Understanding the Solution Behavior of Epinephrine in the Presence of Toxic Cations: A Thermodynamic Investigation in Different Experimental Conditions

Abstract

The interactions of epinephrine ((R)-(−)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol; Eph−) with different toxic cations (methylmercury(II): CH3Hg+; dimethyltin(IV): (CH3)2Sn2+; dioxouranium(VI): UO22+) were studied in NaClaq at different ionic strengths and at T = 298.15 K (T = 310.15 K for (CH3)2Sn2+). The enthalpy changes for the protonation of epinephrine and its complex formation with UO22+ were also determined using isoperibolic titration calorimetry: ΔHHL = −39 ± 1 kJ mol−1, ΔHH2L = −67 ± 1 kJ mol−1 (overall reaction), ΔHML = −26 ± 4 kJ mol−1, and ΔHM2L2(OH)2 = 39 ± 2 kJ mol−1. The results were that UO22+ complexation by Eph− was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye–Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL0.5 parameters. The sequestering ability trend resulted in the following: UO22+ >> (CH3)2Sn2+ > CH3Hg+. For example, at I = 0.15 mol dm−3 and pH = 7.4 (pH = 9.5 for CH3Hg+), pL0.5 = 7.68, 5.64, and 2.40 for UO22+, (CH3)2Sn2+, and CH3Hg+, respectively. Here, the pH is with respect to ionic strength in terms of sequestration.

The Solution Behavior of Dopamine in the Presence of Mono and Divalent Cations: A Thermodynamic Investigation in Different Experimental Conditions

“…The stability constants of CH 3 Hg + /Dop − species at different ionic strengths and temperatures are reported in Table 3. As already observed in previous investigations [18,23,32], the speciation of methylmercury(II) in sodium chloride aqueous solutions is characterized by the formation of the stable MCl species (Table S2 of the Supplementary Material), so that in the presence of dopamine, the formation of the ternary MLCl complex, together with the ML, MLH, and MLOH ones, is observed, as reported in the speciation diagram in Figure 2. In particular, we observe an increase of the formation percentage of the MLCl species with increasing the chloride concentration (i.e., the ionic strength) in the solution, and a formation percentage that reaches ~20% at I = 1.0 mol dm −3 .…”

“…Another attempt of comparison can be made for the CH 3 Hg + /Dop − complexes here determined and those already reported in a previous investigation for the CH 3 Hg + /Eph − (adrenaline) interactions [18]. A similar speciation model has been obtained; if we compare, as a pure example, the stability of the complexes at I = 0.15 mol dm −3 and T = 298.…”

“…The determination of the best speciation model for the metal/dopamine systems and of the corresponding stability constants was obtained by using some general rules and guidelines, already applied in previous papers [ 18 , 24 , 36 ].…”

“…Many years ago, this research group started a systematic investigation on the acid-base properties, solubility, and interaction of molecules of biological and pharmaceutical relevance towards different metal ions [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”

Special Issue “Chemical Speciation of Organic and Inorganic Components of Environmental and Biological Interest in Natural Fluids: Behaviour, Interaction and Sequestration”

“…The Special Issue had satisfactory feedback from researchers, with contributions having cross-field character and being of interest for different industrial, pharmaceutical, chemical, and biological fields [7][8][9][10][11][12][13][14][15][16][17].…”