Spectrophotometric quantification of the thermodynamic constants of the complexes formed by dopamine and Cu(II) in aqueous media

The Effect of Metal Cations on the Aqueous Behavior of Dopamine. Thermodynamic Investigation of the Binary and Ternary Interactions with Cd2+, Cu2+ and UO22+ in NaCl at Different Ionic Strengths and Temperatures

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop-)] with cadmium(II), copper(II) and uranyl(VI) were studied in NaCl(aq) at different ionic strengths (0 ≤ I/mol dm-3 ≤ 1.0) and temperatures (288.15 ≤ T/K ≤ 318.15). From the elaboration of the experimental data, it was found that the speciation models are featured by species of different stoichiometry and stability. In particular for cadmium, the formation of only MLH, ML and ML2 (M = Cd2+; L = dopamine) species was obtained. For uranyl(VI) (UO22+), the speciation scheme is influenced by the use of UO2(acetate)2 salt as a chemical; in this case, the formation of ML2, MLOH and the ternary MLAc (Ac = acetate) species in a wide pH range was observed. The most complex speciation model was obtained for the interaction of Cu2+ with dopamine; in this case we observed the formation of the following species: ML2, M2L, M2L2, M2L2(OH)2, M2LOH and ML2OH. These speciation models were determined at each ionic strength and temperature investigated. As a further contribution to this kind of investigation, the ternary interactions of dopamine with UO22+/Cd2+ and UO22+/Cu2+ were investigated at I = 0.15 mol dm-3 and T = 298.15K. These systems have different speciation models, with the MM'L and M2M'L2OH [M = UO22+; M' = Cd2+ or Cu2+, L = dopamine] common species; the species of the mixed Cd2+ containing system have a higher stability with respect the Cu2+ containing one. The dependence on the ionic strength of complex formation constants was modelled by using both an extended Debye-Hückel equation that included the Van't Hoff term for the calculation of the formation enthalpy change values and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The quantification of the effective sequestering ability of dopamine towards the studied cations was evaluated by using a Boltzmann-type equation and the calculation of pL0.5 parameter. The sequestering ability was quantified at different ionic strengths, temperatures and pHs, and this resulted, in general, that the pL0.5 trend was always: UO22+ > Cu2+ > Cd2+.

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

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop⁻)] with methylmercury(II) (CH₃Hg⁺), magnesium(II), calcium(II), and tin(II) were studied in NaCl(aq) at different ionic strengths and temperatures. Different speciation models were obtained, mainly characterized by mononuclear species. Only for Sn²⁺ we observed the formation of binuclear complexes (M₂L₂ and M₂LOH (charge omitted for simplicity); M = Sn²⁺, L = Dop⁻). For CH₃Hg⁺, the speciation model reported the ternary MLCl (M = CH₃Hg⁺) complex. The dependence on the ionic strength of complex formation constants was modeled by using both an extended Debye–Hückel equation that included the Van’t Hoff term for the calculation of enthalpy change values of the formation and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The sequestering ability of dopamine towards the investigated cations was evaluated using the calculation of pL_0.5 parameter. The sequestering ability trend resulted to be: Sn²⁺ > CH₃Hg⁺ > Ca²⁺ > Mg²⁺. For example, at I = 0.15 mol dm⁻³, T = 298.15 K and pH = 7.4, pL_0.5 = 3.46, 2.63, 1.15, and 2.27 for Sn²⁺, CH₃Hg⁺, Ca²⁺ and Mg²⁺ (pH = 9.5 for Mg²⁺), respectively. For the Ca²⁺/Dop⁻ system, the precipitates collected at the end of the potentiometric titrations were analyzed by thermogravimetry (TGA). The thermogravimetric calculations highlighted the formation of solid with stoichiometry dependent on the different metal:ligand ratios and concentrations of the starting solutions.

Nickel–cobalt double hydroxide nanosheets wrapped amorphous Ni(OH)2 nanoboxes: development of dopamine sensor with enhanced electrochemical properties

The Ni(OH)₂/NiCo-LDHs nanocomposites accelerated the electron transfer and successfully realized dopamine catalytic oxidation.

A new strategy for detecting dopamine in human serum using polymer brushes reinforced with carbon nanotubes

Schematic of dopamine detection in blood serum in presence of ascorbic acid and uric acid using polymer brushes reinforced with MWNTs.