Fatty acids structural variations

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. 

N. Ragendran, O. Matsuda. N. Imamura, and Y. Urushigawa, Variation in microbial biomass and community structure in sediments of eutrophic bays as determined by phospholipid ester-linked fatty acids, Appl. Environ. Microbiol. 58 562 (1992). 

The aims of this contribution are to (i) consider the theoretical principles underlying the use of compound-specific stable isotope analysis in archaeology (ii) consider the practical aspects of undertaking compound-specific stable isotope analyses and (iii) demonstrate the value of linking the structures of amino acids, fatty acids and/or sterols, to their compound-specific stable isotope values to achieve new insights into variations in metabolism and environment in order to enhance archaeological interpretations. 

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... 

The different phosphoglycerides are often named by placing the constituent attached to the phosphate group after phosphatidyl , e.g. phosphatidyl choline (3-in-phosphatidylcholine or l,2-diacyl-sn-glycero-3-phosphoryl-choline). There are many phosphoglycerides because of the possible variation in the fatty acid chains, and when the full chemical structure is known, it should be used (e.g. l-palmitoyl-2-oleoyl-phosphatidylcholine). Nomenclature that entails the use of the DL system should be avoided. 

A microbial strain may produce more than one siderophore. There are variations in fatty acid chains of a lipophilic part or in the amino acids making up the backbone, as well as released intermediates of the biosynthetic chain. These variations belong all to the same structural pattern. However, there is also the possibility that so-called secondary siderophores are encountered. They constitute a different structural type, usually less complex in their constitution but also less efficient in binding Fe " than the primary ones. Secondary siderophores will be produced when the demand for iron is not so severe or in case there is a genetic defect impeding the production of the primary ones. Examples will be found throughout the review. 

Many of the unusual compounds that indicate the exciting chemistry to be discovered in marine natural products are polyketides. Polyketides are a family of structurally complex natural products that include a number of important pharmaceuticals. They are produced primarily by microorganisms through a specialized metabolism that is a variation of fatty acid biosynthesis [430]. Polyketides fall into two structural classes aromatic and complex. Polyketides are formed by enzyme complexes... 

Other substituents of the glucosaminyl-disaccharide, such as D-glucosamine (in Rhodospirillum tenue, position C), 3. The type (normal, branched) and chain length of fatty acids, and 4. The facultative 3-0-acylation of ester-linked 3-hydroxy fatty acids (position D). Variation of these parameters creates a larger number of related, but not identical, chemical structures, i.js. li pid A structures. (For a more detailed discussion of these structures compare (8,31). 

Once bearing some substituents, the decrease of polarity of the sucrose derivatives makes them soluble in less-polar solvents, such as acetone or tert-butanol, in which some lipases are able to catalyze esterifications. Unlike proteases, which necessitate most often the use of an activated acyl donor (such as vinyl or trifluoroethyl esters), lipases are active with simple esters and even the parent carboxylic acids in the presence of a water scavenger. The selectivity of the lipase-catalyzed second esterification is specific for OH-6 allowing the synthesis of mixed T,6 -diesters.123,124 For some lipases, a chain-length dependence on the regiochemistry was observed.125 Selectively substituted monoesters were thus prepared and studied for their solution and thermotropic behavior.126,127 Combinations of enzyme-mediated and purely chemical esterifications led to a series of specifically substituted sucrose fatty acid diesters with variations in the chain length, the level of saturation, and the position on the sugar backbone. This allowed the impact of structural variations on thermotropic properties to be demonstrated (compare Section III.l).128... 

Figure 1 Polyketide biosynthesis. Polyketide backbones are formed via condensations from acyl-CoA thioesters of carboxylic acids. The (3-ketone which results from each condensation can undergo a series of reductive steps analogous to fatty acid biosynthesis. However, either none or only some of the reductive activities may occur in a given cycle. This allows PKSs to generate diversity through selection of priming and extender units, variation of the reductive cycle, and stereoselectivity. (ACP, acyl carrier protein AT, acyl transferase KS, ketosynthase DH, dehydratase ER, enoylreductase KR, ketoreductase TE, thioesterase.) The structure depicted in the lower right-hand corner is representative of the possible structural variations that can arise during polyketide biosynthesis.

Sundh, I., Nilsson, M., and Borga, P. (1997). Variation in microbial community structure in two boreal peatlands as determined by analysis of phospholipid fatty acid profiles. Appl. Environ. Microbiol. 63,1476-1482. 

Figure 24.8. Graphic presentation of the variation in specific optical rotation values for enantiopure MLM type asymmetrically structured TAG products 16a-16h, when varying the chain length of the saturated fatty acid located at the sn-3 position of the glycerol backbone.

There are variations to the above structure such as fatty acid modification but these tend to increase the viscosity significantly thus limiting use in inkjet ink formulations. 

---