Two-dimensional electrochemical turbulence during the electrodissolution of metal disk electrodes: Model calculations

We present numerical studies of the spatio-temporal dynamics of disk electrodes with local limit cycle oscillations. The simulations are done with a realistic 3-D geometry of the electrochemical cell and disk-shaped working electrodes (WE). Spatio-temporal chaos is shown to exist from a critical electrode size onwards. It is analyzed by Karhunen-Loève decomposition and Hilbert transform. The former shows that the chaos becomes more complex with increasing system size, the latter allows features that generate the spatio-temporal complexity to be identified, namely, spatially extended 1-D phase defects and topological defects.     

Sol–gel synthesis of 3-(triethoxysilyl)propylsuccinicanhydride containing fluorinated silane for hydrophobic surface applications

In this paper, novel fluorinated silane compound was prepared by adding hydroxyl terminated Fluorolink D10H oligomer to 3-(triethoxysilyl)propylsuccinicanhydride. The obtained silane system was independently composed with 3-Aminopropyltrimethoxysilane, 3-Glycidyloxypropyltrimethoxysilane and 3-Glycidyloxypropyltriethoxysilane and, then the prepared coating solutions were applied to glass surface by spin-coating method. The chemical bonding between groups in system was investigated by Fourier Transform Infrared Spectroscopy analyses. The elemental composition of coatings was determined using Energy Dispersive X-ray Spectroscopy analyses. Its structure and surface properties were analyzed by scanning electron microscopy, atomic force microscopy, contact angle measurement and Ultraviolet–visible Absorption Spectroscopy. The amounts of fluorine on the coatings prepared with GF20-D10H-AMMO, GF20-D10H-GLYEO and GF20-D10H-GLYMO are 31, 32 and 34% at, respectively. Transparent coatings with smooth surface and uniform thickness were observed. The coatings had nanoscale roughness. The contact angles of coatings for water ranged from 88 to 107^o, and that of n-hexadecane ranged from 53 to 60^o.     

Dynamics of vacancy defects in 2-D crystalline monolayers under chiral smectic thin films studied by scanning tunnelling microscopy

Scanning tunnelling microscopy (STM) can be used to image adsorbed organic molecules in real space and real time. The technique seems especially well suited for imaging 2-D crystalline monolayers formed under liquid crystal films. In addition to observing perfect 2-D crystals, STM provides the ability to observe crystal defects, and to observe how these defects evolve over time. In this study two different vacancy defects in 2-D lamellar monolayers of chiral liquid crystal molecules under bulk smectic films were observed in situ. Both vacancies showed dynamic behaviour and an unexpected transport anisotropy.     

New 3-D La(III)-Cu(II)-containing coordination polymer with a high potential porosity

A new 3-D coordination polymer containing both 3d and 4f ions has been designed. Its chemical formula is La2[Cu(pba)]3(H2O)8 . 8H2O. It crystallizes in the quadratic system, space group I41/a with a = 42.4947(9) Angstrom, c = 16.3378(3) Angstrom, and Z = 16. Its crystal structure can be described as a 3-D molecular framework exhibiting a complex network of interconnected zigzaglike channels. Once crystallization water molecules are removed, this compound presents a high potential porosity and a low density. The porosity has been evaluated using Connolly's algorithm.     

Divide-and-conquer,pattern matching,and relaxation methods in interpretation of 2-D NMR spectra of polypeptides

One task in the interpretation of the 2-D nuclear magnetic resonance (NMR) spectrum is to assign its signal patterns to their corresponding amino acids in proteins or polypeptides. To carry out this task of interpretation, one requires sufficient chemical knowledge and expertise to reason from a set of highly noisy data. We present a system called RUBIDIUM (a Rule-Based Identification in 2-D NMR Spectrum) to formulate the expertise and automate the process of interpretation. Given a protein or polypeptide with a known amino acid sequence and the 2-D NMR spectra (both COSY and NOESY), RUBIDIUM yields plausible assignments of lines that account for most signals observed in the spectrum and conform to prior chemical knowledge. Rules of pattern matching are used to detect plausible signal patterns. The expertise of the sequence-specific assignment task is formulated to assign a signal pattern to amino acids. To cope with ambiguities and noise, RUBIDIUM adopts various low-level data preprocessing techniques, the strategy of divide and conquer, and the relaxation technique to decrease the complexity and recover from overconstrained conditions. The polypeptides oxytocin and vasopressin are used to illustrate the performance of RUBIDIUM. © John Wiley & Sons, Inc.     

2H NMR calculations on polynuclear transition metal complexes: on the influence of local symmetry and other factors

It is now well-known that (2)H solid-state NMR techniques can bring a better understanding of the interaction of deuterium with metal atoms in organometallic mononuclear complexes, clusters or nanoparticles. In that context, we have recently obtained experimental quadrupolar coupling constants and asymmetry parameters characteristic of deuterium atoms involved in various bonding situations in ruthenium clusters, namely D(4)Ru(4)(CO)(12), D(2)Ru(6)(CO)(18) and other related compounds [Gutmann et al., J. Am. Chem. Soc., 2010, 132, 11759], which are model compounds for edge-bridging (μ-H) and face-capping (μ(3)-H) coordination types on ruthenium surfaces. The present work is in line with density functional theory (DFT) calculations of the electric field gradient (EFG) tensors in deuterated organometallic ruthenium complexes. The comparison of quadrupolar coupling constants shows an excellent agreement between calculated and observed values. This confirms that DFT is a method of choice for the analysis of deuterium NMR spectra. Such calculations are achieved on a large number of ruthenium clusters in order to obtain quadrupolar coupling constants characteristic of a given coordination type: terminal-D, η(2)-D(2), μ-D, μ(3)-D as well as μ(4)-D and μ(6)-D (i.e. interstitial deuterides). Given the dependence of such NMR parameters mainly on local symmetry, these results are expected to remain valid for large assemblies of ruthenium atoms, such as organometallic ruthenium nanoparticles.     

A new bimetallic assembly magnet [[Ni(tn)2]5[FeIII(CN)6]3]n(ClO4)n.2.5nH2O (tn = trimethylenediamine) with a novel 3-D tunnel structure

A novel molecular-based magnet of three-dimensional (3-D) cyanide-bridged bimetallic assembly, [[Ni(tn)2]5[FeII(CN)6]3]n(ClO4)n.2.5nH2O where tn = trimethylenediamine, was synthesized and structurally characterized. The compound with an asymmetric unit of C24H52.5Cl0.5Fe1.5N19Ni2.5O3.255 crystallized in the monoclinic system of the space group P2(1)/n with a = 10.173(3) A, b = 16.053(2) A, c = 26.309(3) A, beta = 91.30(2) degrees, and Z = 4. The assembly has a 3-D network structure extended by three different types of FeIII-CN-NiII-NC-FeIII linkages. The iron (FeIII) atoms are located in two different chemical environments, which were confirmed by M?ssbauer experimental results. The nickel (NiII) atoms have three different coordination environments. Cryomagnetic properties revealed that 3-D magnetic ordering occurs over the lattice below the Curie temperature around 10 K.     

In-plane stacking disorder in polydisperse hard sphere crystals

We demonstrate that in random-stacking hard-sphere colloidal crystals the stacking disorder not only exists in the direction perpendicular to the close-packed layers, but also extends in the lateral direction. The existence of such in-plane stacking disorder is suggested by a recent observation of lateral broadening of the Bragg scattering rods in microradian X-ray diffraction and is further confirmed here by real-space confocal microscopy in two hard-sphere colloidal systems with different relative gravity effects. Due to the in-plane stacking disorder, the hexagonal planes consist of islands with different lateral A, B, and C positions with characteristic line defects in between them. The real-space layer-by-layer stacks of images also reveal the 3-D structure of the defects. The chance zeta to find another line-defect above a line-defect in the layer below turns out to be close to 1/2--independent of relative gravity--which can be explained by the two different stacking options above a defect. The stacking of a few sets of several line defects situated on top of each other turns out to be predominantly FCC-like.     

Grand canonical Monte Carlo simulations of the 129Xe NMR line shapes of xenon adsorbed in (+/-)-[Co(en)3]Cl3

The 129Xe NMR line shapes of xenon adsorbed in the nanochannels of the (+/-)-[Co(en)3]Cl3 ionic crystal have been calculated by grand canonical Monte Carlo (GCMC) simulations. The results of our GCMC simulations illustrate their utility in predicting 129Xe NMR chemical shifts in systems containing a transition metal. In particular, the nanochannels of (+/-)-[Co(en)3]Cl3 provide a simple, yet interesting, model system that serves as a building block toward understanding xenon chemical shifts in more complex porous materials containing transition metals. Using only the Xe-C and Xe-H potentials and shielding response functions derived from the Xe@CH4 van der Waals complex to model the interior of the channel, the GCMC simulations correctly predict the 129Xe NMR line shapes observed experimentally (Ueda, T.; Eguchi, T.; Nakamura, N.; Wasylishen, R. E. J. Phys. Chem. B 2003, 107, 180-185). At low xenon loading, the simulated 129Xe NMR line shape is axially symmetric with chemical-shift tensor components delta(parallel) = 379 ppm and delta(perpendicular) = 274 ppm. Although the simulated isotropic chemical shift, delta(iso) = 309 ppm, is overestimated, the anisotropy of the chemical-shift tensor is correctly predicted. The simulations provide an explanation for the observed trend in the 129Xe NMR line shapes as a function of the overhead xenon pressure: delta(perpendicular) increased from 274 to 292 ppm, while delta(parallel) changed by only 3 ppm over the entire xenon loading range. The overestimation of the isotropic chemical shifts is explained based upon the results of quantum mechanical 129Xe shielding calculations of xenon interacting with an isolated (+/-)-[Co(en)3]Cl3 molecule. The xenon chemical shift is shown to be reduced by about 12% going from the Xe@[Co(en)3]Cl3 van der Waals complex to the Xe@C2H6 fragment.     

Synthesis and Characterization of aLead（Ⅱ）Complex with MicroporousStructure

1 INTRODUCTION Recently, much interest has been focused on various extended framework due to their intriguing architectures, new topologies and potential applications in microelectronics, nonlinear optics, molecular selection, ion exchange and catalysis[1~4] . In the last few years, a wide range of infinite structures with diverse topologies has been prepared by the reaction of metal ions with mulriple organic ligands[5～9]. However, up to now, much of the work has been concentrated on c…     

Water splits epitaxial graphene and intercalates

The adsorption and reactions of small molecules, such as water and oxygen, with graphene films is an area of active research, as graphene may hold the key to unique applications in electronics, batteries, and other technologies. Since the graphene films produced so far are typically polycrystalline, with point and line defects that can strongly affect gas adsorption, there is a need to understand their reactivity with environmentally abundant molecules that can adsorb and alter their properties. Here we report a study of the adsorption and reactions of water, oxygen, hydrogen, and ammonia on epitaxial graphene grown on Ru and Cu substrates using scanning tunneling microscopy (STM). We found that on Ru(0001) graphene line defects are extremely fragile toward chemical attack by water, which splits the graphene film into numerous fragments at temperatures as low as 90 K, followed by water intercalation under the graphene. On Cu(111) water can also split graphene but far less effectively, indicating that the chemical nature of the substrate strongly affects the reactivity of the C-C bonds in epitaxial graphene. Interestingly, no such effects were observed with other molecules, including oxygen, hydrogen, and ammonia also studied here.     

Upperbound procedures for the identification of similar three-dimensional chemical structures

Summary This paper describes techniques for calculating the degree of similarity between an input query molecule and each of the molecules in a database of 3-D chemical structures. The inter-molecular similarity measure used is the number of atoms in the 3-D common substructure (CS) between the two molecules which are being compared. The identification of 3-D CSs is very demanding of computational resources, even when an efficient clique detection algorithm is used for this purpose. Two types of upperbound calculation are described which allow reductions in the number of exact CS searches which need to be carried out to identify those molecules from a database which are similar to a 3-D target molecule.     

Metallic behavior and periodical valence ordering in a MMX chain compound, Pt(2)(EtCS(2))(4)I.

A new one-dimensional (1-D) halogen-bridged mixed-valence diplatinum(II,III) compound, Pt(2)(EtCS(2))(4)I (3), has been successfully synthesized from [Pt(2)(EtCS(2))(4)] (1) and [Pt(2)(EtCS(2))(4)I(2)] (2). These three compounds have been examined using UV-visible-near-IR, IR, polarized Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray crystal structure analyses (except for 1). Compound 3 was further characterized through electrical transport measurements, determination of the temperature dependence of lattice parameters, X-ray diffuse scattering, and SQUID magnetometry. 3 crystallizes in the monoclinic space group C2/c and exhibits a crystal structure consisting of neutral 1-D chains with a repeating -Pt-Pt-I- unit lying on the crystallographic 2-fold axis parallel to the b axis. The Pt-Pt distance at 293 K is 2.684 (1) A in the dinuclear unit, while the Pt-I distances are essentially equal (2.982 (1) and 2.978 (1) A). 3 shows relatively high electrical conductivity (5-30 S cm(-1)) at room temperature and undergoes a metal-semiconductor transition at T(M-S) = 205 K. The XPS spectrum in the metallic state reveals a Pt(2+) and Pt(3+) mixed-valence state on the time scale of XPS spectroscopy ( approximately 10(-17) s). In accordance with the metal-semiconductor transition, anomalies are observed in the temperature dependence of the crystal structure, lattice parameters, X-ray diffuse scattering, and polarized Raman spectra near T(M-S). In variable-temperature crystal structure analyses, a sudden and drastic increase in the Pt-I distance near the transition temperature is observed. Furthermore, a steep increase in U(22) of iodine atoms in the 1-D chain direction has been observed. The lattice parameters exhibit significant temperature dependence with drastic change in slope at about 205-240 K. This was especially evident in the unit cell parameter b (1-D chain direction) as it was found to lengthen rapidly with increasing temperature. X-ray diffraction photographs taken utilizing the fixed-film and fixed-crystal method for the metallic state revealed the presence of diffuse scattering with line shapes parallel to the a* axis indexed as (-, n + 0.5, l) (n; integer). Diffuse scattering with k = n + 0.5 is considered to originate from the 2-fold periodical ordering corresponding to -Pt(2+)-Pt(2+)-I-Pt(3+)-Pt(3+)-I- or -Pt(2+)-Pt(3+)-I-Pt(3+)-Pt(2+)-I- in an extremely short time scale. Diffuse lines corresponding to 2-D ordering progressively decrease in intensity below 252 K and are converted to the diffuse planes corresponding to 1-D ordering near T(M-S). Furthermore, diffuse planes condensed into superlattice reflections below T(M-S). Polarized Raman spectra show temperature dependence through a drastic low-energy shift of the Pt-I stretching mode and also through broadening of bands above T(M-S).     

29Si chemical shifts and additivity in pertrimethylsilylated O-methyl,O-benzyl,O-benzoyl and O-acetyl methyl β-D-xylopyranosides

²⁹Si chemical shifts in pertrimethylsilylated O-methyl, O-benzoyl, O-benzoyl and O-acetyl methyl β-D -xylopyranoside derivatives are reported. The chemical shifts in monotrimethylsilyl derivatives with the same O-substituents are in the order: δ(Si-2) > δ(Si-4) > δ(Si-3). When the chemical shifts in bis (trimethylsilyl) and tris(trimethylsilyl) derivatives are assigned according to this rule, all the chemical shifts agree well with a direct additivity rule. The only significant deviation from additivity occurs for methyl 2,4-di-O-benzoyl-3-O-trimethylsilyl-β-D -xylopyranoside, which has a different average conformation from the other compounds studied.     

258. Charge transfer as a molecular probe in systems of biological interest. VI. Interactions between lysozyme and the methyl 2-acetamido-6-O-(N-methyl-isonicotinylium)-2-deoxy-beta-D-glucopyranoside ion

The synthesis of methyl 2-acetamido-6-O-(N-methyl-isonicotinylium)-2-deoxy-β-D -glucopyranoside ion (2; iodide and chloride) is reported. Association with hen-egg-white lyso zyme causes chemical shift changes for its acetamido and glycosidic methyl groups comparable to those observed for the monosaccharide lysozyme inhibitor methyl 2-acetamido-3-deoxy-β-D glucopyranoside. The binding modes of the two compounds to the enzyme in solution therefore appear to be analogous. Furthermore, a charge transfer interaction of the pyridinium: indole type is observed spectrophotometrically, indicating that the 2 /lysozyme complex in solution is similar to that of the monosaccharide (and polysaccharide) inhibitor in crystals (proximity of the ligand O⁶ to the enzyme Trp⁶²).     

Searching of chemical structure data bases with parallel computer hardware

The use of two types of parallel computer hardware for increasing the efficiency of processing in chemical structure data bases is discussed. The distributed array processor can be used for the clustering of 2-D chemical structure data bases by using the Jarvis—Patrick clustering method and for the ranking of output in an experimental system for substructure searching in the 3-D macromolecules in the Protein Data Bank. The Inmos transputer can be used in the construction of PC-based systems for 2-D substructure searching and in the identification of the maximal substructures common to pairs of 3-D molecules.     

Phase behavior of concentrated aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium hydroxy naphthoate (SHN)

We have characterized the phase behavior of mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the organic salt 3-sodium-2-hydroxy naphthoate (SHN) over a wide range of surfactant concentrations using polarizing optical microscopy and X-ray diffraction. A variety of liquid crystalline phases, such as hexagonal, lamellar with and without curvature defects, and nematic, are observed in these mixtures. At high temperatures the curvature defects in the lamellar phase are annealed gradually on decreasing the water content. However, at lower temperatures these two lamellar structures are separated by an intermediate phase, where the bilayer defects appear to order into a lattice. The ternary phase diagram shows a high degree of symmetry about the line corresponding to equimolar CTAB/SHN composition, as in the case of mixtures of cationic and anionic surfactants.     

Three-Dimensional Modeling of the Turbulent Plasma Jet Impinging upon a Flat Plate and with Transverse Particle and Carrier-Gas Injection

Modeling results are presented concerning the turbulent thermal plasma jet impinging normally on a substrate and with transverse injection of feedstock particles and their carrier gas from a single injection tube. The k- two-equation model is employed to model the turbulence, and particle dispersion is studied considering the interaction between the moving particles and turbulent eddies and considering the effect on particle trajectories of the random variation of the turbulent fluctuating velocities in their magnitude and direction. A well-validated three-dimensional (3-D) computer code is used in the modeling. The 3-D effects due to the carrier gas injection on the jet flow field and thus on the particle trajectories and heating histories are shown to be appreciable. The radial location of the injection tube with respect to the plasma jet is shown to be a critical parameter for the study of 3-D effects, besides the carrier-gas/plasma stream mass flux ratio. Particle dispersion considerably widens the distribution of the particle trajectories and heating histories. In addition, although pertinent swirl number is often rather small, swirling may also affect the modeling results.     

A two-dimensional quadrupole ion trap mass spectrometer

The use of a linear or two-dimensional (2-D) quadrupole ion trap as a high performance mass spectrometer is demonstrated. Mass analysis is performed by ejecting ions out a slot in one of the rods using the mass selective instability mode of operation. Resonance ejection and excitation are utilized to enhance mass analysis and to allow isolation and activation of ions for MS(n) capability. Improved trapping efficiency and increased ion capacity are observed relative to a three-dimensional (3-D) ion trap with similar mass range. Mass resolution comparable to 3-D traps is readily achieved, including high resolution at slower scan rates, although adequate mechanical tolerance of the trap structure is a requirement. Additional advantages of 2-D over 3-D ion traps are also discussed and demonstrated.     

Line energy and the relation between advancing, receding, and young contact angles

The line energy associated with the triple phase contact line is a function of local surface defects (chemical and topographical); however, it can still be calculated from the advancing and receding contact angles to which those defects give rise. In this study an expression for the line energy associated with the triple phase contact line is developed. The expression relates the line energy to the drop volume, the interfacial energies, and the actual contact angle (be it advancing, receding, or in between). From the expression we can back calculate the equilibrium Young contact angle, theta0, as a function of the maximal advancing, thetaA, and minimal receding, thetaR, contact angles. To keep a certain maximal hysteresis between advancing and receding angles, different line energies are required depending on the three interfacial energies and the drop's volume V. We learn from the obtained expressions that the hysteresis is determined by some dimensionless parameter, K, which is some normalized line energy. The value of K required to keep a constant hysteresis (thetaA-thetaR) rises to infinity as we get closer to theta0 = 90 degrees.