Macrocyclic
oligoester structures based on a cyclotetrasiloxane
core consisting of tricyclic (60+ atoms) and pentacycylic (130+ atoms)
species were identified as the major components of a lipase-mediated
transesterification reaction. Moderately hydrophobic solvents with
log <i>P</i> values in the range of 2–3 were more
suitable than those at lower or higher log <i>P</i> values.
Temperature had little effect on total conversion and yield of the
oligoester macrocycles, except when a reaction temperature of 100
°C was employed. At this temperature, the amount of the smaller
macrocycle was greatly increased, but at the expense of the larger
oligoester. For immobilized lipase B from Candida antarctica (N435), longer chain length esters and diols were more conducive
to the synthesis of the macrocycles. Langmuir isotherms indicated
that monolayers subjected to multiple compression/expansion cycles
exhibited a reversible collapse mechanism different from that expected
for linear polysiloxanes
