Chemistry Reference
In-Depth Information
Fig. 9.17
Production of 13(
S
)-
hydroperoxy-9(
Z
),11(
E
)-
octadecadienoic acid from linoleic acid
using soybean lipoxygenase (SBLO).
OH
O
myrosinase
HO
HO
S
O
NH
OH
N
OH
S
O
3
SO
epi
-goitrin
Fig. 9.1
8
Formation of
epi
-goitrin from
epi
-progoitrin using myrosinase.
epi
-progoitrin
duction by bacterial fermentation have been dis-
cussed and found to depend largely on the nature of
the hydroxyalkanoate monomer [43]. The use of iso-
lated enzymes as catalysts for polymerisation reac-
tions has several distinct areas of application: the use
of cellulase for the enzymatic polymerisation of acti-
vated glycosidic monomers to produce polysaccha-
rides of defined structure has been reviewed recently
[44,45], as has the use of lipases for the production of
polyesters [45,46]. The latter process can proceed by
the polymerisation of lactones, the self-condensation
of hydroxyesters or by the polymerisation of a
mixture of diol/diester or diol/diacid monomers, as
illustrated in Fig. 9.19.
The polymerisation of lactones is the most well
studied of these options and has been reported
for monomers ranging from butyrolactone to 16-
membered macrolides [47-52]. Isolated lipase pre-
parations from
Candida antarctica
or
Pseudomonas
cepacia
are used most frequently for these reactions,
but thermophilic lipases also are suitable catalysts
[48]. In most cases the degree of polymerisation is
not high, with products typically less than molecu-
lar weight (M
W
) 10 000, but higher values can be
obtained when the reaction is performed in an
organic solvent [49].
The lipase-catalysed self-condensation of hydroxy-
acids or hydroxyesters has not been investigated
extensively but polymerisation of methyl 7-
hydroxyheptanoate by porcine pancreatic lipase has
been reported to yield products with M
W
-12 000 in
low yield (9%) [53]. In contrast, much higher degrees
of polymerisation often are observed during the
lipase-catalysed polymerisation of mixed diester/diol
[54-56] or diacid/diol monomers [57,58]. These
latter reactions can be performed under non-aqueous
[56] or solvent-free conditions [55,58] and products
with M
W
up to 130 000 have been reported [57].
Peroxidase enzymes in combination with hydro-
gen peroxide can replace metal ions as catalysts for
the polymerisation of phenols and anilines, illus-
trated for
para
-substituted phenolic substrates in
Fig. 9.20.
Horseradish peroxidase has been used for the poly-
merisation of phenols [59], thiophenols [60] and ani-
lines [61]. The products, being electrically conducting
redox agents, have a range of useful properties but are
generally of low molecular weight and undefined
chemical structure. In an attempt to elucidate the
nature of the monomer linking during polymerisa-
tion, a nuclear magnetic resonance (NMR) study of
the polymerisation of 8-hydroxyquinoline-5-sulfonic
