E. Ziomek et al., INTERACTION OF A POLY(DIMETHYLSILOXANE) WITH TRIGLYCERIDES IN MONOMOLECULAR FILMS AND APPLICATION TO LIPASE KINETICS, Chemistry and physics of lipids, 81(1), 1996, pp. 1-9
It has been known for some time that poly(dimethylsiloxanes) (PDMS) ca
n form monolayers al the air-water interface. In this paper we show th
at formation of mixed monolayers of PDMS with fatty acids, di- and tri
glycerides is also possible. At the air-water interface silicone can i
nteract and increase the retention of the fatty acids, which otherwise
easily desorb into the aqueous subphase. Unlike fatty acids, long acy
l chain tri- and diglycerides did not desorb into the aqueous subphase
and their interaction with silicone was manifested by a condensing ef
fect and a change in the collapse pressure of the mixed monolayers. Ge
otrichum candidum lipase (GCL) showed a similar level of binding to si
licone monolayer as to an air-water interface. Al low surface pressure
(7.5 mN/m) the lipase hydrolyzed dicaprin in mixed 1,2-sn-dicaprin-PD
MS monolayers at a rate 1.5-fold lower than the desorption rate of the
capric acid from mixed monolayers of capric acid and PDMS. Compressio
n of the dicaprin-PDMS monolayer to 20 mN/m led to a 15-fold increase
in lipase activity (70% of the activity observed for monolayer of pure
dicaprin compressed to the same surface pressure), indicating an incr
ease in dicaprin's surface concentration and its accessibility to the
enzyme. The lipase activity profile determined titrimetrically against
varying amounts of glycerides in mixed glyceride-PDMS emulsions (at c
onstant 5% oil-phase concentration) resembles the lipase activity-surf
ace pressure profile obtained with the monolayer method when using pur
e glycerides. This suggests that the location of glycerides in condens
ed mixed monolayers with PDMS should be similar to that in mixed glyce
ride-PDMS emulsions. By changing the molar fraction of tristearin and
tripalmitin in the mixture with PDMS, it was possible to regulate the
quality of the interface in emulsions and to optimize the enzymatic hy
drolysis of these solid triglycerides.