Search Results
Abstract
Differential scanning microcalorimetry and equilibrium thermohemolysis procedure were used to study the effect of acclimation temperature on thermally induced transitions and thermoresistivity of fish (trout) erythrocyte membranes. Strong correlation has been found between the rates and activation energies of erythrocyte thermohemolysis and acclimation temperature. Transition temperatures of five thermodynamically irreversible and one partially reversible transitions at about 87C as well as the overall shape of microcalorimetric curves of the erythrocyte ghosts do not vary with acclimation temperature. The results suggest an essential conservation of phospholipid microenvironment of membrane skeleton proteins despite the compensatory response in lipid composition of erythrocyte membrane bilayer.
Abstract
The effect of Cr(VI) on Desulfovibrio vulgaris strain Hildenborough bioenergetic metabolism was monitored by microcalorimetry and the concomitant reduction of this metal was studied. Results showed that Cr(VI) is reduced by the bacterium and that the bacterial growth is altered, involving a strong modification of the metabolism of the bacteria. An absence of correlation between Cr(VI) reduction and cell growth is observed, suggesting that Cr(VI) does not yield energy to support anaerobic growth. The analysis of the enzymatic characteristics of Cr(VI) reduction are in progress.
Abstract
The interactions of lanthanide ions (Ln3+) with bovine serum albumin (BSA) under mimetic physiological conditions (310.15 K, pH 6.7, 0.1MNaCl) were studied by microcalorimetry. For the first time, based on Two Sets of Independent Sites Model, molar enthalpies (Δr H m1, Δr H m2) and coordination number (n 1, n 2) of the two sets of binding sites with different affinity were obtained directly from the microcalorimetric results. It was shown that the interactions are endothermic and entropy-driving processes. By combining with fluorescence spectroscopy, other thermodynamic parameters (Δr G m1, Δr S m1) were determined for high-affinity specific sites.
Abstract
Standard entropies of adsorption (Δs 0) of CO on different materials (Cu catalysts, Au catalysts, ZnO and to TiO2) are obtained from static adsorption microcalorimetry, adsorption isobars and temperature-programmed desorption, based on the thermodynamics of adsorption on energetically heterogeneous surfaces. Vibrational entropies of the surfaces s vib α are normally between the rotational and the standard translational entropy of CO in gas phase, and decrease with increasing adsorption energy, which agrees with the explanation of statistical thermodynamics. Δs 0 reflects both the mobility of adsorbates and the specific adsorbate-adsorbent interaction. Limits for reasonable values of the entropy of adsorption are proposed.
Abstract
Acidity and basicity of alumina-boria catalysts supported on porous or non-porous alumina have been studied by adsorption microcalorimetry of probe molecules (ammonia, pyridine and sulphur dioxide). Despite decreasing in initial heats, the total acidity as determined by ammonia adsorption increased in number and strength as a function of percentage of boron oxide. Ammonia, as a strong base, was shown to cover all types sites from strong to weak acid sites. Pyridine, as a weaker probe, was shown to dose only the stronger sites of the samples which stay nearly constant after B2O3 coverage approaching the monolayer. The basic sites of the amphoteric alumina support are neutralized by 10 wt% of boron oxide on non-porous alumina and 20 wt% of B2O3 on porous alumina. The catalytic activity for partial oxidation of ethane increased with acidity and reached a maximum constant value above 20 wt% of boron oxide.
Room-temperature interaction of n-hexane with ZSM-5 zeolites
Microcalorimetric and temperature-programmed desorption studies
Abstract
In this work, room temperature interaction of n-hexane with HZSM-5 (Si/Al=20) and ion-exchanged samples containing one (CuZSM-5, FeZSM-5 and MnZSM-5) or two transition-metal cations (Fe,CuZSM-5; Cu,MnZSM-5 and Fe,MnZSM-5) was studied by microcalorimetry and TPD methods. Both differential heats and the amounts of n-hexane adsorbed per one unit cell were quantitatively determined. Higher heats of adsorption and higher amounts of adsorbed gas were found for ion-exchanged samples than for HZSM-5. The experiments of n-hexane adsorption on hydrated samples were also performed. The amounts of n-hexane adsorbed on hydrated ZSM-5 were lower in comparison with dehydrated samples, while the energies of interaction were similar.
3 K/min to final temperature of 700 K. The adsorption-microcalorimetry experiments were carried out using an isothermal Tian–Calvet type microcalorimeter (BT 2.15 from SETARAM) combined with homemade volumetric–manometric device (a schematic
Investigation of the influence of NaCl concentration on Halobacterium salinarum growth
Microcalorimetry and transmission electron microscopy
Abstract
Microcalorimetry was used to study the influence of NaCl concentration on Halobacterium salinarum growth. From the thermogenic curves and thermokinetic parameters of H. salinarum growth in different concentrations of NaCl, it was found that the optimum NaCl concentration for H. salinarum growth was not a wide range from 3.5 mol L–1 to NaCl saturation (about 5.2 mol L–1), as is generally acknowledged, but just around 230 g L–1 (approximately 3.9 mol L–1). And when external NaCl concentration was above 230 g L–1, the growth metabolism of H. salinarum decreased constantly with the increasing of NaCl concentration. These have never been described before. Further investigation by transmission electron microscopy revealed that H. salinarum growing in approaching NaCl saturation underwent plasmolysis, which interpreted the novel finding of microcalorimetry perfectly. Our work shows that microcalorimetry may reveal more and newer details about microbial growth than the existing methods do. These details are significant to understand biological processes.
Abstract
The design of a rigorous experimental procedure is the basis for any environmental study. In this work, the basic criteria are established for determination of soil health using microcalorimetry as the main technique complemented by the study of physical (temperature, moisture, porosity, hydraulic conductivity, density and plasticity), chemical (pH and C to N ratio) and biological features (most probable number of microorganisms and organic matter content), and also environmental properties in the form of bioclimatic diagrams. The design was elaborated using as a reference a humic eutrophic-Cambisol subjected to afforestation with P. pinaster Aiton situated in Viveiro (Galicia, NW Spain). Main results of this study refer to total heat evolved during the processes (2.65 to 3.81 J g–1), time to reach the maximum of the peak from 16.17 to 19.29 h, and microbial growth rate constant from 0.0732 to 0.1043 h–1. These results change over the year as they are influenced by the action of environmental parameters over soil microbial activity. The results are in close agreement with some others previously reported using different experimental techniques.
Abstract
It is possible to estimate surface tension of high-energy solids combining the immersion microcalorimetry thermodynamics and Van Oss' model. In this study we have applied this method on talc and talc-chlorite samples in order to obtain thermodynamic values which permit to understand surface properties useful in the industrial applications of these solids. Some talcite samples are preferentially used in specific industrial applications because they are less hydrophobic or more lamellar. This method seems to be reliable to classify the solids and predict some properties.
