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 (Cu(2+), UO(2) (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-Hückel 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 Cu(2+)/Eph (−) complexes formation. The sequestering ability of Eph (−) and Alg (2-) on Cu(2+), evaluated by the pL(0.5) calculation, increased with pH and ionic strength. The determination of pM parameter showed that Eph (−) had a higher Cu(2+) affinity with respect to Alg (2-). The formation of Eph (−)/Alg (2-) species was also investigated by UV-Vis spectrophotometry and (1)H NMR measurements. The ternary Cu(2+)/Eph (−)/Alg ( 2- ) and Cu(2+)/UO(2) (2+)/Eph (−) interactions were also studied. The “extra-stability” calculated for the mixed ternary species confirmed that their formation was thermodynamically favorable.