Hematein
Encyclopedia
Hematein or haematein is an oxidized derivative of haematoxylin
, used in staining. Haematein must not be confused with haematin, which is a brown to black iron-containing pigment formed by decomposition of haemoglobin. In the Colour Index (but nowhere else), haematein is called haematine, a confusing word that wrongly implies that the compound is an amine.
Hematein exhibits indicator-like properties, being blue and less soluble in aqueous alkaline conditions, and red and more soluble in alcoholic acidic conditions. In acidic conditions, complexes of hematein with metals (usually aluminium or ferric iron) bind to arginine residues of nuclear histones. The color of the stained nuclei depends on the salt used. Aluminium-haematein complexes are usually blue, whereas ferric complexes are very dark blue or black.
Structures that stain with aluminium-hematein (haemalum) are often said to be basophilic, but the staining mechanism is not as simple as for basic (cationic) dyes with smaller molecules. Truly basophilic structures are ones containing nucleic acids or other polyanions such as glycosaminoglycans of extracellular matrix or acidic glycoproteins in many types of mucus. As usually used, aluminium-hematein stains only nuclear chromatin and a few other materials such as keratohyalin granules and calcified deposits. Very dilute solutions of aluminium-haematein, used at pH3.2 (higher than is usual for staining), contain a cationic dye-metal complex and will slowly stain nucleic acids (Bettinger & Zimmermann 1991). Haemalum solutions used for routine staining are more concentrated and more acidic (pH2-2.5) and are able to stain nuclei after chemical or enzymatic extraction of DNA and RNA from the tissue (Lillie et al., 1976).
Haematoxylin
Haematoxylin, hematoxylin, Natural Black 1, or C.I. 75290 is extracted from the heartwood of the logwood tree. When oxidized it forms haematein, a compound that forms strongly coloured complexes with certain metal ions, the most notable ones being Fe and Al salts. Metal-haematein complexes are used...
, used in staining. Haematein must not be confused with haematin, which is a brown to black iron-containing pigment formed by decomposition of haemoglobin. In the Colour Index (but nowhere else), haematein is called haematine, a confusing word that wrongly implies that the compound is an amine.
Hematein exhibits indicator-like properties, being blue and less soluble in aqueous alkaline conditions, and red and more soluble in alcoholic acidic conditions. In acidic conditions, complexes of hematein with metals (usually aluminium or ferric iron) bind to arginine residues of nuclear histones. The color of the stained nuclei depends on the salt used. Aluminium-haematein complexes are usually blue, whereas ferric complexes are very dark blue or black.
Structures that stain with aluminium-hematein (haemalum) are often said to be basophilic, but the staining mechanism is not as simple as for basic (cationic) dyes with smaller molecules. Truly basophilic structures are ones containing nucleic acids or other polyanions such as glycosaminoglycans of extracellular matrix or acidic glycoproteins in many types of mucus. As usually used, aluminium-hematein stains only nuclear chromatin and a few other materials such as keratohyalin granules and calcified deposits. Very dilute solutions of aluminium-haematein, used at pH3.2 (higher than is usual for staining), contain a cationic dye-metal complex and will slowly stain nucleic acids (Bettinger & Zimmermann 1991). Haemalum solutions used for routine staining are more concentrated and more acidic (pH2-2.5) and are able to stain nuclei after chemical or enzymatic extraction of DNA and RNA from the tissue (Lillie et al., 1976).