A new approach in the use of SIT in determining the dependence on ionic strength of activity coefficients. Application to some chloride salts of interest in the speciation of natural fluids

AbstractThis paper describes a modified version of the SIT (Specific ion Interaction Theory) method and its use in determining the dependence on ionic strength of activity coefficients. In the new approach the interaction coefficients (e) are not constant but depend on ionic strength (I /mol kg-1) according to the simple relationship:e = e∞+ (e0 - e∞) / (l + 1)where e0 and are true constants for I→ 0 and l→ ∞, respectively. To check the two parameter SIT equation, we calculated e0 and for the activity coefficients of HCl, LiCl, NaCl, KCl, MgCl2, CaCl2 and SrCl2, in a wide ionic strength range (0.1 ≤ l/mol kg-1 ≤ 4.5, for KCl; 0.1 ≤ l/mol kg-1 ≤ 6, for HCl, LiCl, NaCl; 0.3 ≤ l/mol kg-1 ≤ 12, for SrCl2; 0.3 ≤ l/mol kg-1 ≤ 15, for MgCl2; 0.3 ≤ l/mol kg-1 ≤ 18, for CaCl2). Results show that the γ values calculated using this approach fit quite well over the whole I-range for all the electrolytes considered. Comparison is made with the analogous one parameter SIT equation. The temperature coefficients of inter..

Thermodynamic Solution Properties of a Biodegradable Chelant (L-glutamic-N,N-diacetic Acid, L-GLDA) and Its Sequestering Ability toward Cd2+

The thermodynamics of the interaction of L-glutamic-N,N-diacetic acid (GLDA) with protons was studied potentiometrically at different temperatures, ionic strengths and ionic media. Four protonation constants and corresponding enthalpy changes occurred at infinite dilution together with temperature and ionic strength coefficients. The medium effect was also interpreted in terms of the formation of weak complexes between the ligand and the cations of supporting electrolytes, resulting in a greater tendency of GLDA to chemically interact with Na+ rather than K+ and, in turn, (CH3)4N+. Formation constants of GLDA with Cd2+ were determined in NaCl(aq) at different ionic strength values. Five complex species were found, namely CdL2−, CdHL−, CdH2L0(aq), Cd2L0(aq), and Cd(OH)L3−, whose formation constant values at infinite dilution were log β = 12.68, 17.61, 20.76, 17.52, and 1.77, respectively. All the species results were relevant in the pH range of natural waters, although the Cd2L0(aq) was observed only for CCd ≥ CGLDA and concentrations of >0.1 mmol dm−3. The sequestering ability of GLDA toward Cd2+, evaluated by means of pL0.5, was maximum at pH~10, whereas the presence of a chloride containing a supporting electrolyte exerted a negative effect. Among new generation biodegradable ligands, GLDA was the most efficient in Cd2+ sequestration.The authors C.B., P.C., A.I., G.L. and C.D.S. thank the University of Messina for the Research and Mobility 2017 Project (cod. 009041). Authors thank COST action CA18202—Network for Equilibria and Chemical Thermodynamics Advanced Research for the support to this study. O.G.-L. is grateful to the project IT-742-13 for Consolidated Research Groups, funded by the Basque Country Government, for her post-doctoral contract

Non-Invasive Approach to Investigate the Mineralogy and Production Technology of the Mosaic Tesserae from the Roman Domus of Villa San Pancrazio (Taormina, Italy)

The archaeological excavations at Villa San Pancrazio (Taormina, Italy) are bringing to light a vast Roman-Imperial residential quarter featuring luxurious dwellings decorated with wall paintings and mosaic floors, pointing it out as one of the most significant archaeological sites of the city. The polychrome and black and white mosaics recovered date back to the middle Imperial period, during the 2nd century AD. This work deals with the first archaeometric investigations of the materials employed for the tesserae production with the aim of elucidating the mineralogical composition and obtaining analytical evidence that can contribute to extracting information related to their production technology. For that purpose, a non-invasive methodology, based on micro energy dispersive X-ray fluorescence (μ-EDXRF) spectrometry and Raman spectroscopy, was used to characterize a wide selection of stone, ceramic and glass tesserae. Chemometric tools were exploited to manage the large set of elemental data collected on black and white lithic samples, providing essential clues for the subsequent investigations. The results evidenced the employment of natural lithotypes (calcareous sedimentary, dolomitic and volcanic) local and imported, and also artificial materials, such as ceramic made firing magnesium-rich clays, soda-lime-silica glasses made with different opacifying and coloring agents (such as calcium antimoniate, cobalt and copper)This work was supported by project IT-742-13 for Consolidated Research Groups, funded by the Basque Country Government. P. Irizar gratefully acknowledges his predoctoral grant (PRE2018-085888) from the MINECO Spanish Ministry. O. Gómez-Laserna is grateful to the University of the Basque Country (UPV/EHU) for her postdoctoral contract. P. Cardiano also thanks University of Messina (FFABR UNIME 2020) for funding

Thermodynamic Solution Properties of a Biodegradable Chelant (L-glutamic-N,N-diacetic Acid, L-GLDA) and Its Sequestering Ability toward Cd2+

The thermodynamics of the interaction of L-glutamic-N,N-diacetic acid (GLDA) with protons was studied potentiometrically at different temperatures, ionic strengths and ionic media. Four protonation constants and corresponding enthalpy changes occurred at infinite dilution together with temperature and ionic strength coefficients. The medium effect was also interpreted in terms of the formation of weak complexes between the ligand and the cations of supporting electrolytes, resulting in a greater tendency of GLDA to chemically interact with Na+ rather than K+ and, in turn, (CH3)4N+. Formation constants of GLDA with Cd2+ were determined in NaCl(aq) at different ionic strength values. Five complex species were found, namely CdL2−, CdHL−, CdH2L0(aq), Cd2L0(aq), and Cd(OH)L3−, whose formation constant values at infinite dilution were log β = 12.68, 17.61, 20.76, 17.52, and 1.77, respectively. All the species results were relevant in the pH range of natural waters, although the Cd2L0(aq) was observed only for CCd ≥ CGLDA and concentrations of >0.1 mmol dm−3. The sequestering ability of GLDA toward Cd2+, evaluated by means of pL0.5, was maximum at pH~10, whereas the presence of a chloride containing a supporting electrolyte exerted a negative effect. Among new generation biodegradable ligands, GLDA was the most efficient in Cd2+ sequestration

Interaction of acrylic-maleic copolymers with H+, Na+, Mg2+ and Ca2+: Thermodynamic parameters and their dependence on medium

Thermodynamic parameters for the interaction of two acrylic-maleic copolymers (MW = 3 and 70 kDa) with H+, Na+, Mg2+ and Ca2+ were obtained from potentiometric and calorimetric measurements. Apparent protonation constants were expressed as a function of a (dissociation degree) using the three parameter model proposed by Ho¨gfeldt and the formation constants of Na+, Mg2+ and Ca2+ complexes were calculated from the differences in protonation constants in the different ionic media. The salt effects on protonation were interpreted in terms of both activity coeffi- cient variations and cation complex formation. Enthalpy changes for protonation, obtained by direct calorimetry (always quite low, the stabilization being mainly of entropic nature), were also expressed as a function of a and I using empirical equations. The formation constants obtained for alkali and alkaline earth metal complexes are quite low for Na+ species (depending on a and on ionic strength, we always found K < 10 L mol 1 ), and fairly high for Mg2+ and Ca2+ species, ML and ML

Lipids in Archaeological Pottery: A Review on Their Sampling and Extraction Techniques

Several studies have been performed so far for the effective recovery, detection and quantification of specific compounds and their degradation products in archaeological materials. According to the literature, lipid molecules are the most durable and widespread biomarkers in ancient pottery. Artificial ageing studies to simulate lipid alterations over time have been reported. In this review, specific lipid archaeological biomarkers and well-established sampling and extraction methodologies are discussed. Although suitable analytical techniques have unraveled archaeological questions, some issues remain open such as the need to introduce innovative and miniaturized protocols to avoid extractions with organic solvents, which are often laborious and non-environmentally friendly

Modelling the dependence on medium, ionic strength and temperature of N-acetyl-L-cysteine acid-base properties, and its interactions with Na+, Mg2+, Ca2+ and Zn2+

N-acetyl-L-cysteine (NAC) is the acetylated precursor of L-cysteine, and it is strictly related to glutathione activity. NAC is used in medicine since more than 30 years, primarily as a mucolytic, though its properties are exploited in the treatment of many diseases, such as acute poisoning by acetaminophen (restoring protective levels of glutathione), HIV, contrast-induced nephropathy, type-2 DM (diabetes mellitus), and it also looks promising in the treatment of several psychiatric disorders [1]. This resulted in a huge number of scientific contributions published during the years on NAC (searching in some scientific databases, more than 10000 papers appear). As expected, most of them are focused on the biological and therapeutic activity of NAC, while relatively few data are reported on the solution chemistry of this molecule, despite the thorough knowledge of its acid-base and coordination behaviour are of fundamental importance for the understanding of its properties in aqueous solution, as biological fluids are. Moreover, the relatively few thermodynamic data available (necessary to assess the speciation of this ligand in the system under study) are reported in single, specific conditions, while it is well known that the most of biological fluids (and natural waters) are, from a chemico-physical perspective, multielectrolyte aqueous solutions of very variable composition, ionic strength, and temperature [2]. Therefore, in this contribution we report the results of an investigation on the modelling of the acid-base properties of NAC in different ionic media (sodium and tetramethylammonium chlorides and tetraethylammonium iodide) at different ionic strengths (0 < I / mol dm-3 ≤ 3.0) and temperatures (283.15 ≤ T / K ≤ 318.15). Due to their importance from a biological perspective, we also report the results on the binding ability of NAC towards Na+, Mg2+, Ca2+ and Zn2+ in NaClaq at T = 298.15 K and different ionic strengths (0 < I / mol dm-3 ≤ 2.0). Surprisingly, despite the importance of these cations and their involvement in many biological mechanisms strictly connected with NAC activity, to our knowledge almost no data (only some for Zn2+) are present in literature on these interactions. The dependence on medium, ionic strength and temperature of the protonation and complex formation constants obtained has been modelled by classical approaches, such as the Extended Debye-Hückel (EDH), Specific ion Interaction Theory (SIT), Pitzer, and by the van’t Hoff equation