Dimanganese complexes of a septadentate ligand. Functional analogues of the manganese pseudocatalase

P. Mathur, M. Crowder, G Charles Dismukes

Research output: Contribution to journalArticle

151 Citations (Scopus)

Abstract

Two new dimanganese(II) complexes have been prepared and characterized as the first functional analogues of the manganese pseudocatalase enzyme of L. plantarum (Beyer, W. F.; Fridovich, I. Biochemistry 1986, 24, 6420). These have the formulas Mn2(L)Cl3 (1) and Mn2(L)(OH)Br2 (2) in which Cl1- and OH-, respectively, serve as one of two bridging ligands, the other coming from the alkoxide group of the binucleating ligand N,N,N′,N′-tetrakis(2-methylenebenz-imidazolyl)-1,3-diaminopropan-2- ol (HL). The solution structure of these complexes has been characterized by EPR spectroscopy at both 34 and 9 GHz. This reveals the presence of two equivalent high-spin Mn(II) ions electronically coupled by a weak electron spin exchange interaction. Analysis of the axial zero-field splitting (D = -0.072 cm-1) of this spin S = 5 complex in terms of the magnetic dipole interaction between the two Mn ions yields a lower limit to their separation of 3.2 Å. Cyclic voltammetry reveals that three separable oxidation processes occur for 2 at Ep = 0.60 V (A), 0.80 V (B), and 1.03 V (C), while 1 exhibits only two oxidations: a reversible one-electron process at 0.57 V (A) analogous to 2 and a second oxidation at 1.18 V corresponding to B + C. The hydroxide bridge in 2 thus appears to stabilize the Mn(III) oxidation state relative to Mn(II) in comparison with the chloride bridge in 1. The binuclear complexes 1 and 2 decompose H2O2 catalytically with an initial rate for 1 proportional to [H2O2]2[Mn2(L)Cl3] 1, while mononuclear Mn(II) is ineffective. The mechanism proceeds through the initial formation of the μ-oxo-containing MnIII intermediate, [Mn2 III(L)(O)]Cl2, which is reduced by a second H2O2 to release O2. A similar mechanism could be operating in the manganese pseudocatalase enzyme of L. plantarum, which is known to contain two Mn(III) per subunit and thus may have a binuclear Mn site.

Original languageEnglish
Pages (from-to)5227-5233
Number of pages7
JournalJournal of the American Chemical Society
Volume109
Issue number17
Publication statusPublished - 1987

Fingerprint

Manganese
Ligands
Electrons
Ions
Oxidation
Enzymes
Biochemistry
Chlorides
Spectrum Analysis
Exchange interactions
Cyclic voltammetry
Paramagnetic resonance
Spectroscopy
pseudocatalase
hydroxide ion

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Dimanganese complexes of a septadentate ligand. Functional analogues of the manganese pseudocatalase. / Mathur, P.; Crowder, M.; Dismukes, G Charles.

In: Journal of the American Chemical Society, Vol. 109, No. 17, 1987, p. 5227-5233.

Research output: Contribution to journalArticle

@article{db82e87dff114402a953dafd6ce40265,
title = "Dimanganese complexes of a septadentate ligand. Functional analogues of the manganese pseudocatalase",
abstract = "Two new dimanganese(II) complexes have been prepared and characterized as the first functional analogues of the manganese pseudocatalase enzyme of L. plantarum (Beyer, W. F.; Fridovich, I. Biochemistry 1986, 24, 6420). These have the formulas Mn2(L)Cl3 (1) and Mn2(L)(OH)Br2 (2) in which Cl1- and OH-, respectively, serve as one of two bridging ligands, the other coming from the alkoxide group of the binucleating ligand N,N,N′,N′-tetrakis(2-methylenebenz-imidazolyl)-1,3-diaminopropan-2- ol (HL). The solution structure of these complexes has been characterized by EPR spectroscopy at both 34 and 9 GHz. This reveals the presence of two equivalent high-spin Mn(II) ions electronically coupled by a weak electron spin exchange interaction. Analysis of the axial zero-field splitting (D = -0.072 cm-1) of this spin S = 5 complex in terms of the magnetic dipole interaction between the two Mn ions yields a lower limit to their separation of 3.2 {\AA}. Cyclic voltammetry reveals that three separable oxidation processes occur for 2 at Ep = 0.60 V (A), 0.80 V (B), and 1.03 V (C), while 1 exhibits only two oxidations: a reversible one-electron process at 0.57 V (A) analogous to 2 and a second oxidation at 1.18 V corresponding to B + C. The hydroxide bridge in 2 thus appears to stabilize the Mn(III) oxidation state relative to Mn(II) in comparison with the chloride bridge in 1. The binuclear complexes 1 and 2 decompose H2O2 catalytically with an initial rate for 1 proportional to [H2O2]2[Mn2(L)Cl3] 1, while mononuclear Mn(II) is ineffective. The mechanism proceeds through the initial formation of the μ-oxo-containing MnIII intermediate, [Mn2 III(L)(O)]Cl2, which is reduced by a second H2O2 to release O2. A similar mechanism could be operating in the manganese pseudocatalase enzyme of L. plantarum, which is known to contain two Mn(III) per subunit and thus may have a binuclear Mn site.",
author = "P. Mathur and M. Crowder and Dismukes, {G Charles}",
year = "1987",
language = "English",
volume = "109",
pages = "5227--5233",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "17",

}

TY - JOUR

T1 - Dimanganese complexes of a septadentate ligand. Functional analogues of the manganese pseudocatalase

AU - Mathur, P.

AU - Crowder, M.

AU - Dismukes, G Charles

PY - 1987

Y1 - 1987

N2 - Two new dimanganese(II) complexes have been prepared and characterized as the first functional analogues of the manganese pseudocatalase enzyme of L. plantarum (Beyer, W. F.; Fridovich, I. Biochemistry 1986, 24, 6420). These have the formulas Mn2(L)Cl3 (1) and Mn2(L)(OH)Br2 (2) in which Cl1- and OH-, respectively, serve as one of two bridging ligands, the other coming from the alkoxide group of the binucleating ligand N,N,N′,N′-tetrakis(2-methylenebenz-imidazolyl)-1,3-diaminopropan-2- ol (HL). The solution structure of these complexes has been characterized by EPR spectroscopy at both 34 and 9 GHz. This reveals the presence of two equivalent high-spin Mn(II) ions electronically coupled by a weak electron spin exchange interaction. Analysis of the axial zero-field splitting (D = -0.072 cm-1) of this spin S = 5 complex in terms of the magnetic dipole interaction between the two Mn ions yields a lower limit to their separation of 3.2 Å. Cyclic voltammetry reveals that three separable oxidation processes occur for 2 at Ep = 0.60 V (A), 0.80 V (B), and 1.03 V (C), while 1 exhibits only two oxidations: a reversible one-electron process at 0.57 V (A) analogous to 2 and a second oxidation at 1.18 V corresponding to B + C. The hydroxide bridge in 2 thus appears to stabilize the Mn(III) oxidation state relative to Mn(II) in comparison with the chloride bridge in 1. The binuclear complexes 1 and 2 decompose H2O2 catalytically with an initial rate for 1 proportional to [H2O2]2[Mn2(L)Cl3] 1, while mononuclear Mn(II) is ineffective. The mechanism proceeds through the initial formation of the μ-oxo-containing MnIII intermediate, [Mn2 III(L)(O)]Cl2, which is reduced by a second H2O2 to release O2. A similar mechanism could be operating in the manganese pseudocatalase enzyme of L. plantarum, which is known to contain two Mn(III) per subunit and thus may have a binuclear Mn site.

AB - Two new dimanganese(II) complexes have been prepared and characterized as the first functional analogues of the manganese pseudocatalase enzyme of L. plantarum (Beyer, W. F.; Fridovich, I. Biochemistry 1986, 24, 6420). These have the formulas Mn2(L)Cl3 (1) and Mn2(L)(OH)Br2 (2) in which Cl1- and OH-, respectively, serve as one of two bridging ligands, the other coming from the alkoxide group of the binucleating ligand N,N,N′,N′-tetrakis(2-methylenebenz-imidazolyl)-1,3-diaminopropan-2- ol (HL). The solution structure of these complexes has been characterized by EPR spectroscopy at both 34 and 9 GHz. This reveals the presence of two equivalent high-spin Mn(II) ions electronically coupled by a weak electron spin exchange interaction. Analysis of the axial zero-field splitting (D = -0.072 cm-1) of this spin S = 5 complex in terms of the magnetic dipole interaction between the two Mn ions yields a lower limit to their separation of 3.2 Å. Cyclic voltammetry reveals that three separable oxidation processes occur for 2 at Ep = 0.60 V (A), 0.80 V (B), and 1.03 V (C), while 1 exhibits only two oxidations: a reversible one-electron process at 0.57 V (A) analogous to 2 and a second oxidation at 1.18 V corresponding to B + C. The hydroxide bridge in 2 thus appears to stabilize the Mn(III) oxidation state relative to Mn(II) in comparison with the chloride bridge in 1. The binuclear complexes 1 and 2 decompose H2O2 catalytically with an initial rate for 1 proportional to [H2O2]2[Mn2(L)Cl3] 1, while mononuclear Mn(II) is ineffective. The mechanism proceeds through the initial formation of the μ-oxo-containing MnIII intermediate, [Mn2 III(L)(O)]Cl2, which is reduced by a second H2O2 to release O2. A similar mechanism could be operating in the manganese pseudocatalase enzyme of L. plantarum, which is known to contain two Mn(III) per subunit and thus may have a binuclear Mn site.

UR - http://www.scopus.com/inward/record.url?scp=0001665764&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0001665764&partnerID=8YFLogxK

M3 - Article

VL - 109

SP - 5227

EP - 5233

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 17

ER -