Peroxide decoloration of azo dyes catalyzed by manganese chlorophyll derivative in micellar solutions

Abstract

A manganese chlorophyll derivative (MnChlorophyll a) with hydrogen peroxide efficiently catalyzed the decoloration of C. I. Acid Orange 7, in various micellar solutions under mild conditions such as pH 6–8 and 25°C. In the experiment, peroxide decoloration was dependent on the structures of the surfactants and the presence of imidazole. The maximum decoloration rate was observed for MnChlorophyll a in hexadecyltrimethylammonium chloride (HDTAC) micellar solution, especially in the presence of imidazole.

Keywords

manganese chlorophyll derivative hydrogen peroxide decoloration rate surfactant solution ligand

Hydrogen peroxide decomposes into water and oxygen, and its effective use as an environmentally, friendly clean bleaching agent is desired.¹ Peroxide bleaching agents such as sodium percarbonate are widely used to bleach natural fabrics by adding sodium carbonate to the bleaching solution to activate hydrogen peroxide under high pH conditions (pH 10.5–11).^2,3 A bleaching agent when used under these conditions causes considerable damage to natural fabrics and, hence, an insight into peroxide bleaching conditions to prevent this damage is required. In future, it will be necessary for detergents to contain bleaching agents that are not only more active than those currently available but also are environmentally safe and cost-effective. For bleaching in aqueous solution, it has been shown that enzymes using biotechnology, inorganic acid salts, cationic activators, surfactants and a catalyst, for example a metal complex, activate the peroxide bleaching under mild conditions, such as a neutral pH and room temperature, in comparison to the use of hydrogen peroxide alone. Morita et al.⁴ reported kinetics of peroxidase catalyzed decoloration of Orange II with hydrogen peroxide. Letcher et al.⁵ reported preparing cotton nonwoven fabrics at low temperatures using hydrogen peroxide that was activated with sodium persulphate. Gürsoy et al.⁶ reported evaluating hydrogen peroxide bleaching with cationic bleach activators in a cold pad-batch process. Hage et al.⁷ reported non-heme manganese ion complex catalyzed low-temperature decoloration of tea-colored cotton, where hydrogen peroxide was used as a bleaching agent. Namboodri and Walsh⁸ reported the decoloration of dyes with hot peroxide catalyzed by a copper phthalocyanine-based dye, Reactive Blue 21. Recently, Sheriff et al.⁹ reported selective dye oxidation using in situ generated hydrogen peroxide catalyzed by manganese (II) ions.

In our previous papers, we reported the effect of various surfactants on the decoloration rate of azo dyes by hydrogen peroxide examined under mild conditions of pH 7 or 8 and 25°C.¹⁰ The decoloration rates were accelerated due to the presence of surfactants under mild conditions, depending on interactions between the dyes and surfactants. Furthermore, we also reported the peroxide decoloration of azo dyes catalyzed by manganese porphyrins.¹¹^–¹⁴ The decoloration rates of azo dyes by hydrogen peroxide in aqueous solutions were accelerated due to the presence of manganese porphyrin derivatives. Interestingly, the decoloration rate also depended on the concentration of ligands and it should be noted that imidazole plays a crucial role in determining this rate. Ishigure et al.¹⁵ reported peroxidative oxidation of C.I. Acid Orange 7 catalyzed by manganese chlorophyll derivatives at the micelles and lipid bilayers with hydrogen peroxide under mild conditions (pH 8, 25°C). Peroxide decoloration was dependent on the structures of manganese chlorophyll derivatives, surfactants, lipids, and the presence of imidazole. However, few studies, if any, have investigated the catalytic effect of chlorophyll complexes on the peroxide decoloration of azo dyes with the decomposition of hydrogen peroxide under mild conditions such as a neutral pH at 25°C. In this paper, we further report the peroxide decoloration of azo dyes, C.I. Acid Orange 7 and C.I. Food Yellow 3, catalyzed by manganese chlorophyll derivatives in micellar solutions of various surfactants with the different carbon numbers, under mild conditions such as pH 6–8 and 25°C. The manganese chlorophyll derivatives with hydrogen peroxide efficiently catalyzed the peroxide oxidation of the azo dyes in micellar solutions under mild conditions, in these reactions imidazole played an important role in increasing the rate of decoloration. A key aspect of peroxidative decoloration is its usefulness in providing insights into the catalytic effect of porphyrin structures on decoloration at the micellar surface. Manganese chlorophyll derivatives were selected because of their environmental safety, usefulness, well-defined biological properties, and industrial applications.

Experimental details

Materials

All reactions and chromatographic separations were carried out under minimum room lighting. Tetrahydrofurane (THF) and triethylamine were distilled and stored over molecular sieves. The other solvents used were of spectral grade or good quality. The silica gel used for column chromatography was silica gel, 70–230 mesh, 60 Å, obtained from Aldrich. Proton nuclear magnetic resonance (¹H NMR) spectra were obtained using the Varian Gemimi-300 NMR spectrometer, with tetramethylsilane used as an internal standard for CDCl₃. The UV absorption spectra were recorded on Hitachi U-3500 spectrophotometers. Mass spectra (MS) were obtained in α-cyano-4-hydroxycinnamic acid (CHCA), using a matrix-assisted laser desorption/ionization mode time of flight (MALDI-TOF) mass spectrometer (Perseptive Biosystems Voyager RN). Manganese-substituted chlorophyll a (MnChlorophyll a) and manganese mesoporphyrin monomethylester (MnMPMME) were prepared according to the process described in our previous papers.^13,15^–¹⁸ The chemical structures of manganese chlorophyll and manganese porphyrin derivatives used in this experiment are shown in Figure 1.

Figure 1.

Manganese chlorophyll derivative and manganese porphyrin derivative.

A 30% solution of hydrogen peroxide was provided by Sigma Pharmaceuticals Limited. The pH of the resulting solution was adjusted with tri(hydroxylmethyl)aminomethane and 1.0 N HCl (aq) to 8 and 7, respectively, and it was also adjusted with potassium dihydrogen phosphate and sodium hydroxide to 6. Azo dyes, C.I. Acid Orange 7 and C.I. Food Yellow 3, were provided by Tokyo Chemical Industry Co, Ltd, and were purified by recrystallization from aqueous ethanol. The chemical structures of these azo dyes are shown in Figure 2. The surfactants used in the experiment were octyltrimethylammonium chloride (OTAC), dodecyltrimethylammonium chloride (DTAC), hexadecyltrimethylammonium chloride (HDTAC), octadecyltrimethylammonium chloride (ODTAC) with carbon numbers 8, 12, 16, 18, respectively. The other surfactants used in the experiment were dodecylbenzenesulfonate (DBS), and polyethyleneglycol mono-p-octylphenyl ether (PEOPE). OTAC, DBS, and PEOPE were obtained from Tokyo Chemical Industry Co, Ltd. DTAC, HDTAC, and ODTAC were obtained from Nacalai Tesque, Inc. All of the surfactants were used without further purification.

Figure 2.

Azo dyes.

Decoloration of azo dyes

The effectiveness of bleaching by hydrogen peroxide in the presence of MnChlorophyll a and MnMPMME was evaluated by determining the decoloration curve of the azo dye in the bleaching solution. The required amount of an aqueous solution of the azo dye, which was further adjusted to the desired pH, was added to 25 ml of bleaching solution at 25°C to obtain an initial concentration of MnChlorophyll a and MnMPMME as 1 × 10⁻⁵mol dm⁻³, that of the azo dye as 1 × 10⁻⁴mol dm⁻³, and that of hydrogen peroxide as 3 × 10⁻²mol dm⁻³. To obtain the decoloration curves, each solution was placed as quickly as possible in a covered quartz optical cell, and the concentration of the coloring matter in the bleaching solution was determined by a spectrophotometric method at appropriate time intervals and the desired temperature using a Shimadzu spectrophotometer UV-160 A equipped with a thermostat. No interference occurred at the absorption maximum of the coloring matter by the products formed during decomposition. Under these conditions, it was observed that the calibration line followed Beer's law. The absorptions of C.I. Acid Orange 7 and C.I. Food Yellow 3 were measured at 484 nm and 481 nm, respectively.

Results and discussion

Figure 3 illustrates that for C.I. Acid Orange 7, the semilogarithmic plots of C ₀ /C _t versus the decoloration time show a straight line that passes through the origin, in the presence and absence of MnChlorophyll a, MnMPMME, and the cationic surfactant in the aqueous solution under the conditions of 25°C and pH 8, C₀ and C_t are the dye concentrations in the initial solution and at time t. The lines appear enhanced because of the presence of MnChlorophyll a. This result indicates that MnChlorophyll a catalyzes the decoloration of the azo dye by hydrogen peroxide under mild conditions.¹⁵ The decoloration rates are first order with respect to the dye concentration for the time. The following equation gives the numerical values that can be used later to compare the influences of various conditions of pH and temperature:

(1)

Figure 3.

Plot of (C₀/C_t) against decoloration time at 25°C for C.I. Acid Orange 7 in the presence of MnChlorophyll a and MnMPMME. Here C₀ and C_t are the dye concentrations in the initial solution at time t. Initial concentration of C.I. Acid Orange 7 = 1 × 10⁻⁴mol dm⁻³, Mn Chlorophyll a and MnMPMME = 1 × 10⁻⁵mol dm⁻³, HDTAC = 8 × 10⁻⁴mol dm⁻³, H₂O₂ = 3 × 10⁻²mol dm⁻³. –•–MnChlorophyll a, –▪–MnMPMME, –○–HDTAC.

The rate constant k based on the first-order kinetics is given in units of min⁻¹. The accuracy of the agreement was confirmed when the extreme values of the equation coefficients were found to be between 0.999 and 0.966 for all of the calculated values. The decoloration products of the azo dye by hydrogen peroxide are very complex. The mechanism for peroxide decoloration of dyes by hydrogen peroxide is not fully understood but the mechanism is believed to be that the hydroxyl radicals react with the organic coloring agent, destroying the azo dye.⁸ Moreover, Chivukula et al.¹⁹ reported that the peroxide oxidation of C.I. Acid Orange 7 caused the decoloration products such as 4-sulphophenyldiazene, 4-nitrosobenzene sulphonic acid, and quinone intermediates.

In our previous study, the effect of various surfactants on the decoloration rate of azo dyes by hydrogen peroxide was examined under mild conditions of pH 7 or 8 and 25°C.¹⁰ The decoloration rates were accelerated due to the presence of surfactants under mild conditions, especially near the critical micelle concentrations (CMCs). The maximum rate was observed in the presence of cationic surfactant, which depended on the interactions between the dyes and surfactants. The decoloration rates for C.I. Acid Orange 7 by hydrogen peroxide were obtained in the presence and absence of the cationic surfactants with the different carbon numbers at various surfactant concentrations.^10,20,21 Figure 4 shows the plots of the rate constant versus surfactant concentration for each case. This figure shows the plots of the decoloration rates for C.I. Acid Orange 7 on bleaching by hydrogen peroxide in the presence of surfactants OTAC, DTAC, HDTAC, and ODTAC. As shown clearly in this figure, for all cases, the decoloration rate increases with the surfactant concentration, and it decreases with further addition of the cationic surfactant. Table 1 lists the rate constants of decoloration by hydrogen peroxide obtained for C.I. Acid Orange 7 and C.I. Food Yellow 3 near the CMC with the addition of various cationic surfactants. As seen clearly in Table 1, the maximum rate constant increases in the order of OTAC < ODTAC < DTAC < HDTAC. Thus, it can be deduced that the enhanced decoloration of C.I. Acid Orange 7 due to the presence of surfactants possibly depends on the carbon number transfer and the transfer of C.I. Acid Orange 7 onto the surface of the micellar structure. These results suggest that the decoloration rate of C.I. Acid Orange 7 by hydrogen peroxide in the presence of surfactants depends not only on the electrostatic interactions between the dye and surfactants but also on the hydrophobic interactions between them. The maximum rate constant increases in the order of C.I. Food Yellow 3 < C.I. Acid Orange 7, indicating that in determining the decoloration rate, the hydrophobic interactions between the dye and the surfactants play a more important role in the rate than the electrostatic interactions between them because of the bulky structure of C.I. Food Yellow 3.²²

Figure 4.

Effect of cationic surfactants on the decoloration rate for C.I. Acid Orange 7 at 25°C, pH 8.0. Initial concentration of C.I. Acid Orange 7 = 1 × 10⁻⁴mol dm⁻³, H₂O₂ = 3 × 10⁻²mol dm⁻³. –○–HDTAC, –•–ODTAC, –▪–DTAC, –□–OTAC.

Table 1.

Rate constants for decoloration of azo dyes by hydrogen peroxide in the presence of cationic surfactants at 25°C and pH 8.0 (H₂O₂; 3 × 10⁻²mol dm⁻³, C.I. Acid Orange 7, C.I. Food Yellow 3; 1 × 10⁻⁴mol dm⁻³)

Surfactant	K_obs × 10² (min⁻¹)
Surfactant	C.I. Acid Orange 7	C.I. Food Yellow 3
None	0.05	0.03
OTAC^a	0.32	0.11
DTAC^b	0.66	0.24
HDTAC^c	0.80	0.42
ODTAC^d	0.33	0.14

OTAC, 2 × 10⁻²mol dm⁻³.

DTAC, 8 × 10⁻³mol dm⁻³.

HDTAC, 8 × 10⁻⁴mol dm⁻³.

ODTAC, 5 × 10⁻⁴mol dm⁻³.

Further, the decoloration rate of C.I. Acid Orange 7 with hydrogen peroxide catalyzed by MnChlorophyll a was examined in the presence of various surfactants at pH 8 to provide an insight into the charge effect of the dye–surfactant interaction as well as the hydrophobic interactions, summarized in Table 2. The decoloration rate with HDTAC, PEOPE, and DBS depended on their concentrations, where the maximum decoloration rate was observed near the CMC. These results also proved that the decoloration rate increased in the order of DBS < PEOPE < HDTAC. The decoloration of the dye observed in the HDTAC micelle was more enhanced than that observed in PEOPE and DBS. This result indicates that HDTAC plays an important role in inducing a complex formation between MnChlorophyll a and the azo dyes, with hydrogen peroxide being oxidized. The result indicates that the decoloration rates depend on the electrostatic interaction between the dye (anion) and the hydrophilic part of the surfactant in a hydrophobic environment, and this result is consistent with that obtained in a previous study.¹⁰ Mitsuishi et al.²³ reported that the interactions between methyl orange anion and dodecyltrimethylammonium cation were interrupted because of the presence of sodium chloride. These results further indicate that in the presence of cationic surfactant, the decoloration rates depend on the electrostatic interaction between the dye and the surfactant. Kawaguchi²⁴ reported that the volume of and surface area of the micellar structure increase with the length of the chain of the sucrose fatty acid monoester. He also reported that the micellar structures of other surfactants show a similar tendency. This result indicates that the phytol group contributes to the increase in the decoloration rate, suggesting that the phytol group plays an important role in hydrophobic domain formation along with HDTAC through the hydrophobic interaction occurring in the micellar reaction. The mechanism that governs the peroxide decoloration of dyes by hydrogen peroxide in such a micellar solution has not yet been completely understood. However, it is presumed that in this mechanism, the hydroxyl radicals react with the organic coloring agent, thus destroying the chromophore at the surface of the micellar structure.^7,15 For example, after the decomposition of C.I. Acid Orange 7, the dye decoloration products were found to be 4-sulphophenyldiazene, 4-nitrosobenzene sulphonic acid, and quinone intermediates as described above.^13,19 It is possible that in the mechanism of decoloration, MnChlorophyll a decomposes hydrogen peroxide and transfers one oxygen atom to the azo dye, presumably via high valent species such as Mn (IV) = O, which are intermediates in the bleaching solution, as shown previously.¹⁵

Table 2.

Rate constants for decoloration of C.I. Acid Orange 7 with H₂O₂ catalyzed by MnChlorophyll a in the presence of surfactants at 25°C and pH 8.0 (H₂O₂; 3 × 10⁻²mol dm⁻³, C.I. Acid Orange 7; 1 × 10⁻⁴mol dm⁻³, MnChlorophyll a; 1 × 10⁻⁵mol dm⁻³)

Catalyst	K_obs × 10² (min⁻¹)
Catalyst	OTAC^a	DTAC^b	HDTAC^c	ODTAC^d	PEOPE^e	DBS^f
None	0.32	0.66	0.80	0.33	0.05	0.07
MnChlorophyll a	100	180	252	227	202	62.0

OTAC, 2 × 10⁻²mol dm⁻³.

DTAC, 8 × 10⁻³mol dm⁻³.

HDTAC, 8 × 10⁻⁴mol dm⁻³.

ODTAC, 5 × 10⁻⁴mol dm⁻³.

PEOPE, 3.3 × 10⁻⁴mol dm⁻³.

DBS, 1 × 10⁻³mol dm⁻³.

The rates of decoloration of C.I. Acid Orange 7 and C.I. Food Yellow 3 with hydrogen peroxide catalyzed by MnChlorophyll a and MnMPMME were further examined in the presence of imidazole at pH 6–8, as summarized in Table 3. The rate of decoloration of C.I. Acid Orange 7 increased because of the presence of MnChlorophyll a in the surfactant aqueous solution at pH 6, as compared with the presence of MnMPMME at pH 8. Interestingly, the decoloration rates increased because of the presence of MnChlorophyll a, even under acidic conditions such as pH 6 for both dyes. The decoloration rates increased with the pH and with the addition of imidazole for MnChlorophyll a and MnMPMME in the micellar solutions, where the decoloration rates increased largely due to the presence of MnChlorophyll a in comparison with the presence of MnMPMME as described previously.¹⁵ Imidazole plays a crucial role in determining the decoloration rate by hydrogen peroxide. It is possible that in the presence of imidazole, MnChlorophyll a, and MnMPMME decompose hydrogen peroxide and transfer one oxygen atom to the azo dye, presumably via high valent species such as Mn (IV) = O which are intermediates in the bleaching solution as described above.^15,25^–²⁷ These results imply that the hydroxyl radicals react with the organic azo coloring agent, thus destroying the chromophore.^13,19 However, further investigations need to be carried out to determine the various roles of imidazole in hydrogen peroxide oxidation catalyzed by MnChlorophyll a.

Table 3.

Rate constants for decoloration of azo dyes with H₂O₂ catalyzed by MnChlorophyll a and MnMPMME at 25°C and various pH values (H₂O₂; 3 × 10⁻²mol dm⁻³, azo dyes; 1 × 10⁻⁴mol dm⁻³, HDTAC; 8 × 10⁻⁴mol dm⁻³)

Catalyst	K_obs × 10² (min⁻¹)
	C.I. Acid Orange 7						C.I. Food Yellow 3
	Imidazole (mol dm⁻³)
	None			1 × 10⁻²			None			1 × 10⁻²
	pH8	pH7	pH6	pH8	pH7	pH6	pH8	pH7	pH6	pH8	pH7	pH6
None	0.80	0.67	0.46	1.05	0.87	0.60	0.42	0.37	0.26	0.57	0.48	0.34
MnChlorophyll a^a	252	201	134	476	427	373	159	127	79	221	197	152
MnMPMME^a	3.46	−	–	36.4	–	–	0.76	–	–	12.1	–	–

MnChlorophyll a and MnMPMME, 1 × 10⁻⁵mol dm⁻³.

Conclusion

MnChlorophyll a with hydrogen peroxide in the presence of imidazole efficiently catalyzed the peroxide oxidation of azo dyes with different structure in micellar solutions of various structures of surfactants under mild conditions such as pH 6–8 and 25°C. The maximum decoloration rate was observed for MnChlorophyll a in HDTAC micellar solution, especially in the presence of imidadole. The decoloration rates increased because of the presence of MnChlorophyll a, even under acidic conditions such as pH 6 for azo dyes. The decoloration rates increased with the pH and with the addition of imidazole for MnChlorophyll a in the micellar solutions. The peroxidation of the azo dyes was dependent on the structures of the surfactant and MnChlorophyll a and the presence of imidazole.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References

Meshitsuka

. Non-chlorine bleaching of pulp. Sen’i Gakkaishi 1994; 50: 151–155.

Ohura

Yoshikawa

. Influence of bleaching by peroxide bleaching agent (part 1) influence of pH in bleaching solution on the decomposition of sodium percarbonate. J Home Econ Jpn 1985; 36: 497–502.

Ohura

. Effect of bleaching by peroxide bleaching agent (part 5) degradation of cellulose by bleaching agent. J Home Econ Jpn 1989; 40: 913–918.

Morita

Ito

Kamidate

Watanabe

. Kinetics of peroxidase catalyzed decoloration of Orange II with hydrogen peroxide. Textile Res J 1996; 66: 470–473.

Letcher

Govender

Lutseke

. Preparing cotton nonwoven fabrics at low temperatures using hydrogen peroxide activated with sodium persulphate. Textile Res J 1994; 64: 761–764.

Gürsoy

Lim

Hinks

Hauser

. Evaluating hydrogen peroxide bleaching with cationic bleach activators in a cold pad-batch process. Textile Res J 2004; 74: 970–976.

Hage

Iburg

Kerschner

Koek

Lempers

Martens

. Efficient manganese catalysts for low-temperature bleaching. Nature 1994; 369: 637–639.

Namboodri

Walsh

. Decolorizing spent dyebath with hot peroxide. Am Dyest Rep 1995; 84: 86–95.

Sheriff

Cope

Ekwegh

. Calmagite dye oxidation using in situ generated hydrogen peroxide catalysed by manganese (II) ions. Dalton Trans 2007; 5119–5122.

10.

Tokuda

Oura

Nango

. Effect of surfactants on decoloration of various dyes by peroxide bleaching agents. Textile Res J 1999; 69: 456–462.

11.

Tokuda

Oura

Nango

. Decoloration of azo dyes by hydrogen peroxide catalyzed by water-soluble manganese porphyrins. Textile Res J 1999; 69: 956–960.

12.

Tokuda

Oura

Iwasaki

Takeuchi

Kashiwada

Nango

. Decolorisation of azo dyes with hydrogen peroxide catalyzed by manganese protoporphyrins. J Soc Dyers Colour 2000; 116(2): 42–47.

13.

Nango

Iwasaki

Takeuchi

Kurono

Tokuda

Oura

. Peroxide decoloration of azo dyes catalyzed by polyethylene glycol-linked manganese halogenated porphyrins. Langmuir 1998; 14: 3272–3278.

14.

Nakamura

Ohura

Ishigure

Iwasaki

Hirose

Nango

. Effect of polymer on peroxide decoloration of azo dye catalyzed by manganese porphyrin derivatives. Porphyrins 2009; 18(1): 21–27.

15.

Ishigure

Mitsui

Kondo

Kawabe

Kondo

Dewa

. Peroxide decoloration of CI Acid Orange 7 catalyzed by manganese chlorophyll derivatives at the surfaces of micelles and lipid bilayers. Langmuir 2010; 26: 7774–7782.

16.

Iida

Nango

Okada

Hikita

Matsuura

Kurihara

. Synthesis and Characterization of Hybrid Porphyrin Dimers and Halogenated Porphyrin Dimers. Bull Chem Soc Jpn 1995; 68: 1959–1968.

17.

Iida

Nango

Matsuura

Yamaguchi

Sato

Tamnaka

. Energy transfer and electron transfer of poly(ethylene glycol)-linked fluorinated porphyrin derivatives in lipid bilayers. Langmuir 1996; 12: 450–458.

18.

Nango

Hikita

Nakano

Yamada

Nagata

Kurono

. Manganese porphyrin-mediated electron transfer across a liposomal membrane and on an electrode modified with a lipid bilayer membrane. Langmuir 1998; 14: 407–416.

19.

Chivukula

Spadarao

Renganathan

. Lignin peroxidase-catalyzed oxidation of sulfonated azo dyes generates novel sulfophenyl hydroperoxides. Biochemistry 1995; 34: 7765–7772.

20.

Fendler

. Catalysis in Micellar and Macromolecular Systems, New York: Academic Press, 1975.

21.

Nakamura

. Effect of cationic surfactants and manganese mesoporphyrin derivatives on bleaching of CI Acid Orange 7 using hydrogen peroxides. Human Sciences 2010; 9: 149–154.

22.

Kamidate

Shibata

Watanabe

Morita

. Decoloration of azo dyes catalysed by peroxidase-hydrogen peroxide bleaching using p-iodophenol as activator. J Jpn Oil Chem Soc 1998; 47: 1345–1350.

23.

Mitsuishi

Yoshida

Urata

Hamada

Ishiwatari

. Effects of ionic strength, temperature, and urea on behaviors of Methyl Orange–dodecyltrimethylammonium complex. Sen’i Gakkaishi 1993; 49: 176–181.

24.

Kawaguchi

. Relation between the length of hydrocarbon chain and the structure of micellar. Interface 1995; 33: 291–294.

25.

Battioni

Renaud

Bartoli

Reina-Artiles

Fort

Mansuy

. Monooxygenase-like oxidation of hydrocarbons by H₂O₂ catalyzed by manganese porphyrins and imidazole: selection of the best catalytic system and nature of the active oxygen species. J Am Chem Soc 1988; 110: 8462–8470.

26.

Poulos

Krant

. The stereochemistry of peroxidase catalysis. J Biol Chem 1980; 255: 8199–8205.

27.

Morita

Yamaguchi

Komatsu

Ito

Kamidate

Watanabe

. Mechanism for the decoloration of Orange II catalyzed by horseradish peroxidase. J Jpn Oil Chem Soc 1999; 48: 793–800.