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Liu Shengrong,Wu Qingping,Zhang Jumei,Mo Shuping 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.6
ε-Poly-L-lysine (ε-PL), produced by Streptomyces or Kitasatospora strains, is a homo-poly-amino acid of Llysine,which is used as a safe food preservative. In this study, the effects of L-lysine and its isomer, D-lysine, on ε-PL biosynthesis and their metabolites by the ε-PLproducing strain Streptomyces ahygroscopicus GIM8 were determined. The results indicated that L-lysine added into the fermentation medium in the production phase mainly served as a precursor for ε-PL biosynthesis during the flask culture phase, leading to greater ε-PL production. At an optimum level of 3 mM L-lysine, a ε-PL yield of 1.16 g/L was attained, with a 41.4% increment relative to the control of 0.78 g/L. Regarding D-lysine, the production of ε-PL increased by increasing its concentrations up to 6 mM in the initial fermentation medium. Interestingly, ε-PL production (1.20 g/L) with the addition of 3 mM D-lysine into the initial fermentation medium in flasks was higher than that of the initial addition of 3 mM L-lysine (1.06 g/L). The mechanism by which D-lysine improves ε-PL biosynthesis involves its utilization that leads to greater biomass. After S. ahygroscopicus GIM8 was cultivated in the defined medium with L-lysine, several key metabolites, including 5-aminovalerate, pipecolate, and L-2-aminoadipate formed in the cells, whereas only L-2-aminoadipate was observed after D-lysine metabolism. This result indicates that Llysine and D-lysine undergo different metabolic pathways in the cells. Undoubtedly, the results of this study are expected to aid the understanding of ε-PL biosynthesis and serve as reference for the formulation of an alternative approach to improve ε-PL productivity using L-lysine as an additional substrate in the fermentation medium.
Real-Time Visualization of Diffusion-Controlled Nanowire Growth in Solution
Ye, Shengrong,Chen, Zuofeng,Ha, Yoon-Cheol,Wiley, Benjamin J. American Chemical Society 2014 NANO LETTERS Vol.14 No.8
<P>This Letter shows that copper nanowires grow through the diffusion-controlled reduction of dihydroxycopper(I), Cu(OH)<SUB>2</SUB><SUP>–</SUP>. A combination of potentiostatic coulometry, UV–visible spectroscopy, and thermodynamic calculations was used to determine the species adding to growing Cu nanowires is Cu(OH)<SUB>2</SUB><SUP>–</SUP>. Cyclic voltammetry was then used to measure the diffusion coefficient of Cu(OH)<SUB>2</SUB><SUP>–</SUP> in the reaction solution. Given the diameter of a Cu nanowire and the diffusion coefficient of Cu(OH)<SUB>2</SUB><SUP>–</SUP>, we calculated the dependence of the diffusion-limited growth rate on the concentration of copper ions to be 26 nm s<SUP>–1</SUP> mM<SUP>–1</SUP>. Independent measurements of the nanowire growth rate with dark-field optical microscopy yielded 24 nm s<SUP>–1</SUP> mM<SUP>–1</SUP> for the growth rate dependence on the concentration of copper. Dependence of the nanowire growth rate on temperature yielded a low activation energy of 11.5 kJ mol<SUP>–1</SUP>, consistent with diffusion-limited growth.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-8/nl501762v/production/images/medium/nl-2014-01762v_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl501762v'>ACS Electronic Supporting Info</A></P>
Chen, Zuofeng,Ye, Shengrong,Wilson, Adria R.,Ha, Yoon-Cheol,Wiley, Benjamin J. The Royal Society of Chemistry 2014 Energy & environmental science Vol.7 No.4
<P>This article reports the fabrication of copper–platinum core–shell nanowires by electroplating platinum onto copper nanowires, and the first demonstration of their use as a transparent, conducting electrocatalyst for the hydrogen evolution reaction (HER). Cu–Pt core–shell nanowire networks exhibit mass activities up to 8 times higher than carbon-supported Pt nanoparticles for the HER. Electroplating minimizes galvanic replacement, allowing the copper nanowires to retain their conductivity, and eliminating the need for a conductive substrate or overcoat. Cu–Pt core–shell nanowire networks can thus replace more expensive transparent electrodes made from indium tin oxide (ITO) in photoelectrolysis cells and dye sensitized solar cells. Unlike ITO, Cu–Pt core–shell nanowire films retain their conductivity after bending, retain their transmittance during electrochemical reduction, and have consistently high transmittance (>80%) across a wide optical window (300–1800 nm).</P> <P>Graphic Abstract</P><P>This article reports the fabrication of copper–platinum core–shell nanowires by electroplating platinum onto copper nanowires, and the first demonstration of their use as a transparent, conducting electrocatalyst for the hydrogen evolution reaction (HER). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4ee00211c'> </P>
Comparing Two Approaches of Analyzing Mixed Finite Volume Methods
Chou, So-Hsiang,Tang, Shengrong 한국산업정보응용수학회 2001 한국산업정보응용수학회 Vol.5 No.1
Given the anisotropic Poisson equation -∇ · K∇p = f, one can convert it into a system of two first order PDEs: the Darcy law for the flux u = -K∇p and conservation of mass ∇· u = f. A very natural mixed finite volume method for this system is to seek the pressure in the nonconforming P1 space and the Darcy velocity in the lowest order Raviart-Thomas space. The equations for these variables are obtained by integrating the two first order systems over the triangular volumes. In this paper we show that such a method is really a standard finite element method with local recovery of the flux in disguise. As a consequence, we compare two approaches in analyzing finite volume methods (FVM) and shed light on the proper way of analyzing non co-volume type of FVM. Numerical results for Dirichlet and Neumann problems are included.
Scavenging Effects of Tea Catechins on Superoxide and Hydroxy Radical
Park Jaeil,Liuji Chen,Xianqiang Yang,Shengrong Shen,Yuefei Wang,Ryu Beung Ho 한국생명과학회 2002 Journal of Life Science Vol.12 No.2
Tea catechins, the most important compounds in tea polyphenols, can efficiently scavenge superoxide anion free-radical (O₂-·), hydroxyl radical. (·OH) The mechanism of scavenging active oxygen free radicals was investigated by ESR spin trapping technique and Chemiluminescence. Results showed that various tea catechins constitute an antioxidant cycle in accordance with the decreasing order of the first reductive potential, and produce the effect of cooperative strength each other. Esterificated catechins could scavenge active oxygen free radicals more effectively than the non-esterificated ones. When ·OH and O₂-·- were scavenged by (-)-epigallocatechin gallate [(-)- EGCG], the stoichiometric factors were 6, and the rate constants of scavenging reaction reached 7.71x10(6) and 3.52x10(11) L mmol-¹ S-¹, respectively. In the mean time, tea catechins could scavenge superoxide anion fiee radical (O₂-·) and hydroxyl radical (·OH) in a dose dependent manner. But at higher concentration or pH value, tea catechins can induce the prooxidant.
Yang, Xiaojuan,Wu, Qingping,Zhang, Jumei,Guo, Weipeng,Mo, Shuping,Liu, Shengrong 한국식품과학회 2016 Food Science and Biotechnology Vol.25 No.4
This study aimed to classify a collection of Enterobacter sakazakii (E. sakazakii) strains previously identified from powdered infant formula (PIF) to species level by recN gene sequencing and biochemical testing to determine the distribution of Cronobacter species in China and investigate the strain diversity by cellular fatty acid (CFA) analysis. Of 24 E. sakazakii isolates, 23 were identified as C. sakazakii and one was C. malonaticus. The 23 C. sakazakii isolates showed the same CFA profiles. The C. malonaticus isolate was discriminated from the C. sakazakii isolates by the significant difference in the amounts of $C_{12:0}$, $C_{14:0}$, and $C_{17:0\;cyclo}$ acids. These results showed that C. sakazakii and C. malonaticus were the common Cronobacter species distributed in PIF in China and that the isolates of the two species exhibited different CFA profiles. These findings are of value for epidemiological investigations and provide an alternative method for confirming various Cronobacter spp.