木质纤维素酶解糖化*

纤维素水解转化为可发酵糖工艺是纤维素乙醇炼制过程中至关重要的环节。酶法水解工艺具有条件温和、副产物少、环境友好等特点,因而受到广泛重视。目前许多学者已针对如何提高木质纤维素酶解效率、降低纤维素酶成本等问题,开展了多种化学、生物技术及工艺耦合的研究。本文综述了近几年木质纤维素酶解领域取得的最新工艺进展和理论研究成果,对原料预处理、多酶复配优化、酶脱附与重复利用、工艺耦合、高固液比反应等方面的研究情况进行了总结,同时展望了木质纤维素酶解工艺的未来发展方向。     

Synthesis,Characterizations, and Structure of Group 4 Metallocene Complexes of Some Difunctional Ligands Containing Oxygen and Sulfur Donors

Reactions of CH₃OCH₂CH₂OH, PhOCH₂CH₂OH, o-CH₃OC₆H₄CH₂OH, or PhSCH₂CH₂OH with Cp₂ZrCl₂ in the presence of NEt₃ gave series monomeric complexes Cp₂ZrClX (X = OCH₂CH₂OCH₃ ( 1 ), OCH₂CH₂OPh ( 2 ), o-OCH₂C₆H₄OCH₃ ( 3 ) or OCH₂CH₂SPh ( 4 )). In a reaction of Cp₂TiCl₂ with PhSCH₂CH₂OH in the presence of NEt₃, the complex Cp₂TiCl(OCH₂CH₂SPh) ( 5 ) was obtained. These complexes were characterized by the ¹H and ¹³C NMR, and the chemical shifts of the Cp rings for complexes 1–4 are nearly identical, despite differences in ligands for an indication of similar structures of these complexes around the metal center. Complex 4 crystallizes into the monoclinic P2₁/c space group with a = 13.806(3) Å, b = 16.394(3) Å, c = 7.838(2) Å, β = 100.85(3)° Z = 4, R = 0.029, R_w = 0.044, and Gof = 1.19. The molecular structure of complex 4 shows that the 2-(phenylthio)ethoxide bonds to the Zr metal center through the alkoxide donor leaving the thioether donor free from coordination.     

Crystal structure and IR spectrum of 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1)

1-O-α- -Glucopyranosyl- -mannitol–ethanol (2/1), (C₁₂H₂₄O₁₁)₂–C₂H₅OH, crystallizes in the monoclinic space group P2₁ with unit cell dimensions a=11.4230(8) Å, b=9.525(4) Å, c=15.854(2) Å, β=102.751(7)° and V=1682.4(7) ų, Z=2, D_x=1.45 Mg m⁻³, λ (Mo-K_α)=0.71069 Å, μ=0.128 mm⁻¹, F(000)=788 and T=293(2) K. The structure was solved by direct methods and refined by least-squares calculations on F² to R₁=0.0371[I>2σ(I)], and 0.0930 (all data, 3542 independent reflections, R_int=0.021). There are two molecules of glucopyranosylmannitol (GPM) and one ethanol molecule in the asymmetric unit, and the glucopyranosyl ring adopts a chair conformation in both GPM molecules. Bond lengths and angles accord well with the mean values of related structures. The conformation along the mannitol side chain for one of the GPM molecules was the same as for the known polymorphs of -mannitol, while the conformation of the other molecule was different, indicating different conformational arrangements in the terminal carbon atoms of the mannitol side chains of the two GPM molecules. The structure in 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1) is held together by a very complex hydrogen bonding system, which consists of an infinte chain propagating along the b-axis and a discontinuous chain, which binds the ethanol molecule to the structure. The FTIR spectra for anhydrous GPM, GPM dihydrate and GPM–ethanol (2/1) were recorded. Both IR and X-ray results indicate the extensive hydrogen bonding in crystalline state.     

Unexpected crystallization and X-ray crystal structure of racemic 1-phenyl-2-(4-pyridyl)ethanol intermediate

We have isolated, by crystallization, the intermediate, 1-phenyl-2-(4-pyridyl)ethanol, from the condensation reaction of 4-methylpyridine with benzaldehyde in which the aim was to obtain the model compound 4-styrylpyridine in absence of a condensing agent. Single crystal X-ray analysis shows the formation of an intermolecular hydrogen bond O–H···N between the nitrogen atom of a pyridine group and the oxygen atom of the OH of the neighboring molecule, which helps to stabilize the crystal structure. Crystal structure determination clearly revealed that the solid is chiral and racemic, as expected. The title compound crystallizes in an orthorhombic system with a space group Pna2₁ with two pairs of R and S enantiomers in each crystal cell (a = 15.591(1) Å, b = 12.691(1) Å, and c = 5.589(1) Å). Spectroscopic NMR data gave evidence that the isolated compound is actually the alcohol just before the dehydration process that yields the double bond of the 4-styrylpyridine.     

甘氨酸在DMF/水和乙醇/水混合溶剂中的焓对相互作用

利用LKB2277生物活性检测仪对298.15K时甘;氨酸在纯水,DBF/水和乙醇/水混合溶剂DBF(或乙醇的质量分数为0.05~0.45,以10%递增)中的稀释焓进行了测定,并利用维里展开式法关联得到焓对相互作用系数值.结果表明,焓对相互作用系数h~2与溶剂的结构性质密切相关.在DBF/水混合物溶剂中,h~2随DBF含量的增加而变得更负;而在乙醇/水混合溶剂中,h~2与乙醇含量近似呈抛物线型关系,在乙醇质量分数为0.25时h~2达到一个极小值。     

Fermentation performance characteristics of a prehydrolyzate-adapted xylose-fermenting recombinant Zymomonas in batch and continuous fermentations

Long-term (149 d) continuous fermentation was used to adapt a xylose-fermenting recombinant Zymomonas mobilis, strain 39676:pZB 4L, to conditioned (overlimed) dilute-acid yellow poplar hemicellulose hydrolyzate (“prehydrolyzate”). An “adapted” variant was isolated from a chemostat operating at a dilution rate of 0.03/h with a 50% (v/v) prehydrolyzate, corn steep liquor, and sugar-supplemented medium, at pH 5.75. The level of xylose and glucose in the medium was kept constant at 4% (w/v) and 0.8% (w/v), respectively. These sugar concentrations reflect the composition of the undiluted hardwood prehydrolyzate. The level of conditioned hardwood prehydrolyzate added to the medium was increased in 5% increments startingata level of 10%. At the upper level of 50% prehydrolyzate, the acetic-acid concentration was about 0.75% (w/v). The adapted variant exhibited improved xylose-fermentation performance in a pure-sugar, synthetic hardwood prehydrolyzate medium containing 4% xylose (w/v), 0.8% (w/v) glucose, and acetic acid in the range 0.4–1.0% (w/v). The ethanol yield was 0.48–0.50 g/g; equivalent to a sugar-to-ethanol conversion efficiency of 94–96% of theoretical maximum. The maximum growth yield and maintenance energy coefficients were 0.033 g dry cell mass (DCM)/g sugars and 0.41 g sugars/g DCM/h, respectively. The results confirm that long-term continuous adaptation is a useful technique for effecting strain improvement with respect to the fermentation of recalcitrant feedstocks.     

己酸铁对乙醇稀溶液的络合萃取

乙醇是重要的化工产品,一般通过发酵法和合成法生产,其在发酵液及合成液中的浓度较低［１～３］．一些工业过程产生的大量废水中往往含有微量乙醇,需要进行脱除或回收．传统上,乙醇的分离和回收多采用蒸馏法［１,４］．但稀溶液蒸馏需要消耗大量的能量．对于含微量醇...     

Fermentation kinetics of ethanol production from glucose and xylose by recombinant Saccharomyces 1400(pLNH33)

Fermentation kinetics of ethanol production from glucose, xylose, and their mixtures using a recombinant Saccharomyces 1400 (pLNH33) are reported. Single-substrate kinetics indicate that the specific growth rate of the yeast and the specific ethanol productivity on glucose as the substrate was greater than on xylose as a substrate. Ethanol yields from glucose and xylose fermentation were typically 95 and 80% of the theoretical yield, respectively. The effect of ethanol inhibition is more pronounced for xylose fermentation than for glucose fermentation. Studies on glucose-xylose mixtures indicate that the recombinant yeast co-ferments glucose and xylose. Fermentation of a 52.8 g/L glucose and 56.3 g/L xylose mixture gave an ethanol concentration of 47.9 g/L after 36 h. Based on a theoretical yield of 0.51 g ethanol/g sugars, the ethanol yield from this experiment (for data up to 24 h) was calculated to be 0.46 g ethanol/g sugar or 90% of the theoretical yield. The specific growth rate of the yeast on glucose-xylose mixtures was found to lie between the specific growth rate on glucose and the specific growth rate on xylose. Kinetic studies were used to develop a fermentation model incorporating the effects of substrate inhibition, product inhibition, and inoculum size. Good agreements were obtained between model predictions and experimental data from batch fermentation of glucose, xylose, and their mixtures.     

Comparative energetics of glucose and xylose metabolism in recombinant Zymomonas mobilis

Recombinant Zymomonas mobilis CP4:pZB5 was grown with pH control in batch and continuous modes with either glucose or xylose as the sole carbon and energy source. In batch cultures in which the ratio of the final cell mass concentration to the amount of sugar in the medium was constant (i.e., under conditions that promote “coupled growth”), maximum specific rates of glucose and xylose consumption were 8.5 and 2.1 g/(g of cell…h), respectively; maximum specific rates of ethanol production for glucose and xylose were 4.1 and 1.0 g/(g of cell…h), respectively; and average growth yields from glucose and xylose were 0.055 and 0.034 g of dry cell mass (DCM)/g of sugar respectively. The corresponding value of Y_ATP for glucose and xylose was 9.9 and 5.1 g of DCM/mol of ATP, respectively. Y_ATP for the wild-type culture CP4 with glucose was 10.4g of DCM/mol of ATP. For single substratechem ostat cultures in which the growth rate was varied as the dilution rate (D), the maximum or “true” growth yield (max Y_a/s) was calculated from Pirt plots as the inverse of the slope of the best-fit linear regression for the specific sugar utilization rate as a function of D, and the “maintenance coefficient” (m) was determined as the y-axis intercept. For xylose, values of max Y _s/s and m were 0.0417g of DCM/g of xylose (Y_ATP=6.25) and 0.04g of, xylose/(g of cell…h), respectively. However, with glucose there was an observed deviation from linearity, and the data in the Pirt plot was best fit with a second-order polynomial in D. At D>0.1/h, Y_ATP=8.71 and m=2.05g of glu/(g of cell…h) whereas at D<0.1/h, Y_ATP=4.9g of DCM/mol of ATP and m=0.04g of glu/(g of cell…h). This observation provides evidence to question the validity of the unstructured growth model and the assumption that Pirt's maintenance coefficient is a constant that is in dependent of the growth rate. Collectively, these observations with individual sugars and the values assign ed to various growth and fermentation parameters will be useful in the development of models to predict the behavior of rec Zm in mixed substrate fermentations of the type associated with biomass-to-ethanol processes.     

Coproduction of ethanol and glycerol

Ethanol and glycerol are both metabolic products of yeasts. There are occasions when coproduction of both is considered desirable in industrial operations. In this article, we describe the potential of integrating the two processes. A LORRE Y8 yeast culture isolated from molasses is capable of efficient glycerol production from glucose, and a yeast Culture 1400 is an excellent producer of ethanol. By controlling the process conditions, the ratio of ethanol and glycerol production can be varied.