Novel cellulose pretreatment solvent: phosphonium-based amino acid ionic liquid/cosolvent for enhanced enzymatic hydrolysis

Abstract

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.

Enzymatic synthesis of methyl β-d-glucoside directly from cellulose pretreated with biocompatible amino acid ionic liquid/cosolvent

“…Cellulase "Onozuka" RS was purchased from Yakult Pharmaceutical Industry Co., Ltd., Tokyo, Japan. The optimum pH was between 4.0 and 5.0, and the optimum temperature was 50°C-60°C (Tao et al 2016b). Tetrabutylphosphonium glycine ([TBP][Gly]) was prepared as described by Tao et al (2016b).…”

“…In addition, pretreatments with [TBP][Gly]/ cosolvent were more efficient, and the yields of methyl β-d-glucoside were approx. 10% higher than those by [Amim]Cl/DMSO, which can be attributed to the higher compatibility of residual [TBP][Gly] with cellulase than that of residual [Amim]Cl in regenerated celluloses (Tao et al 2016b). It is also notable that among the cosolvents observed, DMSO was the most effective one for the synthesis of methyl β-d-glucoside.…”

“…It was already demonstrated that TBP-based AAIL/cosolvent is a new effective pretreatment solvent for enhanced enzymatic hydrolysis of cellulose because of its higher compatibility with cellulase (Tao et al 2016b). Hence, phosphonium-based AAIL/cosolvent systems were further applied to the synthesis of methyl β-d-glucoside from regenerated cellulose and MeOH.…”

“…It was particularly significant to determine how methyl β-d-glucoside is formed by cellulase from insoluble MeOH, whereas an 80% glucose yield was attained in 48 h for the enzymatic hydrolysis of untreated cellulose under the same conditions but without MeOH (Tao et al 2016b). These results indicate that MeOH reduces the enzymatic activity of cellulase and diminishes the total conversion of cellulose.…”

“…Eco-friendly phosphoniumbased amino acid ionic liquid (AAIL)/cosolvent systems served as cellulose pretreatment solvents, which recently demonstrated higher compatibility with cellulase than imidazolium-and halogen-based ILs (Tao et al 2016b). The experimental design was aimed at the utilization of commercial cellulase without any modification.…”