Cu(II) complex formation by ACES buffer.

Area of Science:

• Biochemistry
• Analytical Chemistry
• Coordination Chemistry

Background:

• N-(2-Acetamido)-2-aminoethanesulfonic acid) (ACES) is a widely used buffer in biological research.
• Previous studies on ACES binding with Cu(II) ions have yielded inconsistent results regarding binding constants and stoichiometries.
• Understanding these interactions is crucial for accurate biological measurements involving copper.

Purpose of the Study:

• To establish a consistent set of binding constants and complex stoichiometries for the interaction between ACES and Cu(II) ions.
• To clarify the influence of concentration and ACES:Cu(II) ratio on the binding affinity.
• To provide reliable data for researchers using ACES buffer in copper-related studies.

Main Methods:

• Potentiometry was employed to determine the binding constants of ACES-Cu(II) complexes.
• UV-vis spectroscopy was used to validate potentiometric model selection and binding constant calculations.
• Complex formation and deprotonation events were analyzed under varying conditions.

Main Results:

• A consistent set of Cu(II)-ACES complex stoichiometries was identified, including Cu(2+), CuL(+), CuL2, CuH-1L2(-1), and CuH(-)2L2(-2).
• The binding affinity of ACES for Cu(II) is highly dependent on the ACES:Cu(II) ratio, reaching submicromolar apparent affinities at ratios > 100.
• Cu(II) assisted deprotonation of the amide nitrogen in ACES was observed and quantified.

Conclusions:

• This study provides a reliable and consistent dataset for Cu(II)-ACES binding constants.
• The findings resolve previous discrepancies in the literature concerning ACES-Cu(II) interactions.
• Accurate stability constants determined here will improve the precision of biological measurements involving copper ions buffered with ACES.