Ball, Goodwin, and Morton (1946) have reported that vitamin A1 in contact with solid manganese dioxide is transformed slowly into a substance which displays spectroscopic properties of retinene1. The latter is known to be the precursor of vitamin A1 in the rhodopsin cycle of the retinal rods. The synthetic product is here referred to as "retinene1."
In the present experiments this observation is confirmed. The procedure is recast in the form of a chromatographic oxidation. Manganese dioxide is packed in a column, vitamin A1 solution poured in at the top, and the product drawn off in the filtrate. Depending upon the proportions of manganese dioxide and vitamin A1, the product is either "retinene1," or a new substance which yields with antimony chloride a wine-red product with maximal absorption at 545 mµ (545 mµ chromogen). This procedure is an example of a potentially important class of chromatographic reactions.
The synthetic "retinene1" is virtually identical with the natural substance in absorption spectrum and antimony chloride reaction. It lacks the pH indicator properties of crude natural retinene1.
The 545 mµ chromogen possesses absorption maxima at 380 and 290 mµ in chloroform; at 376 and 290 mµ in ethanol; and at 361 and 277 mµ in hexane. It is non-fluorescent. It has no acidic character, but on the contrary is mildly basic, being extracted from hexane by sulfuric or hydrochloric acids to form orange-red products. In partition between petroleum ether and aqueous methanol it is highly hypophasic. It is adsorbed strongly on calcium carbonate.
Certain peculiarities in spectral behavior indicate the presence of a carbonyl group in the 545 mµ chromogen, and support Morton's proposal that such a group occurs in retinene1. Other properties of the 545 mµ chromogen indicate hydroxyl groups. This substance therefore appears to be a hydroxy-carbonyl derivative of vitamin A1.
The red products which the 545 mµ chromogen forms with antimony chloride or with sulfuric or hydrochloric acids are all markedly light-sensitive. They appear to be formed by the condensation of two molecules with loss of water; and to bear a close generic relation to the prosthetic groups of the visual photopigments.