Some applications of thermomagnetometry to the study of chromindur alloys

Thermomagnetic experiments are shown to be a useful and rapid technique for studying phase changes involving magnetic materials. Particular examples are chosen from Chromindur II (Fe28Cr10.5Co) alloys having different thermal histories. The Curie temperature of the single phase alloy is found to be ～650°C and the metastable spinodal decomposition boundary is at essentially the same temperature. The Cr-rich near equilibrium decomposition product is less magnetic and has a lower T_c, while the Cr-deficient product is more magnetic, with a T_c ? 720°C.Comparisons are made at different heating and cooling rates between temperatures measured using magnetic standards and those measured by a thermocouple in close proximity to the sample.     

Thermal lens spectrometric determination of hexavalent chromium

The applicability of thermal lens spectrometry (TLS) for quantification and routine determination of hexavalent chromium was investigated by using a collinear dual beam thermal lens spectrometer. In aqueous solutions the LOD of 0.1 μg l⁻¹ was obtained for Cr(VI) by using 160 mW laser power. The performance of the technique was verified by the determination of hexavalent chromium in standard reference water samples (NIST SRM 1643a and NIST SRM 1643c) and comparing the results for Cr(VI) in CCA (Cr, Cu, As)-treated timber extracts to concentrations obtained by atomic absorption spectrometry (AAS). Good agreement between the TLS results and reported values for Cr(VI) in SRMs as well as AAS results for Cr(VI) in CCA-treated timbers confirmed that TLS is a reliable and accurate analytical technique applicable for the determination of Cr(VI) in aqueous solutions at concentration levels 0.5–100 μg l⁻¹.     

Application of divergent multi-component reactions in the synthesis of a library of peptidomimetics based on γ-amino-α,β-cyclopropyl acids

The multi-component condensation of organozirconocene, aldimine and zinc carbenoid was applied to the stereoselective synthesis of cyclopropane amino acid derivatives. These compounds served as scaffolds for the preparation of a 46-member library. The C- and N-termini of the cyclopropane amino acid derivatives were diversified by condensations with ten amines and ten acylating agents, respectively. To improve yields and accelerate library synthesis, most products were prepared under microwave irradiation and purified by polymer-bound scavengers and SPE methodology. All compounds were analyzed by LC-MS and a representative selection was fully characterized.     

Analytical investigation of the properties and uses of a new hydrophobic molecular sieve

Distribution coefficients and capacities have been determined for many different organic compounds on a new molecular sieve called silicalite, which does not adsorb water but does adsorb small organic molecules with diameters up to 6 A, from both liquid and gaseous streams. The characteristics of silicalite have been examined closely and new applications for it are briefly described.     

Divergent and stereocontrolled synthesis of the enamide side chains of oximidines I/II/III, salicylihalamides A/B, lobatamides A/D, and CJ-12,950

[reaction: see text] A unified strategy for the divergent and stereocontrolled introduction of the (E)- and (Z)-enamide side-chains of oximidines I, II, and III, salicylihalamides A and B, lobatamides A and D, and CJ-12,950 is detailed. The synthesis relied on the copper-promoted C-N coupling of (E)- and (Z)-vinyl iodides with a protected maleimide hemiaminal followed by deprotection and reaction of the resulting (E)- or (Z)-enelactam hemiaminals with O-methylhydroxylamine or propylidenetriphenylphosphorane.     

Microwave-assisted "libraries from libraries" approach toward the synthesis of allyl- and C-cyclopropylalkylamides

Cascade reactions of internal and terminal alkynes, zirconocene hydrochloride, dimethylzinc, and phosphinoyl imines (prepared in one step from aldehydes and diphenylphosphinoyl amide) lead to allylic phosphinoyl amides after aqueous workup. Microwave acceleration allows the completion of this one-pot reaction sequence in 10 min. These allylic amides can be converted into a variety of derivatives, including carbamates and sulfonamides, or reacted prior to workup with diiodomethane to give novel C-cyclopropylalkylamides. A solution-phase "libraries from libraries" approach was used to generate an intermediate 20-member library which was subsequently expanded to a 100-member library by a series of N-functionalizations. The biological activity was evaluated in an assay for competitive binding to the estrogen receptor (ERalpha), revealing three potent lead compounds of a new structural type.     

Studies on the extraction of chromium(VI) by ketones

A study of the extraction of chromium(VI) from aqueous media by ketones was made. Extraction of chromium was found to be most efficient from aqueous hydrochloric acid solutions. A mechanism for the extraction of chromium(VI) from aqueous hydrochloric acid solutions by methyl isobutyl ketone is proposed involving the formation of a receptor in the organic phase, the exchange of the chloride ion of the receptor for the anionic chromium(VI) species of the aqueous phase, and the solvation of the extracted chromium species. The differences in the abilities of various ketones to extract chromium(VI) from aqueous hydrochloric acid solutions, and the differences in the extraction of chromium (VI) from various aqueous acids by methyl isobutyl ketone are attributed to the differences in the formation of receptors.     

Preparation and reactions of the (dicarbonyl)(η5-cyclopentadienyl)(tetrahydrofuran)iron cation: A convenient route to (dicarbonyl)(η5-cyclopentadiemyl)(η2-olefin)iron cations and related complexes

The versatile reagent [η⁵-C₅H₅)Fe(CO)₂(THF)]BF₄ has been isolated from the reaction of (η₅-C₅H₅)Fe(CO)₂I and AgBF₄ in THF and shown to react in CH₂Cl₂ with olefins to yield [(η⁵-C₅H₅)Fe(CO)₂(η²-olefin)]BF₄ complexes. For most olefins the yields are high. The yield in these reactions can be increased by treating the CH₂Cl₂ solution of [(η⁵-C₅H₅)Fe(Co)₂(THF)]BF₄ and olefin with gaseous BF₃ in order to complex the THF as the BF₃-THF adduct. Most striking is the increase in yield for the cyclohexene complex from 17% to 92%.     

Interaction of polyvinylpyrrolidone and iodine

A nonsolvent preparation of the polyvinylpyrrolidone (PVP) complex provides new insight into the nature of the polymer-iodine interaction. The preparation is obtained by simply mixing PVP with crystalline iodine and is of interest because it provides a system in which no interfering ions are present and only one type of iodine is initially present. The iodine is shown to undergo hydrolysis with moisture in the polymer to give iodide and hypoiodite. The ionic forms of iodine appear to associate with the molecular iodine, resulting in the final stable PVP-iodine complex.     

Extremes of censored and uncensored lifetimes in survival data

Extremes - We consider a random censoring model for survival analysis, allowing the possibility that only a proportion of individuals in the population are susceptible to death or failure, and the...