Luciana Ninni

Water Activity, pH and Density of Aqueous Amino Acids Solutions

The water activity, pH and density of some aqueous amino acid solutions were determined at 25 °C in three different types of solvents. Previous published experimental data on water activity and solubility of amino acids in aqueous solutions were used together with data from this work to test the applicability of a group contribution model. The activity coefficients were estimated by the UNIFAC‐Larsen model combined with the Debye‐Hückel equation, taking also into account the partial dissociation phenomena of species in solution. Interaction energies between the charged species Na+ and Cl− and the specific groups of amino acids (COOH and NH2) were adjusted using experimental solubility data.

Modeling and prediction of pH and water activity in aqueous amino acid solutions

Abstract Water activity and pH of amino acids (alanine, glicine, arginine and proline) in aqueous and buffer solutions were measured at various concentrations and 25°C. The partial dissociation phenomenon was considered and the UNTFAC model, combined with solvation equations, was used for the water activity and pH predictions. The validity of the model was tested for the aminoacids in water and two buffer solutions. Mean deviations of 0.64% for the water activity and 2.5% for the pH were obtained.

Influence of Salt and pH on the Swelling Equilibrium of Ionizable N-IPAAm Based Hydrogels: Experimental Results and Modeling

The influence of sodium chloride and of pH on the equilibrium swelling of ionic hydrogels consisting of N-isopropyl acrylamide (N-IPAAm), a weak cationic comonomer N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) and/or a strong anionic comonomer 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) was investigated in aqueous solutions at 298 K. The mass fraction of the polymerizable substances in the aqueous solution was kept at 0.1. The sum of the mole fractions of the comonomers in the gel was 0.05 while the mole fraction of a single comonomer was varied between 0 and 0.05. The mass fraction of NaCl in the aqueous solution was varied between 3 · 10−6 and 0.25. The pH-sensitive comonomer DMAPMA causes an influence of pH on the degree of swelling. The pH of the aqueous solutions was adjusted by adding HCl or NaOH. A thermodynamic framework was applied to model (i.e., correlate and predict) the experimental results. The calculations revealed that dissolved carbon dioxide (resulting from air that was in contact with the condensed phases) might have a remarkable influence on the swelling behavior.