Prediction of the effects of imperfect construction of a QMS filter

Modelling techniques have previously predicted the observed behaviour of perfectly manufactured QMS mass filters. These methods are extended to examination of the behaviour of imperfect QMS filters; this examination considers the behaviour of QMS filters with one rod displaced radially inward as this is a simple manufacturing defect that arises when a rod does not fit correctly into the mounting.The results demonstrate the well known, but poorly documented property, that exchanging the connections of a poorly performing QMS device sometimes improves performance. This is shown to arise because only a displacement of a y-rod produces a large effect. The results also show that displacement of a y-rod may produce a spurious additional peak known as a precursor. More detailed investigation suggests that precursors are not separate peaks but are formed because a section of the main peak is removed causing an apparent double peak.Finally results confirm that adjustment of the voltage applied to a displaced rod can be used to significantly improve the QMS behaviour. A small change by a fraction alpha in the position of a single rod may be compensated by a change of 2 x alpha in the voltage applied to that rod.     

Roseophilin的合成研究进展

Roseophilin是一种从灰绿链霉菌中分离出来的、由一个十三元大环并一个杂环组成的具有抗肿瘤活性的新型抗生素的活性物质。Roseophilin独特的结构及活性引起了很多学者对其合成的兴趣。通过十三元大环和杂环合成Roseophilin,其中十三元大环的主要合成方法有末端双键的RCM关环、扩环、烷基化关环三种反应类型。     

Reprint of: Synthesis of a tricyclic core of rameswaralide

A tricyclic core containing a 5,7-fused bicyclic unit of rameswaralide was prepared starting from a 1,6-enyne. The synthetic sequence involved (i) ruthenium-catalyzed [5+2]-cycloaddition of 1,6-enyne, (ii) an acyl radical based approach to construct the lactone, and (iii) a regioselective installation of the conjugated double bond by a concomitant sulfenylation-dehydrosulfenylation sequence.     

Synthesis of the glycosyl lactol moiety of halichoblelide

The enantioselective synthesis of the 2-deoxy-α-l-fucosyl lactol moiety of halichoblelide, a potent cytotoxin isolated from an actinomycete of marine origin, was achieved using a diastereoselective addition of a dithianyl anion to a chiral aldehyde intermediate and a stereoselective glycosidation of a hydroxy lactone intermediate derived from the addition product with a protected l-fucal as the key steps.     

The mechanism of reequilibration of solids in the presence of a fluid phase

The preservation of morphology (pseudomorphism) and crystal structure during the transformation of one solid phase to another is regularly used as a criterion for a solid-state mechanism, even when there is a fluid phase present. However, a coupled dissolution-reprecipitation mechanism also preserves the morphology and transfers crystallographic information from parent to product by epitaxial nucleation. The generation of porosity in the product phase is a necessary condition for such a mechanism as it allows fluid to maintain contact with a reaction interface which moves through the parent phase from the original surface. We propose that interface-coupled dissolution-reprecipitation is a general mechanism for reequilibration of solids in the presence of a fluid phase.     

The evolution of nonequilibrium laser plasma of metals with the formation of structures

Processes in a plasma formed by the evaporation of material by middle power laser radiation on a metallic surface are analyzed. In the regime considered the laser radiation is not absorbed by a metallic plasma and the radiation energy is spent in the main for the atomic evaporation. As a result of the plasma relaxation, hard metallic particles of sizes of the order of 10 nm are formed. They are joined in fractal aggregates of micron sizes, and fractal aggregates may be joined in aerogel-like structures of centimeters sizes. Such a laserplasma is an example of a plasma whose evolution leads to fractal object formation. A fireball is considered as a fractal object formed as a result of the evolution of an evaporated plasma. The considered object with aerogel-like structure that is formed in a gas has both scientific and practical interest.     

Fine Structure of Meniscus of a Wetting Liquid

Equilibrium of a capillary meniscus near a wetting film on a solid in a gravitational field is considered. Unlike previous studies, the present study proves that the fine meniscus structure in a gravitational field is a universal feature—it takes place in a wide variety of problems. In the general case, the capillary meniscus is at a certain distance from the wetting film and does not intersect it. The relation for the minimum distance from the arbitrary meniscus to the solid generalizes the Derjaguin formula for a flat slit. An equation that optimally approximates the meniscus with due account of the contribution of the meniscus/film transition region is derived. A refined solution to the problem of a meniscus on a vertical plate is derived within the perturbation theory. Both gravity and nonuniformity of the vertical static film above a capillary–gravitational meniscus do not affect the minimum distance (the influence is less than 0.0001). A general method for solving sophisticated problems of capillary equilibrium in gravitational field is proposed.     

Unprecedented Halogenation of Biginelli Compounds of Salicyldehyde

Unprecedented results are obtained from bromination of the normal/non-bridged and abnormal/bridged Biginelli compound of salicyldehyde. Bromination with 2,4,4,6-tetrabromocyclohexa-2,5-dienone yields a bridged monobromo-derivative and a bridged dibromo-derivative, respectively, whereas bromination with bromine and acetic acid gives a mixture of those two products in each case. Bromination with N-bromosuccinimide gives a third product, namely a tribromo-derivative, in addition to those two products. Iodination of both the substrates using iodine monochloride (Wijs solution) furnishes a bridged monoiodo-derivative only.     

Determination of the Crystal Structure of a New Polymorph of Theophylline

A new approach to crystal structure determination, combining crystal structure prediction and transmission electron microscopy, was used to identify a potential new crystal phase of the pharmaceutical compound theophylline. The crystal structure was determined despite the new polymorph occurring as a minor component in a mixture with Form II of theophylline, at a concentration below the limits of detection of analytical methods routinely used for pharmaceutical characterisation. Detection and characterisation of crystallites of this new form were achieved with transmission electron microscopy, exploiting the combination of high magnification imaging and electron diffraction measurements. A plausible crystal structure was identified by indexing experimental electron‐diffraction patterns from a single crystallite of the new polymorph against a reference set of putative crystal structures of theophylline generated by global lattice energy minimisation calculations.     

An expedient synthesis of the repeating unit of the acidic polysaccharide of the bacteriolytic complex of lysoamidase

The first synthesis of the trisaccharide repeating unit of the acidic polysaccharide of the bacteriolytic complex of lysoamidase is presented. The construction is based on a linear glycosylation strategy that starts from the reducing end and employs thio- and selenoglycosides in a highly stereoselective manner by a single set of activation conditions. The thus-formed trisaccharide is selectively deprotected and oxidised, after which a final deprotection step furnishes the desired repeating unit.     

Effect of cathodic polarization of a steel membrane and the acidity of alcohol solutions of hydrochloric acid on the balance between rates of the reaction of evolution of hydrogen and its solid-phase diffusion

The effect of cathodic polarization of the entrance side of a steel membrane and the concentration of hydrochloric acid (0.99–0.01 M) on the balance between rates of the reaction of evolution of hydrogen and its diffusion through steel (ρ) is studied in hydrochloric-acid solutions of ethanol and ethylene glycol with a constant ionic strength equal to unity. It is demonstrated that ρ lowers down with a shift of the potential of the polarization side of the membrane in the negative direction and increases with diminishing concentration of hydrochloric acid. The results are interpreted with allowance made for the surface coverage by two forms of adsorbed hydrogen, namely, a raised form and a subsurface form.     

Diagram of State of Stiff Amphiphilic Macromolecules

Summary: We studied coil-globule transitions in stiff-chain amphiphilic macromolecules via computer modeling and constructed phase diagrams for such molecules in terms of solvent quality and persistence length. We showed that the shape of the phase diagram essentially depends on the macromolecule degree of polymerization. Relatively short amphiphilic molecules always form a spherical globule in a poor solvent, and the coil-globule transition includes one or two intermediate conformations, depending on the chain's stiffness. These are a disk-like globule in case of high enough Kuhn segment length, and a pearl necklace-like structure of spherical micelles and a disk-like globule in case of relatively flexible chains. The phase diagram of a long stiff amphiphilic chain was found to be more complex still. Thus three specific regions can be distinguished in the poor solvent region, depending on the chain stiffness. These correspond to a cylindrical globule without any specific backbone ordering, a cylindrical globule containing blobs with collagen-like ordering of the chain, and co-existence of collagen-like and toroidal globules. In the intermediate transition region in this case, apart from the pearl necklace-like conformations with spherical micelles, necklace conformations can be also observed where the polymeric chain has collagen-like ordering within each bead.     

Nonlinear Unmixing of Hyperspectral Datasets for the Study of Painted Works of Art

Nonlinear unmixing of hyperspectral reflectance data is one of the key problems in quantitative imaging of painted works of art. The approach presented is to interrogate a hyperspectral image cube by first decomposing it into a set of reflectance curves representing pure basis pigments and second to estimate the scattering and absorption coefficients of each pigment in a given pixel to produce estimates of the component fractions. This two‐step algorithm uses a deep neural network to qualitatively identify the constituent pigments in any unknown spectrum and, based on the pigment(s) present and Kubelka–Munk theory to estimate the pigment concentration on a per‐pixel basis. Using hyperspectral data acquired on a set of mock‐up paintings and a well‐characterized illuminated folio from the 15th century, the performance of the proposed algorithm is demonstrated for pigment recognition and quantitative estimation of concentration.     

Determination of the heats of gasification of polymers using differential scanning calorimetry

The amount of heat that is required to gasify unit mass of material is one of the key properties that define its ignition resistance and fire response. Knowledge of this property is necessary to assess a material's fire hazard in a particular fire scenario. Nevertheless, even for the most common polymers the values of this property are not well established. Here we present a method for determining the heat of gasification using differential scanning calorimetry and apply this method to a set of ten common plastics and engineering polymers.     

New Algorithm of Spectral Analysis of Elements in Presence of Matrix Interferences

Abstract

This work suggests a new algorithm for the elemental analysis, which permits taking into account both the multiplicative and additive matrix effects, a matrix composition being unknown. The use of this algorithm in the development of analysis techniques at any set of objects may appear to be successful at arbitrarily selected measurement conditions. The basis of the algorithm consists of a combination of pattern recognition and standard addition technique (PRSA). The main concept of PRSA is to predict a function approximating satisfactorily a calibration dependence for a specific object and then to determine an unknown concentration using a nonlinear addition technique, all the aforementioned being based on easily obtained information on an analyzed object and measurement conditions. The abilities of the proposed algorithm were demonstrated by the example of strontium determination by the flame atomic absorption spectrometry in superconducting systems.     

Group of symmetry of the periodic system of chemical elements

The concurrence of the group of symmetry of the periodic system of elements with the group of dynamical symmetry of a hydrogenlike atom is employed in the theoretical investigation of atoms. The character of the degeneracy of the eigenvalues of a hydrogenlike atom Hamiltonian, without changing its eigenfunctions, was changed by introducing into this Hamiltonian a term which violates the symmetry in relation to transformations from the subgroup O(4) of the group SO(4, 2). In consequence, it was realized that such “reorganization” of the states of a hydrogenlike atom, which form a representation of the group SO(4, 2), effects the splitting of this representation into finite‐dimensional multiplets, first of which are in full agreement with the experimentally observable composition of electron shells of atoms, and retains the physical meaning of quantum numbers that define electron states. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 499–508, 1999     

多肽树枝状大分子合成的研究进展

多肽树枝状大分子具有不同于链状多肽和其它树枝状大分子的物理化学性质,在化学、生物、医学等领域中有广泛应用。本文综述了近年来所报道的多肽树枝状大分子的合成进展。     

The study of properties of HPLC determination of polycyclic aromatic nitrogen heterocycles

The study of the separation of polycyclic aromatic nitrogen heterocycles (PANHs) by reverse-phase liquid chromatography with an octadecyl stationary phase is presented. The retention behaviour of a mixture of PANHs was studied under different chromatographic conditions. A mixture of phosphate buffer/acetonitrile was used as mobile phase in isocratic and gradient modes. The effect of different pH mobile phase in the range from 2.5 to 6.5 has been investigated to describe retention changes of PANHs as a function of their acid/base properties. Different concentrations of phosphate buffer as a component of the mobile phase were used to study the effect of ionic strength. Very good RP-HPLC separation of 24 PANHs and 16 EPA polycyclic aromatic hydrocarbons (PAHs) was obtained without a pre-separation step in a test mixture and the extract of a real soil sample. Limits of detection of PANHs obtained by two detection techniques, ultraviolet-diode array detection (UV-DAD) and fluorescence detector (FD), are compared. The proposed method is tested with a real soil sample.     

Sugar-assisted kinetic resolution of amino acids and amplification of enantiomeric excess of organic molecules

The origins of biological homochirality have intrigued researchers since Pasteur's discovery of the optical activity of biomolecules. Herein, we propose and demonstrate a novel alternative for the evolution of homochirality that is not based on autocatalysis and forges a direct relationship between the chirality of sugars and amino acids. This process provides a mechanism in which a racemic mixture of an amino acid can catalyze the formation of an optically active organic molecule in the presence of a sugar product of low enantiomeric excess.