Application of Organic Solvents

The use of enzymes in non-aqueous solvents can be an advantageous alternative to reactions in water, especially for poorly water-soluble substrates and products, e. g. in the synthesis of esters, lactones or selected peptides. However, the knowledge of how solvents influence enzyme activity and selectivity is still not profound. As it is impossible to cover all relevant aspects within this chapter, the reader is referred to some selected articles for further reading115, 64 751. Here some of the basics will be discussed briefly in Sect. 7.5.4 reactor concepts for the use of enzymes in organic solvents will be presented. 

There are advantages in performing enzymatic transformations in non-aqueous media  

A very interesting alternative has been published detailing the use of cydodextrins to enhance the solubility of 2-acetylnaphthalene in aqueous solution. The complex between the cydodextrin derivative and the ketone is transformed fast enough to support high reaction rates in an enzymatic reduction [7fil. 

Both stabilizing and destabilizing effects of solvents on enzymes have been reported. A reasonably reliable measure of the compatibility of solvents with enzymes is the log P value, where P is defined as the distribution coefficient of a solvent between water and 1-octanol in a two-phase system[64 791. Solvents with a log P value above 4 are suitable (e. g. aromatics, aliphatics) whereas water-miscible solvents with a log P value below 2 (short chain esters, DMF, short-chain alcohols) are not suitable for employment with biocatalysts. The latter solvents interfere with the water at the boundary of the protein itself and so disrupt the binding forces necessary to maintain an active form of the enzyme. Surprisingly, tert-butanol has a stabilizing effect on some oxidative enzymes(801, despite its low log P value (0.35). 

One-phase systems may consist mainly of water, water plus a water-misdble solvent or a pure organic solvent. Most water-misdble solvents may be used in concentrations up to 20% before enzyme deactivation exceeds the benefits obtained by better solubility of substrates and/or increased selectivity. Using this approach, enzyme activity and enzyme stability have to be examined carefiilly to seled appropriate reaction conditions. 

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Another consequence of application of organic solvents as a reaction medium is associated with the mechanism of enzyme-catalyzed transformations. According to the commonly accepted mechanism, the first product of the interaction of a hydrolytic (serine) enzyme with an ester is an O-acylenzyme (Scheme 5.4). When the reaction is performed in an aqueous solution, water acts as a nucleophile in the next step, to give acid B. If more nucleophilic hydrogen peroxide is present in the reaction mixture, peroxycarboxylic acids C are formed. However, in organic solvents the O-acylenzyme also reacts readily with other nucleophiles, such as... 

Huang, M.-W. Chei, H.-L. Huang, J.P. Shiea, J. Application of Organic Solvents As Matrixes to Detect Air-Sensitive and Less Polar Compounds Using Low-Temperature Secondary lon-MS. Anal. Chem. 1999, 71, 2901-2907. 

Han, S., Wong, H., and Livingston, A. (2005) Application of organic solvent nanofiltration to separation of ionic liquids and products from ionic liquid mediated reactions. Trans. Inst. Chem. Eng., 83 (A3), 309-316. 

Double base compositions can be manufactured without the application of organic solvents by heated rolling and pressing of -> Paste. 

The aliphatic and aromatic hydrocarbons may contain a substituted halogen element and are often referred to as halogenated hydrocarbons. These include, for example, perchloroethylene, trichloroethylene, and carbon tetrachloride. Organic solvents are very useful and have extensive applications in industry because they help in the manufacture of oils, fats, resins, rubber, and plastics. In fact, the role of organic solvents increased in the latter half of the nineteenth century with the development of the coal-tar industry. The wide application of organic solvents grew and became diverse and global. 

D12. Dean, J. A., and Lady, J. H., Application of organic solvent extraction to flame spectrophotometry. Determination of iron in nonferrous alloys. Anal. Chem. 27, 1533-1536 (1955). 

There are many different approaches, for example, application of cattle faeces to remove soot (which is one of the most predominant surface pollutions on paintings), application of acids or application of organic solvents. Even bread or dough was commonly used in previous times and it is still a practice in Scandinavia at the present. 

In certain cases, the application of organic solvents can be helpful, however these should be removed after cleaning. 

In the near future, the use of solvent-tolerant strains will make the application of organic solvents in biotransformations by whole cells a more realistic option. 

Table 22.1.1. Application of organic solvents. [After references 2-4]...

Shiea, J. Application of Organic Solvents As Matrixes to Detect Air-... 

Until 1987, the (/ )-HNL from bitter almonds was the only HNL used as catalyst in the preparation of optically active cyanohydrins. Since the application of organic solvents enabled the preparation of many (/ )-cyanohydrins in high optical yields, it was of great interest to get access to HNLs for synthetic applications, which catalyze the formation of (5)-cy anohy drins. 

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