Studies of Mn II

As part of a study of Mn(ii) dialkyls, Wilkinson, Hursthouse, and co-workers45 reported the ESR spectrum of the approximately octahedral (u-xylyl-ene)Mn(dmpe)2 (Figure 4.11a) (dmpe = Me2PCH2CH2PMe2). 

Bleam.W.F. McBride, M.B. (1985) Cluster formation vs. isolated site formation. A study of Mn(II) and Mg(II) adsorption on boehmite and goethite. J. Colloid Interface Sd. 103 ... 

Oxidation Kinetics of Mn(II). This section addresses the question of whether the Mn(II) oxidation rates shown in Figure 4 can be explained by microbiological or abiotic pathways. Several incubation studies of Mn(II) with natural water, natural particulate matter, or pure cultures reported evidence for microbial catalysis of Mn(II) oxidation (4, 18, 54-58). In bottom waters of Lake Zurich (58) and in water samples from the marine fjord of Saanich Inlet (18) maximum Mn oxidation occurred at around 33 and 20 °C, respectively. These results strongly suggest microbial catalysis. In the case of abiotic catalysis, a steady increase in the oxidation rate with temperature is to be expected (16). Working with water samples from the bottom of Lake Zurich that were spiked with Mn(II) at 2 or 10 xM, Diem (58) found a Michaelis-Menten-type rate law for Mn(II) oxidation ... 

Bleam, W. F., and McBride, M. B. (1985). Cluster fomiation versus isolated-site adsoip-tion a study of Mn(Ii) and Mg(Ii) adsoiption on Boeluinte and Goethite. J. Colloid Interface Sci. 103, 124-132. 

The hydrodynamics of the moving drop are difficult to calculate, particularly the flow characteristics within the droplet itself. However, this technique is still used widely, because it is a simple and straightforward method. It was recently applied to study the stripping-extraction kinetics of Mn(II) in an aqueous-kerosene system [50,51]. The effect of anionic surfactants on the kinetics of extraction of lactic acid from an aqueous phase by Alamine 336 in a toluene phase was also studied by this technique [52]. 

All the ions studied, except phthalate, inhibit the oxidation of Mn(II) to some degree. The relative extent to which these ions (at the concentrations indicated) affect the rate of Mn(II) oxidation is as follows ... 

The rates of Mn(II) removal in some natural waters are similar to the Mn(II) oxidation rates predicted on the basis of these laboratory studies. However, in other cases the rate of manganese removal in natural waters is much faster than that expected on the basis of this work. In these systems significant manganese removal may occur as the result of adsorption, bacterially mediated oxidation, or biological uptake. 

Ohsaka s group has extensively examined the electrochemical behavior of both chemically and electrochemically deposited Mn02, both as discrete NPs and as nanostructured interfacial materials [61,64—81]. We focus here on two of their studies that exemplify the electrocatalytic nature of these nanoscale materials. In the first effort, El-Deab and Ohsaka explored the electrocatalytic behavior of MnOOH nanorods that had been electrodeposited onto Pt electrodes by oxidation of Mn(II) in an aqueous solution of manganese acetate [76]. The nanorods had average diameters of 20 nm and aspect ratios of 45 (i.e. average lengths of 900 nm) and covered nearly... 

By regulating the level of Mn(II), it should be possible to maximize production of either enzyme. In the present study, we examined the interactive effects of carbon, nitrogen and manganese in regulation of LiP and MnP. 

Interaction of Mn(II) with Carbon and Nitrogen. We attempted to determine an optimal carbon concentration and carbonrnitrogen ratio for LiP and MnP over low and high Mn(II) ranges, respectively. Earlier studies had shown that the optimum Mn(n) was less than 1 ppm for LiP and greats than 25 ppm for MnP (72). We wanted... 

Third, the effects of Mn(II) are only conspicuous when nitrogen is limiting. At low carbon levels, LiP is derepressed, but the very low cell yields make even very small Mn(II) concentrations effective in repressing LiP activity. The genetic regulatory elements are not yet known for these enzymes, but recent studies have shown that Mn regulates expression of MnP by P. chrysosporium 14),... 

The oxidation of Mn(II) by oxygen in homogeneous solution is extremely slow (on a time scale of years) (46), but it is catalyzed by the adsorption of Mn(II) on oxide surfaces (47, 48). The main oxidation pathway under natural conditions, however, is assumed to be the microbially mediated oxidation that occurs on the time scale of hours to days. The importance of microbial oxidation of Mn(II) in natural environments has been demonstrated in a number of studies (49-54). 

These results are in broad agreement with the findings in ref. 11, which indicate the reduction of Cr(VI) in the presence of H2S. In Saanich Inlet H2S is always present in the deeper water, whereas in Lake Greifen an intermediate situation is observed with the predominance of Mn(II) in the hypolimnion. The method used for the determination of Cr(III) in ref. 11 would probably include colloidal Cr(III) the present study attempted to determine dissolved Cr(III). 

Recent studies have shown that bacterial oxidation of Mn(II) to Mn(IV) can occur through Mn(III) formation [61], which in seawater can be stabilized by strong organic and inorganic complexes. It was found that Mn(III) forms a layer of high concentration (0.5-4.5 xM, ax = 15.8-16.2 kgm-3) below the... 

The presently accepted mechanism (52) involves the oxidation of an Fe(III) porphyrin by hydrogen peroxide to form an (FeIV=0)P+ analogous to the previously mentioned compound 1 of the heme catalase. This highly oxidized enzyme form subsequently reacts with an equivalent of Mn(II) to give compound 2, (FeIV=0)P, and Mn(III), which can diffuse off of the enzyme and into the medium. There is little restriction for the type of Mn(II) required in the first reductive step however, the subsequent reduction of compound 2 to resting enzyme requires an Mn(II) dicarboxylate or a-hydroxyacid complex. Studies suggest that the enzyme prefers the 1 1 Mn(II) oxalate complex as substrate. The... 

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