Ethyl palmitate system

Figure 3. Mixed monolayers of cholesterol-ethyl palmitate system at 23.5°C. and pH 6...

Once again, only a single data source is available for the ethane/ethyl palmitate system is available. The data is summarised in Table 9 and the phase behaviour of the ethane/ethyl palmitate data is presented in Figme 13. 

In general similar phase behaviour trends were observed between the systems. Tripalmitin is the least soluble in ethane followed by palmitic acid. Methyl palmitate and ethyl palmitate show high solubility in ethane and show total miscibility at pressures below 15 MPa in the temperature range studied. As observed by Schwarz et al. [30] very little difference exists between the phase behaviour of ethane/methyl palmitate and ethane/ethyl palmitate systems, most probably due to the similarity in the nature of their structure. 

Together with their study on the phase behaviour of the ethane/ethyl ester homologous series, Schwarz et al. published data on the piopane/ethyl ester homologous series. This is the only known source of data for the propane ethyl/palmitate system, is summarised in Table 12 and graphically illustrated in Figure 18. 

As for the propane/methyl palmitate system, total solubility can be attained at very low pressures (< 8 MPa) for the propane/ethyl palmitate system. Similar to the observed linear relationship between temperature and the phase transition pressure, Schwarz et al. [30] also foimd a linear relationship between the phase transition pressure and temperature. They also did not observe any three phase behaviour or indications thereof. 

Many of the comments made for the phase behaviour of palmitic acid and its derivatives in CO2 and in ethane are also valid for propane as SC solvent. Figure 21 shows a comparison of the propane/tripalmitin, propane/palmitie acid, propane/methyl palmitate and propane/ethyl palmitate systems. 

Eight binary systems are reported. Six include cholesterol as one component of the mixed film. The second components in these six films were myristic acid, methyl palmitate, ethyl palmitate, 1,2-dimyristin, 1,2-dimyristoyl-3-lecithin, and l,2-didecanoyl-3-lecithin. In addition, the systems trilaurin-dimyristoyl lecithin and triolein-dimyristoyl lecithin... 

Table 5 summarises data available for the system C02/ethyl palmitate and the data is illustrated in Figure 6. Liang and Yeh [50] also studied the solubility of ethyl palmitate in CO2. However, they presented their data only in figures and as a correlation (Chrastil correlation). As such their data has not been included in this study. The data of Crampon et al. [26] and that of Gaschi et al. [51] appear to be in agreement. 

Table 5. Literature data for the CO2 (l)/ethyl palmitate (2) system...

Figure 9. Comparison of the pressure - composition (W2) for the systems CO2 (l)/palmitic acid (2) [34,43], CO2 (l)/methyl palmitate (2) [48,49], COj (l)/ethyl palmitate (2) [26,51] andC02 (l)/tripalmitin (2) [32,43,54] systems at 313.15 K (a) entire composition range and (b) detail of low molecular mass composition range.

The data shows that at both temperatures the esters have the highest solubility followed by palmitic acid and that tripalmitin has the lowest solubility. It is also noted that the systems C02/methyl pahnitate and C02/ethyl palmitate have very similar phase behaviour and similar phase transition pressures. This is expected due to the similarity of the moleeules. However, despite the fact that Bharath et al. [55] foimd that for Ci8 and higher esters the methyl ester has a higher phase transition pressure than the ethyl ester, Figure 9 indicates that the phase transition pressmes are indeed very similar and from the data available in the present analysis no outcome can be given in this regard. 

The data for the ethane/ethyl pahnititate system is veiy similar to that of the ethane/methyl palmitate system and the same comments thus apply. 

Figure 13. Pressure - composition (W2) plot for the ethane (l)/ethyl palmitate (2) system at 333, 343 and 353 K [30],...

Monolayers of ethyl palmitate and ethyl stearate are attractive systems in which to study internal domain anisotropy by BAM. Monolayers of these compounds have two-phase coexistence regions between the LE and EC... 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

Ester synthesis of fatty acid ethyl ester. The lipase-catalyzed esterification of fatty acid and alcohol is well-known. It was also favorable for the esterification of poly unsaturated fatty acids under mild conditions with the enzyme. However, the activity of native lipase is lower in polar organic solvents, i.e. ethanol and methanol. The synthesis of Ae fatty acid ethyl ester was carried out in ethanol using the palmitic acid-modified lipase. As shown in Figure 7, the reactivity of the modified lipase in this system was much higher than that of the unmoditied lipase. 

Fig. 4 Separation of dipalmitoyl phosphatidylcholine and distearoyl phosphatidylcholine. The solvent system used for the TC-CCC was hexane/ethyl acetate/ethanol/1% trifluoroacetic acid (5 5 5 4). The upper phase (organic phase) was mobile. The rotational speed was maintained at 1500-700 rpm. The highest column pressure was 360 psi. Amounts (100 pg each) of phosphatidylcholine dipalmitoyl and phosphatidylcholine distearoyl were loaded. Each fraction was spotted and developed on the HPTLC using chloroform/methanol/ 0.2% CaCl2 (60 32 4). Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipalmitoyl phosphatidylcholine contains 2 mol of esterified palmitic acids. PC C16 0, dipalmitoyl phosphatidylcholine PC C18 0, distearoyl phosphatidylcholine. SF, solvent front.

SCF processing is no different. In fact, a phase behaviour analysis is vital as it provides an estimation of the operating pressitfes required and also indicates whether separation fi om other components will be possible. This section will focus on the phase behavioiu of palmitic acid, methyl palmitate, ethyl pahnitate and tripalmitin in SC CO2, ethane and propane and concentrate on the data available and trends observed therein. In addition, the three solvents will be eompared and the effect of co-solvents, often used to decrease the operating pressiu e, will be eonsidered. In particular this section will focus on the phase transition pressures of the systems studied. The phase transition pressure indieates the pressitfe required for total solubility at the said temperature and composition. For the type of systems studied here, a higher phase transition pressure leads to a lower solubility, therefore lower phase transition pressures indieate improved solubility. 

On silica gel plates impregnated with silver nitrate and eluted with petroleum ether-chloroform-acetone (50 10 17, by vol) vitamin A palmitate had the highest mobility (Revalue, 0.82). Retinol and retinal (Rf= 0.62) were not separated from each other, while vitamin E eluted before vitamin D2 (R/ values of 0.56 and 0.32, respectively) (18). Changing the eluent to hexane-ethyl acetate-diisopropyl ether (2 1 1, by vol) lowered the R/values of all these fat-soluble vitamins. With the latter solvent system retinyl palmitate still moved ahead (Revalue 0.77), but vitamin E eluted even faster than the pair retinol/retinal and vitamin D2 (R/values of 0.54,0.51, and 0.19). 

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