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

Additional file 1 of Evaluation of bacterial hosts for conversion of lignin-derived p-coumaric acid to 4-vinylphenol

Additional file 1. HPLC–UV chromatogram obtained from the lignin liquor at pH 7.5 prepared in this work and used for bioconversion. The sample was diluted 100-fold in water before analysis

Understanding the Interactions of Cellulose with Ionic Liquids: A Molecular Dynamics Study

Ionic liquids (ILs) have recently been demonstrated to be highly effective solvents for the dissolution of cellulose and lignocellulosic biomass. To date, there is no definitive rationale for selecting ionic liquids that are capable of dissolving these biopolymers. In this work, an all-atom force field for the IL 1-ethyl-3-methylimidazolium acetate [C2mim][OAc] was developed and the behavior of cellulose in this IL was examined using molecular dynamics simulations of a series of (1−4) linked β-d-glucose oligomers with a degree of polymerization n = 5, 6, 10, and 20. Molecular dynamics simulations were also carried out on cellulose oligomers in two common solvents, water and methanol, which are known to precipitate cellulose from IL solutions, to determine the extent and energetics of the interactions between these solvents and the cellulosic oligomers. Thermodynamic properties, such as density and solubility, as well as the two-body solute−solvent interaction energy terms, were calculated. The structural and dynamic behavior of solutions was analyzed and the conformations of cellulose oligomers were compared in ionic liquid and water mixtures. It was found that the interaction energy between the polysaccharide chain and the IL was stronger than that for either water or methanol. In addition to the anion acetate forming strong hydrogen bonds with hydroxyl groups of the cellulose, some of the cations were found to be in close contact with the polysaccharides through hydrophobic interactions. These results support the concept that the cation may play a significant role in the dissolution of cellulose by [C2mim][OAc]. It is also observed that the preferred β-(1,4)-glycosidic linkage conformation of the cellulose was altered when dissolved in [C2mim][OAc] as compared to that found in crystalline cellulose dispersed in water. To our knowledge, this report is the first theoretical study that addresses the key factors in cellulose dissolution using an ionic liquid

Physics-Based Machine Learning Models Predict Carbon Dioxide Solubility in Chemically Reactive Deep Eutectic Solvents

Carbon dioxide (CO2) is a detrimental greenhouse gas and is the main contributor to global warming. In addressing this environmental challenge, a promising approach emerges through the utilization of deep eutectic solvents (DESs) as an ecofriendly and sustainable medium for effective CO2 capture. Chemically reactive DESs, which form chemical bonds with the CO2, are superior to nonreactive, physically based DESs for CO2 absorption. However, there are no accurate computational models that provide accurate predictions of the CO2 solubility in chemically reactive DESs. Here, we develop machine learning (ML) models to predict the solubility of CO2 in chemically reactive DESs. As training data, we collected 214 data points for the CO2 solubility in 149 different chemically reactive DESs at different temperatures, pressures, and DES molar ratios from published work. The physics-driven input features for the ML models include σ-profile descriptors that quantify the relative probability of a molecular surface segment having a certain screening charge density and were calculated with the first-principle quantum chemical method COSMO-RS. We show here that, although COSMO-RS does not explicitly calculate chemical reaction profiles, the COSMO-RS-derived σ-profile features can be used to predict bond formation. Of the models trained, an artificial neural network (ANN) provides the most accurate CO2 solubility prediction with an average absolute relative deviation of 2.94% on the testing sets. Overall, this work provides ML models that can predict CO2 solubility precisely and thus accelerate the design and application of chemically reactive DESs

Economic and Environmental Trade-Offs of Simultaneous Sugar and Lignin Utilization for Biobased Fuels and Chemicals

Efficient lignin conversion is vital to the production of affordable, low-carbon fuels and chemicals from lignocellulosic biomass. However, lignin conversion remains challenging, and the alternative (combustion) can emit harmful air pollutants. This study explores the economic and environmental trade-offs between lignin combustion and microbial utilization for producing bisabolene as a representative biobased fuel or chemical. Results for switchgrass and clean pine-based biorefineries show that using lignin to increase fuel yields rather than combusting it reduces the capital expenditures for the boiler and turbogenerator if the facilities process more than 1100 bone-dry metric tons (bdt) feedstock/day and 560 bdt/day, respectively. No comparable advantage was observed for lower-lignin sorghum feedstock. Deconstructing lignin to bioavailable intermediates and utilizing those small molecules alongside sugars to boost product yields is economically attractive if the overall lignin-to-product conversion yield exceeds 11–20% by mass. Although lignin-to-fuel/chemical conversion can increase life-cycle greenhouse gas (GHG) emissions, most of the lignin can be diverted to fuel/chemical production while maintaining a >60% life-cycle GHG footprint reduction relative to diesel fuel. The results underscore that lignin utilization can be economically advantageous relative to combustion for higher-lignin feedstocks, but efficient depolymerization and high yields during conversion are both crucial to achieving viability

Greenhouse Gas Footprint, Water-Intensity, and Production Cost of Bio-Based Isopentenol as a Renewable Transportation Fuel

Although ethanol remains the dominant liquid biofuel in the global market, there is a strong interest in high-energy density and low-hygroscopicity compounds that can be incorporated into gasoline at levels beyond the current ethanol blend wall. Isopentenol (3-methyl-3-buten-1-ol) is one of these promising advanced biofuels that is also an important precursor for isoprene (the main component of natural rubber). In this study, we model the production cost, greenhouse gas (GHG) emissions, and water footprint of biologically produced isopentenol, including the current state of the technology and the impact of potential improvements. We find that the minimum selling price of biobased isopentenol, given the current state of technology demonstrated at bench-scale, is $5.14/L-gasoline equivalent, and the GHG footprint exceeds that of gasoline. However, biobased isopentenol could reach a$0.62/L-gasoline equivalent [$2.4/gal-gasoline equivalent (gge), just 5in an optimized future case where yield and other process parameters are pushed to near their theoretical limits. In this future case, isopentenol could achieve a GHG reduction of 90and a carbon abatement cost of$9.3/metric ton CO2e. Reaching these goals will require dramatic improvements in isopentenol yield, near-100% recovery of ionic liquid used in pretreatment, and low-lignin and high-cellulose and -hemicellulose biomass feedstocks

Influence of Connectivity and Porosity on Ligand-Based Luminescence in Zinc Metal−Organic Frameworks

Applications of metal−organic frameworks (MOFs) require close correlation between their structure and function. We describe the preparation and characterization of two zinc MOFs based on a flexible and emissive linker molecule, stilbene, which retains its luminescence within these solid materials. Reaction of trans-4,4‘-stilbene dicarboxylic acid and zinc nitrate in N,N-dimethylformamide (DMF) yielded a dense 2-D network, 1, featuring zinc in both octahedral and tetrahedral coordination environments connected by trans-stilbene links. Similar reaction in N,N-diethylformamide (DEF) at higher temperatures resulted in a porous, 3-D framework structure, 2. This framework consists of two interpenetrating cubic lattices, each featuring basic zinc carboxylate vertices joined by trans-stilbene, analogous to the isoreticular MOF (IRMOF) series. We demonstrate that the optical properties of both 1 and 2 correlate with the local ligand environments observed in the crystal structures. Steady-state and time-resolved spectroscopic measurements reveal that the stilbene linkers in the dense structure 1 exhibit a small degree of interchromophore coupling. In contrast, the stilbenoid units in 2 display very little interaction in this low-density 3-D framework, with excitation and emission spectra characteristic of monomeric stilbenes, similar to the dicarboxylic acid in dilute solution. In both cases, the rigidity of the stilbene linker increases upon coordination to the inorganic units through inhibition of torsion about the central ethylene bond, resulting in luminescent crystals with increased emission lifetimes compared to solutions of trans-stilbene. The emission spectrum of 2 is found to depend on the nature of the incorporated solvent molecules, suggesting use of this or related materials in sensor applications

Microfluidic Glycosyl Hydrolase Screening for Biomass-to-Biofuel Conversion

The hydrolysis of biomass to fermentable sugars using glycosyl hydrolases such as cellulases and hemicellulases is a limiting and costly step in the conversion of biomass to biofuels. Enhancement in hydrolysis efficiency is necessary and requires improvement in both enzymes and processing strategies. Advances in both areas in turn strongly depend on the progress in developing high-throughput assays to rapidly and quantitatively screen a large number of enzymes and processing conditions. For example, the characterization of various cellodextrins and xylooligomers produced during the time course of saccharification is important in the design of suitable reactors, enzyme cocktail compositions, and biomass pretreatment schemes. We have developed a microfluidic-chip-based assay for rapid and precise characterization of glycans and xylans resulting from biomass hydrolysis. The technique enables multiplexed separation of soluble cellodextrins and xylose oligomers in around 1 min (10-fold faster than HPLC). The microfluidic device was used to elucidate the mode of action of Tm_Cel5A, a novel cellulase from hyperthermophile Thermotoga maritima. The results demonstrate that the cellulase is active at 80 °C and effectively hydrolyzes cellodextrins and ionic-liquid-pretreated switchgrass and Avicel to glucose, cellobiose, and cellotriose. The proposed microscale approach is ideal for quantitative large-scale screening of enzyme libraries for biomass hydrolysis, for development of energy feedstocks, and for polysaccharide sequencing

Influence of Connectivity and Porosity on Ligand-Based Luminescence in Zinc Metal−Organic Frameworks

Applications of metal−organic frameworks (MOFs) require close correlation between their structure and function. We describe the preparation and characterization of two zinc MOFs based on a flexible and emissive linker molecule, stilbene, which retains its luminescence within these solid materials. Reaction of trans-4,4‘-stilbene dicarboxylic acid and zinc nitrate in N,N-dimethylformamide (DMF) yielded a dense 2-D network, 1, featuring zinc in both octahedral and tetrahedral coordination environments connected by trans-stilbene links. Similar reaction in N,N-diethylformamide (DEF) at higher temperatures resulted in a porous, 3-D framework structure, 2. This framework consists of two interpenetrating cubic lattices, each featuring basic zinc carboxylate vertices joined by trans-stilbene, analogous to the isoreticular MOF (IRMOF) series. We demonstrate that the optical properties of both 1 and 2 correlate with the local ligand environments observed in the crystal structures. Steady-state and time-resolved spectroscopic measurements reveal that the stilbene linkers in the dense structure 1 exhibit a small degree of interchromophore coupling. In contrast, the stilbenoid units in 2 display very little interaction in this low-density 3-D framework, with excitation and emission spectra characteristic of monomeric stilbenes, similar to the dicarboxylic acid in dilute solution. In both cases, the rigidity of the stilbene linker increases upon coordination to the inorganic units through inhibition of torsion about the central ethylene bond, resulting in luminescent crystals with increased emission lifetimes compared to solutions of trans-stilbene. The emission spectrum of 2 is found to depend on the nature of the incorporated solvent molecules, suggesting use of this or related materials in sensor applications