edn, 1,1951, p_ l_ E. Schewertnerova and J. Veprek-Siska, CollectCzech. Chem. 4 D. M_ Wagnerova, Commun., 38 (1973) 756_ Biophys., 130 (1969) 257. 5 G. N. Schrauzer and J. W. Sibert, Arch. Biochem, Benjamin, New York, 1968, 6 S_ Benbard, The Structure and Function of Enzymes, p_ 92. E. Schewertnerova and J_ Veprek-Sislra, Collect. Czech- Chem7 D. M. Wagnerova, Commun., 39 (1974) 3 036_ 8 J. E. Falk, in J. E. FaIk, R. Lemberg and R. K. Morton (eds.), Haematin Enzymes, Pergamon, London, 1961, p_ 74. 9 J. E. Falk and J_ N_ Phillips, in D. P. Mellor and F. P_ Dwyer (eds.), Chelating Agents and Chelate Compounds, Academic Press, New York, 1964. 10 R_ Len&erg and J_ W_ Legge, Haematin Compounds and Bile Pigments. Interscience, New York, 1949. 11 J_ N. Phillips, Rev. Pure Appl_ Chem., 10 (1960) 35_ 12 M. Tezuka, 0. Sekiguchi, Y. Ohkatsu and T. Osa, Bull. Chem_ Sot. Jpn., 49 (1976)
2 765_
Journal of &foiecufar Catalysis, 5 (1979) 131 - 138 @ EXsevier Sequoia S-A., Iausanne -Printed in the Netherlands
REDUCTION OF METHYLENE &DE BY EIYDRAZINE BY MANGANESE(III)-IIEMATOPORPHYRIN
ICHIRO
OKURA.
NGUYEN
D
April
KIM THUAN
and TOMINAGA
Tdqm
CATALYZED
KElI
x%zs~stc ofS!'ebSu~,
Si---&
17-1978)
Summary The reduction of methylene blue is catalyzed by manganese (III)-hematoporphyrin_ From kinetic studies of the reaction, a reaction mechanism is proposed in which the catalyst is reduced first by hydrazine, and then methylene blue is reduced by the reduced catalyst_ The effect of additives, such as imidazole, pyrrole, cyanide, and pyridine, on the reaction has been studied- Differences in the stimulation of the catalytic activity are explained by differing abilities of the additives tcr,Zorm enrn$3exes -6%n rnim~7m~3~>1%>herna%~q++in-
Introduction Since manganese(III)-hematoporphyrin (Mn(III)-Hm) was synthesized by Calvin et al.[l] as a model complex in the photosynthetic process, few examples of catalysis by Mn(III)-Hm have been reported except for the autoxidation of hydrazine [2] _ In the autoxidation, the-oxidation state of the central ion has not changed during the reaction_ At higher concentrations of hydrazine, however, the oxidation state of manganese ion changed, evidently, from trivalent to divalent. This raised interest in utilizing the complex for methylene blue reduction due to the redox -z&ion of Mr&I)-Km in -the course of -&tierea-&.io~_ In this paper, the reduction of methylene blue by hydrazine with Mn(III)-Hm is described and the reaction mechanism is discussed on the basis of kinetic data_
Pyrrole (obtained from Yoneyama Yakuhin Co-), imidazole (Tokyo Kasei Co.), potassium cyanide and pyridine (Wako Pure Chemical Ind.), are used without further purification.
1T-
Ail I
A
B
C
Fig_ 1, Apparatus for the reduction ofmethykme (25 “C);33.Reactor; C. MagneZic skirter; D. RoIler off visib‘le @‘3f!CctNR.
blue by hydrazine. A- Tberrnosta~ E_ Spectrophotometer; F. Cell
pump;
Other chemicals used are the same as those described elsewhere [2] _ The reduction of methylene blue was carried out in a recirculating system, as outlined in Fig_ 1, Mn(III)-Hm (0.625mM) and hydrazine (33.3mM) were introduced into a reactor and methylene blue (217mM) added t-3 start the reaction_ The total volume of the reaction mixture was kept constant at 30 ml by adding O-IN sodium hydroxide_ In the studies of the effect of the axial ligands of Mn(III)-Hm, the third component was added just before the introduction of hydrazineThe rate of decolorization of methylene blue was followed by a Sltimadzu sgectro~hotom~, SEiXIel SWS-SMM, us&g a cell of 5.0 mm width, The concentration of methylene blue solution was followed automatically by measuring the absorbance change at 660 nm. The ionic strength was maintained at 0-U for all runs. As the maximum ionic strength of Mn(III)-Hm is 9.37 X lo%%, the Mn(III)-Hm concentration change has no effect on the total ionic strength_ Results and discussion Spectrum studies Mn(III)-Hm is known as a very stable complex in alkaline solution, even kcZti 11) _ ocr BXe &&Sorr oe cancetr~~‘, ‘erawever, [email protected]>-S&n is reduced, as shown in Fig_ 2. Mn(IS‘l-I-Irn wi%h absorption bands at 355,462 and 560 nm is changed by the addition of concentrated hydrazineThe new spectra represented the formation of Mn(II)-Hm [l] _ The introduction of methylene blue into the system caused the regeneration of Mn(III)-Hm, as shown in Fig_ 2. The results gave evidence of the reduction of methy?ene blue by hydrazine catalyzed by Mn(III)-Hm_ Kinetic studies At high concentrations of hydrazine, a zero-order rate law with respect ty methylene blue is obtained in low conversions. As the reduction rate of
133
/-
/
/
.’
_-2;
/“\ / i i i
I i
‘\ ‘\ -\ -\--_
Fig. 2. Effect of hydrazine and methylene blue on the visible spectrum of Mn(III)_Hm. Reaction conditions: [Mn(III)-JSm] 2.1 x 10ezmM; [hydrazine] 33_3mM; [methylene bIue J 3.63 X 10~%nM; reaction temperature, 25 ‘C; -_ catalyst; - - - - - -, catalyst + + methyIene blue. hydrazine; ---I -, catalyst + hydrazine
P
20
40 N2H4
f
dl
Fig, 3_ ReIation between u and the concentration blue] [Mn(III)-Hm] 1.05 X 10%; [ methylene
of hydrazine. Reaction conditions: 1.45 x 10~%nM at 25 “CL
Fig_ 4. Relation between u, and the concentration tions: [Mn(III)-Hin] 1.05 X lo-%M; [hydrazine]
of methylene blue. 33.3mM at 25 “C.
Reaction
condi-
methylene blue was the same in air as in nitrogen atmosphere, the following studies were carried out in air. As methylene blue is reduced by hydrazine, even in the absence of catalyst, the activities of Mn(III)-Hm were expressed by subtracting the noncatalyzed activities. The experiments were carried out at pH 13.1 because the rate was independent of pH between pH 12.5 and 13-Z The reduction rate was proportional to the concentration of catalyst, but showed Langmuir adsorption type dependence on the concentration of
134
hydrazine as well as on the concentration of methylene blue, as shown in Figs. 3 and 4. The conversion of methylene blue to the leuko form is described 133 by two univalent reduction steps, the first of which is considered slow and subject to ca*?alysis. MB + N2H4 v MB- + NaH,
slow
fast H20
MB- + NzH, LMB + NaHa
where MB and LMB represent methylene blue and its leuko form, respectively. The formation of N,H, radical has been proposed in the autoxidation of hydrazine by Wagnerova et aZ_ [4] _ The foIlowing scheme can be considered for the catalytic methylene blue reduction on the basis of the above results and Schrauzer’s mechanism [ 51 with respect to the cobalamin catalyzed reduction of methylene blue by thfol.
-
Mn(III)-Hm
+ N2H4
Mn(III)-Hm-N2H, Mn(II)-Hm
+ MB
Mn(II)-Hm-MB
6.x
,2 K, C
Mn( III)-Hm - NaH, Mn(II)-Hm
KB
k,
Mn( II)-Hm Mn(III)-Hm
(A)
+ N2H3
(B) s
-MB + MB
_
(0 (D)
The above reactions describe a process equivalent to a sequential enzyme-catalyzed reaction with two substrates for which rate expressions have been derived [S] . The rate of methylene blue decolorization is described by eqn_ (I)_
%
=
_W’W dt
or
1 -= v,
1
1
kl[Mn(III)-Hm],
KACN~H& 1 k2[Mn(III)-Hm]0
The validity of the mechanism
(2), as shown in Figs. 5 and 6.
is verified from the linear plot of eqn.
(2)
135
1c 0
8
-ik . In
‘0
0
“x 5
o”
/-
O
0 100 (1 / rf&?[s’i
200 -L n
Fig. 5. Relation between uo and hydrazine concentration_ J!im] 1.05 X lo-‘mM, [methylene blue] l-45 X lo-ImM Fig. 6_ Relation between u,, and the concentration tions: [Mn(iII)-EIm] l-05 x lo-‘mM, [hydrazine]
0
40
20 N2H4 /
Reaction conditions: at 25 “C_
of methylene blue- Reaction 33.3mM at 25 “C_
fMn(III)condi-
60
nM
Fig_ 7. Relation between the reduction rate of Mn(III)-Iim and the concentration hydrazine. Reaction conditions: [Mn(III)-Hm] 1.05 X lo-‘mM at 25 “C_
of
In order to determine these equilibrium and rate constants, it is necessary to obtain more detailed kinetic data- Under these experimental conditions, hydrazine in high concentration could reduce the central manganese ion from the trivalent oxidation state to divalent, as evidenced by the observed spectrum in Fig. 2, In the absence of methylene blue, the reduction of the central metal ion by hydrazine is observed, and the relation between the reduction rate, u, and the concentration of hydrazine is shown in Fig. 7. On the basis of the proposed mechanisms (A) and (B), the reduction rate is expressed as follows_
136
0
LOO
200
600
Fig. 8. Relation between the reduction rate of Mn(III)-Hm hydrazineReaction conditions: similar to the conditions
U=
and the concentration in Fig. 7.
k,~IMn(III)-~ml,CN,H~l,
of
(3)
I+ KJ%Wo
or 1 -= iJ
1
1
WLCMnUWHml,
+
IN2H4lo
1 hr[Mn(III)-Hm],
(4)
.
From the slope and the intercept of the straight line of eqn_ (4) in Fig. 8, KA and k, are calculated. Furthermore, from the linear plot in Figs. 5 and 6, the other rate constants are obtained as follows. KA = 6.25~1 fir
= 1.09
KB = 455 ks
x 10-2s-= X 104M-r
= 4.90
x 10-s s-l.
In this study, nitrogen was the only reaction product_ In addition to the scheme (A) - (D), the following process of the formation of molecular nitrogen from hydrazine was considered, like the alternate reaction schemes proposed by Wagnerova et aZ. [7]
=%J&
K& Effect
Mn(III)-Hm, -2e-
MI?
+
2N2H3
-
N,Hs
-
NzHz
+ N2H4
-N2.
of additives Extensive studies of the reactions of metallo-porphyrins with further ligands have been stimulated by their obvious relevance to the understanding
137
1.
IRIDIZOLE
I t. CYANIDE 8.
PYRWLF
I).
PWDIWE
Fig. 9. Effects of the axial ligands of Mn(III)Hm hydrazine. Reaction conditions: [Mn(III)-Hm] [methylene blue] l-45 X lo-‘mM at 25 “C.
on the reduction l-05 x lO@mM,
of methylene blue by [hydrazine] 33.3mM.
of haemoprotein [S - 111 _Limited comparisons are available of the relative affinities of ligands for ferriporphyrin, for example, cyanide > imidazole > pyridine. As with iron complexes, the manganese chelate in the trivalent state can combine with two more ligands to form pure- or mixed further complexes [ Xl]_ In the case of Mn(III)-Hm, the reduction of methylene blue was initiated by one electron transfer from hydrazine which was present in the axial Mn(III)-Hm coordination site of the catalystThe addition of a third component such as imidazole, pyridine, pyrrole, or cyanide into the reaction system influenced the rate of decolorization of methylene blue, as shown in Fig. 9_ The rate increased with the addition of the third component and then decreased through the maximum in the case of imidazole, pyrcoIe, and cyanide. The maximum was observed at the equimolar addition of the third component to the catalyst. Similar results are reported in the autoxidation of acetaldehyde catalyzed by cobalt-@-methyl)-tetraphenylporphyrin [12] _ A different phenomenon was observed in the case of pyridine, As shown in the Figure, the rate was independent of the amount of pyridine, even in excess concentration. Though no change in the spectrum was observed by the equimolar addition of pyrrole to Mn(III)-Hm, the spectrum of Mn(III)-Hm appeared upon the addition of hydrazine, and the peak decreased in the presence of
138
a further concentration of pyrrole. Similar spectra were also found in the case of imidazole and cyanide, By contrast, Mn(II)-Hm was produced in the same amount regardless of the ratio of pyridine to catalyst. Differences in the stimulation of cataIytic activity are explained by differences in the ability of the third components to complex with Mn(II)-Hm_ Therefore, the effect of the extra Iigand on the reduction rate may be expkined by the concept that an appropriate amount of l&and would coordinate to the central manganese ion of the planar porphyrin molecule as a fifth Iigand. This would facilitate electron transfer from a hydrazine moIecuIe as the sixth ligand to manganese ion. Excess ligand will prevent hydrazine coordination because of the occupation of the sixth position by the third component.
References 361. 1 P. A_ Loach and M. Calvin, Biochemistry, 2 (1963) 125. 2 I. Okura, N. Kim Thuan and T_ Keii, J. Mol. Catal., 5 (1979) 3 L_ Michaelis, in J_ B_ Summer and K_ Myrbach (eds.), The Enzymes, Vol. II, Part 2, Academic Press, New York, Edn, 1,1951, p_ l_ E. Schewertnerova and J. Veprek-Siska, CollectCzech. Chem. 4 D. M_ Wagnerova, Commun., 38 (1973) 756_ Biophys., 130 (1969) 257. 5 G. N. Schrauzer and J. W. Sibert, Arch. Biochem, Benjamin, New York, 1968, 6 S_ Benbard, The Structure and Function of Enzymes, p_ 92. E. Schewertnerova and J_ Veprek-Sislra, Collect. Czech- Chem7 D. M. Wagnerova, Commun., 39 (1974) 3 036_ 8 J. E. Falk, in J. E. FaIk, R. Lemberg and R. K. Morton (eds.), Haematin Enzymes, Pergamon, London, 1961, p_ 74. 9 J. E. Falk and J_ N_ Phillips, in D. P. Mellor and F. P_ Dwyer (eds.), Chelating Agents and Chelate Compounds, Academic Press, New York, 1964. 10 R_ Len&erg and J_ W_ Legge, Haematin Compounds and Bile Pigments. Interscience, New York, 1949. 11 J_ N. Phillips, Rev. Pure Appl_ Chem., 10 (1960) 35_ 12 M. Tezuka, 0. Sekiguchi, Y. Ohkatsu and T. Osa, Bull. Chem_ Sot. Jpn., 49 (1976)
2 765_