On the Analysis of the Mössbauer Spectra of the Rust Converted by Tannic and Phosphoric Acids

Hyperfine Interactions - In previous work, we reported results on the action of rust converters based on a mixture of tannic and phosphoric acids, upon the rust formed on mild steel coupons. There,...     

Achilleol B: a new tricyclic triterpene skeleton from Achillea odorata L

Achilleol B ( ), a new tricyclic triterpene, has been isolated from Achillea odorata L. and its structure established on the basis of its NMR data obtained through n.O.e., short and long-range homo and heteronuclear correlation experiments and other spectroscopic evidence.     

Landau Growth for Students Part I Initial Valuie Problem

This paper is internded to demonstrate to students that electron Landau growth of plasma waves is an easily understood and computed phenomenon. This derivation does not use the usual Fourier-Laplace transform technique with the inversion and final result being obtained by contour integration and residue theory. Instead, a simple treatment, following the original work of Vlasov, is used. Landau's original solution is recovered both for growth and decay, but only the growing part rigorously satisfies the initial assumptions.     

Steady cone-jet electrosprays in liquid insulator baths

This study shows that conducting liquids can be electrosprayed in steady cone-jet mode inside liquid insulator baths. Experimental results show that the current emitted from the meniscus fits well the scaling laws given in the literature for electrosprays in air at atmospheric pressure or vacuum. The technique may be of interest in obtaining fine liquid-liquid emulsions of uniformly sized droplets in the nanometric range.     

Mössbauer characterization of iron oxides and (oxy)hydroxides: the present state of the art

Mössbauer spectroscopy is a powerful direct technique for the identification and quantification of iron oxides and (oxy)hydroxides in soils and sediments. However, further characterization with respect to structural properties such as crystallinity, Al substitution, stoichiometry, water content, etc. is rather limited. With some examples of synthetic and natural goethite and hematite sample series it is illustrated that the hyperfine parameters depend on much more structural features than the Al content and crystallinity alone. Neither the Morin transition in hematite nor the Verwey transition in magnetite is directly applicable for analytical purposes in natural samples.     

First total synthesis of (-)-achilleol B: reassignment of its relative stereochemistry

The first total synthesis of (-)-achilleol B was achieved using a convergent approach with a longest linear sequence of 14 steps. Three key steps were employed, including an enantioselective Robinson annelation for the construction of the bicyclic moiety. The monocyclic synthon was prepared through a Ti(III)-mediated cylization of a chiral monoepoxide obtained via asymmetric dihydroxylation of geranylacetone. The asymmetric preparation of these subunits also permitted us to achieve the enantioselective synthesis of elegansidiol, achilleol A, and farnesiferol B.     

Complete assignments of 1H and 13C NMR data for trypanocidal eremantholide C oxide derivatives

The chemical transformations of eremantholide C (1), a trypanocidal sesquiterpene lactone isolated from Lychnophora trichocarpha Spreng., gave five new oxide derivatives: 3'-hydroxyeremantholide C (2), 1'-formyleremantholide C (3), 1'-carboxyeremantholide C (4), 1'-carbomethoxyeremantholide C (5) and sodium 1'-carboxylate of eremantholide C (6). The (1)H and (13)C NMR data of all these derivatives were assigned based on 1D and 2D techniques. The derivatives were evaluated against Y and CL strains of Trypanosoma cruzi. All of them were inactive against the Y strain. Compounds 2 and 5 displayed 100% activity on the CL strain while compounds 4 and 6 were partially active on the CL strain.     

Use of the plant Bellardia trixago for the enantiospecific synthesis of odorant products

An easy procedure to obtain extracts enriched in trixagol monomalonylesther (1) from aerial parts of the plant Belladia trixago chemotype Trix was developed. Preparation of (+)-dihydro-gamma-ionone (4) was carried out directly from the extracts with good yields by selective oxidation. Other interesting odorant products as alpha-ambrinol (5), ambraldehyde (6) and the tricyclic compound 7 were synthesized very efficiently using (4) as intermediate.     

Efficient synthesis of the anticancer β-elemene and other bioactive elemanes from sustainable germacrone

Highly efficient preparations of anticancer β-elemene and other bioactive elemanes were carried out using the natural product germacrone as a renewable starting material. The syntheses were achieved in only 3-5 steps with excellent overall yields (43-54%). An enantioselective approach to these molecules is also described.