S. Backlund et al., LIPASE-CATALYZED ENANTIOSELECTIVE ESTERIFICATIONS USING DIFFERENT MICROEMULSION-BASED GELS, Colloid and polymer science, 274(6), 1996, pp. 540-547
Chiral esters with high optical purity have been synthesized at 298.2
K from racemic 2-octanol and alkanoic acids using the commercial lipas
es from Chromobacterium viscosum (CV) or Candida sp. (SP 525) immobili
zed in microemulsion-based gelatin gels. The microemulsions consisted
of water and alkanes stabilized by the anionic surfactant sodium 1,4-b
is(2-ethylhexyl) sulfosuccinate (AOT) and the naturally occurring zwit
terionic surfactant soybean lecithin, respectively. The enzymes were s
olubilized both in water-in-oil (W/O) microemulsions and in microemuls
ions with a bicontinuous structure. Different microstructures of the g
els were chosen since the enzyme may undergo conformational changes in
different environments resulting in different catalytic efficiencies
toward competing substrates. Therefore, it is of great fundamental int
erest to know the phase behaviour and the microstructures of the used
microemulsion systems. Phase diagrams were determined at 298.2 K for t
he systems water-hexane-AOT and ethanol/water (1:1)-hexadecane-soybean
lecithin. The former system exhibited a large one-phase W/O microemul
sion region, while in the latter a small one-phase region with biconti
nuous structure was present. The kinetic enantiomeric ratios (E-values
), as determined from enantiomeric excess (e.e.) values at a conversio
n below 0.5, were higher both in the W/O microemulsion as well as in t
he bicontinuous microemulsion using the SP 525 lipase, than using the
CV lipase. On the other hand, the conversions were higher using gels b
ased on W/O microemulsions (AOT stabilized) than using gels based on m
icroemulsions with a bicontinuous structure (lecithin stabilized).