Binary and ternary complexes of epinephrine with alginate and biologically and environmentally relevant metal cations

The speciation of epinephrine (Eph (-)) in the presence of alginate (Alg (2-)) and two biological and environmental relevant metal cations (Cu2+, UO2 (2+)) was investigated at T = 298.15K, I = 0.15-1.00 mol dm(-3) in NaCl(aq). The formation of binary and ternary complexes was evaluated and, since epinephrine can behave as a zwitterion, the Eph (-)/Alg (2-) interaction was studied by means of DOSY NMR. The dependence of the equilibrium constants on ionic strength was studied using an extended Debye-Huckel type equation and the SIT approach. The effect of temperature was investigated by means of isoperibolic titration calorimetry: the entropic contribution was the driving force for the Cu2+/Eph (-) complexes formation. The sequestering ability of Eph (-) and Alg (2-) on Cu2+, evaluated by the pL(0.5) calculation, increased with pH and ionic strength. The determination of pM parameter showed that Eph (-) had a higher Cu2+ affinity with respect to Alg (2-). The formation of Eph (-)/Alg (2-) species was also investigated by UV-Vis spectrophotometry and H-1 NMR measurements. The ternary Cu2+/Eph (-)/Alg ( 2- ) and Cu2+/UO2 (2+)/Eph (-) interactions were also studied. The extra-stability calculated for the mixed ternary species confirmed that their formation was thermodynamically favorable.

Automated summary

In this study, the speciation of epinephrine (Eph (-)) in the presence of alginate (Alg (2-)) and two metal cations (Cu2+, UO2 (2+)) was investigated under different conditions. The interaction between Eph (-) and Alg (2-) was studied using DOSY NMR as Eph (-) can behave as a zwitterion. The equilibrium constants and their dependence on ionic strength were determined using an extended Debye-Huckel type equation and the SIT approach. The sequestering ability of Eph (-) and Alg (2-) on Cu2+ was evaluated and compared, and the formation of ternary complexes involving Cu2+ and UO2 (2+) was also studied.