Higher N-acyl-L-amino acid derivatives

A preparative method is proposed for obtaining higher N-acylamino acids by reaction of free amino acids with fatty acid nitrophenyl esters. It was shown that these acids can transport positive ions through a liquid lipophilic medium. A direct method is proposed for obtaining fatty acid 4-nitro-phenyl esters by boiling 4-nitrophenol and the fatty acid in xylene in a Soxhlet apparatus in the presence of an acid catalyst.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2555–2560, November, 1990.     

高等教育改革

大学教育和一生工作的关系是高等教育中争论最多的问题之一。因培养不出适合工作需要的青年人。大学受到各种批评。大学生们所学的和他们所从事的专业工作中所要用的知识之间的差距已成为高等教育工作者和学生的未来雇主共同关心的主要问题。     

Arsenic Compounds in Higher Fungi

In 50 mushroom species (56 samples) from Slovenia, Switzerland, Brazil, Sweden, The Netherlands and USA, total arsenic was determined by radiochemical neutron activation analysis (RNAA). Arsenic concentrations ranged from 0.1 to 30 μg g⁻¹ (dry mass). Arsenic compounds were determined in methanol extracts from the mushrooms by HPLC–ICP–MS. The aim of the study was not only to quantify arsenic compounds in mushrooms but also to uncover trends relating the methylating ability of a mushroom to its taxonomic or evolutionary status. The main arsenic compound found in many mushrooms (various puffballs, Agaricales and Aphyllophorales) was arsenobetaine. Arsenate [As(V)] was the main arsenic species in Laccaria fraterna and Entoloma rhodopolium and arsenite [As(III)] in Tricholoma sulphureum. A mixture of arsenite and arsenate was present in Amanita caesarea. Dimethylarsinic acid (DMA) and methylarsonic acid were present in many mushrooms, but generally as minor components. In Laccaria laccata, Leucocoprinus badhamii and Volvariella volvacea, DMA was the major metabolite. Arsenocholine (AC) and the tetramethylarsonium ion were present in a few species, generally at low concentrations, except for Sparassis crispa, in which AC was the main compound. Tri- methylarsine oxide was not found in any of the mushrooms. In some species small amounts of unknown compounds were also present. The possible taxonomic significance of the metabolite patterns and the predominance of arsenobetaine in more advanced fungal types are discussed. © 1997 John Wiley & Sons, Ltd.     

Towards a European Higher Education Area

The higher education system in Europe needs to be harmonised in order to enhance its international competitiveness. In the following article Terence N. Mitchell, professor of chemistry at Dortmund University, comments on the Bologna Declaration ‐ a political paper which affirms the creation of a European Higher Education Area. Does this declaration meet the necessary requirements and how does chemistry fit into the Bologna process?     

Biosynthesis of Homoterpenes in Higher Plants

In higher plants, the two homoterpenes 4,8-dimethyinona-1,3,7-triene ( 1 ) and 4,8,12-trimethyltrideca-1,3,7,11-tetraene ( 2 ) are synthesized from the regular terpene alcohols nerolidol and geranyllinalool by fragmentation into the homoterpene and butenone. The biosynthetic pathway is evidenced by conversion of (²H)nerolidol in Hoya purpureo-fusca, Magnolia liliiflora nigra, Robinia pseudoacacia, and Philadelphus coronarius.     

建设高效的公共仪器实验室

随着微电子技术的进步 ,仪器分析相关的技术和方法在最近几十年的发展非常迅速 ,不仅更多的物化性质得到利用 ,而且仪器的自动化程度越来越高 ,日常操作使用不断简化 ,使分析测试、分离等方法在化学、生物及相关材料科学研究中的应用越来越广泛。仪器分析技术的迅速发展 ,对化学类学生的基础理论和实验课教学提出了更高的要求 ,对学生有关仪器原理、操作方法及实际应用等方面的培训也提出了新的要求和目标。为适应形势发展的需要 ,北京大学化学学院将仪器设备合理配置 ,对教学实验内容和学生培养目标进行改革 ,于 1 996年筹建了北京大学化学…     

高碳烯烃氢甲酰化研究

高碳烯烃氢甲酰化是最重要的石化技术之一.本文从均相催化体系和两相催化体系两个方面介绍了国内外近年来在研究与开发上取得的进展.两 相催化体系的开发正在成为研究的主流引人瞩目,预期新催化剂体系和两相体系在高碳烯烃氢甲酰化应用上将有突破.     

Improved Bioprocess with CHO-hTSH Cells on Higher Microcarrier Concentration Provides Higher Overall Biomass and Productivity for rhTSH

Since the recombinant thyroid-stimulating hormone (rhTSH) is secreted by stably transfected Chinese hamster ovary (CHO-hTSH) cells, a bioprocess consisting of immobilizing the cells on a substrate allowing their multiplication is very suitable for rhTSH recovering from supernatants at relative high degree of purity. In addition, such a system has also the advantage of easily allowing delicate manipulations of culture medium replacement. In the present study, we show the development of a laboratory scale bioprocess protocol of CHO-hTSH cell cultures on cytodex microcarriers (MCs) in a 1 L bioreactor, for the preparation of rhTSH batches in view of structure/function studies. CHO-hTSH cells were cultivated on a fetal bovine serum supplemented medium during cell growth phase. For rhTSH synthesis phase, 75% of supernatant was replaced by animal protein-free medium every 24 h. Cell cultures were monitored for agitation (rpm), temperature (°C), dissolved oxygen (% DO), pH, cell concentration, MCs coverage, glucose consumption, lactate production, and rhTSH expression. The results indicate that the amount of MCs in the culture and the cell concentration at the beginning of rhTSH synthesis phase were crucial parameters for improving the final rhTSH production. By cultivating the CHO-hTSH cells with an initial cell seeding of four cells/MC on 4 g/L of MCs with a repeated fed batch mode of operation at 40 rpm, 37 °C, 20% DO, and pH 7.2 and starting the rhTSH synthesis phase with 3 × 10⁶ cells/mL, we were able to supply the cultures with enough glucose, to maintain low levels of lactate, and to provide high percent (∼80%) of fully covered MCs for a long period (5 days) and attain a high cell concentration (∼9 × 10⁵ cells/mL). The novelty of the present study is represented by the establishment of cell culture conditions allowing us to produce ∼1.6 mg/L of rhTSH in an already suitable degree of purity. Batches of produced rhTSH were purified and showed biological activity.     

Totally Synthetic Routes to the Higher Monosaccharides

The evolution of a strategy to synthesize the title compounds is described. Three principal developments allowed realization of this goal: (1) the attainment of high margins of diastereofacial selectivity and regioselectivity in the construction of pyranoid systems via the Lewis acid-catalyzed cyclocondensation reaction of activated dienes and aldehydes; (2) the exploitation of stereoselective reactions for functionalization of the pyranoid matrix; and (3) the discovery of stereoselective reactions for extending the chiral biases of pyranoid systems to newly emerging stereogenic centers on side chains. The coordination of these components in the synthesis of target systems of high biological interest is described.     

Synthesis and Properties of Higher Nuclearity Polyazanes

Polyazanes (i.e., higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5), including the first pentazane ever described, were prepared by the addition of lower-order polyazanes to diazo reagents. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement persists in solution. Although the polyazanes are all reducing agents, they become less so as the number of nitrogens increases.     

Higher Coordination Numbers of the Typical Elements

The bonding in electron-deficient molecules, e.g. the boron hydrides and certain metal alkyls, and in molecules which appear to violate the rare gas rule, e.g. hydrogen bonded complexes, interhalogen compounds and compounds of the typical elements with high coordination numbers such as PCI₅ and SF₆ can be described by a simple molecular orbital treatment involving delocalized α-bonds. The contribution of d-orbitals to the bonding in the interhalogen compounds and rare gas fluorides is very small. The stereochemistry and physical properties of the PX₅ system are explained readily by the delocalization treatment and it is likely that here also the importance of spd hybridization has been overemphasized in the past.     

Higher molecular-deformation derivatives of the configuration-interaction energy

We derive expressions for the first through fourth derivatives of the configuration-interaction (CI) electronic energy with respect to molecular deformation. By using unitary exponential parameterizations of the wavefunction's orbital and configuration amplitude response together with a power-series expansion of the geometry dependence of the hamiltonian, a computationally attractive expression for the CI energy derivatives is obtained. The use of so-called direct methods in evaluating the CI derivatives is discussed as are the relative efforts involved in using our CI-based energy-derivative expressions and those which we obtained earlier for derivatives of the multiconfigurational self-consistent-field energy. The power-series expansion of the geometry dependence of the hamiltonian that we have derived may be used for evaluating molecular-deformation derivatives for any approximate wavefunction constructed from a set of orthonormal orbitals.     

Higher spectra approximations derived from multistep loading

Summary A multistep loading programme for a cross-linked polymer with equidistant discontinuities jumping with constant amplitudes of stress or strain may yield higher approximations of the retardation or relaxation spectra to any degree of accuracy provided that the Boltzmann superposition principle is not violated. In the case of retardation spectra the multistep loading programme can be replaced by an initial creep loading followed by steps of recovery of equal amplitudes and time. In the case when an accurate composite curve of the material is available by application of the principle of reduced variables, this curve yields sufficient information for the tracing of retardation or relaxation spectra to any degree of approximation. Examples are given for the tracing of retardation and relaxation spectra up to their third approximation for an epoxy polymer and a polyurethane elastomer by using the multistep method. Three approximations of relaxation spectra for N.B.S. Polyisobutylene and Polymethylmethacrylate are also derived from their composite curves.

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Zusammenfassung Ein Programm, bei dem ein vernetztes Polymeres mit diskontinuierlichen Sprüngen von gleichem zeitlichem Abstand und konstanter Amplitude in bezug auf Dehnung oder Spannung belastet wird, kann h?here N?herungen für Retardations- und Relaxationsspektra mit einem ausreichenden Grad an Genauigkeit liefern, vorausgesetzt, da? das Boltzmannsche Superpositionsprinzip nicht verletzt wird. Im Falle der Retardationsspektren ist die Mehrstufenbelastung ersetzbar durch eine anf?ngliche Kriechbelastung, gefolgt durch Stufen der Entlastung mit gleichen Amplituden und gleichen Zeitabst?nden. In dem Fall, da? eine exakte Master-Kurve für das Material durch Anwendung des Prinzips der reduzierten Variablen erlangbar ist, gew?hrt diese Kurve genügend Information für die Ermittlung des Retardationsoder Relaxationsspektrum mit ausreichender N?herung. Beispiele werden für die Gewinnung von Retardations- und Relaxationsspektren bis zu ihrer dritten N?herung für ein Epoxidharz und für ein Polyurethan-Elastomeres unter Verwendung der Mehrstufenmethode gegeben. Drei N?herungen der Relaxationsspektren für N.B.S., Polyisobutylen und Polymethylmethacrylat werden aus den Master-Kurven abgelcitct.