Table 3.

The apparent dissociation constants^a of zinc complexes with widely used zinc chelators and fluorogenic or chromophoric probes with pZn ranges of their application.^b Unless otherwise specified, the stability values were determined at pH 7.4, I = 0.1 M and 25 °C. Stoichiometry is simplified to ZnL_x without protonation state.

	Chelator/probe	Donors	Complex stoichiometry	Apparent dissociation constant (Kd)	−log Kd (pKd)	pZn range of the application	References
Zinc chelators	TPEN	N6	ZnL	6.4 × 10−16 M	15.2	14.2–16.2	[44]
	DTPA	N2O4	ZnL	5.6 10−15 M	14.3	13.3–15.2	[44]
	EDTA	N2O4	ZnL	2.3 × 10−14 M	13.6	12.7–14.6	[44]
	HEDTA	N2O3	ZnL	6.6 × 10−13 M	12.2	11.2–13.1	[44]
	EDDSc	N2O4	ZnL	2.3 × 10−11 M	10.6	9.7–11.6	[44]
	BAPTA	N2O4	ZnL	4.9 × 10−10 M	9.3	8.4–10.3	[132]
	EGTA	N2O4	ZnL	6.3 × 10−10 M	9.2	8.2–10.2	[44]
	EDDA	N2O2	ZnL	1.2 × 10−9 M	8.9	8.0–9.9	[44]
	NTA	NO3	ZnL	4.4 × 10−9 M	8.4	7.4–9.3	[133]
	Cyclamd	N4	ZnL	2.0 × 10−9 M	8.7	7.5–9.5	[134]
	IDA	NO2	ZnL	3.2 × 10−5 M	4.5	5.3–6.8	[135]
		N2O4	ZnL2	4.8 × 10−9 M2	8.3
Fluorescent probes	FluoZin-3	N2O3	ZnL	8.9 × 10−9 M	8.1	7.1–9.0	[9]
	RhodZin-3	N2O3	ZnL	1.4 × 10−9 M	8.9	7.9–9.8	[136]
	ZnAF-1	N4	ZnL	7.8 × 10−10 M	9.1	8.2–10.1	[137]
	ZnAF-2	N4	ZnL	2.7 × 10−9 M	8.6	7.6–9.5	[137]
	ZnAF-1F	N4	ZnL	2.2 × 10−9 M	8.7	7.7–9.6	[137]
	ZnAF-2F	N4	ZnL	5.5 × 10−9 M	8.3	7.3–9.2	[137]
	Zinpyr-1e	N3O	ZnL	7 × 10−10 M	9.2	8.2–10.1	[138]
	Zinpyr-4e	N4	ZnL	6.5 × 10−10 M	9.2	8.2–10.1	[139]
	NBD-TPEAf	N5	ZnL	2 × 10−9 M	8.7	7.8–9.7	[140]
	Zinbo-5f	N3O	ZnL	2.2 × 10−9 M	8.7	7.7–9.6	[141]
	Fura-2f	N2O4	ZnL	3 × 10−9 M	8.5	7.5–9.4	[142]
	Mag-Fura-2	NO3	ZnL	2 × 10−9 M	8.7	7.7–9.6	[143]
	NewPort Green DCFg	N3	ZnL	1 × 10−6 M	6.0	5.1–6.9	[144]
	NewPort Green PDXe	N3	ZnL	4 × 10−5 M	4.4	3.9–5.4	[145]
	Zinquinh	N4	ZnL	3.7 × 10−7 M	6.4	7.0–9.3	[146]
			ZnL2	8.5 × 10−13 M2	13.1
Chromophoric probes	Zincon	N2O2	ZnL	1.3 × 10−5 M	4.9	4.2–5.9	[147]
	PAR	N2O	ZnL	2.75 × 10−5 M	4.6	7.3–9.4	[148]
		N4O	ZnL2	7.08 × 10−13 M2	12.2

^aDissociation constants of ZnL and ZnL₂ are defined as [Zn²⁺][L]/[ZnL] and [Zn²⁺][L]²/[ZnL₂], respectively.

^bThe pZn range for application of a particular chelator/probe refers to free zinc values (−log[Zn²⁺]_free) corresponding to 0.9 mM: 1 mM–0.1 mM: 1 mM molar ratio (Zn²⁺: L) range. For IDA the application range refers to 0.45 mM: 1 mM–0.05 mM: 1 mM molar ratio range. In the case of Zinquin and PAR, the pZn range corresponds to 10 μM: 4.5 μM–10 μM: 0.5 μM and 100 μM: 45 μM–100 μM: 5 μM, respectively due to limited solubility and typical range of use. It should be noted that the range of application for some probes is wider due to a higher signal upon Zn²⁺ binding. For those probes, free zinc below 10% of probe saturation can be measured.

^cT = 20 °C.

^dI = 0.2 M.

^epH = 7.0.

^fpH = 7.5.

^gExperimental pH value unknown.

^hData determined in HBBS buffer.