Solid-phase syntheses of 1,2,4-trisubstituted urazole and thiourazole derivatives

Solid-phase syntheses of 1,2,4-trisubstituted urazole and thiourazole derivatives have been accomplished. The synthesis began with the coupling of carbonylimidazole-Wang resin with a disubstituted hydrazine. The resultant carbazate was coupled with an isocyanate or isothiocyanate. Subsequent heating of the resin in the presence of triethylamine or potassium t-butoxide induced cyclization and released the desired (thio)urazole into solution. Most of the products were obtained in high yields and purities. Structural diversity can be further expanded at the R(2) substituent by performing the palladium-mediated Suzuki coupling reaction.     

Evaluation of high-pressure microwave digestion methods for hydride generation atomic absorption spectrometric determination of total selenium and arsenic in sediment

Five closed-vessel microwave digestion methods were compared for the accurate determination of arsenic and selenium in NIST SRM 1645 River Sediment by flow-injection hydride-generation atomic absorption spectrometric methods. The digestion methods using five different acid mixtures (HNO₃/ H₂SO₄, HNO₃/HCl0₄, HNO₃/HCl, HNO₃/HCl/HF, HNO₃/H₂SO₄/HClO₄) were all found to be reliable for the determination of the analytes. Taking into consideration the safety and suitability for the analysis of other metals, the methods based on the use ofaqua regia are recommended for closed vessel microwave digestion with pressure control. Using the quick digestion program, the presence of up to 10% organic content in soil samples did not adversely affect the closed vessel digestion and did not cause the loss of volatile analytes. After digestion, opening the vessel under an inner pressure of below 345 kPa (50 psi) had no effect on the accuracy of the results. The recommended digestion methods (HNO₃/HCl and HNO₃/ HCl/HF) for the reliable determination of arsenic and selenium in different sediment samples were demonstrated. The calculated detection limits (3 _b ) were less than 0.030 g/g and 0.033 g/g for arsenic and selenium, respectively. All analytical results for arsenic and selenium in SRM 1645 River sediment, NRCC BCSS-1 Marine Sediment and NIES CRM Pond Sediment were within or near the certified and reported ranges, with the exception of selenium in NIES CRM No. 2 Pond Sediment.     

Thermal depolarization in ammonium chloride crystals,I

The thermal depolarization of crystals of NH₄Cl polarized above the phase transition temperature (242.5K) by an applied electric field was studied in 13 crystals prepared under a variety of conditions in order to examine the effects of doping with divalent anions or cations and of acid or alkaline conditions during crystal growth. All the features found in crystals grown from solution also occur in a crystal grown from the vapor. We may conclude, therefore, that the depolarization effects observed are properties of crystalline NH₄Cl and are not due to water or urea occluded during crystal growth. Four main depolarizations were observed: one of these is ascribed to space charge and the other three are attributed to dipole relaxation processes. The activation energies for these are 0.58, 0.73, and 0.85 eV, respectively. The various doping experiments lead to the conclusion that one of these is favored by acid conditions and the presence of cation vacancies and the other two by alkaline conditions and the presence of anion vacancies. Specific models for the dipolar defects are formulated and discussed.     

Reference material for radionuclides in sediment IAEA-384 (Fangataufa Lagoon sediment)

A reference material designed for the determination of anthropogenic and natural radionuclides in sediment, IAEA-384 (Fangataufa Lagoon sediment), is described and the results of certification are presented. The material has been certified for 8 radionuclides (⁴⁰K, ⁶⁰Co, ¹⁵⁵Eu, ²³⁰Th, ²³⁸U, ²³⁸Pu, ^239+240Pu and ²⁴¹Am). Information values are given for 12 radionuclides (⁹⁰Sr, ¹³⁷Cs, ²¹⁰Pb (²¹⁰Po), ²²⁶Ra, ²²⁸Ra, ²³²Th, ²³⁴U, ²³⁵U, ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Pu). Less reported radionuclides include ²²⁸Th, ²³⁶U, ²³⁹Np and ²⁴²Pu. The reference material may be used for quality management of radioanalytical laboratories engaged in the analysis of radionuclides in the environment, as well as for the development and validation of analytical methods and for training purposes. The material is available from IAEA in 100 g units. Retired from IAEA in 2003.     

Liquid scintillation spectrometry of beta-emitters in marine samples

Liquid scintillation spectrometry has become the most widespread method for quantitative analysis of low level -emitters in environmental samples. This technique has been applied in the measurements of ²⁴¹Pu, ³H and ⁹⁰Sr in seawater and sediment samples. ²⁴¹Pu can be measured by direct analysis of an electrodeposited source using - discrimination or by extraction of electrodeposited plutonium into a liquid form compatible with scintillation cocktail. Sediment from Mururoa and Fangataufa atolls showed activities ranging from 18 to 44 Bq/kg. A sediment profile sampled around Bikini Atoll in 1997 showed ²⁴¹Pu activities ranging from 0.3 to 30 Bq/kg. ³H activities in pore water sediment from Mururoa and Fangataufa atolls were of the order of 10³ Bq/m³ which demonstrated its underground origin. ⁹⁰Sr was measured in the presence of ⁹⁰Y. The counting efficiency was 92.41.5% and the background 0.027±0.001 s^-1. The average chemical recovery for ⁹⁰Sr was 673%.     

Making and measuring nanostructures: Nanoscience and technology at the Singapore synchrotron light source

Synchrotron radiation facilities are natural places for nanoscience and technology as they may be used for both micro-and nanomanufacturing and the analytic characterization of nanoscale samples. The Singapore Synchrotron Light Source is conducting work in both fields. Examples given refer to the micro-and nanomanufacturing of the first electromagnetic metamaterials for the THz spectral range, the measurement of thin-film parameters such as thickness, density, and roughness in organic and inorganic nanoscale layer systems via X-ray reflectometry; the study of the atomic structure of the so-called carbon nanomesh that is formed through annealing of a SiC wafer at 1100°C by means of high-resolution X-ray photoemission spectroscopy; and the investigation of the chemical states of nanographite via X-ray absorption spectroscopy.

     

Probing the interaction at the C60-SiC nanomesh interface

Synchrotron-based high-resolution photoemission spectroscopy (PES) and in situ scanning tunneling microscopy (STM) are used to investigate the interaction at the C₆₀-SiC nanomesh interface during the sequential deposition and subsequent desorption of C₆₀ molecules. A weak charge transfer occurs at the C₆₀-nanomesh interface, involving electrons transferring from nanomesh to C₆₀ overlayer. The interface interaction originated from the weak charge transfer at the C₆₀-nanomesh interface is stronger than C₆₀ intermolecular interaction (e.g., van-der-Waals force), facilitating the layer-by-layer growth for the first two layers of C₆₀ on SiC nanomesh. The highly corrugated nanomesh surface results in an anisotropic diffusion and high diffusion barrier of C₆₀ on top, and thereby leads to the formation of irregularly shaped C₆₀ islands under submonolayer condition. In contrast, C₆₀ diffusion on HOPG and Ag(1 1 1) surfaces is rather isotropic, resulting in the formation of hexagonally shaped C₆₀ islands with smooth domain boundaries. STM results show the partial desorption of C₆₀ molecules from the SiC nanomesh surface after annealing the 1 ML C₆₀ sample (complete wetting layer of C₆₀ on SiC nanomesh) at around 150 °C for 20 min. Thorough desorption of C₆₀ molecules and full recovery of the clean SiC nanomesh are observed after annealing at around 200 °C for 20 min. In situ PES and STM experiments clearly demonstrate that C₆₀ adsorption and desorption processes do not affect the underlying SiC nanomesh structure, revealing its thermal stability and chemical inertness to C₆₀ molecules.     

On the reaction mechanism of CO2 reforming of methane over a bed of coal char

CO₂ reforming of methane was studied over a bed of coal char in a fixed bed reactor at temperatures between 1073 and 1223 K and atmospheric pressure with a feed composition of CH₄/CO₂/N₂ in the ratio of 1:1:8. Experimental results showed that the char was an effective catalyst for the production of syngas with a maximum H₂/CO ratio of one. It was also found that high H₂/CO ratios were favoured by low pressures and moderate to high temperatures. These results are supported by thermodynamic calculations. A mechanism of seven overall reactions was studied and three catalytic reactions of CH₄ decomposition, char gasification and the Boudouard reaction was identified as being of major importance. The first reaction produces carbon and H₂, the second consumes carbon, and the third (the Boudouard reaction) converts CO₂ to CO while consuming carbon. Equilibrium calculations and experimental results showed that any water present reacts to form H₂ and carbon oxides in the range of temperatures and pressures studied. Carbon deposition over the char bed is the major cause of deactivation. The rate of carbon formation depends on the kinetic balance between the surface reaction of the adsorbed hydrocarbons with oxygen containing species and the further dissociation of the hydrocarbon.     

Isolation and total synthesis of gymnastatin N, a POLO-like kinase 1 active constituent from the fungus Arachniotus punctatus

A high throughput screen against POLO-like kinase 1 (Plk1), an anti-cancer target, identified an active extract from the fungus Arachniotus punctatus. Bioassay guided fractionation led to the isolation of the new natural product, gymnastatin N (1) and the known compound aranorosinol A (2) with IC₅₀ values of 13 and 118 μM, respectively. A 12′-hydroxy analog of gymnastatin N, 3, was also isolated as a minor component. Gymnastatin N (1) was found to be a 52:48 mixture of (1S,6′R) and (1R,6′R) diastereomers, by synthesis of the four possible diastereomers and comparison of the optical rotation and chiral HPLC profile of each diastereoisomer with the natural product. Analogues of 1 were synthesized and evaluated against the Plk1 assay and these SAR studies suggested that the diene and free carboxylic acid moieties might be responsible for its bioactivity.     

Organoruthenium Antagonists of Human A3 Adenosine Receptors

Human A₃ adenosine receptor (hA₃AR) is a membrane‐bound G protein‐coupled receptor implicated in a number of severe pathological conditions, including cancer, in which it acts as a potential therapeutic target. To derive structure–activity relationships on pyrazolo–triazolo–pyrimidine (PTP)‐based A₃AR antagonists, we developed a new class of organometallic inhibitors through replacement of the triazolo moiety with an organoruthenium fragment. The objective was to introduce by design structural diversity into the PTP scaffold in order to tune their binding efficacy toward the target receptor. These novel organoruthenium antagonists displayed good aquatic stability and moderate binding affinity toward the hA₃ receptor in the low micromolar range. The assembly of these complexes through a template‐driven approach with selective ligand replacement at the metal center to control their steric and receptor‐binding properties is discussed.