纤维型植物南荻的生物学及其应用研究进展

南荻(Triarrhena lutarioriparia L.Liu)是我国特有高产纤维素型多年生草本植物,其独特的生态适应性、广泛的用途及其生产开发潜力已引起相关行业的高度关注。概述了南荻的资源分布、生物学特性、繁育栽培及应用的研究现状,并对其纤维素资源的应用进行了展望。     

Characterization of cellulosic fibers and fabrics by sorption/desorption

Three cellulosic substrates: lyocell (CLY), viscose (CV), and modal (CMD) in the form of fibers and fabrics were subjected to wet/dry or wash/dry treatments. The accessibility of untreated and treated substrates to water and iodine was investigated using dynamic water-vapor sorption, moisture retention, and iodine sorption methods, to study the influence of treatments on sorption-desorption hysteresis, fraction of moisture sorbed as a monomolecular layer, water retention, and iodine sorption. It was found that the sorption properties of untreated and treated substrates differed with sorbate type as well as substrate type and form.     

Role of N- and C-terminal domains and non-homologous region in co-refolding of Thermotoga maritima β-glucosidase

Thermotoga maritima β-glucosidase consists of three structural regions with 721 amino acids: the N-terminal domain, middle non-homologous region and a C-terminal domain. To investigate the role of these domains in the co-refolding of two fragments into catalytically active form, five sites coding the amino acid residue at 244, 331 in the N-terminal domain, 403 in the non-homologous region, 476 and 521 in the C-terminal domain were selected to split the gene. All the 10 resultant individual fragments were obtained as insoluble inclusion bodies and found to be catalytically inactive. However, the catalytic activity was recovered when the two fragments derived from N-terminal and C-terminal peptides were co-refolded together. It is quite interesting to find that not only the complement polypeptides such as N476/477C but also the truncated combination (N476/522C, amino acid residues from 477 to 521 is truncated) and overlapped combination (N476/245C and N476/404C, amino acid residues from 245 to 476 and from 404 to 476 are overlapped) also gave catalytically active enzymes. Our results showed that folding motifs consisted of the complete N-terminal domain play an important role in the co-refolding of the polypeptides into the catalytically active form.     

DNase I footprinting of the nucleosome in whole nuclei

DNase I was used to footprint the 147 bp DNA fragment of the nucleosome in whole chicken erythrocyte nuclei. It was found that the higher-order structure imposes an additional protection on nucleosomes at sites close to the entry and exit points of the linker DNA, around the dyad axis (site S 0). The observed protection is extended up to 20 bp on either side of S 0. It is partial (∼50%) and most probably reflects a full protection of different regions in alternatively oriented nucleosomes. These are the same regions which interact with linker histones. The results strongly support the findings by simulation of DNase I digests of unlabelled oligonucleosome fragments in the 30 nm fibre that in all nucleosomes sites S −5 to S −3 and S +3 to S +5 ara on the outside of the fibre exposed to DNase I.     

Advanced water splitting for green hydrogen gas production through complete oxidation of starch by in vitro metabolic engineering

Starch is a natural energy storage compound and is hypothesized to be a high-energy density chemical compound or solar fuel. In contrast to industrial hydrolysis of starch to glucose, an alternative ATP-free phosphorylation of starch was designed to generate cost-effective glucose 6-phosphate by using five thermophilic enzymes (i.e., isoamylase, alpha-glucan phosphorylase, 4-α-glucanotransferase, phosphoglucomutase, and polyphosphate glucokinase). This enzymatic phosphorolysis is energetically advantageous because the energy of α-1,4-glycosidic bonds among anhydroglucose units is conserved in the form of phosphorylated glucose. Furthermore, we demonstrated an in vitro 17-thermophilic enzyme pathway that can convert all glucose units of starch, regardless of branched and linear contents, with water to hydrogen at a theoretic yield (i.e., 12 H₂ per glucose), three times of the theoretical yield from dark microbial fermentation. The use of a biomimetic electron transport chain enabled to achieve a maximum volumetric productivity of 90.2 mmol of H₂/L/h at 20 g/L starch. The complete oxidation of starch to hydrogen by this in vitro synthetic (enzymatic) biosystem suggests that starch as a natural solar fuel becomes a high-density hydrogen storage compound with a gravimetric density of more than 14% H₂-based mass and an electricity density of more than 3000 W h/kg of starch.     

Structural model studies for the high-valent intermediate Q of methane monooxygenase from broken-symmetry density functional calculations

Mössbauer isomer shift parameters have been obtained for both density functional theory (DFT) OPBE and OLYP functionals by linear regressions between the measured isomer shifts and calculated electron densities at Fe nuclei for a number of Fe^2+,2.5+ and Fe^{2.5+,3+,3.5+,4+} complexes grouped separately. The calculated isomer shifts and quadrupole splittings on the sample Fe complexes from OPBE and OLYP functionals are similar to those of PW91 calculations [J. Comput. Chem. 27 (2006) 1292], however the fit parameters from the linear regressions differ between PW91 and OPBE, OLYP. Four models for the active site structure of intermediate Q of the hydroxylase component of soluble methane monooxygenase (MMOH) have been studied, using three DFT functionals OPBE, OLYP, and PW91, incorporated with broken-symmetry methodology and the conductor-like screening (COSMO) solvation model. The calculated properties, including optimized geometries, electronic energies, pK_a’s, Fe net spin populations, and Mössbauer isomer shifts and quadrupole splittings, have been reported and compared with available experimental values. The high-spin antiferromagnetically (AF) coupled Fe⁴⁺ sites are correctly predicted by OPBE and OLYP methods for all active site models. PW91 potential overestimates the Fe-ligand covalencies for some of the models because of spin crossover. Our calculations and data analysis support the structure (our current model II shown in Fig. 8) proposed by Friesner and Lippard’s group [J. Am. Chem. Soc. 123 (2001) 3836-3837], which contains an Fe⁴⁺(μ-O)₂Fe⁴⁺ center, one axial water which also H-bonds to both side chains of Glu243 and Glu114, and one bidentate carboxylate group from the side chain of Glu144, which is likely to represent the active site of MMOH-Q. A new model structure (model IV shown in Fig. 9), which has a terminal hydroxo and a protonated His147 which is dissociated from a nearby Fe, is more asymmetric in its Fe(μ-O)₂Fe diamond core, and is another very good candidate for intermediate Q.     

Efficient Solar‐Driven Water Oxidation over Perovskite‐Type BaNbO2N Photoanodes Absorbing Visible Light up to 740 nm

Photoelectrochemical water splitting using semiconductors absorbing a wide range of visible light is a potentially attractive means of harvesting large portions of the solar spectrum. However, this is also very challenging because narrowing the semiconductor band gap lowers the driving force for photoreactions. Herein, a highly active perovskite BaNbO₂N exhibiting photoexcitation up to 740 nm for water oxidation is reported. The synthesis route, consisting of moderate nitridation and subsequent annealing in inert Ar flow, enhances the crystallinity of the BaNbO₂N surface without inducing the reduction of the Nb species. As a result, a particulate BaNbO₂N photoanode exhibits a photocurrent of 5.2 mA cm^?2 at 1.23 V_RHE under simulated solar irradiation, which is the highest yet reported for an oxynitride responsive at wavelengths above 600 nm. Suppressing the reduction of B‐site cations during the synthesis of perovskite AB(O,N)₃, which otherwise results in surface defects or impurities, is critical for achieving high water oxidation activity.