Second Dissociation Constant of H<Subscript>2</Subscript>Te and the Absorption Spectra of HTe<Superscript>–</Superscript>, Te<Superscript>2–</Superscript> and Te<Subscript>2</Subscript><Superscript>2–</Superscript> in Aqueous Solution

We have measured the second acid dissociation constant, K _2a , at several ionic strengths for hydrogen telluride (H₂Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe⁻ and Te²⁻. Since it is produced in our solutions, we have also determined the spectra of Te₂ ²⁻ both in the uv and in the visible regions. At 25 ^∘C, K _2a = (1.28 ± 0.02) × 10⁻¹² by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm^-3 was estimated to be (8.7 ± 0.2) × 10⁻¹². The solution thermodynamics of these species are also discussed and comparisons are made to related acids.     

Preconcentration of platinum group metals on modified silicagel and their determination by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry in airborne particulates

Modified silicagel (C18) was studied for separation and preconcentration of platinum group metals (Ru, Rh, Pd, Os, Ir and Pt) as ion associates of their chlorocomplexes with cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide. Sample containing HCl and the onium salt was pumped through the column. After elution with ethanol the eluate was evaporated in the presence of HCl. Resulting aqueous solutions were analysed with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Recovery values of 1-20 mug Pt and Pd from 50 ml of synthetic pure solution were 100+/-3 and 100+/-1%, respectively, however, they diminished with increasing sample volume and in the presence of the real sample matrix or nitrate ions. Samples of engine soot (NIES No. 8), decomposed by low pressure oxygen high-frequency plasma, and airborne particulates from dust filters of meteorological stations, leached with HNO(3) and H(2)O(2), were analysed. A reasonable agreement was found between ICP-MS and ICP-AES results for airborne dust samples and the values comparable with those in literature were determined in NIES No. 8.     

Standard molar enthalpy of formation of CH<Subscript>3</Subscript>(CH<Subscript>3</Subscript>SCH<Subscript>2</Subscript>)SO,methyl methylthiomethyl sulfoxide

Summary The standard molar enthalpy of formation of methyl methylthiomethyl sulfoxide, CH₃(CH₃SCH₂)SO, at T=298.15 K in the liquid state was determined to be -199.4±1.5 kJ mol^-1 by means of oxygen rotating-bomb combustion calorimetry.     

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.     

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.     

Dexamethasone delivery to posterior segment of the eye

Due to anatomic barriers and lacrimal drainage it is difficult to obtain therapeutic drug concentrations in the posterior part of the eye after topical drug administrations. Lipophilic cyclodextrins, such as randomly methylated β-cyclodextrin (RMβCD), are known to act both as solubilizers of water-insoluble drugs in aqueous solutions and as penetration enhancers that reduce the barrier function of lipophilic membranes. The purpose of this study was to investigate the effects of RMβCD on dexamethasone delivery from aqueous eye drop solution into rabbit eyes. Dexamethasone (0.5 and 1.5% w/v) drops (50 μl) were administered to the left eye of rabbits (n = 6) and the drug levels measured in different eye tissues 2 h after administration. In aqueous humor dexamethasone levels were 1,190 ± 110 and 1,670 ± 630 ng/g (mean ± SD) after administration of the 0.5 and 1.5% dexamethasone eye drops, respectively. In the retina the levels were 33 ± 7 and 66 ± 49 ng/g, and in optic nerve 41 ± 12 and 130 ± 50 ng/g, respectively. In a previous study the dexamethasone concentration in aqueous humor after topical administration of 1.3% (w/v) dexamethasone eye drops in aqueous 2-hydroxypropyl-β-cyclodextrin (HPβCD) solution was determined to be 320 ± 230 ng/g and 66 ± 20 ng/g after administration of Maxidex^® eye drops. Both the hydrophilic HPβCD and the lipophilic RMβCD enhance topical dexamethasone delivery into the eye, but of the two, the lipophilic RMβCD results in higher dexamethasone concentrations.