title: Introduction of aldehyde vs. carboxylic groups to cellulose nanofibers using laccase/TEMPO mediated oxidation.
abstract: The chemo-enzymatic modification of cellulose nanofibers (CNFs) using laccase as biocatalysts and TEMPO or 4-Amino-TEMPO as mediators under mild aqueous conditions (pH 5, 30 °C) has been investigated to introduce surface active aldehyde groups. 4-Amino TEMPO turned out to be kinetically 0.5-times (50%) more active mediator, resulting to oxoammonium cation intermediacy generated and its in situ regeneration during the modification of CNFs. Accordingly, beside of around 750 mmol/kg terminally-located aldehydes, originated during CNFs isolation, the reaction resulted to about 140% increase of C6-located aldehydes at optimal conditions, without reducing CNFs crystallinity. While only the C6-aldehydes were wholly transformed into the carboxyls after additional post-treatment using NaOH according to the Cannizzaro reaction, the post-oxidation with air-oxygen in EtOH/water medium or NaClO2 resulted to no- or very small amounts of carboxyls created, respectively, at a simultaneous loss of all C6- and some terminal-aldehydes in the latter due to the formation of highly-resistant hemiacetal covalent linkages with available cellulose hydroxyls. The results indicated a new way of preparing and stabilizing highly reactive C6-aldehydes on cellulose, and their exploitation in the development of new nanocellulose-based materials.
authors.affiliation: University of Maribor, Institute for Engineering Materials and Design, Smetanova ul. 17, SI-2000 Maribor, Slovenia.
authors.forename: Darja
authors.initials: D
authors.lastname: Jaušovec
authors.affiliation: University of Maribor, Institute for Engineering Materials and Design, Smetanova ul. 17, SI-2000 Maribor, Slovenia.
authors.forename: Robert
authors.initials: R
authors.lastname: Vogrinčič
authors.affiliation: University of Maribor, Institute for Engineering Materials and Design, Smetanova ul. 17, SI-2000 Maribor, Slovenia. Electronic address: vanja.kokol@um.si.
authors.forename: Vanja
authors.initials: V
authors.lastname: Kokol
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D055162:Biocatalysis; D002264:Carboxylic Acids / Q000737:chemistry; D002482:Cellulose / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry*; D042845:Laccase / Q000737:chemistry*; D057139:Nanofibers / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D000447:Aldehydes; D002264:Carboxylic Acids; D003497:Cyclic N-Oxides; C015527:4-amino-TEMPO; D002482:Cellulose; D042845:Laccase; C003959:TEMPO
keywords: Aldehyde and carboxyl groups; Cellulose nanofibers; Hemiacetal linkages; Laccase; Oxidation; TEMPO