Luminol

• 3- aminophthalhydrazide
• 3- aminophthalhydrazide
• 5-amino- 2 ,3- dihydrophthalazine -1 ,4 -dione

Fixed

319-320 ° C

Attention

> 500 mg · kg -1 ( LD50, rat, oral)

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Luminol is a yellowish to green, shimmering, water-insoluble solid chemical compound formally derived from aniline, phthalic acid and hydrazine.

Extraction and production

The production of luminol via the nitration of phthalic acid to 3 - nitrophthalic acid, the reaction with hydrazine to give 3- Nitrophthalsäurehydrazid and subsequent reduction with sodium dithionite to the luminol.

Use

Luminol is used in forensics to search for clues, even minute amounts of blood can be detected with this. The detection is based on that of luminol with oxidizing agents (usually hydrogen peroxide) to emit bluish light ( chemiluminescence ) responds. This reaction is sufficiently fast only in the presence of a catalyst (in this complexed Fe 2 ), i.e., in practice, in the absence of catalysts, no response or no chemiluminescence observed.

To search for traces two solutions were prepared: A solution of luminol in sodium hydroxide solution and a dilute hydrogen peroxide solution. These are combined shortly before use, and the sprayed surface to be examined. If there are traces of blood on it, so catalyzes the blood pigment hemoglobin (contains heme, an iron complex ) the reaction described above. This therefore results in a bluish chemiluminescence. The test is sensitive enough to detect tiny amounts of blood in the urine, making urine stains also "positive" appear. However, the reaction is catalyzed by the copper ions which interfere with this test therefore.

The addition of other substances, the sensitivity can be varied: In a series of tests could be demonstrated that active ingredients in the dishwashing Fit intensify the fluorescence, but at the same time shorten. The reason for this could be in detergent detergents that make the plasma membranes of red blood cells more permeable, causing the luminol comes quickly in contact with the Fe2 .

A much more important application is the luminol chemiluminescence in the biochemical and medical analysis. Here, for example, so-called reactive oxygen species ( ROS) in tissues extracts and body fluids are directly determined by the intensity of luminol chemiluminescence. Another important method of analysis based on the fact that peroxidases are able to catalyze the luminol reaction. On this principle, numerous immunoassays are constructed, which can be detected extremely low levels of toxins, pathogens, peptides and proteins. The main purpose peroxidase used is horseradish peroxidase (HRP, horseradish peroxidase ). The catalytic effect of horseradish peroxidase, you can test yourself by dropping a few drops of an alkaline luminol / hydrogen peroxide solution on a piece of fresh horseradish.

Chemiluminescence reaction

In the chemiluminescence reaction with luminol is as a starting material to a dicarbonyl compound, a so-called 1,4 -dione.

The material is first dissolved in sodium hydroxide solution, with luminol reacts as acid H cleavage with the hydroxide ions of the sodium hydroxide solution. This reaction is a reversible equilibrium reaction.

The resulting dianions are stabilized by resonance.

The actual reaction begins with the oxidation of the dianion with hydrogen peroxide or another oxidizing agent. In addition to molecular nitrogen results in a phthalate that 3- aminophthalate dianion, as an unstable intermediate in the excited triplet state (T1). The triplet state is a result of two electrons with the same spin in an orbital of an oxygen atom before the (2S 1 = 3 for S = 2 * 1 = 1/2, see multiplicity ). Through a non-radiative transition, the molecule ( S1) goes with a spin - flip in a isoenergetic excited singlet state.

The energy-rich oxidized luminol chemiluminescence in this molecule serves simultaneously as a sensitizer. By the transfer of an electron from the excited to the singlet ground state ( S0), a photon emitted in the blue region of the light spectrum.