Authors:M. Arnal, V. Balsamo, G. Ronca, A. Sánchez, A. Müller, E. Cañizales, and C. Urbina de Navarro
A new technique to thermally fractionate polymers using DSC has been recently developed in our laboratory. The applications of the novel successive self-nucleation and annealing (SSA) technique to characterize polyolefins with very dissimilar molecular structures are presented as well as the optimum conditions to thermally fractionate any suitable polymer sample with SSA. For ethylene/-olefin copolymers, the SSA technique can give information on the distribution of short chain branching and lamellar thickness. In the case of functionalized polyolefins, detailed examinations of SSA results can help to establish possible insertion sites of grafted molecules. The application of the technique to characterize crosslinked polyethylene and crystallizable blocks within ABC triblock copolymers is also presented.
Authors:P. Mitchell, W. Schell, A. McGarry, T. Ryan, J. Sanchez-Cabeza, and A. Vidal-Quadras
Six peat cores taken from three unmodified blanket and raised bogs in Ireland were sectioned and analyzed for a range of radionuclides including134Cs,137Cs,238Pu,239Pu,241Am, and210Pb.134Cs and137Cs were measured by high resolution gamma-spectrometry, while the transuranium nuclides were determined after chemical separation by alpha-spectrometry.241Pu, present on the electroplated discs together with Pu(), was measured directly by low-level liquid scintillation counting. Core chronologies were established by measuring the unsupported210Pb component using low energy photon spectrometry (LEPS). From the resulting profiles, relaxation depths and migration rates for the above mentioned radionuclides have been determined and differences in the values of these parameters interpreted.238Pu/239,240Pu and241Pu/239,240Pu ratios have been examined carefully and are discussed in some detail. Finally, the contribution from Chernobyl to the total radiocaesium inventory in each core has been established using the134Cs/137Cs ratio observed in the initial fallout from Chernobyl.
Authors:P. Mitchell, J. Sanchez-Cabeza, T. Ryan, A. McGarry, and A. Vidal-Quatras
A number of soil and peat cores, sampled throughout Ireland from November 1987 to March 1988, have been analyzed for fallout caesium and plutonium. Specifically,134Cs and137Cs levels were measured by high resolution gamma spectrometry while238Pu and239,240Pu were determined after chemical extraction by alpha spectrometry. The inventories of these nuclides at the locations sampled have been calculated from the resulting profiles and, by extrapolation, preliminary estimates made of the cumulative deposition throughout Ireland. The relative contribution from weapons testing in the atmosphere and the Chernobyl accident to the total caesium inventory have been determined by the134Cs/137Cs isotopic ratio. As expected, no plutonium of Chernobyl origin was detected in surface layers. The cumulative238Pu/239,240Pu ratio measured in Irish soils was found to be consistant with mid-latitude ratios reported by others.
Authors:J. Cubero, V. Valero, D. Narciso, J. Sánchez, A. Rodríguez, and C. Barriga
The use of melatonin as antioxidant has been extensively established. But what would the antioxidant function be if one were to go one step back in the anabolism of that amine, and orally administer its precursor — the amino acid tryptophan? Diurnal animals (
) were administered orally capsules containing 125 or 300 mg L-tryptophan/kg b.w. for 7 days at the end of the light period (20
). A control group received capsules with methylcellulose. The antioxidant function was studied through the reduction of nitroblue tetrazolium (NBT) by superoxide anion, and through the levels of malonaldehyde (MDA) produced in the lipoperoxidation that occurs from the respiratory burst in response to the presence of a foreign particle in phagocytic cells (heterophils), which were extracted at 2
— at the acrophase of melatonin in the blood stream. In the heterophils extracted from the group that received 125 mg kg
b.w. tryptophan, there was less oxidative stress as determined by the NBT reduction than in those from the 300 mg kg
b.w. group. In the study of the lipoperoxidation of the membranes as determined by the levels of MDA, however, no significant variations were observed between the different groups. The lower concentration (125 mg L-tryptophan/kg b.w.), administered orally, succeeded in diminishing the free radicals produced in the heterophils for the destruction of the ingested foreign agent, but not fully or maximally. The possible solution to this prooxidant/antioxidant imbalance would be to administer a lower concentration of tryptophan to attain the perfect balance for application in nutritional treatments.
Authors:A. Borhidi, de la M. Luz Arreguín Sánchez, and R. Galván Villanueva
The Herbarium of the National School of the Biological Science (ENCB) of the Mexican National Polytechnics Institute is the second collection in size and importance among the herbaria of Mexico. According to its catalogue published in 1996 more than 1,000 type specimens of vascular plants are registered in it. In the year 2003 several undetermined collections were revised by the first author belonging to the Rubiaceae family. The result of this work was the description of 7 new species: Arachnothryx latiloba, A. michoacana, A. monticola, Bouvardia lottae, Guettarda guerrerensis, Psychotria diegoae, Rogiera variiflora and Psychotria rzedowskiana as a new name for P. izabalensis subsp. oaxacana.
Authors:C. Kremer, S. Domínguez, M. Pérez-Sánchez, A. Mederos, and E. Kremer
The heavy use of99mTc in nuclear medicine and the recent development of188Re radiopharmaceuticals have encouraged the comparative study of Tc and Re coordination compounds. In this work, the electrochemistry of [MVO2 (amine)2]+ (M=Tc, Re; amine = ethylenediamine, 1,3-diaminopropane, diethylenetriamine, triethylenetetramine) complexes is studied by cyclic voltammetry and the results are compared. The voltammograms of these compounds, obtained at different pH values, show that [ReO2(amine)2]+ cations are thermodynamically stable even when protonated. On the other hand, analogous Tc compounds are not so stable and easily decompose if existing as [TcO(OH) (amine)2]2+.
Authors:J. M. Criado, L. A. Pérez-Maqueda, and P. E. Sánchez-Jiménez
The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation
energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has
been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence
of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach
used for carrying out the kinetic analysis of TG data.
Authors:P. Sánchez-Soto, A. Ruiz-Conde, R. Bono, M. Raigón, and E. Garzón
The thermal evolution of a slate rock sample (Berja, Almería, Spain) has been studied. The phase minerals identified in this
sample were mica (illite), chlorite (clinochlore) and quartz as major components, with minor microcline, iron oxide and a
mixed-layer or interstratified phase (montmorillonite-chlorite). This slate is highly silico-aluminous (48.33 mass% silica,
22.04 mass% alumina), and ca. 20 mass% of other elements, mainly Fe2O3 (8.35 mass%), alkaline-earths and alkaline oxides.
Two main endothermic DTA effects, centered at 640 and 730°C, were observed. The more important contribution of total mass
loss (7.15 mass%) was found between 500–900°C, with two DTG peaks detected at 630 and 725°C. All these effects were associated
to the dehydroxylation of structural OH groups of 2:1 layered silicates mixed in the slate. The dehydroxylation of the layered
silicates evidenced by dilatometry, produced a rapid increase of expansion between 600–800°C. The thermal evolution of the
slate upper 800°C indicated the first sintering effects associated to shrinkage, which is also favoured by its low particle
size (average 23 μm) and the presence of a liquid or vitreous phase as increasing the heating temperature. The application
of thermal diffractometry to the slate sample allowed to study the formation of dehydroxylated crystalline phases from the
layered silicates after heating. At 1000°C, β-quartz, dehydroxylated illite, iron oxide, relicts of microcline and the vitreous
phase were present in the sample. All these results are interesting to know the thermal behaviour of a complex mineral mixture
as identified in the slate.
Authors:S. -P. Ding, J. Fan, J. L. Green, Q. Lu, E. Sanchez, and C. A. Angell
Trehalose dihydrate, on careful dehydration below its fusion point, retains its original crystal facets but becomes X-ray amorphous, an unusual example of direct crystal-to-glass transformation. From DSC studies, the glass obtained by this route seems to be of abnormally low enthalpy, but after an initial scan, the normal form of glass transition is exhibited, withTg=115‡C, a higher value than previously reported. We give a preliminary thermal and mechanical characterization of this material and find it to be a very fragile liquid. The highTg is shown to rationalize the exceptionally high water content of the trehalose+water solution that vitrifies at ambient temperature (i.e.Tg=298 K), and hence helps explain its use by Nature as a desiccation protectant. The spontaneous vitrification of crystalline materials during desolvation is related to the phenomenology of pressure-induced or decompression-induced vitrification of crystals via the concept of limiting metastability.
Authors:P. Sánchez-Soto, M. Villacampa, J. Ginés, A. Ruiz-Conde, M. Avilés, and M. Arias
Several derivatives containing a new organic ring system, the tropane-6-spiro-5′-hydantoin structure (namely 8-alkyl-8-azabicyclo
[3.2.1.] octane-6-spiro-5′-imidazoline-2′,4′-diones) have been characterized by thermal (DSC and simultaneous DTA-TG-DTG)
and spectroscopic techniques (IR,1 H-NMR,13 C-NMR). X-ray powder diffraction and elemental analysis were applied for structural and molecular characterization. All the
compounds melt in the range 160–250°C and undergo decomposition with progressive mass loss after the solid-liquid thermal
transition with molecular degradation. It was found that tropane-6-spiro-5′-hydantoin derivatives with the hydantoin ring
in β position are thermally less stable than those containing this ring in α position.