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81.
Samuel Piña Jr. Diana M. Cedillo Carlos Tamez Nezhueyotl Izquierdo Jason G. Parsons Jose J. Gutierrez 《Tetrahedron letters》2014
Reported here is the reduction of aromatic nitro compounds using sodium borohydride and transition metal sulfides as catalysts. The reaction conditions were optimized using the reduction of nitrobenzene as a model reaction. The catalysts studied were iron sulfide (Fe3S4), copper sulfide (CuS), zinc sulfide (ZnS), cobalt sulfide (Co3S4), and nickel sulfide (NiS). The reduction was monitored using gas chromatography. Quantitative conversions were achieved using Co3S4 and NiS, representing a ten-fold increase in reactivity compared to the non-catalyzed reaction. Fe3S4 and ZnS had no apparent effect on the reduction of nitrobenzene while the reduction using CuS showed a marginal increase. The reduction method was applied to several aryl-nitro derivatives containing either electron-withdrawing or electron-donating groups. Halogen containing aryl-nitro compounds were reduced without dehalogenation. The reduction had no effect on other functional groups such as carboxylic acids, esters, amides, or alkenes, indicating that the reduction is highly chemoselective. 相似文献
82.
Kevin B. Lavelle Samuel Glover William B. Connick Henry Spitz 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):677-683
This paper summarizes a new method for preconcentration of rusty metal samples using DIPEX® Actinide Resin from Eichrom Technologies prior to analysis for trace environmental actinides. This method allows for preconcentration of actinides for which the existing lanthanum coprecipitation method is ill-suited. The new and existing methods were shown to provide comparable results for plutonium analysis. Performance was compared for both lab-prepared controls and environmental samples. Using actinide resin, a mean 238Pu activity of 46 ± 13 % mBq (2σ) was measured, while 238Pu activity of 40 ± 6 % mBq (2σ) was measured using lanthanum coprecipitation. Small quantities of 239+240Pu, likely attributable to fallout, were also detected. 相似文献
83.
Alejandro Cañas Samuel Valdebenito Pablo Richter 《Analytical and bioanalytical chemistry》2014,406(8):2205-2210
A novel extraction approach was developed based on rotating-disk sorptive extraction (RDSE). In this approach the rotating-disk extraction device consists of a Teflon disk, with a cavity that is loaded with a commercial sorbent phase selected according to the polarity of the analyte. To avoid leakage of the sorbent, the cavity is covered with a fiberglass filter and sealed with a Teflon ring. The proposed novel analytical RDSE technique was used in this study to determine florfenicol levels in plasma as a model analyte, or sample system, to describe the pharmacokinetics of a veterinary formulation. The sorbent used for this application was the copolymer of divinylbenzene and N-vinylpyrrolidone (Oasis HLB), which was selected because the florfenicol molecule contains both hydrophilic and lipophilic moieties. After the extraction, final determination of the analyte was performed by HPLC–DAD. Calibration plots and other analytical features were obtained after 90 min of extraction. The calibration plot was linear over the interval 0.4–16 μg mL?1 (n?=?6), with R 2?=?0.9999. Recovery and repeatability were determined using a blank plasma sample spiked with 4.8 μg mL?1 florfenicol. A recovery of 91.5 %, with a relative standard deviation (RSD) of 8.8 %, was obtained when the extraction was evaluated using six different rotating-disk devices. Precision was also assessed, using the same disk (containing the same sorbent phase) for eight aliquots of the same sample. The RSD under these conditions was 10.2 %, clearly indicating that the sorptive phase could possibly be re-used. Accordingly, RDSE is a suitable sample preparation alternative to liquid–liquid extraction (LLE), solid-phase extraction (SPE), and stir-bar sorptive extraction (SBSE). 相似文献
84.
Antony Wing Hung Ng Samuel Kin-Man Lai Chi-Chung Yee Ho Yu Au-Yeung 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202110200
A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide–alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications. 相似文献
85.
Samuel Macario Padilla-Jimnez María Valentina Angoa-Prez Hortencia Gabriela Mena-Violante Guadalupe Oyoque-Salcedo Jos Luis Montaez-Soto Ernesto Oregel-Zamudio 《Molecules (Basel, Switzerland)》2021,26(2)
In the present study, organic volatile markers of three strawberry varieties (Albion, Festival and Frontera) during the maturation process were investigated. Forty metabolites associated with aroma in fresh strawberries were monitored during seven stages of maturation using gas chromatography–mass spectrometry (GC-MS) equipped with headspace-solid phase microextraction (HS-SPME). The data were evaluated using multivariate analysis to observe correlations between the organic volatile compound profile and the seven phenological stages of maturation for each strawberry variety. The dynamic levels of butanoic acid methyl ester, hexanoic acid methyl ester, octylcyclohexane, cyclohexane,1,1,2-trimethyl, linalool, tetradecane, and α-muurolene underwent distinctive changes in concentration during the maturation process. The multivariate analysis also allowed the identification of these compounds as possible volatile markers to measure the maturation of strawberry fruits in all three varieties. These findings highlight the importance of the timing of harvest and maturation stage in each variety to preserve or improve the desirable aromatic characteristics of strawberry fruits. 相似文献
86.
Can quantum-information theory shed light on black-hole evaporation? By entangling the in-fallen matter with an external system we show that the black-hole information paradox becomes more severe, even for cosmologically sized black holes. We rule out the possibility that the information about the in-fallen matter might hide in correlations between the Hawking radiation and the internal states of the black hole. As a consequence, either unitarity or Hawking's semiclassical predictions must break down. Any resolution of the black-hole information crisis must elucidate one of these possibilities. 相似文献
87.
Yogesh K. Vohra Gopi K. Samudrala Samuel L. Moore Jeffrey M. Montgomery Georgiy M. Tsoi Nenad Velisavljevic 《高压研究》2015,35(3):282-288
Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two-stage diamond anvil with 300?µm culet and with a CVD diamond second stage of 50?µm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86?GPa. The micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86?GPa. 相似文献
88.
The Use of Poly(Vinyl Alcohol) to Cross‐link Penicillinase for the Fabrication of a Penicillin Potentiometric Biosensor 下载免费PDF全文
Chemically cross‐linked PVA films are permeable matrices for the fabrication of biosensors. PVA provides an attractive immobilisation method as it preserves the enzymatic activity. Penicillinase (P’nase) was cross‐linked with poly(vinyl alcohol) (PVA) and bovine serum albumin (BSA). The optimum conditions for the of BSA‐PVA‐P’nase film were: 2.5 % w/v PVA, 0.006 % w/v BSA, 2.4 mM penicillin (Pen) and 16 U/mL P’nase. The minimum detectable concentration was 1.7 µM. The linear concentration range obtained for the BSA‐PVA film was 7.5–283 µM. The BSA‐PVA P’nase biosensor detected penicillin in amoxycillin with an average percentage recovery of 97±12 %. Higher penicillin concentrations (10–20 ppm) were detected more successfully than lower concentrations (≤5 ppm). These results indicate that further work is required to enable the successful detection of lower penicillin concentrations such as 5 ppm. 相似文献
89.
Large Hexagonal Bi‐ and Trilayer Graphene Single Crystals with Varied Interlayer Rotations 下载免费PDF全文
Zheng Yan Yuanyue Liu Long Ju Zhiwei Peng Dr. Jian Lin Dr. Gunuk Wang Dr. Haiqing Zhou Changsheng Xiang E. L. G. Samuel Carter Kittrell Dr. Vasilii I. Artyukhov Prof. Feng Wang Prof. Boris I. Yakobson Prof. James M. Tour 《Angewandte Chemie (International ed. in English)》2014,53(6):1565-1569
Bi‐ and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high‐quality large‐size bi‐ and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid‐like hexagonal bi‐ and trilayer graphene single‐crystal domains on Cu foils using chemical vapor deposition is reported. The as‐produced graphene domains show almost exclusively either 0° or 30° interlayer rotations. Raman spectroscopy, transmission electron microscopy, and Fourier‐transformed infrared spectroscopy were used to demonstrate that bilayer graphene domains with 0° interlayer stacking angles were Bernal stacked. Based on first‐principle calculations, it is proposed that rotations originate from the graphene nucleation at the Cu step, which explains the origin of the interlayer rotations and agrees well with the experimental observations. 相似文献
90.
Tuning Thiophene with Phosphorus: Synthesis and Electronic Properties of Benzobisthiaphospholes 下载免费PDF全文
Yunyan Qiu Joshua C. Worch Danielle N. Chirdon Aman Kaur Andrew B. Maurer Samuel Amsterdam Christopher R. Collins Prof. Tomislav Pintauer Prof. David Yaron Prof. Stefan Bernhard Prof. Kevin J. T. Noonan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7746-7751
1,4‐Dimercapto‐2,5‐diphosphinobenzene and 3,6‐bis(hexyloxy)‐1,4‐dimercapto‐2,5‐diphosphinobenzene were synthesized and combined with various acid chlorides to obtain a series of benzobisthiaphospholes. Electrochemical and photophysical properties of the substituted benzobisthiaphospholes have been evaluated, and the observed reductions are more facile than the related benzothiaphospholes and 2,6‐diphenylbenzobisthiazole. A benzobisthiaphosphole with C6H4‐p‐CN substituents was reduced at E1/2=?1.08 V (vs. saturated calomel electrode (SCE)). X‐ray diffraction data for several of these phosphorus heterocycles has been obtained, and DFT calculations at the B3LYP level have been performed. 相似文献