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1.
Random walk properties and correlation factors for diffusion via the vacancy mechanism are calculated and compared for various three-dimensional lattices. By applying the theory of random walks on an imperfect lattice, the correlation factor for impurity diffusion is calculated rigorously for the five jump frequency model in the fee lattice.Presented at the Symposium on Random Walks, Gaithersburg, MD, June 1982. 相似文献
2.
Kazuhisa Sato Shunya Tashiro Shuhei Matsunaga Yohei Yamaguchi Takanori Kiguchi Toyohiko J. Konno 《哲学杂志》2018,98(21):1945-1960
We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg97Zn1Gd2 cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0?0?0?1)Mg plane is notable compared to the out-of-plane growth in the [0?0?0?1]Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)3Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg97Zn1Gd2 alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram. 相似文献
3.
Detection of oxygen addition peaks for terpendole E and related indole–diterpene alkaloids in a positive‐mode ESI‐MS 下载免费PDF全文
Yayoi Hongo Takemichi Nakamura Shunya Takahashi Takayuki Motoyama Toshiaki Hayashi Hiroshi Hirota Hiroyuki Osada Hiroyuki Koshino 《Journal of mass spectrometry : JMS》2014,49(6):537-542
This report describes that a regular positive electrospray ionization mass spectrometry (MS) analysis of terpendoles often causes unexpected oxygen additions to form [M + H + O]+ and [M + H + 2O]+, which might be a troublesome in the characterization of new natural analogues. The intensities of [M + H + O]+ and [M + H + 2O]+ among terpendoles were unpredictable and fluctuated largely. Simple electrochemical oxidation in electrospray ionization was insufficient to explain the phenomenon. So we studied factors to form [M + H + O]+ and [M + H + 2O]+ using terpendole E and natural terpendoles together with some model indole alkaloids. Similar oxygen addition was observed for 1,2,3,4‐tetrahydrocyclopent[b]indole, which is corresponding to the substructure of terpendole E. In tandem MS experiments, a major fragment ion at m/z 130 from protonated terpendole E was assigned to the substructure containing indole. When the [M + H + O]+ was selected as a precursor ion, the ion shifted to m/z 146. The same 16 Da shift of fragments was also observed for 1,2,3,4‐tetrahydrocyclopent[b]indole, indicating that the oxygen addition of terpendole E took place at the indole portion. However, the oxygen addition was absent for some terpendoles, even whose structure resembles terpendole E. The breakdown curves characterized the tandem MS features of terpendoles. Preferential dissociation into m/z 130 suggested the protonation tendency at the indole site. Terpendoles that are preferentially protonated at indole tend to form oxygen addition peaks, suggesting that the protonation feature contributes to the oxygen additions in some degrees. © 2014 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd. 相似文献
4.
Total synthesis of the proposed structure 2 for phomopsin B was achieved by using an intramolecular olefin metathesis as a key step. The spectral data, however, did not match with those of the natural product reported. Re-examination of the reported NMR data led to the structural revision of phomopsin B to known dothiorelone A 18. The R configuration of dothiorelone A was determined by total synthesis through a cross-metathesis with a chiral olefin 19. 相似文献
5.
Carina I. Jette Irina Geibel Shoshana Bachman Masaki Hayashi Shunya Sakurai Hideki Shimizu Jeremy B. Morgan Brian M. Stoltz 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4341-4345
Herein, we report the first Pd‐catalyzed enantioselective arylation of α‐substituted γ‐lactams. Two sets of conditions were developed for this transformation, allowing for the use of either aryl chlorides or bromides as electrophiles. Utilizing a highly electron‐rich dialkylphosphine ligand we have been able to construct α‐quaternary centers in good yields (up to 91 % yield) and high enantioselectivities (up to 97 % ee). 相似文献
6.
Asymmetric Induction by a Nitrogen 14N/15N Isotopomer in Conjunction with Asymmetric Autocatalysis 下载免费PDF全文
Dr. Arimasa Matsumoto Hanae Ozaki Shunya Harada Kyohei Tada Tomohiro Ayugase Hitomi Ozawa Prof. Dr. Tsuneomi Kawasaki Prof. Dr. Kenso Soai 《Angewandte Chemie (International ed. in English)》2016,55(49):15246-15249
Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N2,N2,N3,N3‐tetramethyl‐2,3‐butanediamine containing nitrogen (14N/15N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis. 相似文献
7.
Synthesis of (23E)-cycloart-23-ene-3beta,25-diol (1) and its 23Z-isomer 2 was achieved by using cycloartenol as a starting material, thus revising the proposed structure of natural 2 to 1 unequivocally. These synthetic studies revealed that the structural revision (Z-form --> E-form) should also be applied to terpenoids such as (23Z)-3beta-acetoxyeupha-7,23-diene-25-ol, (23Z)-tirucalla-7,23-diene-3beta,25-diol, quadrangularol A, quadrangularic acid K, and daurichromene C. 相似文献
8.
Matsumoto Yutaka Takeo Yoko Egawa Satoru Yamaguchi Gota Yokomae Shunya Takei Masashi Yumoto Hirokatsu Koyama Takahisa Ohashi Haruhiko Tono Kensuke Yabashi Makina Mimura Hidekazu Kimura Takashi 《Optical Review》2022,29(1):7-12
Optical Review - A microfluidic device was developed for coherent diffraction imaging using an X-ray free-electron laser (XFEL-CDI). Liquid samples, which are separately packed in reservoirs of the... 相似文献
9.
Kaho Tanaka Naohiko Akasaka Tomoyuki Kosai Shunya Honda Yuya Ushijima Shintaro Ishida Takeaki Iwamoto 《Molecules (Basel, Switzerland)》2021,26(6)
π-Electron systems of silicon have attracted attention because of their narrow HOMO-LUMO gap and high reactivity, but the structural diversity remains limited. Herein, new dialkylboryl-substituted disilenes were synthesized by the selective desilylation-borylation of the corresponding trimethylsilyl-substituted disilenes. The dialkylboryl-substituted disilenes were fully characterized by a combination of NMR spectroscopy, MS spectrometry, single-crystal X-ray diffraction analysis, and theoretical calculations. The longest-wavelength absorption bands of boryldisilenes were bathochromically shifted compared to the corresponding silyl-substituted disilenes, indicating a substantial conjugation between π(Si=Si) and vacant 2p(B) orbitals. In the presence of 4-(dimethylamino)pyridine (DMAP), the dialkylboryl groups in the boryl-substituted disilenes were easily converted to trimethylsilyl groups, suggesting the dialkylboryl-substituted disilenes in the presence of a base serve as the surrogates of disilenyl anions (disilenides). 相似文献
10.
Takahashi S Souma K Hashimoto R Koshino H Nakata T 《The Journal of organic chemistry》2004,69(13):4509-4515
The C(2)-symmetric macrodiolide core 2 of an antiviral agent, macroviracin A (1), was constructed in a single step by the intermolecular macrodimerization of C(22)-hydroxy carboxylic acid 3 with 2-chloro-1,3-dimethylimidazolinium chloride and DMAP in the presence of sodium hydride (NaH). The use of potassium hydride instead of NaH caused the intramolecular cyclization, predominantly providing the corresponding monomer 26. The acid 3 was synthesized through a series of reactions such as the coupling reaction of acetylene 5 and oxirane 6, stereoselective glycosidation with the trichloroacetimidate method, and Jones oxidation. 相似文献