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排序方式: 共有250条查询结果,搜索用时 15 毫秒
1.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
2.
Yu-Ting Tseng Dr. Wei-Min Ching Prof. Wen-Feng Liaw Prof. Tsai-Te Lu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):11917-11921
Continued efforts are made for the utilization of CO2 as a C1 feedstock for regeneration of valuable chemicals and fuels. Mechanistic study of molecular (electro-/photo-)catalysts disclosed that initial step for CO2 activation involves either nucleophilic insertion or direct reduction of CO2. In this study, nucleophilic activation of CO2 by complex [(NO)2Fe(μ-MePyr)2Fe(NO)2]2− ( 2 , MePyr=3-methylpyrazolate) results in the formation of CO2-captured complex [(NO)2Fe(MePyrCO2)]− ( 2-CO2 , MePyrCO2=3-methyl-pyrazole-1-carboxylate). Single-crystal structure, spectroscopic, reactivity, and computational study unravels 2-CO2 as a unique intermediate for reductive transformation of CO2 promoted by Ca2+. Moreover, sequential reaction of 2 with CO2, Ca(OTf)2, and KC8 established a synthetic cycle, 2 → 2-CO2 → [(NO)2Fe(μ-MePyr)2Fe(NO)2] ( 1 ) → 2 , for selective conversion of CO2 into oxalate. Presumably, characterization of the unprecedented intermediate 2-CO2 may open an avenue for systematic evaluation of the effects of alternative Lewis acids on reduction of CO2. 相似文献
3.
S. K. Liaw S. Wang C. S. Shin N. K. Chen K. C. Hsu A. Manshina Y. Tver’yanovich C.-F. Su L. K. Wang 《Laser Physics》2010,20(7):1608-1611
A single-longitudinal-mode selection is realized in a linear-cavity fiber laser construction using a loop-back optical circulator
and a partial reflectance fiber Bragg grating as the cavity ends. At 1551 nm wavelength, the measured signal-to-noise-ratio
is 56 dB and with a line width less than 1 MHz obtained using multiple subring cavities as mode filters. The pumping efficiency
is 10% improved by recycling the residual pump power to gain medium. 相似文献
4.
Cheng‐Hung Chang Kun‐Li Wang Jyh‐Chiang Jiang Der‐Jang Liaw Kueir‐Rarn Lee Juin‐Yih Lai Kuo Yuan Chiu Yuhlong Oliver Su 《Journal of polymer science. Part A, Polymer chemistry》2010,48(24):5659-5669
A series of highly organosoluble polyamides with high modulus having propeller‐shaped triarylamine were synthesized using aromatic diacid chlorides by low‐temperature solution polycondensation. The polyamide films had strong, tough, flexible, and amorphous properties. These polymers revealed electrochromic characteristics both in the visible range and near‐infrared (NIR) region, with a color change from pale yellowish at its neutral state to green and blue at its oxidized state at applied potentials ranging from 0.00 to 1.35 V. Cyclic voltammetry (CV) of the polymer films cast onto an indium tin oxide (ITO)‐coated glass substrate exhibited two reversible redox couples at potentials of 0.80–0.87 V and 1.19–1.25 V, respectively, vs. Ag/Ag+ in acetonitrile solution. From the combination of the experimental and computational study, we proposed an oxidation mechanism based on molecular orbital (MO) theory, which well explains the CV experimental result. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
5.
This paper reports the effect of water vapour on particulate matter (PM) during the separate combustion of in situ volatiles and char generated from chromated-copper-arsenate-treated (CCAT) wood at 1300 °C. Combustion of in situ volatiles produces only PM with aerodynamic diameter?<1?µm (i.e., PM1), dominantly PM with aerodynamic diameter?<0.1?µm (i.e., PM0.1). Water vapour could significantly enhance the nucleation, coagulation and condensation of fine particles and reduce the capture of Na and K by the alumina reactor tube via reduced formation of alkali aluminates, leading to increases in both yield and modal diameter of PM0.1. Water vapour could also enhance char fragmentation hence increase the yield of PM with aerodynamic diameter between 1 and 10?µm (i.e., PM1–10) during char combustion. For trace elements, during in situ volatiles combustion, volatile elements (As, Cr, Ni, Cu and Pb) are only presented in PM1 and water vapour alters the particle size distributions (PSDs) but has little effect on the yields of these trace elements. During char combustion, As, Cr, Cu and Ni are present in both PM1 and PM1–10 while the non-volatile Mn and Ti are only present in PM1–10. Increasing water vapour content increases the yields of As, Cr, Cu, Ni, Mn and Ti in PM1-10 due to enhanced char fragmentation. During char combustion, water vapour also originates less oxidising conditions locally for enhancing As release, promotes the generation of gaseous chromium oxyhydroxides and inhabits the production of NiCl2 (g), leading to increased yields of As and Cr and decreased yield of Ni in PM0.1. 相似文献
6.
Abstract Stress intensity factors are evaluated for a singly or doubly cracked fastener hole with frictional traction in an anisotropic plate, using a special kernel boundary integral equation (BIE) approach. The integration kernel (Green's function) used in this BIE approach has already taken the presence of the crack (or cracks) into account, thus.avoiding the need for element discretization to model the stress singularity at the crack tip. The Green's function employed is that of an infinite anisotropic plate containing an elliptical hole or crack, and subjected to an arbitrarily positioned point force. Several types of normal and shear traction conditions at the pinhole interface are considered. Numerical results are obtained for various geometrical and loading conditions and are compared with known solutions, where available, for their isotropic counterparts. 相似文献
7.
Yu‐Liang Yang Dr. Wen‐Ying Liao Wan‐Yun Liu Chih‐Chuang Liaw Dr. Chia‐Ning Shen Dr. Zih‐You Huang Shih‐Hsiung Wu Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11573-11580
Six photosensitive polyketides, malbranpyrroles A–F, were discovered from the thermophilic fungus Malbranchea sulfurea by using intact‐cell desorption/ionization on silicon mass (ICD‐MS) and LC‐SPE‐NMR. These two strategies facilitate the searching and structural determination of unstable natural products. The ICD‐MS indicated that only brown hyphae of M. sulfurea can produce malbranpyrroles. The biosynthetic pathway of malbranpyrroles was evidenced by 13C isotope precursors and amino acid feeding experiments. The cytotoxicity data revealed that the conformation of the conjugated system in malbranpyrroles does not affect cytotoxic potency against cancer cell lines. In addition, the chlorine atom was shown to be the pharmacophore for cytotoxicity. 相似文献
8.
X‐Ray Emission Spectroscopy: A Spectroscopic Measure for the Determination of NO Oxidation States in Fe–NO Complexes 下载免费PDF全文
Prof. Tsai‐Te Lu Dr. Tsu‐Chien Weng Prof. Wen‐Feng Liaw 《Angewandte Chemie (International ed. in English)》2014,53(43):11562-11566
Extensive study of the electronic structure of Fe‐NO complexes using a variety of spectroscopic methods was attempted to understand how iron controls the binding and release of nitric oxide. The comparable energy levels of NO π* orbitals and Fe 3d orbitals complicate the bonding interaction within Fe? NO complexes and puzzle the quantitative assignment of NO oxidation state. Enemark–Feltham notation, {Fe(NO)x}n, was devised to circumvent this puzzle. This 40‐year puzzle is revisited using valence‐to‐core X‐ray emission spectroscopy (V2C XES) in combination with computational study. DFT calculation establishes a linear relationship between ΔEσ2s*‐σ2p of NO and its oxidation state. V2C Fe XES study of Fe? NO complexes reveals the ΔEσ2s*‐σ2p of NO derived from NO σ2s*/σ2p→Fe1s transitions and determines NO oxidation state in Fe? NO complexes. Quantitative assignment of NO oxidation state will correlate the feasible redox process of nitric oxide and Fe‐nitrosylation biology. 相似文献
9.
10.
Der‐Jang Liaw Ching‐Cheng Huang En‐Tang Kang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2901-2911
Diblock copolymers of 5‐(methylphthalimide)bicyclo[2.2.1]hept‐2‐ene (NBMPI) and 1,5‐cyclooctadiene were synthesized by living ring‐opening metathesis polymerization with a well‐defined catalyst {RuCl2(CHPh)[P(C6H11)3]2}. Unhydrogenated diblock copolymers showed two glass transitions due to poly(NBMPI) and polybutadiene segments, such as two glass‐transition temperatures at ?86.5 and 115.3 °C for poly 1a and ?87.2 and 115.3 °C for poly 1b . However, only one melting temperature could be observed for hydrogenated copolymers, such as 119.8 °C for poly 2a and 121.7 °C for poly 2b . The unhydrogenated diblock copolymer with the longer poly(NBMPI) chain (poly 1a ; temperature at 10% mass loss = 400 °C) exhibited better thermal stability than the one with the shorter poly(NBMPI) chain (poly 1b ; temperature at 10% mass loss = 385 °C). Two kinds of hydrogenated diblock copolymers, poly 2a and poly 2b , exhibited relatively poor solubility but better thermal stability than unhydrogenated diblock copolymers because of the polyethylene segments. Poly[(hydrochloride quaternized 2‐norbornene‐5‐methyleneamine)‐b‐butadiene]‐1 (poly 3a ) was obtained after the hydrolysis and quaternization of poly 1a . Dynamic light scattering measurements indicated that the hydrodynamic diameters of the cationic copolymer (poly 3a ) in water (hydrodynamic diameter = 1580 nm without salt), methanol/water (4/96 v/v; hydrodynamic diameter = 1500 nm without salt), and tetrahydrofuran/water (4/96 v/v; hydrodynamic diameter = 1200 nm without salt) decreased with increasing salt (NaCl) concentration. The effect of temperature on the hydrodynamic diameter of hydrophobically modified poly 3a was also studied. The inflection point of the hydrodynamic diameter of poly 3a was observed at various polymer concentrations around 30 °C. The critical micelle concentration of hydrophobically modified poly 3a was observed at 0.018 g dL?1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2901–2911, 2006 相似文献