Extracting Encapsulated Compounds

The final types of materials that may cause you problems in extraction are membrane-bound or encapsulated compounds. In the past, these have been removed by adding detergent to break the membrane, pulling everything in to solution and then extracting out the compound of interest. It is difficult to get clean separations because of the soap emulsification that is created. The detergent often contaminates the subsequent chromatography. 

A better method is to first add an equal volume of dimethylsulfoxide (DMSO) or dimethylformamide (DMF) to the aqueous sample. This breaks both biological and encapsulation membranes and pulls polar and nonpolar material into solution. The second step is to dilute the sample with 10 volumes of water. At this point, nonpolars can be removed by solvent extraction or with a Cig SFE. Charged molecules can be recovered with pH-controlled extraction or with ion pairing reagents. The DMSO or DMF stays with the water layer. Customers have told me they can achieve almost complete recovery of both fat-soluble and water-soluble vitamins from polymer-encapsulated mixtures. Vitamins are encapsulated to protect potency from air-oxidation. Water-soluble vitamins have nonpolar encapsulation fat-soluble vitamins have polar encapsulation. Either vitamin can be extracted by themselves, but they are difficult to extract under the same condition unless DMSO or DMF are used to break both capsules. 

It also should offer promise for cell extractions, which, after all, are lipid/protein encapsulated mixtures of polar and nonpolar compounds. It would be interesting to see the effect of DMSO or DMF on the extraction of proteins. My guess is that protein might denature in 50% DMSO and precipitate so they could be filtered off or might renature and refold on lOx dilution in water and stay in solution. This might make an interesting research problem for recovering membrane-bound proteins. 

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In the extraction of biologically active compounds, care must be taken to avoid the loss of activity that often occurs by contact with organic diluents. Thus a series of systems have been developed specifically with these compounds in mind. The first of these uses mixtures of aqueous solutions containing polymers and inorganic salts that will separate into two phases that are predominately water. A second system uses supercritical conditions in which the original two-phase system is transformed into one phase under special temperature-pressure conditions. Also the active organic compound can be shielded from the organic diluent by encapsulation within the aqueous center of a micelle of surface active compounds. AU these systems are currently an active area for research as is discussed in Chapter 15. 

Semiconductor Grade Epoxies. As was the case for the semiconductor grade silicone-epoxy, there was no difference between FR and non-FR epoxies recorded by either DSC or EGA below 200°C. However, the nominally equivalent non-FR epoxy exhibited significantly lower thermal stability as indicated by the Isothermal TGA data. Furthermore, the aqueous extract of the non-FR compound contained more than twice as much Cl as the combined concentrations of Cl and Br in the FR epoxy. Although there have been no direct comparisons on device aging with these two epoxies, the above findings indicate that the FR compound, being cleaner and more thermally stable, could actually be the better material for encapsulation applications. 

Supercritical fluids can be used to extract substances from natural products, as solvents or as anti-solvents to micronize drugs and biodegradable polymers, encapsulate drugs in polymeric matrices, resolve racemic mixtures of pharmacologically active compounds, fractionate mixtures of polymer and proteins, and sterilize bacterial organisms. 

To date, all the confirmed isolable endohedral fullerenes contain metals either scandium, yttrium, or one of the f-block elements may be encapsulated, and compounds containing up to three metals have been reported. The proportions of the endohedral fiillerenes observed depends upon the manner by which they are extracted from the soot. For lanthanum, predominantly La Cg2 and l. i2 C%o are isolated by solvent extraction techniques, whereas direct sublimation from the soot yields La C6o, La C7o, La C74, and La C82- An explanation for this behavior is that most of the endohedral fullerenes are present as insoluble salts, e.g. [La C6o]" [Ceo], and only La Cg2 and La2 C8o are sufficiently redox stable to be extracted as the neutral molecules. 

These cyclohexa-(-hepta-, -octa-)amyloses are arranged in the crystal lattice of C. in such a way that open, intramolecular channels are formed in which guest molecules can be enclosed in varying amounts up to saturation ("molecular encapsulation ), e.g., gases, alcohols, or hydrocarbons. a-C. also forms a blue-colored inclusion compound with iodine in which the iodine atoms are arranged like a string-of-pearls in the channels. On account of this property C. are used in the production of food, cosmetics, pharmaceuticals, and pesticides as well as for solid phase extractions and for use as high performance separation phases for enantiomeric and diastereomeric mixtures. 

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