Effect of matrix crystal structure on ion abundance of carbohydrates by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry

Sample preparation techniques for carbohydrate analysis using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) are explored, with particular emphasis on analyte/matrix co-crystallization procedures. While carbohydrates are known to prefer 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix of choice, these analytes are quite specific about matrix crystal structure, which in turn is dependent on the rate of drying of analyte/matrix spots on the MALDI target. With N-acetylglucosamine (GlcNAc) and N-acetylneuraminic acid (sialic acid or NeuAc) as test monosaccharides, significant increases in ion abundances are demonstrated with 2,5-DHB/NeuAc spots (>10-fold improvement) and 2,5-DHB/GlcNAc spots ( approximately 5-fold improvement) with active drying. The fine structure of crystals generated in active and passive drying was investigated using powder diffraction. Passively dried samples were shown to consist of an ordered polymorph, crystallizing in the space group P2(1)/a, while the actively dried samples produced a disordered phase crystallizing in the space group Pa. These data provide the wherewithal to engineer a matrix best suited for carbohydrate analyses.     

Krametosan, a new trinorlignan from the roots of Krameria tomentosa

A new phenylcoumarone type trinorlignan, krametosan (1), along with the known norlignans, ratanhiaphenol I (2) and 2-(2'-hydroxy-4',6'-dimethoxyphenyl)-5-(E)-propenylbenzofuran (3), the lignan conocarpan (4) and dinorlignan decurrenal (5), were isolated from the CHCl3 extract of the roots of Krameria tomentosa. The structure of these compounds were elucidated by the spectroscopic methods.     

Total synthesis of a 28-member stereoisomer library of murisolins

Total syntheses of two 16-member libraries of murisolin isomers are reported. In the first library, fluorous PMB (p-methoxybenzyl) groups encode configurations, and four mixtures of four dihydroxy-tetrahydrofurans are prepared by Shi epoxidation followed (optionally) by Mitsunobu reaction. The mixtures are coupled by Kocienski-Julia reaction with a single hydroxybutenolide followed by hydrogenation. Demixing and detagging provide the 16 pure stereoisomers. In the second synthesis, a single mixture of four fluorous-tagged dihydroxy-tetrahydrofurans is coupled with a four-compound mixture of hydroxybutenolides that bear derivatives of DMB (dimethoxybenzyl) groups with oligoethylene glycol (OEG) units that encode the configurations at C4 and C34. The 16-compound mixture is subjected to hydrogenation, double demixing, and detagging to provide the 16 isomerically pure murisolins. Twelve of these isomers are new, while four match samples from the first library.     

Intramolecularly sensitized precipitons: a model system for application to metal sequestration

We have investigated light-triggered or catalytically activated precipitation agents and have proposed the name "precipiton" for such molecules or molecular fragments. A phase separation is induced when the precipiton isomerizes to a low-solubility form. In this paper we describe the first intramolecularly activated precipitons. The isomerization process is induced by intramolecular triplet energy transfer from a covalently attached metal complex. As expected, intramolecular sensitization leads to a more rapid isomerization than can be achieved by intermolecular sensitization at accessible concentrations. Two isomeric bichromophoric precipiton species, each containing [Ru(bpy)(3)](2+) and 1,2-bis(biphenyl)ethene units covalently linked together by an ether tether, have been synthesized and characterized, and their photochemical properties have been investigated. The rates of photoisomerization of these complexes, [((Z)-1,2-bis(biphenyl)ethene-bpy)Ru(bpy)(2)](PF(6))(2) (2Z) and [((E)-1,2-bis(biphenyl)ethene-bpy)Ru(bpy)(2)](PF(6))(2) (2E), were compared to those of their untethered analogues, (Z)-1,2-bis(biphenyl)ethene-OTBS (1Z) and (E)-1,2-bis(biphenyl)ethene-OTBS (1E), where ruthenium sensitization occurred through an intermolecular pathway. Upon irradiation with visible light (lambda > or = 400 nm) in degassed solution, 2Z/E and 1Z/E obeyed reversible first-order rate kinetics. The intramolecularly sensitized precipiton 2Z isomerized 250 times faster (k(2Z-->2E) = 1.0 x 10(-3) s(-1) with a 51% neutral density filter) than the intermolecular case 1Z (k(1Z-->1E) = 0.80 x 10(-5) s(-1)). For 1E and 2E, the isomerization rates were k(1E-->1Z) = 11.0 x 10(-5) s(-1) and k(2E-->2Z) = 1.6 x 10(-3) s(-1), respectively. The average Z/E mole ratio at the photostationary state was 62/38 for 2Z/E and 93/7 for 1Z/E. The impetus for this study was our desire to evaluate the possibility of using metal-binding precipitons that would precipitate only upon metal-to-precipiton binding and would be inert to visible light in the absence of metals.     

ON THE IMPULSIVE BEVERTON–HOLT EQUATION AND EXTINCTION CONDITIONS IN POPULATION DYNAMICS

Abstract This paper is devoted to investigate extinction and nonextinction conditions of the extended Beverton–Holt equation (BHE) for dynamics of populations in Ecology when potential discontinuities at sampling points are included in the model. The proposed model is described by means of four sequences of parameters. Two of them are the intrinsic growth rate and the carrying capacity sequences which are included in the basic BHE model. The other two ones, namely, the harvesting (i.e., the hunting or fishing quota) and the internal consumption (which can include positive and negative migrations in the considered population habitat) sequences are included to parameterize the model discontinuities. Such discontinuities are related to impulses in the corresponding continuous‐time logistic equation. The obtained results establish how the harvesting quota and/or the internal consumption has to be fixed to guarantee the population nonextinction or, eventually, its extinction. Finally, some controllability results related to the search of a carrying capacity sequence such that the solution of the proposed impulsive BHE tracks a reference one are obtained.     

AN APPROXIMATE PROJECTION SCHEME FOR INCOMPRESSIBLE FLOW USING SPECTRAL ELEMENTS

An approximate projection scheme based on the pressure correction method is proposed to solve the Navier–Stokes equations for incompressible flow. The algorithm is applied to the continuous equations; however, there are no problems concerning the choice of boundary conditions of the pressure step. The resulting velocity and pressure are consistent with the original system. For the spatial discretization a high-order spectral element method is chosen. The high-order accuracy allows the use of a diagonal mass matrix, resulting in a very efficient algorithm. The properties of the scheme are extensively tested by means of an analytical test example. The scheme is further validated by simulating the laminar flow over a backward-facing step.     

Relation between interface states and temperature behavior of the barrier height of silver contacts on clean cleaved n-type silicon

The properties of silver-silicon interfaces formed by cleaving n-type silicon in ultra high vacuum (UHV) in a stream of evaporating silver atoms were studied. The barrier heights of these contacts were measured at different temperatures by using C-V techniques. All measurements were performed in UHV. The dependence of the barrier height upon temperature did not follow the temperature dependence of the Si band gap as it is usually found. The measured temperature behavior depended on the roughness of the Si surface. The temperature behavior can be explained by assuming a specific band structure of the interface states. For Ag contacts on atomically smooth n-type Si, the interface states were found to be arranged in two bands, one band 4 × 10^?3 eV wide with acceptor type states 0.18 eV below the intrinsic level E_i and a density of 10¹⁷ states/cm² eV, and the other 1 eV wide with donor type states with its upper edge 0.28 eV below E_i, and a density of 4 × 10¹⁴ states/cm²eV.     

广义BBM方程有理Chebyshev谱逼近的大时间性态

本文考虑广义BBM方程的初值问题,建立了方程的有理Chebyshev谱格式,给出了谱格式的误差估计,并证明了原问题和近似问题所生成的算子半群分别具有整体吸引子A和AN,且AN关于A 是上半连续的．     

ABSOLUTELY UNSTABLE WAVES IN INVISCID HYDROELASTIC SYSTEMS

The effect of inviscid plug flow on the stability of several hydroelastic systems is investigated by determining the absolute or convective nature of the instability from the linear dispersion relation. The fluid-structure systems consist of plates and membranes with bounded and unbounded flow. A method is proposed to derive systematically in parameter space the boundary between convective and absolute instability, based on the particular symmetries of the dispersion relation as originally noted by Crighton and Oswell. This method is then applied to the case of plates with superimposed tension, thick plates with rotary inertia and walls made of plates or membranes bounding channel flow, oscillating in a sinuous or varicose mode of deformation. A relation is drawn with solutions by previous authors for plates, for pipes and for the Kelvin-Helmholtz instability with surface tension. To illustrate these results some temporal evolutions are calculated by using an integration in the wavenumber space. Based on the large set of new cases solved in the paper some general trends are discussed as to the influence of flow velocity, confinement and structural stiffness on the existence of absolutely unstable waves in inviscid hydroelastic systems.     

香菇多糖L-2A的结构表征

从香菇子实体中提取纯化得到香菇多糖级分L-2A,利用紫外光谱、红外光谱、凝胶渗透色谱和气相色谱分析其结构特征.香菇多糖L-2A糖含量为90.14%;重均分子量是2.03×10 5道尔顿;具有D-葡萄吡喃糖构型,单糖组成主要是由吡喃型葡萄糖组成;香菇多糖L-2A多糖含有o-糖苷键,且主要是o-Ser连接方式;具有与刚果红结合的螺旋结构.香菇多糖L-2A为首次从香菇子实体中分离得到.