N‑Heterocyclic Carbene Promoted Decarboxylation of Lignin-Derived Aromatic Acids

Decarboxylation is an important reaction in organic synthesis and drug discovery, which is typically catalyzed by strong bases or metal-based catalysts bearing low yield and selectivity. For the first time, we demonstrated a new strategy of decarboxylation of hydroxyl cinnamic acids such as <i>p</i>-coumaric acid, ferulic acid, sinapinic acid, and caffeic acid in the presence of N-heterocyclic carbene (NHC) precursors (i.e., 1-ethyl-3-methyl imidazolium acetate [C₂C₁Im]­[OAc]), achieving high yields and selectivities up to 100% under relatively mild conditions. [C₂C₁Im]­[OAc] showed excellent recyclability as organocatalysis during three times of recycling using biphasic reaction system. A mechanistic study revealed that the decarboxylation was catalyzed by NHCs that were in-situ generated by self-deprotonation of [C₂C₁Im]­[OAc]. Our demonstrated route is especially appealing for the production of lignin-derived renewable aromatics

Life-Cycle Greenhouse Gas and Water Intensity of Cellulosic Biofuel Production Using Cholinium Lysinate Ionic Liquid Pretreatment

Cellulosic biofuels present an opportunity to meet a significant fraction of liquid transportation fuel demand with renewable, low-carbon alternatives. Certain ionic liquids (ILs) have proven effective at facilitating hydrolysis of lignocellulose to produce fermentable sugars with high yields. Although their negligible vapor pressure and low flammability make ILs attractive solvents at the point of use, their life-cycle environmental impacts have not been investigated in the context of cellulosic biorefineries. This study provides the first life-cycle greenhouse gas (GHG) and water use inventory for biofuels produced using IL pretreatment. We explore two corn stover-to-ethanol process configurations: the conventional water-wash (WW) route and the more recently developed integrated high gravity (iHG) route, which eliminates washing steps after pretreatment. Our results are based on the use of a representative IL, cholinium lysinate ([Ch]­[Lys]). We find that the WW process results in unacceptably high GHG emissions. The iHG process has the potential to reduce GHG emissions per megajoule of fuel by ∼45% relative to gasoline if [Ch]­[Lys] is used. Use of a protic IL with comparable performance to [Ch]­[Lys] could achieve GHG reductions up to 70–85%. The water intensities of the WW and iHG processes are both comparable to those of other cellulosic biofuel technologies

Chemoselective Methylation of Phenolic Hydroxyl Group Prevents Quinone Methide Formation and Repolymerization During Lignin Depolymerization

Chemoselective blocking of the phenolic hydroxyl (Ar–OH) group by methylation was found to suppress secondary repolymerization and charring during lignin depolymerization. Methylation of Ar–OH prevents formation of reactive quinone methide intermediates, which are partly responsible for undesirable secondary repolymerization reactions. Instead, this structurally modified lignin produces more relatively low molecular weight products from lignin depolymerization compared to unmodified lignin. This result demonstrates that structural modification of lignin is desirable for production of low molecular weight phenolic products. This approach could be directed toward alteration of natural lignification processes to produce biomass that is more amenable to chemical depolymerization

Dimethyl Sulfoxide Assisted Ionic Liquid Pretreatment of Switchgrass for Isoprenol Production

The production cost and viscosity of certain ionic liquids (ILs) are among the major factors preventing the establishment of economically viable IL-based biomass pretreatment technologies. Recently, mixtures of an IL with an organic solvent have been proposed for cellulose processing and biomass pretreatment. Dimethyl sulfoxide (DMSO) is an inexpensive organic solvent that is industrially produced from lignin, a byproduct of the pulping process. We carry out a mechanistic study of DMSO-assisted IL pretreatment of switchgrass. The physical structures of biomass samples are studied by X-ray diffraction (XRD), N₂ adsorption analysis, and small angle neutron scattering (SANS). Both dry and aqueous suspensions of biomass samples are measured by SANS which provides unique information on biomass pretreatment. A mixture of 42 wt % [C₂C₁Im]­[OAc] and 58 wt % DMSO is proposed as the optimal pretreatment solution, and the recycling and reuse of the mixture of solvents are also studied. The fermentability of the hydrolysates generated after pretreatment is evaluated using an E. coli strain engineered to produce isoprenol. This study suggests an avenue for developing more efficient and cost-effective IL-based processes for the production of lignocellulosic biofuels and bioproducts

Survey of Lignin-Structure Changes and Depolymerization during Ionic Liquid Pretreatment

A detailed study of chemical changes in lignin structure during the ionic liquid (IL) pretreatment process is not only pivotal for understanding and overcoming biomass recalcitrance during IL pretreatment but is also necessary for designing new routes for lignin valorization. Chemical changes in lignin were systematically studied as a function of pretreatment temperature, time, and type of IL used. Kraft lignin was used as the lignin source, and common pretreatment conditions were employed using three different ILs of varying chemical structure in terms of acidic or basic character. The chemical changes in the lignin structure due to IL pretreatment processes were monitored using ¹H–¹³C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR), ³¹P NMR, elemental analysis, gel permeation chromatography (GPC), and Fourier transform infrared (FT-IR), and the depolymerized products were analyzed using gas chromatography mass spectrometry (GC-MS). Although, with pretreatment in acidic IL, triethyl­ammonium hydrogensulfate ([TEA]­[HSO₄]) results in the maximum decrease in the β-aryl ether bond, maximum dehydration and recondensation pathways were also evident, with the net process showing a minimum decrease in the molecular weight of regenerated lignin. However, 1-ethyl-3-methyl­imidazolium acetate ([C₂C₁Im]­[OAc]) pretreatment yields a smaller decrease in the β-aryl ether content along with minimum evidence of recondensation, resulting in the maximum decrease in the molecular weight. Cholinium lysinate ([Ch]­[Lys]) pretreatment shows an intermediate result, with moderate depolymerization, dehydration, and recondensation observed. The depolymerization products after IL pretreatment are found to be a function of the pretreatment temperature and the specific chemical nature of the IL used. At higher pretreatment temperature, [Ch]­[Lys] pretreatment yields guaiacol, [TEA]­[HSO₄] yields guaiacylacetone, and [C₂C₁Im]­[OAc] yields both guaiacol and guaiacylacetone as major products. These results clearly indicate that the changes in lignin structure as well as the depolymerized product profile depend on the pretreatment conditions and the nature of the ILs. The insight gained on lignin structure changes and possible depolymerized products during IL pretreatment process would help future lignin valorization efforts in a potential IL-based lignocellulosic biorefinery

Pylum composition of microbial communities from mesophilic and thermophilic enrichments on rice straw.

<p>Pylum composition of microbial communities from mesophilic and thermophilic enrichments on rice straw.</p

Image_1_Microbial Community Structure and Functional Potential Along a Hypersaline Gradient.TIF

<p>Salinity is one of the strongest environmental drivers of microbial evolution and community composition. Here we aimed to determine the impact of salt concentrations (2.5, 7.5, and 33.2%) on the microbial community structure of reclaimed saltern ponds near San Francisco, California, and to discover prospective enzymes with potential biotechnological applications. Community compositions were determined by 16S rRNA amplicon sequencing revealing both higher richness and evenness in the pond sediments compared to the water columns. Co-occurrence network analysis additionally uncovered the presence of microbial seed bank communities, potentially primed to respond to rapid changes in salinity. In addition, functional annotation of shotgun metagenomic DNA showed different capabilities if the microbial communities at different salinities for methanogenesis, amino acid metabolism, and carbohydrate-active enzymes. There was an overall shift with increasing salinity in the functional potential for starch degradation, and a decrease in degradation of cellulose and other oligosaccharides. Further, many carbohydrate-active enzymes identified have acidic isoelectric points that have potential biotechnological applications, including deconstruction of biofuel feedstocks under high ionic conditions. Metagenome-assembled genomes (MAGs) of individual halotolerant and halophilic microbes were binned revealing a variety of carbohydrate-degrading potential of individual pond inhabitants.</p

Rarefaction curves from pyrotag data for enriched mesophilic and thermophilic microbial communities.

<p>Dashed lines indicate ±1 standard error.</p

Contig cluster properties for selected clusters (Figure 3) with high abundance or large contigs in thermophilic and mesophilic communities.

*<p>T, thermophilic community; M, mesophilic community.</p

Ecological measures for microbial communities from mesophilic and thermophilic enrichments on rice straw.

<p>Ecological measures for microbial communities from mesophilic and thermophilic enrichments on rice straw.</p