Cu(II) complex formation by ACES buffer.
ACES (N-(2-Acetamido)-2-aminoethanesulfonic acid), a popular Good's buffer, binds Cu(II) ions with a moderate affinity. Although this interaction was the subject of previous studies, no consensus in the literature was found. We used potentiometry to establish binding constants, and controlled the potentiometric model selection and binding constant calculations by UV-vis spectroscopy. As a result, we obtained a consistent set of complex stoichiometries and binding constants in this system, which contains Cu(2+), CuL(+), CuL2, CuH-1L2(-1) and CuH(-)2L2(-2) complexes. The negative indexes at H atoms in these formulae denote the Cu(II) assisted deprotonation of the amide nitrogen present in the ACES molecule. The affinity of ACES for Cu(II) strongly depends on the concentration and ACES:Cu(II) ratio, reaching submicromolar apparent affinities at ratios higher than 100. These results will enable more accurate determinations of biologically relevant stability constants of Cu(II) complexes using ACES buffer.
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland.
Izabela
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Zawisza
Małgorzata
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Rózga
Jarosław
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Poznański
Wojciech
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Bal
D002021:Buffers; D003300:Copper / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013654:Taurine / Q000031:analogs & derivatives* / Q000737:chemistry
D002021:Buffers; D013654:Taurine; C024789:N-(2-acetamido)-2-aminoethanesulfonic acid; D003300:Copper
ACES buffer; Cu(II) complex; Potentiometry; Spectroscopy; Stability constant