排序方式: 共有62条查询结果,搜索用时 31 毫秒
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本文采用有限元电磁仿真设计了基于开路谐振环的微带线谐振器,并利用该谐振器搭建了电子自旋共振测试系统.该谐振器的3 dB带宽为58.7 MHz,且具有开放式的平面结构.对不同质量的二苯基三硝基苯肼(DPPH)样品测试结果显示本系统的室温自旋探测灵敏度可以达到9.66×1012 spins/Gs Hz1/2;对以微晶玻璃和硅片为基底的DPPH样品测试结果表明本系统能实现对大尺寸、高损耗样品的电子自旋共振信号的非破坏性测量.本系统为薄膜材料的缺陷研究以及相关的微波性能表征提供了便捷的手段. 相似文献
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Kevin Hwang Peiwen Wu Taejin Kim Lei Lei Shiliang Tian Prof. Yingxiao Wang Prof. Yi Lu 《Angewandte Chemie (International ed. in English)》2014,53(50):13798-13802
DNAzymes, which are sequences of DNA with catalytic activity, have been demonstrated as a potential platform for sensing a wide range of metal ions. Despite their significant promise, cellular sensing using DNAzymes has however been difficult, mainly because of the “always‐on” mode of first‐generation DNAzyme sensors. To overcome this limitation, a photoactivatable (or photocaged) DNAzyme was designed and synthesized, and its application in sensing ZnII in living cells was demonstrated. In this design, the adenosine ribonucleotide at the scissile position of the 8–17 DNAzyme was replaced by 2′‐O‐nitrobenzyl adenosine, rendering the DNAzyme inactive and thus allowing its delivery into cells intact, protected from nonspecific degradation within cells. Irradiation at 365 nm restored DNAzyme activity, thus allowing the temporal control over the sensing activity of the DNAzyme for metal ions. The same strategy was also applied to the GR‐5 DNAzyme for the detection of PbII, thus demonstrating the possible scope of the method. 相似文献
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在研究消除水负峰的基础上,建立离子色谱法测定水中F–,Cl–,NO2–,H2PO4–,Br–,NO3–,SO42–7种阴离子的方法。经实验确定淋洗液为4.5 mmol/L NaHCO3–4.0 mmol/L Na2CO3,淋洗液流量为1.0 mL/min,柱箱温度为35℃。在底液中加入与淋洗液同浓度的Na2CO3–NaHCO3可有效消除水负峰。该方法对7种阴离子的检出限为0.004~0.034 mg/L,测定结果的相对标准偏差为0.69%~3.57%(n=6),加标回收率为95%~105%。该法能有效消除水负峰及其对F–测定的影响,操作简便、测定结果准确可靠,适用于水中F–、Cl–等7种阴离子的测定。 相似文献
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The Equally Important Role of Adenine Derivatives to That of Pyrimidine Derivatives in Near‐0 eV Electron‐Induced DNA Lesions 下载免费PDF全文
The role of adenine (A) derivatives in DNA damage is scarcely studied due to the low electron affinity of base A. Experimental studies demonstrate that low‐energy electron (LEE) attachment to adenine derivatives complexed with amino acids induces barrier‐free proton transfer producing the neutral N7‐hydrogenated adenine radicals rather than conventional anionic species. To explore possible DNA lesions at the A sites under physiological conditions, probable bond ruptures in two models—N7‐hydrogenated 2′‐deoxyadenosine‐3′‐monophosphate (3′‐dA(N7H)MPH) and 2′‐deoxyadenosine‐5′‐monophosphate (5′‐dA(N7H)MPH), without and with LEE attachment—are studied by DFT. In the neutral cases, DNA backbone breakage and base release resulting from C3′?O3′ and N9?C1′ bond ruptures, respectively, by an intramolecular hydrogen‐transfer mechanism are impossible due to the ultrahigh activation energies. On LEE attachment, the respective C3′?O3′ and N9?C1′ bond ruptures in [3′‐dA(N7H)MPH]? and [5′‐dA(N7H)MPH]? anions via a pathway of intramolecular proton transfer (PT) from the C2′ site of 2′‐deoxyribose to the C8 atom of the base moiety become effective, and this indicates that substantial DNA backbone breaks and base release can occur at non‐3′‐end A sites and the 3′‐end A site of a single‐stranded DNA in the physiological environment, respectively. In particular, compared to the results of previous theoretical studies, not only are the electron affinities of 3′‐dA(N7H)MPH and 5′‐dA(N7H)MPH comparable to those of hydrogenated pyrimidine derivatives, but also the lowest energy requirements for the C3′?O3′ and N9‐glycosidic bond ruptures in [3′‐dA(N7H)MPH]? and [5′‐dA(N7H)MPH]? anions, respectively, are comparable to those for the C3′?O3′ and N1‐glycosidic bond cleavages in corresponding anionic hydrogenated pyrimidine derivatives. Thus, it can be concluded that the role of adenine derivatives in single‐stranded DNA damage is equally important to that of pyrimidine derivatives in an irradiated cellular environment. 相似文献
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We demonstrate the preparation of extremely cross-linked poly(dimethylsiloxane) (PDMS)-based materials and report optical, mechanical, and surface properties. Transparent monolithic molded objects are prepared catalytically with no byproducts; parts per million levels of platinum (catalyst) remain in the articles. Essentially the same material was prepared in 1993 and described as a "hard transparent glass." We confirm the thermal stability and chemical structure described in this report. We show that the catalytic reaction used, which was reported in 1999 always to exhibit a "violent exotherm", can be controlled conveniently using a low (parts per million) catalyst concentration. The combination of low surface energy, transparency, hardness, elasticity, and thermal stability makes this an unusual and interesting material. That it can be prepared from commercially available low-viscosity monomers adds to its interest. We comment that the class of materials known as siloxanes or silicones and PDMS in particular is not currently generally well understood (or taught) and review aspects of the structure, properties, and cross-linking chemistry of PDMS. 相似文献
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Tetramethylammonium silanolate-initiated ring-opening copolymerization of octamethylcyclotetrasiloxane (D(4)) and bis(heptamethylcyclotetrasiloxanyl)ethane (bis-D(4)) renders cross-linked network polymers that contain ethylene bridges and active silanolate end groups. These "living" reactive anionic species are not neutralized by ambient atmosphere exposure (are stable to water, oxygen, CO(2)) and promote thermally activated equilibration among different network isomers and cyclic oligomers. The cross-link density of these living networks can be controlled by the ratio of D(4):bis-D(4), and the density of active chain ends is determined from the initiator:monomer ratio. We report that samples prepared with particular ratios of initiator:D(4):bis-D(4) can be cut with a sharp knife, even into two pieces, and can heal by siloxane equilibration to restore the original strength of the silicone sample. Fracture toughness measurements were carried out and revealed complete (mechanical) healing. Broken and healed samples generally failed in locations other than the initially cracked region. We call attention to publications and patents from the 1950s that suggest that this self-healing behavior was likely obvious 60 years ago. 相似文献
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Fei Wen Wangqing Zhang Peiwen Zheng Xu Zhang Xinlin Yang Yao Wang Xiaowei Jiang Guanwei Wei Linqi Shi 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1192-1202
A method of one‐stage soap‐free emulsion polymerization to synthesize narrowly dispersed core‐shell microspheres is proposed. Following this method, core‐shell microspheres of poly(styrene‐co‐4‐vinylpyridine), poly(styrene‐co‐methyl acrylic acid), and poly[styrene‐co‐2‐(acetoacetoxy)ethyl methacrylate‐co‐methyl acrylic acid] are synthesized by one‐stage soap‐free emulsion polymerization of a mixture of one or two hydrophobic monomers and a suitable hydrophilic monomer in water. The effect of the molar ratio of the hydrophobic monomer to the hydrophilic one on the size, the core thickness, and the shell thickness of the core‐shell microspheres is discussed. The molar ratio of the hydrophobic and hydrophilic monomers and the hydrophilicity of the resultant oligomers of the hydrophilic monomer are optimized to synthesize narrowly dispersed core‐shell microspheres. A possible mechanism of one‐stage soap‐free emulsion polymerization to synthesize core‐shell microspheres is suggested and coagglutination of the oligomers of the hydrophilic monomers on the hydrophobic core is considered to be the key to form core‐shell microspheres. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1192–1202, 2008 相似文献
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CHEN Peiwen ZHU Lianjie CHANG Zhuangzhuang GAO Hongjia CHEN Deyou QIU Mo 《高等学校化学研究》2020,36(6):1108-1115
Well-dispersed mesoporous spherical Cu2O assembled by small nanoparticles was synthesized by a green and rapid solution route at room temperature under assistance of ultrasonic, using eco-friendly ascorbic acid(AA) as the main reducing agent and glucose as a weak reducing agent and soft template. The Cu2O spheres were characterized by XRD, SEM, HRTEM, XPS and N2 adsorption-desorption isotherm. Its optical property was studied by UV-Vis diffuse reflectance absorption spectrum and the photocatalytic activities were evaluted by photodegradations of me-thylene blue(MB) under different light sources. The results show that each spherical Cu2O(ca. 200 nm in diameter) was accumulated by numerous small nanoparticles of 8-10 nm and mesopores exist between the nanoparticles, which result in a high BET surface area. The spherical Cu2O exhibits good light-harvesting ability in both UV and visible light region and excellent photodegradation activities to high concentrations of MB solutions under both UV-visible light and visible light. 相似文献