Chapter 3
Special Techniques
Most biocatalysts can be used in a straightforward manner by regarding them as
chiral catalysts and by applying standard methodology, i.e., in buffered aqueous
solution. In order to broaden the applicability of enzymes, some special techniques
have been developed. In particular, using biocatalysts in nonaqueous media rather
than in water can lead to the gain of some significant advantages as long as some
specific guidelines are followed [1]. Furthermore, ‘fixation’ of the enzyme by
immobilization may be necessary, and the use of membrane technology may be
advantageous as well. For both of the latter topics only the most simple techniques
which can be adopted in an average organic chemistry laboratory are discussed
(Sect. 3.3).
3.1 Enzymes in Organic Solvents
Water is a poor solvent for nearly all reactions in preparative organic chemistry
because most organic compounds are poorly soluble in this medium. Furthermore,
the removal of water is tedious and expensive due to its high boiling point and high
heat of vaporization. Side-reactions such as hydrolysis, racemization, polymerization, and decomposition are often facilitated in the presence of water. These
limitations were circumvented by the introduction of organic solvents for the
majority of organic chemical processes. On the other hand, conventional biocatalysis has mainly been performed in aqueous solutions due to the perceived notion
that enzymes are most active in water and it has been tacitly assumed that organic
solvents only serve to destroy their catalytic power. However, this commonly held
opinion is certainly too simplistic, bearing in mind that in nature many enzymes or
multienzyme complexes function in hydrophobic environments, for instance, in
the presence of, or bound onto, a membrane [2]. Therefore it should not be
surprising that enzymes can be catalytically active in the presence of organic
solvents [3–14]. The role of water in biocatalytic systems is contradictory: On the
© Springer International Publishing AG 2018
K. Faber, Biotransformations in Organic Chemistry,
DOI 10.1007/978-3-319-61590-5_3
315
Special Techniques
Most biocatalysts can be used in a straightforward manner by regarding them as
chiral catalysts and by applying standard methodology, i.e., in buffered aqueous
solution. In order to broaden the applicability of enzymes, some special techniques
have been developed. In particular, using biocatalysts in nonaqueous media rather
than in water can lead to the gain of some significant advantages as long as some
specific guidelines are followed [1]. Furthermore, ‘fixation’ of the enzyme by
immobilization may be necessary, and the use of membrane technology may be
advantageous as well. For both of the latter topics only the most simple techniques
which can be adopted in an average organic chemistry laboratory are discussed
(Sect. 3.3).
3.1 Enzymes in Organic Solvents
Water is a poor solvent for nearly all reactions in preparative organic chemistry
because most organic compounds are poorly soluble in this medium. Furthermore,
the removal of water is tedious and expensive due to its high boiling point and high
heat of vaporization. Side-reactions such as hydrolysis, racemization, polymerization, and decomposition are often facilitated in the presence of water. These
limitations were circumvented by the introduction of organic solvents for the
majority of organic chemical processes. On the other hand, conventional biocatalysis has mainly been performed in aqueous solutions due to the perceived notion
that enzymes are most active in water and it has been tacitly assumed that organic
solvents only serve to destroy their catalytic power. However, this commonly held
opinion is certainly too simplistic, bearing in mind that in nature many enzymes or
multienzyme complexes function in hydrophobic environments, for instance, in
the presence of, or bound onto, a membrane [2]. Therefore it should not be
surprising that enzymes can be catalytically active in the presence of organic
solvents [3–14]. The role of water in biocatalytic systems is contradictory: On the
© Springer International Publishing AG 2018
K. Faber, Biotransformations in Organic Chemistry,
DOI 10.1007/978-3-319-61590-5_3
315