title: Macrocyclic Oligoesters Incorporating a Cyclotetrasiloxane Ring.
abstract: 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 P values in the range of 2-3 were more suitable than those at lower or higher log P 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.
authors.affiliation: †Department of Chemistry and Centre for Biotechnology and ‡Department of Physics, Brock University, St. Catharines, Ontario Canada, L2S 3A1.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Frampton
authors.affiliation: †Department of Chemistry and Centre for Biotechnology and ‡Department of Physics, Brock University, St. Catharines, Ontario Canada, L2S 3A1.
authors.forename: Drew
authors.initials: D
authors.lastname: Marquardt
authors.affiliation: †Department of Chemistry and Centre for Biotechnology and ‡Department of Physics, Brock University, St. Catharines, Ontario Canada, L2S 3A1.
authors.forename: Tim R B
authors.initials: TR
authors.lastname: Jones
authors.affiliation: †Department of Chemistry and Centre for Biotechnology and ‡Department of Physics, Brock University, St. Catharines, Ontario Canada, L2S 3A1.
authors.forename: Thad A
authors.initials: TA
authors.lastname: Harroun
authors.affiliation: †Department of Chemistry and Centre for Biotechnology and ‡Department of Physics, Brock University, St. Catharines, Ontario Canada, L2S 3A1.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Zelisko
mesh_terms: D061565:Cycloaddition Reaction; D005656:Fungal Proteins / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008049:Lipase / Q000378:metabolism*; D015394:Molecular Structure; D012833:Siloxanes / Q000138:chemical synthesis*
chemical_list: D005656:Fungal Proteins; D012833:Siloxanes; D008049:Lipase; C431349:lipase B, Candida antarctica