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91.
A novel series of monodisperse, multi-dipolar zigzag oligoaryleneethynylenes DA(n) and D-Ar-A(n), bearing electron-donating dibenzothiophene and electron-accepting dibenzothiophene dioxide as arenes, with up to six charge-transfer (dipolar) units have been designed and synthesized by palladium-catalyzed Sonogashira coupling reactions. The linear and nonlinear optical properties of these multi-dipolar oligoaryleneethynylenes can easily be modified or enhanced by incorporating/extending with various central aryleneethynyl moieties such as phenylethynyl, oligo(9,9-dibutylfluorenyl)ethynyl, and oligothienylethynyl within the donor-acceptor units. Interestingly, the absorption and emission of these zigzag oligoaryleneethynylenes are not dependent on the number of covalently linked dipolar chromophores; however, the fluorescence quantum efficiencies consistently decrease with increased number of covalently linked dipolar units. These zigzag oligoaryleneethynylenes exhibit a linear increase in the two-photon absorption (TPA) cross-sections with increased number of covalently linked dipolar units without red-shifting the absorption and emission spectra. In addition, very large TPA cross-sections in the femtosecond regime (sigma(800) = 1306 GM in DMF or sigma(750) = 1522 GM in CH(2)Cl(2)) were obtained for D-TF-A(4) despite the moderate strength of the donor-acceptor pair. Our results suggest that the TPA properties of these zigzag oligoaryleneethynylenes including TPA wavelength and TPA cross-section can easily be tuned by means of modifying the central aryleneethynylene units and increasing the number of dipolar units, respectively. This approach provides an alternative means to tune or enhance the TPA cross-section at a specific wavelength. 相似文献
92.
Mingpeng Chen Di Liu Baoye Zi Yuyun Chen Dong Liu Xinyu Du Feifei Li Pengfei Zhou Ye Ke Jielei Li Kin Ho Lo Chi Tat Kwok Weng Fai Ip Shi Chen Shuangpeng Wang Qingju Liu Hui Pan 《Journal of Energy Chemistry》2022,(2):405-414
Design and synthesis of noble-metal-free bifunctional catalysts for efficient and robust electrochemical water splitting are of significant importance in developing clean and renewable energy sources for sustainable energy consumption.Herein,a simple three-step strategy is reported to construct cobalt-iron nitride/alloy nanosheets on nickel foam(CoFe-NA/NF)as a bifunctional catalyst for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The electrocatalyst with optimized composition(CoFe-NA2/NF)can achieve ultralow overpotentials of 73 mV and 250 mV for HER and OER,respectively,at a current density of 10 mA cm-2 in 1 M KOH.Notably,the electrolyzer based on this electrocatalyst is able to boost the overall water splitting with a cell voltage of 1.564 V to deliver 10 mA cm-2 for at least 50 h without obvious performance decay.Furthermore,our experiment and theoretical calculation demonstrate that the combination of cobalt-iron nitride and alloy can have low hydrogen adsorption energy and facilitate water dissociation during HER.In addition,the surface reconstruction introduces metal oxyhydroxides to optimize the OER process.Our work may pave a new pathway to design bifunctional catalysts for overall water splitting. 相似文献
93.
94.
95.
Hiu Yung Lam Rannveig Ingebrigtsen Gaarden Xuechen Li 《Chemical record (New York, N.Y.)》2014,14(6):1086-1099
Daptomycin, the first antibiotic of its class, provides a new structural motif for the development of new antibiotics. Recently, we have completed the total synthesis of daptomycin. The development of the successful synthetic strategy is described here, including the application of serine/threonine ligation mediated peptide cyclization to the daptomycin macrocyclization. 相似文献
96.
97.
Mahdi Faghih Zheng Chen Jialong Huo Zhuyin Ren Chung K. Law 《Proceedings of the Combustion Institute》2019,37(2):1505-1512
The outwardly propagating spherical flame (OPF) method is popularly used to measure the laminar flame speed (LFS). Recently, great efforts have been devoted to improving the accuracy of the LFS measurement from OPF. In the OPF method, several assumptions are made. For examples, the burned gas is assumed to be static and in chemical equilibrium. However, these assumptions may not be satisfied under certain conditions. Here we consider low-pressure and super-adiabatic propagating spherical flames, for which chemical non-equilibrium exists and the burned gas may not be static. The objective is to assess the chemical non-equilibrium effects on the accuracy of LFS measurement from the OPF method. Numerical simulations considering detailed chemistry and transport are conducted. Stoichiometric methane/air flames at sub-atmospheric pressures and methane/oxygen flames at different equivalence ratios are considered. At low pressures, broad heat release zone is observed and the burned gas cannot quickly reach the adiabatic flame temperature, indicating the existence of chemical non-equilibrium of burned gas. Positive flow in the burned gas is identified and it is shown to become stronger at lower initial pressure. Consequently, the LFS measurement from OPF at low pressures is not accurate if the burned gas is assumed to be static and at chemical equilibrium. For super-adiabatic spherical flames, the burned gas speed is found to be negative due to the local temperature overshoot at the flame front. Such negative speed of burned gas can also reduce the accuracy of LFS measurement. It is recommended that the direct method measuring both flame propagation speed and flow speed of unburned gas should be used to determine the LFS at low pressures or for mixtures with super-adiabatic flame temperature. 相似文献
98.
Extraction of molybdenum and technetium with diamides of dipicolinic acid from nitric acid solutions
J. L. Lapka A. Paulenova M. Yu. Alyapyshev V. A. Babain R. S. Herbst J. D. Law 《Journal of Radioanalytical and Nuclear Chemistry》2009,280(2):307-313
The concentration of molybdenum(VI) in dissolved spent nuclear fuel is comparable with the concentrations of Tc, and the minor
actinides (Np, Am). Therefore it is of great interest to understand its behavior under conditions imposed by separation processes.
The simultaneous extraction ability of ortho, meta, and para isomers of N,N′-diethyl-N,N′-ditolyl-dipicolinamide (EtTDPA) for molybdenum and technetium were investigated in a large range of nitric and hydrochloric
acid conditions. Molybdenum shows no increase in extraction at higher concentrations of nitric acid giving a solvate number
n=0 with all isomers of EtTDPA, while Mo shows great extractability from HCl. Technetium distribution ratios decrease with
increasing concentrations of nitrate showing indication of ion exchange occurring between TcO4
− and NO3
− anions. Et(m)TDPA and Et(p)TDPA show the greatest extractability, with 60% of the total technetium extracted into the organic
phase at 1M HNO3. 相似文献
99.
Richard Law Oliver Barker John J. Barker Thomas Hesterkamp Robert Godemann Ole Andersen Tara Fryatt Steve Courtney Dave Hallett Mark Whittaker 《Journal of computer-aided molecular design》2009,23(8):459-473
Fragment-based drug discovery (FBDD) represents a change in strategy from the screening of molecules with higher molecular
weights and physical properties more akin to fully drug-like compounds, to the screening of smaller, less complex molecules.
This is because it has been recognised that fragment hit molecules can be efficiently grown and optimised into leads, particularly
after the binding mode to the target protein has been first determined by 3D structural elucidation, e.g. by NMR or X-ray
crystallography. Several studies have shown that medicinal chemistry optimisation of an already drug-like hit or lead compound
can result in a final compound with too high molecular weight and lipophilicity. The evolution of a lower molecular weight
fragment hit therefore represents an attractive alternative approach to optimisation as it allows better control of compound
properties. Computational chemistry can play an important role both prior to a fragment screen, in producing a target focussed
fragment library, and post-screening in the evolution of a drug-like molecule from a fragment hit, both with and without the
available fragment-target co-complex structure. We will review many of the current developments in the area and illustrate
with some recent examples from successful FBDD discovery projects that we have conducted. 相似文献
100.
Hao‐Hao Wang Yi‐Xiang J. Wang Prof. Ken Cham‐Fai Leung Prof. Doris W. T. Au Prof. Shouhu Xuan Dr. Chun‐Pong Chak Simon K. M. Lee Dr. Hui Sheng Dr. Ge Zhang Dr. Ling Qin Prof. James F. Griffith Prof. Anil T. Ahuja Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12417-12425
Small polyhedral superparamagnetic iron oxide (SPIO) nanoparticles (<10 nm) coated with a thin layer of silica were prepared (SPIO@SiO2 and SPIO@SiO2‐NH2). Surface modification of the small polyhedral silica‐coated SPIO nanoparticles with amines led to substantially higher mesenchymal stem cell (MSC) labelling efficiency without the use of additional transfecting agents. Therefore, amine surface‐modified nanoparticles (SPIO@ SiO2‐NH2) appeared to be the preferred candidate for MSC labelling. In vitro studies demonstrated that controlled labelling of SPIO@SiO2 and SPIO@SiO2‐NH2 did not cause MSC death or proliferation inhibition. MSCs labelled with SPIO@SiO2‐NH2 nanoparticles retained differentiation potential and showed osteogenic, adipogenic and chondrogenic differentiations. The noncytotoxic polyhedral SPIO@SiO2‐NH2 nanoparticle‐labelled MSCs were successfully implanted in rabbit brain and erector spinae muscle, and demonstrated long‐lasting, durable MRI labelling efficacy after 8–12 weeks. 相似文献