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991.
ExtensivestudiesofradiationorchemicalinjuryofbiologicaltargetmoleculesdemonstratethatOHradical,themostreactiveoxygenspecies,reactswithbiologicalmacromolecules,suchasDNA,inducingbasealterations,basicsites,andstrandbreaks,resultedinvariouspathogenesis,such… 相似文献
992.
(Z, E)-9, 11-Tetradecadienyl-l-acetate (1), a major component of the sex pheromone of Spodoptera litura (F.), and (Z, E}-9, 11-pentadecadienyl-1-acetate (2) were synthesized by the Wittig reaction between (E)-2-alkenal (3) and the ylid derived from 9-hydroxynonyltriphenylphosphonium bromide (4). 相似文献
993.
The UV light irradiation of isoniazid (I) in methanol four products, isonicotinic acid (II), isonicotinamide (III), N, N′-bis(isonicotinic acid)hydrazide (IV) and isonicotinaldehyde isonicotinyl hydrazone (V), in ethanol three products, (III), (IV) and acetaldehyde isonicotinyl hydrazone (VI) were isolated and identified. Also, the photoreaction mechanism of isoniazid in methanol and ethanol were discussed. 相似文献
994.
995.
Solid Phase Extraction and Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Zinc and Cobalt Ions in Water Samples 总被引:1,自引:0,他引:1
A simple and rapid method for the preconcentration of Co2+ and Zn2+ as their 2-guanidino-benzimidazole chelates is proposed using an octadecyl silica cartridge. The retained analytes were recovered with a mixture of 5mL of 0.01M HNO3 and 5mL of methanol. The metal ions in the effluent were determined by flame atomic absorption spectrometry. The effect of different parameters, such as sample matrix, amount of ligand, type of eluent for elution of ions from cartridge, flow rates of sample solution and eluent, breakthrough volume, and limit of detection, were evaluated. The effects of various cationic and anionic interferences on the percent recovery of Co2+ and Zn2+ were also studied. Quantitative extraction efficiencies were obtained by elution of the cartridge with a minimal amount of solvent. Hence, with a typical preconcentration factor of 50, the limits of detections of the proposed method are 0.26 and 1.62ngmL–1 for Zn2+ and Co2+, respectively. The method was applied to the determination of zinc and cobalt ions in different water samples. 相似文献
996.
Darja?Rudan-Tasic Cveto?KlofutarEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(7):773-784
Summary. The freezing temperatures of dilute aqueous solutions of some poly(oxyethylene) glycols (PEG, HO–(CH2CH2O)
n
–H, n varying from 4 to 117) were measured over a solute to solvent mass ratio from 0.0100 to 0.3900. The second and third osmotic virial coefficient (A
22 and A
222) of poly(oxyethylene) glycols in aqueous solution were determined. The molecular weight dependence of the second virial coefficient can be described by a simple relation A
22=2×10–5
M
n
1.86, and the third virial coefficient is A
222=0.038A
22
2. The activity coefficients of the solute were calculated using the Gibbs-Duhem equation as applied by Bjerrum. From the osmotic and activity coefficients the excess Gibbs energies of solution, as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were estimated. The second and the third osmotic virial coefficients are correlated with the Mc-Millan-Mayer virial coefficients. 相似文献
997.
Analysis of inorganic mercury species associated with airborne particulate matter/aerosols: method development 总被引:6,自引:0,他引:6
Feng X Lu JY Grègoire DC Hao Y Banic CM Schroeder WH 《Analytical and bioanalytical chemistry》2004,380(4):683-689
This paper describes a method for speciation of Hg associated with airborne particulate matter. This method uses a mini-sampler for sample collection and analysis, thermal desorption for separating Hg species, and inductively coupled plasma mass spectrometry (ICP–MS) for identification and quantification of Hg. Coal fly ash spiked with different Hg compounds (e.g. Hg0, HgCl2, HgO, and HgS) was used for qualitative calibration. A standard reference material with a certified value for Hg concentration was used to evaluate the method. When the temperature of the furnace was programmed at a linear rate of increase of 50° min–1, different Hg compounds could clearly be separated. Three airborne particulate matter samples were collected in parallel in Toronto, ON, Canada and analyzed using this method. Reproducible results were obtained and Hg0, HgCl2, HgO, and HgS species from these samples were detected. 相似文献
998.
手性配体的空间结构与产物对映选择性的关系 总被引:2,自引:0,他引:2
首次采用4-烷氧羰基噻唑烷、E唑烷作为手性配体,诱导烷基锌对醛类的亲核加成反应,获得产物是烷基化的醛,最高达90%ee,产率98%的(S)-二级醇。系统地考察了该类手性配体三维空间结构变化与产物对映选择性的关系,当配体4-位烷氧羰基上的R、2-位R′基和环体上原子X发生变化时都会引起产物(S)-二 级醇的对映选择性发生规律性变化。对五种不同结构的底物醛在同一手性配体催化下,诱导烷基锌对醛类的亲核加成反应,底物结构变化也会引起(S)-二级醇对映选择性变化。 相似文献
999.
Thirty-five chemical solutions, acids, bases, complexing, argentometric, reducing, oxidising, salts and eluent mixtures, were studied continuously over a 7.5-month period. Twenty-seven remained reasonably stable and had acceptable expiration dates, which were equal to or more than 2 months longer than the established average deviation of ±2% relative to the initial value. Exceptions were made for potassium permanganate (0.1 M), perchloric acid (0.1 M) and disodium hydrogen phosphate (10%) solutions, as well as for HPLC eluent mixtures, which showed stability with expiration dates equal to stated values or shorter by 1 month. The eight chemical solutions presenting expiration dating higher than 6 months were hydrochloric acid (0.1 and 1 M), sulphuric acid (0.5 and 1.5 M), ethylenediamine tetraacetic acid (EDTA) (0.1 M), silver nitrate (0.1 M), ammonium thiocyanate (0.1 M) and iodine (0.1 M). The present data is a suitable guideline for the date of several chemical solutions routinely used in the analytical laboratories. 相似文献
1000.
Fe-Co-Ni合金纳米线有序阵列的模板合成与磁性 总被引:10,自引:0,他引:10
以二次阳极氧化的氧化铝膜为模板,用电化学沉积的方法成功地合成了Fe-Co-Ni三组份有序纳米线阵列.扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察表明纳米线表面光滑、有序、高长径比;磁性测量表明,其矫顽力较同组份的膜材料有较大的提高.将样品在惰性气体氛围中不同温度下退火,随着退火温度增加,其纵向矫顽力有一个极值,而对应的横向矫顽力没有类似的变化,关于这一现象的机理,本文进行了初步的讨论. 图5参15 相似文献