共查询到20条相似文献,搜索用时 31 毫秒
2.
3.
4.
5.
6.
7.
浅论绿茶与乌龙茶氟含量对人体健康的影响 总被引:2,自引:0,他引:2
分别用重蒸水和自来水,通过蒸煮法和浸泡法制出不同浓度的绿茶液和乌龙茶液,对比测定研究茶液中氟含量,结果表明,茶液中的氟含量随茶叶浓度增加而增加,且乌龙茶高于绿茶,当茶叶浓度超过10.0g/L时,茶液中的氟含量即超过国家饮水卫生标准,提示人们饮用水茶液浓度在5.0g/L左右为宜。 相似文献
8.
9.
With vinyl monomers, viz., styrene, butyl methacrylate, dimethylaminoethyl methacrylate, and ethyl acrylate, it was noted that higher per cent grafting was obtained with “recrystallized” cellulose than with “amorphous” cellulose. The possibility of the production of a porous structure in cellulose as a result of γ-irradiation followed by the dissolution of the reactive regions is suggested. DTA and DTG data of irradiated cellulose triacetate (CTA) reveal lowering of the melting point on irradiation, indicating a decrease in crystallinity. Decrease in density of cellulose on irradiation by γ-rays also indicates loosening of the structure of cellulose. It is postulated that grafting occurs in those regions of cellulose which were crystalline before irradiation, as well as in less crystallinie regions. 相似文献
10.
分子印迹聚合物(molecular imprinting polymers,MIPs)是利用分子印迹技术合成的一种交联高聚物.分子印迹技术(molecular imprinting technique,MIT)是在近十几年来才发展起来的一门边缘科学技术.它结合了高分子化学、生物化学等学科,是模拟抗体-抗原相互作用的一种新技术,具有选择性识别位点的性质,作为传感器的理想敏感材料的制备方法日益受到研究者们的重视.本文综述了分子印迹技术的原理和分子印迹聚合物的制备方法,及其应用于传感器敏感材料的研究现状,并展望了其发展前景. 相似文献
11.
构建了纳米囊泡的原位凝胶系统. 以卵磷脂(PC)和胆固醇(CH)为纳米囊脂质材料, 按m(PC):m(CH)=3:1及m(脂质材料):m(药物)=5:1称取PC, CH和药物, 溶于无水乙醚作为有机相, 以质量分数为0.5%的吐温-80的磷酸盐(pH=7.4)缓冲液为水相(有机相与水相体积比为1.5:1), 采用薄膜分散-高压均质法制备了叶黄素纳米囊泡. 将普朗尼克F127(F127)和普朗尼克F68(F68)分散于纳米囊泡中水化, 制备了纳米囊泡原位凝胶系统. 以试管倒置法测定人工泪液和添加剂对F127-F68纳米囊泡原位凝胶系统胶凝温度的影响; 采用流变学研究了系统升温过程中溶胶-凝胶转变过程及上述辅料对该转变过程的影响; 分别以无膜溶蚀法和高效液相色谱(HPLC)法探讨了系统的体外溶蚀动力学和体外释药行为. 结果表明, 优化的纳米囊泡凝胶系统在25 ℃呈溶液态, 在眼部微环境下形成凝胶, 且药物释放及凝胶溶蚀均以恒定的速率进行, 为零级动力学特征. 相似文献
12.
DFT calculations have been performed to explore the aminotriazine adsorption on graphene surfaces.Relative energies,equilibrium geometries and electronic structures of monomer and dimer of aminotriazine molecules adsorbed at the surface were investigated and analyzed in details.It was found that the hydrogen atoms in the NH2 group of aminotriazine molecules are directed toward the graphene surface,and the adsorption energy increases as the NH2 group is added.The adsorbed aminotriazine molecules facilely form a dimer through the hydrogen bonding interactions,and the two aromatic rings of optimized structure of 2-amino-1,3,5-triazine(B) dimmer(denoted by B2) and melamine(D) dimmer(denoted by D2) are parallel to the graphene sheet.The large deviation of the averaged adsorption energy of B2 and D2 compared to monor adsorption may reflect the increase of π-π repulsion and the effect of hydrogen bond formation.The electronic structure analyses reveal that the formation of hydrogen bonds in melamine dimer has great influence on the adsorption mode at the graphene surface. 相似文献
13.
松香的主要成份是枞酸型树脂酸,其因共轭双键的存在而易被氧化,大大降低了其附加值。经氢化后的松香具有抗氧性好、脆性小、热稳定性高、颜色浅等特点,因而广泛应用于胶粘剂、合成橡胶、涂料、油黑、造纸、电子、食品等工业部门[1]。采用催化加氢的方法可使枞酸型树脂酸中的共轭双键消除[2]。以枞酸为代表的反应式为:松香催化加氢主要有熔融法[3]和溶剂法[4],所用催化剂主要是Pd和N i。熔融法制氢化松香,当反应温度低于200℃时,枞酸加氢速度较慢,反应不完全。温度升高,氢化松香中枞酸含量显著地减少,但温度高于250℃时,树脂酸脱羧严重,甚至… 相似文献
14.
聚合物材料的吸音系数-温度-频率三元关系的研究 总被引:1,自引:0,他引:1
用驻波管技术研究了聚甲基丙烯酸乙酯(PEMA)和聚氯乙烯(PVC)的吸声系数。结果表明,在玻璃化转变区域材料的吸声系数较高,PEMA和PVC均具有特征吸收频率。当乍于玻璃化转变区域时,PEMA和PVC的特征吸收峰的数目增加,用自由体积理论对此进行了解释。得到PEMA和PVC的吸声系数-温度-频率的三维关系图。 相似文献
15.
Yasuo Kusama Akira Udagawa Masaaki Takehisa 《Journal of polymer science. Part A, Polymer chemistry》1978,16(10):2607-2616
The effect of radiation on polystyrene was studied in the presence and absence of silica gel by molecular weight measurement with GPC. Polystyrene crosslinked under vacuum in the absence of silica gel, but it either crosslinked or degraded by radiation, depending on the molecular weight of the polymer in the presence of silica gel. Part of the deposited polymer bonded to silica gel by radiation; the G value for graft-chain formation is in the range of 0.01–0.1. Irradiation of polystyrene grafted on silica gel resulted in degradation of the graft chain because of the transfer of energy from silica gel. The G value for main chain scission was about 2 when graft polymer was irradiated in the absence of homopolymer. The degradation of graft polymer was suppressed when the polymer was irradiated in the presence of homopolymer, and the amount of unextractable polymer from silica gel increased with increasing irradiation. This adds evidence to the estimation that an increase in grafting percent coupled with a slight decrease in molecular weight at a later stage of radiation-induced polymerization of styrene adsorbed on silica gel is due to a secondary effect of radiation on the polymer. 相似文献
16.
Li-jun Liang Qi Wang Tao Wu Jia-wei Shen Yu Kang 《化学物理学报(中文版)》2009,22(6):627-634
The adsorption dynamics of a model protein (the human insulin) onto graphene surfaces with different sizes was investigated by molecular dynamics simulations. During the adsorption, it has different effect on the stability of the model protein in the fixed and non-fixed graphene systems. The tertiary structure of the protein was destroyed or partially destroyed, and graphene surfaces shows the selective protection for some α-helices in non-fixed Systems but not in fixed systems by reason of the flexibility of graphene. As indicated by the interaction energy curve and trajectory animation, the conformation and orientation selection of the protein were induced by the properties and the texture of graphene surfaces. The knowledge of protein adsorption on graphene surfaces would be helpful to better understand stability of protein on graphene surfaces and facilitate potential applications of graphene in biotechnology. 相似文献
17.
酞菁金属配合物是光动力治疗的新一代光敏剂,其治疗作用的机理以及引起的生物效应一直是人们研究的热点.本文选用色氨酸作为与喹啉氧基酞菁金属配合物作用的靶分子,讨论了配合物的组成结构与其光敏化氧化色氨酸能力的相关性.结果表明,酞菁环内中心金属离子和环周边取代基的组成结构以及取代位置与数目都影响其光敏化氧化色氨酸能力,中心金属离子为闭壳层电子结构、取代基位于α位以及提高取代基数目均有利于提高光敏化氧化活性,同时显示,取代基的组成结构对靶分子有一定选择性,研究结果可为研发该类光敏剂提供依据. 相似文献
18.
A novel gas sensor for the determination of ethanol was proposed in the present work, which was based on the generated cataluminescence emission from catalytic oxidation of ethanol on the surface of ZnO nanoparticles. The cataluminescence characteristics and the effect of different parameters on the signal intensity, such as morphology of synthesized ZnO, temperature and flow rate, were discussed in detail. Under the optimized experimental conditions, the calibration curve of cataluminescence intensity versus ethanol vapor concentration was linear in the range 1.0-100 ppm, and with a detection limit of 0.7 ppm (S/N = 3). Compared with the traditional electrical conductivity-based ZnO gas sensor for the determination of ethanol, the proposed ethanol sensor showed the advantages of high sensitivity, high selectivity and low working temperature. 相似文献
19.
Yosuke Tsuzuki Yuta Oikubo Yoshinari Matsuura Kiyoshi Itatani Seiichiro Koda 《Journal of Sol-Gel Science and Technology》2008,47(2):131-139
We studied the effect of vacuum ultraviolet (vuv) irradiation on siliceous coatings of polycarbonate (PC) substrates derived
by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. Methyltriethoxysilane with
colloidal silica was used to prepare the sol solution. The sol solution was spin-coated on PC and this was followed by vuv
irradiation with a Xe excimer lamp at 172 nm under N2 atmosphere. The PC substrate with vuv irradiated coating retained its high transmittance in the visible region for about
3 or more times of scraping turns by a steel wool tester on the surface, compared with the non-irradiated or mercury lamp-irradiated
coatings, which demonstrated the remarkable improvement of the abrasion resistance by the vuv irradiation. The chemical changes
under the vuv irradiation were also investigated by FTIR–ATR spectroscopy, composition analysis conducted with X-ray photoelectron
spectroscopy and hardness measurements. It was concluded that the vuv light irradiation resulted in degrading the Si–CH3 bond in sol–gel derived siliceous coatings to yield hardening of the coatings. The transmittance of the coating in vuv region
also increased with the Xe lamp irradiation. 相似文献
20.
以脂多糖类似物(KLA)诱导的RAW264.7细胞为研究对象,采用代谢组学研究手段,研究水飞蓟素对脂多糖诱导炎症模型中花生四烯酸代谢通路的影响。以超高效液相色谱-三重四极杆质谱联用为平台,对不同浓度水飞蓟素作用下KLA诱导RAW264.7炎症细胞分泌的类二十烷酸代谢物进行定量分析,通过考察主成分分析(PCA)、正交偏最小二乘法判别分析(OPLS-DA)的VIP值和Kruskal-Wallis秩和检验结果显著性差异(P)值筛选代谢标记物。建立了59种类二十烷酸(含15种同位素内标)在5 min内实现快速分离的液相色谱-质谱联用方法;确定了细胞存活率在58%~80%的水飞蓟素浓度为50~150μmol/L;筛选出数据处理结果同时满足变异权重参数(VIP)值1且结果P值0.05的类二十烷酸代谢标记物12-OxoLeukotriene B4(12-OxoLTB4);通过分析柱状图和炎症信号通路,确定水飞蓟素借助其抗氧自由基特性发挥抗炎作用,通过抑制脂氧合酶-5(5-LOX)的活性及阻断5-LOX代谢通路中产生氧自由基的脂质过氧化反应来减少氧自由基及过氧化物的形成。综上所述,所建立的方法能快速准确地定量分析多种类二十烷酸,并从代谢组学角度解释了水飞蓟素的抗炎机制。 相似文献