Abstract
It is a well known fact that some ionic liquids (ILs) have the potential to dissolve crystalline, water-insoluble cellulose that could be used as a source of glucose and subsequently derived molecules. Nevertheless, in the presence of high IL concentrations, cellulase activity and, even more so, cellulase stability are still challenging difficulties that need to be overcome. Therefore four fungal cellulase preparations were assayed in the presence of 30% (v/v) of five different ILs. Thereby the cellulase from Aspergillus sp. (Sigma-Aldrich) was not only remarkably active (up to 28 U/mg in 30% (v/v) IL ([BMMIM]Cl)), but furthermore stayed active during several weeks in the presence of 60% (v/v) IL (up to 50% relative activity after 9 weeks).
Highlights
The enzymatic conversion of cellulose into glucose, and subsequently biofuels, could provide a renewable and sustainable energy source
ionic liquids (ILs) could be used as a reaction medium for the enzymatic hydrolysis of cellulose, if cellulases were shown to be active and stable in the presence of high IL concentrations
The cellulases derived from Trichoderma reesei and T. viride were almost inactive in the presence of 30% (v/v) of all tested ILs (Figure 1), whereby 30% (v/v) IL was chosen, as it turned out to be a critical concentration in previous studies [3]
Summary
The enzymatic conversion of cellulose into glucose, and subsequently biofuels, could provide a renewable and sustainable energy source. Several ionic liquids (ILs) have been shown to dissolve water-insoluble cellulose and/or wood. Among these is 1-butyl-3methylimidazolium chloride ([BMIM]Cl) [1,2]. ILs could be used as a reaction medium for the enzymatic hydrolysis of cellulose, if cellulases were shown to be active and stable in the presence of high IL concentrations. Catalysts 2013, 3 active in the presence of ILs. The majority of cellulases, including a preparation from Trichoderma reesei, appear to be inactive in the presence of IL concentrations above 20% (v/v) [3,4]. Some thermostable cellulases have shown high activity in the presence of about 30% (v/v) IL [5,6]. Fungal enzymes are often more stable due to glycosylation, and have been shown to be persistent in the presence of proteases, high temperatures, and surfactants [7,8,9]
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