Oxidation of natural targets by dioxiranes. Part 6: on the direct regio- and site-selective oxyfunctionalization of estrone and of 5α-androstane steroid derivatives

Using methyl(trifluoromethyl)dioxirane (1b), 3β,6α,17β-triacetoxy-5α-androstane (6) could be selectively transformed into its C-14 hydroxy derivative (7) and into the valuable C-12 ketone steroid (8), in high yields under mild reaction conditions. Similarly, the oxidation of 3α-estrone acetate (4) with 1b was carried out to yield selectively the steroid C-9 hydroxy derivative (5). The high regio- and site-selectivity attained demonstrates that the powerful dioxirane 1b is the reagent of choice to synthesize valuable oxyfunctionalized steroid derivatives.     

Calix[4]azacrowns as ionophores for liquid?Cliquid extraction and facilitated transport of biological supramolecular complexes

The native and methyl ester amino acids have been extracted by calix[4]azacrowns 1 (1,3-[ethylene-bis-aminocarbonylmethoxy)]-p-tert-butylcalix[4]arene) and 2 (1,3-[propylene-bis-aminocarbonylmethoxy)]-p-tert-butyl-calix[4]arene) from an aqueous phase into a chloroform phase and transported through a chloroform liquid membrane as ion pairs in the presence of picrate or tropaeolin 00 as counter ions aiming their separation. The amino acids under study exhibited good extractability by calix[4]azacrowns 1 and 2. Both receptors 1 and 2 showed good extractability towards amino acids under study. The results are discussed in term of correlation of structural properties of amino acids and calix[4]azacrowns involved in experiments. In this respect, the influence of chain length of receptors upon extraction and transport of amino acids, and the nature of anions used as counter ions are evaluated.     

Understanding the pyrolysis of CCA-treated wood: Part II. Effect of phosphoric acid

The pyrolysis process of chromated copper arsenate-treated wood impregnated with phosphoric acid (2–6 wt.%) has been investigated using a Kugelrohr short-path distillation apparatus. The presence of phosphoric acid is shown to change the overall pyrolysis kinetics and yields of products resulting in a decrease in the amount of volatile products and an increase in the char formation. The yield of levoglucosan was found to decrease in the presence of relatively higher concentrations of phosphoric acid, while the yield of levoglucosenone increased. The pyrolysis of chromated copper arsenate-treated wood in the presence of phosphoric acid gave rise to 22% (on water-free tar basis) levoglucosenone. Such data demonstrates the potential for a new pathway toward the rational utilization of chromated copper arsenate-treated wood waste.     

Anamorsin is a [2Fe-2S] cluster-containing substrate of the Mia40-dependent mitochondrial protein trapping machinery

Human anamorsin was implicated in cytosolic iron-sulfur (Fe/S) protein biogenesis. Here, the structural and metal-binding properties of anamorsin and its interaction with Mia40, a well-known oxidoreductase involved in protein trapping in the mitochondrial intermembrane space (IMS), were characterized. We show that (1), anamorsin contains two structurally independent domains connected by an unfolded linker; (2), the C-terminal domain binds a [2Fe-2S] cluster through a previously unknown cysteine binding motif in Fe/S proteins; (3), Mia40 specifically introduces two disulfide bonds in a twin CX(2)C motif of the C-terminal domain; (4), anamorsin and Mia40 interact through an intermolecular disulfide-bonded intermediate; and (5), anamorsin is imported into mitochondria. Hence, anamorsin is the first identified Fe/S protein imported into the IMS, raising the possibility that it plays a role in cytosolic Fe/S cluster biogenesis also once trapped in the IMS.     

Fostering and Understanding Iron Detection at the Ultratrace Level by Adsorptive Stripping Voltammetry with Catalytic Enhancement

Iron detection at the ultratrace level in seawater is at the forefront in chemical oceanography research and analytical methodologies for its determination are actively sought. Voltammetric methods and specifically cathodic stripping voltammetry (CSV) with catalytic enhancement, are particularly fit for this purpose as they avoid any separation and pretreatment step, showing high sensitivity and robustness towards the saline matrix. Here we introduce a simplification in the instrumentation for iron detection by CSV using 2,3‐dihydroxynaphthalene (DHN) as the ligand, atmospheric oxygen as the catalytic enhancer and a small 0.5 mL cell. The simplification involves the use of a standard, non‐specialized voltammetric cup as a holder for the small cell and the introduction of a simple silver wire as a pseudoreference electrode. The latter reduces the risk of sample contamination and is perfectly suited for employment with the small, 0.5 mL volume cell. Extensive optimization was performed in both ultrapure and seawater: a square wave frequency of 10 Hz was adopted, whereas the ligand concentration did not significantly influence the limit of detection (around 10 and 40 pM for ultrapure and seawater, respectively). The latter difference in signal to noise ratio was explained by the kinetics of iron complex reduction. The method was successfully validated by the analysis of a seawater sample with consensus value.     

The formation of alkali and alkaline earth cation complexes with cucurbit[6]uril in aqueous solution: a critical survey of old and new results

The solubility of cucurbit[6]uril in aqueous and in different solutions of alkali and alkaline earth salts has been measured. Due to the complex formation the solubility of the ligand increases. From this increase the stability constants of the cations are calculated. The solubility of cucurbit[6]uril in salt solutions after extrapolation to zero salt concentrations differs from salt to salt. These values of the solubility are different from the direct measured value of the solubility. The measured values of the stability constants with different salts are in accordance with most of the values reported. However, the presented method for the calculation of stability constants fails if the values of the stability constants exceed a certain value. This limiting value depends on the solubility of the ligand examined.     

Multivariate analysis of laser-induced breakdown spectroscopy chemical signatures for geomaterial classification

A large suite of natural carbonate, fluorite and silicate geological materials was studied using laser-induced breakdown spectroscopy (LIBS). Both single- and double-pulse LIBS spectra were acquired using close-contact benchtop and standoff (25 m) LIBS systems. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to identify the distinguishing characteristics of the geological samples and to classify the materials. Excellent discrimination was achieved with all sample types using PLS-DA and several techniques for improving sample classification were identified. The laboratory double-pulse LIBS system did not provide any advantage for sample classification over the single-pulse LIBS system, except in the case of the soil samples. The standoff LIBS system provided comparable results to the laboratory systems. This work also demonstrates how PCA can be used to identify spectral differences between similar sample types based on minor impurities.     

The relationship between catalyst precursors and chain end groups in homogeneous propene polymerization catalysis

The chain transfer to monomer reactions promoted by primary and secondary growing chains in the propene polymerization promoted by ansa‐zirconocenes and postmetallocene precursors are studied by using DFT methods. From the theoretical results it comes out that the prevalence of propene insertion over β‐hydrogen transfer to the monomer decreases drastically in the presence of a secondary chain. Furthermore, we explained the reason why C₂‐symmetric metallocene catalysts promote the selective formation of cis but‐2‐enyls end group after a 2,1 inserted unit whereas for octahedral bis(phenoxy‐imine)titanium‐based catalysts, chain release promotes exclusively the formation of allyl terminated chain end. These results might be useful to design ligand precursors able to obtain not only high M_n PP polymers but also tuned chain end groups to build new polymer architectures. Overall, a more general picture of the enantioselectivity of the chain transfer to monomer processes is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 699–708, 2010