Fatty acids structure, discussion

A complete review of the subject has recently been pulolished (2). Sufficient for our discussion are the variables in fatty acid structures that influence antimicrobial activity chain length, unsaturation and esterification. 

The physical properties of fatty acids and their simple esters will be discussed in considerable detail. Fatty acids are key components in most lipids and the present section should provide a basis for the understanding of physical effects due to variations in fatty acid structure such as chain length, presence of double bonds, branches, etc. 

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

We turn now to the biosynthesis of lipid structures. We begin with a discussion of the biosynthesis of fatty acids, stressing the basic pathways, additional means of elongation, mechanisms for the introduction of double bonds, and regulation of fatty acid synthesis. Sections then follow on the biosynthesis of glyc-erophospholipids, sphingolipids, eicosanoids, and cholesterol. The transport of lipids through the body in lipoprotein complexes is described, and the chapter closes with discussions of the biosynthesis of bile salts and steroid hormones. 

Allelochemic effects of aquatic macrophytes on algae are discussed. Bloassays of chromatographic fractions from Eleocharls mlcrocarpa Torr. Indicate that oxygenated fatty acids are the causative agents. Methods of Isolation of these materials from aquatic macrophytes and from natural waters are described. Purification and structure determinations show that prominent components of the fraction are C q tri-hydroxycydopentyl and hydroxycydopentenone... 

Next, the morphological and structural variations of the monolayers on the water surface were investigated by using two kinds of fatty acids with different Tms, in order to confirm the Tsp dependence of the morphology and structure for the monolayer, as discussed in Figures 9... 

Histone deacetylases are linked to the pathogenesis of malignancy from a mechanistic perspective. The capacity of HDAC inhibitors (HDACi) to interfere with the enzyme fimction has led to the observed prechnical and clinical activity in cancer therapy. Although the exact mechanism of anti-tumor activity is not fully elucidated, various cellular pathways have been shown to be involved. From the first chnical trials involving HDACi with short chain fatty acids to the newer generation hydroxamic acid derivatives and cychc tetrapeptides, a number of structurally diverse compounds have made the transition from the laboratory to the chnical arena. For purposes of this part of the discussion, HDACi are arbitrarily divided into the hydroxamates and nonhydroxamates. 

Structural information of LB films has also been obtained from FTIR studies. In the carboxylate form of the fatty acid, the relative intensities of the vs(C02-) and va(C02-) signals are dependent on the orientation of the chain axis. The dipole moments of the vs(C02-) and va(C02 ) stretches are parallel to and perpendicular to the chain axis, respectively. In transmission mode the electric vector of the IR radiation interacts strongly with dipole moments parallel to the substrate. This means that in transmission mode the vs(C02-) will be most intense, and the va(C02-) the weakest, for films with the chain axis perpendicular to the substrate. The opposite is true for the FTIR-RA mode. There is general consensus that in M-FA films the chain axis is approximately perpendicular to the substrate while the protonated form of the acid after exposure to H2S has a tilt relative to the substrate. Further discussion of FTIR as an investigative tool into the reaction of M2+-FA films with dihydrogen chalcogenides is given in later sections. 

The use of FTIR to study reaction kinetics and chemical equilibria is based on the disappearance of a v(COO—) vibrational mode of the deprotonated fatty acid in concurrence with the appearance of the v(C=0) mode of the protonated FA. This type of data has been used to support reaction times of a few minutes to several hours or even days. Also, the extent of the reaction has been reported to be stoichiometric (22,23,39,43,47,53), based on the complete disappearance of the v(COO—) vibrational mode, whereas other studies indicate less than 100% conversion (Fig. 3.5.8) of the carboxylate to the protonated form (48,61,66,70). The effect of film structure on reaction rate has been discussed (61,66,70) however, discrepancies of the extent of the reaction of M-FA with H2S have not been previously addressed. FTIR spectroscopy has also been used to determine the effect of film thickness on reaction rate. For example, for 11-, 21-, and 31-layer CdSt films deposited at 37.5 mN in-1, reactions with H2S were found to slop at 42, 78, and 140 h, respectively (66). 

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