Mössbauer studies of heterobimetallic and heterotrimetallic compounds containing iron and tin

A series of ferrocene derivatives was prepared and studied by⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy, as well as by other techniques such as NMR and IR spectroscopies. These complexes can be divided into three types: mercurated, organotin derivatives of ferrocene, and bi- and trimetallic derivatives of 1,1-bis(diphenylphosphino)ferrocene. Iron did not show great variation in its Mössbauer parameters in the compounds, in spite of their diversity; tin, however, gave important Mössbauer data for the elucidation of bonding and structural features of the complexes.     

The effect of acidity behaviour of Y zeolites on the catalytic degradation of polyethylene

Thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses were used to investigate the effect of the acidity behaviour of Y zeolites on the catalytic degradation of polyethylene (PE). The acidity behaviour of these zeolites was modified by ion exchange treatments. Two Y zeolites with similar Si/Al atomic ratios were subjected to an ion exchange treatment using NaNO₃ for H-form (HY) and NH₄NO₃ for Na-form (NaY). The activity and the deactivation behaviour of the Y zeolites were determined in the samples by TGA measurements, using a polymer/catalyst ratio of 9:1. The sample residues obtained after an isothermic TGA, were analysed by DSC, in order to evaluate the crystallinity of each mixture. The HY zeolite, which has the strongest acidity, reduced the onset temperature resulting in more rapid degradation of the polymer. It is shown that the ion exchange treatment over Y zeolites enhances the selective catalytic degradation of polymer in detriment of the rapid deactivation.     

A new generation of track etched membranes for microfiltration and ultrafiltration. Part I. Preparation and characterisation

A new experimental apparatus for porous track etched membrane production has been designed, tested and installed near the core of the IEA-R1 nuclear reactor at IPEN-Sao Paulo. The thermal neutron flux close to the centre of the reactor core has been used to produce fission fragments from uranium sample which was deposited on a rod located at the centre of an evacuated aluminium chamber.     

Minor gamma-lactones from Trichilia catigua (Meliaceae) and its precursors by GC-MS

NMR and GC-MS analysis of fractions of the CHCl3 extract of Trichilia catigua bark led to the identification of a mixture of three omega-phenyl alkanes, three omega-phenyl alkanoic acids, five omega-phenyl-gamma-lactones, two alkyl-gamma-lactones, one alkenyl-gamma-lactone and a mixture of fatty acids ranging from C-14 to C-26. Beta-sitosterol, stigmasterol and campesterol as free alcohols were also identified.     

Determination of molybdenum in silicates by flame atomic absorption spectrometry exploiting activated carbon as collector

An analytical procedure has been developed for molybdenum determination in geological silicate materials using flame atomic absorption spectrometry (injection method), after sorption of the molybdenum-ammonium pyrrolidinedithiocarbamate complex (MoAPDC) on activated carbon.     

A stable lipase fromCandida lipolytica

Although Upases have been intensively studied, some aspects of enzyme production like substrate uptake, catabolite repression, and enzyme stability under long storage periods are seldom discussed in the literature. This work deals with the production of lipase by a new selected strain ofCandida lipolytica. Concerning nutrition, it was observed that inorganic nitrogen sources were not as effective as peptone, and that oleic acid or triacylglycerides (TAG) were essential carbon sources. Repression by glucose and stimulation by oleic acid and long chain TAG (triolein and olive oil) were observed. Extracellular lipase activity was only observed at high levels at late stationary phase, whereas intracellular lipase levels were constant and almost undetectable during the cultivation period, suggesting that the produced enzyme was attached to the cell wall, mainly at the beginning of cultivation. The crude lipase produced by this yeast strain shows the following optima conditions: pH 8.0–10.0, temperature of 55°C. Moreover, this preparation maintains its full activity for at least 370 d at 5°C.     

Crystalline Structure of Mangiferin,a C‐Glycosyl‐Substituted 9H‐Xanthen‐9‐one Isolated from the Stem Bark of Mangifera indica

The crystalline structure of mangiferin (=2‐β‐D ‐glucopyranosyl‐1,3,6,7‐tetrahydroxy‐9H‐xanthen‐9‐one; 1 ), a biologically active xanthenone C‐glycoside, isolated from the stem bark of Mangifera indica (Anacardiaceae), was unambiguously determined by single‐crystal X‐ray diffraction (XRD). The crystal structure is summarized as follows: triclinic, P1, a=7.6575(5), b=11.2094(8), c=11.8749(8) Å, α=79.967(5), β=87.988(4), γ=72.164(4)°, V=955.3(1) ų, and Z=2. The structure also shows two molecules in the asymmetric unit cell and five crystallization H₂O molecules. The packing is stabilized by several intermolecular H‐bonds involving either the two symmetry‐independent mangiferin molecules 1a and 1b , or the H₂O ones.     

Adsorption of phenylphosphonic acid on GaAs (100) surfaces

The adsorption of phenylphosphonic acid (PPA) on GaAs (100) surfaces from solutions in acetonitrile/water mixtures was studied using Fourier transform infrared spectroscopy in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and atomic force microscopy (AFM). ATR/MIR in situ showed that the accumulation of PPA molecules near the GaAs surface increased with the water concentration in the solution. For water contents lower than 4%, ATR/MIR and XPS results are consistent with the formation of a low-density monolayer. A mechanism is proposed for H2O percentages lower than 4% involving the creation of interfacial bonds through a Br?nsted acid-base reaction, which involves the surface hydroxyl groups most probably bound to Ga. It was found that the morphology of the final layer depended strongly on the water concentration in the adsorbing solution. For water concentrations equal to or higher than 5%, the amount of adsorbed molecules drastically increased and was accompanied by modifications in the infrared spectral region corresponding to P-O and P=O. This sudden change indicates a deprotonation of the acid. XPS studies revealed the presence of extra oxygen atoms as well as gallium species in the layer, leading to the conclusion that phosphonate and hydrogenophosphonate ions are present in the PPA layer intercalated with H3O+ and Ga3+ ions. This mechanism enables the formation of layers approximately 10 times thicker than those obtained with lower H2O percentages. HREELS indicated that the surface is composed of regions covered by PPA layers and uncovered regions, but the uncovered regions disappeared for water contents equal to or higher than 5%. XPS results are interpreted using a model consisting of a monolayer partially covering the surface and a thick layer. This model is consistent with AFM images revealing roughness on the order of 7 nm for the thick layer and 0.2-0.5 nm for the thin layer. Sonication proves to be an effective method for reducing layer thickness.