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The isothermal titration calorimetry (ITC) technique supported by potentiometric titration data was used to study a buffer contribution to the formation enthalpy of copper(II)-bicine complex obtained directly from the ITC experiments. The calorimetric measurements were carried out at 298.15 K in 100 mM buffer solutions with a pH of 6. In experiments two biologically relevant pH buffers were used, namely Mes and Caco. These buffers do not bind copper(II) ions and thus do not affect the binding constant. However, due to their different ionization enthalpy, they affect the conditional (observed) enthalpy of binding of the metal ion to a ligand owing to the proton transfer during the interactions. To calculate the conditional-independent binding enthalpy ∆ H, the equation based on the Hess's law was used. Furthermore, pH-independent and buffer-independent parameters ( K, ∆ G and ∆ S) of the interactions were calculated as well. The relationship between the ionization enthalpy of the buffer components and the thermodynamic parameters has been discussed. [ABSTRACT FROM AUTHOR]

The isothermal titration calorimetry (ITC) technique supported by potentiometric titration data was used to study the interaction of zinc ions with pH buffer substances, namely 2-( N-morpholino)ethanesulfonic acid (Mes), piperazine- N, N′-bis(2-ethanesulfonic acid) (Pipes), and dimethylarsenic acid (Caco). The displacement ITC titration method with nitrilotriacetic acid as a strong, competitive ligand was applied to determine conditional-independent thermodynamic parameters for the binding of Zn(II) to Mes, Pipes, and Caco. Furthermore, the relationship between the proposed coordination mode of the buffers and the binding enthalpy has been discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Isothermal titration calorimetry (ITC) and potentiometric titration (PT) methods were used to study the interactions of cobalt(II) and nickel(II) ions with buffer substances 2-( N-morpholino)ethanesulfonic acid (Mes), dimethylarsenic acid (Caco), and piperazine- N, N′-bis(2-ethanesulfonic acid) (Pipes). Based on the results of PT data, the stability constants were calculated for the metal-buffer complexes ( T = 298.15 K, ionic strength I = 100 mM NaClO). Furthermore, calorimetric measurements (ITC) were run in 100 mM Mes, Caco, and Pipes solutions with pH 6, at 298.15 K. The enthalpies (Δ H) of the metal-buffer complexation reactions were calculated indirectly by displacement titration using nitrilotriacetic acid (HNTA) as a strong-binding, competitive ligand. Finally, to verify obtained results, the number of protons released by HNTA due to complexation of the cobalt(II) and nickel(II) ions was determined from calorimetric data and compared with results of calculations. [ABSTRACT FROM AUTHOR]

Isothermal titration calorimetry (ITC) and potentiometric titration methods have been used to study the process of proton transfer in the copper(II) ion-glycylglycine reaction. The stoichiometry, conditional stability constants, and thermodynamic parameters (Δ G, Δ H, and Δ S) for the complexation reaction were determined using the ITC method. The measurements were carried out at 298.15 K in solutions with a pH of 6 and the ionic strength maintained with 100 mM NaClO. Carrying out the measurements in buffer solutions of equal pH but different enthalpies of ionization of its components (Mes, Pipes, Cacodylate) enabled determination of the enthalpy of complex formation, independent of the enthalpy of buffer ionization. The number of protons released by glycylglycine on account of complexation of the copper(II) ions was determined from calorimetric and potentiometric measurements. [ABSTRACT FROM AUTHOR]