Table 1. Deprotonation Constants for Shep I Peptide and Stability Constants for Its Complexes with Cu(II) and Zn(II) Ions in an Aqueous Solution of 4 mM HClO₄ with I = 0.1 M NaClO₄ at 298 K^a.

Shep I				Shep I–Cu(II)			Shep I–Zn(II)
species	log βjkb	pKb,c	residue	species	log βjkd	pKae	species	log βjke	pKae
[H10L]9+	72.20(1)	5.29	His
[H9L]8+	66.91(2)	5.76	His	[CuH8L]9+	67.57(5)
[H8L]7+	61.15(3)	6.04	His	[CuH7L]8+	63.21(2)	4.36
[H7L]6+	55.11(5)	6.40	His	[CuH6L]7+	58.22(2)	4.99	[ZnH6L]7+	54.09(3)
[H6L]5+	48.71(6)	6.54	His	[CuH5L]6+	52.42(2)	5.80	[ZnH5L]6+	48.35(2)	5.74
[H5L]4+	42.17(4)	6.97	His	[CuH4L]5+	45.92(2)	6.50	[ZnH4L]5+	42.04(2)	6.31
[H4L]3+	35.20(3)	7.21	His	[CuH3L]4+	38.54(3)	7.38	[ZnH3L]4+	34.92(2)	7.12
[H3L]2+	27.99(2)	8.03	His	[CuH2L]3+	30.74(3)	7.80	[ZnH2L]3+	26.72(3)	8.20
[H2L]+	19.96(1)	9.58	NH2	[CuHL]2+	21.57(4)	9.17	[ZnHL]2+	17.27(3)	9.45
[HL]	10.38(1)	10.38	Tyr	[CuL]+	11.89(4)	9.68	[ZnL]+	7.59(3)	9.68
				[CuH–1L]	1.95(3)	9.94
				[CuH–3L]2–	–20.00(3)

^aC_L = 0.5 mM; molar ratio M/L = 0.9:1. The standard deviations are reported in parentheses as uncertainties on the last significant figure.

^bProtonation constants are presented as cumulative log β_jk values. β(H_jL_k) = [H_jL_k]/([H]_j[L]_k), in which [L] is the concentration of the fully deprotonated peptide.

^cpK_a = log β(H_jL_k) – log β(H_j – 1L_k).

^dCu(II) and Zn(II) stability constants are presented as cumulative log β_ijk values. L stands for a fully deprotonated peptide ligand that binds Cu(II) and Zn(II) ions. β(M_iH_jL_k) = [M_iH_jL_k]/([M]_i[H]_j[L]_k), where [L] is the concentration of the fully deprotonated peptide.

^epK_a = log β(M_iH_jL_k) – log β(M_iH_j – 1L_k).