J.C. van Miltenburg

Synthesis of strontium and barium cerate and their reaction with carbon dioxide

The log p co2 versus 1/T relationships of the equilibria (1) ACO 3 +CeO 2 ⇄ACeO 3 +CO 2 and (2) ACO 3 ⇄AO+CO 2 , in whichA=Sr or Ba, were investigated. The methods which have been used are: thermodynamic equilibrium calculations, simultaneous thermogravimetry-differential thermal analysis and high-temperature X-ray diffraction. In pure N 2 atmosphere, the synthesis of the cerates proceeds via (1) ACO 3 -AO+CO 2 and (2) AO+CeO 2 -ACeO 3 , which is not calculated thermodynamically, but is apparently kinetically more favourable at low temperatures. SrCeO 3 and BaCeO 3 react with 1 atm CO 2 below 1190 o C and 1185 o C,respectively. For mixtures of CO 2 with other gases, the decomposition temperatures can be estimated from the figures presented

The vapour pressure of solid and liquid naphthalene

Abstract Vapour-pressure measurements of solid and liquid naphthalene between 270 and 385 K are reported. The results were obtained by a static method employing two diaphragm manometers calibrated on a dead-weight gauge. Results can be summarized with the following quantities: δG ° sub (298.15 K) = −(5989.4±4) J mol −1 , δH ° sub (298.15 K) = (72.513±0.07) kJ mol − , δC ° p sub (298.15 K) = −(57.5±4) J K −1 mol −1 , δG ° vap (373.00 K) = −(24161±6) J mol −1 , δH ° vap (373.0 K) = (50.25±0.15) kJ mol −1 .

Phase behavior of stratum corneum lipids in mixed Langmuir-Blodgett monolayers

The lipids found in the bilayers of the stratum corneum fulfill the vital barrier role of mammalian bodies. The main classes of lipids found in stratum corneum are ceramides, cholesterol, and free fatty acids. For an investigation of their phase behavior, mixed Langmuir-Blodgett monolayers of these lipids were prepared. Atomic force microscopy was used to investigate the structure of the monolayers as a function of the monolayer composition. Three different types of ceramide were used: ceramide extracted from pigskin, a commercially available ceramide with several fatty acid chain lengths, and two synthetic ceramides that have only one fatty acid chain length. In pigskin ceramide-cholesterol mixed monolayers phase separation was observed. This phase separation was also found for the commercially available type III Sigma ceramide-cholesterol mixed monolayers with molar ratios ranging from 1:0.1 to 1:1. These monolayers separated into two phases, one composed of the long fatty acid chain fraction of Sigma ceramide III and the other of the short fatty acid chain fraction of Sigma ceramide III mixed with cholesterol. Mixtures with a higher cholesterol content consisted of only one phase. These observations were confirmed by the results obtained with synthetic ceramides, which have only one fatty acid chain length. The synthetic ceramide with a palmitic acid (16:0) chain mixed with cholesterol, and the synthetic ceramide with a lignoceric acid (24:0) chain did not. Free fatty acids showed a preference to mix with one of these phases, depending on their fatty acid chain lengths. The results of this investigation suggest that the model system used in this study is in good agreement with those of other studies concerning the phase behavior of the stratum corneum lipids. By varying the composition of the monolayers one can study the role of each lipid class in detail.

Construction of an adiabatic calorimeter measurements of the molar heat capacity of synthetic sapphire and of n-heptane

Abstract The construction of an adiabatic calorimeter for the temperature range between 10 and 350 K is described. Emphasis is given to the construction of the cryostat and the regulation of the shields. For a measurement of heat capacity from 5 to 100 K about 3 to 4 dm 3 of liquid helium is needed. The performance of the apparatus was checked by measuring the molar heat capacity of a standard sample of synthetic sapphire and of a sample of n -heptane. Results are within 0.2 per cent of the accepted literature values.

Thermodynamic properties of molecular organic crystals containing nitrogen, oxygen, and sulphur 1. Vapour pressures and enthalpies of sublimation

Abstract We report the enthalpies of sublimation of 28 organic substances containing nitrogen, oxygen, and sulphur. The enthalpies of sublimation are derived from the dependence of vapour pressure on temperature. We used both the dynamical method as combined mass-loss effusion and torsion effusion, and a static method.

The heat capacity and derived thermodynamic functions of La2Zr2O7 and Ce2Zr2O7 from 4 to 1000 k

Abstract The heat capacities of cerium and lanthanum zirconate (Ce 2 Zr 2 O 7 and La 2 Zr 2 O 7 ) were measured from 4 to 400K by adiabatic calorimetry. The derived thermodynamic functions, H °, S ° and {G ° − H °(0)} T were calculated. The standard molar entropies at 298.15K were determined as 230.21 ± 0.46 J/mol · K and 238.53 ± 0.48 J/mol · K. Enthalpy increments relative to 298.15 K were measured by drop calorimetry from 500 to 900 K. From these data the thermodynamic functions, including the enthalpy and Gibbs free energy of formation of the two compounds were derived for temperatures up to 1000 K.

Thermodynamic properties of molecular organic crystals containing nitrogen, oxygen, and sulfur II. Molar heat capacities of eight compounds by adiabatic calorimetry

Molar heat capacities are reported of the simple organic substances: cyanamid, imidazole, formamide, acetamide, cyanuric acid, urethane, maleic anhydride and 1,4-cyclohexanedione. Measurements were made using an automatic adiabatic calorimeter in the temperature range 80 to 370 K. Molar enthalpies of melting ΔslHm and the temperatures at which they appear are: H2NCN, 11.3 kJ · mol−1, 318.71 K; , 12.8 kJ · mol−1, 362.69 K; HCONH2, 8.7 kJ · mol−1, 275.60 K; CH3CONH2, 15.6 kJ · mol−1, 353.33 K; H2NCO2C2H5, 16.8 kJ · mol−1, 321.41 K; , 13.6 kJ · mol−1, 325.72 K; , 11.3 kJ · mol−1, 351.6 K.

The thermal behaviour of water in hydrogels

Abstract The melting enthalpy and the absorption enthalpy of water in polymethacrylic acid and copolymers of methacrylic acid and hydroxyethylmethacrylate have been determined. The melting enthalpy of water in hydrogels increased by increasing the equilibration time at −15°C, but was always smaller than that of pure water. The absorption enthalpy of water was negative and decreased by increasing the initial water content of the hydrogels. However, the observed lack in melting enthalpy of water was not fully compensated by the negative change in absorption enthalpy. This led to the conclusion that a part of the water does not freeze during the cooling-heating process. The glass transition temperatures were determined as a function of the water content. Upon hydration, the glass transition temperature decreased in temperature. The amount of water necessary to decrease the glass transition temperature to 0°C was approximately equal to the amount of non-freezable water in the hydrogels. These observations lead to the conclusion that the amount of non-freezable water cannot be explained by different types of water, but is based either on a restriction of the diffusion of water in hydrogels or on a restriction of a further growth of ice crystals after transformation of the hydrogel from rubbery state (high flexibility of the polymer network) to glassy state (low flexibility of the polymer network).

Inhibition of mediator release in RBL-2H3 cells by some H1-antagonist derived anti-allergic drugs: Relation to lipophilicity and membrane effects

In a model for mucosal mast cells (RBL-2H3 cells) a set H1-antagonist derived anti-allergic drugs containing a diphenylmethyl piperazinyl moiety was examined for their ability to inhibit release of the mediatorβ-hexosaminidase. Cells were activated with antigen or the calcium ionophore A23187, whether or not in combination with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Oxatomide, hydroxyzine and cetirizine inhibit the antigen inducedβ-hexosaminidase release. The release triggered by A23187, whether or not in combination with TPA is hardly influenced by the compounds. A biphasic dependence of the inhibition of exocytosis in RBL cells on lipophilicity is observed with the optimum at log P is 5–6. The extremely lipophilic compounds meclozine and buclizine are not active in this model. pH dependence of the effect of the drugs shows that especially the uncharged species are active in inhibiting exocytosis. The investigated compounds show an effect on phase transitions in L-α-phosphatidylcholine dipalmitoyl liposomes as assayed with differential scanning calorimetry (DSC). For the less extremely lipophilic compounds the induced changes in the phospholipid membranes increased with lipophilicity. The relation between structural features of the drug and the interaction with phospholipids is discussed in view of the DSC results. We conclude that location of the active drugs at the membrane or the membrane/protein interface is important for the inhibiting activity on exocytosis. This could affect several membrane related processes, which are abundant in the early phases of the IgE-mediated signal transduction process.

The thermodynamic properties of BaCeO 3 at temperatures from 5 to 940 K

Abstract Low-temperature heat capacities of BaCeO 3 have been measured from 5 to 370 K by adiabatic calorimetry, and the high-temperature enthalpy increments have been measured from 510 to 940 K by drop calorimetry. From the results, smoothed thermodynamic functions have been tabulated at selected temperatures up to 1500 K. For the standard molar entropy of BaCeO 3 , the value S °(298.15 K) = (144.5 ± 0.3) J K − 1 mol − 1 has been found.