Aldehyde-fuchsin: historical and chemical considerations.

The staining mechanisms of Gomori's aldehyde-fuchsin are not yet fully understood. It seemed therefore timely to review the history of this dye class in context with current dye and aldehyde chemistry. In 1861 Lauth treated basic fuchsin with acetaldehyde. This dye became known as Aldehyde Blue, but consisted of violet and blue dyes. Schiff (1866) studied several aldehyde-fuchsins; these compounds contained two molecules of dye and three molecules of aldehyde. Acetaldehyde-fuchsin prepared according to Schiff's directions showed staining properties similar to those of Gomori's aldehyde-fuchsin. This dye class was soon superseded by new dyes more suitable for textile dyeing, and chemical investigations of aldehyde-fuchsins ceased around the turn of the century. Gomori's aldehyde-fuchsin has been regarded as a Schiff base. However, according to chemical data, low molecular aliphatic aldehydes and aromatic amines tend to form condensation products. Correlations of chemical and histochemical observations suggest such processes during aging of dye solutions. Models of dimers and polymers of aldehyde-fuchsin could be built without steric hindrance. The nature of the bonds formed by various components of aldehyde-fuchsin solutions is not clear. However, cystine in proteins, e.g. in basement membranes, apparently does not play a role in the binding of aldehyde-fuchsin by unoxidized Carnoy- or methacarn-fixed sections.