No abstract

Compound-specific carbon isotope analysis of acetic acid is useful for origin discrimination and quality control of vinegar. Intramolecular carbon isotope distributions, which are each carbon isotope ratios of the methyl and carboxyl carbons in the acetic acid molecule, may be required to obtain more detailed information to discriminate such origin. In this study, improved gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) was used to measure the intramolecular carbon isotope distributions of acetic acid in 14 Japanese vinegars. The results demonstrated that the methyl carbons of acetic acid molecules in vinegars produced from plants were mostly isotopically depleted in (13)C relative to the carboxyl carbon. Moreover, isotopic differences (δ(13)C(carboxyl) - δ(13)C(methyl)) had a wide range from -0.3 to 18.2‰, and these values differed among botanical origins, C3, C4, and CAM plants.

The Met16Phe mutant of the type 1 copper protein pseudoazurin (PACu), in which a phenyl ring is introduced close to the imidazole moiety of the His81 ligand, has been characterized. NMR studies indicate that the introduced phenyl ring is parallel to the imidazole group of His81. The mutation has a subtle effect on the position of the two S(Cys)-->Cu(II) ligand-to-metal charge transfer bands in the visible spectrum of PACu(II) and a more significant influence on their intensities resulting in a A(459)/A(598) ratio of 0.31 for Met16Phe as compared to a A(453)/A(594) ratio of 0.43 for wild-type PACu(II) at pH 8. The electron paramagnetic resonance spectrum of the Met16Phe variant is more axial than that of the wild-type protein, and the resonance Raman spectrum of the mutant exhibits subtle differences. A C(gamma)H proton of Met86 exhibits a much smaller hyperfine shift in the paramagnetic (1)H NMR spectrum of Met16Phe PACu(II) as compared to its position in the wild-type protein, which indicates a weaker axial Cu-S(Met86) interaction in the mutant. The Met16Phe mutation results in an approximately 60 mV increase in the reduction potential of PACu. The pK(a) value of the ligand His81 decreases from 4.9 in wild-type PACu(I) to 4.5 in Met16Phe PACu(I) indicating that the pi-pi contact with Phe16 stabilizes the Cu-N(His81) interaction. The Met16Phe variant of PACu has a self-exchange rate constant at pH 7.6 (25 degrees C) of 9.8 x 10(3) M(-)(1) s(-)(1) as compared to the considerably smaller value of 3.7 x 10(3) M(-)(1) s(-)(1) for the wild-type protein under identical conditions. The enhanced electron transfer reactivity of Met16Phe PACu is a consequence of a lower reorganization energy due to additional active site rigidity caused by the pi-pi interaction between His81 and the introduced phenyl ring.

The isotopic analyses of rare earth elements (REE), Pb and U in several kinds of minerals from the clay and black shale layers above the Bangombé natural reactor, Gabon, were performed using a sensitive high-resolution microprobe (SHRIMP) to investigate the migration and retardation processes of fission products released from the reactor. REE isotopic data of the secondary minerals found in clays and black shales show that most of fission products were effectively trapped in the clays and not distributed into the black shales over the clays, which reveals that the clays play an important role in preventing fission products from spreading.Zircon crystals in the clays heterogeneously contain high-U regions (up to 28.3 wt%) with normal 235 U/ 238 U ratios (=0.00725) and significant amounts of fissiogenic REE, which suggest the occurrence of significant chemical fractionation between REE and U during the dissolution of reactor uraninite and the recrystallization of secondary U minerals. The Pb data suggest that galena grains in the clays were also formed by the mixing of the two components during a recent alteration event, and that a significant amount of Pb was derived from 2.05-Ga-old original uraninite rather than reactor uraninite. The U-Pb systematics of zircon provide chronological information on the old igneous activity associated with the basement rock formation at 2.8 Ga and geochemical evidence of the incomplete mixing of independent Pb and U sources. This result is consistent with previous chronological results in this area.