Lipid transport and lipoprotein interconversions

Serum lipoproteins were isolated from various sources including normal and hyperlipemic human, dog, and rabbit serum through preparative ultracentrifugation. These lipoprotein fractions were extracted with cold ether, and the ether-modified products were studied for sedimentation and flotation properties in an analytical ultracentrifuge. Results indicate that a relatively small number of ether-modified residues are obtained from the entire lipoprotein spectrum of all species studied. It is suggested that these moieties may be closely related to actual lipid-transporting components of the lipoprotein system. In addition, a fraction of lipoprotein-free human serum (probably closely related to beta globulin) has been identified, which will bind certain phospholipids. This protein-phospholipid complex may be separated from other serum proteins through ultracentrifugation and studied electrophoretically.

Rubber. Part XIV. The Behavior of Rubber with Iodine Chloride and with Dithiocyanogen

1. The Determination of the Iodine Number of Rubber The investigation of carotinoids has shown us that a large excess of iodine chloride must be employed if conjugated systems of double bonds are to be completely attacked. If, for example, with isoprene 150% of the calculated quantity of iodine chloride is used, then the reaction reaches after one day and after one week only 1.77 and 1.80 double bonds, respectively. 200% of iodine chloride must be used in order to obtain the correct number of double bonds. A still greater excess of iodine chloride does not then change the results any further. Such isoprene systems, which have added a halogen atom on every carbon atom in the chain, are obviously stable to substitution by iodine chloride. The frequently discussed question of whether in rubber a pair of conjugated double bonds is present as a terminal group, therefore a true isoprene system, has been proved by Pummerer and Mann by means of iodine chloride. At that time, however, the results did not apply to isoprene. For that reason it was necessary again to titrate the rubber with a great excess of iodine chloride. In this way it was shown that trustworthy results were obtained only by using 110–120% of iodine chloride (100% = 1 mol. of iodine chloride per C5H8 group), accordingly with an excess of from 10–20% iodine chloride. Within this range the results of the titration did not vary. Also only very few (often none at all) acids appeared with the titration, and these could be disregarded. On the contrary, if a greater excess of iodine chloride is used, the iodine numbers and acid values are essentially higher, which, as is well known, indicate substitution. Thus with 200% iodine chloride a value of 147 was obtained. The same phenomenon is true of gutta-percha. The earlier titrations of rubber were accidentally carried out within the favorable range of excess iodine chloride, so that the values for sol-rubber have undergone scarcely any correction. We have now carried out iodine chloride titrations with six fractions of crepe sol-rubber extracted with cold acetone, then fractionally dissolved in cold ether, and in this way we have found, as for sol-rubber, values for alkali-purified latex. They are very close to 100 (Fraction I: 100.1; II: 100.3; III: 99.9, IV: 99.6; V: 100.0; VI: 99.9). No difference in the titre was established by the various fractions.

IV. Researches on the hydrocarbons of the series C n H 2 n +2 .—No. V

Oxidation Products . In a former communication I have shortly described the action of different oxidizing agents upon some of the saturated hydrocarbons; the following paper contains some further results which I have since then obtained. One of the most striking properties of these compounds is, that they are with the greatest difficulty acted upon by any oxidizing substance in the cold. On heating them, however, a reaction sets in, and either they are completely burnt up to carbonic dioxide and water, or other oxidation products besides those two are formed in comparatively small quantities; thus chromic acid produces some acetic acid. Fuming nitric acid, which in the cold shows no action whatever, even if left in contact with one of these hydrocarbons for months, acts rather violently on gently heating; acid of the specific gravity 1.4 acts in a similar way, and produces the same products, but the reaction is much less violent. The apparatus which I used consisted of a glass flask of about one litre capacity, the narrow neck of which was several feet in length, and surrounded by a wider tube through which cold water flowed. The hydrocarbons treated in this way were hexylhydride and octylhydride (from petroleum), and diamyl. They were heated with the acid as long as red fumes were evolved; the liquid left in the flask was then distilled in a retort, until the unaltered hydrocarbon together with the greater part of the diluted nitric acid had passed over. The syrupy residue was heated in a steam-bath as long as nitric acid vapours escaped. A thick syrupy mass was left, from which, on cooling, a crystallized acid was deposited; on adding water these crystals dissolved, whilst a thick yellowish oil separated. This oil is insoluble in water, but somewhat soluble in the aqueous solution of the crystalline acid, which therefore cannot be obtained quite free from the oily substance by recrystallization only; but this may be effected by washing the crystals with cold ether, which dissolves very little of them, whilst the oil itself is very soluble. The acid obtained from octylhydride and that from diamyl melted at 180° C., and showed all the characteristic reactions of succinic acid; that from hexylhydride, from which I obtained only a very small quantity, could not be completely freed from the yellow oil, and therefore did not show a definite melting-point; it began to fuse at about 120°, and became perfectly liquid at 150°; it exhibited, however, all the reactions of succinic acid; and the following analyses, although they do not agree very well, yet show that it was this compound. From the acids the calcium and the silver-salt were prepared by neutralizing the aqueous solution with calcium carbonate and concentrating the filtered solution by boiling, when the salt separated in microscopic needles. Calcium succinate obtained in this way has the formula C 4 H 4 CaO 4 + H 2 O; the quantities of water and calcium found agree with this composition. The water was determined by drying the salt at 180° C., and the calcium by heating the dried salt over the blowpipe until the residue had a constant weight.