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.