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Lipase selectivity in functional polyester synthesis
KTH, School of Biotechnology (BIO), Biochemistry.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Enzyme selectivity means that the enzyme´s preferences towards competing substrates will be different. In this thesis, the enzyme selectivity has been studied for utilization in synthesis of functionalized macromonomers. The aim was to study how the inherent –or introduced – selectivity of lipases can be used to introduce thiol‐ or enefunctionalities into short polyesters. Thiol‐ and ene‐functionalized renewable organic precursor molecules in combination with thiol‐ene click chemistry opens up for a sustainable material production. Lipases do not normally affect ene‐moieties and the preference towards thiols is low, enabling introduction of these functional groups for further modifications. In addition, lipases have been shown to be good catalysts in the formation of polyesters, both via ring‐opening and polycondensation polymerization.

In paper I Candida antarctica lipase B was used to end‐functionalize poly(ε‐caprolactone) with free thiols in a one‐pot reaction. The advantage of using achemoselective lipase as catalyst was that no protection of the thiol was needed. The chemoselectivity displayed by Candida antarctica lipase B turned out to be 88 000 in favour of the alcohol (paper II). Rhizomucor miehei lipase showed less pronounced chemoselectivity. The largest contribution to the selectivities was derived from the more than two orders of magnitude higer KM towards the thiol compared to the alcohol. Thiols can be cross‐linked with enes in radical reactions to form networks, enabling formation of materials.

One promising renewable molecule containing an acrylate moiety is itaconic acid. In paper III the selectivity towards the two esters in dimethyl itaconate was investigated and the active site of Candida antarctica lipase B was redesigned to generate variants with increased and decreased selectivity. One variant showed 14‐fold higher selectivity and could regioselectively add dimethyl itaconate onto a diol. This variant could be used in end‐functionalizations of polymers, introducing acrylate‐ester end‐groups.

The enzyme selectivity towards lactones and their corresponding polyesters is of importance when designing a ring‐opening polymerization reaction. In paper IV Candida antarctica lipase B was found to prefer ω‐pentadecalactone and polyesters over ε‐caprolactone ten‐fold, while Humicola insolens cutinase preferred ε‐caprolactone and its corresponding polyester four‐fold over ω‐pentadecalactone and its polyester. From a selectivity point of view, Candida antarctica lipase B and Humicola insolens cutinase would be equally good in ring‐opening polymerization of ω‐pentadecalactone, while in the case of ε‐caprolactone Humicola insolens cutinase would be the preferred choice.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 49 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2011:20
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:kth:diva-34023ISBN: 978-91-7501-007-6OAI: oai:DiVA.org:kth-34023DiVA: diva2:418616
Public defence
2011-06-17, FD5, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110608Available from: 2011-06-08 Created: 2011-05-23 Last updated: 2011-06-08Bibliographically approved
List of papers
1. Thiol end-functionalization of poly(epsilon-caprolactone), catalyzed by Candida antarctica lipase B
Open this publication in new window or tab >>Thiol end-functionalization of poly(epsilon-caprolactone), catalyzed by Candida antarctica lipase B
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2005 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 38, no 3, 647-649 p.Article in journal (Refereed) Published
Abstract [en]

The use of Candida antarctica Lipase B (CALB) chemoselective catalyst in the Thiol End-Functionalization of Poly(ε-caprolacetone) was discussed. Thiol-functionalization of poly(ε-caprolacetone)(PCL) was made by an initiation reaction catalyzed by CALB in bulk. 2-Mercaptoethanol (1) was used to initiate the enzyme-assisted ring opening polymerization of ε-caprolacetone(2) to give the desired thiol-functionalized polymer. The structure of the terminated PCL was confirmed by 13C nuclear magnetic resonance .

Keyword
ring-opening polymerization, epsilon-caprolactone, polymers, monolayers, polyesters, surfaces
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-14502 (URN)10.1021/ma048056r (DOI)000226764500001 ()2-s2.0-13444258041 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-06-08Bibliographically approved
2. Lipase chemoselectivity towards alcohol and thiol acyl acceptors in a transacylation reaction
Open this publication in new window or tab >>Lipase chemoselectivity towards alcohol and thiol acyl acceptors in a transacylation reaction
2010 (English)In: Journal of Molecular Catalysis B: Enzymatic, ISSN 1381-1177, Vol. 66, no 1-2, 120-123 p.Article in journal (Refereed) Published
Abstract [en]

The lipase chemoselectivity towards an alcohol and a thiol was investigated for the two lipases Candida antarctica lipase B (CalB) and Rhizomucor miehei lipase (Rml). Hexanol and hexanethiol were used as acyl acceptors in a transacylation reaction with ethyl octanoate in cyclohexane. CalB showed the highest chemoselectivity ratio (k(cat)/K-M)(OH)/(k(cat)/K-M)(SH), of 88,000 while the ratio for Rml was 1200. That could be compared with the ratio, k(OH)/k(SH), of 120 for the non-catalyzed reaction. Thus, the enzyme contribution to the chemoselectivity between hexanol and hexanethiol was 730 for CalB and 10 for Rml. High K-M values displayed towards hexanethiol (above 1.8 M) were the largest contribution to the selectivity. No saturation was achieved. The K-M values were more than two orders of magnitude higher than those of hexanol.

Keyword
Chemoselectiviry, Acylation, Lipase, Kinetics, Active site titration
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-25232 (URN)10.1016/j.molcatb.2010.04.005 (DOI)000280928200015 ()2-s2.0-77957827548 (ScopusID)
Note
QC 20101013Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2011-06-08Bibliographically approved
3. Selectivity towards itaconic acid esters by Candida antarctica lipase B andvariants
Open this publication in new window or tab >>Selectivity towards itaconic acid esters by Candida antarctica lipase B andvariants
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-34439 (URN)
Available from: 2011-06-08 Created: 2011-06-08 Last updated: 2011-06-08Bibliographically approved
4. Competition between lactones and polyesters in enzyme catalyzed ring-opening polymerization
Open this publication in new window or tab >>Competition between lactones and polyesters in enzyme catalyzed ring-opening polymerization
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-34441 (URN)
Available from: 2011-06-08 Created: 2011-06-08 Last updated: 2011-06-08Bibliographically approved

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