. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). THIONIN C. I. NO. 920 Synonym: Lauth's violet. (A basic dye; absorption maximum about 602.)* Thionin, having two amino groups, is a strongly basic dye. The exact structural formulae of this dye and its derivatives, as well as many others in which two benzene rings are similarly joined, are in some dispute. At least two types of formulae are possible for the thiazins and oxazins, as well as for the xanthene dyes (Chapter VII). One t>pe is known as the or
. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). THIONIN C. I. NO. 920 Synonym: Lauth's violet. (A basic dye; absorption maximum about 602.)* Thionin, having two amino groups, is a strongly basic dye. The exact structural formulae of this dye and its derivatives, as well as many others in which two benzene rings are similarly joined, are in some dispute. At least two types of formulae are possible for the thiazins and oxazins, as well as for the xanthene dyes (Chapter VII). One t>pe is known as the orthoquinoid, the other as the paraquinoid. It will be recalled (see p. 13) that when the quinoid ring is formed the two hydrogen atoms replaced by atoms or groups with double valency bonds may be either in the para or in the ortho position to each other. It will also be recalled from elementary chemistry that sulfur and oxygen may be either bivalent or tetravalent. These facts make it possible for a thiazin or an oxazin to have either one or the other of the different structures represented by the following two formulae for the theoretical thionin base: OH. paraquinoid formula OH NH. "N= orthoquinoid formula In the case of the paraquinoid formula the compound is an am- monium base of the type discussed on p. 15, which is capable of salt formation thru its pentavalent nitrogen. In the case of the orthoquinoid formula the salt formation takes place thru the tetravalent sulfur, the base being of the type known as a sulfonium base. There are arguments in favor of either formula, and from the standpoint of the biologist it does not matter which is preferred. Possibly both forms actually exist simultaneously. For the sake of uniformity the paraquinoid form will be sho^-n in the following pages wherever possible; but with the understanding that the orthoquinoid form is equally permissable. The dye, thionin, is a salt, generally a chloride, of the above mentioned base; and on t
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