The chemical states of iron in ashes made from umoregi woods excavated in the foothills of Mt. Chokai in 2015, were characterized by using ⁵⁷Fe-Mössbauer spectroscopy and complementary analytical techniques. Four kinds of ancient trees, Japanese oak, Japanese chestnut, Japanese cedar, and Japanese zelkova were burned at 650-710°C. The ashes showed brown, reddish brown, or yellowish brown colors. Elements (> Na) in the ashes were determined by X-ray fluorescence spectrometry using a compact spectrometer. ⁵⁷Fe-Mössbauer spectra of the ashes and soil from the excavation site were recorded at 293 and 78 K. Raman scattering of the ashes was measured in the 1200-900 cm^-1 range. It was confirmed that calcium ferrite, Ca₂Fe₂O₅, was formed in the three ashes and its formation rate depended on the Fe/Ca ratio. Mössbauer spectra suggested that CaFe₂O₄ and/or similar iron oxides were contained in the two ashes. In the case of Fe/Ca > 2, sextet components assigned to α-Fe₂O₃ were also detected in the Mössbauer spectra. It was proposed that the color tone of the ashes was affected by Fe oxides. Mössbauer spectra suggested that some parts of Ca₂Fe₂O₅ formed in the ashes were such a fine particle that superparamagnetic phenomena were observable.

Scalar-relativistic density functional calculations were applied to the complexation of Eu(III) and Am(III) ions with alkyldithiophosphinic acid (S-donor) and alkylphosphinic acid (O-donor) from the viewpoint of the bonding nature of valence orbitals of a metal ion. Two and four conformers for the S-donor and O-donor complexes, respectively, were optimized at the ZORA-BP86 level. The stabilization energies by complex formation between the metal ions and the ligands toward the hydrated metal ions were estimated at the ZORA-B2PLYP level; these calculations reproduced the experimental Am/Eu selectivities, where the S-donor ligand preferably coordinates to Am(III) ion rather than Eu(III) ion, whereas O-donor ligand selectively coordinates to Eu(III) ion rather than Am(III) ion. Electron population analyses based on the molecular orbitals indicated that the d-orbital electrons in both the Eu and Am complexes participate in bonding covalent interactions with donor atoms and have surprisingly similar contributions. This result suggests that the covalent interaction between the d-orbital electrons in the metal ion and the ligands may be due to the geometrical similarity of the molecular structures of the Eu and Am complexes. In contrast, the contributions of the f-orbital electrons in the metal ions were different in the Eu and Am complexes. In the case of the S-donor complexes, non-bonding and bonding contributions were observed for the Eu and Am complexes, respectively, and in the case of the O-donor complex, bonding and anti-bonding contributions were observed for the Eu and Am complexes, respectively. This result implies that the selectivities of Eu(III) and Am(III) ions were determined by the difference in the participation of their f-orbital electrons, not their d-orbital electrons, in covalent interactions.

Concentrations of stable and radioactive carbon isotopes of organic matter were determined for suspended solids in surface water from the shallow and semi-closed Lake Kiba, Japan during June 2014 - March 2016. Particulate organic carbon (POC) concentrations were 0.44-5.01 mg L^-1, and δ¹³C and Δ¹⁴C values were, respectively, -30.3 to -22.8 ‰ and -156 to -33 ‰. The organic matter in suspended solid samples consistently showed depleted ¹⁴C, with an average Δ¹⁴C value of -81 ± 37‰. The carbon isotopes showed seasonal variation, being higher in summer, and with a positive correlation to POC contents. These results suggest that the POC characteristics are controlled by a mixture of two endmembers, organic matter produced by phytoplankton activity within the lake and the watershed organic matter, under a shallow and semi-closed environment.

The oxidation number and spin state of Fe in sample of ancient trees (umoregi trees) excavated from the foothills of Mt. Chokai in Japan were determined from the ⁵⁷Fe Mössbauer spectra. Moreover, basic structures of the Fe compounds were investigated using Mössbauer spectroscopy and complementary analytical techniques. The umoregi wood samples were prepared from the trunks of four tree species: Japanese cedar and Japanese zelkova which were brown and dark green, respectively; and Japanese oak and Japanese chestnut which were a pure black tone. Treatment with oxalic acid removed these characteristic colors from the samples. Mössbauer spectra were recorded at 293 K and 78 K, and their absorption line-shapes were analyzed using a curve-fitting method. At 293 K and 78 K, the respective isomer shifts of Fe were in the range of 0.21(3)-0.43(1) mm/s and 0.44(3)-0.53(1) mm/s, and the respective quadrupole splitting values were in the range of 0.62(6)-1.06(2) mm/s and 0.84(5)-1.07(1) mm/s. Although the resulting Mössbauer parameters confirmed that Fe in the umoregi wood was trivalent and its spin momentum number was 5/2 (i.e. high-spin state), no changes in spectral shape due to paramagnetic relaxation were observed even at 78 K. From this comprehensive investigation, it was determined that Fe³⁺ in Japanese oak and Japanese chestnut umoregi wood forms multinuclear complexes and has some differences in its first coordination sphere from Fe³⁺ in Japanese cedar and Japanese zelkova umoregi wood. Furthermore, it was suggested that the molecular structure of the Fe³⁺ complexes significantly affects the umoregi wood color tone.