Nuclear magnetic resonance studies of acetic acid inhibition of rec Zymomonas mobilis ZM4(pZB5)

The fermentation characteristics and effects of lignocelulosic toxic compounds on recombinant Zymomonas mobilis ZM4(pZB5), which is capable of converting both glucose and xylose to ethanol, and its parental strain, ZM4, were characterized using ¹³C and ³¹P nuclear magnetic resonance (NMR) in vivo. From the ³¹P NMR data, the levels of nucleoside triphosphates (NTP) of ZM(pZB5) using xylose were lower than those of glucose. This can be related to the intrinsically slower assimilation and/or metabolism of xylose compared to glucose and is evidence of a less energized state of ZM4(pZB5) cells during xylose fermentation. Acetic acid was shown to be strongly inhibitory to ZM4(pZB5) on xylose medium, with xylose utilization being completely inhibited at pH 5.0 or lower in the presence of 10.9 g/L of sodium acetate. From the ³¹P NMR results, the addition of sodium acetate caused decreased NTP and sugar phosphates, together with acidification of the cytoplasm. Intracellular deenergization and acidification appear to be the major mechanisms by which acetic acid exerts its toxic effects on this recombinant strain.     

Reply to “Comment on ‘Calculation of Two-center Nuclear Attraction Integrals over Integer and Noninteger N-slater-type Orbitals in Nonlined-up Coordinate Systems” ’

The comments of Guseinov on our recent paper (T. Özdo?an, S. Gümü? and M. Kara, J. Math. Chem. 33 (2003) 181) are critically analyzed. It is proved that the expansion formula for the product of two normalized associated Legendre functions and the expressions for two-center nuclear attraction integrals over Slater type orbitals have been obtained independently, by the use of basic mathematical rules.     

氨基酸的光化学诱导动态核极化

维生素B₂与氨基酸和氨基酸衍生物水溶液体系的光化学诱导动态核极化(photo chemically induced dynamic nuclear polarization, CIDNP)研究表明,在维生素B₂作为光敏化剂的体系中,N-乙酰-L-酪氨酸和N_α-乙酰-L-组氨酸显示很强的极化信号,而其它氨基酸和衍生物则未观察到。     

H-MCM-22沸石分子筛中Brnsted/Lewis酸协同效应的~1H 和~(27)Al双量子魔角旋转固体核磁共振研究

采用各种固体核磁共振 (NMR) 技术详细研究了 H-MCM-22 分子筛中 Brnsted/Lewis 酸的协同效应. 二维 1H 双量子魔角旋转 (DQ-MAS) NMR 结果表明, 在脱铝 H-MCM-22 分子筛中 Brnsted 酸位 (骨架桥式羟基) 和 Lewis 酸位 (非骨架铝羟基) 之间是空间邻近的, 暗示着可能存在 B/L 酸协同效应. 二维 27Al DQ-MAS NMR 结果揭示了各种铝物种之间的空间邻近性, 表明 B/L 酸协同效应优先发生在 H-MCM-22 分子筛超笼中的骨架 T6 位铝和非骨架铝物种之间. 2-13C-丙酮探针分子实验发现, 因 B/L 酸协同效应而导致脱铝 H-MCM-22 分子筛酸性明显增强, 氘代吡啶探针分子实验也证实在 H-MCM-22 分子筛的超笼中发生了 B/L 酸协同效应. 上述结果将有助于我们理解在脱铝 H-MCM-22 分子筛上发生的多相催化机理.     

刺楸中新七糖皂苷的结构解析

从刺楸Kalopanax septemlobus(Thunb．)Koidz．树皮乙醇提取物中分离得到一种七糖三萜皂苷(1),其分子结构经化学方法和波谱分析(IR,ESI-MS,^1H NMR,^13C NMR,^1H-^1H COSY,^1H-^1H TOCSY,HMQC,HMBC)鉴定为3-O-β-D-吡喃木糖(1→4)-β-D-吡喃木糖(1→3)-α-L-吡喃鼠李糖(1→2)-α-L-吡喃阿拉伯糖常春藤皂苷配基28-O-α-L-吡喃鼠李糖(1→4)-β-D-吡喃葡萄糖(1→6)-β-D-吡喃葡萄糖酯苷,命名为刺皂苷Ⅰ(septemlosideⅠ)。     

核磁共振波谱在分析化学领域应用的新进展

发展检测物质的化学组成、结构及其变化的新方法、新技术是分析化学的核心科学问题之一. 波谱分析(光谱、质谱及核磁共振)是分析化学中常用的主要仪器分析手段. 核磁共振能在液态、固态和气态条件下提供复杂体系中分子组成、原子分辨的三维结构、相互作用和动态过程等丰富信息, 在生物分析中发挥着越来越重要的作用. 本文将综合阐述核磁共振技术在生物大分子体系、复杂体系以及与其他分析手段联用的进展情况.     

Construction of recombinant Escherichia coli strais for production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate)

Plastic wastes constitute a worldwide environmental problem, and the demand for biodegradable plastics has become high. One of the most important characteristics of microbial polyesters is that they are thermoplastic with environmentally degradable properties. In this study, pUC 19/PHA was cloned and transformed into three different Escherichia coli strains. Among the three strains that were successfully expressed in the production of polyhydroxyalkanoates (PHA), E. coli HMS174 had the highest yield in the production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[HB-HV]). The cell dry weight and PHA content of recombinant HMS174 reached as high as 10.27 g/L and 43% (w/w), respectively, in fed-batch fermentor culture. The copolymer of PHA, P(HB-HV), was found in the cells, and the biopolymers accumulated were identified and analyzed by gas chromatography, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. We demonstrated clearly that the E. coli host for PHA production has to be carefully selected to obtain a high yield. The results obtained indicated that a superior E. coli with high PHA production can be constructed with a desirable ratio of P(HB-HV), which has potential applications in industry and medicine.     

A Carbene‐Rich but Carbonyl‐Poor [Ir6(IMe)8(CO)2H14]2+ Polyhydride Cluster as a Deactivation Product from Catalytic Glycerol Dehydrogenation

The title cluster, a deactivation product in the catalytic dehydrogenation of glycerol, was characterized by XRD, DFT calculations, HRMS, FTIR spectroscopy, and NMR spectroscopy. Experimental/computational studies located the 14 H ligands, and all ¹H and ¹³C{¹H} NMR resonances were assigned. The structure contains an unprecedented Ir₆H₁₄ core with two CO and eight IMe ligands.