Table 4. Stability Constants (log β) and pK_a Values of the Mn(II)/Peptide Systems^a.

peptide	species	log βb	pKac	deprotonating residue
P1	[MnH4L]+	37.88(6)
	[MnH3L]	31.42(5)	6.46	His
	[MnH2L]−	23.23(7)	8.19	Cys
	[MnHL]2–	14.46(7)	8.77	Cys
	[MnLH–1]4–	–6.07(4)		Cys, Owater
P2	[MnH5L]6+	42.29(4)
	[MnH4L]5+	38.65(2)	3.64	Glu
	[MnH3L]4+	33.45(3)	5.20	His
	[MnH2L]3+	26.12(4)	7.33	Cys
	[MnHL]2+	17.53(4)	8.59	Cys
	[MnL]+	8.20(4)	9.33	Cys
	[MnLH–2]2–	–12.21(4)		Owater, Owater/Owater, Lys

^aT = 298 K; I = 0.1 M NaClO₄; standard deviations (3σ values) are given in parentheses.

^bOverall stability constants (β) expressed by the equation β([MnH_nL](ⁿ⁺²)⁺) = [[MnH_nL]⁽ⁿ⁺²⁾⁺]/[Mn(II)][[L]ⁿ⁺][H⁺]ⁿ).

^cAcid dissociation constants (pK_a) expressed as pK_a = log β([MnH_nL]⁽ⁿ⁺²⁾⁺) – log β([MnH_n–1L]⁽ⁿ⁺¹⁾⁺).