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31.
Adams LA Aggarwal VK Bonnert RV Bressel B Cox RJ Shepherd J de Vicente J Walter M Whittingham WG Winn CL 《The Journal of organic chemistry》2003,68(24):9433-9440
A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3]. 相似文献
32.
Measurement of rheological properties of corn stover suspensions 总被引:1,自引:0,他引:1
Corn stover is currently being evaluated as a feedstock for ethanol production. The corn stover suspensions fed to reactors
typically range between 10 and 40% solids. To simulate and design bioreactors for processing highly loaded corn stover suspensions,
the rheologic properties of the suspension must be measured. In systems with suspended solids, rheologic measurements are
difficult to perform owing to settling in the measurement devices. In this study, viscosities of corn stover suspensions were
measured using a helical ribbon impeller viscometer. A calibration procedure is required for the impeller method in order
to obtain the shear rate constant, k, which is dependent on the geometry of the measurement system. The corn stover suspensions are described using a power law
flow model. 相似文献
33.
34.
Svihla C. Kurt Dronawat Sundeep N. Hanley Thomas R. 《Applied biochemistry and biotechnology》1995,(1):355-366
It can be difficult to obtain reliable rheological data for filamentous fermentation broths using conventional instruments.
One common approach is to measure the torque drawn by an impeller rotating in the suspension (1–7). Many previous workers have assumed that the applicable shear rate in such a device is related to the impeller speed by
a fluid-independent constant determined by calibration with Newtonian and non-Newtonian fluids (1–9). The rheology ofAspergillus niger broths have been characterized using the impeller viscometer approach. The changes in the broth rheology were measured, and
used to interpret the growth of biomass and the evolution of the microorganism morphology. 相似文献
35.
36.
B.T. Luke 《SAR and QSAR in environmental research》2013,24(1):41-57
While quantitative structure-activity relationships attempt to predict the numerical value of the activities, it is found that statistically good predictors do not always do a good job of qualitatively determining the activity. This study shows how Fuzzy classifiers can be used to generate Fuzzy structure-activity relationships which can more accurately determine whether or not a compound will be highly inactive, moderately inactive or active, or highly active. Four examples of these classifiers are presented and applied to a well-studied activity dataset. 相似文献
37.
July 1969, 528 pages, illustrated, $25.50 相似文献
38.
Unraveling σ and π Effects on Magnetic Anisotropy in cis‐NiA4B2 Complexes: Magnetization,HF‐HFEPR Studies,First‐Principles Calculations,and Orbital Modeling
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Dr. Gaëlle Charron Dr. Elena Malkin Dr. Guillaume Rogez Dr. Luke J. Batchelor Dr. Sandra Mazerat Dr. Régis Guillot Dr. Nathalie Guihéry Dr. Anne‐Laure Barra Dr. Talal Mallah Dr. Hélène Bolvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16850-16862
By using complementary experimental techniques and first‐principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2v, has been investigated. Four complexes have the general formula [Ni(bpy)X2]n+ (bpy=2,2′‐bipyridine; X2=bpy ( 1 ), (NCS?)2 ( 2 ), C2O42? ( 3 ), NO3? ( 4 )). In the fifth complex, [Ni(HIM2‐py)2(NO3)]+ ( 5 ; HIM2‐py=2‐(2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2‐py. Analysis of the high‐field, high‐frequency electronic paramagnetic resonance (HF‐HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from ?1 to ?10 cm?1. First‐principles SO‐CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3 , on one hand, and 4 and 5 , on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters (D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg‐like orbitals and is due to the difference in the σ‐donor strength of NO3? and bpy or HIM2‐py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g‐like orbitals; and 2) the anisotropy of complexes 1 – 3 arises from the small splitting of the t2g‐like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. 相似文献
39.
Miroslav Jelínek Petr Písařík Tomáš Kocourek Josef Zemek Jaroslav Lukeš 《Applied Physics A: Materials Science & Processing》2013,110(4):943-947
A hybrid PLD system with ion bombardment of films was developed. Growing DLC films were modified during the laser deposition (10 J?cm?2) by argon ions with energy in the range from 40 eV to 210 eV and cathode current of 0.15 A and 0.5 A. The content of sp2 “graphitic” and sp3 “diamond” bonds was measured using XPS. Sp3 bonds changed from 60 % to 81 %. We found the highest sp3 content for energy of 40 eV. Hardness (and reduced Young’s modulus) were determined by nanoindentation and reached 49 GPa (277 GPa). Film adhesion was studied using the scratch test and was up to 14 N for titanium substrates. Relations among deposition conditions and measured properties are presented. 相似文献
40.
Zhiyuan Qian Luke Galuska William W. McNutt Michael U. Ocheje Youjun He Zhiqiang Cao Song Zhang Jie Xu Kunlun Hong Rene B. Goodman Simon Rondeau‐Gagn Jianguo Mei Xiaodan Gu 《Journal of Polymer Science.Polymer Physics》2019,57(23):1635-1644
Thermomechanical properties of polymers highly depend on their glass transition temperature (T g). Differential scanning calorimetry (DSC) is commonly used to measure T g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T g in such type of polymers. The changes in specific heat capacity (Δc p) at T g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc p from flexible polymer (0.28 J g?1 K?1 for polystyrene) to rigid CPs (10?3 J g?1 K?1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc p at T g by a factor of 10, confirming that backbone rigidity reduces the Δc p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc p. We conclude that the difficulties of determining T g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1635–1644 相似文献