A note on the Σ1 collection scheme and fragments of bounded arithmetic

We show that for each n ≥ 1, if T₂ⁿ does not prove the weak pigeonhole principle for Σ^b_n functions, then the collection scheme B Σ₁ is not finitely axiomatizable over T₂ⁿ. The same result holds with Sⁿ₂ in place of T 2ⁿ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoredox chemistry of nitrosylpentacyanoferrate(II) in methanolic medium

The solvent complexes [Fe(CN)₅(CH₃OH]^2? and [Fe(CN)₅CH₃O]^3? were found to be the main products of the photochemical reactio     

Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.     

Solvent complexes of the type [FeIII(CN)5L]n−

The title complexes have been prepared in situ by photolyzing the [Fe(CN)₅NO]^2? ion in some aliphatic alcohols, formamide and its derivatives, pyridine, acetonitrile and dimethylsulphoxide. Characterization of the complexes was made on the basis of three pieces of evidence: (i) the spectral properties, (ii) the presence of the titratable hydrogen in the complexes with protogenic solvents, and (iii) the anation reaction with the N₃^? and NCS^? ions.     

Differential scanning microcalorimetry study of thermal stability of nevirapine and azidothymidine mixture

A differential scanning calorimetry study of the thermal behavior of nevirapine and azidothymidine in water solution was carried out. For nevirapine scan rate dependent and irreversible endothermic peak were found. Thermal degradation of nevirapine as well as NVP – AZT mixture is relatively well described by the model involving only one irreversible step determined by a first-order rate constant. The estimated kinetic constants and activation energies indicate that the degradation process proceeds slower for nevirapine in presence of AZT ligands than without them.     

Flotation method for separation of elemental Te with Se as collector

Summary A method combining co-precipitation of traces of elemental Te on Se as carrier with organic solvent flotation is described. The best reduction and flotation conditions (hydrochloric and phosphinic acid concentrations, amount of Se, solvent used) were chosen. The recoveries for 100g of Te(IV) (AAS measurement in MIBK) and 2g of Te (radiochemical measurement with¹²⁷Te) were 98% and 84–88%. The method was applied for separation of Te(IV) from copper metallurgy dust and slag.

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Flotationsverfahren zur Abtrennung von elementarem Tellur mit Selen als Kollektor

Zusammenfassung Die Kombination der Mitfällung von Spuren elementaren Tellurs auf Selen als Trägersubstanz mit der Flotation mit Hilfe eines organischen Lösungsmittels wurde beschrieben. Die besten Bedingungen zur Reduktion und Flotation (Salzsäure-und Phosphinsäurekonzentration, Selenmenge, Lösungsmittel) wurden ausgewählt. Die Wiederfindungsraten für 100g Te(IV) (AAS-Bestimmung in MIBK) und 2g Te (radiochemische Messung mit¹²⁷Te) waren 98% bzw. 84–88%. Das Verfahren wurde zur Trennung von Te(IV) aus dem Staub und der Schlacke der Kupfermetallurgie verwendet.

     

The interaction of formohydroxamic acid with carbon monoxide: FTIR matrix isolation and quantum chemistry studies

Argon matrix infrared spectra of the complexes formed between formohydroxamic acid (HCONHOH) and carbon monoxide have been recorded. The experimental results indicate formation of three isomeric complexes. In two complexes the NH or OH groups of formohydroxamic acid are attached to the carbon atom of the CO molecule and in the third complex the NH group interacts with the oxygen atom of CO. The formohydroxamic acid complex with two CO molecules is also trapped in the matrix. One of the two CO molecules interacts with the NH group and the second one with the OH group of HCONHOH, in both cases the site of interaction is the carbon atom of CO. Theoretical studies of the structure and spectral characteristics of the complexes were carried out on the DFT(B3LYP)/6-311++G(2d,2p) level. The calculated vibrational frequencies for the complexes present in the matrices are in good agreement with the experimental data. The calculations show also an additional potential energy minimum corresponding to the complex in which the OH group of formohydroxamic acid is attached to the oxygen atom of carbon monoxide.     

The interaction of formohydroxamic acid with nitrogen: FTIR matrix isolation and ab initio studies

Argon matrix infrared spectra of the complexes formed between formohydroxamic acid, HCONHOH (FHA) and nitrogen have been recorded. The experimental results indicate formation of two isomeric complexes in which the nitrogen atom of the N₂ molecule is attached to the NH or OH groups of FHA. Theoretical studies of the structure and spectral characteristics of the complexes were carried out on the MP2 level with the 6-311++G(2d,2p) basis set. The calculated vibrational frequencies for the complexes present in the matrices are in good agreement with the experimental data.     

Osmotic coefficients of aqueous rare-earth perchlorates and nitrates

Osmotic coefficients of aqueous solutions of La(ClO₄)₃, Pr(ClO₄)₃, Nd(ClO₄)₃, Sm(ClO₄)₃, Gd(ClO₄)₃, Dy(ClO₄)₃, Ho(ClO₄)₃, Er(ClO₄)₃, Tm(ClO₄)₃, Yb(ClO₄)₃, Lu(ClO₄)₃, Nd(NO₃)₃, Sm(NO₃)₃, and Gd(NO₃)₃ in the molality range from 0.1 mol kg^?1 nearly to saturation at 298.15 K have been determined by the isopiestic method. The results obtained agree very well with those of Rard et al. published recently. A distinct two-series effect has been observed for the constant-molality values of rare-earth perchlorates. The results are discussed in terms of hydration of the cations and ionic association.     

5-Dethia-5-oxacephams: toward correlation of absolute configuration and chiroptical properties

The relationship between chiroptical properties of differently substituted 5-dethia-5-oxacephams and their respective molecular structures was investigated. The amide chromophore of the beta-lactam unit in these compounds was found to be nonplanar with a shallow pyramidal configuration at the nitrogen atom. Due to the nonplanarity, the beta-lactam system becomes inherently dissymmetric, which is supported by a high magnitude of the n --> pi* CD band. It was also found that the helicity of the lactam moiety in investigated oxacephams is controlled by the absolute configuration at the C(6) carbon atom. On this basis, a helicity rule correlating a positive (negative) sign of the n right arrow pi Cotton effect with a negative (positive) O [double bond] C [bond] N [bond] C(6) torsional angle for policyclic beta-lactam derivatives possessing a nonplanar amide chromophore was formulated.