Thermokinetics on the reaction of formation of Dy[(C<Subscript>5</Subscript>H<Subscript>8</Subscript>NS<Subscript>2</Subscript>)<Subscript>3</Subscript>(C<Subscript>12</Subscript>H<Subscript>8</Subscript>N<Subscript>2</Subscript>)]

The enthalpy change of formation of the reaction of hydrous dysprosium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen?H₂O) in absolute ethanol at 298.15 K has been determined as (-16.12 ± 0.05) kJ?mol^-1 by a microcalormeter. Thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), rate constant and kinetics parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the reaction have also been calculated. The enthalpy change of the solid-phase reaction at 298.15 K has been obtained as (53.59 ± 0.29) kJ?mol^t-1 by a thermochemistry cycle. The values of the enthalpy change of formation both in liquid-phase and solid-phase reaction indicated that the complex could only be synthesized in liquid-phase reaction.     

Controlling the DNA binding specificity of bHLH proteins through intramolecular interactions

Reversible control of the conformation of proteins was employed to probe the relationship between flexibility and specificity of the basic helix-loop-helix protein MyoD. A fusion protein (apaMyoD) was designed where the basic DNA binding helix of MyoD was stablized by an amino-terminal extension with a sequence derived from the bee venom peptide apamin. The disulfide-stabilized helix from apamin served as a nucleus for a helix that extended for a further ten residues, thereby holding apaMyoD's DNA recognition helix in a predominantly alpha-helical conformation. The thermal stability of the DNA complexes of apaMyoD was increased by 13 degrees C relative to MyoD-bHLH. Measurements of the fluorescence anisotropy change on DNA binding indicated that apaMyoD bound to E-box-containing DNA sequences with enhanced affinity relative to MyoD-bHLH. Consequently, the DNA binding specificity of apaMyoD was increased 10-fold.     

Fragmentation of N-linked glycans with a matrix-assisted laser desorption/ionization ion trap time-of-flight mass spectrometer

N-Linked glycans were ionized from several matrices with a Shimadzu-Biotech AXIMA-QIT matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometer. [M+Na]+ ions were produced from all matrices and were accompanied by varying amounts of in-source fragmentation products. The least fragmentation was produced by 2,5-dihydroxybenzoic acid and the most by alpha-cyano-4-hydroxycinnamic acid and 6-aza-2-thiothymine. Sialic acid loss was extensive but could be prevented by formation of methyl esters. Fragmentation produced typical low-energy-type spectra dominated by ions formed by glycosidic cleavages. MS(n) spectra (n = 3 and 4) were used to probe the pathways leading to the major diagnostic ions. Thus, for example, an ion that was formed by loss of the core GlcNAc residues and the 3-antenna was confirmed as being formed by a B/Y rather than a C/Z mechanism. The proposed structures of several cross-ring cleavage ions were confirmed and it was shown that MS3 spectra could be obtained from as little as 10 fmol of glycan.     

Period-doubling and chaotic oscillations in the ferroin-catalyzed Belousov-Zhabotinsky reaction in a CSTR

The ferroin-catalyzed Belousov-Zhabotinsky(BZ) reaction,the oxidation of malonic acid by acidic bromate,is the most commonly investigated chemical system for understanding spatial pattern forma-tion. Various oscillatory behaviors were found from such as mixed-mode and simple period-doubling oscillations and chaos on both Pt electrode and Br-ISE at high flow rates to mixed-mode oscillations on Br-ISE only at low flow rates. The complex dynamic behaviors were qualitatively reproduced with a two-cycle coupling model proposed initially by Gy?rgyi and Field. This investigation offered a proper medium for studying pattern formation under complex temporal dynamics. In addition,it also shows that complex oscillations and chaos in the BZ reaction can be extended to other bromate-driven nonlinear reaction systems with different metal catalysts.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

Mesoporous amorphous MnO<Subscript>2</Subscript> as electrode material for supercapacitor

A kind of novel mesoporous, electrochemical active material, amorphous MnO₂ has been synthesized by an improved reduction reaction and using supramolecular as template. The synthesized sample was characterized physically by thermogravimetric analysis, X-ray diffraction, transmission electron microscope (TEM), and Brunauer–Emmett–Teller (BET) surface area measurement, respectively. Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in 2 mol/l KOH aqueous solution electrolyte. The results of BET and TEM analysis indicated that supramolecular template plays an important role in the process of big specific surface area mesoporous material forming. After sintering at 200 °C, the sample still remained an amorphous structure, and its specific capacitance reached 298.7 F/g and presented a very stable capacitance after 500 cycles. In addition, the electrochemical process, such as ion transfer and electrical condition, was also investigated with electrochemical impedance spectroscopy.     

On the three-phase mass transfer with solid particles adhered to the gas-liquid interface

A heterogeneous, multi-layer mass transfer model is proposed for prediction of the effect of multi-layer packing of catalyst particles adhered to the gas-liquid interface. The behavior of the mass transfer rate with respect to the multi-layer packing, to the particle size and mass transfer coefficient without particles is discussed. It is shown that enhancement can be considerably increased by multi-layer packing compared to that of mono-layer packing, depending on the values of particle size and mass transfer coefficient. The predicted mass transfer rates using the proposed model was verified with experimental data taken from the literature. The model presented should be superior to that of published in the literature.     

Cluster Chemsitry. 96. Penta- and hexa-nuclear ruthenium cluster complexes derived from reactions of cyclopentadienes with Ru5(μ5-C2PPh2)(μ-PPh2)(CO)13

The reactions between Ru₅( ₅-C₂PPh₂)(gm-PPh₂(CO)₁₃ (1) and cyclopentadienes afforded the hexanuclear clusters Ru₆( ₆-C)( ₃-PPh₂)₂(CO)₁₀(-C₅ R ₅) [R ₅ = H₅ (2), H₄Me (3), Me₅ (4)] which contain an encapsulated carbide and a face-capping ₃-CH group, formed by cleavage of CC and CP bonds of the C₂PPh₂ moiety in1. In the reaction with cyclopentadiene, the unusual ligand C₁₃H₁₂O, formed by combination of C₂, CO and two molecules of C₅H₆ (or one molecule of dicyclopentadien), was characterized in the complex Ru₅( ₄-PPh) ( ₄-C₁₃H₁₂O)(-PPh₂(CO)₁₁(-C₅H₅) (5). In the reaction with pentamethylcyclopentadiene, the vinylidene complex Ru₅( ₃-CCHPh)( ₄-PPh)( ₄-PPh) (-PPh₂)(CO)₉(-C₅Me₅) (6) was also formed.     

Structures and stability of N7+ and N7− clusters

Ab initio molecular orbital theory and density functional theory have been used to study nine isomers of N₇ ionic clusters with low spin at the HF/6-31G*, MP2/6-31G*, B3LYP/6-31G*, and B3LYP/6-311(+)G* levels of theory. All stationary points are examined with harmonic vibrational frequency analyses. Four N₇ ⁺ isomers and five N₇ ⁻ isomers are determined to be local minima or very close to the minima on their potential-energy hypersurfaces, respectively. For N₇ ⁺ and N₇ ⁻, the energetically low lying isomers are open-chain structures (C _{2 v} and C _{2 v} or C₂). The results are very similar to those of other known odd-number nitrogen ions, such as N₅ ⁺, N₉ ⁺, and N₉ ⁻, for which the open-chain structures are also the global minima. This research suggests that the N₇ ionic clusters are likely to be stable and to be potential high-energy-density materials if they could be synthesized. Received: 16 July 2001 / Accepted: 8 October 2001 / Published online: 21 January 2002     

Efficient synthesis of cellulose furoates in 1-<Emphasis Type="Italic">N</Emphasis>-butyl-3-methylimidazolium chloride

The ionic liquid 1-N-butyl-3-methylimidazolium chloride ([C₄mim]⁺Cl⁻) was investigated as reaction media for the homogeneous acylation of cellulose with 2-furoyl chloride in the presence of pyridine. The preparation of cellulose furoate depending on the reaction conditions, the cellulose type and the pyridine content was studied. Cellulose furoates with a degree of substitution in the range from 0.46 to 3.0 were accessible, i.e., under mild conditions, with a low excess of reagent and in a short reaction time. The products were characterized by elemental analysis, perpropionylation, ¹H- and ¹³C NMR spectroscopy and FTIR spectroscopy. Thomas Heinze is the member of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu