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121.
本文报导的方法是在南京大学高鸿教授研究的K_3Fe(CN)_6示波极谱滴定法(在PH8的K_2HPO_4—KH_2PO_4—KBr底液中,用0.04660mol/LK_3Fe(CN)_6标准溶液对纯抗坏血酸测定)的基础上,考虑到L—抗坏血酸(以下简称V_e)在碱性、中性介质中稳定性差,如用于V_e含量很微的果蔬测定,对结果影响大。本文改为H_2C_2O_4—KBr的酸性介质作底液,用 相似文献
122.
聚氯乙烯—丁腈橡胶—氯丁橡胶三元共混物的研究 总被引:1,自引:0,他引:1
测定了聚氯乙烯(PVC)-丁脯橡胶(NBR-29)-氯丁橡胶(CR)三元共混物的冲击性能和应力-应变行为,用动态力分析、扫描电和透射电镜研究了共混物的相容性和形态结构。结果表明,NBR-29对PVC,CR有良好的增容作用,三元共混物是部分相容的二相体系,具有良好的抗冲击性能。 相似文献
123.
Kang De Yao Tao Peng Han Bao Feng Yu Ying He 《Journal of polymer science. Part A, Polymer chemistry》1994,32(7):1213-1223
The aqueous swelling kinetics of a series of crosslinked chitosan (cr-CS) with glutaraldehyde (GA) interpenetrating polyether hydrogels have been studied as functions of pH, the N-deacetylation degree of chitosan, the amount of crosslinking agent, the electrolyte composition in solution, temperature, and gel composition. Based on these results, the swelling mechanism of the hydrogels was discussed. The release profiles of chlorhexidini acetas from the semi-IPN were also investigated. © 1994 John Wiley & Sons, Inc. 相似文献
124.
Spherical, smooth-surfaced and mechanically stable alginate-poly(L-histidine) (PLHis) microcapsules with narrow particle size distributions were prepared by incubating calcium alginate beads in aqueous solutions of PLHis. The in vitro release characteristics, drug loading and encapsulation efficiency of the microcapsules were investigated using bovine erythrocytes hemoglobin (Hb) as a model drug. The results showed that the concentration of Ca(2+) ions had a considerable effect on the drug loading, encapsulation efficiency and in vitro release behavior of the microcapsules. When the concentration of CaCl(2) in the PLHis solution was increased from 0 to 3.0% (w/v), the drug loading and encapsulation efficiency decreased significantly from 38.0 to 4.3% and from 92.9 to 8.0%, respectively, while the total cumulative release of Hb from microcapsules in phosphate buffered saline solution (PBS, pH 6.8) decreased from 96.2 to 72.8% in 24 h. No significant protein release was observed during 70 h of incubation in hydrochloric acid solution (pH 1.2). However, under neutral conditions (PBS, pH 6.8), the Hb was completely and stably released within 24-70 h. An explosion test showed that the stability of alginate-PLHis microcapsules depended strongly on the concentration of PLHis and the calcium ions in solution. [Diagram: see text] Microscopy photo of Hb-loaded alginate-PLHis microcapsules. 相似文献
125.
In this paper, we develop a novel adjacency matrix, He-matrix, corresponding to the dualist graph. Without using the graph center concept, we advance a novel nomenclature of polycyclic aromatic hydrocarbons. Further, we derive some distinguishing theorems about PAH molecules and present some results of our automatic derivatization and automatic classification counting of fused PAH molecules. 相似文献
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128.
We report studies of supersonically cooled indan using two-color resonantly enhanced multiphoton ionization and two-color zero-kinetic-energy photoelectron spectroscopy. With the aid of ab initio and density-functional calculations, vibrational modes of the first electronically excited state of the neutral species and those of the cation have been assigned, and the adiabatic ionization energy has been determined to be 68458 +/- 5 cm(-1). Similar to the ground state and the first electronically excited state of the neutral molecule, the ground state of the cation is also proven to be nonplanar, with an estimated barrier of 213 cm(-1) and a puckering angle of 15.0 degrees. These conclusions will be discussed in comparison with a previous study of an indan derivative 1,3-benzodioxole. 相似文献
129.
Dragulescu-Andrasi A Zhou P He G Ly DH 《Chemical communications (Cambridge, England)》2005,(2):244-246
Guanidine-based peptide nucleic acid (GPNA) with a d-backbone configuration and alternate spacing binds sequence-specifically to RNA and is readily taken up by both human somatic and embryonic stem (ES) cells. 相似文献
130.
The bicyclic keto lactone 26 was synthesized for the purpose of developing a viable route to marine diterpenes of the crenulatan type. Following the efficient conversion of (S)-citronellol ( 5 ) to the allylated alcohol 9a (Scheme 2), the αβ-unsaturated lactone 12 was efficiently accessed in preparation for stereocontrolled conjugate addition. The hydroxymethyl equivalent most suited to this task was (i-PrO)Me2SiCH2MgCl, which gave 13 predominantly in the presence of CuI and Me3SiCl. Once the OH group was deprotected (→ 14 ), it proved an easy matter to implement acid-catalyzed isomerization to lactone 15 , oxidation of which gave the pivotal aldehyde 16 . Condensation of 16 with PhSeCH2Li led via 21 to 22 (Scheme 3). Once the OH group was protected (→ 22b ), it proved possible to effect aldolization with crotonaldehyde (→ 23 ). Exposure of 23 to acid gave the sub-target compound 25 . Its subsequent oxidation and thermal activation resulted in sequential selenoxide elimination with Claisen rearrangement (→ 26 ). The structural features of 26 require that a chair-like transition state be adopted during the [3.3]sigmatropic event. With the clarification of these issues, a highly serviceable and more advanced assault on the crenulatans should prove capable of being mounted. 相似文献