Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following crystalline compounds: diphenylacetic acid, between 357.27 and 379.08 K; triphenylacetic acid, between 418.98 and 436.97 K; 2,2-diphenylpropanoic acid, between 366.08 and 386.00 K; 3,3-diphenylpropanoic acid, between 366.09 and 386.03 K; 3,3,3-triphenylpropanoic acid, between 402.17 and 420.10 K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p0 = 105 Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. The measured thermodynamic properties are compared with literature results for phenylacetic and phenylpropanoic acids and correlations for estimation of the vapor pressures from the enthalpy of sublimation and the temperature of fusion of these and other compounds are presented.
Authors:Manuel Monte, Luís Santos, José Fonseca, and Carlos Sousa
The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following
temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic
acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic
acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs
energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values
of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure
of para substituted benzoic acids at the temperature of 298.15 K are proposed.
Authors:Cristina Sousa, Jorge Azevedo, Amélia Silva, Carlos Viegas, Rui Reis, Manuela Gomes, and Isabel Dias
This study aimed to assess serum total alkaline phosphatase (ALP) and its bone isoform (BALP) levels during the ageing and in different physiologic states of sheep, in order to expand the knowledge about the variation of these biomarkers over the sheep lifespan. Ninety female sheep were divided into nine groups of various ages and physiological states (dry, lactation and pregnancy). Serum ALP, BALP and mineral levels were determined by commercial immunoassay, molecular absorbance spectrophotometry and chemical luminescence for BALP determination. Serum ALP and BALP decreased as sheep aged, and no statistically significant differences were obtained between ewes in different physiologic states. The continuous decline of serum BALP concentration along the sheep lifespan, namely in mature and old sheep, is a sign of decreasing bone turnover associated with ageing. Serum calcium concentrations increased slightly until 2 years of age and then showed a tenuous but statistically significant decrease in mature sheep, while serum phosphorus maintained an uninterrupted decrease as sheep matured. The knowledge of serum values of bone biomarkers throughout the sheep lifespan may be useful in preclinical orthopaedic research studies and for animal science studies using sheep.
Authors:Bianca V. Sousa, Karoline D. Brito, José J. N. Alves, Meiry G. F. Rodrigues, Carlos M. N. Yoshioka, and Dilson Cardoso
Current specifications for gasoline impose strong restrictions on the content of aromatic compounds. Isomerization of normal paraffins to isoparaffins is considered an important petroleum reaction for the production of clean gasoline to improve its Research Octane Number (RON) and Motor Octane Number (MON). The isoparaffins are considered as an alternative to the use of oxygenated and aromatic compounds, whose maximum contents are subjected to strict regulations in order to protect the environment. In this work, catalysts supported on mordenite were obtained by competitive ion exchange using aqueous solutions of platinum complexes. Different concentrations of platinum were tested for the isomerization of n-hexane. All the catalysts obtained were shown to be selective to the formation of isomers with high-octane number, which are the products of greatest interest in the oil refining industry. The highest conversion and the best selectivity for 2,3-dmC4 di-branched component, the isomer with the highest octane number, were found with the 1.10 wt% Pt/HMOR.