Manganese L-Edge X-ray Absorption Spectroscopy of Manganese Catalase fromLactobacillus plantarumand Mixed Valence Manganese Complexes

<p>Being one of Earth&#180;s most redox-active elements, manganese participates in a great variety of environmental processes and is recognized as a key player controlling carbon turnover and oxidative transformation of organic and inorganic pollutants in soils. Moreover, Mn(III), Mn(IV) or mixed-valence Mn(III/IV) oxides and (oxy)hydroxides are highly effective sorbents for metal pollutants and nutrients in soils. Chemical reactivity, mobility, and bioavailability of Mn depend crucially on its speciation (chemical form). Yet, speciation studies on soil Mn are scarce. Therefore, we employed Mn K-edge (6,539 eV) X-ray absorption spectroscopy (XAS) to determine the oxidation states and local coordination environment (<5 &#197;) of Mn in oxic bulk soils (Cambisols, Luvisols, Stagnosol) from various field sites in Germany. Our XAS analyses cover 23 soil L, O, A, B, and C horizons exhibiting total Mn concentrations of between 200 and 2,300&#160;mg/kg. For comparison, we also analyze a suite of 31 Mn reference compounds, including Mn carbonate, phosphate, oxides and (oxy)hydroxides, silicates, organic Mn compounds as well as clay and hydroxide minerals with adsorbed Mn(II). X-ray absorption near-edge structure (XANES) spectra are evaluated for the oxidation states of soil Mn using linear combination fit (LCF) analysis. In addition, the average local coordination environment of Mn in the soil samples is assessed by shell-fitting of extended X-ray absorption fine structure (EXAFS) spectra. Based on our XAS results, we will test the following hypotheses: (1) Soil L/O horizons comprise predominantly organically complexed Mn(II) and Mn(III), dominated by the former Mn species; (2) soil A horizons are dominated by Mn(III/IV) in Mn(III/IV)-oxide structures owing to high microbial activity, release of Mn(II) from primary silicates and/or plant residues, and its subsequent (a)biotic oxidation and precipitation as Mn(III/IV) oxides; (3) soil B horizons of different genesis differ in their bulk Mn speciation; Bt horizons of Luvisols are dominated by Mn(II) associated with phyllosilicates, whereas the Stagnosol Bg horizon is dominated by layer-type Mn(III/IV) oxides. In summary, our study will provide first comprehensive data on bulk Mn speciation in three major European soil types. This knowledge is a prerequisite for a better understanding of the biogeochemical Mn cycle in soils.</p>

Download Full-text

X-RAY ABSORPTION SPECTROSCOPY IN NaCo2O4, LaCoO3andSrCoO3

Surface Review and Letters ◽

10.1142/s0218625x02003755 ◽

2002 ◽

Vol 09 (02) ◽

pp. 1327-1331 ◽

Cited By ~ 4

Author(s):

TOMOHIRA MATSUSHITA ◽

MASAICHIRO MIZUMAKI ◽

NAOSHI IKEDA ◽

MAKOTO NAKAZAWA ◽

AKANE AGUI ◽

...

Keyword(s):

Charge Transfer ◽

Absorption Spectroscopy ◽

Mixed Valence ◽

Layered System ◽

X Ray ◽

Best Fitting ◽

Ionic States ◽

X Ray Absorption ◽

Fitting Parameters ◽

Oxygen Atoms

We have performed Co 2p X-ray absorption spectroscopy (XAS) on a mixed valence hexagonal layered system NaCo 2 O 4, which shows large thermopower and metallic conductivity. We also measured XAS for SrCoO 3 and LaCoO 3 as examples of typical Co ionic states. The Co ions of the last two materials are octahedrally surrounded by oxygen atoms. A Co atom in NaCo 2 O 4 also has octahedral coordination with oxygen atoms but it is distorted slightly. The Co ions in SrCoO 3 and LaCoO 3 are in the d5 and d6 configuration respectively. The spectrum of NaCo 2 O 4 resembles that of LaCoO 3 rather than that of SrCoO 3; the Co ions in NaCo 2 O 4 can be regarded as the d6 configuration. Also, we have tried to calculate the XAS spectra by using the charge-transfer multiplet model (CT-M). Although we could not find out the best-fitting parameters, the results suggested the itinerancy of the Co 3d states.

Download Full-text

SOFT X-RAY ABSORPTION SPECTROSCOPY (MnL2,3 AND O K) IN MIXED VALENCE MANGANITES

Surface Review and Letters ◽

10.1142/s0218625x02003366 ◽

2002 ◽

Vol 09 (02) ◽

pp. 1071-1078 ◽

Cited By ~ 16

Author(s):

G. SUBÍAS ◽

J. GARCÍA ◽

M. C. SÁNCHEZ ◽

J. BLASCO ◽

M. G. PROIETTI

Keyword(s):

Absorption Spectroscopy ◽

Transition Metal Oxides ◽

Mixed Valence ◽

Spectral Shape ◽

Weighted Linear Combination ◽

Intermediate Composition ◽

X Ray ◽

Mixed Valence Manganites ◽

X Ray Absorption ◽

Doping Ratio

Several series of oxides with Mn in a mixed valence state were studied by means of soft X-ray absorption spectroscopy in order to understand better the nature of the electronic structure of these 3d transition metal oxides. XANES spectra of REMnO 3, RE 1-x Ca x MnO 3 (RE: La, Pr and Tb) and RE 0.5 A 0.5 MnO 3 (RE–A: La–Ca, Pr–Ca, Tb–Ca and Pr–Sr) series were recorded at both Mn L 2,3 and O K edges as a function of temperature. The Mn 2p spectra shift towards higher energies with increase of the formal valence of the Mn atom. Moreover, the spectral shape shows minor changes both with the doping ratio (x) and the variation of the RE and/or A cations. No significant changes are also found with temperature across the different magnetic and electrical phase transitions. On the other hand, the O 1s spectra are much more sensitive to the variation of RE (A) cations. The spectra show a prepeak structure at the Fermi energy corresponding to empty states in the O-2p band. This prepeak feature shifts to lower energies and increases its intensity as the formal valence of the Mn atom increases. Finally, neither O K-edge nor Mn L-edge XANES spectra of RE 1-x Ca x MnO 3 compounds can be reproduced by a weighted linear combination of REMnO 3 and CaMnO 3 spectra, indicating that these intermediate composition oxides cannot be described as fluctuating Mn 3+– Mn 4+ mixed valence systems.

Download Full-text