排序方式: 共有34条查询结果,搜索用时 31 毫秒
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Keng Lung Lee Joey Feld Dr. Paul Hume Prof. Tilo Söhnel Dr. Erin Leitao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(2):815-824
A series of ammonium monosubstituted H-phosphonate salts were synthesized by combining H-phosphonate diesters with amines in the absence of solvent at 80 °C. Variation of the ester substituent and amine produced a range of ionic liquids with low melting points. The products and by-products were analyzed by spectroscopic and spectrometric techniques in order to get a better mechanistic picture of the dealkylation and formal dearylation observed. For dialkyl H-phosphonate diesters, (RO)2P(O)H (R=alkyl), the reaction proceeds via direct dealkylation with the reactivity increasing in the order R=iPr<Et<Me corresponding to DFT calculated activation enthalpies of 22.6, 20.8, and 17.9 kcal mol−1. For the diphenyl H-phosphonate diesters, (PhO)2P(O)H, the dearylation was found to proceed via phenol-assisted formation of a 5-coordinate intermediate, (PhO)3PH(OH), from which P(OPh)3 and water were eliminated. The presence of an equivalent of water then facilitated the formation of P(OH)2OPh and the amine, R'NH2, subsequently abstracted a proton from it to yield [(PhO)PH(O)O]-[R'NH3]+. 相似文献
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Gabriela Ionita Petre Ionita Victor EM. Sahini Constantin Luca 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):269-271
The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin. 相似文献
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The cosmological remnants of a first-order phase transition generally depend on the perturbations that the walls of expanding bubbles originate in the plasma. Several of the formation mechanisms occur when bubbles collide and lose their spherical symmetry. However, spherical bubbles are often considered in the literature, in particular for the calculation of gravitational waves. We study the steady state motion of bubble walls for different bubble symmetries. Using the bag equation of state, we discuss the propagation of phase transition fronts as detonations and subsonic or supersonic deflagrations. We consider the cases of spherical, cylindrical and planar walls, and compare the energy transferred to bulk motions of the relativistic fluid. We find that the different wall geometries give similar perturbations of the plasma. For the case of planar walls, we obtain analytical expressions for the kinetic energy in the bulk motions. As an application, we discuss the generation of gravitational waves. 相似文献
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We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux
lines in low T
c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line
lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends
to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the
destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has
employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo
technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing
μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation
of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors. 相似文献
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Yandong Wu Wei Chen Yimin Jiang Yanzhi Xu Bo Zhou Leitao Xu Chao Xie Ming Yang Mengyi Qiu Dongdong Wang Qie Liu Prof. Qinghua Liu Prof. Shuangyin Wang Prof. Yuqin Zou 《Angewandte Chemie (International ed. in English)》2023,62(30):e202305491
Synthesis of cyclohexanone oxime via the cyclohexanone-hydroxylamine process is widespread in the caprolactam industry, which is an upstream industry for nylon-6 production. However, there are two shortcomings in this process, harsh reaction conditions and the potential danger posed by explosive hydroxylamine. In this study, we presented a direct electrosynthesis of cyclohexanone oxime using nitrogen oxides and cyclohexanone, which eliminated the usage of hydroxylamine and demonstrated a green production of caprolactam. With the Fe electrocatalysts, a production rate of 55.9 g h−1 gcat−1 can be achieved in a flow cell with almost 100 % yield of cyclohexanone oxime. The high efficiency was attributed to their ability of accumulating adsorbed hydroxylamine and cyclohexanone. This study provides a theoretical basis for electrocatalyst design for C−N coupling reactions and illuminates the tantalizing possibility to upgrade the caprolactam industry towards safety and sustainability. 相似文献
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Jingcheng Wu Leitao Xu Zhijie Kong Kaizhi Gu Yuxuan Lu Xianwen Wu Prof. Yuqin Zou Prof. Shuangyin Wang 《Angewandte Chemie (International ed. in English)》2023,62(45):e202311196
Alanine is widely employed for synthesizing polymers, pharmaceuticals, and agrochemicals. Electrocatalytic coupling of biomass molecules and waste nitrate is attractive for the nitrate removal and alanine production under ambient conditions. However, the reaction efficiency is relatively low due to the activation of the stable substrates, and the coupling of two reactive intermediates remains challenging. Herein, we realize the integrated tandem electrochemical-chemical-electochemical synthesis of alanine from the biomass-derived pyruvic acid (PA) and waste nitrate (NO3−) catalyzed by PdCu nano-bead-wires (PdCu NBWs). The overall reaction pathway is demonstrated as a multiple-step catalytic cascade process via coupling the reactive intermediates NH2OH and PA on the catalyst surface. Interestingly, in this integrated tandem electrochemical-chemical-electrochemical catalytic cascade process, Cu facilitates the electrochemical reduction of nitrate to NH2OH intermediates, which chemically couple with PA to form the pyruvic oxime, and Pd promotes the electrochemical reduction of pyruvic oxime to the desirable alanine. This work provides a green strategy to convert waste NO3− to wealth and enriches the substrate scope of renewable biomass feedstocks to produce high-value amino acids. 相似文献
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In three dimensions there is a logarithmically divergent contribution to the entanglement entropy which is due to the vertices located at the boundary of the region considered. In this work we find the corresponding universal coefficient for a free Dirac field, and extend a previous work in which the scalar case was treated. The problem is equivalent to find the conformal anomaly in three-dimensional space where multiplicative boundary conditions for the field are imposed on a plane angular sector. As an intermediate step of the calculation we compute the trace of the Green function of a massive Dirac field in a two-dimensional sphere with boundary conditions imposed on a segment of a great circle. 相似文献
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在200℃脉冲吸附吡啶或2,6—二甲基吡啶饱和后,进行TPD实验。结果表明,无论是总酸还是B酸都随铈含量的增加而降低。脉冲吸附碱法比TPD法所得酸量大,在Pt-Ce/v-Al2O3催化剂中,主要是B酸,B酸和总酸的TM值随铈含量的变化而异。总酸的TM(TM≈290℃)降低,B酸的TM(TM≈265℃)增高 相似文献