Pelargonic acid in enhanced oil recovery

Oxidation of monounsaturated fatty acids, such as erucic and oleic acids, results in the formation of dibasic fatty acids, such as brassylic and azelaic acids. Dibasic acids find many industrial applications. Pelargonic acid is the co-product of the process. Expanded use of dibasic acids would require an expansion in the existing and possibly new uses for pelargonic acid and its derivatives. In this study, the potential for using pelargonic acid in enhanced oil recovery is investigated. Experimental results are presented for the enhanced oil recovery by waterflooding with the aid of a surfactant.In situ formation of surfactant at the oil-water interface vs. the formation of surfactant in the floodwater prior to injection is examined.     

Ultrasound-assisted synthesis of santalbic acid and a study of triacylglycerol species inSantalum album (Linn.) seed oil

Methyl ricinoleate (1) was treated with bromine and the dibromo derivative (2) was reacted with ethanolic KOH under ultrasonic irradiation to give 12-hydroxy-octadec-9-ynoic acid upon acidification with dil. HCl. The latter compound was methylated with BF₃/methanol to give methyl 12-hydroxy-octadec-9-ynoate (3). Compound3 was treated with methanesulfonyl chloride in the presence of triethylamine in CH₂Cl₂ to give methyl 12-mesyloxy-octadec-9-ynoate (4). Reaction of methyl 12-mesyloxy-octadec-9-ynoate with aqueous KOH under ultrasonic irradiation (20 kHz) gave (11E)-octadecen-9-ynoic acid (5, santalbic acid, 40%) and (11Z)-octadecen-9-ynoic acid (6, 60%) on acidification with dil. HCl. These isomers were separated by urea fractionation. The¹³C nuclear magnetic resonance (NMR) spectroscopic properties of the methyl ester and the triacylglycerol (TAG) esters of these enynoic fatty acid isomers were studied. The carbon shifts of the unsaturated carbon nuclei of the methyl ester of theE-isomer were unambiguously assigned as 88.547 (C-9), 79.287 (C-10), 109.760 (C-11), and 143.450 (C-12) ppm while the unsaturated carbon shifts of the (Z)-enynoate isomer appeared at 94.277 (C-9), 77.561 (C-10), 109.297 (C-11), and 142.668 (C-12) ppm. In the¹³C NMR spectral analysis of the TAG molecules of type AAA containing either the (Z)-or (E)-enyne fatty acid, the C-1 to C-6 carbon atoms on the α- and β-acyl positions were differentiated. The unsaturated carbon atoms in the α- and β-acyl chains were also resolved into two signals except that of the C-11 olefinic carbon. Sandal (Santalum album) wood seed oil (a source of santalbic acid) was separated by silica chromatography into three fractions. The least polar fraction (7.2 wt%) contained TAG which had a random distribution of saturated and unsaturated fatty acids, of which oleic acid (69%) was the predominant component. The second fraction (3.8 wt%) contained santalbic acid (58%) and oleic acid (28%) together with some other normal fatty acids. Santalbic acid in this fraction was found in both the α- and β-acyl positions of the glycerol “backbone”. The most polar fraction (89 wt%) consisted of TAG containing santalbic acid only. The distribution of the various fatty acids on the glycerol “backbone” was supported by the results from the¹³C NMR spectroscopic analysis.     

Alteration of soybean oil composition by plant breeding

Experimental lines selected from the cross PI 90406 × PI 92567 are being used in an attempt to improve soybean (Glycine max [L.] Merr.) oil by altering fatty acid composition through plant breeding. Preliminary evidence shows that the concentration of linolenic acid in soybean oil is reduced by selection for high levels of oleic acid. Levels of poly-unsaturated acids in “high oleic” selections are lower, to various degrees, but the concentration of saturated fatty acids is not different from that of the variety Dare, a representative southern commercial cultivar. In triglyceride from the “high oleic” selection, N70-3436, levels of palmitic, stearic, oleic, linoleic, and linolenic acid are 9.5, 2.0, 40.1, 43.3, and 5.1 mol %, respectively. The types of triglyceride structures observed in the experimental lines which were examined also are changed. The combined level of triolein, monooleyl-dilinolein, and dioleyl-mono-linolein in seed from N70-3436 is doubled and constitutes ca. 50% of the oil.     

Periodate-permanganate oxidations for determining location and amount of unsaturation in monounsaturated fatty acids

Conclusions Periodate-permanganate oxidation of three samples of oleic acid considered to be of high purity has given reproducible but less than theoretical amounts of total dibasic acids. Recovery approximated 92% with about 90.3% of the expected azelaic acid. Recovery of other dibasic acids indicated that about 1.5% of the total unsaturation of these samples of oleic acid was present in positions 8 or 10 in the fatty acid molecule. Oxidation of elaidic acid produced from one of the oleic acids has given total dibasic acid yield of about 96%, with a smaller amount of its total unsaturation in the same position as in the parent oleic acid. Oxidation of high purity 9,10-dihydroxystearic acid has given essentially quantitative yield of total dibasic acids. The method described should be useful in determining the composition of similar unsaturated positional isomers. Controls showing the effect of the method on azelaic acid and on a mixture of azelaic acid with pelargonic have shown essentially quantitative recovery of azelaic acid. Failure to establish quantitative recovery on oxidation of oleic acid must be caused by some unknown factor during oxidationper se. The experimental technique described was satisfactory for quantitative studies of the type undertaken. Oxidation of moderate-purity, mono-unsaturated fatty acids, such as erucic, 10-undecenoic, and vaccenic acid, has given mixed dibasic acids corresponding to the respective positions of unsaturation. The data indicate that the method described shows the position of minor unsaturation within about 1%. Presented at meeting of American Oil Chemists' Society, Chicago, Ill., September 24–26, 1956.     

Polymerization of unsaturated fatty acids

Summary A method is proposed for the preparation of polybasic fat acids or “dimer” acids directly from fatty acids which is readily adaptable to commercial use. The presence of moisture maintained in the reaction vessel by steam pressure substantially prevents decomposition and decarboxylation of the fatty acids. By this method a larger percentage of dibasic acids, as compared to tribasic acids, is produced than by the previously described methods. The method of high temperature polymerization of fatty acids in the presence of moisture is also used to remove polyunsaturated fatty acids from commercial oleic acid. Presented at 20th fall meeting, American Oil Chemists’ Society, Chicago, Ill., Oct. 30–Nov. 1, 1946.     

A review of soybean oil reversion flavor

Crude soybean oil has a characteristic “greenbeany” flavor, which during refining, bleaching and deodorization is eliminated to produce a bland tasting, light colored oil. However, flavor returns during storage and has been characteristically called the “reversion flavor” of soybean oil. This deleterious characteristics flavor has influenced the utilization of soybean oil and its fatty acids. Several theories for the cause of reversion flavor include: (a) oxidation of linolenic acid; (b) oxidation of isolinoleic acid of the 9,15-diene structure; (c) phosphatide reactions; (d) unsaponifiables; and (e) oxidative polymers. References are presented that support or contradict these theories. Recent publications concerning the isolation and characterization of the components of reversion flavor indicate slight oxidation of the fatty acids is the major cause. Techniques that are effective in increasing the flavor stability of soybean oil are presented.     

The importance of glycerol in the fatty acid industry

Historically, glycerol, a valuable by product of the fatty acid insutry, is priced higher in the market-place than any of the common fatty acids. Glycerol “credit” from fat-splitting, frequently in time of economic stress, makes the difference between a profitable stearic acid operation and an economically unsound one. Theoretical yields of glycerol for the common fats and oils range from 9–13.5%; practical plant yields, corrected for FFA and upgrading yield losses, are 9–12.8% on 100% glycerol basis, or 10.3–14.8% on an 88% glycerol basis. Glycerol “credit” per pound of fatty acid ranges from 1 to 3 cents/pound. Upgrading “sweetwaters” from splitting operations in the fatty acid industry requires removal of dissolved salts, elimination of color, and fat and oil impurities, concentration (evaporation of water) and/or distillation. For Twitchellized sweetwaters this generally involves (a.) lime treatment. (b.) filtration, (c.) evaporation to half-crude, (d.) precipitation of excess lime, (e.) filtration, (f.) evaporation to a concentration of 88–90%, and probably, (g.) distillation. For autoclave or continuous process sweetwaters the upgrading includes (a.) light lime treatment, (b.) filtration, (c.) evaporation concentration to 88–90%, and probably, (d.) distillation. Glycerol may also be upgraded by ion-exchange processing followed by evaporation concentration in which distillation may be eliminated. Ion-exclusion (Dow process) is also feasible. Many special triglyceride products are required of different fatty acid homolog distribution than those of the parent or hydrogenated fats and oils. These are prepared by splitting the fats or hydrogenated oils, fractionating the fatty acids, upgrading the glycerol, and recombining the desired fractionated acids with glycerol by reesterification. One example is high lauric triglyceride from coconut oil suited for use as a coco butter substitute.     

The plant geneticist’ contribution toward changing lipid and amino acid composition of safflower

Current research on the fatty acid composition of the seed oil of safflower (Carthamus tinctorius L.) has shown the following: (1) there is a possibility that the oleic acid content can be increased above 80%, though probably not above 85%, by use of modifying genes and the major geneol; (2) wild species do not look very promising as a source of genes for modifying fatty acid composition; (3) commercially grown high linoleic and high oleic types are temperature stable; (4) an experimental type with about equal amounts of oleic and linoleic acids is responsive to temperature, with high temperature increasing oleic acid and low temperature increasing linoleic acid; and (5) stearic acid in another experimental type with higher levels of stearic acid (5–10%) is reduced by low temperatures. One of seven papers presented at the Symposium, “The Plant Geneticist’s Contribution Toward Changing Lipid and Amino Acid Composition of Oilseeds,” AOCS Meeting, Houston, May 1971.     

Fractionation of tallow fatty acids. Preparation of purified oleic acid and an inedible olive oil substitute

Summary Tallow fatty acids have been fractionally crystallized from acetone at temperatures ranging from 0° to −60° C. By crystallizing at 0° to −20° C., a saturated acid fraction which amounts to 40 to 50% by weight of the starting material has been obtained. This fraction corresponds to “double- or triple-pressed stearic acid.” The filtrate acids from the crystallization at −20° C. contain over 90% of the oleic acid present in the starting material, and in fatty acid composition this mixture is similar to olive oil. From this fraction. which amounts to about 50% by weight of the starting material, a synthetic triglyceride with, properties approximating those of olive oil has been prepared. By low-temperature crystallization of this oleic-acid-rich fraction at −50° to −60° C., followed by fractional distillation, a good yield of purified oleic acid (oleic acid content, over 95%) has been obtained. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.     

Synthesis of azelaic acid and suberic acid fromVernonia galamensis oil

We have demonstrated the potential ofVernonia galamensis seed oil as a source of dibasic acids. Reaction of nitric acid withV. galamensis oil afforded a homologous series of dibasic acids that include butanedioic acid, pentanedioic acid, hexanedioic acid (adipic), heptanedioic acid (pimelic), octanedioic acid (suberic), nonanedioic acid (azelaic), decanedioic acid (sebacic), and undecanedioic acid. Using a combination of chloroform extraction and subsequent water crystallizations, we have isolated suberic acid (∼95% purity by GC) and azelaic acid (∼95% purity by GC). The isolated yield of suberic acid is 15% and of azelaic acid is 11%. Reported reaction of nitric acid with ricinoleic acid (from castor oil) gave 8.8% suberic acid and 7.2% of a mixture of suberic and azelaic acids.     

Fatty acid spectrum of mediterranean wild cruciferae

Seed samples of 54 species of wild Cruciferae were newly collected from natural populations of the west Mediterranean and adjacent areas in a search for “new” oil crops. Oil contents and fatty acid compositions were determined simultaneously by gas liquid chromatography using methyl heptadecanoate as the internal standard. The study revealed large variations in oil content (6–48.8%), oleic acid (5–31.3%), linoleic acid (2–24.8%), linolenic acid (1.7–64.1%), and erucic acid (0–55.1%). Correlation coefficients between component fatty acids inter se and oil content were determined separately for all species, the tribe Brassiceae, and the genusBrassica. The promising species identified are being studied further.     

Industrial uses of high erucic oils

Vegetable oils rich in erucic acid have desirable properties for a variety of applications. At present, only a fraction of the potential that exists for commercial exploitation of high erucic oils in the United States is fulfilled with 10 million pounds of rapeseed oil imported annually. Though rape is not a crop in the United States, another member of the mustard family, crambe, has been recommended by the USDA as a practical crop for domestic cultivation. Compared to rapessed oil, crambe oil is more suitable for industrial use because it consistently contains a higher percentage of erucic acid. High erucic oils, as examplified by crambe, can be employed as lubricants in continuous steel casting, in formulated lubricants and in the manufacture of rubber additives. Both the hydrogenated oil and derived wax esters have properties comparable to commercial waxes. Useful nitrogen derivatives can be prepared from either the erucic acid or mixed acids from the oil; behenyl amine is used in a corrosion inhibitor, disubstituted amides are effective plasticizers and erucamide is an excellent slip and antiblocking agent for plastic films. Oxidative ozonolysis of erucic acid produces the dibasic acid, brassylic, and the monoacid, pelargonic. Mixed diacids, mainly brassylic and azelaic, can be obtained by ozonolysis of fatty acids from the oil. Alkyl diesters of brassylic, or of the mixed diacids, are excellent low temperature plasticizers. Two new nylons (13 and 1313), which are derived from C-13 difunctional products of erucic acid ozonolysis, contain repeating units that have longer uninterrupted polymethylene chains than other nylons. Moderate melting points and exceptionally low water absorption are a consequence of this structure. The low-melting characteristic is an advantage in adhesive uses and facilitates fluidized-bed coating, molding and extrusion; low moisture affinity contributes to excellent electrical properties and dimensional stability. One of 9 papers presented at the Symposium, “Cruciferous Oil-seeds”. ISF-AOCS World Congress. Chicago, September 1970. No. and Eastern Utilliz. Rev. Div., ARS, USDA.     

Relation of days after flowering to chemical composition and physiological maturity of sunflower seed

Hybrid sunflower seed (achene) were collected from plants at 7-day intervals after the initiation of flowering which occurred 58 days after planting. The seed were analyzed for moisture, total oil, free fatty acids, lipid classes, and fatty acid composition. Seed dry weight, oil and triglyceride contents were maximum 35 days after the initiation of flowering (DAF) when the seed moisture content was about 36%. This point was defined as “physiological maturity” for sunflowers. The fatty acid composition of the oil extracted from the seed was determined at each stage of maturity. Total saturated fatty acids were 27% at 7 DAF and then decreased to a constant 9% by 35 DAF. At 7 DAF, linolenic acid content was 10.7% then decreased to less than 0.1% by 28 DAF. Oleic acid was about 12% at 7 DAF, increased to 59.6% at 14 DAF, and then gradually decreased to 31.4% by 56 DAF. On the other hand, linoleic acid was about 48% at 7 DAF, decreased to 23% by 14 DAF, but then gradually increased to 59.2% by 56 DAF. An analysis of variance of linoleic and oleic acid contents from 21 DAF to 70 DAF showed a highly significant change in composition with maturation time. The changes in the composition of these fatty acids from 21 DAF to 70 DAF appeared to be related to the environmental temperature which gradually decreased until 56 DAF. Increase in free fatty acids after physiological maturity indicated that deterioration of seed oil was beginning to occur.     

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)—Effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Triplicate groups of Atlantic salmon (Salmo salar L.) were fed four diets containing different oils as the sole lipid source, i.e., capelin oil, oleic acid-enriched sunflower oil, a 1∶1 (w/w) mixture of capelin oil and oleic acid-enriched sunflower oil, and palm oil (PO). The β-oxidation capacity, protein utilization, digestibility of dietary fatty acids and fatty acid composition of lipoproteins, plasma, liver, belly flap, red and white muscle were measured. Further, the lipid class and protein levels in the lipoproteins were analyzed. The different dietary fatty acid compositions did not significantly affect protein utilization or β-oxidation capacity in red muscle. The levels of total cholesterol, triacylglycerols, and protein in very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and plasma were not significantly affected by the dietary fatty acids. VLDL, LDL, and HDL fatty acid compositions were decreasingly affected by dietary fatty acid composition. Dietary fatty acid composition significantly affected both the relative fatty acid composition and the amount of fatty acids (mg fatty acid per g tissue, wet weight) in belly flap, liver, red and white muscle. Apparent digestibility of the fatty acids measured by adding yttrium oxide as inert marker, was significantly lower in fish fed the PO diet compared to the other three diets.     

Fatty acid composition and its relationship with physicochemical properties of pecan (Carya illinoensis) oil

The composition and physicochemical properties of pecan (Carya illinoensis) kernels and oils from different native trees of the central region of Mexico were investigated. The main compositional characteristic of the kernel was the high lipid content (70–79% w/w on dry basis) with elevated concentration of oleic acid (55–75% w/w). The results confirmed the relationship in the biosynthesis of linoleic and linolenic acids from oleic acid existing in oilseeds. Our results indicate that in pecans such relationship is a function of pecan tree age. The proportion of oleic, linoleic, and linolenic fatty acids determined the oxidative stability, viscosity, and melting/crystallization behavior of pecan oil. In general, these properties in pecan oils were similar or superior to extra-virgin olive oil and unrefined sesame oil. Although all native pecan oils studied showed a significant concentration of oleic acid, a particular group of native Mexican pecan trees produces an oil with a fatty acid composition with the nutritional appeal that consumers demand nowadays (i.e., very high oleic acid, 60–75%), with excellent natural oxidative stability (i.e., induction time for oxidation between 8.5 and 10.8 h), and substantially higher concentrations of α-, γ-, and δ-tocopherol than in pecan varieties previously reported in the literature.     

Fatty acid composition of oil from soybean leaves grown at extreme temperatures

Leaves from soybean (Glycine max (L.) Merr.) plants were assayed to determine if the relationship between temperature and relative fatty acid composition observed in the seed oil also existed for the triglycerides in the leaf oil. Leaf samples were harvested from eight soybean lines (A5, A6, C1640, Century, Maple Arrow, N78-2245, PI 123440 and PI 361088B) grown at 40/30,28/22 and 15/ 12°C day/night. At 40/30 and 28/22°C, seven fatty acids were observed at a level greater than 1.0%. These included the five major fatty acids found in the seed oil: palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2) and linolenic (18:3) acid; plus two fatty acids that had retention times the same as palmitoleic (16:1) and γ-linolenic (18:3 g) acid. In addition, an eighth fatty acid that had a retention time the same as behenic (22:0) acid was found in the leaves of all lines at 15/12°C. Palmitic, palmitoleic and stearic acid content did not differ significantly over temperatures. The oleic and linoleic acid content were each highest at 15/12°C, while the γ-linolenic and the linolenic acid content were each highest at 40/30°C. The fatty acid composition of the triglyceride portion of the leaf oil did not display the same pattern over temperatures as that observed for seed oil.     

Fatty acid composition of erythrocyte,platelet, and serum lipids in strict vegans

The fatty acid composition of erythrocytes, platelets, and serum lipids was compared between subjects who had been eating a strict uncooked vegan diet (“living food”) for years and omnivore controls. The vegan diet contains equal amounts of fat but more monounsaturated and polyunsaturated and less saturated fatty acids than the mixed diet of the control group. In vegans, the proportion of linoleic acid was greater in all lipid fractions studied. Also, the levels of other n−6 fatty acids were greater, with the exception of arachidonic acid levels, which were similar in most fractions. In erythrocytes, platelets and serum phospholipid fractions, this increase was mainly at the expense of the n−3 fatty acids. The proportions of eicosapentaenoic and docosahexaenoic acid were only 29–36% and 49–52% of those in controls, respectively. In vegans the ratio of n−3 to n−6 fatty acids was only about half that in omnivores. In addition to the lower levels of n−3 fatty acids, the proportions of palmitic and stearic acids were lower in serum cholesteryl esters, triglycerides and free fatty acids of vegans. The proportion of oleic acid was slightly lower only in serum cholesteryl esters and erythrocyte phosphatidylserine. The results show that, in the long term, the vegan diet has little effect on the proportions of oleic and arachidonic acids, whereas the levels of n−3 fatty acids are depressed to very low levels with prolonged consumption of the high linoleic and oleic acid components of this diet.     

Effect of nitrogen and zinc fertilization and plant growth retardants on cottonseed, protein, oil yields, and oil properties

The increase in the population in Egypt makes it imperative to explore promising approaches to increase food supply, including protein and oil, to meet the needs of the Egyptian people. Cotton is the principal crop of Egyptian agriculture. It is grown mainly for its fiber, but cottonseed products are also of economic importance. Cottonseed is presently the main source of edible oil and meal for livestock in Egypt. Field experiments were conducted in two successive seasons at the Agricultural Research Center (Giza, Egypt) on cotton (Gossypium barbadense L. cv. Giza 75) to determine the effect of nitrogen (N) fertilizer rate (107 and 161 kg of N/ha applied as ammonium nitrate containing 33.5% N in two equal doses at 6 and 8 wk after sowing), together with foliar applications of plant growth retardants (mepiquat chloride “Pix”, chloromequat chloride “Cycocel”, and daminozide “Alar”, each applied once at 288 g active ingredient/ha, after 75 d from sowing) and zinc (Zn) (applied in chelated form after 80 and 95 d from sowing at 48 g of Zn/ha) on seed, protein and oil yields and oil properties of cotton. The higher N-rate, as well as the application of all growth retardants and Zn, resulted in an increase in cottonseed yield, seed protein content, oil and protein yields/ha, seed oil refractive index, unsaponifiable matter, and total unsaturated fatty acids (oleic and linoleic). These treatments tended to decrease oil acid value, saponification value, and total saturated fatty acids. The seed oil content tended to decrease as N-rate increased and increased with the application of all growth retardants and Zn. There were some differences between Pix, Cycocel, and Alar regarding their effects on the studied characters. The highest increase in seed, oil, and protein yields/ha was found with Pix, followed by Cycocel. The Cycocel treatment gave the lowest total saturated fatty acids oil content, followed by Alar.     

13C nuclear magnetic resonance spectroscopic analysis of the triacylglycerol composition of some margarines

The triacylglycerol fraction of three samples of margarine, namely “Flora” (Holland), “Kaliakra” (Bulgaria), and “Corona” (Holland), were studied by¹³C nuclear magnetic resonance spectroscopy. By examining the various carbon chemical shifts of the saturated and unsaturated carbon nuclei, “Flora” margarine was shown to contain a mixture of hydrogenated and unhydrogenated vegetable oils. This technique allowed all major acyl groups (saturated, oleate, linoleate, and linolenate) and minor acyl components [different positional isomers of long-chain (E)- and (Z)-monoenoic moieties, arising as by-products during catalytic hydrogenation] to be identified. The amount of each fatty acid present in the margarine was also estimated from the relative intensities of the corresponding signals. “Kaliakra” margarine consisted of a blend of unhydrogenated natural fats and oils that contained saturated fatty acids, oleate, and linoleate. There were no signs in the spectrum of “Kaliakra” of any (E)-isomers, nor signals associated with positional unsaturated acyl groups (other than oleate and linoleate). The sample of “Corona” margarine consisted of a mixture of hydrogenated and unhydrogenated vegetable oils and butter (1.3%). The presence of butter in this sample was identified by the characteristic carbon shifts of the C-1 to C-4 carbon atoms of butyrate. The distribution of the fatty acids on the glycerol “backbone” also was estimated by this technique.     

Human erythrocyte phosphoglycerides. II. Diet and lecithin structure

Lecithins (separated on basic silicic acid columns) were obtained from humans fed three different diets: eitherad-libitum or diets containing 40% of calories from linoleic acid (as corn oil) or from oleic acid (as triolein). Four lecithin subfractions were studied from each dietary group. Lecithin fractions eluting earliest (and apparently the least polar) contained the highest molar ratios of unsaturated fatty acids and the highest proportion of C-20 to C-22 polyunsaturated fatty acids. A slight increase in proportions of diunsaturated molecules occurred in corn oil and triolein groups. However, over 90% of lecithins of each dietary group were maintained as themonosaturated - monounsaturated type. Therefore, in contrast to human adipose tissue triglycerides, the saturated/unsaturated fatty acid ratio of lecithins of the erythrocyte membrane is largely unaffected by immense increases in dietary unsaturated fatty acid. Major shifts of oleic and linoleic acid occurred but proportions were unaltered of longer chain length (>C-18) polyunsaturated fatty acids. The relevance of these findings to membrane structure and function and to glycerophosphatide biosynthesis is discussed.