Reinvestigation of the synthesis of isoliquiritigenin: application of Horner-Wadsworth-Emmons reaction and Claisen-Schmidt condensation

Isoliquiritigenin [ILG, (E)-1] was readily prepared via the Horner-Wadsworth-Emmons reactions using β-ketophosphonates 5a, b. An improved protocol for the synthesis of (E)-1 via the Claisen-Schmidt condensation was also presented.     

A hydrogenase model system based on the sequence of cytochrome c: photochemical hydrogen evolution in aqueous media

The diiron carbonyl cluster is held by a native CXXC motif, which includes Cys14 and Cys17, in the cytochrome c sequence. It is found that the diiron carbonyl complex works well as a catalyst for H(2) evolution. It has a TON of ～80 over 2 h at pH 4.7 in the presence of a Ru-photosensitizer and ascorbate as a sacrificial reagent in aqueous media.     

57Fe-Mössbauer spectroscopic studies of ferrocenylruthenocenium salts

Ferrocenylruthenocene was oxidized in sulfuric acid containing NH₄BF₄, giving a diamagnetic monocationic salt determined as ferrocenylruthenocenium⁺BF ₄ ^– .sd[1]Ferroceno[1]ruthenocenophane was oxidized with BF₃-Et₂O containing benzoquinone, giving a paramagnetic monocationic salt determined as [1]ferroceno[1]ruthenocenophanium⁺BF ₄ ^– . Based on the results of⁵⁷Fe-Mössbauer spectroscopic studies of the salts, it was concluded that an antiferromagnetic Ru(III)-Ru(III) bond is formed in the solid state.     

Nano-SIMS analysis of Mg, Sr, Ba and U in natural calcium carbonate.

Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10-20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A approximately 4 nA O- primary beam was used to sputter a 5-6-microm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500-5000 at 10% peak height was attained by an entrance slit set at 40 microm, and each exit slit at 50 microm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5-6 microm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to +/- 38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at < 10 microm scale.     

Crystal structure and mixed-valence state in 1′,1‴-dibutylbiferrocenium triiodide

In 1′, 1‴-dibutylbiferrocenium triiodide crystals A show temperature-independent trapped-valence state, while crystals B show a valence-delocalization of the mixed-valence state. The mixed-valence states of both crystals are discussed in relation to their crystal structures. Address after October 1991: Department of Chemistry, Faculty of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 724, Japan     

Level of dangling bond centres and its broadening due to disorder in amorphous silicon as elucidated by optically detected magnetic resonance measurements

The position of the energy level of dangling bond centres and its broadening have been investigated by optically detected magnetic resonance measurements in aSi, aSi:H and aSi:H, F. Correlation between level broadening and increase in the bandgap energy is discussed.