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81.
82.
Abe M Adam W Hara M Hattori M Majima T Nojima M Tachibana K Tojo S 《Journal of the American Chemical Society》2002,124(23):6540-6541
Photodenitrogenation of the diazenes 4 affords exclusively the housanes 5 through intramolecular cyclization of the spectrally detected and characterized singlet diradicals 3. The lifetime of singlet diradical 3, determined by transient absorption measurements, depends on the Y and Z substituents at the para position of the phenyl ring and has the following order: Y, Z = OMe, OMe > OMe, CN > CN, CN > OMe, H > Cl, Cl approximately CN, H approximately Me, Me > H, H. This unprecedented substituent effect reveals stabilization of the singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals 3 through radical, zwitterionic, pi-bonding, and hyperconjugative structures. 相似文献
83.
Ishihara S Hill JP Shundo A Richards GJ Labuta J Ohkubo K Fukuzumi S Sato A Elsegood MR Teat SJ Ariga K 《Journal of the American Chemical Society》2011,133(40):16119-16126
Porphyrin derivatives bearing 2,6-di-tert-butylphenol substituents at their 5,15-positions undergo reversible photoredox switching between porphyrin and porphodimethene states as revealed by UV-vis spectroscopy, fluorescence spectroscopy, and X-ray single-crystal analyses. Photoredox interconversion is accompanied by substantial variations in electronic absorption and fluorescence emission spectra and a change of conformation of the tetrapyrrole macrocycle from planar to roof-shaped. Oxidation proceeds only under photoillumination of a dianionic state prepared through deprotonation using fluoride anions. Conversely, photoreduction occurs in the presence of a sacrificial electron donor. Transient absorption spectroscopy and electron spin resonance spectroscopy were applied to investigate the processes in photochemical reaction, and radical intermediates were characterized. That is, photooxidation initially results in a phenol-substituent-centered radical, while the reduction process occurs via a delocalized radical state involving both the macrocycle and 5,15-substituents. Forward and reverse photochemical processes are governed by different chemical mechanisms, giving the important benefit that conversion reactions are completely isolated, leading to better separation of the end states. Furthermore, energy diagrams based on electrochemical analyses (cyclic voltammetry) were used to account for the processes occurring during the photochemical reactions. Our molecular design indicates a simple and versatile method for producing photoredox macrocyclic compounds, which should lead to a new class of advanced functional materials suitable for application in molecular devices and machines. 相似文献
84.
Denuders are widely used for atmospheric analysis. Annular denuders are especially well-suited for preconcentration of trace gases compared to simpler single tube designs. While traditionally coated annular denuders have both bounding surfaces that behave as sinks, annular denuders/membrane-based scrubbers with the same basic geometric design and with only one of the annular surfaces functioning as sink (e.g., a membrane tube whose outer surface behaves as a sink disposed within an inert jacket tube) have become common. However, the gas collection efficiency of such devices cannot be expressed as a simple equation with fixed constants and there is no presently available tool to a priori determine the denuder performance or to design denuders with specific removal efficiencies at specific sampling rates. This paper presents a simple to use “spreadsheet calculator” for concentric annular denuders of any dimension based on known solutions to analogous heat transfer problems. The results from the present spreadsheet calculator are compared with results from a commercial computational fluid dynamics package (Fluent™; this takes significant expertise and development effort to run)—the two approaches produce essentially the same results. The present spreadsheet calculator can be used easily and simply without training and will be a useful tool for denuder users and designers. 相似文献
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A sealed tube dry combustion method that is simple, accurate, and precise for ultramicro determination of halogens in organic compounds has been developed. Samples below 1 mg are heated at 580 °C for 1 h in an electric furnace. After the combustion and absorption of the gaseous halogen, the interior of the tube is rinsed. Subsequent titration is carried out potentiometrically with silver nitrate and yielded standard deviations of 0.21% for chlorine, 0.17% for bromine, and 0.25% for iodine. 相似文献
88.
Manabu Kiguchi Tatsuya Konishi Shinichi Miura Kei Murakoshi 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):530
We have mechanically fabricated Ni and Cu nano-constrictions in solution to study their quantized conductance behavior under electrochemical potential control. Conductance quantization was observed at both metals in solution at room temperature for the first time. The conductance of Cu nano-constriction was quantized in units of G0(=2e2/h). A sharp 1G0 peak was observed in the conductance histogram. For Ni, a rather broad peak at 1–1.5G0 was observed in the histogram. The conductance quantization behavior was discussed by comparing previously documented results of nano-constrictions fabricated in air or ultra-high vacuum conditions, with those fabricated in solution. 相似文献
89.
Back Cover: CH Activation Generates Period‐Shortening Molecules That Target Cryptochrome in the Mammalian Circadian Clock (Angew. Chem. Int. Ed. 24/2015) 下载免费PDF全文
Tsuyoshi Oshima Dr. Iori Yamanaka Dr. Anupriya Kumar Dr. Junichiro Yamaguchi Dr. Taeko Nishiwaki‐Ohkawa Kei Muto Rika Kawamura Dr. Tsuyoshi Hirota Prof. Dr. Kazuhiro Yagita Prof. Dr. Stephan Irle Prof. Dr. Steve A. Kay Prof. Dr. Takashi Yoshimura Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2015,54(24):7200-7200
90.
Supramolecular Polyelectrolyte Complexes of Bone Morphogenetic Protein‐2 with Sulfonated Polyrotaxanes to Induce Enhanced Osteogenic Differentiation 下载免费PDF全文