尿激酶活性测定方法的比较

根据中国及日本药典,对测定尿激酶活性的两种方法的灵敏度和重复性进行了考察对比,对不同样品测定结果进行了比较。     

Shear modulus of sintered 'house of cards'-like assemblies of crystals

A cell model of a 'house of cards'-like assembly of crystals is used for the study of the evolution of the shear modulus during sintering. The crystals are assumed to have a lozenge shape. The cell model takes different crystal-crystal contacts into account. The force needed to separate two sintered crystals is calculated using the minimum surface area (MSA) approximation. By varying the thickness, long axis, and short axis of the crystals, it is possible to make space-filing configurations which have a nonzero shear modulus at crystal volume fraction that can be as low as phi = 0.03. This is significantly lower than the volume fractions phi > 0.52 that are found in studies where the MSA approximation is applied to assemblies of spherical particles. It is found that sintering may cause a nonlinear volume fraction dependence of the shear modulus, which depends on the shape of the crystals, the type of crystal-crystal contacts, and the character of the crystal assembly. The calculated shear modulus is analyzed using the phenomenological expression (phi - phi0)beta, where phi0 represents the volume fraction at the start of sintering. The exponent beta is found to vary between 1 and 2. The interpretation of the shear modulus using a fractal model is also discussed.     

Milestones of the development of kinetics of electrode reactions

The birth and the development of the kinetics of electrode processes?Cmostly focusing on the case of the hindered charge transfer step and the early period?Care reviewed. It is shown how this important branch of electrochemistry was established and how and why the ideas of chemical kinetics have been introduced in electrochemistry. The history of electrode kinetics represents a good example for the progress of science in general, since it can be followed how the experimental observations conduce to the development of theory and how the theory influences further research. It is also demonstrated that the acceptance of new ideas is a thorny path. An attempt is made to acknowledge the merit of the scientists whose experimental or theoretical contributions brought paradigmatic changes in the thinking about the nature of electrode processes. In this context, the appropriate naming of equations is also discussed by using the example of the Erdey-Grúz?CVolmer vs. Butler?CVolmer equation. A discussion concerning the present trends is also included, which perhaps may predict the near future. A longer prognosis is avoided since the history of science teaches us that the real breakthroughs could not be predicted.     

渣油悬浮床加氢水溶性催化剂预硫化研究 Ⅱ 钼酸盐硫化产物的XPS分析

通过XPS分析法对钼酸盐的硫化行为进行了考察,分别考察了四价钼物种质量分数和硫钼元素的质量分数比，发现硫化产物的表面化学组成中四价钼质量分数和硫钼元素质量分数比不成正比，证实了该产物表面钼的硫化物不完全以MoS2形式存在。未经过临氢加热的硫化产物表面的四价钼物种的质量分数显著低于经过临氢加热的样品的质量分数，说明临氢加热在钼酸盐的硫化过程中起了重要作用。氯化铵是钼酸盐硫化过程中有效的助硫化剂，当它的用量增大时，硫化产物表面四价钼的质量分数也增大。以蒽为探针，使用化学探针法测定了硫化产物在渣油加氢过程中的催化活性，发现随着氯化铵用量的增加，产物的催化活性也相应提高，印证了XPS测定结果。     

Study of the influence of concentration on the time for first appearance of crystallization of polyethylene from xylene

An experiment is reported in which a simple laser light-scattering technique is used to measure the time for a critical turbidity to appear during the crystallization of polyethylene in xylene. The effect is examined over the entire range of solution concentration, and it is found that the relation between this concentration and temperature is linear for all solutions, provided that the time for turbidity to develop is arranged to be the same in all cases. In the appendix it is reasoned that similar results could have been obtained if, instead, times had been measured to a given degree of crystallinity rather than of turbidity. Departures from this linearity at low concentrations are taken as indicating multimolecular nucleation for all concentrations greater than about 1%.     

Crucial importance of translational entropy of water in pressure denaturation of proteins

We present statistical thermodynamics of pressure denaturation of proteins, in which the three-dimensional integral equation theory is employed. It is applied to a simple model system focusing on the translational entropy of the solvent. The partial molar volume governing the pressure dependence of the structural stability of a protein is expressed for each structure in terms of the excluded volume for the solvent molecules, the solvent-accessible surface area (ASA), and a parameter related to the solvent-density profile formed near the protein surface. It is argued that the entropic effect originating from the translational movement of water molecules plays critical roles in the pressure-induced denaturation. We also show that the exceptionally small size of water molecules among dense liquids in nature is crucial for pressure denaturation. An unfolded structure, which is only moderately less compact than the native structure but has much larger ASA, is shown to turn more stable than the native one at an elevated pressure. The water entropy for the native structure is higher than that for the unfolded structure in the low-pressure region, whereas the opposite is true in the high-pressure region. Such a structure is characterized by the cleft and/or swelling and the water penetration into the interior. In another solvent whose molecular size is 1.5 times larger than that of water, however, the inversion of the stability does not occur any longer. The random coil becomes relatively more destabilized with rising pressure, irrespective of the molecular size of the solvent. These theoretical predictions are in qualitatively good agreement with the experimental observations.     

Theoretical study of mechanism and selectivity of copper-catalyzed C-H bond amidation of indoles

Density functional theory calculations are used to study the reaction mechanism and origins of C2 selectivity in a copper(I)-catalyzed amidation of indoles. It is shown that concerted metalation-deprotonation is not able to reproduce the observed regioselectivity. Instead, an unprecedented mechanism based on a four-center reductive elimination is proposed to be responsible for the reaction outcome. This mechanism has a lower reaction barrier and is able to reproduce the experimentally observed selectivity. A possible alternative mechanism involving a Cu(II) species instead of Cu(III) is presented, but it is shown that higher energy barriers are associated with this mechanism. An important technical detail is that addition of dispersion effects to the B3LYP results is necessary to reproduce the observed selectivity, although not important for the overall mechanistic proposal.     

Spectrophotometric determination of traces of selenium with diaminobenzidine

Diaminobenzidine is suitable for the spectrophotometric determination of traces of selenium. The reaction is very sensitive, the molecular extinction coefficient being as high as 10,200. The reaction is specific, the most common ions causing no perturbation. The procedure is especially valuable for the determination of traces selenium in tellurium and in sulfur, provided that the latter is present in the sulfate form.     

Determination of small quantities of xanthate

A new spectrophotometric method for the determination of very small amounts of xanthate in solutions, particularly cyanide solutions from gold-extraction plants, is described. It is based on the formation and extraction of copper(II) xanthate. The coefficient of variation is 1.0% at the 40-ppm level and 3.4% at the 4-ppm level and the lower limit of determination is approximately 0.5 ppm. Copper(II) xanthate normally decomposes into copper(I) xanthate and dixanthogen, but in the proposed method the decomposition is delayed.     

Electrophoresis of a concentrated aqueous dispersion of non-Newtonian drops

The electrophoresis of a concentrated dispersion of non-Newtonian drops in an aqueous medium, which has not been investigated theoretically in the literature, is analyzed under conditions of low zeta potential and weak applied electric field. The results obtained provide a theoretical basis for the characterization of the nature of an emulsion and a microemulsion system. A Carreau fluid, which has wide applications in practice, is chosen for the non-Newtonian drops, and the unit cell model of Kuwabara is adopted to simulate a dispersion. The effects of the key parameters of a dispersion, including its concentration, the shear-thinning nature of the drop fluid, and the thickness of the double layer, on the electrophoretic behavior of a drop are discussed. In general, the more significant the shear-thinning nature of the drop fluid is, the larger the mobility is, and this effect is pronounced as the thickness of the double layer decreases. However, if the double layer is sufficiently thick, this effect becomes negligible. In general, the higher the concentration of drops is, the smaller the mobility is; however, if the double layer is either sufficiently thin or sufficiently thick, this effect becomes unimportant.     

柴油对流动改进剂感受性差异的原因表征与分析

柴油对低温流动改进剂具有较高的选择性。流动改进剂对不同的炼油厂、不同原油以及不同的加工工艺炼制的柴油的感受性和降冷滤效果截然不同。主要是由柴油的化学组成决定。一般认为，柴油中正构烷烃的摩尔分数和分布是影响其低温流动改进剂使用效果的主要因素。正构烷烃摩尔分数越低，碳数分布越广，添加低温流动改进剂效果越好；此外，柴油中所含的单环芳烃是高碳数烷烃的优良溶剂，其摩尔分数越高，柴油低温蜡析出量越少，加低温流动改进剂效果越好。     

Photometric complex-formation titrations of submicromole amounts of metals in the presence of an approximately equivalent amount of indicator

The photometric titration of the metal indicator complex MI with a ligand L is discussed. A tangent procedure is adopted for the determination of the end-point. From this procedure, in combination with an assumed maximum titration error, titration conditions have been derived. A procedure is introduced which, in conjunction with the derived titration conditions, permits the selection of a suitable titration medium by means of a diagram in which log K, log alpha and log chi are plotted vs. pH. The procedure is applied to determination of lead and zinc in the presence of citric acid, the medium used for their paper-electrophoretic separation. The use of citric acid introduces some limitations; it is shown that the method developed is generally applicable.     

Application of absorption spectrum of sodium vanadate to determination of vanadium

A method is proposed for the determination of small amounts of vanadium as found in certain ores, rocks and minerals. After fusion of the sample, the 8-hydroxy-quinoline complex is extracted with chloroform and converted to sodium ortho-vanadate. The absorbancy of this compound is measured at a wavelength of 270 mμ. The present method does not depend on the formation of a colored complex and, hence, is independent of such conditions as time and temperature.     

Infrared determination of traces of sulfate in reagent chemicals

A method for determining traces of sulfate in reagent-grade chemicals is presented. The sample is passed through an alumina column in acid solution to isolate the sulfate, which is then eluted with ammonia. Potassium bromide is added to an aliquot of the eluate, and the solution is freeze-dried. The resulting powder is pressed into a disk whose infrared spectrum is recorded. The method is reasonably accurate and requires a minimum of operator time per sample because a large number of samples can be processed together     

紫外光谱法测定甲壳素的脱乙酰化值

用紫外光谱测定甲壳素脱乙酰程度，该法快速简便，重现性好，试样无需特殊处理。     

Investigation of some modes of flat-bed chromatography

A comparison of different chromatographic methods is presented: column liquid chromatography (CLC), thin layer chromatography (TLC), and continuous-elution flat-bed chromatography (CEFBC), which is in fact a combination of the first two methods. In CEFBC a sample is applied to a sorbent layer in a steady flow of eluent, and the components are detected directly on the layer, or immediately upon leaving it, during the separation process. It is shown that evaluation of the separation processes in CEFBC is best accomplished in terms of the parameters applicable in CLC. The reproducibility of the analytical results obtained by CEFBC is better than in the case of TLC by a factor of 6 to 10, and approaches that known for CLC.     

自由基聚合中平均聚合度的学习

自由基聚合是《高分子化学》课程的重要一章 ,其中 ,平均聚合度是自由基聚合微观动力学的重要研究内容。正确理解其概念 ,掌握各种数学表达式的涵义 ,对高分子化学的学习十分有益 ,本文对不同终止和链转移情况下平均聚合度的表述方法进行了讨论     

Indirect atomic-absorption determination of ppM levels of arsenic by combustion of an MIBK extract of arsenomolybdic acid

An indirect atomic-absorption method for arsenic has been developed. Arsenic(III) is oxidized to arsenic(V) by iodine, then arsenomolybdic acid is formed and extracted into MIBK from 0.2-1.6M hydrochloric acid. Excess of molybdate is scrubbed from the organic phase, and then the molybdenum in the heteropoly acid is determined by its atomic absorption at 313.3 nm. Silicate and phosphate interfere. A procedure is described for determination of ppM levels of arsenic in water.     

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The recently discovered scaling law for the relaxation times, tau(T,upsilon) = I(Tupsilon(gamma)), where T is temperature and upsilon the specific volume, is derived by a revision of the entropy model of the glass transition dynamics originally proposed by Avramov [J. Non-Cryst. Solids 262, 258 (2000)]. In this modification the entropy is calculated by an alternative route. The resulting expression for the variation of the relaxation time with T and upsilon is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover. From this analysis, which is valid for any model in which the relaxation time is a function of the entropy, we find that the scaling exponent gamma can be identified with the Gruneisen constant.     

The effect of the order of the autocatalysis on the transverse stability of reaction fronts

A linear stability analysis of planar reaction fronts to transverse perturbations is considered for a system based on an autocatalytic reaction of general order p. Dispersion curves, plots of the growth rate sigma against a transverse wavenumber k, are obtained for a range of values of p and D, where D is the ratio of the diffusion coefficients of autocatalyst and substrate. A value D(0) of D, dependent on p, is found at which sigma(max), the maximum value of sigma in the unstable regime, is largest, with D(0) increasing as p is increased. An asymptotic analysis for small wavenumbers is derived, which enables the region in the (p, D) parameter space for instability to be determined. An analysis for D small is undertaken, which leads to upper bounds on the wavenumber for a possible instability.