Evaluation of thermoporometry for characterization of mesoporous materials

The accuracy of thermoporometry (TPM) in terms of the characterization of SBA-15 is examined based on a model that classifies the water in the mesopores into two different types: freezable pore water, which can form cylindrical ice crystals, and nonfreezable pore water, which cannot undergo a phase transition during a differential scanning calorimetry (DSC) measurement. Applying the empirical relationship between the sizes of the ice crystals formed in the mesopores and the solidification temperature of the freezable pore water to a thermogram (a recording of the heat flux during the solidification of the freezable pore water) yielded a size distribution of the ice crystals. The size of the ice crystals increased slightly with repetitive freezing, indicating that the mesopores were enlarged by formation of the ice crystals. Adding the thickness, t(nf), of the nonfreezable pore water layer to the ice crystal-size distribution calculated from the thermogram allowed for the determination of the porous properties of SBA-15. The porous properties attained from TPM experiments were compared with the results attained through the combination of Ar gas adsorption experiments and nonlocal density functional theory (NLDFT) analysis. The porous properties determined by TPM were confirmed to be quite sensitive to the t(nf) value.     

Unifying criteria for dissolution kinetics of various hydroxyapatite preparations

A powder suspension method has been used to study the dissolution rate behavior of various hydroxyapatite (HAP) preparations in acidic media containing different levels of calcium and phosphate. Despite the reported variabilities in the properties among differently prepared samples, the present study indicates that, with regard to the dissolution rate behavior, there is an important common characteristic dissolution rate component. There appears to be a dissolution site common to most HAP preparations that may be associated with the predominant surface of the HAP crystal. Also, an attempt is made to correlate the dissolution rate data with the study of Young and Holcomb on the properties of different HAP preparations.     

Luminescent palladium complexes containing thioamide-based SCS pincer ligands

Thioamide-based tridentate ligands, 1,3-benzenedicarbothioamides (1a-c), were used to afford pincer palladium(II) complexes (Pd(1-H)Cl, 2a-c) with η³-S,C,S type coordination. The complexes exhibit strong emission in a glassy frozen state as well as in the solid state. The decay lifetime of the emission from the complexes is in a range of 8-9 × 10⁻⁵ s, which is indicative of phosphorescent emission.     

Synthesis of optically active β-alkyl aspartate via [3,3] sigmatropic rearrangement of α-acyloxytrialkylsilane

The synthesis of four types of optically active β-carbon-substituted analogs of threo-β-hydroxy aspartate (THA) and a β-carbon-substituted analog of threo-β-benzyloxy aspartate (TBOA), which are potent blockers of excitatory amino acid transporters in the mammalian central nervous system, via the chirality-transferring ester-enolate Claisen rearrangement of α-acyloxytrialkylsilane is described.     

Cascade ultrafiltering of 210Pb and 210Po in freshwater using a tangential flow filtering system</p> </p>

Summary A rapid method was developed using ultrafilters with a tangential flow filtering system for molecular size separation of naturally occurring ²¹⁰Pb and ²¹⁰Po in a freshwater sample. Generally, ultrafiltering of a large volume water sample for measuring the nuclides was too time consuming and not practical. The tangential flow filtering system made the filtering time short enough to adapt for in-situ ultrafiltering the large volume sample. In this method, a 20 liter water sample was at first passed through the 0.45mm pore size membrane filter immediately after sample collection to obtain suspended particle matter [>0.45mm particulate fraction (PRT)]. Two ultrafilters (Millipore Pellicon 2^ò) were used sequentially. The nuclides in the filtrate were separated into three fractions: high molecular mass (100 kDa-0.45mm; HMM), low molecular mass (10 k-100 kDa; LMM) and ionic (<10 kDa; INC) fractions. It took 80 minutes to process the sample after collection. The cut-off molecular size of each ultrafilter was confirmed by size exclusion chromatographs (SEC) of the LMN and the HMM fractions. Adsorption of the nuclides and organic compounds in the sample onto the ultrafilters was negligibly small. Good reproducibility of the nuclide concentrations in each fraction was confirmed by repeated experiments. The method was successfully applied to obtaine the molecular size distributions of ²¹⁰Pb and ²¹⁰Po in an oligotrophic lake, Lake Towada located in the northern area of Japan.</p> </p>     

Some aspects of environmental radioactivity around the former Soviet Union"""s Semipalatinsk nuclear test site: Local fallout Pu in Ust"""-Kamenogorsk district

The ¹³⁷Cs, ²³⁸Pu and ^239,240Pu activity concentrations were determined together with the atomic ratios of ²⁴⁰Pu/²³⁹Pu for the soil samples at 19 sites from the Ust"-Kamenogorsk district, located more than 300 km east of the Semipalatinsk nuclear test site (SNTS). The mean areal deposition of ¹³⁷Cs ranged from 1,500 to 4,100 Bq/m². However, some hot spot-like areas showing high concentrations of 5,500–7,700 Bq/m² were foundat some sites within the city. The ^239,240Pu levels ranged from <50 to 510 Bq/m², however most of them ranged between 120–200 Bq/m². These levels are nearly the same as those around the Semipalatinsk City. At most of the sites within the city and its adjacent areas, both nuclides were found in the soil layers up to a depth of 30 cm. A fraction of 20–50% of ^239,240Pu was not leached by hot digestion with concentrated HNO₃ containing a small amount of H₂O₂. Generally, such tightly bound fraction showed a trend to decrease with increasing distance from the SNTS. The fraction of these radionuclides that were deposited in Ust"-Kamenogorsk district from global and from SNTS fallouts have been determined using the ²⁴⁰Pu/²³⁹Pu atomic ratios in both Pu fractions: one which can be leached with hot HNO₃ + H₂O₂ and another that is a non-leacheable for each soil layer of core samples. As a result a fraction of 21–80% (mostly 30–60%) of total ^239,240Pu were found to be due to the local fallout of Pu from the SNTS debris. For ¹³⁷Cs, the contribution (mostly 10–20%) of local fallout from the SNTS were estimated to be far lower as compared to ^239,240Pu.