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991.
共缩聚聚酰胺胶囊的制备及其性质的研究 总被引:7,自引:1,他引:7
界面缩聚法是制备微胶囊的常用办法之一,在医药、农药、生物工程等各个领域得到了广泛的研究与应用.此法制备聚酰胺胶囊具有制备方法简单、缩聚速度快、囊壁孔隙大等优点.在制备胶囊时,一般以一种二元胺或多元胺作为水溶性单体,制备的微胶囊存在很大的缺陷.当用二元胺作为水溶性单体时,得到具有线型结构的聚酰胺胶囊,囊壁的机械强度差.采用多元胺作为水溶性单体时,反应深度小,制备的胶囊囊壁薄、孔隙小.我们采用二元胺和多元胺的混合物作为水溶性单体,得到了不规则缩聚的共缩聚胶囊.改变二元胺与多元胺的比例,改善囊壁的机械强度和对KCl 的渗透系数,从而制备出具有较高机械强度和较大渗透系数的胶囊,以适应实际应用中对芯材控制释放的要求. 相似文献
992.
运用HF/3-21G方法和密度泛函理论(DFT)的B3LYP/6-31G*方法, 对羰基硼化合物(BCO)n(n=1~12)的各种可能结构进行了优化, 对在B3LYP/6-31G*水平上得到的几何构型、电子态、结合能、振动频率、核独立化学位移(NICS)、能量二次差分和热力学性质进行了理论研究, 得到了(BCO)n(n=1~12)结构的稳定性信息. 十二种基态结构都是端配位(μ1-CO), (BCO)n(n=1~3, 5, 6) 的基态是线型或平面结构, (BCO)n(n=4, 7~12)的基态是笼状结构; B—C平均键能呈现奇偶交替现象, 偶数的结构比奇数稳定; 能量二次差分得到同样的结论;羰基的振动频率与实验值非常吻合; 热力学性质的研究对实验具有重要的指导意义. 相似文献
993.
994.
Rabindra N. Roy Julie A. Carlsten Jodi Niederschmidt William S. Good J. Michelle Rook Christina Brewe Amanda J. Kilker Lakshmi N. Roy Kathleen M. Kuhler 《Journal of solution chemistry》1997,26(3):309-317
ThepK
2
values for 3-[(l,l-Dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO), and 3-[N,N-Bis(-hydroxyethyl)amino]-2-hydroxypropanesulfonic
acid (DIPSO) have been determined at 12 temperatures over the range 5 to 55‡C by measurements of the emf of cells without
liquid junction containing hydrogen and silver-silver chloride electrodes. The values of pK
2 for AMPSO and DIPSO were found to be 9.138 and 7.576, respectively, at 25‡C. The thermodynamic quantities, δG‡, δH‡, δS‡,
and δC
p
‡
were calculated from the change of the equilibrium constants with temperature. These buffer substances are useful as secondary
pH standards in the physiological region of pH 7 to 9.
Camille and Henry Dreyfus Fellow, 1994–1996. 相似文献
995.
Subir K. Basak Ajoy Velayudhan Michael R. Ladisch 《Applied biochemistry and biotechnology》1994,44(3):243-261
Buffers used in electrophoresis and electrochromatography must have a relatively low ionic strength in order to minimize ohmic
heating in the presence of an applied potential. Calculation of pH, ionic strength, and the van Slyke buffer capacity, β,
is therefore important. This paper describes thea priori calculation of these parameters for tris buffer made up with either glycine (a zwitterion) or HCl. A quadratic expression
for pH, valid over wide ranges, is obtained for both buffer systems. The calculated values of pH, ionic strength, and buffer
capacity are shown to agree with experimental results as a function of tris, HCl, and glycine concentrations ranging from
1 to 50 mM. A new parameter, the electrokinetic buffer effectiveness factor, is introduced to characterize buffers being considered
for use in electrokinetic systems such as electrochromatography, and is used to determine the appropriate composition ranges
for the buffer components. 相似文献
996.
De-Cai Fang P. Fabian Zoltan Szekely Xiao-Yuan Fu Ting-Hua Tang Imre G. Csizmadia 《Journal of Molecular Structure》1998,430(1-3):161-170
Ab initio (HF/6-31G** and B3LYP/6-31 + + G**) methods have been used to study the stability and structure of complexes between CH3SO−3 and CH3NH+3 or C(NH2)+3. Results show that no hydrogen jump is involved in the complex formations, which is different from previous work studying complexes between CH3COO− and CH3NH+3. In addition, we have studied complexes between CH3SO−3 and HC(NH2)+3 or +H3NC(NH2)3, all of which have a cage structure. 相似文献
997.
Chromone derivatives bearing a quaternary ammonium functionality which bind to human hair were synthesised. The radical scavenging activity, according to the DPPH assay, of the chromone derivatives is considerably lower compared with flavonoids. The compounds show interesting UV absorption properties that depend on the position of a methoxy substituent. A bathochromic shift of 29 nm was observed when the methoxy group on the ammonium salts were shifted from position 7 to position 6. 相似文献
998.
The degree of compatibilization between natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated by two different methods. NBR was chemically modified with maleic anhydride in a screw twin mixer with and without reaction initiator, benzoyl peroxide. Also, the effects of molecular weight of liquid natural rubber (LNR) as a compatibilizer were studied. The degree of compatibilization between NBR and NR is determined indirectly through measurements of mechanical properties and impact resistance. The maleic anhydride and benzoyl peroxide concentrations influence the mechanical properties and impact resistance of the blends. Also, the mechanical properties of the blends showed that the molecular weight of LNR played an important role in determing their performance. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
999.
Tailor and Control of Acidic Strength in Ordered Mesoporous Aluminosilicates by Using Preformed Zeolite Precursors 总被引:1,自引:0,他引:1
The acidic strength of ordered mesoporous aluminosilicates of MAS-2, MAS-3, MAS-7 and MAS-9 and microporous crystals of Y, L, beta, and ZSM-5 zeolites was systemically investigated by temperature-programmed desorption of ammonia (NH3-TPD). Due to the use of preformed zeolite precursors of Y, L, beta and ZSM-5, the ordered mesoporous aluminosilicates with distinguished acidic strength were obtained, being dependent on the type of preformed zeolite precursors. Therefore, the acidic strength of these mesoporous aluminosilicates could be tailored and controlled. 相似文献
1000.
Potassium phosphate buffer is often used in methods such as equilibrium dialysis, high performance liquid chromatography (HPLC), and affinity capillary electrophoresis (ACE) for characterizing the binding of drugs and hormones with proteins or other ligands within the body. In these experiments, the buffer density is often approximated to be that of water and the concentrations of all reagents are assumed to be constant with temperature. However, some difference in density between phosphate buffer and water would be expected, and variations in this density could lead to significant changes in the concentrations of dissolved solutes with temperature. This, in turn, could affect the binding observed for a solute-ligand system in such a buffer. In this study, the densities of potassium phosphate buffers with concentrations up to 0.10 M were measured at or near physiological pH for temperatures ranging from 4-45 °C. The general change in density versus temperature followed a quadratic equation, while the changes in density with concentration and pH followed a linear response. The results were used to formulate a general equation that could be used to calculate the density of potassium phosphate buffer at any pH, temperature, and concentration within the tested range. This equation and more specialized relationships developed in the temperature, concentration, and pH studies were found to give much greater accuracy in describing the density of these buffers versus a previous relationship developed for solutions containing only potassium dihydrogen phosphate. 相似文献