. 2021 Dec 8;60(24):19448–19456. doi: 10.1021/acs.inorgchem.1c03285

Table 1. Cumulative Protonation and Stability Constants (log β) and Stepwise Constant (pK_a) Values for Aβ_5–9 (L) and Its Ni(II) Complexes at I = 0.1 M (KNO₃) and 25 °C^a.

species	log β^b	pK_a	assignment	coordination mode
[HL]¹⁺	7.37(1)	7.37	Arg1 N-term.
[H₂L]²⁺	13.51(1)	6.13	His-2
[H₃L]³⁺	16.67(1)	3.17	Asp3
[NiH_–1L]¹⁺	–0.90(1)	5.96^c		3N [N^am, N^–, N^im] +H₂O
[NiH_–2L]⁰	–9.74(1)	8.84		3N [N^am, N^–, N^im] + OH^–
[NiH_–3L]^1–	–19.49(1)	9.75		4N [N^am, 3 N^–]

K_a stands for an acidic dissociation constant.

For a general species Ni_pH_qL_r, the stability constant β is defined as β_NipHqLr = [Ni_pH_qL_r]/([Ni]^p × [H⁺]^q × [L]^r). Standard deviations on the last digits provided by HYPERQUAD, given in parentheses, represent the statistical errors of constant determinations. Assignments are based on literature values.^12,18,24

Calculated based on the distribution diagram presented in Figure 1.

Table 1. Cumulative Protonation and Stability Constants (log β) and Stepwise Constant (pKa) Values for Aβ5–9 (L) and Its Ni(II) Complexes at I = 0.1 M (KNO3) and 25 °Ca.

Table 1. Cumulative Protonation and Stability Constants (log β) and Stepwise Constant (pK_a) Values for Aβ_5–9 (L) and Its Ni(II) Complexes at I = 0.1 M (KNO₃) and 25 °C^a.