Hematein (US spelling) or haematein is an oxidized derivative of

haematoxylin Haematoxylin American and British English spelling differences#ae and oe, or hematoxylin (), also called natural black 1 or Colour Index International, C.I. 75290, is a chemical compound, compound extracted from wood#Heartwood and sapwood, heart ...

, used in staining. Haematein should not be confused with

haematin Haematin (also known as hematin, ferriheme, hematosin, hydroxyhemin, oxyheme, phenodin, or oxyhemochromogen) is a dark bluish or brownish pigment containing iron in the ferric state, obtained by the oxidation of haem. Haematin inhibits the synt ...

, which is a brown to black iron-containing pigment formed by decomposition of

haemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobi ...

. In the Colour Index (but nowhere else), haematein is called haematine.

Properties

Hematein exhibits indicator-like properties, being blue and less soluble in aqueous

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

conditions, and red and more soluble in alcoholic

acidic An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

conditions. Dissolved haematein slowly reacts with atmospheric

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

, yielding products that have not found applications.

Applications

In acidic solutions, complexes of hematein with metals (usually

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

, but also

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...

and several others) are used as biological stains. Aluminium-haematein (haemalum) is the "routine" stain for cell nuclei in sections of human and other animal tissues. Metal-haematein stains are available also for objects other than nuclei, including

myelin sheath Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

s of nerve fibres and various cytoplasmic

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s. The color of the stained objects depends on the salt used. Aluminium-haematein complexes are usually blue, whereas ferric complexes are very dark blue or black. Aluminium-haematein complexes (haemalum) bind to the chromatin of the nuclei of cells. Although haemalum staining methods have been in use since the 1860s, the chemical identity of the substance or substances that bind the dye-metal complex is still not known with certainty. Some histochemical investigations clearly indicate that a cationic aluminium-haematein complex is attracted to the

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

anions of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

. Others implicate the

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

residues of nuclear

histone In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei and in most Archaeal phyla. They act as spools around which DNA winds to create structural units called nucleosomes ...

s as the substrate of nuclear staining by haemalum. Structures that stain with aluminium-hematein (haemalum) are often said to be

basophilic Basophilic is a technical term used by pathologists. It describes the appearance of cells, tissues and cellular structures as seen through the microscope after a histological section has been stained with a basic dye. The most common such dye ...

, but the staining mechanism is not as simple as for basic (cationic) dyes with smaller molecules. Truly basophilic structures are ones containing

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

s or other

polyanions Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are th ...

such as glycosaminoglycans of extracellular matrix or acidic

glycoprotein Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

s 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 pH 3.2 (higher than is usual for staining), contain a cationic dye-metal complex and will slowly stain nucleic acids. Haemalum solutions used for routine staining are more concentrated and more acidic (pH 2-2.5) and are able to stain nuclei after chemical or enzymatic extraction of DNA and RNA from the tissue.

References

{{reflist Staining dyes Phenol dyes Catechols Tertiary alcohols Cyclopentenes