Abstract:The potential of halogen-free and imidazoliumfree phosphonium-based amino acid ionic liquids (AAILs) has been investigated as new solvents for cellulose pretreatment for the subsequent enzymatic hydrolysis of cellulose. AAILs alone did not dissolve cellulose (Avicel), even at 120°C. However, when polar solvents such as dimethylsulfoxide (DMSO) were added as cosolvents, AAILs became an acceptable solvent for cellulose at 30°C. The solubility of cellulose in tetrabutylphosphonium glycine ([TBP][Gly])/cosolvent reached 15%. The enzymatic hydrolysis of cellulose was dramatically enhanced by pretreatment with AAIL/cosolvent, and the glucose yield reached 100% when the novel AAIL tetrabutylphosphonium N,N-dimethylglycine ([TBP][DMGly]) was used in combination with DMSO as cosolvent. The enzymatic conversion of cellulose to glucose in 6% and 13% [TBP] [DMGly]/DMSO buffer solutions reached 98% and 79%, respectively. The decrease in cellulase activity owing to residual [TBP][DMGly]/DMSO was not significant. Hence, it is possible to conduct the dissolution and enzymatic hydrolysis of cellulose in a one-batch process in a phosphonium-based AAIL/cosolvent system.

To improve the solubility of cellulose at lower temperatures, several polar organic solvents were examined as cosolvents in imidazolium ionic liquid (IL). All tested cosolvents increased the solubilization efficiency of ILs at lower temperatures. Among these, N-methylimidazole, N-methyl-2-pyrrolidone, and dimethyl sulfoxide (DMSO) were notably efficient; in case of Avicel the solubility was increased, with 12–15% cellulose dissolution in 1-allyl-3-methylimidazolium chloride ([Amim]Cl) at 30°C. IR spectra of the regenerated celluloses from IL/cosolvent systems showed characteristic features of cellulose II and/or amorphous cellulose. Thermogravimetric analyses showed significantly higher thermal stability of regenerated cellulose from [Amim]Cl/DMSO compared with that without DMSO. Moreover, dimethylacetamide (DMAc) increased the solubility of filter paper pulp in 1-ethyl-3-methylimidazolium acetate ([Emim]OAc), with 12% pulp dissolution at 30°C. No decrease in the degree of polymerization (DP) of cellulose was observed with [Emim]OAc/DMAc, whereas 8–9% DP decrease was observed with [Emim]OAc, even at 30°C. These results indicate that some cosolvents including DMSO and DMAc increase solubilization efficiency and have superior cellulose-protective effects during enhanced dissolution in ILs.

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Abstract:A new approach for the enzymatic synthesis of methyl β-d-glucoside was proposed, based on commercially available cellulase and cellulose pretreated with phosphonium-based amino acid ionic liquid/cosolvent. The pretreatments were quite effective and methyl β-dglucoside was successfully synthesized with 40% yield from cellulose (Avicel) pretreated with tetrabutylphosphonium glycine/dimethyl sulfoxide (DMSO), whereas the yield was only 1.4% from untreated cellulose. Preparative-scale synthesis from 1 g cellulose with a reduced amount of cellulase was also conducted, achieving a 33% isolated yield. Results of additional studies with cellobiose and glucose as substrates have been interpreted as cellulose being first enzymatically hydrolyzed to cellobiose, which then reacted with methanol to produce methyl β-d-glucoside by transglycosylation.