Oxidation of acylglycerols and phosphoglycerides by soybean lipoxygenase

Lipoxygenase (EC 1.13.11.12) catalyzes the incorporation of oxygen into polyunsaturated fatty acids, resulting in the formation of their corresponding hydroperoxides. The ability of a commercial preparation of soybean (Glycine max L. Merr.) lipoxygenase to catalyze the oxidation of acylglycerols and phosphoglycerides was investigated. The oxidation rate of trilinolein increased nearly 100% when 5 mM deoxycholate was added to the reaction medium. With further increases in the concentration of deoxycholate, the oxidation rate decreased slightly. The pH profile of trilinolein oxidation was bell-shaped. The rate of oxidation was maximal at pH 8, and it decreased to near zero at pH 5 and pH 11. Even under optimal conditions, the rate of trilinolein oxidation was only 3% of that of linoleic acid, and analysis of time course data showed that, at most, 15% of available linoleate was oxidized. In contrast to the slow rate of trilinolein oxidation, tested phosphoglycerides and diacylglycerols were oxidized at moderate rates. The rate of phosphoglyceride oxidation depended upon the structure of the polar head group and varied between 7–28% of the rate of linoleic acid oxidation. Diacylglycerols reacted at a rate that was 40% of that of linoleic acid. Analysis of the time course of 1,3-dilinolein oxidation showed that as much as 67% of the available linoleate could be converted to the corresponding hydroperoxide. Analyses by high-performance liquid chromatography revealed that more than 20% of the 1,3-dilinolein was converted to unidentified products that are not hydroperoxides.     

Stereospecific analysis of triacylglycerols and major phosphoglycerides fromLipomyces lipoferus

The stereospecific distribution of fatty acids in triacylglycerols, phosphatidylcholines and phosphatidylethanolamines ofLipomyces lipoferus was determined. Position sn-1 of the triacylglycerols had a predominance of unsaturated fatty acids of which C_18∶1 (61%) was the major component. Position sn-2 of the triacylglycerols contained 88% C_18∶1 and was more unsaturated than position sn-1 by 24.6%. Position sn-3 had equal proportions of saturated and unsaturated fatty acids. Phosphatidylcholine had a quantitatively distinctive fatty acid distribution in that position sn-2 was 26.7% more unsaturated than position sn-1. In phosphatidylethanolamine, position sn-2 was 10.8% more unsaturated than position sn-1. Positions sn-1 and sn-2 of these phosphoglycerides had a different fatty acid profile from positions sn-1 and sn-2 of the triacylglycerols. These results suggest a nonrandom distribution of fatty acids in the triacylglycerols and phosphoglycerides. Because triacylglycerols and phosphoglycerides are both derived from 1,2-diacylglycerols, these data suggest two possibilities: some selectivity in utilization of species of diacylglycerols to form triacylglycerols and phosphoglycerides or modification of the triacylglycerols and phosphoglycerides after they are formed or both. This study is the first of its kind in a yeast. Presented in part at the AOCS Fall Meeting, Ottawa, Canada, September 1972.     

Properties and structure of oil shale ash pastes. II: Mechanical properties and structure

Compressive strength, drying-shrinkage and expansion in water of oil shale ash pastes were studied and compared to the corresponding properties of portland cement paste. X-ray diffraction and some scanning electron microscopy runs were also included in the study. It was concluded that the structure and properties of the ash pastes can be described and explained by the same models which have been suggested for portland cement paste. The only exception was the total porosity of the ash paste which remained unchanged with time. A suitable modification in the structural model of the portland cement paste was suggested to allow for this specific behaviour.     

Chlorinated high density polyethylene. II. Solid state structure

Chlorination of high density; polyethylene results in polymers which consist of unmodified methylene units and chlorinated methylene co-units. The effect of the concentration and distribution of chlorinated units on the solid state structure has been examined by thermal, wide angle X-ray diffraction and dynamic mechanical analysis. As the substitution becomes more random, the crystallinity, crystallite size, and crystalline perfection decrease for a given chlorine content. The chlorinated units are shown to be capable of co-crystallizing, and the concentration of chlorine in the crystalline phase increases as the distribution is made more random. Concurrently, the chlorine concentration of the amorphous phase decreases. Segregation of chlorine into the amorphous regions is most efficient when the substitution is blocky.     

Fatty acid composition of triglycerides and phosphoglycerides during growth inGlomerella cingulata

The fatty acid composition of triglycerides and phosphoglycerides accumulated at selected ages during the growth ofGlomerella cingulata was investigated. Glyceride accumulation was taken as mg glyceride/mg N and the nitrogen content of the fungus at the ages investigated was used as an index of growth. The fatty acids produced were identified by comparing their retention times on gas liquid chromatography with that of known standards. The results showed that whereas total glyceride and fatty acid content varied from age to age, the fatty acid composition at the various ages remained the same.     

Randomly branched styrene/divinylbenzene copolymers. II. Solution properties and structure

The [η] of randomly branched PSty/DVB continually decreases from linear polystyrene with increasing conversion. On the other hand, the relation of the 〈S²〉 to M of both low and high conversion series is equivalent, although the actual size is smaller than that of linear polystyrene of the same M. This fact, in conjunction with the previously published reactivity ratios, allows the following interpretation of the mechanism of copolymerization: namely, that branched molecules are formed in which the center core is higher in DVB content than is the periphery. Only about 1/7 of the available DVB units act as effective tetrafunctional branch points. An analysis of GPC data correlated with light scattering and viscosity dimensions allows the g value to be determined in the lightly and highly branched fractions. The viscosity ration is related to g^x, where x is 0.65 for low conversion fractions (A series) and becomes 1.41 for high conversion fractions (B series). This change in exponent is postulated to arise from an increase in branching density as conversion increases. The ratio of the hydrodynamic radius to the radius of gyration is higher for branched than for linear polymers. The theta temperature (θ) in cyclohexane for randomly branched polystyrene compared to linear polystyrene is always higher and can be as much as 2° higher.     

Polymer structure formed in radiation-induced graft polymerization. II

Methyl methacrylate was grafted onto viscose rayon, wood pulp, cellophane, and poly(vinyl alcohol) with preirradiation techniques using γ-rays from a Co-60 source, and the stereoregularities of the grafted polymers separated from the trunk polymers and homopolymers were determined. The stereoregularity of the polymers grafted onto rayons is different from that of the polymers grafted onto wood pulp, mercerized wood pulp, cellophane, and poly(vinyl alcohol), confirming our previous results.     

Copper(II)-catalyzed lipid peroxidation in liposomes and erythrocyte membranes

Cu⁺⁺ was uniquely capable of catalyzing the peroxidation of rat erythrocyte membrane lipid in the presence of 10 mM H₂O₂, whereas several other transition metal ions were without significant effect. In contrast, peroxidation of soybean phospholipid liposomes could be catalyzed with decreasing efficiency by Co⁺⁺, Cu⁺⁺, Pb⁺⁺, or Cr⁺⁺⁺ also in the presence of H₂O₂. The effect of imidazole on Cu⁺⁺-catalyzed lipid peroxidation was stimulatory in liposomes and inhibitory in membrane preparations, whereas EDTA, histidine, citrate and alanine inhibited peroxidation in both systems. EDTA could stop the peroxidation after initiation, but catalase could not, indicating that Cu⁺⁺ alone was necessary for the propagation of the chain reaction. Competitive inhibition studies with various scavengers of hydroxyl radicals or singlet oxygen and the absence of significant reaction enhancement by D₂O indicated that neither of these reactive oxygen species was a major mediator in the Cu⁺⁺-H₂O₂ oxidative system. A copper-oxygen complex may be directly involved in the initiation of peroxidation. Normal erythrocyte membranes and phospholipid liposomes also differ in their sensitivities toward external oxidative stress. In the absence of H₂O₂, Cu⁺⁺ (0.2 mM) was capable of catalyzing lipid peroxidation in liposomes, aged erythrocyte membranes and membranes from vitamin-E-deficient rats; however, freshly prepared membranes from control rats and liposomes containing α-tocopherol required H₂O₂ greater than 2 mM for the catalytic effect of Cu⁺⁺ to be observed.     

卵磷脂的应用与开发

介绍了卵磷脂的发展现状、化学组成及超临界态二氧化碳脱脂工艺,并对其应用及开发前景作了简述     

Soybean lecithin fractionation and functionality

Soybean lecithin contains primarity PC, PE, and PI. Fractionation of these phospholipids (PL) is desirable for certain applications. Ethanol was used to fractionate PC and PI, which have different solubilities in this solvent. Various concentrations of ethanol (90, 95, and 100%) and ethanol/gum ratios (0.5, 1.0, 1.5, 2.0, and 2.5) were used. Ethanol concentration significantly influenced the yield of the PC-enriched fraction and the PC and PI fractionation: The highest ethanol concentration resulted in the highest yield of PC fraction, the most PC in the PC fraction, and the most PI in the PI fraction. The ethanol/gum ratio significantly affected the yield of PC-enriched fraction, but did not affect the relative PL composition of the PC-enriched fraction. Ethanol of 90% concentration with a solvent/gum ratio of 3 was used for further large-scale fractionation. Such fractionation resulted in a PC-enriched fraction containing 73% PC, 24% PE, and 3% PI based on the total PL content, whereas the PI fraction contained 26% PC, 35% PE, and 39% PI. Functional properties of these two purified fractions, i.e., surface tension reduction, emulsion stability, and oxidative stability, were investigated. The PI-enriched fraction had a much lower critical micelle concentration than the PC-enriched fraction, which suggests the PI-enriched fraction has a higher surface tension reduction capability. For the emulsion stability test, the PI-enriched fraction performed better than the PC fraction in both water-in-oil and oil-in-water emulsions. An oxidative stability test showed that these PL were very stable to lipid oxidation.     

Structure and properties of impact copolymer polypropylene. II. Phase structure and crystalline morphology

In this work, an impact copolymer polypropylene (ICPP) was separated into 4 fractions, A, B, C, and D. The phase structure, thermal behavior, and crystalline morphology of the ICPP and its 4 fractions were studied thoroughly using scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and polarized light microscopy (PLM). Results of SEM and DMA show that ethylene–propylene rubber (EPR) and part of the ethylene–propylene segmented copolymer disperse as toughening particles in the ICPP. The size and size distribution of these particles are determined by chain structure of the fractions of ICPP. From fraction A to fraction D, the morphology changes from noncrystalline to semicrystalline gradually, as shown by DSC. DSC results also indicate that thermal behavior of the ICPP agrees greatly with its chain structure. PLM demonstrates that it is difficult for the ICPP to grow perfect spherulites, that is, partially, because the matrix of ICPP, fraction D, has defects in its macromolecular chain. Another cause is that there is a good compatible structure in the ICPP and so the noncrystalline component (including all fractions) hinders the growth of the spherulite. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 103–113, 1999     

BIMS/filler interactions. II. Effects of filler concentration and BIMS structure

Brominated isobutylene para‐methylstyrene (BIMS) elastomer is a terpolymer of isobutylene, para‐methylstyrene (PMS), and para‐bromomethylstyrene (BrPMS). Viscoelastic measurements have been used to characterize the blends of this BIMS elastomer with different concentrations of a carbon black (CB) filler, N234. Data in the low temperature/high frequency region suggest that N234 at a concentration less than or equal to 15 vol % in BIMS appears not to affect the T_g of BIMS although a slight increase in relaxation time in the transition zone is observed. Also, the effects of BrPMS and PMS contents in BIMS on BIMS/N234 CB interactions have been qualitatively investigated by using the bound rubber measurements. To assess BIMS/CB interactions with reference to diene rubber/CB interactions, mixing of BIMS with various amounts of a polybutadiene rubber in the presence of CB has been performed. Atomic force microscopy and image processing have been employed to quantify filler phase distributions in these blends for a practical ranking of polymer/CB interactions. Preferential partition of CB in the BIMS or BR phase depends on the BrPMS content in BIMS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 659–667, 2006     

Photooxidation of amine crosslinked epoxies II. Influence of structure

We have studied the photooxidation of networks based on three diepoxides containing isopropylidene or methylene bisphenol structures and three diamines of the dianiline type, with, respectively, methylene (DDM), ether (DDE), or sulfone (DDS) bridges. The results are discussed in terms of photoinitiated radical oxidation mechanisms. The comparison of the different systems shows that the photoinitiating species essentially derive from the phenoxy part, whereas the propagation essentially depends on amine concentration and electron density at the nitrogen atom. The amine structure also plays a very important role in color development.     

Silk‐inspired polyurethane containing GlyAlaGlyAla tetrapeptide. II. physical properties and structure

Biomedical polyurethane (BPU) and silk fibroin have similarly molecular architecture in their primary and aggregate structure, both of which have amide bonds and microphase separation, and they have been employed as scaffold materials for biomedical applications. Based on this, as the featured peptide sequence of silkworm silk fibroin, GlycineAlanineGlycineAlanine (GlyAlaGlyAla) tetrapeptide was synthesized by using traditional liquid‐phase peptide synthesis method with Boc‐protected glycine and alanine as starting materials, and was transformed to its derivative with two amine‐terminated functional groups. The derivative was introduced as a chain extender into the backbone to form the hard segment of a silk‐inspired PU with urea‐linkage. Related measurements show that molecular weight of the synthesized silk‐inspired PU ranged from 13,000 to 15,000. Fourier transform infrared (FTIR) absorption bands of Amides I and II are at 1651 cm^?1 and 1534 cm^?1, and Raman absorption band of Amide III is at 1302 cm^?1. UV‐Vis absorption peak of the silk‐inspired PU is at 266 nm. This new concept and strategy may allow the fabrication of a new class of thermoplastic polyurethane elastomers to mimic the structure and properties of silk fibroin of silkworms and spiders. Information provided by this study may be used to better understand the correlation between the natural and man‐made materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crosslinking structure of keratin. II. Intermolecular and intramolecular crosslinks in potassium-cyanide-treated wool fibers

The crosslinking structure of keratin fibers has been investigated. The reaction of wool with aqueous KCN was studied by means of chemical and physical methods. Quantitative conversion of disulfide (SS) groups of the cystine (Cys) residues into stable thioether (S) linkages was confirmed. In terms of mechanically effective and noneffective crosslinkages, the amounts of intermolecular and intramolecular crosslinks in the KCN-treated wools were determined from the analysis of the corresponding amino acids and mechanical experiment in which the shear modulus of swollen, rubberlike samples is determined from the relation between equilibrium stress and strain for simple extension of the fiber in a diluent. A modified elastic equation of state was used for the calculation of the number of intermolecular crosslinks. The front factor in the equation used was determined by combining the results obtained from purely chemical kinetics and the values of shear modulus of the swollen wools. The ratio of the number of intermolecular and intramolecular SS crosslinkages in the Lincoln wool, was found to be 64:36. The reactivity of the former is much higher than that of the latter, and these two types of SS crosslinks form substantially the same type of S crosslinks. The fraction of the Cys residues accessible to cyanideions depends mainly on the reaction temperature.     

High modulus polypropylene fibers. II. Influence of fiber preparation upon structure and morphology

The influence of drawing on the limiting draw ratio upon formation of the morphological structure of fibers spun from binary polypropylene (PP) blends was studied. Fibers were spun from a fiber‐grade CR‐polymer and from the blends of a fiber‐grade CR‐polymer with a molding‐grade polymer in the composition range of 10–50 wt % added. As‐spun fibers were immediately moderately and additionally highly drawn at the temperature of 145°C. The structure and morphology of these fibers were investigated by small‐angle X‐ray scattering, wide‐angle X‐ray scattering, differential scanning calorimetry, scanning electron microscopy, density, birefringence, and sound velocity measurements. It was shown that continuously moderately drawn fibers are suitable precursors for the production of high tenacity PP fibers of very high modulus, because of so called oriented “smectic” structure present in these fibers. With drawing at elevated temperature, the initial metastable structure of low crystallinity was disrupted and a c‐axis orientation of monoclinic crystalline modification was developed. Hot drawing increased the size of crystallites and crystallinity degree, the orientation of crystalline domains, and average orientation of the macromolecular chains and resulted in extensive fibrillation and void formation. It was found that the blend composition has some influence on the structure of discontinuously highly drawn fibers. With increasing the content of the molding‐grade polymer in the blend, the size of crystalline and amorphous domains, density and crystallinity, as well as amorphous orientation decreased. Relationship has been established between the mechanical properties, crystallinity, and orientation of PP fibers. It was confirmed that by blending the fiber‐grade CR‐polymer by a small percentage of the molding‐grade polymer, maximization of elastic modulus is achieved, mainly because of higher orientation of amorphous domains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1067–1082, 2006     

Egg-yolk lipid fractionation and lecithin characterization

Egg-yolk lecithin has phospholipid (PL) classes and a FA composition that differ from soybean lecithin and may have unique functional properties. The purposes of this research were to develop an effective method for extracting a sufficient amount to lecithin from fresh egg yolks and to evaluate its functional properties. Ethanol was used to dehydrate and partially extract the PL, after which hexane was used to extract the total lipids. A phase separation of the combined extracts resulted in neutral and polar lipid fractions. An acetone precipitation of PL from the final polar lipid fraction was necessary to remove the residual neutral lipids, especially cholesterol. The purity of PL in the lecithin product was 95%. Surface tension reduction, emulsion stability, and oxidative stability studies were conducted to characterize the functional properties of egg-yolk lecithin. Egg-yolk lecithin and soy lecithin had similar surface activities, as evaluated by the surface tension reduction in an aqueous system and the critical micelle concentration. Soybean lecithin created a more stable emulsion than egg-yolk lecithin. However, egg-yolk lecithin was more oxidatively stable than soybean lecithin.     

Sunflower lecithin and possibilities for utilization

Sunflower lecithin is an important product in countries producing large amounts of sunflower oil. Due to its high phosphatidylcholine and essential fatty acid contents, it can be well utilized as an additive in food and feedstuffs. After refinement and fractionation, its utilization in food products and cosmetics can be greatly increased and further extended after appropriate modification. Utilized as an additive in the feedstuff to piglets and porklings, it results in higher bodyweight and shortened breeding and fattening periods. It is also suitable for adjusting the energy level of broiler feeds and, owing to its choline content, the use of synthetic choline chloride can be eliminated.