Search Results
Abstract
Isothermal heat conduction microcalorimetry was adopted as a novel characterization method to investigate the polymerization processes of silica when the combination of silica sol and potassium sodium silicate was stirred at 25.0, 35.0, and 45.0 °C. Thermodynamic and kinetic parameters were simultaneously obtained. The enthalpy change was greater at each higher temperature. The reaction orders (m, n) instantaneously varied, up and down in an alternate manner. At 25.0, 35.0, and 45.0 °C, the rate constants were different; the maximum rate constant occurred at 25.0 °C. These phenomena reflect a two-stage oligomeric mechanism of silica monomers. The measurements of particle size showed the complex chemical composition of aqueous silicates, which can be qualitatively designated by the particle size distribution in two parts. The results further indicate that the colloidal particles in the mixed silica sol and silicates first dissolved. Then the “active” silica in the silicates redeposited to make a distinct particle size distribution influenced by K+ and Na+ ions as well as by temperature.
Abstract
In a search for new storable high performance propellants for the European Space Agency (ESA), the solid oxidiser hydrazinium nitroformate (HNF) has been identified as a very promising ingredient for a new storable composite propellant. The purity and stability of HNF after production are very important indicators for the quality of HNF. In order to characterise HNF,many thermal analysis techniques as DSC and TG/DTA were performed to obtain more information about its stability and its (in)compatibility with other materials. Also some less familiar techniques such as the vacuum stability test and microcalorimetry have been performed. In relation to the safety, a relation between the friction and impact sensitivity and the physical-chemical properties is made.
The effect of m -alkoxyphenol compounds on the Chromobacterium violaceum respiration metabolic rate
Microcalorimetric and theoretical investigations
Abstract
A structure-activity relationship study (SAR) was applied to correlate the biological activities of m-alkoxyphenol compounds on Chromobacterium violaceum respiration with chemical structure properties. The biological activities of these compounds on metabolism rates were obtained through microcalorimetry. The calculations to estimate several physicochemical properties were carried out at the semi-empirical AM1 and ab initio DFT levels using the CEP-31G basis set and were parameterized using the continuum-solvation model COSMO for solvent contribution. m-alkoxyphenols properties were evaluated by chemometric analyses to carry out a correlation between the physicochemical properties and their biological effects. These compound effects increase with lateral hydrocarbon chain length, volume, dipole moment, proton affinity, energies of HOMO and LUMO, partition coefficient and enthalpy of formation and decrease with solvent effects and ionization enthalpy.
Abstract
The complexation of β-lactam antibiotics, amoxicillin (AMPC), ampicillin (ABPC) and benzylpenicillin (PCG), with 2-hydroxypropyl-β-cyclodextrin (HPCD) was studied at various pH values using microcalorimetry, 1H NMR spectroscopy, and molecular dynamic simulation. In the strong acid solution, two different types of inclusion complex with a 1:1 stoichiometry, Complex I with a phenyl ring of β-lactam antibiotics penetrated into the cavity of HPCD and Complex II with a penam included in the cavity, were formed by hydrophobic interaction, and Complex II was more stable than Complex I. In aqueous solution at pH≥4.5, only Complex I was formed, where the penam of PCG was more deeply penetrated into the cavity to keep it stable than those of AMPC and ABPC. The charged carboxyl-group on the penam was less affinity to form Complex II.
Abstract
Microcalorimetry was applied to study the effect of cephalosporins (cefazolin sodium and cefonicid sodium) on the E. coli growth. The microbial activity was recorded as power-time curves through an ampoule method with a TAM Air Isothermal Microcalorimeter at 37°C. The parameters such as the growth rate constant (k), inhibitory ratio (I), the maximum power output (P m) and the time corresponding to the maximum power output (t m) were calculated. The change tendencies of k, with the increasing of concentration (C) of the two cephalosporins, are similar which show that cefazolin sodium and cefonicid sodium have the same inhibitory mechanism. The experimental results reveal that cefonicid sodium has a stronger antibacterial activity towards E. coli than that of cefazolin sodium and this was coincide with the clinical manifestations.
Abstract
Using TAM III multi-channel calorimetry combined with direct microorganism counting (bacteria, actinomycetes and fungi) under laboratory conditions, we determined the microbial population count, resistance and activity toward cadmium (Cd(II)) and hexavalent chromium (Cr(VI)) toxicity in soil. The thermokinetic parameters, which can represent soil microbial activity, were calculated from power-time curves of soil microbial activity obtained by microcalorimetric measurement. Simultaneous application of the two methods showed that growth rate constant (k), peak-heat output power (P max) and the number of living microorganisms decreased with increasing concentration of Cd and Cr. The accumulation of Cr on E. coli was conducted by HPLC-ICP-MS. Cr6+ accumulation by Escherichia coli was increased steadily with increasing Cr6+ concentration. The results revealed that the change in some thermo-kinetic parameters could have good corresponding relationship with metal accumulation. Our work also suggests that microcalorimetry is a fast, simple, more sensitive, on-line and in vitro method that can be easily performed to study the toxicity of different species of heavy metals on microorganism compared to other biological methods, and can combine with other analytic methods to study the interaction mechanism between environmental toxicants and microbes.
Abstract
The identification of the calorimetric curves corresponding to liquid mixtures for different injection flows, given by a flow microcalorimeter, permits to classify in a kinetic way the studied mixtures. For this purpose, it is determined the establishment time constant of the mixture (τmix) that allows us to estimate the length occupied by the dissipation (through the parameter λmix) and thus to justify the sensitivity variation obtained in different chemical calibrations.
Abstract
The microcalorimetric method has been used to study the effects of cefpiramide and ceftizoxime sodium on the E. coli growth. The results revealed that these two cephalosporins may alter the metabolic way of the E. coli. Moreover, the lethal doses of cefpiramide and ceftizoxime sodium are 2.000 and 0.2000 μg mL−1, respectively. Combining with the relationships between growth rate constant (k), the maximum power output (P m ), the time corresponding to the maximum power output (t m ) and cephalosporins concentration (C), one can draw the conclusion that the ceftizoxime sodium has a stronger inhibition effects on the growth of E. coli than that of cefpiramide and they both have the possibility to induce the drug fever.
Abstract
The DSC curve of freeze-dried amorphous sucrose shows the glass transition, the crystallization and the melting (just before decomposition) of the sample. Sucrose crystallization occurs below 100°C: this phenomenon can therefore be observed with the microcalorimeter Setaram Micro-DSC used in the scanning mode. Mixtures of amorphous and crystalline sucrose in known proportions were used to calibrate the instrument. Low level amorphism (down to about 0.5%) could be detected and quantitatively evaluated on the basis of the crystallization enthalpies determined. The calibration curve obtained can be applied to determine the degree of amorphism in milled sucrose. A simple gravimetric method, based on the desorption of water induced by recrystallization of the amorphous layer can be used to obtain similar data more rapidly. This simple method is particularly useful for controlling the amorphism on line during a process, and is also briefly described.
