BackgroundIonic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields. To improve process economics of pretreatment, higher biomass loading is desirable. The goal of this work is to establish, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yield.ResultsThe pretreated switchgrass/IL slurries show frequency dependent shear thinning behavior. The switchgrass/IL slurries show a crossover from viscous behavior at 3 wt% to elastic behavior at 10 wt%. The relative glucan content of the recovered solid samples is observed to decrease with increasing levels of lignin and hemicelluloses with increased biomass loading. The IL pretreatment led to a transformation of cellulose crystalline structure from I to II for 3, 10, 20 and 30 wt% samples, while a mostly amorphous structure was found for 40 and 50 wt% samples.ConclusionsIL pretreatment effectively reduced the biomass recalcitrance at loadings as high as 50 wt%. Increased shear viscosity and a transition from ‘fluid’ like to ‘solid’ like behavior was observed with increased biomass loading. At high biomass loadings shear stress produced shear thinning behavior and a reduction in viscosity by two orders of magnitude, thereby reducing the complex viscosity to values similar to lower loadings. The rheological properties and sugar yields indicate that 10 to 50 wt% may be a reasonable and desirable target for IL pretreatment under certain operating conditions.

SummarySoluble starch synthase (SSS) I was purified 361-fold from hand-diseacted endosperm tissue of inbred maize (Zea maya, cv. B73) to specific acUvitlse ranging between 5 and 9 t~mol min -1 mg -1. A key to this purification protocol was the Introduction of a size-exclusion chromatography step, a size-based fractionstion which provided abundant levels of deealted SSS forms I and II. The native molecular masses calculated for SSS forms I and II were 75.5 kDa and 180 kDa, raspoctlvely. SSSl was then further purified by hydrophobic interaction chromatography on Phenyl-Superose and by FPLC on Mono Q. Analysis of column peaks by SDS-PAGE and scanning densitometry revealed that a 76 kDa polypeptide is strongly correlated with SSSI activity. Antibodies were then generated ageinst a "/6 kl)a polypeptide extracted from starch granules. These antibodies, which were monospeciflc for the soluble 76 kDa polypeptide, neutralized greater than 90% of SSSI activity, and precipitated the 76 kDa protein. These results establish the 76 kDa protein as an SSSI in the B73 line of Inbred maize. An immunologically similar 76 kDa protein also appears to be tightly associated with the starch granule.

3-Methyladenine DNA glycosylase II (AlkA) is an enzyme that cleaves a wide range of damaged bases from DNA. The gas-phase thermochemical properties (tautomerism, acidity, and proton affinity) have been measured and calculated for a series of AlkA purine substrates (7-methyladenine, 7-methylguanine, 3-methyladenine, 3-methylguanine, purine, 6-chloropurine, xanthine) that have not been heretofore examined. The damaged nucleobases are found to be more acidic than the normal nucleobases adenine and guanine. Because of this increased acidity, the damaged bases would be expected to be more easily cleaved from DNA by AlkA (their conjugate bases should be better leaving groups). We find that the gas-phase acidity correlates to the AlkA excision rates, which lends support to an AlkA mechanism wherein the enzyme provides a nonspecific active site, and nucleobase cleavage is dependent on the intrinsic N-glycosidic bond stability.

The first isolable, photoswitchable N-heterocyclic carbene was synthesized and found to undergo reversible electrocyclic isomerization upon successive exposure to UV and visible radiation. The UV-induced ring closure afforded substantial changes to the electronic structure of the dithienylethene-based NHC, as evidenced by changes in the corresponding UV/Vis absorption and (13)C NMR spectra. Likewise, molecular orbital calculations revealed diminished electron density at the carbene nucleus upon photocyclization, consistent with the enhanced electrophilicity displayed by the ring-closed form. The photoswitchable NHC was successfully switched between its ring-opened and ring-closed states with high fidelity over multiple cycles. Furthermore, the ring-closed isomer was found to undergo facile N-H bond activation, allowing for the controlled capture and release of ammonia upon cycling between its isomeric states.