DAPI

• DAPI
• 2 - (4- carbamimidoylphenyl ) - 1H-indole -6- carboximidamide

Yellow, odorless solid ( dihydrochloride)

Fixed

~ 330 ° C ( decomposition)

Soluble in water

Template: Infobox chemical / molecular formula search available

4 ',6- diamidine -2-phenylindole, short DAPI, a fluorescent dye is employed in fluorescence microscopy to label DNA.

DAPI as the fluorescent dye

The connection is deposited preferentially to AT-rich regions in the minor groove of DNA. Upon excitation with ultraviolet light DAPI fluoresces in the visible range with blue color to cyaner. In connection with double-stranded DNA, the absorption maximum at a wavelength of 358 nm, the emission peak at 461 nm

DAPI can bind to RNA that is present in large quantities in most of the active cells. These are intercalated in the RNA. However, the fluorescence is five times weaker than when it is bound to AT-rich DNA. The emission maximum is then up to 500 nm, the emission maxima of DNA - and RNA - bound DAPI thus differ enough to separate them with the help of optical filters and beamsplitters can. DAPI is therefore used to (only ) to stain DNA and represent, for example, cell nuclei. This is not possible with many other Nucleinsäurefarbstoffen because the emission spectra of the DNA - and RNA - bound dye molecules are almost identical. DAPI is therefore often referred to as " DNA - specific " although this is, strictly speaking, only for the emission at 461 nm (blue ) holds.

DAPI emits the short-wavelength ( blue ) end of the spectrum of visible light. Therefore, at the same time more fluorescent dyes can be used with longer wavelength emission maxima in the same preparation without causing signal overlaps ( "bleed through" ). DAPI can for example be used concomitantly with green, yellow or red fluorescent markers such as fluorescein, Alexa 488, GFP, Texas Red, and many others. Because of the simple staining technique DAPI is still one of the most important fluorescent dyes. The ultraviolet radiation which is necessary for the excitation produces radicals which bleach, other fluorophores. DAPI is therefore proposed, in some applications as the last dye and visualized in order to protect other markers. The fading ( fading ) of DAPI can be delayed by the use of anti-fading agents and the observation period be extended to the microscope.

DAPI is able to permeate intact cell membrane, but only very slowly, as opposed to the DNA dye Hoechst 33342, which has similar spectral features as well as stains living cells rapidly. DAPI is therefore rarely used for the staining of living cells. In addition, the high-energy ultraviolet radiation, which is used for excitation, harmful to living cells. Because of the DNA-binding properties, it is toxic and mutagenic.