How to realize the linear scale-up process for rapid purification using high-performance counter-current chromatography

This study used the isolation of six constituents from Selaginella tamariscina as an example to demonstrate how to achieve rapid and predictable linear scale-up processes in both normal- and reversed-phase high-performance counter-current chromatography. After systematic optimization of solvent systems, sample concentration, sample loading volume, rotation speed and flow rate on the analytical Mini-DE centrifuge, the optimized parameters obtained were directly transferred to the preparative Midi-DE centrifuge, with nearly the same purities, resolutions and elution times but with 50 times the throughput. Amentoflavone (446.7 mg, 97.8%), robustaflavone (21.6 mg, 89.4%), bilobetin (80.7 mg, 92.7%), hinokiflavone (15.1 mg, 85.5%), isocryptomerin (34.8 mg, 89.6%) and an apigenin-diglucoside (46.3mg, 96.4%) were obtained with amounts and purities shown in parentheses as analysed by HPLC. The process, therefore, offers an efficient and rapid method of obtaining sufficient quantities of target compounds with significantly increased throughput after a linear scale-up.     

How to design a kinetic-catalytic method of analysis based on ligand substitution reactions

From a mechanistic consideration on the formation constant of a metal complex, the catalytic effect of a third ligandA on ligand substitution reaction is found to be given by log(k _f ^A )=E(A)+H(A)+E(A), wherek _f andk _f ^A refer to the rate constants for a non-catalyzed reaction path and catalyzed reaction path, respectively, andE andH are the electron donor constant and basicity constant of the specified ligand, respectively,,, and are constants characteristic of a metal ion and their values have been estimated from the mechanistic consideration on the reactivity of a metal ion and its complex. With this equation and the parameters,,,E, andH, the acceleration effect of halide ions on the ligand substitution reaction of mercury(II)-4-(2-pyridylazo)resorcinol complex with l,2-cyclohexanediamine-N,N,N,N-tetraacetic acid was quantitatively demonstrated. With the same parameters some possibilities to design a new kinetic-catalytic method of analysis based on ligand substitution reactions were proposed.     

Molecular and electronic structures by design: tuning symmetrical and unsymmetrical linear trichromium chains

The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr(3)(L)(4)X(2) (L = equatorial ligands dipyridylamide (dpa) or di-4,4'-ethyl-2,2'-pyridylamide (depa), and X = axial ligands, e.g., halide or pseudohalide ions) with large variations in metal-metal distances are reported here. These complexes, which belong to a broad class of fundamentally interesting trinuclear molecules over which the electrons may or may not be delocalized, pose significant theoretical and experimental challenges which are dealt with in this report. Complexes with strongly donating axial or equatorial ligands tend to favor a symmetrical (D(4)) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C(4)) structures; the physical properties of these two classes of compounds are discussed fully, and important comparisons with a reported DFT model of the electronic structures of the compounds are made.     

Highly enantioselective addition of linear alkyl alkynes to linear aldehydes

It is discovered that the use of biscyclohexylamine (Cy₂NH) as an additive can greatly enhance the enantioselectivity for the reaction of linear alkyl alkynes with linear aldehydes. The combination of (S)-BINOL (20 mol %), Cy₂NH (5 mol %), ZnEt₂ (2 equiv), and Ti(OⁱPr)₄ (0.5 equiv) catalyzes the reaction at room temperature in diethyl ether solution with 81-89% ee and 57-77% yield.     

Correlating molecular design to microstructure in thermally convertible oligothiophenes: the effect of branched versus linear end groups

The thin film microstructure development of functionalized oligothiophenes with branched, thermally removable groups at each end of conjugated cores with five, six, and seven thiophene rings was monitored during their thermal conversion from solution processible precursors to insoluble semiconductor products. The change in end group character provides a comparison of branched vs linear end group functionalization in oligothiophenes. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy confirmed that branched alpha-, omega-substitutions of the precursors strongly influenced the packing of the conjugated core. The quinque- and sexithiophene precursors oriented perpendicular to the substrate, whereas the septithiophene precursor oriented parallel to the substrate, providing one of the first examples of length dependence in oligothiophene orientation. This dependence may be due to a packing mismatch between the conjugated cores and the branched end groups. The convertible septithiophene exhibits four distinct microstructures as it converts from precursor to product that correlate strongly with its field-effect hole mobility in field-effect transistors. The extent of septithiophene order and the surface-relative orientation of its ordered phases clearly influence field-effect transistor performance.     

怎样鉴别葡萄糖和果糖

据我们所知,高中学生和高中化学教师都想知道怎样鉴别葡萄糖和果糖,而我们的教材、教学大纲都没有涉及,也不要求鉴别葡萄糖和果糖.可是学生在学了糖类一章的知识以后,这个问题就很自然地提出来了.淀粉、维生素可以用碘水鉴别;蔗糖、麦芽糖可以用银氨溶液或碱性氢氧化铜鉴别,那么如何鉴别葡萄糖和果糖应是补充的实验.现介绍鉴别葡萄糖和果糖的原理和实验方法.     

A linear programming approach to weak reversibility and linear conjugacy of chemical reaction networks

A numerically effective procedure for determining weakly reversible chemical reaction networks that are linearly conjugate to a known reaction network is proposed in this paper. The method is based on translating the structural and algebraic characteristics of weak reversibility to logical statements and solving the obtained set of linear (in)equalities in the framework of mixed integer linear programming. The unknowns in the problem are the reaction rate coefficients and the parameters of the linear conjugacy transformation. The efficacy of the approach is shown through numerical examples.     

熵教学中的几点体会

结合教材、文献与教学的体会,对熵判据、温熵图和理想气体混合熵变计算等知识点作简单论述,以帮助初学热力学第二定律的学生更好地理解熵判据、温熵图的含义及其应用计算。     

如何制备金属钾

工业上约于850℃时用钠还原熔融态氯化钾的方法制备金属钾,Na(l) KCl(l)K(g) NaCl(l)。从金属活泼性看,钠略弱于钾,ΔfH m[NaCl(s)]=-411kJ/mol,ΔfH m[KCl(s)]=-435 kJ/mol,就是说上述正向是吸能即ΔrH m为正值的反应。因钾比钠容易挥发,沸点分别为756·5℃、881℃,在该温度下     

How to silence silencing

Two recent reports describe the stunning crystal structures of complexes between a viral protein that suppresses RNA silencing and a 21 nucleotide small interfering (si)RNA.     

How to improve guanidinium cations for oxoanion binding in aqueous solution?: The design of artificial peptide receptors

Guanidinium cations are a prominent recognition motif for oxoanion binding both in Nature and in abiotic systems. However, simple ion pairing based on alkyl guanidinium cations is not strong enough to achieve an efficient complexation in aqueous solvents. Nature uses the less polar microenvironment of a protein to shield the ion pair from the solvent thereby increasing complex stability. For artificial supramolecular systems other ways to improve the binding affinity of guanidium cations have to be found. We will describe herein our use of modified acylguanidinium cations with additional H-bond donor sites to achieve oxoanion binding in aqueous solvents. The thermodynamic characterization of such systems is described as well as some applications from the field of bioorganic chemistry (e.g. artificial receptors for anionic biomolecules).     

How to identify a pharmacophore

The inhibition of chitinases by argifin and progressively dissected analogs had been studied by a combination of kinetic and crystallographic methods (Andersen et al., 2008). This work also leads to a general understanding of structure-activity relationships for inhibitors with one distinct pharmacophor.     

How to implement process-oriented care

Dutch hospitals are in the midst of a transition towards process-oriented organisation to realise optimal and undisturbed care processes. Between 2004 and 2007, the University Hospital of Maastricht conducted a case study implementing process-oriented in-hospital stroke unit care. The case study consisted of four steps: (1) process analysis; (2) identification of bottlenecks; (3) setting goals for process-oriented care, and selection of coordination measures; and (4) implementation and evaluation. Implementation of process-orientation via the coordination measures chosen streamlined the process and led to a better performance of in-hospital stroke unit care; the length of stay was reduced from 12 to 7 days, and the percentage of patients who could not be admitted to the stroke unit was reduced from 31% to 2%. The implementation of coordination measures is a useful means of controlling the activities of the stroke care process from a process point of view. The coordination measures used will not automatically be applicable to other care processes because of the specific nature of each care process. Nevertheless, the general principles of visual representation, bottleneck reduction, and elimination of waste and uncertainty would be applicable in many settings. Presented at the conference “Quality in the Spotlight”, March 2008, Antwerp, Belgium.     

关于学习物理化学的一点思考

阐述了建立知识体系的必要性。简要介绍在学习化学热力学及统计热力学时所建立的知识体系     

怎样上好聚合物流变学

之目的在于探讨工科院校中聚合物流变学课程的教学重点与教学措施,提出了"以高分子物理为依托,服务于聚合物成型工艺,强调课程实用性"的教学思路。聚合物流变学在高分子专业本科教学过程中是承上启下的关键课程,地位与作用明显;聚合物流变学课程又不同于一般流变学课程,有着自身的特点;工科院校中,应突出其实用功能,同时不放弃对经典流变学理论的介绍与适当深入。文中,还对国内外聚合物流变学教材的特点作了评述,对于如何上好聚合物流变学提出了自己的观点。     

How to starve a tumor

The formation of new blood vessels, termed angiogenesis, Is a central process In the evolution of a tumor and its subsequent metastasis. Angiogenesis is potently inhibited by the fumagillins, a family of epoxide-containing natural products. The recent identification of a protein target for these compounds may help decipher the mechanisms underlying endothelial cell growth. The fact that binding is irreversible may Inspire the design of electrophilic inhibitors of other, poorly understood cellular processes.     

维生素E的催化合成路线分析

维生素E具有多种特异的生理活性,同时也是一种优良的抗氧化剂,已经逐渐成为维生素领域中的焦点,市场需求不断增加。目前合成维生素E占据市场的80%以上,提升维生素E的产量和生产效率势在必行。天然维生素E包括四种生育酚类物质和四种生育三烯酚类物质,其中α-生育酚含量最大,生理活性也最高。本综述简要介绍α-生育酚的合成路线,其中包括2, 3, 5-三甲基氢醌和异植物醇的合成以及它们二者缩合的反应。本文着重阐述路线的设计和催化剂的选择,并对存在的问题及潜在的解决办法进行评述和展望。     

Equilibrium theory-based design of simulated moving bed processes under reduced purity requirements linear isotherms

The design of simulated moving bed processes under reduced purity requirements for systems whose isotherm is linear is considered. Based on the equilibrium theory of chromatography, explicit equations to uniquely identify the separation region that will ensure specified extract and raffinate purities are derived. The identification of the region requires only the knowledge of Henry constants of the solutes, the concentration of the solutes in the feed and the purity specifications. These results are validated using numerical simulations.