II. On the supposed identity of biliverdin with chlorophyll, with remarks on the constitution of chlorophyll

Abstract

I have lately been enabled to examine a specimen, prepared by Professor Harley, of the green substance obtained from the bile, which has been named biliverdin, and which was supposed by Berzelius to be identical with chlorophyll. The latter substance yields with alcohol, ether, chloro­form, &c., solutions which are characterized by a peculiar and highly di­stinctive system of bands of absorption, and by a strong fluorescence of a blood-red colour. In solutions of biliverdin these characters are wholly wanting . There is, indeed, a vague minimum of transparency in the red; but it is totally unlike the intensely sharp absorption-band of chlorophyll, nor are the other bands of chlorophyll seen in biliverdin. In fact, no one who is in the habit of using a prism could suppose for a moment that the two were identical; for an observation which can be made in a few seconds, which requires no apparatus beyond a small prism, to be used with the naked eye, and which as a matter of course would be made by any chemist work­ing at the subject, had the use of the prism made its way into the chemical world, is sufficient to show that chlorophyll and biliverdin are quite distinct. I may take this opportunity of mentioning that I have been for a good while engaged at intervals with an optico-chemical examination of chlorophyll. I find the chlorophyll of land-plants to be a mixture of four substances, two green and two yellow, all possessing highly distinctive optical properties. The green substances yield solutions exhibiting a strong red fluorescence; the yellow substances do not. The four substances are soluble in the same solvents, and three of them are extremely easily decomposed by acids or even acid salts, such as binoxalate of potash ; but by proper treat­ment each may be obtained in a state of very approximate isolation, so far at least as coloured substances are concerned. The phyllocyanine of Fremy is mainly the product of decomposition by acids of one of the green bodies, and is naturally a substance of a nearly neutral tint, showing however ex­tremely sharp bands of absorption in its neutral solutions, but dissolves in certain acids and acid solutions with a green or blue colour. Fremy’s phylloxanthine differs according to the mode of preparation. When pre­pared by removing the green bodies by hydrate of alumina and a little water, it is mainly one of the yellow bodies; but when prepared by hydro­chloric acid and ether, it is mainly a mixture of the same yellow body (partly, it may be, decomposed) with the product of decomposition by acids of the second green body. As the mode of preparation of phylloxantheine is rather hinted at than described, I can only conjecture what the sub­stance is ; but I suppose it to be a mixture of the second yellow substance with the products of decomposition of the other three bodies. Green sea­ weeds ( Chlorospermeæ ) agree with land-plants, except as to the relative proportion of the substances present; but in olive-coloured sea-weeds ( Melanospermeæ ) the second green substance is replaced by a third green sub­stance, and the first yellow substance by a third yellow substance, to the presence of which the dull colour of those plants is due. The red colouring-matter of the red sea-weeds ( Rhodospermeæ ), which the plants contain in addition to chlorophyll, is altogether different in its nature from chloro­phyll, as is already known, and would appear to be an albuminous substance. I hope, before long, to present to the Royal Society the details of these researches.