Thermal Decomposition and Crystallization of Aqueous Sol-Gel Derived Zirconium Acetate Gels: Effects of the Additive Anions

Zirconia powders were prepared by forming gels by desiccation of aqueous precursor solutions of zirconium acetate containing nitric or sulfuric acid at pH 2.4 and 1.4 and pyrolyzing the gels to temperatures up to 825°C. The structure development in the gels and solid pyrolysis products was investigated. The crystalline zirconia structures produced monoclinic (m), metastable cubic (c) and tetragonal (t) polymorphs. The structure transition temperatures were strongly dependent on the pH, the anions and the stoichiometry of the zirconium complex in the precursor solution. The monoclinic polymorph fraction in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing sulfuric acid at pH 2.4 to 750°C approaches zero while this ratio in the zirconia formed by pyrolyzing the gel formed from the precursor solution containing nitric acid at pH 1.4 to 825°C is 0.7.     

Significance of hydrophobic interactions in water–organic binary solvents

A LFE (Linear Free Energy) analysis of kinetic data for different organic reactions in various organic aqueous solutions was carried out. The rate constants of these reactions were compared with those for the solvolysis of tert-butyl chloride in the same solvents in terms of the LFE Relationships, and linear plots were observed in a wide range of the co-solvent content. This similarity points to a common nature of the solvent effect in these reactions in variety of water–organic mixtures, regardless of largely different reaction mechanisms. We explain these results by the prevalence of hydrophobic stabilization of the initial state of these reactions in water-rich solvent mixtures. Recently the same conclusion was also made on the basis of investigations into sonication effects in kinetics of organic reactions. A considerable contribution of hydrophobic effects to the Y scale by Grunwald and Winstein was deduced.     

Kinetics of the Temperature-Dependent eaq− and ⋅OH Radical Reactions with Cr(III) Ions in Aqueous Solutions

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (e_aq⁻) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical (⋅OH). It was found that Cr³⁺ did not react significantly with the ⋅OH radical, but the first hydrolysis species, Cr(OH)²⁺, did with a rate coefficient of k= (7.2±0.3)×10⁸ M⁻¹ s⁻¹ at 25 °C. The oxidation of Cr(OH)²⁺ by the ⋅OH radical formed an absorbing product species that ultimately oxidized to give Cr(VI). These newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high-level nuclear waste via vitrification processes.     

The Study of Water Structure in Aqueous Solutions of Butoxyethanol by Enthalpy of Mixing Measurements

In order to confirm the existence of regions I and II in aqueous solutions of butoxyethanol(BE), the concentration and temperature dependences of enthalpies of mixing of aqueous BE solutions with some organic solvents were measured. It has been found that the increments of apparent enthalpies of mixing per mole of water with respect to the mole fraction of BE change irregularly at a certain concentration. This concentration nearly corresponds to the reported boundary between regions I and II. Although similar behavior has also been observed in aqueous solutions of iso-butoxyethanol, aqueous solutions oftert-butoxyethanol have shown no anomalous behaviors. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new way to Prepare ts-2 with Silica sol as Silicon Source

The addition of suitable amounts of aqueous ammonia into precursor gel with silica sol as silicon source, TS-2 with small particle size and high titanium content has been successfully synthesized. It displays the same excellent performance in hydroxylation of phenol as the sample prepared with TEOS as silicon source.     

Interaction of methyltin(IV) compounds with carboxylate ligands. Part 2: formation thermodynamic parameters,predictive relationships and sequestering ability

Thermodynamic data of mono‐, di‐ and tri‐methyltin(IV)‐carboxylate complexes (acetate, malonate, succinate, oxydiacetate, diethylenetrioxydiacetate, malate, citrate, 1,2,3‐tricarballylate, 1,2,3,4‐butanetetracarboxylate, 1,2,3,4,5,6‐benzenehexacarboxylate) in aqueous solution are reported at t = 25 °C and I = 0 mol l⁻¹. Thermodynamic parameters obtained were analysed to formulate empirical predictive relationships as a function of different parameters, such as the number of carboxylate groups of the ligand and the charge of the alkyltin(IV) cation. Sequestration diagrams of citrate and 1,2,3‐tricarballylate towards alkyltin(IV) cations at different pH values are also reported and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

A variable effluent splitter for simultaneous sniffing-MS-monitoring

Summary A variable effluent splitter for simultaneous sniffing-MS or (FID, FDP)-MS monitoring is described. The performance of the system is documented by an application to trace analysis of relevant passion-fruit flavour compounds.     

Thallium(III) coordination compounds: chemical information from 205Tl NMR longitudinal relaxation times

²⁰⁵Tl longitudinal relaxation rate measurements were performed on several thallium(III) complexes with the composition Tl(OH)_n(H₂O)_6?n^(3?n)+ (n = 1,2), Tl(Cl)_n(H₂O)_m?n^(3?n)+, Tl(Br)_n(H₂O)_m?n^(3?n)+ (m = 6 for n = 1–2, m = 5 for n = 3, m = 4 for n = 4), Tl(CN)_n(H₂O)_m?n^(3?n)+ (m = 6 for n = 1–2, m = 4 for n = 3–4) in aqueous solution, at different magnetic fields and temperatures. ¹³C and ²D isotopic labelling and ¹H decoupling experiments showed that the contribution of the dipolar relaxation path is negligible. The less symmetric lower complexes (n < 4) had faster relaxation rate dominantly via chemical shift anisotropy contribution which depended on the applied magnetic field: T₁ values are between 20 and 100 ms at 9.4 T and the shift anisotropy is Δσ = 1000–2000 ppm. The tetrahedral complexes, n = 4, relax slower; their T₁ is longer than 1 s and the spin–rotation mechanism is probably the dominant relaxation path as showed by a temperature dependence study. In the case of the TlCl₄^? complex, presumably a trace amount of TlCl₅^2? causes a large CSA contribution, 300 ppm. Since the geometry and the bond length for the complexes in solution are known from EXAFS data, it was possible to establish a correlation between the CSA parameter and the symmetry of the complexes. The relaxation behaviour of the Tl–bromo complexes is not in accordance with any known relaxation mechanism. Copyright © 2002 John Wiley & Sons, Ltd.     

STRUCTURE, MOLECULAR WEIGHT AND BIOACTIVITIES OF (1→3)-β-D- GLUCANS AND ITS SULFATED DERIVATIVES FROM FOUR KINDS OF LENTINUS EDODES

Lentinan samples, (1→3)-β-D-glucans containing 4.6-15.2 wt% proteins, coded as L-I1, L-I2, L-I3 and L-I4 (L-I)were isolated from four kinds of Lentinus edodes. These glucans were treated with acetone to remove the protein in order to obtain free protein glucans coded as LNP-I1, LNP-I2, LNP-I3 and LNP-I4 (LNP-I). The free-protein polysaccharides were sulfated to give derivatives (S-LNP-I) with degree of substitution (DS) from 0.4-0.8. The structural features and weight- average molecular weight (Mw) of the samples were investigated by using infrared spectroscopy, elemental analysis,13C-NMR, size exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry. The effects of structure and conformation of the polysaccharides on antitumor activities were assayed in vivo (Sarcoma 180 solid tumors)and in vitro (Sarcoma 180, HL-60, MCF-7 and Vero tumors). The results indicated that the predominant species of the samples L-I and LNP-I in 0.2 mol/L NaCl aqueous solution existed as triple-helical chains with high rigidity and in dimethyl sulfoxide (DMSO) as single-flexible chains. Interestingly, the antitumor activities of LNP-I are lower than those of the native glucans (L-I), whereas their sulfated derivatives have higher inhibition ratio against Sarcoma 180 than LNP-I. The results reveal that the binding of protein, sulfated modification and the triple helix conformation are important factors in the enhancement of the antitumor activities of polysaccharides on the whole.     

Sonication effects on non-radical reactions. A sonochemistry beyond the cavitation?

The kinetics of pH-independent hydrolysis of 4-methoxyphenyl dichloroacetate were investigated under ultrasonic irradiation with an application of 10% of the maximum power of the equipment and without sonication in acetonitrile–water binary mixtures with a content of acetonitrile ranging from 0.008 to 35 wt.%. Similar kinetic investigations were performed at intensities corresponding to 10%, 20%, 30%, 40%, and 50% of the input energy in solvent mixtures containing 10 wt.% and 25 wt.% acetonitrile. In parallel, the responses of KI and terephthalic acid dosimeters at applied irradiation levels were registered under the same experimental conditions. Significant kinetic sonication effects were found at sound intensities presumably not inducing cavitation in the solution. This result provides an experimental evidence of kinetic effects of ultrasound in the absence of cavitation. A disturbing impact of cavitation on the ultrasonic acceleration of the reaction was found. The implications of these findings were discussed.