A99Tc-ADP complex was prepared when KTcO4 was reduced in aquous medium by SnCl2, Na2S2O4, NaBH4 or Zn in the presence of ADP in excess. The resulting solution was studied by chromatography and spectrophotometry. Electrochemical reduction and substitution on [TcIII(tu)6]3+ were investigated as alternative synthetic routes. The anionic Tc-ADP complex was isolated as a solid. Cerimetric titrations confirmed the oxidation state +3 for the central atom. IR and1H-NMR data showed that the purine base is bonded to the Tc central atom but not the ribose moiety. No oxo groups seemed to be directly bonded to the Tc atom. The complex is rather stable in neutral solutions. However, it decomposes to pertechnetate and TcO2 at extreme pH values.
Authors:M. López Manchado, J. Biagiotti, L. Torre, and J. Kenny
The effect of the incorporation of an amorphous immiscible polymer (ethylene-propylene-diene- terpolymer) on the PP crystallization
kinetics and thermodynamics is investigated by thermal analysis. The results of the investigation have shown that EPDM acts
as a nucleant agent. A marked decrease of the half time of PP crystallization, τ1/2 , as well as a sensible increase of the overall crystallization rate, Kn , has been observed in the presence of EPDM. Moreover, at any crystallization temperature, a minimum of τ1/2 , is obtained at 25% EPDM content in the blend. The Avrami model has been successfully applied to describe the crystallization
kinetics of the blend. The kinetic curves obtained under non-isothermal conditions confirm the results obtained under isothermal
conditions and demonstrate the nucleant action of the EPDM phase on the PP crystallization.
Authors:J. Santana, L. Lima, J. Torres, F. Martínez, and S. Olivares
Vegetable tannin sorbent is evaluated as ion exchange resin using a multitracer study on the adsorption behavior of various elements. Lisiloma latisiliqua L. tannins, polycondensated into spherical pellets were chosen as sorbent resin material. Sorption evaluation of Ce, Cu(II), U(VI), Eu, Fe(III), Th, Nd as representatives of different classes of metal ions were done at different pH values. The distribution ratio of the studied elements was calculated from laboratory experiments. Tannic ion exchange material shows excellent ability for actinides and rare earth elements adsorption from waters. Using radiotracers, the number of catechins subunits involve in each tannin-metal complex was determined.
Authors:A. Negrón-Mendoza, G. Albarrán, C. Treviño, and J. Torres
The gamma radiolysis of malonic acid, succinic acid and their corresponding nitriles was carried out over a wide interval of radiation doses. The radiolytic products detected were H2, CO2, CO, NH3 and carboxylic acids. The results obtained supported the hypothesis that in the prebiotic milieu, ionizing radiation might have contributed to the synthesis of compounds of relevance in biological systems.
Authors:E. Torres-Garcia, J. Balmaseda, L. del Castillo, and E. Reguera
Divalent transition metal nitroprussides form a family of microporous
materials which lose their crystallization water (coordinated and zeolitic)
below 100°C and then remain stable up to above 150°C. The dehydration
process of representative samples in their stable phases was studied by thermo-gravimetry
(TG) and differential scanning calorimetry (DSC). The copper complex dehydrates
in a single step through a practically irreversible process. For cadmium and
cobalt complexes the water evolution on heating takes place in two stages.
The first one, where only zeolitic waters are removed, is dominated by a diffusion
mechanism while, during the loss of the strongly bonded waters (second stage)
the material framework effect is added. The involved activation energy and
its dependence on the conversion degree were estimated evaluating the thermo-gravimetric
data according to an isoconversion model.
Authors:E.A. Franceschi, P.S. Torres, and J.P. Lewis
The floodplain herbaceous vegetation of the Paraná River (Argentina) was destroyed by a catastrophic extraordinary flood in 1982-83. The main communities were Panicum prionitis tall grasslands. According to a succession model, they were seral communities that would have evolved to hygrophilous forest. After the flood, the area was surveyed in 1984, 1988 and 2002 and analyzed with numerical methods. First, the area was invaded by a community of annual species, which were the sparse species of tall grasslands, but five years after the colonization this community disappeared and was replaced by the original tall grasslands and turfs. The tall grasslands rapid recovery and the absence of woody species support the hypothesis that this community is a stable community which was rejuvenated by catastrophic floods and was prevented to develop into woody species communities.
Authors:T. Cabello, M. Gámez, A. Torres, and J. Garay
Insect parasitoids have been widely studied, particularly due to their ecological implications through the study of the special relationships observed among this kind of species, as well as to their expression in mathematical models. However, there are still scarce studies on parasitoid relationships and their expression in more realistic mathematical models. The present work is aimed at deepening into competition relationships among parasitoids. Bearing this purpose in mind, the system shaped by two parasitoids was chosen: Trichogramma brassicae (idiobiont egg parasitoid) and Chelonus oculator (koinobiont egg-larval parasitoid). Both species compete against each other for the same host species (Lepidoptera). The results obtained in the laboratory point out that T. brassicae may be considered a better competitor than Ch. oculator. This is the result of the extrinsic competition due to the substances injected by the female during parasitization. However, our results show this classification into better and worse competitors inaccurate. Thus, these interspecific competition influences are detrimental to both parasitoid species. This is the first time that the effect of this competition is mentioned regarding parasitoid functional response. Our results and their ecological implications are reported and discussed.
Authors:A. Jiménez, A. Iannoni, L. Torre, and J. Kenny
Thermogravimetric analysis (TG) was used in this work to study the degradation kinetics of industrial PVC plastisols. In order
to model the pyrolitic degradation of plastisols in nitrogen, a kinetic model based on phenomenological considerations was
developed. Two different processes were observed during the first degradation stage. The model parameters, such as activation
energies and pseudo orders of reaction, were calculated using a non-linear regression analysis. The model developed was able
to describe the degradation behaviour both in isothermal and in dynamic modes. The results of such analysis were applied to
obtain long-term data from short-term experiments as an engineering approach to evaluate the thermal resistance of plastisols.
Authors:B. Zapata, J. Balmaseda, E. Fregoso-Israel, and E. Torres-García
Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis.
According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its
three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas
products were mainly CO2, CO, and CH4. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H2O was also detected. The Eα on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is
controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds.
These results could explain the non-autocatalytic character of the reactions during the decomposition process.