Table 2.

The apparent dissociation constants and competitivity indices (CI)^a of zinc complexes with common chemicals and natural products. Unless otherwise specified, the stability values were determined at pH 7.4, I = 0.1 M and 25 °C.

Ligands	Zinc ligand	Complex stoichiometryb	Donors c	Apparent dissociation constant (Kd)	pKd	Competitivity Index (−logCI)a	References
pH buffers	Tris	ZnL	NO∗	3.29 × 10−2 M	1.48	1.48	[110]
	Bis-Tris	ZnL	NO∗	5.03 × 10−3 M	2.30	2.30	[111]
	Bis-Tris propane	ZnL	NO∗	1.19 × 10−4 M	2.93	3.32	[112]
		ZnL2	N2O2∗	2.15 × 10−6 M2	5.66
	Bicine	ZnL	NO∗	7.50 × 10−5 M	4.12	4.39	[88]
		ZnL2	N2O2∗	3.12 × 10−7 M2	6.51
	Tricine	ZnL	NO∗	6.47 × 10−5 M	4.19	4.19	[89]
Reductants	TCEP	ZnL	O3P	3.29 × 10−3 M	3.29	3.29	[93]
	β-Mercaptoethanol	Zn2L3-Zn6L15	S2–S4 (S4)	n.c.	n.c.	3.60d	[92]
	DTT	ZnL2, Zn3L4 (ZnL)	S4 (S4)	2.83 × 10−10 M2	9.55	8.32	[90]
	DTBA	ZnL2 (ZnL, Zn2L3)	S4 (S4)	5.38 × 10−13 M2	12.27	9.29	[91]
Carboxylic acids	α-Ketoglutaric acid	ZnL, ZnL2	O2, O4	∼2 × 10−2 M2	∼1.7	1.13d	[113]
	Pyruvic acid (pyruvate)	ZnL, ZnL2	O2, O4	∼2 × 10−3 M2	∼2.7	1.26d	[114]
	Succinic acid (succinate)	ZnL	O2	2.54 × 10−2 M	1.60	1.60	[115]
	Glutaric acid (glutarate)	ZnL	O2	2.52 × 10−2 M	1.60	1.60	[115]
	Lactic acid (lactate)	ZnL	O2	1.38 × 10−2 M	1.86	1.86	[116]
	Lipoic acide	ZnL	O2	3.7 × 10−3 M	2.43	2.43	[117]
	Malic acid (malate)	ZnL	O2	1.52 × 10−4 M	3.82	3.82f	[118]
	Folic acid (folate)	ZnL2	N2O2	2.2 × 10−6 M2	5.67	2.84g	[119]
	Oxalic acid (oxalate)	ZnL	O2	3.16 × 10−4 M	3.50	3.50	[120]
	Orotic acid (orotate)	ZnL	NO	2.20 × 10−4 M	3.66	4.80f	[121]
		ZnL2	N2O2	2.40 × 10−8 M2	7.62
	Dipicolinic acid	ZnL	NO2	5.74 × 10−4 M	3.24	8.70h	[122]
		ZnL2	N2O4	1.33 × 10−12 M2	11.88
	Citric acid (citrate)	ZnL2 (ZnL)	O6 (O6)	1.17 × 10−12 M2	11.93	8.93	[41]
Amino acids	Glutamic acid (glutamate)	ZnL	NO	2.85 × 10−3 M	2.54	2.70	[66]
		ZnL2	N2O2	2.18 × 10−5 M2	4.66
	Glycine	ZnL	NO	2.40 × 10−3 M	2.62	2.82	[87]
		ZnL2	N2O2	1.29 × 10−5 M2	4.89
	Aspartic acid (aspartate)	ZnL	NO	3.92 × 10−4 M	3.40	3.54	[44]
		ZnL2	N2O2	4.13 × 10−6 M2	5.38
	N-Ac-Cys	ZnL2 (ZnL)	O2S2 (OS)	6.77 × 10−8 M2	7.17	4.06	[123]
	Histidine	ZnL	N2O	3.22 × 10−4 M	3.49	5.48	[40]
		ZnL2	N4O2	3.05 × 10−9 M2	8.52
	Cysteine	ZnL2 (ZnL)	N2S2 (NS)	9.77 × 10−12 M2	11.01	7.84i	[124]
	d-penicillamine	ZnL2 (ZnL)	N2S2 (NS)	2.81 × 10−12 M2	11.55	8.38i	[124]
Nucleotides	AMP	ZnL	NO	1.84 × 10−3 M	2.73	2.73	[125]
	ADP	ZnL	NO2	9.73 × 10−5 M	4.38	4.38	[125]
	ATP	ZnL	NO3	7.68 × 10−6 M	5.11	5.11	[125]
Redox buffers	GSSG	ZnL (Zn2L)	N2O2 (NO)	5.3 × 10−5 M	4.28	4.28	[66]
	GSH	ZnL	NOS	1.65 × 10−4 M	3.78	5.16	[126]
		ZnL2	NOS2	8.74 × 10−9 M2	8.06
	Bacillithiol	ZnL	NSO2∗	4.0 × 10−6 M	5.40	9.05j	[73]
		ZnL2	N2S2∗	5.38 × 10−13 M2	12.27
Others	Tetracycline	ZnL	O2	6.77 × 10−3 M	2.17	2.17f	[127]
	Carnosine	ZnL	NO	4.55 × 10−3 M	2.34	2.34	[128]
	Oxytetracycline	ZnL	O2	2.24 × 10−3 M	2.65	2.65f	[127]
	Diphosphate (pyrophosphate)	ZnL	O2	1.91 × 10−3 M	2.72	2.72	[32]
	Gentamicin C1a	ZnL	NO∗	1.60 × 10−3 M	2.79	2.79	[129]
	Histamine	ZnL	N2	2.98 × 10−3 M	2.53	2.96	[130]
		ZnL2	N4	5.41 × 10−6 M2	5.27
	Triphosphate	ZnL	O3	1.35 × 10−7 M	6.87	6.87	[33]
	Tetraphosphate	ZnL	O4∗	5.72 × 10−8 M	7.24	7.24	[34]
	Pyrithione	ZnL2k (ZnL)	O2S2k (OS)	5.0 × 10−12 M2	11.30	8.30	[76]
	Phytic acid (phytate)	ZnL	O5∗	3.7 × 10−11 M	10.44	10.44	[35]
	Nicotianamine	ZnL	N3O3	1.60 × 10−11 M	10.48	10.48	[82], [131]

^aCI is the apparent dissociation constant of ZnZ complex (zinc complex of theoretical molecule Z), such that [ZnZ] = Σ_ijk [ZniHjLk], at a given overall component concentration. The concentrations of Z were set at 2 mM, and those of Zn²⁺ at 0.5 mM.

^bComplexes in brackets are the minor species.

^cDonors in brackets refer to complex as minor species.

^dI = 0.5 M.

^eDihydrolipoic acid (reduced form of lipoic acid) is assumed to bind Zn²⁺ more tightly.

^f37 °C, I = 0.15 M.

^g20 °C, I = 0.01 M.

^h20 °C.

ⁱI = 0.2 M.

^jApparent dissociation constant determined at pH 7.7, I = 0.15 M.

^kComplex in crystals present as dinuclear Zn₂L₄ species with S₃O₂ donors. n.c. – not calculated. Asterisks denote putative donor atoms.