Study of manganese oxidation

Much effort has been devoted to the study of manganese oxides as positive electrode materials. Manganese oxides are very promising materials due to their abundance, environmental compatibility, low cost, favorable charge density, relatively high electronic conductivity, and suitable electrode potentials. Different structures of manganese oxides have been investigated and the best known, and the first to be... 

Another situation is observed when salts or transition metal complexes are added to an alcohol (primary or secondary) or alkylamine subjected to oxidation in this case, a prolonged retardation of the initiated oxidation occurs, owing to repeated chain termination. This was discovered for the first time in the study of cyclohexanol oxidation in the presence of copper salt [49]. Copper and manganese ions also exert an inhibiting effect on the initiated oxidation of 1,2-cyclohexadiene [12], aliphatic amines [19], and 1,2-disubstituted ethenes [13]. This is accounted for, first, by the dual redox nature of the peroxyl radicals H02, >C(0H)02 and >C(NHR)02 , and, second, for the ability of ions and complexes of transition metals to accept and release an electron when they are in an higher- and lower-valence state. 

The most direct evidence for surface precursor complex formation prior to electron transfer comes from a study of photoreduc-tive dissolution of iron oxide particles by citrate (37). Citrate adsorbs to iron oxide surface sites under dark conditions, but reduces surface sites at an appreciable rate only under illumination. Thus, citrate surface coverage can be measured in the dark, then correlated with rates of reductive dissolution under illumination. Results show that initial dissolution rates are directly related to the amount of surface bound citrate (37). Adsorption of calcium and phosphate has been found to inhibit reductive dissolution of manganese oxide by hydroquinone (33). The most likely explanation is that adsorbed calcium or phosphate molecules block inner-sphere complex formation between metal oxide surface sites and hydroquinone. 

Ratieuville Y, Wu BE, Lincot D, Vedel J, Yu LT (1999) Voltammetric and electrogravimetric study of manganese dioxide thin film electrodes. J Electrochem Soc 146 S-1-17/23. Bakardjieva S, Bezdicka P, Grygar T, Vorm P (2000) Reductive dissolution of microparticulate manganese oxides. J Solid State Electrochem 4 306-313. 

A significant result was obtained in the study of manganese porphyrin behavior in aqueous solutions [70], Manganese porphyrins (Mn3+P) in aqueous alkaline solutions are easily oxidized to corresponded Mn4+P, which, in their turn, are able to catalyze H202 synthesis in accordance with the following reaction ... 

Although the aforementioned routes provided the desired y-amino acids, it was desirable to develop a synthesis which incorporates the carboxylic acid oxidation state prior to coupling. We hypothesized that manganese-mediated radical addition would accomplish this objective, and therefore initiated a study of manganese-mediated coupling of alkyl iodides with y-hydrazonoesters [104]. We had already shown that the manganese-mediated radical addition conditions offer excellent chemoselectivity, but it remained to be seen whether the stereocontrol model would be disrupted would an additional Lewis basic ester function in the hydra-zone interfere with the role of In(III) in two-point binding and rotamer control ... 

Fleinlling A, Ruiz-Duenas FJ, Martinez MJ et al (1998) A study on reducing substrates of manganese-oxidizing peroxidases from Pleurotus eryngii and Bjerkandera adusta. FEBS Lett 428 141-146... 

The cluster molecular-orbital approach has also been successfully applied to studies of the electronic structures of manganese oxide minerals and related compounds, notably in the work of Sherman (1984) using the MS-SCF-2fa method. Calculations were performed on the clusters... 

Proton relaxation studies on chloroplast membranes have been presented. (791) Chloroplasts are the sites for the photosynthetic process, many details of which are still unknown. Manganese is known to be essential for oxygen evolution and thus it is important to be able to monitor manganese in its bound state. Water proton Ti values in chloroplast thylakoid membrane suspensions were used to monitor membrane-bound manganese. The results indicate that there may be a mixture of manganese oxidation states in the dark-adapted chloroplasts, with Mn(ii) and Mn(iii) being the most likely states. 

Manganese is cycled by microorganisms in similar ways to iron. Mineralization of manganese oxides (e.g., bimessite) is often attributed to a variety of bacteria, including Gallionella, Leptothrix, Sphaerotilus, Pseudomonas, and Pedomicrobium spp. Enzymes involved in Mn oxidation have been studied in some detail (e.g., Brouwers et al. 2000). 

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