Surfactants synthesis using enzymes

Novel chiral. separations using enzymes and chiral surfactants as carriers have been realized using facilitated transport membranes. Japanese workers have reported the synthesis of a novel norbornadiene polymeric membrane with optically active pendent groups that show enantio.selectivity, which has shown promi.se in the. separation of propronalol. 

However, the above does not answer the main question how can one employ isolated enzymes for the preparation of surfactants In fact, the answer is simple Use hydrolytic enzymes in nonaqueous media. Indeed, many hydrolytic enzymes, such as lipases, proteases, and glycosidases, available in large quantities, are very robust and inexpensive, and do not require any cofactors to manifest their catalytic activity. As any other catalyst, enzymes cannot influence the equilibrium of a chemical reaction and therefore the removal of water from the reaction medium forces them to work in reverse, i.e., to synthesize a chemical bond rather than to break it. Consequently, there is a principal difference between microbial and enzymatic synthesis of surfactants regarding the type of enzymes involved and the reaction medium. The former is a biosynthetic process catalyzed by living microorganisms and as such dependent solely on their viability, whereas the latter is an organic synthesis whereby enzymes are used as substitutes for chemical catalysts. The two approaches are complementary not only in terms of the production methods but because the surfactant structures amenable to both methodologies are quite different. 

The enzymatic synthesis of surfactants, on the other hand, is in essence a chemical reaction in which an enzyme (in a form isolated from its source or even as whole cells) replaces a conventional chemical catalyst. In contrast to the microbial surfactants mentioned above, the surfactants obtained by the use of single enzymes are simpler in structure but can be designed to have the desired physicochemical features. The scope of this chapter is limited to production of surfactants using enzymes and will not include microbial surfactants. 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme catalysed synthesis. In case of lipases, the hydrolysis of p-nitrophenyl esters in w/o-microemulsions is often used as a model reaction [19, 20]. The auto-hydrolysis of these esters in w/o-microemulsions is negligible. Because of the microstructure of the reaction media itself and the changing solvent properties of the water within the reverse micelles, the absorbance maximum of the p-nitrophenol varies in the microemulsion from that in bulk water, a fact that has to be considered [82]. Because of this, the water- and surfactant concentrations of the applied micro emulsions have to be well adjusted. 

Proteins and enzymes have been successfully entrapped in surfactant-solubilized water pools in organic solvents [268-278]. Furthermore, many reversed-micelle-entrapped enzymes retained their activity and could be used for peptide synthesis [273,274]. That the water pools corresponding to very small w-values exhibited freezing points Mow — 50°C enabled both the enzyme structures and the rates of enzyme-catalyzed reactions to be investigated at low temperatures. These studies much aided the development of cryoenzymology [279, 180],... 

The objective of the present work was to study the synthesis of monolaurin by direct lipase-catalyzed esterification between glycerol and lauric acid without any solvent or surfactant. The effects of lauric acid/ glycerol molar ratio, enzyme concentration, and temperature were studied using an experimental design. The reuse of the commercial immobilized lipase, to reduce the process cost, was also investigated. 

Examples of LLC phases for enzyme stabilization and bio catalysis include the micellar and LLC phases water (or glucose in water)/oclanol/octyl-/3-D-glucoside LLC system for accelerating /3-D-glucosidase-calalyzed hydrolysis of octyl-/ -n-glucoside to form glucose and octanol [108] and the use of LLC phases of numerous commercial surfactants to accelerate the (S)-hydroxynitrile lyase-catalyzed synthesis of (S)-mandelonitrile [109]. 

The specific activity of the enzymes is often good, comparable with the best alternative enzyme forms. The enzyme molecules should all be well accessible to the medium, and mass transfer limitations avoided. However, solubilized enzymes have not achieved widespread use by those mainly concerned with applications in synthesis. An extra step is required to separate the enzyme from the final reaction mixture containing the products. It may be even harder to separate solubilising additives, notably surfactants, from the products. Thus I in general would not recommend solubilized enzymes for synthetic applications. One exception is where it is wished to attack polymeric or solid-state substrates, where the enzyme molecules may need to be able to move to contact the substrate, rather than vice versa. 

The method of synthesis ATP from adenine using Corynebacterium ammoniagenes cells as enzyme sources, which was free from enzyme purification, has been developed (33). In this system, cells were permeabilized by the treatment with surfactant and organic solvent. Phosphoribosylpyrophosphate and ATP were supplied by the metabolism of the cells from glucose. In the same manner, CDP-choline was produced by the... 

The use of enzymes in esterification reactions to produce industrially important products, such as emulsifiers, surfactants, wax esters, chiral molecules, biopolymers, modified fats and oils, structured lipids, and flavor esters, is well documented. The use of lipases in aqueous and nonaqueous media has found applications in organic synthesis, chiral synthesis or resolution, modification of fats and oils, and in many other fields. Moreover, lipases are highly stable even under adverse conditions such as organic solvents and high temperatures (Gandhi et al., 2000 Hari Krishna Karanth, 2002). 

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