Fluorescein

• Fluorescein
• Fluorescein
• Resorcinphthalein
• 6-hydroxy -9 -(2- carboxyphenyl) - (3H)- xanthen- 3-one
• 2 - (6 -hydroxy-3 -oxo- (3H)- xanthen- 9-yl) -benzoic acid
• C. I. 45350

• 2321-07-5 (acid)
• 518-47-8 (sodium salt)

• S01JA01
• V04CX03

Red crystals

Fixed

314-316 ° C ( decomposition)

Insoluble in water, slightly soluble in ethanol, DMSO, diethyl ether, and alkalies

Attention

Template: Infobox chemical / molecular formula search available

Fluorescein is a fluorescent dye selected from the group consisting of xanthene dyes.

History

Fluorescein and other phthaleins were discovered in 1871 by Adolf von Baeyer. The alternative name Resorcinphthalein owes the fabric to the starting materials from which it synthesized Adolf von Baeyer. He mixed phthalic anhydride ( phthalic acid is also used ) with resorcinol and added concentrated sulfuric acid are added as a dehydrating agent. He then heated the mixture to a thick liquid melt and then treated the cooled melt with warm water and ammonia, then he brought the approach in plenty of distilled water.

Representation

Fluorescein (2) is usually prepared by condensation of one equivalent of phthalic anhydride (1) and two equivalents of resorcinol with elimination of water to a catalyst shown. Suitable catalyst is either concentrated sulfuric acid or anhydrous zinc chloride.

Properties

Fluorescein exists in two different structures. The more stable is the open - acid form is present in the solid state as a red crystal. In addition there exists the spiro -lactone form, which forms an unstable yellow compound.

• Extinction coefficient: 93 000 l · cm -1 · mol -1 ( pH 9)
• Quantum yield: 0.93 (50 micromol fluorescein in 0.1 mol sodium borate buffer, pH 9.5)

Use

Fluorescein is used in analytical chemistry as an indicator. In addition, it is designed to detect bromides, the source of staining and staining of soaps and bath extracts / salts. Fluorescein is a further fluorescent dye which upon excitation with blue light ( maximum absorption at a wavelength of 496 nm, for example, by an argon -ion laser ) emits green light (wavelength 520 to 530 nm ). Related reactive dyes such as fluorescein isothiocyanate (FITC ) can be coupled to and be used for fluorescence microscopy or flow cytometry with various antibodies ( immunoglobulins ). This allows in fluids, cells or tissues, then specific surface properties (antigens), for example, pathogens can be detected. We call this technique work as a direct immunofluorescence. Furthermore, fluorescein is used as a coloring agent in ophthalmology at the fluorescein angiography and applanation tonometry.

Fluorescein has a high quantum yield of up to 93 %, its usefulness for the fluorescent labeling but is constrained by a number of disadvantages: The fluorescence intensity depends on the pH and drops sharply below pH 7 ( pK a ≈ 6.4 ). Under illumination, the fluorescence also goes back ( strong photobleaching ) quickly. The fluorescence maximum is not very sharp, the corresponding absorption band quite wide.

Analysis

The classical detection is based on the bromination by the red eosin ( Tetrabromfluorescein ) is formed. In addition, dilute solutions of fluorescein fall by their yellow-green fluorescence color, on which also the name is based on.

Uranin

The water-soluble sodium salt of fluorescein is called uranine (same CI number 45350 ) and is a manifold used yellow under UV and sunlight green fluorescent dye.

Uranine in aqueous solution has an enormous coloring ( thus leads against a white background already a Uraninkonzentration of 0.1 mg / l to a visible discoloration).

Thus, when shipwrecked or after Ditchings can with a lot of just 500 g Uranin a sea area of ​​about 4000 m2 colored conspicuous and thus the discovery by search parties, just from the air, to be facilitated.

The dye is still used in many ways, especially for coloring foam baths, bath additives, shampoos, cosmetics and antifreeze for car radiator ( to be able to view the addition of antifreeze to the coolant). Uranin is considered biologically safe. Therefore, it is used by hydrologists and hydrogeologists as so-called tracer for tracing groundwater flows and underground rivers. 1877 has one at Immendingen 10 kg uranine in the Danube introduced and noticed 60 hours in the river Aach a distinct fluorescence, thereby Donauversickerung could be elucidated. Furthermore, you use it also with the tightness testing of flat roofs and tanks.

Uranin is also used for decoration, for example fluorescent colors in nightclubs or scene images ( in science fiction or horror movies: lightened with UV light Uranin sees " toxic - radioactive " from ). Every year on March 17, St. Patrick 's Day, was the Chicago River, which flows through Chicago, colored with uranine green. Due to the intervention of the EPA Uranin is replaced by another dye since 2003.