A wide range of [1-14C] monoenoic (32) and polyenoic (8) fatty acids and two unlabelled fatty acids containing a 6,7-cyclopropene ring were prepared by existing methods. Several procedures for the conversion of oleic acid to its C17 iodide with concomitant decarboxylation were investigated without success. The CMR spectra of (27) saturated, (65) cis and trans monoenoic, (39) monoynoic, (2) cyclopropene, (20) cis-polyenoic, (14) diynoic and (10) mixed-function diunsaturated acids and methyl esters were recorded and interpreted. An empirical approach, based on the shielding and deshielding influence of functional groups on the rest of the molecule, was employed, and the assignment of 13C resonances by this method agreed with those obtained by other researchers using different methods. The shielding and deshielding effects were generally additive, except when two function groups were close together. CMR spectroscopy can be used to distinguish cis and trans olefins, locate double and triple bond positions and interpret patterns of polyunsaturation. The specificity of the mammalian desaturases was examined by incubating [1-14C] fatty acids with a rat liver microsomal preparation and analysing the products formed after one hour. The Delta9 desaturase was believed to hold its substrate by the binding of the CoA moiety at the carboxyl end and by the fit of the alkyl chain into a deep, narrow cleft, where, except at the active centre, it was constrained to take up predominantly trans conformations. This model is confirmed. Trans monoenoic acids were generally Delta9 desaturated to give as high conversions as saturated acids, and the Delta7t and Delta11t monoenoic acids gave the corresponding Delta7t9c and Delta9c11t conjugated dienes. Cis monoenoic acids, which were not expected to fit into the enzyme cleft between C(5) and C(15), were not Delta9 desaturated unless the double bond position was beyond Delta13, and even then they were much poorer substrates than stearic acid. The Delta6 desaturase shows a much wider substrate specificity than was previously anticipated. The enzyme can accommodate a wide range of substrate chain lengths (at least C14 to C22) and the Delta9 cis double bond is not obligatory for Delta6 desaturation. The model advanced for the enzyme contains two distinct features. Firstly, a region of steric constraint between C(10) and C(13) on the substrate geometry acceptable to the enzyme is proposed. Secondly, pi-bond binding sites on the enzyme surface in the C(9) to C(13) region are envisaged. Dienoic acids with a Delta9c double bond and adjacent olefinic unsaturation (Delta11- Delta13) were much better substrates than monoenoic acids or dienoic acids containing a Delta9c double bond and a second double bond beyond the Delta13 position. Therefore, to bed substrate for Delta6 desaturation the co-operative binding of two ands, separated by 0-2 methylene groups, to these Delta-binding is essential. The Delta5 desaturase also shows a wider substrate specificity than was previously anticipated. The principal feature is a high degree of chain length specificity. Within the C16-C20 range tested C20 was the optimum chain length while minimal Delta5 desaturation occurred when the chain length dropped to C16. A region of steric constraint between C(10) and C(13) on the substrate geometry acceptable to the enzyme is envisaged. However, the range of acids tested was not extensive and an evaluation of the role of Delta-bonds in substrate-enzyme binding was not possible. No Delta4 des1aturation was observed. This agreed with other studies.

Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (I)), ethoxyquin nitroxide (II), 2,6-dihydro-2,2,4-trimetbyl-6-quinolone (III) and l,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline (IV) were prepared and purified in order to study their antioxidant properties in fish meal and/or oil. I (also commercally available) and III were equally effective in fish meal, but III and IV were better in oil than I and II. In AIBN initiated methyl linoleate autoxidation, the order of efficiency in terms of the stoichiometric factor (n), using BHT as a standard, was IV > I > BHT > II. On the other hand, III gave very little inhibition in this system. In fish meal and oil, I was converted to III and to a 1,8'-dimer (V). The same products were formed in tert-butoxy oxidation of I. The nitroxide (II) was also formed from I but this was only seen by ESR in various organic solvents. It is likely to play some role in the antioxidant mechanism of I. The 1,8'-dimer was isolated and found to have no antioxidant properties in oil. Another reaction product of 1,2,4-dimethyl-6-ethoxyquinoline was also prepared. It was found to show prooxidant effects in fish oil.

An attempt has been made to compare anodic synthesis, malonation, and chain-extension with enamines as procedures for converting readily-available acids to higher homologues. Anodic synthesis was successfully employed to prepare esters of several olefinic acids (20:1 11c, 22:1 13c, 20:2 11c 14c, 22:2 13c 16c, 20:3 8c 11c 14c), acetylenic acids (18:1 16a, 18:1 17a), and saturated acids of 'odd' chain length (13:0, 15:0, 17:0, 19:0, 21:0). The desired esters were recovered from the reaction products by column chromatography and further purified when necessary by crystallisation. Yields were usually in the range 40-50%. Some difficulty was encountered with acids having △5 and △6 unsaturation and this made the chain-extension of γ-linolenic acid by this procedure unsatisfactory. A possible reason for this is discussed. An electrolytic procedure for converting long-chain acids (RCO H) to their nor-alcohols (ROH) has been examined: oleic, linoleic, and ricinoleic acid were converted to the corresponding C17 alcohols. Oleic, linoleic, ɑ-linolenic and γ -linolenic acids were successfully converted to their C20 homologues in 70-80% yield by an improved malonation procedure which was recently described. In one case the malonation was repeated to give a C22 acid. The enamine chain-extension procedure was briefly examined using cyclopentanone and cyclohexanone to furnish heneicosanoic and eicbsanoic acids respectively The 13C NMR spectra of the starting materials and products have been recorded. It has proved possible to allocate the observed resonances (with greater or lesser certainty) to all the constituent carbon atoms and some interesting generalisations are presented. A minor study was concerned with the preparation of long-chain hydroperoxides and peroxides by reaction of the mesylates of some primary alcohols (stearyl, oleyl, linoleyl) with hydrogen peroxide and t-butyl peroxides. Some secondary peroxides were formed by a similar reaction with allylic bromides.

Part I. The preparation and reactions of long-chain acids containing sulphur. Much is known about long-chain hydroxy esters and the epoxides which can be derived from them but information about the corresponding sulphur compounds is sparse. Using various methods, methyl 12-mercaptostearate, methyl 9-mercaptostearate, methyl 12-mercapto-oleate, methyl 12-mercapto-elaidate, methyl 9(10)-mercaptostearate, methyl 12"hydroxy-9(10)-mercaptostearate, methyl 9-hydroxy-12(13)-mercaptostearate and 1-mercapto-octadec-4- and 5-ene have been prepared. In reaction with sodium hydrogen sulphide without the rigorous exclusion of air the major product produced from methyl 9-mesyloxy- octadec-cis-12-enoate was methyl 9,12-epithiostearate. A similar result was observed with another γ-mercapto alkene (1-mercapto-octadec-4-ene) and with a 8-mercapto alkene (l-mercapto-octadec-5-ene), but not with a hydroxy alkene (methyl ricinoleate). For confirmation of these conclusions methyl 9,12-epithiostearate was synthesised by an independent and unambiguous route. By an extension of the procedures applied for monomercapto esters, 1,2-dithiols (methyl erythro- and threo-9,10-dlmercapto- stearate), a 1,3-dithiol (methyl 10,12-dimercaptostearate), and a 1,4-dithiol (methyl 9,12-dimercaptostearate) have been prepared from the corresponding dihydroxy compounds. The 1,3- and 1,4-dithiols are readily converted to cyclic epidisulphides by oxidation. The infrared, NMR and mass spectral properties of these compounds have been investigated. 1,2-Epithiostearates (methyl cis and trans-9,10-epistearate) have been prepared by two different routes and their chromatographic (TLC, GLC) and spectroscopic (NMR, MS) behaviour studied. Part II: The synthesis of some C₁₆ and C ₁₈-acids of geneal formula CH₃ (CH₂)[sub]m(CH=CH)[sub]n CO₂H. Commercially available trienoic (△ 2, 4, 6) and tetraenoic acids (△2, 4, 6, 8) of medium chain length have been used successfully in the study of acyl-CoA synthetases of medium chain length specificity. But their activity with long chain acyl-CoA synthetases is rather low. The synthesis of C ₁₆ and C ₁₈ trienoic and tetraenoic acids has therefore been examined. The triene esters were successfully prepared by the reaction of appropriate aldehydes with phosphonates prepared from methyl 6-bromo-hexa-2,4-dienoate and the tetraene esters by interaction of 2,4-dienals with a phosphorane. The C₁₂, C₁₄ and C₁₆ dienals were prepared from l-methoxybut-1-en-3-yne by condensation with the appropriate saturated aldehyde. The chromatographic (GLC) and spectroscopic (UV, IR, NMR, and MS) properties of these acids have been examined and some simple thiol esters made. Their biochemical use as reagents for the estimation of long-chain Co-A synthetases is being conducted elsewhere.

No description available.

M.Sc. (Botany) / Senescence of carnation flowers is accompanied by an increase in the sensitivity of the petals to ethylene. It appears that ethylene sensitivity during normal senescence and under stress conditions is induced by the production of short-chain saturated fatty acids ranging in chain-length from C7-C10 during the early stages. During pollination-induced senescence these acids are synthesized in the styles as a result of wounding and transported to the corolla where they induce an increase in ethylene sensitivity of the petals to ethylene, causing an advancement in the timing of the climacteric peak in ethylene production. It appears that the cell membrane is the site' of action for short-chain fatty acids in their regulation of ethylene sensitivity in plant tissues. These acids cause an increase "in the ability of the tissue to bind ethylene by affecting the physical properties of the cell membranes. Treatment with STS results in a suppression of ethylene sensitivity by stabilizing the cell membranes, thereby decreasing the ability of ethylene to bind to its receptor sites in the cell membranes. Treatment with short-chain fatty acids overrides this stabilizing effect to a great extent by increasing the permeability of cellular membranes and thus the sensitivity of the carnation petal tissue to ethylene.

No description available.

The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.

No description available.

The underlying cause was sought for "inactivation", a heat-induced change in the surface of veneer that inhibits diffusion of moisture into the wood. It was demonstrated, by the use of Douglas fir wood, that the formation of an inactivated surface could be prevented by extraction with certain organic solvents, but not with water, either before or after the wood was dried. When the extractable materials were removed, or were originally absent, no specimen examined showed degradation, through the effect of heat, of the potential for forming strong glue bonds. The frequently postulated statement related to formation of ether linkages from hydroxyl groups, in heated wood, was found to be not correct. Although oxidation had been suggested as a contributing factor, inactivated surfaces were prepared in the absence of oxygen in anything but minute amounts. Veneer was collected from Coastal and Interior type Douglas fir trees that exhibited severe, moderate or no susceptibility to the development of inactivation. Representative samples were extracted with simple alkanes and a complete separation of the various components carried out, using the techniques of gas/liquid, paper and thin-layer chromatography. Qualitative variability was found, between and within trees. Strong correlation was found between the formation of an inactivated surface and the presence of saturated fatty acids with carbon-chain lengths in excess of eighteen atoms. The role of long-carbon-chain, saturated fatty acids as the causal agent of inactivation was substantiated by the application of commercially-prepared acids, of various chain lengths, to veneer that had proven insusceptible. When heated, this veneer developed an inactivated surface. A theory was proposed, based on the work described in this thesis, and the information available in the literature, to explain the mechanism of surface modification. It states that removal of some or all of the last molecular layer of water from the wood surface, and the application of heat, permits the saturated long-chain fatty acids to hydrogen-bond with the hydroxyl groups contained in the wood cellulose. The surface of the wood is then shielded by a hydrocarbon layer with very low free surface energy that is not- readily wet-table by the water contained in applied glue. / Forestry, Faculty of / Graduate