Composition of mixed octadecadienoates via ozonolysis,chromatography and computer solution of linear equations

An approach to the analysis of 55 possible nonconjugated positional isomers of octadecadienoic acid is described and tested with mixtures of individual synthetic methyl esters. In the first example, by ozonolysis a sevencomponent mixture consisting ofcis,cis 5,12-, 6,10-, 6,11-, 6,12-, 7,12-, 8,12-, and 9,12-octadecadienoates was converted to aldehydes, aldehyde-esters and dialdehydes. These fragments were separated on a 50 m×0.2 mm free fatty acid phase (FFAP) vitreous silica capillary column. Equations for an arbitrarily restricted 12×15 matrix of linear simultaneous equations and a computer solution of the matrix provided the composition of the initial methyl octadecadienoate mixture. The power and significance of this method became apparent with the observation that only two of the seven isomers in the known mixture were resolved as single peaks by state-of-the-art capillary gas chromatography, but all seven were identified and estimated with acceptable error by the ozonolysis-capillary gas chromatography-computer procedure. In a generalized approach to the analysis of the 55 possible nonconjugated isomers, a computer program selects the appropriate matrix of linear simultaneous equations based on the aldehyde data supplied by the analyst. Twenty of 21 combinations of seven isomeric esters taken five at a time have been analyzed to assess the efficiency of the method. To illustrate applicability at this stage of development, the method has been used to analyze the diene products of the hydrazine reduction of γ-linolenic acid and the diene products from the biological desaturation of isomeric monoenes. The possibility of distinguishing geometric and positional isomers of 18∶2 has been opened by the observed separation ofcis-andtrans-unsaturated aldehydes and aldehyde-esters. Presented in part at the 16th World Congress of the International Society for Fat Research, October 4–7, 1983, in Budapest, Hungary, and at the American Oil Chemists' Society Meeting, May 15, 1986, in Honolulu, Hawaii.     

Electro-organic reactions—VIII. The methylation and trifluoromethylation of pyridine by anodically generated radicals

A comparison of the anodic methylation and trifluoromethylation reactions of pyridine is drawn from the results of electrolyses of solutions of acetic and trifuoroacetic acids in aqueous pyridine. The anodically generated radicals are trapped inefficiently (3–20%) but the proportions of α, β, and γ-isomers are markedly dependent on the medium. The efficiency and positional selectivity of the nuclear substitution is rationalised in terms of the relative concentrations of pyridine and pyridinium ion and the likely role of the anode.     

Reduced adipose 18∶3ω3 with weight loss by very low calorie dieting

The human undergoing rapid and sustained weight loss by very low calorie dieting (VLCD) derives the majority of daily energy needs from adipose fatty acids. To evaluate the rates of metabolic utilization of individual fatty acids in humans, two groups of adult women outpatients were studied during major weight loss by VLCD. The diets used were either food or formula, providing the recommended dietary allowance for minerals and vitamins, with fat contents of 2–20 g/d. Group 1 consisted of 10 subjects [initial body mass index (BMI) 32.7, 157% of ideal body weight (IBW)] with a mean loss of 17.7 kg in 3–5 months. Group 2 consisted of 14 subjects (initial BMI 36.7, 167% of IBW) with a mean loss of 25.6 kg in 4–5 months. Adipose tissue biopsies were obtained by needle aspiration from Group 1 before and after weight loss and from Group 2 before, at the midpoint, and after weight loss. With weight loss in Group 1, the adipose tissue content of 18∶1ω9, 18∶2ω6, and 20∶4ω6 did not change, but 18∶3ω3 fell (0.67 to 0.56 wt%, p<0.0001) as did 20∶5ω3 (0.08 to 0.05, p<0.01). Adipose tissue 22∶6ω3 rose from 0.03 to 0.07 (p<0.01). In Group 2, only 18∶3ω3 showed a change, falling from 0.71 to 0.69 to 0.59 wt% across weight loss (p=0.03 by analysis of variance). We conclude that the major fatty acids are oxidized in proportion to their composition in adipose triglyceride. The significant reduction in the concentration of 18∶3ω3 during weight loss is unique among fatty acids. Its accelerated removal from adipose tissue indicates either a preferential step in β-oxidation or a defined need during supplemented fasting which exceeds its rate of provision from adipose stores. This work was presented in part at the Annual Meeting of the American Society for Clinical Nutrition, Washington, D.C., 1988.     

Identification and analysis of wax esters by mass spectrometry

Several ions in the mass spectra of wax esters were related to the molecular structures. Assigned structures of ions were confirmed by deuterium labeling. A simple, direct method for quantititive analyses of mixtures was developed. The method involved a comparison of sets of three ions, RCO₂H⁺, RCO₂H₂ ⁺ and [R′−1]⁺ from all compounds in the mixture. The method was found applicable for mixtures of unsaturated wax esters after reduction with tetradeuterio hydrazine. Presented in part before the ISF-AOCS World Congress, Chicago, September 1970. Part III of a series of mass spectrometry of lipids. For VI see Lipids.     

Pyrolysis chromatography of lipids. I. Mass spectrometric identification of pyrolysis products of hydrocarbons

The products of pyrolysis at 600C of normal paraffins C₁₀−C₁₈, 2-methyl octadecane, 4-methyl octadecane, 6-methyl octadecane, cyclohexyl decane, cyclopentyl decane, 2,2,4,4,6,8,8-heptamethyl nonane, pristane and phytane were studied by means of a pyrolysis gas chromatograph directly coupled to a mass spectrometer. n-Paraffins yield a homologous series of n-olefins. Branched paraffins yield two homologous series, one of n-olefins and one of branched olefins. The n-olefin corresponding to the position of the branch is not formed. Interpretation of pyrolograms is similar in principle to the interpretation of mass spectra. Presented at the Symposium on “Mass Spectrometry of Lipids”, AOCS Cincinnati, October 1965.     

Detection and measurement of hydroperoxides by near infrared spectrophotometry

Summary Near-infrared spectra have been measured on a group of hydroperoxides of fatty acid esters and related substances. Only those substances having an −OOH group were found to absorb at 1.46 and 2.07 μ. Dialkyl peroxides and ozonized unsaturated substances had no such maxima in their near infrared spectra although they had high iodometric peroxide values. In a study of the thermal decomposition of methyl oleate hydroperoxide and a study of the autoxidation of methyl linoleate, the intensity of absorption at 1.46 and 2.07 μ paralleled the iodometric peroxide value. This work was aided by grants-in-aid from the Hormel Foundation, the Atomic Energy Commission (Contract AT-11-1-108), the Office of Naval Research (Contract N8 onr66218), the National Live Stock and Meat Board, and the National Diary Council. Hormel Institute Publication No. 170.     

A comparison of pyrrolidide and picolinyl ester derivatives for the identification of fatty acids in natural samples by gas chromatography-mass spectrometry

The pyrrolidide and picolinyl ester derivatives of the fatty acids in two natural lipid samples rich in unsaturated fatty acids, pig testis lipids and cod liver oil were satisfactorily resolved on capillary columns of fused silica coated with stationary phases of varying polarity. The picolinyl esters, in particular, when subjected to gas chromatography-mass spectrometry on a column containing a cross-linked methyl silicone, gave distinctive mass spectra, which could be interpreted in terms of both the numbers and positions of the double bonds.