Sixteen phenolic compounds, 14 of which naturally occurring, were compared to the synthetic 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and violuric acid (VA) in terms of their ability to act as mediators/enhancers in: (1) laccase oxidation of veratryl alcohol as a lignin model compound, and (2) electrochemical oxidation of kraft and flax lignins. HPLC analysis revealed that the syringyl-type phenols methyl syringate and acetosyringone were the most efficient natural enhancers in the laccase oxidation of veratryl alcohol. Both compounds, though far from the performance of ABTS were able to generate veratraldehyde in amount similar to that obtained with VA. By contrast, the best performing phenolic enhancers for the electrochemical oxidation of lignins were sinapinaldehyde, vanillin, acetovanillone, and syringic acid. Catalytic efficiencies close to those achieved with ABTS and VA were calculated for these phenolic compounds.
The covalent grafting of alkyl gallates on wool through a laccase catalysed reaction in 80/20 (v/v, %)aqueous–ethanol mixture provided in a one-step process a multifunctional textile material with antioxidant, antibacterial and water repellent properties. Gallic acid and its alkyl esters ethyl, propyl, octyl and
dodecyl gallate have been enzymatically grafted on wool fibres in order to study the effect of alkyl chain length on wool functional modification. The capacity of laccase to oxidise these phenolic compounds in an aqueous–organic medium has been verified by electrochemical techniques. The increase of CH2, CH3 groups in the FTIR spectra, together with the XPS analysis of the enzymatically modified fabrics confirmed
the covalent grafting of ester gallates on wool. The result obtained in this work for antibacterial, water repellent as well as antioxidant properties show that the length of the alkyl chain of gallates molecule
play an important role on wool functionalisation.
Electronic version of an article published as "Enzyme and microbial technology", 08 Desembre 2009, p. 1-5
Wool fibres have been modified with nordihydroguaiaretic acid (NDGA) to improve their performance at use. This water insoluble bi-functional phenolic compound has been grafted on wool through a laccase enzyme catalyzed reaction in an aqueous-ethanol mixture. The capacity of laccase to oxidise NDGA in this aqueous-organic medium has been studied electrochemicaly. The increase of CH2, CH3 and aromatic groups signal in the DRIFT spectra, together with SEM images of the enzymatically-modified fabrics confirmed the covalent grafting of NDGA on wool. This one step enzymatic process for grafting of NDGA improved the physical and mechanical properties of wool fabrics such as shrink resistance, crease recovery and tensile strength. Furthermore, the NDGA imparted to the textile material strong antioxidant activity and UV-protection.
The natural phenolic compounds syringaldehyde and vanillin were compared to the synthetic mediators 1-hydroxybenzotriazole, violuric acid and promazine in terms of boosting efficiency in a laccase-assisted biobleaching of eucalyptus kraft pulp. Violuric acid and 1-hydroxybenzotriazole revealed to be the most effective mediators of the bioprocess. Nevertheless, laccase-syringaldehyde system also improved the final pulp properties (28% delignification and 63.5% ISO brightness) compared to the process without mediator (23% and 61.5% respectively), in addition to insignificant denaturation effect over laccase. The efficiency of the biobleaching process was further related to changes in non-conventionally used optical and chromatic parameters of pulp, such as (L*), chroma (C*) and dye removal index (DRI) showing good correlation. Adverse coupling reactions of the natural phenolic mediators on pulp lignin were predicted by electrochemical studies, demonstrating the complexity of the laccase-mediator reaction on pulp.