Metal–organic complexation in the marine environment

Table 2 Electrochemical and stability constant data for Fe(III) complexes with selected "model" ligands⁴⁷and natural siderophores.[48] Measurements were made in 5 mM Bistris buffer adjusted to 0.1 M ionic strength with NaCl

Complex^a	pH	E'_p ^b/V vs. SCE	Log K_i ^c(I = 0.1, 25°C)
Model ligands
1. [FeCDTA]^-	7	-0.145	30.0
2. [FeNTAtiron]^--	7	-0.182	31.7
3. [FeNTAcat]^2-	7	-0.211	32.9
4. [Fe(cat)₂]^-	7	-0.354	34.7
5. [Fe(4Ncat)₃]^3-	7	-0.440	40.0
6. [Fe(cat)₃]^3-	10	-0.680	43.7
7. [Feent]^3-	7	-0.924	49.0
Siderophores
8. [Fe(Alt-B)₂]	6	-0.428	37.6
9. [Fe(Alt-B)₂]	8.2	-0.672	43.6
10. Fe-PCC7002 No. 1	7	-0.445	38.1
11. Fe-PCC7002 No. 3	7	-0.618	42.3
12. Decapeptides mefpl	7	~-0.510	39.6
13. mefpl	7	-0.542	41.6

^aCDTA = cis-l,2-cyclohexylenedinitrilotetraacetate, NTA = nitrilo-triacetate, tiron = 4,5-dihydoxy-l,3-benzene disulfonic acid, cat = catechol, 4Ncat = 4-nitrocatechol, ent = enterobactin, Alt-B = altero-bactin B, PCC7002 = Synechococcus sp. PCC7002 isolates (complex stoichiometry is not known for eqn.(10) and (11)). ^b± 10 mV. ^cSee Table 1 of ref. 47 for references.

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