Fluorescein-6-isothiocyanate is a fluorescent isomeric haptenic probe. It has Kds of 8.74, 2.72 and 1.88 for N-Acetyl-L-Lysine, normal mouse IgG and 4-4-20, respectively.

Physicochemical Properties

Molecular Formula	C21H11NO5S
Molecular Weight	389.3807
Exact Mass	389.035
CAS #	18861-78-4
PubChem CID	2762652
Appearance	Light yellow to brown solid powder
Density	1.5±0.1 g/cm3
Boiling Point	719.1±60.0 °C at 760 mmHg
Flash Point	388.7±32.9 °C
Vapour Pressure	0.0±2.4 mmHg at 25°C
Index of Refraction	1.754
LogP	4
Hydrogen Bond Donor Count	2
Hydrogen Bond Acceptor Count	7
Rotatable Bond Count	1
Heavy Atom Count	28
Complexity	668
Defined Atom Stereocenter Count	0
InChi Key	GTQFZXYECNSNNC-UHFFFAOYSA-N
InChi Code	InChI=1S/C21H11NO5S/c23-12-2-5-15-18(8-12)26-19-9-13(24)3-6-16(19)21(15)17-7-11(22-10-28)1-4-14(17)20(25)27-21/h1-9,23-24H
Chemical Name	3',6'-dihydroxy-5-isothiocyanatospiro[2-benzofuran-3,9'-xanthene]-1-one
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month Note: This product requires protection from light (avoid light exposure) during transportation and storage.
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

References	[1]. Fluorescence measurements of immune complexes of Mab 4-4-20 with isomeric haptens. Biophys J. 1991 Mar;59(3):619-28.
Additional Infomation	Fluorescein 6-isothiocyanate is the 6-isomer of fluorescein isothiocyanate.

Solubility Data

Solubility (In Vitro)

DMSO : ~250 mg/mL (~642.05 mM)

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 2.08 mg/mL (5.34 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL. Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 2: ≥ 2.08 mg/mL (5.34 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Solubility in Formulation 3: ≥ 2.08 mg/mL (5.34 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	2.5682 mL	12.8409 mL	25.6819 mL
	5 mM	0.5136 mL	2.5682 mL	5.1364 mL
	10 mM	0.2568 mL	1.2841 mL	2.5682 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.