Simultaneous determination of solubility, dissolution and dilution enthalpies of a substance from a single calorimetric experiment

The thermodynamics of dissolution in water of a set of substances has been studied calorimetrically. The examined substances were: potassium chloride, (glycyl-glycyl)diketopiperazine, (alanyl-alanyl)diketopiperazine, (leucyl-glycyl)diketopiperazine. They were chosen on the basis of their solubilities, going from a highly soluble electrolyte to the sparingly soluble diketopiperazines. It is shown that, using a commercially available calorimeter, it is possible to perform in a single calorimetric experiment the simultaneous determination of all thermodynamic parameters characterizing dissolution of a substance in a given solvent, i.e. solubility, dissolution enthalpy and dilution enthalpy. The solubility values in water obtained through the proposed method are in good agreement with those reported in the literature and obtained by other techniques.     

Students’ mathematical work on absolute value: focusing on conceptions,errors and obstacles

ZDM – Mathematics Education - This study investigates students’ conceptions of absolute value (AV), their performance in various items on AV, their errors in these items and the...     

α-Substituted Silyl and Phosphonyl Phosphonates. An Extensive Study of their Synthesis and Properties

Abstract

Phosphoryl and silyl chlorides phosphonoalkylation lead to the direct generation of phosphonyl-phosphonyl and phosphonyl-silyl carbanions the properties of which are discussed.     

Calorimetric, conductometric and density measurements of iteratively filtered water using 450, 200, 100 and 25 nm Millipore filters

This study presents some experimental results on the variation of the physico-chemical properties of pure MilliQ water, when subjected to a procedure of iterated filtration through Millipore filters with porosity ranging from 450 to 25 nm. The parameters measured were: calorimetry, electrical conductivity, density, and pH. Release of chemical impurities can be ruled out due to the nature of the materials used. As in the case of iteratively filtered water prepared using Pyrex glass filters, the specific electrical conductivity and the pH were found to increase with increasing number of iterations. There was also a dependence on the average pore size of the filters. The idea of water as a system capable of self-organization triggered by various perturbations (mechanical and/or electromagnetic) is gaining momentum. It responds to such perturbations by forming dissipative structures, i.e., far-from-equilibrium systems.     

The role of ethanol in extremely diluted solutions

We carried out a systematic study on the role of ethanol as a cosolvent in the preparation of aqueous extremely diluted solutions (EDS). We have studied EDS prepared in water containing 1 % ethanol and measured their electrical conductivity and heat of mixing to determine how these solutions differ from those prepared in pure water. The results showed that, as occurs also for the EDS in water, these ethanolic solutions exhibit peculiar effects relating to container volume and storage time (ageing). Our data show a remarkable increase in the conductivity of the EDS in 1 % ethanol, as compared to EDS prepared in water solvent, especially after prolonged storage higher than about 250 days (ageing effect). In each case, the values of conductivity for the hydroalcoholic solvent were approximately four times those for water after an ageing period of 2,178 days. For the study of volume effect, we found that conductivity changes only slightly with decreasing volume. It’s important to underline that the studied volumes were in the 0.25/2.0 mL range. The calorimetric measurements reveal that the presence of ethanol affects heat of mixing with alkaline solutions differently compared to the conductivity. In fact, heat of mixing is not very sensitive to the presence of ethanol, but in contrast with conductivity it shows remarkable sensitivity to volume effects. Our working hypothesis to account for these peculiarities is the presence of water molecule aggregates.     

Secondary Metabolites,including a New 5,6-Dihydropyran-2-One,Produced by the Fungus Diplodia corticola. Aphicidal Activity of the Main Metabolite,Sphaeropsidin A

An undescribed 5,6-dihydropyran-2-one, namely diplopyrone C, was isolated and characterized from the cultures of an isolate of the fungus Diplodia corticola recovered from Quercus suber in Algeria. The structure and relative stereostructure of (5S,6S,7Z,9S,10S)-5-hydroxy-6-(2-(3-methyloxiran-2-yl)vinyl)-5,6-dihydro-2H-pyran-2-one were assigned essentially based on NMR and MS data. Furthermore, ten known compounds were isolated and identified in the same cultures. The most abundant product, the tetracyclic pimarane diterpene sphaeropsidin A, was tested for insecticidal effects against the model sucking aphid, Acyrthosiphon pisum. Results showed a toxic dose-dependent oral activity of sphaeropsidin A, with an LC₅₀ of 9.64 mM.     

Correction to: Interlaboratory Reproducibility of Contour Method Data Analysis and Residual Stress Calculation

Experimental Mechanics - The original version of this article has been corrected to include authors middle initials in the author list. The details given in this correction are correct.