Thesis (M.S.)--Miami University, Dept. of Chemistry and Biochemistry, 2003. / Title from first page of PDF document. Document formatted into pages; contains viii, 105 p. : ill. Includes bibliographical references.

Thesis (M.S.)--Miami University, Dept. of Chemistry and Biochemistry, 2002. / Title from first page of PDF document. Document formatted into pages; contains vi, 105 p. : ill. Includes bibliographical references (p. 99-105).

Thesis (Ph. D.)--Washington State University, December 2006. / Includes bibliographical references (p. 89-94).

Lipid analyses of the leaves of Empetrum nigrum subspp. hermaphroditum with an upland distribution in the U.K. and the lowland E. nigrum subspp. nigrum revealed a) that the lowland subspecies had higher total and neutral lipid levels throughout 1979 b) that total lipid levels remained constant within the leaves of both subspecies throughout the year. c) that storage lipid (triacylglycerols) contributed 1.4% and 4.5% to the total lipid of subspecies hermaphroditum and nigrum respectively. This data is inconsistent with the suggestion that the high leaf total lipid levels associated with alpine species represent high levels of storage lipid. Instead it is suggested that the high lipid content of Empetrum leaves may be a reflection of a well-developed waxy cuticle. It'is pseudacorus occupies habitats characterized by poor O2 availability and is able to tolerate up to two months total anoxia without any loss in viability. By contrast the cultivated Iris qerrnanica var Quechei typically a plant of well drained soils suffers 100% mortality during 8 weeks anoxia. Further the cut primary shoot of I. germanica was observed to be more susceptible to anoxic injury than the I. remainder of the rhizome. As the biosynthesis of polyunsaturated fatty acids requires the participation of molecular oxygen it was thought profitable to compare what changes occurred in the anoxia tolerant I. pseudacorus and intolerant I. germanica when subject to anoxic stress. In I. pseudocorus there were a number of lipid modification during anoxia. Glycolipids declined dramatically and although all fatty acids declined it was surprising that saturated acids decreased the most. It was suggested that the decline in glycolipids might reflect mobilization of carbohydrate reserves and/or a replenishment of the fatty acid pool through glycolipid breakdown. The significance of the alterations in membrane fluidity which might be expected to result from alterations in the saturated /unsaturated ratio remain unexplained. By complete contrast, the anoxia intolerant I. germanica although possessing a highly similar lipid profile exhibited no changes in lipid composition in response to anoxia. Therefore membrane dysfunction through lipid component omission is not a major factor in anoxic mortality. Through production of cytotoxic species such as H2O2, O2, OH and 1O2, O2 may bring about peroxidative damage. On rexposure to air it was found that the highly anoxia sensitive primary shoot tissue of I. germanica produced 38 times more malondialdehyde (M.D.A. - a lipid peroxidation product) than material which was maintained aerobically. 1. pseudacorus did not exhibit such differences. Although the overall levels of M.D.A. are higher in I. pseudacorus it may be that the primary shoot tissue contains efficient endogenous secondary protection mechanisms to make good peroxidative damage. However, in the natural environment it is unlikely that the species would ever be exposed to such rapid alterations in O2 concentrations.

The large-scale purification of the major spinach thylakoid lipids by a combination of silica and carboxymethyl-cellulose chromatography is described. Yields of hundreds of milligrams of the lipids, representing 25-40% of the original lipid, have been obtained. In addition, routine purities in excess of 99.7% of the isolated lipids has been demonstrated. The structures of the purified lipids have been confirmed by fatty acid analysis, thin layer chromatography, and ¹³C-NMR. Some minor reassignments to previously published ¹³C-NMR for these compounds are described. In addition, the ¹H-NMR spectra for the glycolipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol (SQDG), are shown. The resonance assignments for MGDG and SQDG have been obtained by a combination of off-resonance decoupling experiments and by two-dimensional COSY ¹H-NMR experiments. Similar experiments with DGDG have failed to resolve the proton assignments due to extensive overlapping of the proton resonances. Interbilayer interactions between large unilamellar vesicles of DGDG in aqueous salt solutions have been examined by light scattering, freeze-fracture electron microscopy, and X-ray diffraction. When suspended in aqueous salt solutions, vesicles of 100 nm diameter were found to aggregate in a rapid and reversible manner to yield aggregates greater than 1000 nm in diameter. Freeze-fracture electron microscopy showed these aggregates to consist of appressed, but not fused, vesicles. Quasi-elastic light scattering and turbidity experiments showed that aggregation was not due to charged impurities of the lipid behaving in accordance with electrostatic double layer theory. Experiments testing the efficacies of various chloride salts indicated a strong correlation existed between ionic radius and ability of the salt to promote aggregation. Similar experiments examining the effect of sodium salts, glycerol, and pH on vesicle aggregation implicate an interaction between the DGDG head group and structured water as underlying the aggregation process. The effect of additions of other lipids on the extent of DGDG aggregation has been examined. Addition of 0.5 to 5.0% of either anionic lipid phosphatidylglycerol (PG) or SQDG inhibited the aggregation of DGDG vesicles, probably by the development of an electrostatic potential. Different effects of PG and SQDG on the concentration of Mg²⁺ required for aggregation indicated that PG may form a bidentate ligand with Mg²⁺ at ≥ 5 mol% PG. SQDG did not show this behavior, indicating that its negatively charged sulfonate group is unavailable for cation complex formation. Addition of MGDG to DGDG up to 50 mol% had no effect on the Mg²⁺ requirement for aggregation, but at ≥ 25 mol% triggered irreversible vesicle aggregation. This suggests that the MGDG head group is as effective at causing aggregation as the DGDG head group. Further, MGDG probably triggers vesicle fusion at ≥ 25 mol%. The results suggest that the galactolipids may contribute to the close approach of thylakoids in higher plant chloroplasts. The permeability properties of large unilamellar vesicles of DGDG to ⁸⁶Rb⁺, ³⁶Cl⁻, and ³H-glucose have been determined. In addition, the permeabilities of binary, ternary, and quaternary mixtures of thylakoid lipids to ⁸⁶Rb⁺ have also been measured. Vesicles of DGDG were found to be 60-130 fold more permeable to Rb⁺ and 46-76 fold less permeable to CI⁻ than phosphatidylcholine vesicles. Vesicles of DGDG and PC were similar in glucose permeability. Electron spin resonance measurement of DGDG bilayer fluidity indicated that fluidity differences could not account for the observed differences in ion permeability. The addition of 50 mol% of MGDG to DGDG vesicles had no effect on Rb⁺ permeability, suggesting that the HII phase preference of MGDG does not increase bilayer permeability. The addition of SQDG led to a large increase of Rb⁺ permeability. The calculated permeability coefficient to Rb⁺ for a DGDG/MDGD/SQDG/PG (1/2/0.5/0.5) mixture similar to that of thylakoid membranes was 2.0-10⁻⁹ cm-s⁻¹. This value is three orders of magnitude higher than that for phospholipid systems, and ten-fold higher than that for vesicles of pure DGDG. It is concluded that the permeability properties of thylakoid lipids are dominated by oriented surface dipoles and not by bilayer fluidity or acyl chain packing considerations. It is also proposed that the high permeability of thylakoid lipids to cations is the main cause of low observed thylakoid membrane electrical potentials, and large proton gradients across thylakoid membranes. It has been proposed previously that the high proportions of saturated phosphatidylglycerols (ie. DPPG) found in chilling-sensitive plants may promote the formation of gel phase lipid, and cause increased metabolite leakage, in the thylakoids of these species at chilling temperatures. The leakage of ⁸⁶Rb⁺ from large unilamellar vesicles of thylakoid lipids containing proportions of disaturated PG (as DPPG) mimicking those of chilling-sensitive and chilling-resistant plants has been measured. This data indicated that no increase in Rb⁺ permeation occurred between any of the tested vesicles systems between 7° and 30° C. Differential scanning calorimetry showed no heat flow indicative of gel to liquid- crystalline phase separation in any of the lipid mixtures, even with DPPG levels as high as 12 mol%. It is concluded that a direct effect of disaturated PG on chilling injury in sensitive plants by an increase of low-temperature thylakoid permeability is unlikely. / Science, Faculty of / Botany, Department of / Graduate

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

No description available.

No description available.

The overall objective of this study was the optimization of a model enzymatic system in organic solvent media for the biosynthesis of selected phenolic lipid compounds. The model enzymatic system consisted of cinnamic acid and oleyl alcohol as substrates using commercial immobilized lipase (Novozym 435) from Candida antarctica. The experimental findings showed that an increase in the hydrophobicity of the solvent mixture and a decrease in the aw values of the reaction medium increased the initial enzymatic activity and bioconversion yield; the use of an iso-octane and butanone solvent mixture (85:15, v/v) and an initial aw of 0.05 resulted in an initial enzymatic activity of 192.7 nmol product/g enzyme/min and a corresponding bioconversion yield of 95.3% after a 16-day reaction period.

Six different lots of soya beans (Glycine max (L.) Merr.) were examined. Seed hydroperoxide levels were highly correlated with viability, but not with moisture contents. It was proposed that moisture contents may exert a similar antioxidant effect at intermediate levels as has been observed in dry foods. Seeds treated with ferrous sulphate were significantly (S% level) invigorated. Furthermore, this treatment was observed to give rise to a reduction in the peroxide value of soya bean axes over the first hour of imbibition, an increase in 2,3,S-triphenyl-tetrazolium chloride reduction and protein synthesis, and a decline in electrolyte leakage. It was proposed that this was due to the antioxidant activity of the ferrous iron, leading to an attenuation of free-radical induced autoxidation. Ferrous sulphate treated seeds produced more aldehydes than untreated seeds. This result suggested that aldehydes may not be responsible for declining seed vigour. Hexanal, pentanal and butanal production from heated dry seeds was significantly correlated with seed germination, CVG and hydroperoxide levels. The thermal breakdown of the hydroperoxides was postulated to be the source of these compounds. A GC technique was developed using model systems of oxidized methyl oleate, linoleate, linolenate and soya bean bulk oil. The analysis of seed lipid oxidation products revealed marked differences in the proportions of the products compared to bulk and monolayer oxidation. The selective production of the 13-hydroperoxide implicated enzymatic or metalloprotein involvement. The implications of the results of this study with regard to the present theories of seed ageing were discussed. / Thesis (Ph.D.)-University of Natal, Durban, 1990.