Mössbauer studies on some Argentinian soil: Mollisols from Bahia Blanca

Clay fractions of a Mollisol sample as is, treated with ammonium oxalate (AO), with dithionite-citrate-bicarbonate (DCB) and with dithionite-ethilene-diamine-tetraacetic acid (D-EDTA) methods, were studied. Illite-montmorillonites together with hematites, goethites and maghemites, all of the AI-substituted and with a wide range of sizes, were identified. It is found that the AO attack extracts little iron, whereas the other two attacks extract the magnetic signal. Furthermore, the DCB attack facilitates the reduction of the Fe³⁺ ions, while the D-EDTA method does not. Instead, this attack extracts more clay mineral Fe ions. A comparison with large grain soil samples is made.     

Computational studies of the 3-Dimensional structure of cyclopenta polycyclic aromatic hydrocarbons containing a gulf region

Recently, some cyclopenta-fused polyaromatic hydrocarbons, an environmentally relevant subclass of chemicals, have been shown to have carcinogenic activity in animals. It has been suggested that benz[l] aceanthrylene ( I ), an active member of this subclass with a gulf region, has a trans dihydrodiol metabolite that is nonplanar and has two distinct spatial configurations. We have used MMP 2(85) and AM 1 to investigate the three-dimensional structure of this dihydrodiol and other similar derivatives of ( I ) and have found that although ( I ) is somewhat nonplanar the relevant derivatives are all nearly planar. Further, we have computed potential functions for the bending of the angular ring in the gulf region using MMP 2(85), AM 1, and ab initio computed energies for AM 1 spatial configurations and find that these molecules all have only a single potential minimum. We have performed the same calculations for benzo[c]phenanthren and its 1,12 dimethyl derivative, molecules with a similar gulf region for which crystallographic data exists. In agreement with that data, we find that two distinct spatial configurations exist separated by significant barries. The differences between the results generated by the three different methods of computation will be discussed.     

Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane

Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.     

Absence of magnetic hyperfine field on 99Ru in chromium

The dilute impurity hyperfine field on ruthenium nuclei in a chromium matrix has been measured to be zero in the temperature range 2.3–330 K using the time-differential perturbed angular correlation technique. Possible mechanisms responsible for the observed result are discussed.     

1,3-Diyl trapping reactions. Fundamental investigations with application to the synthesis of linearly fused tricyclopentanoids

A comparison of the inter- and intramolecular diyl trapping routes to linearly fused tricyclopentanoids is presented. In addition, several of the factors which are responsible for the stereoselectivity which is associated with the intramolecular process are examined and it is concluded that conformational rather than electronic (secondary orbital) factors play the dominant role. It is shown that gem methyl groups located on the acyclic chain which joins the diyl and diylophile (in reference to 32 and 35, but not to 47) have no practical effect upon the outcome of the trapping reaction. The intramolecular process is stereospecific with respect to diylophile geometry, and highly stereoselective with respect to the ring junction stereochemistry. Finally, an abortive attempt to synthesize the marine natural product Δ⁹⁽¹²)-capnellene (19) as well as a successful synthesis of the mold metabolite d,l- hirsutene (18) is presented.     

Potassium N‐(6‐oxo­cyclo­hexa‐1,3‐dien‐5‐yl­idene­methyl)­glycinate

We are very interested in characterizing ligands derived from salicyl­aldehyde and α‐amino acids. These ligands form interesting complexes with different transition metals, which are very useful for understanding some biological systems. For Schiff bases derived from salicyl­aldehyde and different alkyl­amines or aryl­amines, the enol–imine form is predominant. The title compound, (I), shows bond distances which are clearly in agreement with the keto–amine form.     

Correction to: Finite Element Approximation of the Spectrum of the Curl Operator in a Multiply Connected Domain

Foundations of Computational Mathematics - In the published article, Figure 5 corresponds to an eigenfunction associated not with the first smallest positive eigenvalue.     

Automorphisms for Skew PBW Extensions and Skew Quantum Polynomial Rings

In this work, I study the automorphisms of skew PBW extensions and skew quantum polynomials. I use Artamonov's works as reference for getting the principal results about automorphisms for generic skew PBW extensions and generic skew quantum polynomials. In general, if I have an endomorphism on a generic skew PBW extension and there are some x _i , x _j , x _u such that the endomorphism is not zero on these elements and the principal coefficients are invertible, then endomorphisms act over x _i as a _i x _i for some a _i in the ring of coefficients. Of course, this is valid for quantum polynomial rings, with r = 0, as such Artamonov shows in his work. We use this result for giving some more general results for skew PBW extensions, using filtred-graded techniques. Finally, I use localization to characterize some class the endomorphisms and automorphisms for skew PBW extensions and skew quantum polynomials over Ore domains.