Kinetics of chlorination of tantalum pentoxide in mixture with sucrose carbon by chlorine gas

The mechanism and kinetics of β-Ta₂O₅ chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method, and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is 144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable mechanism for the carbochlorination of β-Ta₂O₅ is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta₂O₅, (3) oxidation of carbon, and (4) recrystallization of β-Ta₂O₅.     

Sources of GABAergic input to the inferior colliculus of the rat

We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.     

Detection of antibiotic resistance in Enterococcus sp. Comparison of GPS-TA (BioMérieux-Vitek), Uniscept MIC-3 (bioMérieux-Vitek) and conventional methods

BACKGROUND: The treatment of severe enterococcus infections requires synergism of a beta-lactamic or glycopeptide and a aminoglycoside, but when resistance to first one or high-level resistance to aminoglycosides are present, synergism would be lost. We compared the adequacy of two commercially available systems to detect antibiotic resistance. METHODS: We studied 158 isolates of Enterococcus sp., with high-level resistance to gentamicin (40 isolates) and streptomycin (89 isolates), resistance to ciprofloxacin (34 isolates), resistance to ampicillin (7 isolates) and with intermediate susceptibility to vancomycin (3 isolates). No one was beta-lactamase producer by Cefinase disk method. We use disk diffusion as reference technique to detect high-level streptomycin resistance. The susceptibility to the remainder antibiotics was studied by agar dilution method, according to NCCLS. We studied the accuracy of GPS-TA cards and Uniscept MIC-3 in relation to the degree of agreement with conventional means, following FDA criteria. RESULTS: Essential agreement for MIC was less than 90 with MIC-3 for ampicillin (81.5%) and ciprofloxacin (71.3%). Categorical agreement rate was less than 90% (76.4%) and major error rate was higher than 3% (10.9%) with the use of MIC-3 for ciprofloxacin. Very major errors for ampicillin, vancomycin and ciprofloxacin were not produced by any system. The very major error rates for high level resistance to gentamicin and streptomycin with GPS-TA card were 5 and 15.7%, respectively. CONCLUSIONS: We do not recommend the use of the Uniscept MIC-3 panel with visual reading to detect susceptibility to ciprofloxacin. Detection of high levels of aminoglucoside resistance by GPS-TA card should be supplemented with conventional techniques because of the high rate of major error. Due to the low number of strains that have been studied, we can not assure the suitability of these systems to detect ampicillin or vancomycin resistance.     

Dyslipemia in a population with a high rate of cardiovascular mortality

The activity of N-acetyltransferase (NAT) and catalase was measured in the tissues of placenta, full venous blood and full umbilical cord blood in 141 complicated pregnancies. The control group consisted of 34 physiological pregnancies. The enzymes activity was marked by use of biochemical methods. It has been shown that NAT and catalase is the most active in the group of physiological pregnancies. The decrease of NAT and catalase in venous and umbilical cord blood is correlated with the decrease of the activity these enzymes in placenta.     

Liver glutathione content and glutathione-dependent enzymes of two species of freshwater fish as bioindicators of chemical pollution

Glutathione content and glutathione-dependent enzymes were measured in the liver of two fish species, gudgeon (Gobio gobio) and roach (Rutilus arcasii), from the river Bernesga (Spain) caught downstream and upstream of the waste site of several chemical industries. Animals from contaminated sites display a reduced glutathione concentration and a tendency to the decrease of glutathione S-transferase activity. Glutathione peroxidase activity was significantly elevated only in the liver of Gobio gobio and glutathione reductase activity in that of Rutilus arcasii. Our data indicate that the glutathione system constitutes a sensitive biochemical indicator of chemical pollution. Relative changes of glutathione and glutathione-dependent enzymes in both fish species suggest a different susceptibility to toxins.