耦合反应扩散体系中分布式延迟对图灵斑图的影响

在许多信息传递系统中都存在延迟现象,相关研究表明,耦合振子系统中的延迟作用能导致振死、多节律混沌、空间斑图和波等现象,其中多数现象已经得到的实验验证．图灵斑图与生物成型素具有潜在的联系,使其在理论和实验方面得到了多方面的研究．Barrio等发现图灵体系间的耦合作用可以得到与生物界相似的复杂斑图．Yang等也在耦合体系中发现了一系列新型图灵斑图．     

Spontaneous Formation of Microgroove Arrays on the Surface of p‐Type Porous Silicon Induced by a Turing Instability in Electrochemical Dissolution

Self‐organization plays an imperative role in recent materials science. Highly tunable, periodic structures based on dynamic self‐organization at micrometer scales have proven difficult to design, but are desired for the further development of micropatterning. In the present study, we report a microgroove array that spontaneously forms on a p‐type silicon surface during its electrodissolution. Our detailed experimental results suggest that the instability can be classified as Turing instability. The characteristic scale of the Turing‐type pattern is small compared to self‐organized patterns caused by the Turing instabilities reported so far. The mechanism for the miniaturization of self‐organized patterns is strongly related to the semiconducting property of silicon electrodes as well as the dynamics of their surface chemistry.     

The chemistry of phase selectivity in the synthesis of high-silica zeolites

In this review we discuss the roles that inorganic and organic components play in the synthesis of high-silica zeolites. We discuss the effects that heteroatom identity, heteroatom substitution, and SDA shape have on synthesis products. Then we summarize recent developments in zeolite synthesis that have been made by performing syntheses in concentrated fluoride media and by using germanium as a tetravalent heteroatom. Finally, we examine the combined roles that framework stability, framework/SDA interactions, and silanol defects may have in determining phase selectivity.     

Localized electric field induced transition and miniaturization of two‐phase flow patterns inside microchannels

Strategic application of external electrostatic field on a pressure‐driven two‐phase flow inside a microchannel can transform the stratified or slug flow patterns into droplets. The localized electrohydrodynamic stress at the interface of the immiscible liquids can engender a liquid‐dielectrophoretic deformation, which disrupts the balance of the viscous, capillary, and inertial forces of a pressure‐driven flow to engender such flow morphologies. Interestingly, the size, shape, and frequency of the droplets can be tuned by varying the field intensity, location of the electric field, surface properties of the channel or fluids, viscosity ratio of the fluids, and the flow ratio of the phases. Higher field intensity with lower interfacial tension is found to facilitate the oil droplet formation with a higher throughput inside the hydrophilic microchannels. The method is successful in breaking down the regular pressure‐driven flow patterns even when the fluid inlets are exchanged in the microchannel. The simulations identify the conditions to develop interesting flow morphologies, such as (i) an array of miniaturized spherical or hemispherical or elongated oil drops in continuous water phase, (ii) “oil‐in‐water” microemulsion with varying size and shape of oil droplets. The results reported can be of significance in improving the efficiency of multiphase microreactors where the flow patterns composed of droplets are preferred because of the availability of higher interfacial area for reactions or heat and mass exchange.     

Platinum Metallacycle-Based Molecular Recognition: Establishment and Application in Spontaneous Formation of a [2]Rotaxane with Light-Harvesting Property

Macrocyclic molecule-based host–guest systems, which provide contributions for the design and construction of functional supramolecular structures, have gained increasing attention in recent years. In particular, platinum(II) metallacycle-based host–guest systems provide opportunities for chemical scientists to prepare novel materials with various functions and structures due to the well-defined shapes and cavity sizes of platinum(II) metallacycles. However, the research on platinum(II) metallacycle-based host–guest systems has been given little attention. In this article, we demonstrate the host–guest complexation between a platinum(II) metallacycle and a polycyclic aromatic hydrocarbon molecule, naphthalene. Taking advantage of metallacycle-based host–guest interactions and the dynamic property of reversible Pt coordination bonds, a [2]rotaxane is efficiently prepared by employing a template-directed clipping procedure. The [2]rotaxane is further applied to the fabrication of an efficient light-harvesting system with multi-step energy transfer process. This work comprises an important supplement to macrocycle-based host–guest systems and demonstrates a strategy for efficient production of well-defined mechanically interlocked molecules with practical values.     

Formation of periodic zigzag patterns in the twist-bend nematic liquid crystal phase by surface treatment

ABSTRACT

Zigzag patterns were successfully generated in the twist-bend nematic (N_TB) phase of 1-(4-cyanobiphenyl-4′-yl)-6-(4-cyanobiphenyl-4′-yloxy)hexane (CB6OCB) via simple surface treatment. A detailed microscopy study using polarised optical microscopy and fluorescence confocal polarising microscopy was performed to observe the director arrangement in the zigzags, where distinctive periodic patterns were found to be aligned perpendicular to the rubbing direction. These patterns originate from the structural instability and generation of splay deformation with focal conic domain-like structures that are typically found in smectic phases, revealing that the N_TB phase has physical properties similar to those of the smectic phase. Observation of these unusual zigzag patterns in the N_TB phase opens an avenue for use of this phase in potential applications such as optical modulators and gratings.     

Synthesis of orthogonally protected optically pure ketopiperazine, diketopiperazine, ketodiazepane, and 3-aminopyrrolidone building blocks for peptidomimetic combinatorial chemistry

A simple and convenient synthesis of orthogonally protected multi-tethered, optically pure 2-ketopiperazine, diketopiperazine, 2-ketodiazepane and 3-aminopyrrolidone scaffolds for Fmoc combinatorial chemistry has been developed. It utilizes accessible chiral amino acid precursors, sequentially applying reductive alkylation, dipeptide coupling and regioselective ring formation as key steps. These scaffolds are expansion of our ‘pool of privileged building blocks’ and can introduce valuable drug-like properties in three independent directions to any medicinally relevant piperazine-, diazepane- and pyrrolidone-based motif by ‘around-the-scaffold’ drug optimization. The synthetic routes reported in this work are general and applicable for the preparation of a diverse library of scaffolds, controlling chirality, arm position and length as well as the nature of functional moieties at the arms for further diversification in three independent directions. In addition, these building blocks have a wide application scope in managing fast and efficient multi-cyclic optimization processes in the combinatorial chemistry and drug design fields.     

Stereospecific control of peptide gas‐phase ion chemistry with cis and trans cyclo ornithine residues

We report non‐chiral amino acid residues cis‐ and trans‐1,4‐diaminocyclohexane‐1‐carboxylic acid (cyclo‐ornithine, cO) that exhibit unprecedented stereospecific control of backbone dissociations of singly charged peptide cations and hydrogen‐rich cation radicals produced by electron‐transfer dissociation. Upon collision‐induced dissociation (CID) in the slow heating regime, peptide cations containing trans‐cO residues undergo facile backbone cleavages of amide bonds C‐terminal to trans‐cO. By contrast, peptides with cis‐cO residues undergo dissociations at several amide bonds along the peptide ion backbone. Diastereoisomeric cO‐containing peptides thus provide remarkably distinct tandem mass spectra. The stereospecific effect in CID of the trans‐cO residue is explained by syn‐facially directed proton transfer from the 4‐ammonium group at cO to the C‐terminal amide followed by neighboring group participation in the cleavage of the CO―NH bond, analogous to the aspartic acid and ornithine effects. Backbone dissociations of diastereoisomeric cO‐containing peptide ions generate distinct [b_n]⁺‐type fragment ions that were characterized by CID‐MS³ spectra. Stereospecific control is also reported for electron‐transfer dissociation of cis‐ and trans‐cO containing doubly charged peptide ions. The stereospecific effect upon electron transfer is related to the different conformations of doubly charged peptide ions that affect the electron attachment sites and ensuing N―C_α bond dissociations.     

A comparative study of particle swarm optimization and its variants for phase stability and equilibrium calculations in multicomponent reactive and non-reactive systems

Particle swarm optimization is a novel evolutionary stochastic global optimization method that has gained popularity in the chemical engineering community. This optimization strategy has been successfully used for several applications including thermodynamic calculations. To the best of our knowledge, the performance of PSO in phase stability and equilibrium calculations for both multicomponent reactive and non-reactive mixtures has not yet been reported. This study introduces the application of particle swarm optimization and several of its variants for solving phase stability and equilibrium problems in multicomponent systems with or without chemical equilibrium. The reliability and efficiency of a number of particle swarm optimization algorithms are tested and compared using multicomponent systems with vapor–liquid and liquid–liquid equilibrium. Our results indicate that the classical particle swarm optimization with constant cognitive and social parameters is a reliable method and offers the best performance for global minimization of the tangent plane distance function and the Gibbs energy function in both reactive and non-reactive systems.     

Phase equilibria and crystal chemistry of the R-Cu-Ti-O systems (R=lanthanides and Y)

As part of the study of interaction of the Ba₂RCu₃O_6+z (R=lanthanides and Y) superconductor with SrTiO₃ buffer, phase equilibria of the subsystem, R₂O₃-TiO₂-CuO (R=Nd, Y, and Yb), have been investigated in air at 960 °C. While the phase relationships of the two phase diagrams with smaller R (Y and Yb) are similar, substantial differences were found in the Nd₂O₃-TiO₂-CuO system, partly due to different phase formation in the binary R₂O₃-TiO₂ and R₂O₃-CuO systems. R₂CuTiO₆ and R₂Cu₉Ti₁₂O₃₆ were the only ternary phases established in all the three diagrams. R₂Cu₉Ti₁₂O₃₆ belongs to the perovskite-related [AC₃](B₄)O₁₂ family which is cubic Im3. Depending on the size of R³⁺, R₂CuTiO₆ crystallizes in two crystal systems: Pnma (R=La-Gd), and P6₃cm (R=Dy-Lu). The structure and crystal chemistry of the Pnma series of R₂CuTiO₆ (R=La, Nd, Sm, Eu, and Gd) are discussed in detail in this paper. Patterns for selected members of R₂CuTiO₆ have also been prepared and submitted for inclusion in the Powder Diffraction File (PDF).     

The effect of NaCl and Na2SO4 concentration in aqueous phase on the phase inversion temperature O/W nanoemulsions

The effect of NaCl and Na₂SO₄ concentrations in aqueous phase on the phase inversion temperature (PIT) in nanoemulsions of water/Brij30/n-hexadecane system has been studied separately, and then compared. The variation of conductivity with temperature was measured by Cyber Scan PC510 conductivity meter for emulsions with 20 wt% hexadecane and 8 wt% Brij30 concentration and different concentrations of NaCl and Na₂SO₄ in aqueous phase. The results showed that with increasing concentrations of NaCl and Na₂SO₄ in aqueous phase, the PIT of nanoemulsions decreases. The effect of the elevation of concentration on the decrease of PIT was more for Na₂SO₄ in aqueous phase than NaCl with equal concentrations.     

Identification of the phase of a fluid using partial derivatives of pressure, volume, and temperature without reference to saturation properties: Applications in phase equilibria calculations

The phase of a fluid (liquid, vapor) at a given state is normally identified by comparing the properties of the fluid at the given state with saturation properties. In this paper we present a thermodynamic method for determining the phase of a fluid from the partial derivatives of pressure, volume and temperature without reference to saturated properties. The method has immediate application in a variety of phase equilibria calculations, particularly for liquid-liquid or vapor-liquid-liquid equilibria calculations in process simulators.     

阳离子表面活性剂中相微乳的形成和特性

自1943年SdriAn。等人山发现微乳液体系并予以命名以来，对微乳液研究不断深入·微乳液是由油、水、表面活性剂和助表面活性剂组成的各向同性、透明的、热力学稳定的分散体系，微乳液可分为单相微乳液和多相微乳液问．中相微乳液是多相微乳液中，与过剩盐水相和过剩油相达到三相平衡的Winsor皿型微乳液，它在三次采油、日用化工、微环境、酶催化等方面具有特殊重要的应用I‘，‘］．近年来对阴离子表面活性剂中相微乳液的形成和特性进行了较多研究［5。8］．但对阳离子表面活性剂中相微乳液的研究，目前尚未见报导，本文以澳代十四烷基毗…     

Structural phase transitions and crystal chemistry of the series Ba2LnB′O6 (Ln=lanthanide and B′=Nb or Sb)

The structures of 28 compounds in the two series Ba₂LnSbO₆ and Ba₂LnNbO₆ have been examined using synchrotron X-ray and in selected cases neutron powder diffraction at, below and above ambient temperature. The antimonate series is found to undergo a sequence of phase transitions from monoclinic to rhombohedral to cubic symmetry with both decreasing ionic radii of the lanthanides and increasing temperature. Compounds in the series Ba₂LnNbO₆, on the other hand, feature an intermediate tetragonal structure instead of the rhombohedral structure exhibited by the antimonates. This difference in symmetry is thought to be caused by π-bonding in the niobates that is absent in the antimonates. The bonding environments of the cations in these compounds have also been examined with overbonding of the lanthanide and niobium cations being caused by the unusually large B-site cations.     

Multiisotopic modeling of fragmentation ion patterns in mass spectra of organometallic and coordination compounds

Investigation of hardly interpretable complex patterns can lead to an explanation of details of fragmentation and, therefore, the identification of ion clusters can be a significant procedure of mass spectra interpretation. The modeling presented remains a simple tool for mass spectra interpretation and determination of parameters of complex cluster components. Good adjustment of model to experimental data suggests that such components must be considered in the pattern interpretation; approach results in the model fits within a 1% precision for the cluster of two or more components. Applications of the Multiisotopic Modeling of Fragmentation Ion Patterns (MMFIP method) are presented for bis(dibutyldithiophosphate)‐zinc(II)‐[(C₄H₉O)₂PS₂]₂Zn, 1′,1‴‐dibenzylbiferrocene‐C₃₄H₃₀Fe₂ and 1,1′,2,2′,3,3′‐hexachloroferrocene‐C₁₀H₄Cl₆Fe as examples. It seems that the isotopic cluster modeling based on the least squares method can be a helpful aid for determination of the complex pattern components. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 354–365, 2001     

The first open-paddlewheel structures in diruthenium chemistry: examples of intermediate magnetic behaviour between low and high spin in Ru2(5+) species

The reaction of [Ru(2)Cl(O(2)CMe)(DPhF)(3)] (DPhF=N,N'-diphenylformamidinate) with aqueous HCl leads to the substitution of the acetate ligand to give the complex [Ru(2)Cl(2)(DPhF)(3)] (1). Similar reaction of [Ru(2)(O(2)CMe)(DPhF)(3)(H(2)O)]BF(4) with aqueous HBr or HI produces [Ru(2)Br(2)(DPhF)(3)] (2), and [Ru(2)I(2)(DPhF)(3)] (3), respectively. The reaction of 1 with AgBF(4) to form the highly unsaturated unit [Ru(2)(DPhF)(3)](2+), which is isolated as [Ru(2)(BF(4))(DPhF)(3)(H(2)O)]BF(4) (4), and [Ru(2)(MeCN)(2)(DPhF)(3)](BF(4))(2) (5), is also reported. The use of AgNO(3) instead of AgBF(4) leads to [Ru(2)(NO(3))(2)(DPhF)(3)] (6). The magnetic behaviour of complexes 1-4 and 6 is intermediate between high- and low-spin configurations. A relationship between the magnetic behaviour and the visible-near-infrared (Vis-NIR) spectra is apparent. In addition, the crystal structure determinations of 2, 4.THF, and 6, have been carried out. Complexes 1-3, 5 and 6 are the first examples of open-paddlewheel structures in diruthenium chemistry. The BF(4) (-) bridging the metal centres in 4THF is activated and forms very short Ru-F bonds.     

Different properties of exciplexes and excited states of CT complexes in the solid phase

The fluorescence, excitation and absorption spectra and fluorescence decay kinetics of charge-transfer (CT) complexes and exciplexes ofheteroaromatic cations and some other electron acceptors were investigated in ethanol at 77 K. Experimental data indicate that the fluorescence state of the exciplex may differ from that of the CT complex.     

The chemistry of the phosphates of barium and tetravalent cations in the 1:1 stoichiometry

The chemistry of phosphates of barium and tetravalent cations [BaM^IV(PO₄)₂] is reviewed. Such phosphates crystallise in the C2/m space group for M^IV=Ti, Zr, Hf, Ge, Sn, and Mo, and in the P2₁/n space group for BaTh(PO₄)₂. The existence of BaM^IV(PO₄)₂ in which M^IV=Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaM^IV(PO₄)₂ compounds and practical applications are briefly discussed.