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| Names | |
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| Pronunciation | /flʊəˈrɛsi.ɪn,flʊəˈrɛsiːn/ |
| IUPAC name 3′,6′-dihydroxyspiro[isobenzofuran-1(3H),9′-[9H]xanthen]-3-one | |
| Other names Resorcinolphthalein, C.I. 45350, solvent yellow 94, D&C yellow no. 7, angiofluor, Japan yellow 201, soap yellow | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| DrugBank |
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| ECHA InfoCard | 100.017.302 |
| EC Number |
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| KEGG |
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| MeSH | Fluorescein |
| UNII | |
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| Properties | |
| C20H12O5 | |
| Molar mass | 332.311 g·mol−1 |
| Melting point | 314 to 316 °C (597 to 601 °F; 587 to 589 K) |
| Slightly | |
| Pharmacology | |
| S01JA01 (WHO) | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H319 | |
| P305,P338,P351 | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Fluorescein is anorganic compound anddye based on thexanthene tricyclic structural motif, formally belonging totriarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is used as afluorescenttracer in many applications.[1]
The color of its aqueous solutions is green by reflection and orange by transmission (its spectral properties are dependent onpH of the solution),[2] as can be noticed inbubble levels, for example, in which fluorescein is added as acolorant to thealcohol filling the tube in order to increase the visibility of the air bubble contained within. More concentrated solutions of fluorescein can even appear red (because under these conditions nearly all incident emission is re-absorbed by the solution).
It is on theWorld Health Organization's List of Essential Medicines.[3]
Fluorescein sodium, the sodium salt of fluorescein, is used extensively as a diagnostic tool in the field ofophthalmology andoptometry, where topical fluorescein is used in the diagnosis ofglobe rupture,[4]corneal abrasions,corneal ulcers andherpetic corneal infections. It is also used inrigid gas permeable contact lens fitting to evaluate the tear layer under the lens. It is available as sterile single-use sachets containing lint-free paper applicators soaked in fluorescein sodium solution.[5]
The thyroxine ester of fluorescein is used to quantify thethyroxine concentration inblood.[1]
Fluorescein is also known as a color additive (D&C Yellow no. 7). The disodium salt form of fluorescein is known asuranine orD&C Yellow no. 8.
Fluorescein is a precursor to the red dyeeosin Y by bromination.[1]
Oral and intravenous use of fluorescein can causeadverse reactions, includingnausea,vomiting,hives,acutehypotension,anaphylaxis and relatedanaphylactoid reaction,[6][7] causingcardiac arrest[8] and sudden death due toanaphylactic shock.[9][10]
Intravenous use has the most reported adverse reactions, including sudden death, but this may reflect greater use rather than greater risk. Both oral and topical uses have been reported to cause anaphylaxis,[11][12] including one case of anaphylaxis with cardiac arrest (resuscitated) following topical use in an eye drop.[8] Reported rates of adverse reactions vary from 1% to 6%.[13][14][15][16] The higher rates may reflect study populations that include a higher percentage of persons with prior adverse reactions. The risk of an adverse reaction is 25 times higher if the person has had a prior adverse reaction.[15] The risk can be reduced with prior (prophylactic) use of antihistamines[17] and prompt emergency management of any ensuing anaphylaxis.[18] A simple prick test may help to identify persons at greatest risk of adverse reaction.[16]
The fluorescence of this molecule is very intense; peak excitation occurs at 495 nm and peak emission at 520 nm. Values for the deprotonated form in basic solution.[citation needed]
Fluorescein has apKa of 6.4,[2] and its ionization equilibrium leads to pH-dependentabsorption andemission over the range of 5 to 9. Also, the fluorescence lifetimes of the protonated and deprotonated forms of fluorescein are approximately 3 and 4 ns, which allows for pH determination from nonintensity based measurements. The lifetimes can be recovered usingtime-correlated single photon counting or phase-modulationfluorimetry. Upon exhaustive irradiation with visible light fluorescein decomposes to releasephthalic andformic acids andcarbon monoxide, effectively acting as a photoCORM. The remainingresorcinol rings react withsinglet oxygen formedin situ to give oxidized,ring-opened products.[19]
Fluorescein has anisosbestic point (equal absorption for allpH values) at 460 nm.
Many derivatives of fluorescein are known. Examples are:
Inoligonucleotide synthesis, several phosphoramidite reagents containing protected fluorescein, e.g.6-FAM phosphoramidite2,[20] are used for the preparation of fluorescein-labeledoligonucleotides.
The extent to which fluorescein dilaurate is broken down to yieldlauric acid can be detected as a measure of pancreaticesterase activity.
Approximately 250 tons were produced in the year 2000. The method involves the fusion ofphthalic anhydride andresorcinol,[1] similar to the route described byAdolf von Baeyer in 1871.[21] In some cases, acids such aszinc chloride andmethanesulfonic acid are employed to accelerate theFriedel-Crafts reaction.[22][23]
Fluorescein is afluorophore commonly used inmicroscopy, in a type ofdye laser as thegain medium, inforensics andserology to detect latent blood stains, and indye tracing. Fluorescein has anabsorption maximum at 494 nm andemission maximum of 512 nm (in water). The major derivatives arefluorescein isothiocyanate (FITC) and, inoligonucleotide synthesis,6-FAM phosphoramidite.
In cellular biology, theisothiocyanate derivative of fluorescein is often used to label and trackcells influorescence microscopy applications (for example,flow cytometry). Additional biologically active molecules (such asantibodies) may also be attached to fluorescein, allowing biologists to target the fluorophore to specific proteins or structures within cells. This application is common inyeast display.
Fluorescein can also be conjugated tonucleoside triphosphates and incorporated into aprobe enzymatically forin situ hybridisation. The use of fluorescein amidite, shown below right, allows one tosynthesize labeledoligonucleotides for the same purpose. Yet another technique termedmolecular beacons makes use of synthetic fluorescein-labeled oligonucleotides. Fluorescein-labelled probes can be imaged usingFISH, or targeted byantibodies usingimmunohistochemistry. The latter is a common alternative todigoxigenin, and the two are used together for labelling two genes in one sample.[24]
Intravenous or oral fluorescein is used influorescein angiography in research and to diagnose and categorize vascular disorders including retinal disease,macular degeneration,diabetic retinopathy, inflammatory intraocular conditions, and intraoculartumors. It is also being used increasingly during surgery forbrain and spine tumors.[25]
Diluted fluorescein dye has been used to localise multiple muscular ventricular septal defects during open heart surgery and confirm the presence of any residual defects.[26]
Fluorescein is used as a rather conservativeflow tracer in hydrologicaltracer tests to help in understanding of water flow of bothsurface waters andgroundwater. The dye can also be added torainwater in environmental testing simulations to aid in locating and analyzing any water leaks, and in Australia and New Zealand as amethylated spirit dye.
As fluorescein solution changes its color depending on concentration,[27] it has been used as a tracer in evaporation experiments.
One of its more recognizable uses was in theChicago River, where fluorescein was the first substance used to dye the river green onSt. Patrick's Day in 1962. In 1966, environmentalists forced a change to a vegetable-based dye to protect local wildlife.[28]
Fluorescein dye solutions, typically 15% active, are commonly used as an aid to leak detection duringhydrostatic testing ofsubseaoil and gaspipelines and other subsea infrastructure. Leaks can be detected by divers orROVs carrying an ultraviolet light.
Fluorescein has often been used to track water movement ingroundwater to study water flow and observe areas of contamination or obstruction in these systems. Thefluorescence that is created by the dye makes problem areas more visible and easily identified. A similar concept can be applied to plants because the dye can make problems in plant vasculature more visible. Inplant science, fluorescein, and other fluorescent dyes, have been used to monitor and studyplant vasculature, particularly thexylem, which is the main water transportation pathway in plants. This is because fluorescein is xylem-mobile and unable to crossplasma membranes, making it particularly useful in tracking water movement through the xylem.[29] Fluorescein can be introduced to a plant's veins through the roots or a cut stem. The dye is able to be taken up into the plant the same way as water and moves from the roots to the top of the plant due to a transpirational pull.[30] The fluorescein that has been taken up into the plant can be visualized under afluorescent microscope.
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