Search results for "isothermal"
showing 10 items of 212 documents
Effect of Nitrogen Methylation on Cation and Anion Coordination by Hexa- and Heptaazamacrocycles. Catalytic Properties of These Ligands in ATP Dephos…
1996
The stability constants of the complexes formed by 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane (L1) with Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+), as well as that for the formation of PbL2(2+) (L2 = 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu(2+) complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-hexaazacyclooctadecane (L3), and 1,4,…
Interactions of lysozyme with hydrophilic and hydrophobic polymethacrylate stationary phases in reversed phase chromatography (RPC)
1994
Two silicas, one with a mean pore diameter of 30 nm and the other non-porous, were coated with polymethacrylates of increasing hydrophobicity in the sequence: poly-2-hydroxyethylmethacrylate (P2HEMA)1 polyethylmethacrylate (PEMA) and poly-n-octylmethacrylate (POMA). Association constants, Kass, between lysozyme and the coated silicas were determined by means of frontal analysis, and the apparent heats of adsorption, delta Happ, by means of microcalorimetry. Using Kass and delta Happ the changes in the apparent free energy, delta Gapp, and in the apparent entropy, delta Sapp, were calculated at a concentration of lysozyme < 10 mumol/l. The association between the lysozyme and the coated sili…
Mechanisms and parameters controlling the tricalcium aluminate reactivity in the presence of gypsum.
2007
International audience; To understand the mechanisms and the parameters controlling the reactivity of tricalcium aluminate in the presence of gypsum at an early age, a study of the hydration of the “C3A–sulphate” system by isothermal microcalorimetry, conductimetry and a monitoring of the ionic concentrations of diluted system suspensions have been carried out with various gypsum quantities. The role of C3A source and its fineness were also studied. This work shows the fast initial formation of AFm phase followed by ettringite formation during the period when the sulphate is consumed. It has been highlighted that the time necessary to consume all the gypsum varies with the type of C3A and i…
Early C3A hydration in the presence of different kinds of calcium sulfate.
2009
International audience; Hydration reactions of C3A with various amounts of calcium sulfate hemihydrate, gypsum or a mixture of two, were investigated by isothermal microcalorimetry, and a monitoring of the ionic concentrations of diluted suspensions. This study shows that sulfate type used modifies the early C3A-CaSO4 hydration products and the rate of this hydration. The fast initial AFm formation observed before ettringite precipitation in the C3A-gypsum system is avoided as soon as hemihydrate is present in the suspension. This was attributed to.higher super saturation degrees and then higher nucleation frequency with regard to the ettringite obtained in the presence of hemihydrate. More…
Switching of easy-axis to easy-plane anisotropy in cobalt(ii) complexes
2021
A tetranuclear cubane-type complex [Co4(ntfa)4(CH3O)4(CH3OH)4] (1) with a {Co4O4} core, and a mononuclear complex [Co(ntfa)2(CH3OH)2] (2) have been rationally obtained by adjusting the ratio of the β-diketonate and Co(II) ions, with the synthetic processes being monitored by in situ microcalorimetry. Then, following synthetic conditions to obtain 2, but using three distinct N-donor coligands - 2,2'-bipyridyl (bpy), 6,6'-dimethyl-2,2'-bipyridyl (6,6-(CH3)2-bpy) and 5,5'-dimethyl-2,2'-bipyridyl (5,5-(CH3)2-bpy) - three novel mononuclear complexes have been obtained, [Co(ntfa)2(bpy)2] (3), [Co(ntfa)2(6,6-(CH3)2- bpy)2] (4) and [Co(ntfa)2(5,5-(CH3)2-bpy)2] (5). The introduction of different cap…
Microemulsions: Phase transitions and their dynamics
2007
By differential scanning microcalorimetry we investigate temperature-induced phase transitions and their dynamics in mixtures of water, oil and a non-ionic surfactant. Special emphasis is on an investigation of the transition from a lamellar to a microemulsion phase and on the emulsification failure. The first-order phase transition from a lamellar to a microemulsion phase leads to heat changes up to 1k BT per surfactant molecule. These large values for the latent heat are quantitatively described by an interfacial model which takes into account the temperature dependence of the spontaneous curvature.
The comparison of seven different methods to quantify the amorphous content of spray dried lactose
2006
The purpose of this work was to verify the usefulness, advantages and disadvantages of seven methods that are widely used to detect, and quantify the amorphous contents in pharmaceutical solids. Here, StepScan DSC, a type of modulated temperature calorimetry method, was applied for the first time to quantify amorphicity. The comparison of the analytical methods was undertaken with real (non-artificial) test samples, i.e. spray-dried lactose samples with various degrees of crystallinity. In these samples, it was essential that the amorphous and the crystalline portions are not present as separate particles, which is the case when physical (artificial) mixtures of totally amorphous and totall…
Effects of Ethanol to Water Ratio in Feed Solution on the Crystallinity of Spray-Dried Lactose
2002
In the present study, the effects of ethanol to water ratio in feed solution on the physical properties of spray-dried alpha-lactose monohydrate were evaluated. Crystallinity of the spray-dried lactose was determined by isothermal microcalorimetry (IMC) and by differential scanning calorimetry (DSC). Water content of the spray-dried lactose was determined by thermogravimetric analysis and the surface area was evaluated by Brunauer, Emmett, and Teller (BET) method. The crystallinity of spray-dried lactose varied from 0% to 100%, depending on the ratio of ethanol to water in the feed solution. Lactose spray dried from pure ethanol was 100% crystalline and contained hydrate water. Lactose spra…
Hydrophobic effects in the stabilisation of copper(I) by the macrocyclic ligands 16,17,19,20-tetramethyl-2,6,9,13-tetraaza[14]paracyclophane and 14,1…
1996
Abstract The interaction of Cu 2+ with the para -azacychlophanes 16,17,19,20-tetramethyl-2,6,9,13-tetraazal[14]paracyclophane (L1) and 14,15,17,18-tetramethyl-2,5,8,11-tetraaza[12]paracyclophane (L2) has been studied by potentiometry, and direct microcalorimetry at 298.1±0.1 K in 0.15 mol dm −3 NaClO 4 . The stability constants (log K CuLi = 13.35(3), log K CuL2 = 9.32(4)) and the thermodynamic parameters ( ΔH ° CuL1 = −47.3(8) kJ mol −1 , ΔH ° CuL2 = 20.9(8) kJ mol −1 ) evidence that not all four nitrogen atoms in the ligands are involved in the coordination to the metal centre. These results, particulary in the case of L1, are similar to those reported for the analogous cyclophanes contai…
Binding of Short Alkyl Chain Surfactants to the (Ethylene oxide)13−(Propylene oxide)30−(Ethylene oxide)13and (Ethylene oxide)75−(Propylene oxide)30−(…
2002
The enthalpy of transfer (ΔHt) of neutral copolymers, at a fixed and low concentration ca. 10-3 mol kg-1, from water to the aqueous surfactant solutions as a function of the surfactant concentration (fSmS) was determined at 25 °C. The surfactants studied are sodium octanoate, sodium decanoate, N-octylpyridinium chloride (OPC), and N,N-dimethyloctylamine-N-oxide (ODAO). The copolymers are (ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 (L64) and (ethylene oxide)75−(propylene oxide)30−(ethylene oxide)75 (F68). The two copolymers show different hydrophilic−hydrophobic ratios, the larger being for F68. As a general feature, the shape of the ΔHt vs fSmS curve depends on the nature of t…