Number range CHAPTERBiocatalytic Polyester Synthesis: Leads and
Scientific Breakthrough for Green Chemistry

Nawal K. Sharma and Alan J. Russell

The number of applications of polyesters and related block copolymers
has attracted the attention of many biological synthesis experts over
the last decade. Some of the featured products include: fibers,
coatings, foams, agriculture films, drug delivery systems, matrices for
tissue engineering, implant materials for bone graft and other
biomedical uses.

It has always been a formidable task to synthesize polyesters through
classical chemical methods which involve "dirty" chemical processes by
the use of acidic catalysts, very high temperature (nearly 200 °C) and
generation of pounds of waste per pound of product. At the high
temperatures needed to perform polymerizations dehydration of diols,
such as 1, 4-butanediol which forms tetrahydrofuran and cyclization
reactions to form lactones are undesired side reactions. In addition,
the strongly acidic catalysts used, promote discoloration and hydrolysis
of reaction products if the catalyst is not neutralized or separated
from products. We have studied the possibility of using a natural
biological catalyst which could operate at ambient conditions to provide
the driving force for polyester synthesis. Our technology makes the same
materials at 50 °C and atmospheric pressure instead of 200 °C and high
pressure.

We have focused on the use of enzymes in green environments such as
supercritical fluids and ionic liquids. Additionally, non-aqueous
enzymology has advantages such as increased thermal stability,
solubility of hydrophobic compounds and elimination of microbial
contamination. We have conducted an extensive study of the mechanism of
biocatalytic processes in anhydrous reaction media, enabling the
generation of a predictive model to explain and address the issues
related to the activity and specificity of enzymes as a function of
properties of the solvents in which it placed. We have demonstrated that
the size of the polymer that can be synthesized in solvent-free
biocatalytic polymerizations is dependent on the diffusion of the
reactants to the catalyst surface. We have translated this finding into
the ability to make polymers that are impossible to synthesize easily
using chemical means, such as polyesters with pendant reactive groups.
The use of enzymes allows us to capitalize on their inherent specificity
to accomplish polyester synthesis using green approaches.

We have focused on the use of enzymes in green environments such as
supercritical fluids and ionic liquids. Additionally, non-aqueous
enzymology has advantages such as increased thermal stability,
solubility of hydrophobic compounds and elimination of microbial
contamination. We have conducted an extensive study of the mechanism of
biocatalytic processes in anhydrous reaction media, enabling the
generation of a predictive model to explain and address the issues
related to the activity and specificity of enzymes as a function of
properties of the solvents in which it placed. We have demonstrated that
the size of the polymer that can be synthesized in solvent-free
biocatalytic polymerizations is dependent on the diffusion of the
reactants to the catalyst surface. We have translated this finding into
the ability to make polymers that are impossible to synthesize easily
using chemical means, such as polyesters with pendant reactive groups.
The use of enzymes allows us to capitalize on their inherent specificity
to accomplish polyester synthesis using green approaches.

Non-aqueous biocatalysis present a real opportunity for environmentally
benign, low energy, low waste and interdisciplinary process development.
This research has contributed significantly to the growth of
biotechnological approaches to real world problems, especially in
biocatalytic toxic waste remediation and novel biomaterial synthesis.