title: Chain length selectivity during the polycondensation of siloxane-containing esters and alcohols by immobilized Candida antarctica lipase B.
abstract: We have examined the chain length selectivity for a series of acyl donors by lipase B from Candida antarctica (CalB). CalB accepted aliphatic diesters of C4, C6 and C12 chain lengths equally. The introduction of a carbon-carbon double bond into the C4 esters dramatically lowered the rate constant associated with polymerization highlighting the role of geometry in catalysis; fumarate esters were polymerized at a reduced rate compared to the succinate esters, while the maleate esters were not polymerized above 5% over the course of 24h. A disiloxane-containing diester impeded catalysis by CalB. We examined a series of vinyl siloxane esters and alcohols, and learned that the Z arrangement around the double bond stalled esterification by CalB completely. The distance between the ester carbonyl and the dimethylsiloxy group was shown to be an important factor in mediating catalysis. The rate constants were similar when the methylene spacer was 3, 4, or 5 units in length; beyond 6 methylene units, the rate constants increased. This has been tentatively attributed to the local reduction on the steric bulk when the larger siloxane moiety lies outside of the active site of the enzyme.
authors.affiliation: Department of Chemistry and Centre for Biotechnology, 500 Glenridge Avenue, Brock University, St. Catharines, Ontario, Canada.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Frampton
authors.affiliation: Department of Chemistry and Centre for Biotechnology, 500 Glenridge Avenue, Brock University, St. Catharines, Ontario, Canada. Electronic address: pzelisko@brocku.ca.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Zelisko
mesh_terms: D000438:Alcohols; D055162:Biocatalysis; D001704:Biopolymers; D002175:Candida / Q000201:enzymology; D004800:Enzymes, Immobilized / Q000378:metabolism*; D004951:Esterification; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D008049:Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010168:Palmitates / Q000378:metabolism; D011091:Polyesters; D011145:Polyvinyls / Q000378:metabolism; D012833:Siloxanes / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D000438:Alcohols; D001704:Biopolymers; D004800:Enzymes, Immobilized; D005656:Fungal Proteins; D010168:Palmitates; D011091:Polyesters; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane; D008049:Lipase; C431349:lipase B, Candida antarctica
keywords: Lipase; Silicon biotechnology; Silicon chemistry; Siloxane-polyesters; Substrate tolerance