Table 2. Stability Constants (log β^a and pK_a Values) of Cu(II) Complexes of Aβ_5–9, Aβ_5–12, and Aβ_5–16 (L) at I = 0.1 M (KNO₃), Determined by Potentiometry at 25 °C^b.

Species	Log βa	pKa	Assignment	Coordination Mode
Aβ5–9
CuL	9.48(1)			3N+H2O
CuH–1L	5.66(1)	3.82	Asp7	3N+H2O
CuH–2L	–3.69(1)	9.35	Equatorial H2O	3N+OH–
Total 3N+H2O		3.61		3N+H2O
Aβ5–12
CuH2L	23.72(3)			3N+H2O
CuHL	20.44(1)	3.23	Asp7	3N+H2O
CuL	15.76(1)	4.69	Glu11	3N+H2O
CuH–1L	6.29(2)	9.47	Tyr10/H2O	3N/Tyr10 and 3N+OH–
CuH–2L	–3.76(2)	10.05	H2O/Tyr10	3N+OH–
Total 3N+H2O		3.66
Aβ5–16
CuH5L	46.00(2)			3N+H2O
CuH4L	42.79(1)	3.212	Asp7	3N+H2O
CuH3L	38.62(1)	4.169	Glu11	3N+H2O
CuH2L	33.46(1)	5.159	His13/14	3N+N
CuHL	26.11(2)	7.35	His13/14	3N+N
CuL	16.43(3)	9.68	Equatorial H2O/Tyr10/Lys16	3N+N/3N+OH–
CuH–1L	6.56(3)	9.87
CuH–2L	–3.38(2)	9.94
Cu2HL	31.50(1)
Cu2L	25.37(1)	6.134	His13/14 N–	3N+H2O + 2N
Cu2H–1L	19.08(1)	6.29		3N+H2O + 3N
Cu2H–2L	10.15(1)	8.93	Val12/Glu11 N–	3N+H2O + 4N
Cu2H–3L	1.05(1)	9.1	Equatorial H2O	3N/OH- + 4N
Cu2H–4L	–9.4(1)	10.45	Lys16/Tyr10	3N/OH- + 4N
Cu2H–5L	–19.94(9)	10.54		3N/OH- + 4N
Total 3N+H2O		3.62

^aβ(Cu_mH_nL) = [M_mH_nL]/([M]_m[L][H⁺]_n).

^bStandard deviations on the last digits provided by HYPERQUAD,²⁸ given in parentheses, represent statistical errors of constant determinations. Assignments are based on literature values.^20,21,29,30 Coordination modes are derived from the analysis presented below.