To
address the current limitations of enzymatic reactions, we develop
a novel strategy to conduct stirring-free biphasic enzymatic reactions.
This strategy involves translation of a conventional biphasic enzymatic
reaction to a water-in-oil (W/O) Pickering emulsion system by adding
a small amount of solid particle emulsifier. In such a system, enzymes,
for example, a Candida Antarctica lipase B (CALB),
are compartmentalized within millions of micron-sized water droplets,
while organic substrates are dissolved in the oil phase (outside the
droplets). It was demonstrated that CALB-catalyzed hydrolysis kinetic
resolution of racemic esters in the stirring-free Pickering emulsion
system gave favorable reaction efficiency and enantioselectivity as
compared to those for the conventional biphasic system under stirring
conditions, which was due to the large reaction interfacial area and
the short molecule distances created by the Pickering emulsion droplets.
The specific activity was found to depend on the water droplet size,
highlighting the importance of the presence of droplets in the reaction
system. Moreover, the convenient and effective recycling of CALB could
be achieved through simple demulsification by centrifugation. After
27 reaction cycles, the ee values of ester and alcohol were still
as high as 87.5% and 99%, respectively, which significantly exceed
those of the conventional biphasic reaction. The high recyclability
may be attributed to avoiding stirring that often causes damage to
the three-dimensional structure of enzymes. This study compellingly
demonstrates that a Pickering emulsion is an innovative platform to
efficiently process enzymatic reactions without need for stirring
and immobilization.