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991.
[reaction: see text] Alpha-nitro ketones can be transformed selectively into trialkyl-substituted pyrazines via reaction with alpha-amino ketones using octyl viologen as an electron-transfer reagent. The new synthetic method, and the optimal reaction conditions that allow for the regiochemical control, are described. 相似文献
992.
Two procedures are proposed for the potentiometric determination of Ag(I), Pd(II) and Au(III) in binary mixtures, by titration with potassium iodide solution, and use of a commercial iodide electrode as sensor. In the first procedure, two aliquots of the mixture are titrated, at pH 2.0 ± 0.2 and 9.0 ± 0.2, adjusted with dilute sulphuric acid and ammonia solution. At pH 2.0, the titrant reacts with both metals, whereas at pH 9.0, Ag(I) is the only reactant. The second procedure utilizes titration of two aliquots of the mixture in the presence and absence of a selective masking agent. The methods have been applied to the determination of these metals in some jewellery alloys. 相似文献
993.
The DDQ mediated oxidative cyclisation reactions of a series of dihydronaptho[2,1-b]furans were examined. In the presence of an acid catalyst, the reaction yielded polycyclic ethers and lactones in good to excellent yields. 相似文献
994.
995.
Modulation of Aggregation‐Induced Emission and Electroluminescence of Silole Derivatives by a Covalent Bonding Pattern 下载免费PDF全文
Han Nie Bin Chen Changyun Quan Dr. Jian Zhou Prof. Huayu Qiu Dr. Rongrong Hu Prof. Shi‐Jian Su Prof. Anjun Qin Prof. Zujin Zhao Prof. Ben Zhong Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8137-8147
The deciphering of structure–property relationships is of high importance to rational design of functional molecules and to explore their potential applications. In this work, a series of silole derivatives substituted with benzo[b]thiophene (BT) at the 2,5‐positions of the silole ring are synthesized and characterized. The experimental investigation reveals that the covalent bonding through the 2‐position of BT (2‐BT) with silole ring allows a better conjugation of the backbone than that achieved though the 5‐position of BT (5‐BT), and results in totally different emission behaviors. The silole derivatives with 5‐BT groups are weakly fluorescent in solutions, but are induced to emit intensely in aggregates, presenting excellent aggregation‐induced emission (AIE) characteristics. Those with 2‐BT groups can fluoresce more strongly in solutions, but no obvious emission enhancements are found in aggregates, suggesting they are not AIE‐active. Theoretical calculations disclose that the good conjugation lowers the rotational motions of BT groups, which enables the molecules to emit more efficiently in solutions. But the well‐conjugated planar backbone is prone to form strong intermoelcular interactions in aggregates, which decreases the emission efficiency. Non‐doped organic light‐emitting diodes (OLEDs) are fabricated by using these siloles as emitters. AIE‐active silole derivatives show much better elecroluminescence properties than those without the AIE characterisic, demonstrating the advantage of AIE‐active emitters in OLED applications. 相似文献
996.
Mahamed G. H. Omran Salah al-Sharhan Ayed Salman Maurice Clerc 《Computational Optimization and Applications》2013,56(2):457-480
In this paper, we investigate the use of low-discrepancy sequences to generate an initial population for population-based optimization algorithms. Previous studies have found that low-discrepancy sequences generally improve the performance of a population-based optimization algorithm. However, these studies generally have some major drawbacks like using a small set of biased problems and ignoring the use of non-parametric statistical tests. To address these shortcomings, we have used 19 functions (5 of them quasi-real-world problems), two popular low-discrepancy sequences and two well-known population-based optimization methods. According to our results, there is no evidence that using low-discrepancy sequences improves the performance of population-based search methods. 相似文献
997.
998.
R. Kefi C. Ben Nasr F. Lefebvre M. Rzaigui 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2231-2246
Along a systematic study of open-framework materials aiming at producing new molecular sieves, we characterized a new zincophosphate Zn(HPO4)Cl[C4H10N]. It was synthesized under mild conditions (r.t.) in the presence of pyrrolidinium as an organic-structure directing agent. The structure of this compound, determinated by single crystal X-ray diffraction, consists of anionic parallel [Zn(HPO4)Cl]? sheets alternating with thick slabs of organic molecules (C4H10N)+. These latters are linked to the anionic sheets through hydrogen bonds. Zn(HPO4)Cl[C4H10N] crystallizes in the monoclinic system and the space group C2/c (No. 9) with cell parameters a = 24,83(9), b = 9,258(5), c = 8.778(3), β = 110,45(4), Z = 8, V = 1891.0(14) Åt3, R = 0.045, and Rw = 0.07. Solid state 31P and 13C MAS NMR spectroscopies are in agreement with the X-ray structure. 相似文献
999.
Olfa Tabbene Dorra Gharbi Imen Ben Slimene Salem Elkahoui Mohamed Najib Alfeddy Pascal Cosette Maria Luisa Mangoni Thierry Jouenne Ferid Limam 《Applied biochemistry and biotechnology》2012,168(8):2245-2256
In the present study, we evaluated the antioxidant and the scavenging ability of C14, C15 and C16 bacillomycin D-like lipopeptides produced by B38 strain. They all displayed strong reducing power activity, hydroxyl and superoxide anion radicals scavenging activities and inhibition of lipid peroxidation. In addition, they were found to protect plasmid DNA damage from hydroxyl radical oxidation. Data suggested that their antioxidant potency can be attributed to the hydrophobic and aromatic side-chain groups of their amino acids as well as to the aliphatic chain of their beta amino fatty acids. Note that the hydrocarbon chain length did not interfere with the antioxidant power. Overall, such bacillomycin D lipopeptides which exhibit antioxidant and radical scavenging activities may be useful for cosmetic, therapeutic or pharmaceutical purposes in order to delay or prevent oxidative deterioration of manufactured products. 相似文献
1000.
R. Ebdelli A. Rouis R. Mlika I. Bonnamour N. Jaffrezic H. Ben Ouada J. Davenas 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):109-117
The development of sensors for the detection of transition metal ions has attracted a special attention because of the toxic impact of these elements on our environment. Due to their sensitivity, reliable, inexpensive and easy use for on site analysis, optical chemical sensors (optodes) have received an increasing attention for a rapid determination of toxic species in water. A new chromogenic calix[4]arene has been investigated on the basis of the high recognition properties of calixarenes associated to the optical response provided by their functionalization with a phenyl azo group. Thin tetrakis-(phenylazo) calix[4]arene amide derivative layers deposited on a glass suprasil substrate have been characterized by contact angle measurements showing a good surface coverage whereas a uniform morphology of the calixarene membrane in acetonitrile solvent was observed by scanning electron microscopy (SEM). The ability of the tetrakis-(phenylazo) calix[4]arene amide derivative thin film to complex Hg2+, Ni2+ and Eu3+ ions have been demonstrated by the modification of the calixarenes main absorption band at 343?nm and appearance of a new absorption band at 500?nm upon addition of Eu3+. The different sensors could be regenerated with hydrochloric acid. The dynamic concentration range, ion selectivity, response time, repeatability and reproducibility are discussed. These results are suitable to the development of optodes for the detection of metal pollutants. 相似文献