Protonation constants of macropa^a and macropa-β-ala and thermodynamic stability constants of their alkaline earth complexes determined by pH potentiometry (25 °C and I = 0.1 M KCl).

	Macropa-β-ala4−f	Macropa2−
log Ka1	11.25(0.11), 11.36(0.01)b	7.41c, 7.41d
log Ka2	7.49(0.03)	6.90c, 6.85d
log Ka3	6.90(0.02)	3.23c, 3.32d
log Ka4	4.32(0.03)	2.45c, 2.36d
log Ka5	3.19(0.01)	1.69d
log Ka6	2.51(0.05)
log KBaL	11.06(0.10)	11.11c
log KBaHL	11.18(0.05)	3.76c
log KBaH2L	4.54(0.03)	2.49c
log KBaH3L	3.67(0.03)
log KSrL	9.58(0.13)	9.44c, 9.57e
log KSrHL	10.97(0.12)	3.35c, 4.16e
log KSrH2L	4.59(0.03)
log KCaL	6.15(0.05)	5.79c, 5.25e
log KCaHL	10.78(0.06)

^aData provided for comparison.

^bFrom combined UV spectrophotometric-potentiometric titrations.

^cRef. 55, I = 0.1 M KCl.

^dRef. 47, I = 0.1 M KCl.

^eRef. 48, I = 0.1 M KNO₃.

^fValues in parentheses correspond to one standard deviation.