Complex with trivalent manganese

Several other examples of porphycene complexes with trivalent metals have also appeared in the literature.3.4.12,29,29-32 These include the aluminum(III) complexes 3.75a-d and 3.76, as well at the manganese(III), cobalt(III) iron(III), indium(III), and gallium(III) complexes 3.77-3.81 (Figure 3.1.16). Interestingly, a p-oxo-dialuminum(III)porphycenate 3.85 analogous to the p-oxo-diiron(III)porphycenates 3.72 and 3.73 has also been prepared. This was accomplished by heating the aluminum(III)porphycenato hydroxide complex 3.76 to 350 °C under reduced pressure (Scheme 3.1.12). 

While the stoichiometries of the Mn SOD enzymes appear to vary, the properties of the Mn-binding site do not. This is borne out in the electronic spectra of these proteins, which display a great degree of similarity despite the diversity of sources from which they have been isolated (Table II). This type of spectrum is distinctive for manganese in the trivalent oxidation state (3). The native enzymes are EPR silent, as might be anticipated if they contained Mn solely as the trivalent ion (S = 2) (1, 6,12,18-20, 24). However, when the enzymes are denatured, the characteristic six-line pattern of Mn(II) (I = 5/2) appears. Magnetic susceptibility studies with the E. coli SOD were consistent with the presence of a monomeric Mn(III) complex with a zero-field splitting of 1 to 2 cm-1 (4). The enzymes are additionally metal specific (however, see Refs. 36 and 37) metal reconstitution studies with E. coli and B. stearothermophilus revealed a strict requirement for Mn for superoxide dismutase activity (2, 22, 23). 

Structurally characterized trivalent manganese imidazole or imid-azolate complexes are also extremely rare. Current examples are limited to Mn(III) porphyrins (61), Mn(III) thiolates (Section III,B)> a Mn(III) salicylate complex (Section IV,B) and Mn(III) and Mn(IV) carboxylate complexes (Section VI,B) (62). None of these complexes contains a Mn-to-imidazole ratio greater than two consequently, no structural model for Mn SOD exists presently in Mn coordination chemistry. However, a five-coordinate Mn(II) monomer with three imidazole ligands, Mn(2-Me-ImH)3Cl2 (ImH = imidazole), has been characterized by X-ray diffraction techniques (63). 

Inman first showed that trivalent manganese formed a complex with transferrins by adding hydrogen peroxide to a mixture of Mn2+ and the apoenzyme (118). Displacement studies revealed that the order of binding for both the human serum enzyme and ovotransferrin was Fe3+ > Mn3+ > Cu2+. The Mn complex displayed a distinctive visible band maximum at 429 nm. Further studies of the Mn-containing protein by... 

For zinc and the first transition series metals manganese, iron, cobalt, and nickel, the free hydrated divalent cation form dominates the dissolved inorganic speciation. The trivalent metal cations Al +, Ga +, Tl +, Fe " ", and Bi + are strongly hydrolyzed (i.e., they form strong complexes with... 

Autoxidation of a,j8,y,5-tetraphenylporphorin-chromium(II), [TPPCr(II)], in tolulene solution proceeds in two stages with intermediate formation of a jii -oxo-chromium(III) complex [TPPCr(III)]20 prior to the chromium(II) product [TPPCr(IV)0]. Reaction of [TPPCrO] with [TPPCr(II)] yields the chromium (III) dimer. A pH-dependent equilibrium involving intramolecular electron transfer between Mn(II)-02 and Mn(III)-O2 is observed in the reaction of a tetrasulfonated-phthalocyanine manganese(II) complex with O2. The superoxide species is found only at pH 11.5-13.5. A manganese(II)-02 complex is also required to explain the absence of spectroscopic characteristics for both (II) and (III) oxidation states of manganese in the reaction of a trivalent pentadentate Schiff base derivative with O2. 

The redox polymerization of acrylonitrile initiated by dimethylsulf-oxide-Mn in H2SO4 and HCIO4 was investigated by Devi and Mahadevan [87-89]. Trivalent manganese forms a complex with dimethyl sulfoxide, followed by a reversible electron transfer. The radicals formed from the dissociation radical ion initiates the polymerization ... 

Complexes of pyridine-2-carboxylic acid (picolinic add, picH) and its substituted derivatives commonly exhibit the N—O bidentate nature of this aromatic amino add. From aqueous solutions chelates are obtained with the coordinated carboxylic group deprotonated, or neutral ligand forms may be isolated from non-aqueous media. Bis chelates are common in either case with bivalent metal ions. The tris chelates of trivalent cobalt and manganese have been structurally characterized recently. The latter is tetragonally distorted in a structure similar to Mn (oxine)j. 

The attractiion of the procedure is that manganese in alkaline medium gives a reddish-brown product with formaldoxime, HaC = NOH. The compound is said to be (CH2NO)3Mn, with the metal in the trivalent state. The same complex is also obtained with Mn(//) and Mn(/y). The procedure given here was developed by Koroleff (1974), mainly based on the technique used by Bradfield (1957). The complex is formed at a pH of about 10.5 in the... 

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