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Abstract The interaction of polyaspartic acid 2 kDa (PASP) biopolymer with the major cationic constituent of natural fluids (H+, Na+, K+, Mg2+, Ca2+) were studied by ISE-H+ titrations. The acid-base properties of PASP were determined in different ionic media [NaNO 3 , NaCl, KCl, (CH 3) 4 NCl and (C 2 H 5) 4 NI] at different temperatures and ionic strengths. The data analysis was performed according to the diprotic like model, assuming that a monomeric unit consists of two α and two β aspartyl residues, finding four protonation constants in the range 2.0 < pH < 8.0. Corresponding thermodynamic data (Δ G 0, Δ H 0 and T Δ S 0) revealed a slightly endothermic process for the 1st and 2nd steps and a slightly exothermic process for the 3rd and 4th steps, suggesting that amino groups are not involved in the proton binding. The CaL species is more stable than the MgL one at low ionic strength and T = 298.15 K, the contrary is observed at I = 1.0 mol kg−1 and T = 318.15 K, indicating that the latter process is endothermic, while the former is exothermic. Finally, speciation diagrams in the conditions of sea water and human blood plasma are drawn. In sea water, for example, PASP is present as MgL (48%), CaL (41%), Na 2 L (8%) and NaL species (3%). Graphical abstract Unlabelled Image Highlights • Diprotic like model was used to analyze potentiometric data of polyaspartate (PASP). • N-atoms are not involved in acid-base equilibria, PASP can be treated as a tetracarboxylate. • The stability trend is: Ca2+ ~ Mg2+ > Na+ ~ K+ > (CH 3) 4 N+ > (C 2 H 5) 4 N+. • PASP does not significantly lower the levels of free Ca2+ and Mg2+ in sea water. • A small, even significant, lowering (8–15%) occurs in blood plasma. [ABSTRACT FROM AUTHOR]

• Thermodynamic studies on the Al3+/Dop- in NaCl (aq) , the main inorganic compound of biological fluids and natural waters. • Use of ISE-[H+] potentiometry, UV–Vis spectrophotometry, 1H NMR and thermogravimetry for the speciation studies. • Modelling of I /mol dm−3 and T /K by means of the modified extended Debye-Hückel, Specific Ion Interaction Theory. • Modelling of the sequestering ability at different I /mol dm−3, T /K and pH. The interactions of dopamine (Dop−) with aluminum were studied in NaCl (aq) at different ionic strengths (0.15 ≤ I /mol dm−3 ≤ 1.0) and temperatures (288.15 ≤ T /K ≤ 310.15). The investigations were carried out by using ISE-[H+] potentiometry, UV–Vis spectrophotometry and 1H NMR. The results obtained from the different techniques were in good agreement, both in terms of speciation model and stability constants of the complexes. The speciation model is featured by mononuclear complexes, namely: AlDop; AlDopOH; AlDop(OH) 2 and AlDop(OH) 3 (charges omitted). From 1H NMR investigations, it resulted that both the amino and the phenolic groups in meta position of aromatic ring are involved in the protonation equilibria, while the Al3+ complexation occurs from the catechol side of the ligand. The dependence on the ionic strength and temperature of the complex formation constants was modelled by a modified extended Debye-Hückel equation, containing a term for the dependence on T /K. The SIT approach allowed the calculation of the specific ion interaction coefficients of the aluminum:dopamine complexes. From the enthalpy change values obtained, it resulted that the formation of the species is exothermic in nature and that the entropy is the driving force of the processes. The sequestering ability of dopamine towards Al3+ was evaluated by the calculation of pL 0.5 parameter at different ionic strengths, pHs and temperatures; the dependence of the pL 0.5 on these variables was modelled by using an empirical predictive equation that allows the calculation of the effective sequestering ability of dopamine at desired conditions. The precipitates collected at the end of the potentiometric titrations were studied by means of thermogravimetric (TGA) analysis. [ABSTRACT FROM AUTHOR]

The binding ability of N -acetylcysteine (NAC) towards Pb 2 + , Zn 2 + , Cd 2 + and Hg 2 + metal cations was studied by potentiometry, UV spectrophotometry and 1 H NMR spectroscopy. For all the systems, very similar speciation models were obtained, with the formation of ML 0 , ML 2 2 − and ML(OH) − species. Their stability was found to be quite different: as an example, at I = 0.1 mol·L − 1 and t = 25 °C, logβ (ML 0 ) = 32.11, 7.21, 6.53 and 5.52 for Hg 2 + , Pb 2 + , Cd 2 + and Zn 2 + , respectively. The speciation models and the coordination mode of the complexes formed were discussed on the basis of spectroscopic results. The sequestering ability of NAC towards metal cations was evaluated by determining the concentration of the ligand able to complex half of the metal ion fraction (pL 0.5 ). The values such obtained were very different, ranging from a maximum of 12.4 for Hg 2 + to a minimum of 3.7 for Zn 2 + (at pH = 7.4 and I = 0.15 mol·L − 1 ), following the order: Hg 2 + ≫ Pb 2 + > Cd 2 + > Zn 2 + . [ABSTRACT FROM AUTHOR]

The metal speciation behavior of the amino functionalized 1-(2′-diethylamino)ethyl-3-methylimidazolium-based ILs, bearing anions featured by different coordination properties (chloride, perchlorate, acetate) is reported. Sequestering ability of this family of ILs towards Hg 2 + , CH 3 Hg + , Sn 2 + , (CH 3 ) 2 Sn 2 + , UO 2 2 + , evaluated by the determination of pL 0.5 parameter, was found to be a function of the nature of anions and/or pH. The acetate IL displayed a high affinity towards Hg 2 + and CH 3 Hg + , both at acidic and basic conditions, with respect to chloride and perchlorate derivatives, suggesting that a cation-anion cooperation mechanism is operating in the sequestering process. Conversely, UO 2 2 + sequestration resulted a function of pH and independent on the nature of the anion. The extraction capabilities of hydrophobic 1-(2′-diethylamino)ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide towards Hg 2 + and CH 3 Hg + after treatment with acetate IL were also checked. AAS measurements showed the almost complete removal of both mercury species from water solution. [ABSTRACT FROM AUTHOR]