Table II.

The pKa, log K_Fe(III), and pFe³⁺ values of phytosiderophores as determined by potentiometric and spectrophotometric titration

Phytosiderophore	pKa Values					log KFeIII	pFeIII
	pKa1	pKa2	pKa3	pKa4	pKa5		pH 5.5	pH 7.0
PSII	2.30	2.72	3.47	7.54	9.56	18.5	13.46	16.15
MA	2.39	2.76	3.40	7.78	9.55	17.7	12.66	15.19
DMAa	2.35b	2.74b	3.20	8.25	10.00	18.4	12.24	15.01
eHMAa	2.35b	2.74b	3.25	7.10	9.62	17.7	13.04	15.60

^a Data from Murakami et al., 1989. 

^b Estimated from analogous studies with MA and PSII.