Brazilwood, sappanwood, brazilin and the red dye brazilein: from textile dyeing and folk medicine to biological staining and musical instruments.

Brazilin is a nearly colorless dye precursor obtained from the heartwood of several species of trees including brazilwood from Brazil, sappanwood from Asia and the Pacific islands, and to a minor extent from two other species in Central America, northern South America and the Caribbean islands. Its use as a dyeing agent and medicinal in Asia was recorded in the 2(nd) century BC, but was little known in Europe until the 12(th) century AD. Asian supplies were replaced in the 16(th) century AD after the Portuguese discovered vast quantities of trees in what is now Brazil. Overexploitation decimated the brazilwood population to the extent that it never fully recovered. Extensive environmental efforts currently are underway to re-create a viable, sustainable population. Brazilin is structurally similar to the better known hematoxylin, thus is readily oxidized to a colored dye, brazilein, which behaves like hematein. Attachment of the dye to fabric is by hydrogen bonding or in conjunction with certain metallic mordants by coordinative bonding. For histology, most staining procedures involve aluminum (brazalum) for staining nuclei. In addition to textile dyeing and histological staining, brazilin and brazilein have been and still are used extensively in Asian folk medicine to treat a wide variety of disorders. Recent pharmacological studies for the most part have established a scientific basis for these uses and in many cases have elucidated the biochemical pathways involved. The principal use of brazilwood today is for the manufacture of bows for violins and other stringed musical instruments. The dye and other physical properties of the wood combine to produce bows of unsurpassed tonal quality.