Aaron M. Socha

Efficient biomass pretreatment using ionic liquids derived from lignin and hemicellulose

Significance Ionic liquids (ILs) have unique properties applicable to a variety of industrial processes. Nearly universal solvating capabilities, low vapor pressures, and high thermal stabilities make these compounds ideal substitutes for a wide range of organic solvents. To date, the best performing ILs are derived from nonrenewable sources such as petroleum or natural gas. Due to their potential for large-scale deployment, ILs derived from inexpensive, renewable reagents are highly desirable. Herein, we describe a process for synthesizing ILs from materials derived from lignin and hemicellulose, major components of terrestrial plant biomass. With respect to overall sugar yield, experimental evaluation of these compounds showed that they perform comparably to traditional ILs in biomass pretreatment. Ionic liquids (ILs), solvents composed entirely of paired ions, have been used in a variety of process chemistry and renewable energy applications. Imidazolium-based ILs effectively dissolve biomass and represent a remarkable platform for biomass pretreatment. Although efficient, imidazolium cations are expensive and thus limited in their large-scale industrial deployment. To replace imidazolium-based ILs with those derived from renewable sources, we synthesized a series of tertiary amine-based ILs from aromatic aldehydes derived from lignin and hemicellulose, the major by-products of lignocellulosic biofuel production. Compositional analysis of switchgrass pretreated with ILs derived from vanillin, p-anisaldehyde, and furfural confirmed their efficacy. Enzymatic hydrolysis of pretreated switchgrass allowed for direct comparison of sugar yields and lignin removal between biomass-derived ILs and 1-ethyl-3-methylimidazolium acetate. Although the rate of cellulose hydrolysis for switchgrass pretreated with biomass-derived ILs was slightly slower than that of 1-ethyl-3-methylimidazolium acetate, 90–95% glucose and 70–75% xylose yields were obtained for these samples after 72-h incubation. Molecular modeling was used to compare IL solvent parameters with experimentally obtained compositional analysis data. Effective pretreatment of lignocellulose was further investigated by powder X-ray diffraction and glycome profiling of switchgrass cell walls. These studies showed different cellulose structural changes and differences in hemicellulose epitopes between switchgrass pretreatments with the aforementioned ILs. Our concept of deriving ILs from lignocellulosic biomass shows significant potential for the realization of a “closed-loop” process for future lignocellulosic biorefineries and has far-reaching economic impacts for other IL-based process technology currently using ILs synthesized from petroleum sources.

Understanding pretreatment efficacy of four cholinium and imidazolium ionic liquids by chemistry and computation

Certain ionic liquids (ILs) offer a potentially more sustainable and environmentally responsible alternative to organic solvents for many industrial applications, including biorefineries, where they are used to pretreat lignocellulose. To gain a more robust understanding of the roles of cations and anions in the process, we monitored the impact of the respective ILs on Panicum virgatum (switchgrass) in terms of lignin content, cellulose crystallinity, and enzymatic digestibility. The behaviors of four ILs, based on one of two cations, 1-ethyl-3-methylimidazolium ([C2mim]+) and cholinium ([Ch]+), and one of two anions, acetate ([OAc]−) and lysinate ([Lys]−), were compared. While all four ILs were effective in pretreating switchgrass, ILs containing [Lys]− anions provided greater delignification (70–80% vs. 16–50%) after addition of water as an anti-solvent and higher glucose yields (78–96% vs. 56–90%) compared to those obtained by the use of ILs containing [OAc]− anions. Measurements of the Kamlet–Taft parameters using a series of dyes indicated a greater hydrogen bond basicity for the ILs with [Lys]− anions as compared to acetate ILs. To understand the effective delignification ability of lysinate-based ILs, interaction energies of individual ions and ion pairs with a model dilignol substrate were determined by quantum chemical calculations. The results show that the addition of antisolvent significantly influenced the interaction energies governing lignin removal during the process.

Diversity-oriented synthesis of cyclic acyldepsipeptides leads to the discovery of a potent antibacterial agent

A class of cyclic acyldepsipeptide antibiotics collectively known as the enopeptins has recently attracted much attention because of their activity against multidrug-resistant bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. These antibiotics are further distinguished by their novel mechanism of action in which they bind and deregulate the tightly controlled activity of the cytoplasmic protease ClpP. Although the natural products have poor pharmacological properties, a synthetic derivative called acyldepsipeptide 4 (ADEP 4) showed remarkable antibacterial activity both in vitro and in mouse models of bacterial infections. A novel route to the ADEP 4 peptidolactone core structure, featuring the Joullié-Ugi three-component reaction, was developed. This multicomponent reaction and a related multicomponent reaction, the Ugi four-component reaction, were used to prepare analogs that were designed using the principles of conformational analysis. These cyclic acyldepsipeptides were tested for their activity against drug-resistant, clinical isolates of Staphylococci and Enterococci. One ADEP 4 analog in which the pipecolate was replaced by 4-methyl pipecolate exhibited in vitro antibacterial activity against Enterococci that was fourfold higher than the parent compound.

Structure–activity studies of echinomycin antibiotics against drug-resistant and biofilm-forming Staphylococcus aureus and Enterococcus faecalis

Four echinomycin antibiotics were isolated from the culture broth of a marine streptomycete, and their structures were determined by a combination of chemical and spectroscopic analyses. Antibiotic activities were measured against drug-resistant and biofilm-forming strains of Staphylococcus aureus and Enterococcus faecalis. Minimum inhibitory concentrations ranging from 0.01 microM to greater than 14 microM clearly defined structure-activity relationships for antibiotic potency. Echinomycin was the most active compound with a MIC of 0.03 microM against methicillin-resistant S. aureus and 0.01 microM against biofilm-forming E. faecalis.

Efficient conversion of triacylglycerols and fatty acids to biodiesel in a microwave reactor using metal triflate catalysts

We report that catalytic quantities of the Lewis acidic metal catalysts scandium triflate and bismuth triflate promote conversion of oleic, linoleic, palmitic and myristic acids and their glyceryl triesters to the corresponding methyl esters (biodiesel) in greater than 90% yield upon microwave heating. Additionally, both catalysts could be recovered and reused in esterification reactions at least six times.

Comparison of sugar content for ionic liquid pretreated Douglas-fir woodchips and forestry residues

BackgroundThe development of affordable woody biomass feedstocks represents a significant opportunity in the development of cellulosic biofuels. Primary woodchips produced by forest mills are considered an ideal feedstock, but the prices they command on the market are currently too expensive for biorefineries. In comparison, forestry residues represent a potential low-cost input but are considered a more challenging feedstock for sugar production due to complexities in composition and potential contamination arising from soil that may be present. We compare the sugar yields, changes in composition in Douglas-fir woodchips and forestry residues after pretreatment using ionic liquids and enzymatic saccharification in order to determine if this approach can efficiently liberate fermentable sugars.ResultsThese samples were either mechanically milled through a 2 mm mesh or pretreated as received with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [C2mim][OAc] at 120°C and 160°C. IL pretreatment of Douglas-fir woodchips and forestry residues resulted in approximately 71-92% glucose yields after enzymatic saccharification. X-ray diffraction (XRD) showed that the pretreated cellulose was less crystalline after IL pretreatment as compared to untreated control samples. Two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) revealed changes in lignin and hemicellulose structure and composition as a function of pretreatment. Mass balances of sugar and lignin streams for both the Douglas-fir woodchips and forestry residues throughout the pretreatment and enzymatic saccharification processes are presented.ConclusionsWhile the highest sugar yields were observed with the Douglas-fir woodchips, reasonably high sugar yields were obtained from forestry residues after ionic liquid pretreatment. Structural changes to lignin, cellulose and hemicellulose in the woodchips and forestry residues of Douglas-fir after [C2mim][OAc] pretreatment are analyzed by XRD and 2D-NMR, and indicate that significant changes occurred. Irrespective of the particle sizes used in this study, ionic liquid pretreatment successfully allowed high glucose yields after enzymatic saccharification. These results indicate that forestry residues may be a more viable feedstock than previously thought for the production of biofuels.