Meso Structure Research Articles

ChemInform Abstract: An Enantiodivergent Route to α-Cuparenone Utilizing Chiral Cyclopentenol Having a Latent meso Structure.

Abstract An efficient enantiodivergent route to α-cuparenone, a sesquiterpene isolated in both enantiomeric forms, has been developed utilizing a chiral cyclopentanoid starting material having a latent meso structure.

New thinking on the financial crisis

PurposeThe purpose of this paper is to expand understanding of the current global financial crisis in light of other large‐scale financial crises.Design/methodology/approachThe phenomenon of large‐scale financial crisis has not been modeled well by neo‐classical general equilibrium approaches; the paper explores whether evolutionary and complex systems approaches might be more useful. Previous empirical work and current data are coalesced to identify fundamental drivers of the boom and bust phases of the current crisis.FindingsMany features of financial crisis occur naturally in evolutionary and complex systems. The boom phase leading to this current crisis (early 1980s through 2006) and bust phase (2007‐) are associated with structural changes in institutions, technologies, monetary processes, i.e. changing “meso structures”. Increasingly, purely financial constructs and processes are dominant infrastructures within the global economy.Research limitations/implicationsRigorous analytical predictions of financial crisis variables are at present not possible using evolutionary and complex systems approaches; however, such systems can be fruitfully studied through simulation methods and certain types of econometric modeling.Practical implicationsCommon patterns in large‐scale financial crises might be better anticipated and guarded against. Better money‐liquidity supply decisions on the part of official institutions might help prevent economy‐wide money‐liquidity crises from turning into systemic solvency crises.Originality/valueScholars, policymakers, and practitioners might appreciate the more comprehensive evolutionary and complex systems framework and see that it suggests a new political economy of financial crisis. Despite a huge scholarly literature (organized recently as first‐ second‐ and third‐generation models of financial crises) and a flurry of topical essays in recent months, systemic understanding has been lacking.

A macro-meso constitutive law for concrete having imperfect interface and nonlinear matrix

The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete. Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained in concrete.

Efficient synthesis of quinoxaline derivatives over ZrO2/MxOy (M=Al, Ga, In and La) mixed metal oxides supported on MCM-41 mesoporous molecular sieves

Abstract Mesoporous Si-MCM-41 was synthesized by a hydrothermal crystallisation method. Various weight percentages of ZrO 2 /M x O y (where M = Al, Ga, In and La) mixed metal oxides were loaded by wet impregnation using methanol solutions. The characteristic structural features of the materials were determined by various physico-chemical techniques, such as XRD, BET surface area measurement, ammonia TPD, SEM and TEM. The regular meso structure of Si-MCM-41 with a uniform pore size is very well preserved after optimum loading of binary metal oxides. XRD patterns revealed the hexagonal nature of the support; it retained its structure with maximum loading of 17 wt.% ZrO 2 and 4 wt.% M x O y mixed oxides. BET measurements show the abrupt decrease in surface area, pore size and pore volume at higher loading of metal oxides. TEM studies of the material shows regular arrangement of hexagonal pores present in the host Si-MCM-41 and the fine dispersion of metal oxides over the support. NH 3 -TPD experiments indicated the variations in the acid strength as the metal oxides were loaded. The acid strength of the catalysts follows the order: 17% ZrO 2 /4% Ga 2 O 3 /MCM-41 ≈ 17% ZrO 2 /4% Al 2 O 3 /MCM-41 > 17% ZrO 2 /4% La 2 O 3 /MCM-41 > 17% ZrO 2 /4% In 2 O 3 /MCM-41 > 17% ZrO 2 /MCM-41. Medicinally important quinoxaline derivatives were efficiently synthesized by the liquid phase condensation reaction of various 1,2-diamines with 1,2-diketones using the prepared catalysts. Various reaction parameters were optimized to improve product yield.

Gem-Dimethylcyclopropanation of dibenzylideneacetone using triisopropyl sulfoxonium tetrafluoroborate

The reaction between dibenzylideneacetone (dba) and triisopropyl sulfoxonium tetrafluoroborate has been reinvestigated. The stereochemistry of the major diasteromeric bis(gem-dimethylcyclopropane) adduct has now been assigned as [(1RS,3RS)-2,2-dimethyl-3-phenylcyclopropyl][(1SR,3SR)-2,2-dimethyl-3-phenylcyclopropyl]methanone, C(23)H(26)O, by X-ray crystallographic studies on a twinned crystal. The asymmetric unit contains two molecules of the adduct, the conformations of which differ in the orientation of the phenyl ring relative to the adjacent cyclopropanated double bond. The carbonyl groups of each adduct are aligned approximately along the a axis and in opposite directions to each other. The molecules pack to give a sinusoidal pattern along the b axis. This is the first acyclic bis(dimethylcyclopropyl) ketone for which an X-ray crystal structure determination has been reported, and is also the first bis-cyclopropanated dba analogue. The knowledge that the major diastereomer has the meso structure (and therefore the confirmation that the minor isomer is the racemate) will prove invaluable in future studies to utilize bis(dimethylcyclopropyl) ketones as reagents, in rearrangement processes, and as potential ligands and ligand precursors in organometallic chemistry.

Synthesis, structure and characterisation of rac and meso– ansa-bridged permethylindenyl cobalt complexes

Disodium ethylene-bis-hexamethylindenyl, {(C 9Me 6) 2C 2H 4}Na 2 (EBI∗Na 2), has been prepared in good yield by the reaction of lithium heptamethylindenyl with cyanogen bromide followed by treatment with sodium naphthalenide. EBI∗Na 2 reacts with anhydrous Co(acac) 2 to give a mixture of rac and meso-ethylene-bis -hexamethylindenyl cobalt(II) (EBI∗Co). The isomers can be separated by fractional crystallisation and the rac-isomer has been structurally characterised. Oxidation of the reaction mixture yields both rac and meso-ethylene-bis -hexamethylindenyl cobalt(III) which have both been structurally characterised.

Tailoring the Metallocene Structure To Obtain LLDPE by Ethene Homopolymerization: An Experimental and Theoretical Study

The mechanism of formation of branched polyethylene in the polymerization promoted by meso-metallocene/MAO systems has been investigated by combining DFT calculations and experimental results on differently featured meso-zirconocenes. A possible explanation for the required meso structure in the formation of branches considers a competition of ethene insertion and β-hydrogen transfer to the monomer. General mechanistic considerations in order to design catalytic systems able to synthesize LLDPE by ethene homopolymerization have been outlined.

Deformation macrolocalisation and fracture in ultrafine-grained armco iron

The banded structure formed in armco iron specimens as a result of equal-channel angular extrusion causes their strong shear localisation under quasi-static tension. Applying transmission electron microscopy technique, a fine structure of meso- and macroscopic shear bands was revealed. The character of shear band propagation was studied by calculation of the maximum in-plane shear strain through a digital image correlation procedure. It was shown two different patterns of macroband propagation: two parallel shear bands with oppositely directed shears or a cross of shear bands oriented along the conjugate direction of maximum tangential stresses. The necking was revealed to be caused by the disturbance of self-consistent propagation of deformation macrobands.

N-(Trifluoromethylsulfonyl)aryloxytrifluoromethylsulfoximines [ArO−SO(CF3)NTf] and N-Aryltriflimides Ar−N(Tf)2 by Thermal and Photolytic Dediazoniation of [ArN2][BF4] in [BMIM][Tf2N] Ionic Liquid: Exploiting the Ambident Nucleophilic Character of a “Nonnucleophilic” Anion

Arenediazonium tetrafluoroborate salts undergo metathesis on immobilization in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonato)amide [BMIM][Tf(2)N]. The "noncoordinating", "nonnucleophilic" [Tf(2)N] anion acts as an ambident nucleophile toward the aryl cations, formed via thermal dediazoniation, to give predominantly the oxy anion quenching products [ArO-SO(CF(3))=NTf], with minimal formation of ArN(Tf)(2), irrespective of the nature of the substituent(s) on the ArN(2)+. Strong preference for the formation of oxygen trapping products did not change under photolytic conditions, where dediazoniation occurs at room temperature. A minimal amount of the Schiemann product ArF is also formed in both thermal and photolytic dediazoniation, depending on the substituent(s). Progress of dediazoniation in the IL (both thermal and photolytic) and the evolution of the products were directly monitored by (1)H and (19)F NMR. According to DFT (Density Functional Theory) calculations, PhN(Tf)(2) is more stable than PhO-SO(CF(3))=NTf by 15-17 kcal/mol, depending on the basis set. Inclusion of solvation effects (PCM, with acetone and with CH(2)ClCH(2)Cl as solvent) did not change this preference. The [ArN(2)][BF(4)] dediazoniation in [BMIM][Tf(2)N] resulted in synthesis and characterization of a series of hitherto unknown [ArO-SO(CF(3))=NTf] compounds. The X-ray structure of MesO-SO(CF(3))=NTf (Mes = mesityl) is reported. On the basis of extraction studies, suitable solvent systems have been identified that remove the products without dissolving [BMIM][NTf(2)], thus overcoming product recovery difficulties typically associated with the use of this IL.

2146 繊維強化複合材料のミクロ・メゾモデリングと強度評価(S12-4 繊維強化複合材料,S12 先端材料システムの強度・機能評価とメゾメカニックス)

Mechanical properties of fiber reinforced composites are depended on the micro and meso structures however it is difficult to predict those. In this study, we have proposed an evaluation method by which mechanical property of fiber bundle can be obtained with micro structure model under periodic boundary conditions. The strength in several directions can be evaluated by the damage development analysis. The macroscopic mechanical properties can be also obtained with meso structure model by the same method. In case of textile composites, it is also difficult even to make a finite element mesh, because we have to fill the space between fiber bundles with the resin meshes. To solve this problem, a new modeling method in which fiber bundle and resin meshes can be modeled individually, has been proposed.

Algorithm for Exhaustive and Nonredundant Organic Stereoisomer Generation

Generation of organic stereoisomers with R/S, Z/E, and/or M/P configurations that may contain heteroatoms, multiple bonds, and any kind of cycle (isolated, spiro, condensed, and nested) is described. Inputs for processing are molecular structures in a N_tuple format resident on an automatic (canonical) or manual (non canonical) generated file which are processed by doing internal molecular graph construction, a weighted bipartite tree construction for all atoms and bonds to detect stereocenters, and symmetrical atom groups (SAG) with some specific SAG parameters that constitute a novel way for redundancy elimination of meso structures. Finally, determination of ligand CIP priorities allows for writing the output N_tuples with stereoisomer description. Several examples showing application of this methology to a wide number of structures are also presented.

In Meso Structure of the Cobalamin Transporter, BtuB, at 1.95 Å Resolution

Crystals of the apo form of the vitamin B 12 and colicin receptor, BtuB, that diffract to 1.95 Å have been grown by the membrane-based in meso technique. The structure of the protein differs in several details from that of its counterpart grown by the more traditional, detergent-based ( in surfo) method. Some of these differences include (i) the five N-terminal residues are resolved in meso, (ii) residues 57–62 in the hatch domain and residues 574–581 in loop 21–22 are disordered in meso and are ordered in surfo, (iii) residues 278–287 in loop 7–8 are resolved in meso, (iv) residues 324–331 in loop 9–10, 396–411 in loop 13–14, 442–458 in loop 15–16 and 526–541 in loop 19–20 have large differences in position between the two crystal forms, as have residues 86–96 in the hatch domain, and (v) the conformation of residues 6 and 7 in the Ton box (considered critical to signal transduction and substrate transport) are entirely different in the two structures. Importantly, the in meso orientation of residues 6 and 7 is similar to that of the vitamin B 12-charged state. These data suggest that the “substrate-induced” 180° -rotation of residues 6 and 7 reported in the literature may not be a unique signalling event. The extent to which these findings agree with structural, dynamic and functional insights gleaned from site-directed spin labelling and electron paramagnetic resonance measurements is evaluated. Packing in in meso grown crystals is dense and layered, consistent with the current model for crystallogenesis of membrane proteins in lipidic mesophases. Layered packing has been used to locate the transmembrane hydrophobic surface of the protein. Generally, this is consistent with tryptophan, tyrosine, lipid and C α B-factor distributions in the protein, and with predictions based on transfer free energy calculations.

Activation process of 3-alkyl-substituted ansa-bis(indenyl) zirconocenes by MAO

The ansa-indene compound {1-Me 2Si(3-C 9H 6Et) 2} ( 1) was prepared by alkylation of the unsubstituted ansa-indene. This compound was converted, by reaction with nBuLi, to the dilithium compound [Li 2{1-Me 2Si(3-C 9H 5Et) 2}] ( 2). ansa-Zirconocene [Zr{1-Me 2Si(3-η 5-C 9H 5Et) 2}Cl 2] ( 3) was prepared by the reaction of ZrCl 4 with 2 in ether/toluene at −78 °C. The molecular structure of meso- 3 was determined by single crystal X-ray diffraction studies. The ansa-zirconocene 3 exhibits a greater activity in ethylene polymerization than reference complexes such as [Zr{1-Me 2Si(η 5-C 9H 6) 2}Cl 2] and [Zr{1-C 2H 4(η 5-C 9H 5) 2}Cl 2] and, in addition, it maintained a reasonable level of activity after 12 h of contact with MAO solution. Furthermore, the different elementary steps in the activation process of ethylene polymerization for substituted complexes [Zr{1-Me 2Si(3-η 5-C 9H 5R) 2}Cl 2] (R = Et 3, Me 4, nPr 5 and nBu 6) by commercial methylaluminoxane (MAO) have been studied by UV–vis spectroscopy. Addition of MAO in large excess ([Al]/[Zr] = 2000) at −78 °C yields a previously unreported intermediate in the activation process of metallocenes; this intermediate has an absorption band centered at λ = 639 nm. We report here the influence of the type of catalyst, ring substitution, type of cocatalyst and addition of THF on the activation process of these metallocenes.

Organometallic Rhodium Complexes Encapsulated in Mesoporous Molecular Sieves

Rh(III) complexes both dimmer [Cp * RhCl]2(l-Cl)2 and monomer ([RhCp * (S)3] 2+ ) were encapsulated into MCM-41 channels. All silica MCM-41 molecular sieve and aminosililated MCM-41 matrix were used for rhodium complexes accommodation. Reactivity of Cp * rhodium complexes encapsulated in meso structure was estimated on the grounds of their susceptibility to interaction with CO molecules resulting in the formation of carbonyl complexes. Formation of Cp * Rh carbonyls was recorded by means of FTIR spectra. It was found that accommodation of Rh(III) complexes in MCM-41 molecular sieves activated the complex and led to the formation of Rh(III)Cp * carbonyls as a result of contact with CO. Contact of rhodium (III) complexes encapsulated in MCM-41 matrix with CO did not result in rhodium (III) reduction, whereas in the presence of amine groups in aminosililated MCM-41 the reduction of Rh(III) to Rh(I) occurred relatively easily and formation of Cp * Rh(CO)2 complex containing Rh(I) was noted. Encapsulated rhodium complexes showed some activity in methanol carbonylation reaction carried out under heterogeneous conditions. For the most active catalyst the amount of methyl acetate reached about 8 mol.%, however, deactivation of catalyst occurred and after 2 h on stream methyl acetate was not found in the product.

Gas–oil cracking activity of hydrothermally stable aluminosilicate mesostructures (MSU-S) assembled from zeolite seeds: Effect of the type of framework structure and porosity

Aluminosilicate mesostructures (MSU-S BEA) assembled from zeolite Beta (BEA) seeds exhibited relatively high hydrothermal stability and were significantly more active in the cracking of gas–oil compared to MCM-41 after severe steaming pretreatment. The MSU-S BEA mesoporous materials with wormhole framework structure and those having morphology of solid nanoparticles with high interparticle mesoporosity were more steam-stable and more active after severe steaming than those with hexagonal pore structure. Differences in acid sites strength between the MSU-S BEA materials and MCM-41 could not be probed by the complex reaction system of the large hydrocarbon molecules of gas–oil.

Buckling in Thin Walled Micro and Meso Structures of Lightweight Materials and Material Compounds

Modern materials and material compounds for application in lightweight structures exhibit, in addition to the use of constituents of high specific stiffness and strength, very special micro- and meso-structures. Typical representatives of such material compounds are sandwiches with thin homogeneous or composite face layers and structured core materials (for instance honeycombs and closed or open cell foams). The load carrying capacity of lightweight structures made of such materials and material compounds, respectively, is limited by a considerable number of rather different but interconnected instability modes occurring at length scales which are several orders of magnitude smaller than the size of the structural part. These non-global instabilities are the subject of the presented key-note paper.

Acquisition, Synthesis, and Rendering of Bidirectional Texture Functions

Abstract One of the main challenges in computer graphics is still the realistic rendering of complex materials such as fabric or skin. The difficulty arises from the complex meso structure and reflectance behavior defining the unique look‐and‐feel of a material. A wide class of such realistic materials can be described as 2D‐texture under varying light‐ and view direction, namely, the Bidirectional Texture Function (BTF). Since an easy and general method for modeling BTFs is not available, current research concentrates on image‐based methods, which rely on measured BTFs (acquired real‐world data) in combination with appropriate synthesis methods. Recent results have shown that this approach greatly improves the visual quality of rendered surfaces and therefore the quality of applications such as virtual prototyping. This state‐of‐the‐art report (STAR) will present the techniques for the main tasks involved in producing photo‐realistic renderings using measured BTFs in details.

Computer Simulation of Cyclic Block Copolymer Microphase Separation

The dissipative particle dynamics (DPD) simulation method is applied to study the mesoscopic phase formation of cyclic diblock copolymer c-AmBn (m + n = 20). The phase diagram is constructed by simulating at different interaction parameters and composition fractions. The resulted phase diagram is similar to that of the linear diblock copolymer; i.e., the ordered structures such as lamellae, perforated lamellae, hexagonal cylinders, and body-centered-cubic spheres can be identified in the parameter space. Melted structures such as micelle-like, liquid rod, and random network phases have also been found in the phase diagram. The observed (χN)ODT is in agreement with the theoretical prediction, if a finite chain length mapping is applied. Cyclization of a linear block copolymer can induce remarkable changes in the morphology of the organized meso structure. This is attributed to the reduced chain length of the cyclic block copolymer. The existence of the melted structures between totally disordered and the o...

Bulge deformation measurement and elastic modulus analysis of nanoporous alumina membrane using time sequence speckle pattern interferometry

Nanoporous alumina membranes containing parallel regular pores of uniform size and normal to substrate surface were fabricated by anodically oxidizing high purity aluminum foils in acid solutions. The continuous out-of-plane displacement and current load of the porous membranes were obtained through bulge test combining time sequence speckle pattern interferometry (TSSPI) observation system. Then the deformation of whole field under different loads was deduced through point-to-point scan analysis and the elastic modulus was calculated through an analytical model. Measurement of mechanical properties indicates unusual mechanical behavior of these anodic alumina films compared with bulk alumina materials or dense alumina films. This method is useful and convenient for mechanical test on membranes with such structure and bring further understanding on connecting of micro–meso structure and mechanical properties.

Polymerization of ethene with zirconocene catalysts: an experimental and quantum chemical study of the influence of para-substituent in benzyl in bis{η 5-(1-benzyl)indenyl}zirconium dichlorides

The meso- and rac-like isomers of bis{η 5-(1-benzyl)indenyl}zirconium dichloride ( 5), bis{η 5-(1- para-methoxybenzyl)indenyl}zirconium dichloride ( 6), bis{η 5-(1- para-fluoro-benzyl)indenyl}zirconium dichloride ( 7) and bis{η 5-(1-phenylethyl)indenyl}zirconium dichloride ( 8) were synthesized and isolated. Solid-state structures of meso- and rac-like 5 were determined by X-ray structure analysis. Polymerization properties of the methylaluminoxane (MAO) activated diastereomers of complexes 5– 8 were studied in ethene polymerizations under different monomer concentrations. The rac-like isomer of 1-phenylethyl-substituted 8/MAO showed significantly higher activity than the 1-benzyl substituted analogs 5– 7/MAO. In addition, rac- 8/MAO behaves like a single center catalyst producing polyethene with narrow molar mass distribution (1.8–1.9), while diastereomers of 5– 7/MAO produce polymers with molar mass distributions varying from 2.7 up to 10.3. The rac and meso-like isomers of 5– 7/MAO have different response on the monomer concentration. Quantum chemical calculations suggest a strong interaction between the benzyl substituent and the electron deficient zirconium center. The phenyl metal coordination energies depend on the electronic properties of the para-substituent. In 8/MAO, due to the ethyl spacer, the coordination does not have a significant role and therefore much higher activity and single center polymerization behavior is observed.