Fatty value chains

Another approach to characterise the site of absorption in the lipid bilayer is to analyse the dielectric properties of this site. The permittivity e in the hydro-phobic core of the membrane is very small (s of approximately 2 to 3), and rises outwards until it reaches the value in the aqueous phase (e = 78) [6], s is about 30 at the location of the carboxy groups of the fatty acid chain [150], Other measurements averaged to e of 30 to 33 at the interface between polar head groups and the hydrocarbon core [176]. The e of the absorption site of... 

Influence of Intermolecular Spacing on Enzymic Hydrolysis of Lecithin Monolayers. When snake venom phospholipase A is injected under a lecithin monolayer, it splits lecithin into lysolecithin and free fatty acid. The change in polar groups of the monolayer results in a change of surface potential. However, if prior to injection of enzyme into the subsolution, a lecithin monolayer is compressed to such a surface pressure that the active site of the enzyme is unable to penetrate the monolayer, hydrolysis does not proceed. For monolayers of dipalmitoyl, egg, soybean, and dioleoyl lecithins the threshold surface pressure values at which hydrolysis does not proceed are 20, 30, 37, and 45 dynes per cm., respectively (40). This is also the same order for area per molecule in their surface pressure-area curves, indicating that enzymic hydrolysis of lecithin monolayers is influenced by the unsaturation of the fatty acyl chains and hence the intermolecular spacing in monolayers (40). 

At very high values of n the monolayer collapses (buckles). Both the cross-sectional area per molecule in the monolayer and the collapse pressure can be determined. For typical fatty acids, regardless of chain length, the area covered is only 0.2 nm2 per molecule indicating that the fatty acid chains are stacked vertically to the surface in the monolayer. The collapse... 

The elution volumes of the fatty acid derivatives are affected principally by the number of carbon atoms and the number of unsaturated bonds in the fatty acid chains. In acetonitrile-water, unlike methanol-water, the number of unsaturated bonds seemed to be of greater importance. Also, the effect of the column temperature was important. A value of 30°C was used to shorten the analysis time, with good resolution. Thus, satisfactory resolution and favorable retention times (within 15 min) of the C 0 0-C22 6 fatty acid hydrazides were obtained in RP-HPLC with isocratic elution using acetonitrile-water (85 15), as shown in Fig. 5b. 

Isomerization and conjugation change the properties of natural methylene-interrupted fatty acids, leading to new applications and potential added value. Chain shortening or extension produces fatty acids not readily isolated from natural sources and is also used to introduce radioactive or stable isotope labels. Metathesis provides a flexible method for modifying the alkyl chain. 

The refractive index (RI) is a parameter that relates to molecular weight, fatty acid chain length, degree of unsaturation, and degree of conjugation. A mathematical relationship between refractive index and iodine value (IV) has been described by Perkins (1995b) as... 

The Tx -values for the side chains of DPL in deuterochloroform or sonicated DPL in deuterium oxide buffer were found to increase from the central glycerol moiety toward both the ends of the fatty acid chains and the trimethyl quaternary ammonium group of the choline (Metcalfe et al., 1971). This means that molecular motion becomes more restricted in moving from a methylene further from the glycerol skeleton to one that is closer to this backbone. Additionally, the 13C nmr spectrum of human erythrocyte membranes (10% w/w) in D20 buffer at 28° was also obtained (Metcalfe et al., 1.971). 

Willstatter ef al. 196, 301) found that activation could be observed in an alkaline medium but not in an acid medium. Inhibition of tributyrin hydrolysis by bile salts at pH values below 7.0 was also observed by Click and King (297), and Wills (302) found that, although triolein hydrolysis by lipase was stimulated by sodium taurocholate in an alkaline medium, it was inhibited at pH values below 7.0. The effect of the bile salt may also depend on the length of fatty acid chain of the triglyceride under investigation. Thus Click and King (297) showed that, at pH 7.0, sodium taurocholate inhibited tributyrin hydrolysis but stimulated triolein hydrolysis. Similar results were obtained by Wills (302), who found that triacetin hydrolysis was inhibited and triolein hydrolysis stimulated by equivalent concentrations of sodium taurocholate. 

Together with fatty acids and glycerine, they form the raw material base for the oleochemistry value chain (Figure 9.1.38). 

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