Table 1. Protonation and Stability Constants (log β) for His-Leu (L) and Its Cu(II) Complexes at an Ionic Strength of 0.1 M (KNO₃) at 25 °C^a.

species	log β	pK	assignment of the deprotonation event
HL	7.55(1)	7.55	Nam His
H2L	13.56(1)	6.01	Nim His
H3L	16.05(1)	2.49	COO– Leu
CuHL	12.31(2)
CuL	8.70(1)	3.61	Nam His/Nim His/COO– Leu
CuH–1L	2.00(1)	6.70	N– Leu
CuH–2L	–8.47(1)	10.47	OH–
CuHL2	20.04(3)
CuL2	14.84(1)	5.20	Nim His

^aStandard deviations in parentheses.