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81.
Mitamura K Sakai T Nakai R Wakamiya T Iida T Hofmann AF Ikegawa S 《Analytical and bioanalytical chemistry》2011,400(7):2061-2072
Previous work from this laboratory has reported the chemical synthesis of N-acetylcysteine (NAC) conjugates of natural bile acids (BAs) and shown that such novel conjugates can be formed in vivo in
rats to which NAC has been administered. The subsequent fate of such novel conjugates is not known. One possible biotransformation
is sulfation, a major pathway for BAs N-acylamidates in patients with cholestatic liver disease. Here, we report the chemical synthesis of the 3-sulfates of the
S-acyl NAC conjugates of five natural BAs (cholic, chenodeoxycholic, deoxycholic, ursodeoxycholic, and lithocholic). We also
measured the sulfation of N-acetylcysteine–natural bile acid (BA-NAC) conjugates when they were incubated with a rat liver cytosolic fraction. The chemical
structures of the BA-NAC 3-sulfates were confirmed by proton nuclear magnetic resonance, as well as by means of electrospray
ionization-linear ion trap mass spectrometry with negative-ion detection. Upon collision-induced dissociation of singly and
doubly charged deprotonated molecules, structurally informative product ions were observed. Using a triple-stage quadrupole
instrument, selected reaction monitoring analyses by monitoring characteristic transition ions allowed the achievement of
a highly sensitive and specific assay. When BA-NACs were incubated with a rat liver cytosolic fraction to which 3’-phosphoadenosine
5’-phosphosulfate was added, sulfation occurred, but the dominant reaction was hydrolysis of the S-acyl linkage to form the unconjugated BAs. Subsequent sulfation occurred at C-3 on the unconjugated BAs that had been formed
from the BA-NACs. Such sulfation was proportional to the hydrophobicity of the unconjugated bile acid. Thus, NAC conjugates
of BAs as well as their C-3 sulfates if formed in vivo are rapidly hydrolyzed by cytosolic enzymes. 相似文献
82.
H Hirai S Kagawa T Tanaka T Matsuoka T Yagi Y Ohishi S Nakano Y Yamamoto T Irifune 《The Journal of chemical physics》2012,137(7):074505
Low-temperature and high-pressure experiments were performed on the filled ice Ic structure of hydrogen hydrate at previously unexplored conditions of 5-50 GPa and 30-300 K using diamond anvil cells and a helium-refrigeration cryostat. In situ x-ray diffractometry revealed that the cubic filled ice Ic structure transformed to tetragonal at low temperatures and high pressures; the axis ratio of the tetragonal phase changed depending on the pressure and temperature. These results were consistent with theoretical predictions performed via first principle calculations. The tetragonal phase was determined to be stable above 20 GPa at 300 K, above 15 GPa at 200 K, and above 10 GPa at 100 K. Further changes in the lattice parameters were observed from about 45-50 GPa throughout the temperature region examined, which suggests the transformation to another high-pressure phase above 50 GPa. In our previous x-ray study that was performed up to 80 GPa at room temperature, a similar transformation was observed above 50 GPa. In this study, the observed change in the lattice parameters corresponds to the beginning of that transformation. The reasons for the transformation to the tetragonal structure are briefly discussed: the tetragonal structure might be induced due to changes in the vibrational or rotational modes of the hydrogen molecules under low temperature and high pressure. 相似文献
83.
Takahiro Matsuoka Naohisa Hirao Yasuo Ohishi Katsuya Shimizu Akihiko Machida Katsutoshi Aoki 《高压研究》2013,33(1):64-67
We present the first successful in situ simultaneous measurement of the electrical resistance and X-ray diffraction of FeH x (x~ 1) under high-pressure H2 up to 25.5 GPa and low temperatures down to 9 K. The electrical resistivity ρ showed a sharp increase with the formation of iron-hydride FeH x (x~ 1) at 3.5 GPa. The ?′-phase of FeH x was found to be metallic up to 25.5 GPa. The ρ vs. T curves up to 16.5 GPa approximately follow Fermi-liquid law below 25 K. However, T 5 was found to be better fitting at 25.5 GPa. This change can be considered to be related to the previously reported ferromagnetism collapse at corresponding pressure. 相似文献
84.
Electrical conductivity of FeO was measured up to 141 GPa and 2480 K in a laser-heated diamond-anvil cell. The results show that rock-salt (B1) type structured FeO metallizes at around 70 GPa and 1900 K without any structural phase transition. We computed fully self-consistently the electronic structure and the electrical conductivity of B1 FeO as a function of pressure and temperature, and found that although insulating as expected at ambient condition, B1 FeO metallizes at high temperatures, consistent with experiments. The observed metallization is related to spin crossover. 相似文献
85.
We investigate supercontinuum (SC) generation in highly nonlinear tellurite microstructured fibers pumped by a continuous wave (cw)/quasi-cw laser. We investigate two types of tellurite fibers. One type has the constant core diameter, and the other type has a longitudinally varying core diameter. For the fibers with a constant core diameter, when pumped in the anomalous dispersion region, the SC is symmetric in a fiber that has a zero dispersion wavelength close to the pump wavelength. For the fibers with a longitudinally varying diameter, the calculated phase-matching conditions show that they have a broad wavelength range of dispersive waves, and therefore the measured SC spectrum can be broader than one octave. In this work, the fiber lengths are as short as several tens of centimeters, and the pump power is in the watt level. 相似文献
86.
87.
Takaya Mitsui Naohisa Hirao Yasuo Ohishi Ryo Masuda Yumiko Nakamura Hirotoshi Enoki Kouji Sakaki Makoto Seto 《Journal of synchrotron radiation》2009,16(6):723-729
An energy‐domain 57Fe‐Mössbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh‐pressure measurements. The main optical system consists of a single‐line pure nuclear Bragg reflection from an oscillating 57FeBO3 single crystal near the Néel temperature and an X‐ray focusing device. The developed spectrometer can filter the Doppler‐shifted single‐line 57Fe‐Mössbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X‐rays make it easy to measure a small specimen in the DAC. The present paper introduces the design and performance of the SR 57Fe‐Mössbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure‐induced magnetic phase transition of polycrystalline 57Fe3BO6 and an unknown high‐pressure phase of Gd57Fe2 alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mössbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core. 相似文献
88.
Daisuke Taniguchi Akihiro Handa Risa Kodama Yohei Okada Kazuhiro Chiba 《Electroanalysis》2019,31(12):2299-2302
Although acid/base reactions are used widely to denature proteins during food processing, the application of reduction/oxidation (redox) reactions are relatively rare in this field. Herein, we demonstrate a “redox denaturation” of proteins, using egg plasma as a model. Electrochemical treatment of egg plasma in the presence of iodide ion (I?) selectively induced intramolecular disulfide bond formations, resulting in a different type of denaturation than that achieved via heat treatment. The reaction mechanism was examined through electrochemical analysis using cyclic voltammetry. Although the involvement of hypervalent iodine (“I+”) cannot be ruled out, molecular iodine (I2) generated at the surface of anode is the most likely oxidizing agent that formed the disulfide bonds. We believe that the redox denaturation of proteins described herein would be a promising approach in food processing and can find practical applications in this field. 相似文献
89.
Recently, many reports have emerged about circularly polarized luminescence (CPL) based on excimer emission of pyrenes. The intense CPL was observed from various pyrene derivatives such as pyrenes having chiral side chains, chiral oligomers bearing multiple pyrene rings, and pyrenes encapsulated by γ-cyclodextrins. The luminescence dissymmetry factor was found to be obviously higher than the absorption one in those pyrenes. In addition, several pyrenes revealed reversible “on-off” CPL switching upon the complexation/decomplexation of metal ions. 相似文献
90.