A. J. De Koning

The 2-thiobarbituric acid reagent for determination of oxidative rancidity in fish oils

A method has been devised for the quantitative determination of malonaldehyde in oxidized fish oils by means of the 2-thiobarbituric acid reagent in alcoholic solution. TBA numbers and peroxide values have been determined at intervals during hydroperoxidation of pilchard oil. The curves follow the same general pattern but the numerical relationship between them depends upon the temperature of oxidation.In alcoholic solution, the reaction between thiobarbituric acid and malonaldehyde is carried out in the dark, because sunlight causes a decrease in optical density of the TBA-malonaldehyde complex at 532 mμ with the appearance of a second maximum at 452 mμ. The nature of the compounds responsible for absorption at these two wave-lengths is discussed.

Synthesis, characterization and properties of some organozinc hydride complexes

The synthesis and characterization of the monopyridine complexes of ethylzinc hydride and phenylzinc hydride are described. On treatment with TMED these complexes are converted into R2Zn3H4. TMED species through a combination of ligand-exchange and disproportionation. The formation of organozinc hydrides from ω-functionally-substituted diorganozinc compounds is only successful when the intramolecular coordination in these starting materials is weak and easily broken by pyridine. The results of these investigations are used as a basis for a discussion of the factors governing the formation of stable organozinc hydrides. The RZnH.py complexes easily reduce ketones and aldehydes, but no unusual stereoselectivity was observed in the reduction of substituted cyclohexanones. EtZnH.py reacts with an excess of pyridine with formation of the bis pyridine complex of ethyl(1,4-dihydro-1-pyridyl)zinc, a soluble compound, which is monomeric in benzene. The corresponding phenylzinc complex, however, cannot be isolated; disproportionation to Ph2Zn .2py and the bis pyridine complex of bis(1,4-dihydro-1-pyridyl)zinc occurs.

Hydrolysis of phospholipids with hydrochloric acid

Abstract The hydrolysis of dl -α-lecithin, dl -α-cephalin and sphingomyelin with 2 N HCl was investigated. The main hydrolytic products were identified and quantitatively estimated. From the data obtained a reaction mechanism for the acid hydrolysis of the above-mentioned compounds is postulated.

Specific and selective reduction of aromatic nitrogen heterocycles with the bis-pyridine complexes of bis(1,4-dihydro-1-pyridyl)zinc and bis(1,4-dihydro-1-pyridyl)magnesium

Aromatic nitrogen heterocycles, e.g. quinoline, 2,2‘-bipyridyl and 1,10-phenanthroline, are reduced in a uniquely specific and selective way by the bispyridine complexes of bis(1,4-dihyro-1-pyridyl)zinc and bis(1,4-dihydro-1-pyridyl)magnesium. The reactions occur by hydrogen transfer from the metal-bound 1,4-dihydropyridyl moieties to the substrates and yield zinc or magnesium salts of the 1,4-dihydroazaaromatic derivatives. Upon hydrolysis, the 1,4-dihydroazaaromatic compounds are liberated from the metal ions. The isolation and purification of several of the (novel) reduced compounds, e.g. 1,4-dihydroquinoline and 1,4-dihydro-1,10-phenanthroline, are described.

Phospholipids of the South African pilchard(Sardina ocellata Jenyns)

Chromatographic resolution of phospholipids from the flesh of the South African pilchard(Sardina ocellata Jenyns) revealed the presence of cardiolipins, cephalins, inositol phosphatides, cerebrosides, sphingomyelins, lecithins, lysoleci-thins and plasmalogens. Column and paper Chromatographic techniques were used to identify ethanolamine, serine, cho-line, sphinogsine and inositol in pilchard phos-pholipid hydrolysates. The fatty acids of pilchard phospholipids com-prised large amt of C22 hexaenoic, C20 pentaenoic and C16 saturated acids, with smaller amt of C18 dienoic, C18 monoenoic and C18 saturated acids.

A sensitive method for the microdetermination of choline

Abstract A sensitive method for the determination of choline (0.1–3 μmoles), particularly in phospholipids, is described. Choline is precipitated as the insoluble phosphomolybdate, the excess phosphomolybdic acid is carefully removed and phosphorus determined spectrophotometrically in the precipitate by reduction to molybdenum blue. Compounds capable of forming insoluble phosphomolybdates interfere. Interference of ammonia can be prevented by the addition of formaldehyde.

SYNTHESIS, CHARACTERIZATION AND PROPERTIES OF SOME ORGANOZINC HYDRIDE COMPLEXES

Summary The synthesis and characterization of the monopyridine complexes of ethylzinc hydride and phenylzinc hydride are described. On treatment with TMED these complexes are converted into R2Zn3H4_ TMED species through a combination of ligand-exchange and disproportionation. The formation of organozinc hydrides from w-functionally-substituted diorganozinc compounds is only successful when the intramolecular coordination in these starting materials is weak and easily broken by pyridine. The results of these investigations are used as a basis for a discussion of the factors governing the formation of stable organozinc hydrides. The RZnH.py complexes easily reduce ketones and aldehydes, but no unusual stereoselectivity was observed in the reduction of substituted cyclohexanones. EtZnH.py reacts with an excess of pyridine with formation of the bis pyridine complex of ethyl(l,4-dihydro-1-pyridyl)zinc, a soluble compound, which is monomeric in benzene. The corresponding phenylzinc complex, however, cannot be isolated; disproportionation to Ph,Zn_2py and the bis pyridine complex of bis(l,4-dihydro-l-pyridyl)zinc occurs.