Buffer contribution to formation enthalpy of copper(II)–bicine complex determined by isothermal titration calorimetry method

Abstract

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 DH, the equation based on the Hess's law was used. Furthermore, pH-independent and buffer-independent parameters (K, DG and DS) of the interactions were calculated as well. The relationship between the ionization enthalpy of the buffer components and the thermodynamic parameters has been discussed.

Site-Specific Incorporation of a Cu2+ Spin Label into Proteins for Measuring Distances by Pulsed Dipolar Electron Spin Resonance Spectroscopy

“…Interestingly, the minor long distance components were reduced in H 2 O, consistent with an origin in aggregation. We also prepared the sample in Tris-H 2 O buffer, which is a stronger chelator of Cu 2+ ( K f ≈ 10 8 ) than MES buffer, which does not bind cupric ion . The considerably diminished signal produces a distribution in which the primary peak is maintained, but the short distance component is lost (Figure S3).…”

“…We also prepared the sample in Tris-H 2 O buffer, which is a stronger chelator of Cu 2+ (K f ≈ 10 8 ) 55 than MES buffer, which does not bind cupric ion. 56 The considerably diminished signal produces a distribution in which the primary peak is maintained, but the short distance component is lost (Figure S3). This result suggests that the 20 Å feature may arise from a weakly bound Cu 2+ ion.…”

Dihydroxy-Substituted Coumarins as Fluorescent Probes for Nanomolar-Level Detection of the 4-Amino-TEMPO Spin Label

“…The electrode was calibrated according to IUPAC recommendations [55]. All details for the measuring devices and the experimental setup were described previously [56]. All the solutions were prepared immediately before the measurements.…”

Probing the binding selected metal ions and biologically active substances to the antimicrobial peptide LL-37 using DSC, ITC measurements and calculations

“…The reference cell contained the distilled water. All details of the measuring devices and the experimental setup were described previously [20,21]. The experiment consisted of injecting of 10.02 lL (29 injections, 2 lL for the first injection only) of ca 1 mM buffered solution of LL-37 into the reaction cell which initially contained ca 0.1 mM buffered solution of the Cu 2?…”