Solubility and modeling acid–base properties of adrenaline in NaCl aqueous solutions at different ionic strengths and temperatures

Solubility and acid–base properties of adrenaline were studied in NaCl aqueous solutions at different ionic strengths (0 < I/mol L−1 < 3.0) and temperatures (T = 298.15 and 310.15 K), by means of different techniques: potentiometry, UV-spectrophotometry and spectrofluorimetry. The intrinsic solubility of the ligand was calculated from simple mass balance equations, by using the free hydrogen concentration and the protonation constants of the ligand determined in the same experimental conditions of the solubility measurements. The salting-In or Out parameters and the activity coefficient of the neutral species were calculated by means of the Setschenow equation.The dependence of the protonation constants on the ionic strength was modeled by means of the Debye–Hückel type equation and of the SIT (Specific ion Interaction Theory) approach. The specific interaction parameters of the ion pairs were also reported. For the protonation constants, the following thermodynamic values at infinite dilution were obtained: T = 298.15 K, log K1H0 = 10.674 ± 0.018 and log K2H0 = 8.954 ± 0.022; T = 310.15 K, log K1H0 = 10.355 ± 0.018 and log K2H0 = 8.749 ± 0.030.

Graphical abstractActivity coefficients of adrenaline neutral species at different ionic strengths and temperatures. Legend: • T = 310.15 K and ■ T = 298.15 K.Figure optionsDownload full-size imageDownload high-quality image (58 K)Download as PowerPoint slide