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561.
The absolute configuration of a binaphthyl-azobenzene dyad 2b, which has a chiral axis and a chiral plane, was determined by comparing the experimental circular dichroism (CD) spectra with the theoretical CD spectra calculated by the time-dependent (TD)-DFT method. The CD signals of the trans-azobenzene moiety indicated that the two benzene rings of this moiety are twisted unidirectionally. It is suggested that these dyads with shorter linkers may be suitable for use as chiroptical switches. 相似文献
562.
A new diffusive sampling method for the simultaneous determination of ozone and carbonyls in air has been developed. In this method, silica gel impregnated with a mixture of trans-1,2-bis(2-pyridyl)ethylene (2BPE) and 2,4-dinitrophenylhydrazine (DNPH) is used as the absorbent; further, a porous sintered polyethylene tube (PSP-diffusion filter), which acts as a diffusive membrane, and a small polypropylene syringe (PP-reservoir) for elution of the analytes from the absorbent are used. The carbonyls present in air react with DNPH in the absorbent to form hydrazone derivatives. Concurrently, ozone in the air reacts with 2BPE to form pyridine-2-aldehyde, which immediately reacts with DNPH to form a pyridine-2-aldehyde hydrazone derivative. All the hydrazones derived from airborne carbonyls, including pyridine-2-aldehyde (formed from ozone), are completely separated and analyzed by high-performance liquid chromatography. The sampling rates of ozone (44.6 mL min(-1)) and formaldehyde (72.0 mL min(-1)) are determined by comparison with the rates obtained in an active sampling method. The sampling rates of other carbonyl compounds are calculated from the respective molecular weights according to a rule based on Graham's law. The calculated sampling rates agree with the experimental values. The DSD-BPE/DNPH method is advantageous because it is simple and allows for the simultaneous analysis of ozone and carbonyls. 相似文献
563.
Taniguchi T Ishita A Uchiyama M Tamura O Muraoka O Tanabe G Ishibashi H 《The Journal of organic chemistry》2005,70(5):1922-1925
Bu3SnH-mediated radical cyclizations of 2-(2-bromophenyl)-N-ethenylacetamide gave 6-exo cyclization product 15 as the major product, whereas N-[2-(2-bromophenyl)ethyl]-N-ethenylamides gave almost exclusively 7-endo cyclization products. These results indicated that the position of the carbonyl group on enamide played an important role in deciding the course of the cyclization. The 7-endo selective cyclization was applied to concise construction of a cephalotaxine skeleton. 相似文献
564.
Hydride generation-flame atomic-absorption spectrometry as an arsenic detector for high-performance liquid chromatography 总被引:1,自引:0,他引:1
Hydride generation-flame atomic-absorption spectrometry (HG-FAAS) was used as a continuous detection system for arsenic in the eluate from high-performance liquid chromatography (HPLC). Four arsenic species (arsenite, arsenate, monomethylarsonate and dimethylarsinate) were detected separately with the HPLC-HG-FAAS system equipped with an anion-exchange column. When hijiki (Hizikia fusiforme) extract was examined, arsenate was found predominantly and arsenite and dimethylarsinate were also detected. Liver supernatant fraction obtained from mice administered orally with arsenite was also studied with the HPLC-HG-FAAS system equipped with a gel permeation column. In addition to free or low-molecular-weight ligand-bound arsenic, high-molecular-weight protein-bound arsenic fractions were also detected. 相似文献
565.
Assoc. Prof. Mineto Uchiyama Yukihiro Murakami Prof. Kotaro Satoh Prof. Masami Kamigaito 《Angewandte Chemie (International ed. in English)》2023,62(4):e202215021
We report a novel method to synthesize degradable poly(vinyl ether)s with cleavable thioacetal bonds periodically arranged in the main chains using controlled cationic copolymerization of vinyl ethers with a 7-membered cyclic thioacetal ( 7-CTA ) via degenerative chain transfer (DT) to the internal thioacetal bonds. The thioacetal bonds, which are introduced into the main chain by cationic ring-opening copolymerization of 7-CTA with vinyl ethers, serve as in-chain dormant species to allow homogeneous propagation of vinyl ethers for all internal segments to afford copolymers with controlled overall and segmental molecular weights. The obtained polymers can be degraded into low- and controlled-molecular-weight polymers with narrow molecular weight distributions via hydrolysis. Various vinyl ethers with hydrophobic, hydrophilic, and functional pendants are available. Finally, one-pot synthesis of multiblock copolymers and their degradation into diblock copolymers are also achieved. 相似文献
566.
Measurement of Local Sodium Ion Levels near Micelle Surfaces with Fluorescent Photoinduced‐Electron‐Transfer Sensors 下载免费PDF全文
Dr. Seiichi Uchiyama Eiko Fukatsu Dr. Gareth D. McClean Prof. A. Prasanna de Silva 《Angewandte Chemie (International ed. in English)》2016,55(2):768-771
The Na+ concentration near membranes controls our nerve signals aside from several other crucial bioprocesses. Fluorescent photoinduced electron transfer (PET) sensor molecules target Na+ ions in nanospaces near micellar membranes with excellent selectivity against H+. The Na+ concentration near anionic micelles was found to be higher than that in bulk water by factors of up to 160. Sensor molecules that are not held tightly to the micelle surface only detected a Na+ amplification factor of 8. These results were strengthened by the employment of control compounds whose PET processes are permanently “on” or “off”. 相似文献
567.
Improvement in Aqueous Solubility of Retinoic Acid Receptor (RAR) Agonists by Bending the Molecular Structure 下载免费PDF全文
Michiaki Hiramatsu Yuki Ichikawa Dr. Shusuke Tomoshige Prof. Makoto Makishima Dr. Atsuya Muranaka Prof. Masanobu Uchiyama Dr. Takao Yamaguchi Prof. Yuichi Hashimoto Dr. Minoru Ishikawa 《化学:亚洲杂志》2016,11(15):2210-2217
Aqueous solubility is a key requirement for many functional molecules, e. g., drug candidates. Decrease of the partition coefficient (log P) by chemical modification, i.e., introduction of hydrophilic group(s) into molecules, is a classical strategy for improving aqueous solubility. We have been investigating alternative strategies for improving the aqueous solubility of pharmaceutical compounds by disrupting intermolecular interactions. Here, we show that introducing a bend into the molecular structure of retinoic acid receptor (RAR) agonists by changing the substitution pattern from para to meta or ortho dramatically enhances aqueous solubility by up to 890‐fold. We found that meta analogs exhibit similar hydrophobicity to the parent para compound, and have lower melting points, supporting the idea that the increase of aqueous solubility was due to decreased intermolecular interactions in the solid state as a result of the structural changes. 相似文献