They found a glassy black substance, and further investigation revealed that it included several proteins associated with brain tissue, along with adipic and margaric fatty acids found in sebum and hair.
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For many species, margaric acid plays a role as a semiochemical - specifically it possesses pheromonic and allomonic properties. Margaric acid has been identified in the subcaudal gland secretions of the European badger (Meles meles) and in the occipital gland secretions of male Bactrian camels (Camelus bactrianus) where it is one of the many pheromonic chemicals responsible for aiding in the finding and selection of mates. Margaric acid is an attractant of the khapra beetle (Trogoderma granarium) and the yellow fever mosquito (Aedes aegypti) but as a repellent of the common house mosquito (Culex pipiens). Margaric acid is also found in the precloacal gland secretions of many reptiles belonging to the order squamata, including the common leopard gecko (Eublepharis macularius) and the European viper (Vipera berus), where it is used for the identification of sexual partners.
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However, in the 19th and early 20th centuries, there were numerous reports of the acid being found in natural fats in significant amounts. Most likely, these were cases of misidentifying a eutectic mixture of palmitic and stearic acids.Чёт или нечет? Занимательные очерки по химии, pages 116-120 Salts and esters of margaric acid are called heptadecanoates.
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Using these additions to his own work, Theodore Gobley in 1874 crowned this long, patient and unyielding series of steps through a final proposal of a complete structure for lecithin, whose hydrolysis yields exactly one oleic acid, one margaric acid, one glycerophosphoric acid and one choline ("Sur la lécithine et la cérébrine", Gobley J Pharm Chim 1874, 19, 346). Fig 1. 1 example of variant phosphatidylcholine, palmitoyl-oleyl-sn- phosphatidylcholine.
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Margaric acid, or heptadecanoic acid, is a saturated fatty acid. Its molecular formula is CH3(CH2)15CO2H. Classified as an odd-chain fatty acid, it occurs as a trace component of the fat and milkfat of ruminants, but it does not occur in any natural animal or vegetable fat at high concentrations. For example, it comprises only 2.2% of the fats from the fruit of the durian species Durio graveolens.
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Heinrich Wilhelm Heintz Catalogus Professorum Halensis He was one of six founding members of the Deutsche Physikalische Gesellschaft and the only chemist. At Halle, Heintz supervised Johannes Wislicenus's Ph.D. work, although Wislicenus' pro forma advisor at Zurich was Georg Karl Andreas Städeler.Bilirubin: Jekyll and Hyde Pigment of Life by David A. Lightner With Christoph Gottfried Giebel, he was editor of the Zeitschrift für Naturwissenschaften.Zeitschrift für Naturwissenschaften Internet Archive In 1853 he analyzed margaric acid as simply a combination of stearic acid and palmitic acid.
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Palmitoyl-oleyl-sn- phosphatidylcholine, a phosphatidylcholine. This phospholipid is composed of a choline head group and glycerophosphoric acid, with a variety of fatty acids. Usually, one is a saturated fatty acid (in the given figure, this is palmitic acid (hexadecanoic acid, H3C-(CH2)14-COOH); margaric acid (heptadecanoic acid, H3C-(CH2)15-COOH), identified by Gobley in egg yolk, also belong to that class); and the other is an unsaturated fatty acid (here oleic acid, or 9Z-octadecenoic acid, as in Gobley's original egg yolk lecithin). However, there are also examples of disaturated species.
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Later studies expanded the egg yolk lecithin into a wide family of lecithins answering to this structure, combining with a choline head and glycerophosphoric acid a variety of fatty acids. In general, a lecithin, or more precisely a phosphatidylcholine is obtained using a saturated fatty acid, in the example here palmitic acid or hexadecanoic acid H3C-(CH2)14-COOH (margaric acid identified by Gobley in egg yolk, now named heptadecanoïc acid H3C-(CH2)15-COOH, belongs to that class) and an unsaturated fatty acid, here oleic acid or 9Z-octadecenoic acid as in Gobley's original egg yolk lecithin).
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In the course of the next three years 1848–1850, Theodore Gobley extended the scope of his research in parallel over egg yolk, carp fish eggs, fish roe, and brain tissue. In 1850 ("Recherches chimiques sur les œufs de carpe"), he evidenced the presence of his "matière phosphorée", with identical properties, in carp fish eggs; he proposed for it the name of lecithin which history upheld, from the Greek lekithos (egg yolk) (Journal de Pharmacie et de Chimie, Paris, 1850, 17, 401), thus underlining the clear link with his early studies. And in its wake he demonstrated that lecithin, however obtained (from egg yolk, carp fish eggs, fish roe, human brain), and even though not totally purified, always yields a mix of oleic acid, margaric acid and glycerophosphoric acid when hydrolyzed, and under no circumstances whatsoever anything like phosphoric acid which would have been expected if ordinary fat matter acids, such as phospho-oleic acid, had been involved ("Recherches chimiques sur la laitance de carpe." Journal de Pharmacie et de Chimie 1851, t19, 406).
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