No abstract

No abstract

From the reaction of 1H-imidazole (1a), 4,5-dichloro-1H-imidazole (1b), 1H-benzimidazole (1c), 1-methyl-1H-imidazole (1d), and 1-methyl-1H-benzimidazole (1f) with methyl 4-(bromomethyl)benzoate (2), symmetrically and nonsymmetrically 4-(methoxycarbonyl)benzyl-substituted N-heterocyclic carbene (NHC) precursors, 3a -3f, were synthesized. These NHC precursors were then reacted with silver(I) acetate (AgOAc) to yield the NHC -silver acetate complexes (acetato-kO){1,3-bis[4-(methoxy-, and (acetato-kO){1-[4-(methoxycarbonyl)benzyl]-3-methyl-2,3-dihydro-1H-benzimidazol-2-yl}silver (4f), respectively. The three NHC -AgOAc complexes 4a, 4c, and 4d were characterized by single-crystal X-ray diffraction. All compounds studied in this work were preliminarily screened for their antimicrobial activities in vitro against Gram-positive bacteria Staphylococcus aureus, and Gram-negative bacteria Escherichia coli using the qualitative disk-diffusion method. All NHC -AgOAc complexes exhibited weak-to-medium antibacterial activity with areas of clearance ranging from 4 to 7 mm at the highest amount used, while the NHC precursors showed significantly lower activity. In addition, NHC -AgOAc complexes 4a and 4b, and 4d -4f exhibited in preliminary cytotoxicity tests on the human renal-cancer cell line Caki-1 medium-to-high cytotoxicities with IC 50 values ranging from 3.3 AE 0.4 to 68.3 AE 1 mm.

Current enzymatic methods for hemicellulosic biomass depolymerization are solution-based, typically require a harsh chemical pre-treatment of the material and large volumes of water, yet lack in efficiency. In our study, xylanase (E.C. 3.2.1.8) from Thermomyces lanuginosus is used to hydrolyze xylans from different sources. We report an innovative enzymatic process which avoids the use of bulk aqueous, organic or inorganic solvent, and enables hydrolysis of hemicellulose directly from chemically untreated biomass, to low-weight, soluble oligoxylosaccharides in >70% yields.

Enzymes can be used in moist solid reaction mixtures to effectively depolymerize biomass to fermentable sugars.

No abstract

Converting hemicellulose into valuable platform chemicals is a key step in developing an integrated biorefinery. Traditionally, hemicellulose conversion into xylitol is done in two steps, using mineral acids and enzymes. Here we report a onepot hydrolysis−hydrogenation of hemicellulose to xylitol. We used a combination of either heteropoly acid or biomass-derived organic acid and Ru on carbon as catalyst. Silicotungstic acid, phosphotungstic acid, and lactic acid can be used efficiently in the hydrolysis part. Phosphomolybdic acid was not very active (<5% yield). The reduction can be done using either hydrogen gas or isopropanol as the reductant. The entire process runs in water, at relatively mild temperatures and pressures (140°C and 20 bar). Lactic acid or phosphotungstic acid combined with Ru/C gave around 70% xylitol yield in 3 h using H 2 as a reductant. With isopropanol as a reductant, phosphotungstic acid and Ru/C gave a high xylitol yield (82%), while only ∼20% xylitol yield was obtained with lactic acid.

Lignocellulosic material is an abundant renewable resource with the potential to replace petroleum as a feedstock for the production of fuels and chemicals. The large scale deployment of biomass saccharification is, however, hampered by the necessity to use aggressive reagents and conditions, formation of side-products, and the difficulty to reach elevated monosaccharide concentrations in the crude product. Herein we report the high efficacy of Reactive Aging (or Raging, a technique where enzymatic reaction mixtures, without any bulk aqueous or organic solvent, are treated to multiple cycles of milling and aging) for gram-scale saccharification of raw lignocellulosic biomass samples from different agricultural sources (corn stover, wheat straw, and sugarcane bagasse). The solvent-free enzymatic conversion of lignocellulosic biomass was found to proceed in excellent yields (ca. 90%) at protein loadings as low as 2% w/w, without the need for any prior chemical pre-treatment or high temperatures, to produce highly concentrated (molar) monosaccharides. This crude product of mechanoenzymatic depolymerization is non-toxic to bacteria and can be used as a carbon source for bacterial growth.