Application of degradation kinetics to the rheology of poly(hydroxyalkanoates)

The time‐dependent rheological behavior of a series of 3‐hydroxybuytrate‐based semicrystalline copolymers is employed to determine the expected rheological curves that would be generated in the absence of any polymer degradation. Both dynamic frequency sweep and shear rate sweep experiments were analyzed. A model for the degradation kinetics, coupled with standard rheological relationships, was employed to extrapolate the measured sweeps to predicted curves at time zero, prior to degradation. The model is broadly applicable over a wide range of frequencies or shear rates, and generates a single degradation rate constant k for each polymer studied. A similar, although ad hoc, procedure was applied to the dynamic storage and loss moduli. The model provides a method for determining the rheological behavior of degrading polymers over a time interval, typically found in processing applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1794–1802, 2006     

一种危险分析软件的设计与实现

危险分析是一个复杂的系统工程,单凭手工完成是难以想象的。本文系统地介绍了系统安全性分析中的危险分析及几种危险分析方法,并提出了一种计算机辅助危险分析的软件设计,最后指出了目前关于危险分析计算机化尚存在的问题,为今后的继续研究提出了新的思路。     

Improvement of the production of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate‐co‐4‐hydroxybutyrate) terpolyester by manipulating the culture condition

BACKGROUND: The aim of this work is to enhance the production of terpolyester poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate‐co‐4‐hydroxybutyrate) (P(3HB‐co‐3HV‐co‐4HB)) produced by a locally isolated bacterium, Cupriavidus sp. USMAA2‐4. The monomer composition was varied by supplementing different carbon precursors and by manipulating the culture condition through one‐stage cultivation. The effect of C/N ratio and different concentrations of carbon source and precursors were investigated in order to produce higher content of this terpolyester. Although research on this biodegradable polyester is abundant, studies on terpolyester P(3HB‐co‐3HV‐co‐4HB) are still limited. RESULTS: Supplementation of oleic acid in accumulation medium increased the bacterial growth and polyhydroxyalkanoate (PHA) accumulation. It was also shown that medium consisting of assorted carbon precursors at C/N 20 gave relatively high dry cell weight and P(3HB‐co‐3HV‐co‐4HB) content. Various compositions of terpolyester were obtained when the concentration of oleic acid and 4HB precursors were manipulated. The combination of oleic acid with γ‐butyrolactone and 1‐pentanol was found to be the best combination to produce high PHA content (81 wt%). The composition of monomer in P(3HB‐co‐3HV‐co‐4HB) was produced in the range 8–13 mol% for 3HV and 9–24 mol% for 4HB, respectively. CONCLUSIONS: The production of P(3HB‐co‐3HV‐co‐4HB) in shake‐flasks successfully produced 81 wt% of PHA content. This manipulated culture condition can be used at larger scale to provide modeling for the production of terpolyester in a bioreactor. Copyright © 2012 Society of Chemical Industry     

电离辐射与淋巴细胞

早期的临床工作是了解淋巴细胞的辐射剂量与效应关系,作为初期最敏感的指标之一。对原子弹受害者的淋巴细胞也进行了远期效应的观察。实验室工作方面研究了淋巴细胞的活力、死亡率,玫瑰花结、细胞膜和DNA等分子的变化。染色体畸变,微核率及其相互关系的研讨也引起人们重视。 应用PHA、ConA、PWM、LPS分别激活淋巴细胞的各个亚群,研究其辐射效应。有关PHA激活的T淋巴细胞的辐射效应研究得较多。作者察觉PWM和ConA激活的淋巴细胞对辐射敏感,均减弱了辅助B淋巴细胞转化的作用,PHA激活的淋巴细胞受影响较轻,LPS激活的淋巴细胞变化最小。 单克隆抗体技术研究淋巴细胞亚群的进展为进一步研究淋巴细胞的辐射效应提供条件,可以了解辐射影响免疫功能的主要环节。 有的作者研究了各种病人的淋巴细胞的辐射敏感性,以了解免疫方面存在的缺陷,还可作为制定辐射治疗某些白血病方案的依据。     

PMMA‐multigraft copolymers derived from linseed oil,soybean oil,and linoleic acid: Protein adsorption and bacterial adherence

Synthesis of Poly(methyl methacrylate), PMMA‐multigraft copolymers derived from linseed oil, soybean oil, and linoleic acid PMMA‐g‐polymeric oil/oily acid‐g‐poly(3‐hydroxy alkanoate) (PHA), and their protein adsorption and bacterial adherence have been described. Polymeric oil/oily acid peroxides [polymeric soybean oil peroxide (PSB), polymeric linseed oil peroxide (PLO), and polymeric linoleic acid peroxide (PLina)] initiated the copolymerization of MMA and unsaturated PHA‐soya to yield PMMA–PLO–PHA, PMMA–PSB–PHA, and PMMA–PLina–PHA multigraft copolymers. PMMA–PLina–PHA multigraft copolymers were completely soluble while PMMA–PSB–PHA and PMMA–PLO–PHA multigraft copolymers were partially crosslinked. Crosslinked parts of the PLO‐ and PSB‐multigraft copolymers were isolated by the sol gel analysis and characterized by swelling measurements in CHCl₃. Soluble part of the PLO‐ and PSB‐multigraft copolymers and completely soluble PLina‐multigraft copolymers were obtained and characterized by spectroscopic, thermal, gel permeation chromatography (GPC), and scanning electron microscopy (SEM) techniques. In the mechanical properties of the PHA–PLina–PMMA, the elongation at break is reduced up to ～ 9%, more or less preserving the high stress values at its break point (48%) when compared to PLina‐g‐PMMA. The solvent casting film surfaces were studied by means of adsorption of blood proteins and bacterial adhesion. Insertion of the PHA into the multigraft copolymers caused the dramatic increase in bacterial adhesion on the polymer surfaces. PHA insertion into the graft copolymers also increased the protein adsorption. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Inhibitors of Polyhydroxyalkanoate (PHA) Synthases: Synthesis,Molecular Docking,and Implications

Polyhydroxyalkanoate (PHA) synthases (PhaCs) catalyze the formation of biodegradable PHAs that are considered to be ideal alternatives to non‐biodegradable synthetic plastics. However, study of PhaCs has been challenging because the rate of PHA chain elongation is much faster than that of initiation. This difficulty, along with lack of a crystal structure, has become the main hurdle to understanding and engineering PhaCs for economical PHA production. Here we report the synthesis of two carbadethia CoA analogues—sT‐CH₂‐CoA ( 26 a ) and sTet‐CH₂‐CoA ( 26 b )—as well as sT‐aldehyde (saturated trimer aldehyde, 29 ), as new PhaC inhibitors. Study of these analogues with PhaEC_Av revealed that 26 a / b and 29 are competitive and mixed inhibitors, respectively. Both the CoA moiety and extension of PHA chain will increase binding affinity; this is consistent with our docking study. Estimation of the K_ic values of 26 a and 26 b predicts that a CoA analogue incorporating an octameric hydroxybutanoate (HB) chain might facilitate the formation of a kinetically well‐behaved synthase.     

Improved polyhydroxybutyrate (PHB) production in transgenic tobacco by enhancing translation efficiency of bacterial PHB biosynthetic genes

Polyhydroxybutyrate [P(3HB)] was produced in the transgenic tobacco harboring the genes encoding acetoacetyl-CoA reductase (PhaB) and polyhydroxyalkanoate synthase (PhaC) from Ralstonia eutropha (Cupriavidus necator) with optimized codon usage for expression in tobacco. P(3HB) contents in the transformants (0.2mg/g dry cell weight in average) harboring the codon-optimized phaB gene was twofold higher than the control transformants harboring the wild-type phaB gene. The immunodetection revealed an increased production of PhaB in leaves, indicating that the enhanced expression of PhaB was effective to increase P(3HB) production in tobacco. In contrast, codon-optimization of the phaC gene exhibited no apparent effect on P(3HB) production. This result suggests that the efficiency of PhaB-catalyzed reaction contributed to the flux toward P(3HB) biosynthesis in tobacco leaves.     

硼酸铝纳米晶须增强聚羟基脂肪酸酯的研究

为了提高生物降解材料聚羟基脂肪酸酯(PHA)的机械性能,利用具有高强度的硼酸铝纳米晶须作为增强体,制备成复合材料。采用溶胶凝胶法制备出直径为20~50 nm,长度约为1 mm的Al_(18)B_4O_(33)纳米晶须。纳米晶须增强了PHA复合材料的机械性能,实验结果表明:在添加量为0.4%时达到最大抗拉强度为38.5 MPa,增大了109%;抗屈服强度提高到26.2 MPa,提高了将近三倍;断裂伸长率提高了24.5%;复合材料的杨氏模量最大为7.6 MPa,提高了四倍多。说明Al_(18)B_4O_(33)纳米晶须的添加既可以改善PHA的韧性又提高的材料的刚性。另外,断裂面表明Al_(18)B_4O_(33)纳米晶须和PHA有较好的结合力。复合材料中PHA主要是保护Al_(18)B_4O_(33)纳米晶须不与外界直接接触,固定Al_(18)B_4O_(33)纳米晶须的位置,当材料受到外力时将载荷传递和分散给Al_(18)B_4O_(33)纳米晶须,而Al_(18)B_4O_(33)纳米晶须承受主要的力,从而提高了材料的性能。     

用KOH提取重组大肠杆菌中的PHA

用碱消化法从重组大肠杆菌中提取了PHA. 研究了碱液浓度、温度、消化时间及消化过程液固比等参数对产品PHA质量的影响. 提出了二段消化工艺,提高了PHA的产品纯度,所得PHA产品纯度为98.3%,同时较大幅度地降低了PHA的提取成本.     

Simultaneous biohydrogen (H2) and bioplastic (poly-β-hydroxybutyrate-PHB) productions under dark,photo, and subsequent dark and photo fermentation utilizing various wastes

The present study is focused on bio hydrogen (H₂) and bioplastic (i.e., poly-β-hydroxybutyrate; PHB) productions utilizing various wastes under dark fermentation, photo fermentation and subsequent dark-photo fermentation. Potential bio H₂ and PHB producing microbes were enriched and isolated. The effects of substrate (rice husk hydrolysate, rice straw hydrolysate, dairy industry wastewater, and rice mill wastewater) concentration (10–100%) and pH (5.5–8.0) were examined in the batch mode under the dark and photo fermentation conditions. Using 100% rice straw hydrolysate at pH 7, the maximum bio H₂ (1.53 ± 0.04 mol H₂/mol glucose) and PHB (9.8 ± 0.14 g/L) were produced under dark fermentation condition by Bacillus cereus. In the subsequent dark-photo fermentation, the highest amounts of bio H₂ and PHB were recorded utilizing 100% rice straw hydrolysate (1.82 ± 0.01 mol H₂/mol glucose and 19.15 ± 0.25 g/L PHB) at a pH of 7.0 using Bacillus cereus (KR809374) and Rhodopseudomonas rutila. The subsequent dark-photo fermentative bio H₂ and PHB productions obtained using renewable biomass (i.e., rice husk hydrolysate and rice straw hydrolysate) can be considered with respect to the sustainable management of global energy sources and environmental issues.