Synthesis of Surfactants Using Enzymes

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. 

Surfactants from Renewable Resources Edited by Md el Kjellin and Ingeg d Johansson (c) 2010 John Wiley Sons, Ltd 

Although much of the research in the area has involved the use of organic solvents to increase the solubility of the reactants and products, the trend is towards development of solvent-free processes since they are safer, more environmentally benign, provide higher space-time yields and are hence more attractive for industrial applications [14]. 

Biocatalysis has been used for synthesis of surfactants with different hydrophilic groups that are linked to the hydrophobic fatty chain via ester, amide or glycosidic bonds. Among the most crucial parameters to be considered for enzymatic synthesis are the different solubility characteristics of the hydrophobic and hydrophilic reactants. The use of hydrophilic solvents for increasing the solubility of hydrophilic components increases the toxicity of the medium and affects enzyme activity. An alternative would be to modify the hydrophilic moiety in order to increase its solubility in the hydrophobic component. Solubility may also be improved by increasing the temperature, for which the use of thermostable enzymes would be beneficial. Various groups of surfactanfs for which enzymafic synthesis has been applied are described below. 

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Another recent approach has consisted in the synthesis of monodispersed polymer/enzyme adducts with the aim of developing surfactants. Nolte reported the first example of that kind by using a head group made of lipase B, which can catalyze the hydrolysis of esters in water and then-... 

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. 

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. 

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 chemical modification of proteins is not desirable, because of the harsh reaction conditions, the nonspecificity, and the difficulty of removing reagents from the final product [2]. Enzymatic reaction has several advantages, such as the mild reaction conditions, high specificity, and fast reaction rates [3]. Moreover, the use of the enzyme, which occurs naturally in living cells, is acceptable by consumers from the viewpoint of safety. We describe examples of the enzyme-catalyzed synthesis of protein-based surfactants in this chapter. 

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