THE PURE PIGMENTS, CAROTIN AND XANTHOPHYLL, AND THE TSWETT ADSORPTION METHOD

Abstract

Ever since the yellow plastid pigments have been investigated in plant organs, especially in leaves, there has been considerable controversy regarding the nature and the number of the pigments present. Stokes supposed that there were two and Sorby three xanthophylls. Borodin observed that many crystallizable yellow substances, whose solubilities differed, were present in leaves. He recognized two groups, the carotins, to which belong crystals easily soluble in benzene and difficultly soluble in alcohol, and a second group the representatives of which dissolve very slightly in benzene and easily in alcohol. Arnaud believed that only a single yellow pigment was present and that this was carotin. Monteverde, Tschirch, Tswett and Schunck confirmed and enlarged upon these observations. Later Willstatter and Mieg isolated a representative of each of the groups as designated by Borodin. The large yield of carotinoids obtained by Willstatter and his coworkers makes it seem highly improbable that other yellow plastid pigments are present (10). A very complete review of the literature is given in the monograph of Willstatter and Stoll in chapter XII. Tswett by means of his chromatographic adsorption apparatus has attempted to further resolve the yellow pigments. For example, by filtering a carbon disulphide solution of the leaf pigments through a column of calcium carbonate, carotin passes through without being adsorbed. In addition to the green pigmented zones are four zones of yellow pigments, which Tswett distinguished as a, a1, a11, and 3In the spectrum they show small relative differences in the position of their absorption bands, and as yet these pigments have not been crystallized or isolated in the pure state. Tswett holds the view that the xanthophyll of Willstatter and his coworkers is a mixture of two or three isomorphic xanthophylls while Willstatter has suggested that it is possible that the original pigments have been changed by oxidation during the process of separation. It is the purpose of this paper to support the contention of Willstatter.