Synthesis of the repeating unit of the lipoteichoic acid of Streptococcus pneumoniae

The lipoteichoic acid repeating unit of Streptococcus pneumoniae is a complex pseudopentasaccharide (3). It consists of one ribitol-phosphate, one 2-acetamino-4-amino-2,4,6-trideoxy-galactose, one glucose and two galactosamine residues each differently linked, but both carrying one phosphocholine substituent, at position 6. Suitable building blocks (6–10) for efficient and diastereocontrolled ligations were designed, thus providing, after complete deprotection, the target molecule in high purity. Biological tests revealed that repeating unit 3, lacking the lipid moiety, did not stimulate a pro-inflammatory response in human monocytes (hMNCs).     

On the generalization of the Edgeworth/Gram-Charlier series

Berberan-Santos relates one probability distribution to another wherein one distribution is expressed in terms of the derivatives of the other Berberan-Santos (J Math Chem 42:585, 2007). We derive the result in a straightforward manner based on a generalization of the Edgeworth/Gram Charlier.     

On the role of triflic acid in the metal triflate-catalysed acylation of alcohols

The acylation of alcohols by anhydrides, catalysed by a wide range of metal triflates, is a powerful and mild method for the preparation of a variety of esters. Mechanistic insights demonstrate that triflic acid is generated under these reaction conditions and that, at least, two competing catalytic cycles are operating at the same time: a rapid one involving triflic acid and a slower one involving the metal triflate.     

Crotylation versus propargylation: two routes for the synthesis of the C13-C18 fragment of the antibiotic branimycin

The C13-C18 fragment 3 of the novel antibiotic branimycin was prepared along two highly stereocontrolled routes. The first one uses a standard Roush crotylation protocol, whereas the second one proceeds via an allenyl silane propargylation with unexpected stereochemical consequences, which are discussed in detail.     

Determination of the nature and concentration of solutes using the swelling granule method

A procedure and instrument for the determination of dissolved electrolytes and nonelectrolytes in solutions are described. The analysis was performed by measuring the size of a polymer granule placed in the test solution. It was found that various polymers can be used for the determination of the nature or concentration of a solute. This allows one to perform the analysis in various solvents. The use of small granules allows one to decrease the sample volume to tenths fractions of a microliter.     

Computation of the pseudorotation matrix to satisfy the Eckart axis conditions

A general solution for satisfying the Eckart axis conditions [C. Eckart, Phys. Rev. 47, 552 (1935)] is presented. The goal is to find such a pseudorotation matrix T that the vector product between the reference molecular conformation R and another transformed conformation r' is zero [ summation operator(a)m(a) r(a) 'xRa=0; r(a) '=Tr(a)]. Our solution avoids the limitations of the earlier one [H. M. Pickett and H. L. Strauss, J. Am. Chem. Soc. 92, 7281 (1970)], which fails when one of the involved intermediate matrices is singular. We also discuss how to choose among the always nonunique pseudorotation matrices T the one that represents a true rotation for situations when an alignment of the two conformations is desired.     

A theory for the construction of the irreducible representations of finite groups. II

The restriction on a method for computing irreducible representations of finite groups, requiring that in the irreducible representation to be constructed, at least one group element has at least one nondegenerate eigenvalue, is removed. The method is thus shown to be applicable to an arbitrary finite group and constitutes a practical algorithm for handling groups of order less than 400.     

Determination of trace elements by chemical analysis and neutron activation in meteorites of the collection of the viennese museum of natural history

In the present paper a thorough analysis is described of six olivine-hypersthene chondrites, one pyroxene-plagioclase-achondrite, one medium and one coarse octahedrite as well as of an ataxite of high nickel content.For the wet-chemical determination of the main constituents a rapid method of analysis has been developed which has been found to be very suitable. For the final determination of the elements methods based on chelatometric fluorescence titration in ultra-violet light are employed.Also for the trace elements a separation method was developed which, at the present stage, allows the analysis of twelve elements in one operation. This separation technique is applicable after neutron activation and to isotopes with half lives exceeding 24 hours.With 8 FiguresThis paper has been dedicated to Professor Dr.Friedrich Wessely on the occasion of his 70th birthday.     

Quantum mechanical models of the resting state of the vanadium-dependent haloperoxidase

Density functional theory has been used to investigate structural and electronic properties of complexes related to the resting form of the active site of vanadium haloperoxidase as a function of environment and protonation state. Results obtained by studying models of varying size and complexity highlight the influence of environment and protonation state on the structure and stability of the metal cofactor. The study shows that, in the trigonal bipyramidal active site, where one axial position is occupied by a key histidine, the trans position cannot contain a terminal oxo group. Further, a highly negatively charged vanadate unit is not stable. Protonation of at least one equatorial oxo ligand appears necessary to stabilize the metal cofactor. The study also indicates that, while at rest within the protein, the vanadate unit is most likely an anion with an axial hydroxide and an equatorial plane containing two oxos and a hydroxide. For the neutral, protonated state of the vanadate unit, there were two minima found. The first structure is characterized by an axial water with two oxo and one hydroxo group in the equatorial plane. The second structure contains an axial hydroxo group and an equatorial plane composed of one oxo and two hydroxo oxygen atoms. These two species are not significantly different in energy, indicating that either form may be important during the catalytic cycle. These data support the initial crystallographic assignment of an axially bound hydroxide, but an axial water is also a possibility. This study also shows that the protonation state of the vanadate ion is most likely greater than previously proposed.     

Chemical Constituents from the Leaves of Zanthoxylum Schinifolium

cis‐Fagaramide ( 1 ), a new amide, together with fifty known compounds, have been isolated from the leaves of Zanthoxylum schinifolium. These known compounds include twenty‐one coumarins, eleven alkaloids, one furan, four benzenoids, three chlorophylls, four triterpenoids, one diterpenoid, one sesquiterpenoid, and four steroids. The structures of these compounds were determined by means of spectral analyses.     

法治建设的国家能力基础：从国族认同建构能力切入

援引“国家能力”的概念及其学说来讨论中国法治问题,如今正逐渐在中国法学界成为一种新潮流。但当将这些出自非法学研究者之手的理论运用来研究中国法治问题时,其中有些概念乃至分析框架,应当事先做一番必要的检讨与调整,再非常谨慎地予以借用。尤其是要适当超越“国家能力”学说有可能过度凸显的某种“自上而下支配”的面向。国族认同建构能力可被用来将国家能力问题与法治建设勾连起来进行讨论。作为国家能力之内容的重要组成部分,国族认同建构能力不仅是在全球化时代最大程度地维系一国法治之自身正当性的基础,也是有助于在一国范围内以最小成本高质量地构建回应型法治的润滑剂。     

Characterizing the properties of the N7,N9-dimethylguaninium chloride ion pairs: prospecting for the design of a novel ionic liquid

The structures, infrared spectra, and electronic properties of the N7,N9-dimethylguaninium chloride have been studied. The interaction of one cation with one to four Cl anions and one Cl anion with two cations were investigated. Fifteen stable conformers are obtained. It is found that there are four acidic regions in the vicinity of the guaninium cations. In these regions, the cation could H-bond with one to three Cl anions but no more than three nearest anions. One Cl anion could H-bond with two cations. Additionally, evidence of a Cl...pi interaction between the anion and cation is observed. Among these structures, one cation interaction with two anions and two cations interaction with one anion have the larger interaction energies than the other series. Natural bond orbital analyses and molecular orbitals reveal that the charge transfer from anion(s) to the cation(s) occurs mainly through either the Cllp --> sigma C-H, Cllp --> sigma N-H, or Cllp --> pi C8-N7 interactions. The interaction between Cl and sigma (C/N-H) or pi C-N produces a small bond order. This indicates that the Cl...H (Cl...pi) interaction exhibits a weak covalent character and suggests a strong ionic H-bond (Cl...pi bond). What's more, formation of Cl...H/Cl...pi bond decreases the bond order of the associated C/N-H bond or C8-N7 bond. In addition, examination of vibrational spectrum of each conformer explains the origin of H-bonding character.     

Differential method for the determination of the order of reaction and the rate constants

A method is proposed whereby the orders and rate constants for processes obeying the rate law ?dA/dt = kAⁿ may be determined. The method is illustrated in two ways. First, simulated data for processes of various orders are treated, and the treatment is shown to be capable of reproducing orders and rate constants to a high degree of accuracy. The factors affecting the accuracy with which n and k can be determined are considered. These are inaccuracy in the determination of concentration values, irregularity of the time intevals between concentration determinations, and the length of those time intervals. It is shown that if concentrations are determined at times that are close together, the effect of the other two factors is small, but if the time intervals are made longer, the errors due to the other two factors affect the calculated values of n and k much more seriously. Second, the method was applied to two homogeneous reactions, of which one was first-order and one was second order, and three heterogeneous reactions, of which one was found by the original workers to be first order, one to be zero order, and one to vary between zero and first order, depending on the initial pressure. The present method gives results in agreement with these conclusions and reproduces the rate constants to within ±5% in all cases.     

Investigations on the luminescence of titanium-activated stannates and zirconates

The luminescence of several titanium-activated stannates and zirconates with spinel, perovskite, K₂NiF₄, pyrochlore, and fluorite structure is reported. For most compounds two emissions are observed, one blue and one yellow. Some compounds show only yellow emission and there is one compound with only blue emission. These results can be explained by one model, based on the occurrence of two different titanate centres, viz., a regular center and a defect center.     

Nature of the catalytically labile oxygen at the active site of xanthine oxidase

In this paper we report the results of molybdenum K-edge X-ray absorption studies performed on the oxidized active site of xanthine oxidase at pH 6 and 10. These results indicate that the active site possesses one terminal oxygen ligand (Mo=O), two thiolate ligands (Mo-S), one terminal sulfido ligand (Mo=S), and one Mo-OH moiety. EXAFS analysis demonstrates that the Mo-OH bond shortens from 1.97 A at pH 6 to 1.75 A at pH 10, which is consistent with the generation of a Mo-O- moiety. This study provides convincing structural evidence that the catalytic oxygen donor at the oxidized active site of xanthine oxidase is Mo-OH rather than the Mo-OH2 ligation previously suggested by X-ray crystallography. These results support a mechanism initiated by base-assisted nucleophilic attack of the substrate by Mo-OH.     

Some demonstrations of the effect of the heating rate on thermoanalytical curves

Thermoanalytical curves of two parallel competitive reaction systems and of two systems in which two mutually independent reactions occur concurrently are made by simulation, as well as isothermal curves of the systems. From these curves, an effect of heating rate is illustratively shown; one peak is observed in a derivative thermoanalytical curve at one heating rate, while a shoulder or two peaks appear in another derivative curve of the same reaction system at another heating rate. An advantage of thermal analysis over isothermal experiments, and its limitations, are discussed.     

Study of the one-channel resonance states. Method without a stabilization procedure in the framework of the optical potential model

The resonances of some one-dimensional systems are studied in the framework of the optical potential model. Analysis of the discrepancies between the observed and exact resonance energy values shows that these differences come from the partial waves reflected upon the optical potential wall. When these disturbing waves have a small amplitude, an autocorrective procedure enables one to accurately determine the resonance energy if one only knows two approximate values of it deduced from a finite representation and the corresponding complex incoming and outgoing wave amplitudes.     

Diagrammatic expansion of the long-range intermolecular potential and the total contribution of the first hyperpolarizability

The potential for pure dispersion forces can be defined in terms of a simple classical cluster expansion. The diagrams for the first hyperpolarizability contribution are summed for a one frequency model.     

Solvent effect in the reaction of n-sulphonilsulphilimines with benzenethiol

Rate coefficients for the reactions of S,S-dimethyl-, S-methyl-S-phenyl- and S,S-diphenyl-N-tosylsulphilimine with benzenethiol in various alcohols have been determined at different temperatures. Multiparametric equations, involving specific and non-specific solute-solvent interactions, have been used to interpret quantitatively the data. The results on the solvent effect and the activation parameters indicate that the reactions proceed through the rate-determining formation of a thiol-sulphilimine adduct which occurs most likely through a cyclic transition state involving one molecule of thiol, one of sulphilimine, and one of alcohol.