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排序方式: 共有193条查询结果,搜索用时 15 毫秒
1.
Dr. Qigang Zhong Dr. Artur Mardyukov Dr. Ephrath Solel Dr. Daniel Ebeling Prof. André Schirmeisen Prof. Peter R. Schreiner 《Angewandte Chemie (International ed. in English)》2023,62(46):e202310121
On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of unstable or unconventional molecules, which could not be obtained via traditional synthetic methods. A case in point is the on-surface synthesis of the structurally elusive cyclotriphosphazene (P3N3), an inorganic aromatic analogue of benzene. Here, we report the preparation of this fleetingly existing species on Cu(111) and Au(111) surfaces at 5.2 K through molecular manipulation with unprecedented precision, i.e., voltage pulse-induced sextuple dechlorination of an ultra-small (about 6 Å) hexachlorophosphazene P3N3Cl6 precursor by the tip of a scanning probe microscope. Real-space atomic-level imaging of cyclotriphosphazene reveals its planar D3h-symmetric ring structure. Furthermore, this demasking strategy has been expanded to generate cyclotriphosphazene from a hexaazide precursor P3N21 via a different stimulation method (photolysis) for complementary measurements by matrix isolation infrared and ultraviolet spectroscopy. 相似文献
2.
The paper refers to the solution of the integral equation for the acceleration (or pressure) potential for the study of subsonic linearized unsteady flow in view of aeroelastic applications. The case considered is relevant to a trapezoidal wing infinitely thin surface without discontinuities. As is well known [1, 2], the kernel of the integral equation exhibits three singularities, two of which are integrable in elementary form, whereas, for the third one integration in principal part according to Hadamard's rule is necessary. The kernel is therefore reworked in such a way that all the singularities are separated from the regular part, and eventually the discretization is performed in such a way that only the regular part is to be recalculated for each new value of the reduced frequency. Convergence tests, comparison with other methods of solution, and time saving associated with the technique of separation are also shown.Sommario. II lavoro tratta la risoluzione del problema relativo alla equazione integrale nel potenziale di accelerazione (o di pressione) per lo studio di una corrente subsonica linearizzata nonstazionaria, in vista di applicazioni aeroelastiche. Il caso considerato è quello di una superficie alare a pianta trapezoidale in assenza di discontinuità di spessore infinitesimo. Come è noto [1, 2], il nucleo della equazione integrale in parola presenta tre singolarità, due sole delle quali sono integrabili in forma elementare, (o riconducibili ad essa), mentre per la terza è necessario far ricorso alla integrazione in parte principale alla Hadamard. Il nucleo stesso viene quindi rielaborato in modo da isolare tutte le singolarità dalla componente regolare del nucleo; si procede così alla discretizzazione dell' equazione integrale, e, per ogni valore della frequenza ridotta, va ricalcolata solo la parte regolare della matrice risolvente. Vengono poi effettuati tests di convergenza, confronti con altri metodi di soluzione, analisi sui tempi di calcolo e risparmio di tempo di calcolo dovuto alla tecnica di separazione. 相似文献
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An emulsion interface materialization method was used to obtain amphiphilic silica Janus nanoparticles. Reducing the photosynthesis of aquatic organisms after water pollution. PW12O403− was introduced onto Janus particles by ion exchange, and an amphiphilic particle emulsion catalyst (PWO-J) was prepared. Hydrogen peroxide was used as the oxygen source, and the amphiphilicty of the catalyst was used to assemble the catalyst at the Pickering emulsion interface. The PWO-J catalyst was found to exhibit very high catalytic activity toward the oxidation of oleic acid in water-in-oil systems. The results showed that PWO-J catalysis of oxidation had similar results as CTAB and phosphotungstic acid (control system) under the same conditions. The azelaic acid recovery rate was 86.7%, and PWO-J could be reused 4 times. A reaction mechanism was proposed, and the constructed model was used to calculate a reaction rate constant of 15.32 × 10−5L•mol−1•s−1 for the PWO-J system. The PWO-J system had a lower activation energy than the control system, showing that the catalytic oxidation of oleic acid into azelaic acid was more likely to occur in the PWO-J system. 相似文献
6.
Mohammed A. Al-Nuri Nidal A. Za'tar Maher A. Abu-Eid Mohammad A. Hannoun Waheed J. Al-Jondi Ahmad I. Hussein 《光谱学快报》2013,46(8):1539-1543
A new method for isolation and specrophotometric determination of emodin is presented. Emodin was isolated by thin layer chromatography (tlc) and column chromatography (cc) techniques, as an orange long crystalline substance. Emodin exhibits two absorption maxima, at 420 and 520 nm. Stability of the color and the effect of pH were studied. Beer's law is obeyed in the range 2–30 ppm. The method is applied to the determination of emodin in roots, stems, and leaves of Rumex cyprius plant. 相似文献
7.
Abstract The cyclopentylmethyl free radical has been generated in argon matrices by UV irradiation of the corresponding diacyl peroxide at T = 20K. The infrared spectrum of the radical reveals an out-of-plane deformation of the radical center at 563 cm?1 characteristic of primary alkyl radicals. 相似文献
8.
以脱脂、除蛋白后的人乳为原料,联合运用阴离子交换色谱(AEC)、凝胶渗透色谱(GPC)和多孔石墨化碳色谱(PGC)等多种分离纯化技术制备了18种中性人乳寡糖,并采用电喷雾碰撞诱导串联质谱(ESI-CIDMS/MS)技术对其结构进行了鉴定.结果表明,所制备的中性人乳寡糖主要为三至九糖,含有半乳糖(Gal)、葡萄糖(Glc)、N-乙酰葡萄糖胺(GlcNAc)和岩藻糖(Fuc).所有寡糖的还原端均含有乳糖核心(Galβ1-4Glc),非还原端均含有乳糖胺(Galβ1-3/4GlcNAc),并且Fuc以α1-2,α1-3和α1-4连接于主链的Gal,Glc和GlcNAc上. 相似文献
9.
Kwenga Sichilongo 《International journal of environmental analytical chemistry》2013,93(13):973-984
Signal losses due to precursor ion isolation in a quadrupole-ion-trap mass spectrometer were studied using selected pesticides as model compounds. These signal losses originate from isolations of ion populations employing the broadband isolation (bbiso) waveform used in the Varian quadrupole ion-trap precursor ion isolation protocol. Signal losses were found to be ‘precursor ion structure’ dependent upon isolation using the bbiso. The effect of the bbiso waveform on the ionic structure and nature of substituents on the precursor ion was investigated. Isolation of old electron radical molecular ions of the type [M+?] showed remarkable signal losses compared with isolation of fragment ions derived from the same compounds. The impact of the bbiso waveform on the response of the instrument using mass spectrometry/mass spectrometry and the bbiso waveform was also examined. The response of the instrument as related to the calculated Instrument Detection Limits was observed to parallel ion population losses. 相似文献
10.
LI Cun-man XIAO Yuan-sheng XUE Xing-ya FENG Jia-tao ZHANG Xiu-li LIANG Xin-miao . Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian P. R. China . Hebei Research Centre of Analysis Testing Hebei University of Science Technology Shijiazhuang 《高等学校化学研究》2011,(3):392-396
An efficient preparative method was successfully developed for isolation and purification of unstable components from medicinal plant extracts, using a combined method of preparative high performance liquid chro-matography(HPLC) and solid-phase extraction(SPE). The aim of this study was to obtain an effective method with high preparative efficiency and importantly to avoid the transformation of unstable compounds. The preparative HPLC system was based on an LC/MS controlled four-channel autopurification sys... 相似文献