Synthesis of polystyrene brush on multiwalled carbon nanotubes treated with KMnO4 in the presence of a phase‐transfer catalyst

Multiwalled carbon nanotubes (MWNTs) were effectively functionalized with KMnO₄ in the presence of a phase‐transfer catalyst at room temperature. The hydroxyl functionalized MWNTs were reacted with a vinyl‐group carrying silane‐coupling agent and the terminal vinyl groups were used to fabricate polystyrene (PS) brushes by solution polymerization. Finally, PS‐encapsulated MWNTs were obtained. The synthesis results were verified from FT‐Raman, thermal gravimetric analysis, energy dispersive X‐ray analysis, and transmission electron microscope. PS‐encapsulated MWNTs had much improved dispersion stability in hydrophobic medium, toluene since grafted hydrophobic PS interacts with media and has improved compatibility. This functionalization technique would provide a facile route to prepare various polymer brushes on the surface of MWNTs to improve the dispersion of MWNTs for potential applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4413–4420, 2007     

"Nanoscale zippers" in Gd5(SixGe(1-x))4: symmetry and chemical influences on the nanoscale zipping action

One critical parameter influencing the structural nature of the phase transitions in magnetocaloric materials Gd5(SixGe(1-x))4 is the Si/Ge ratio (x/1-x), because transition temperatures and structures depend crucially on this value. In this study, single-crystal X-ray diffraction indicates that Si and Ge atoms are neither completely ordered nor randomly mixed among the three crystallographic sites for these elements in these structures. Ge atoms enrich the T sites linking the characteristic slabs in these structures, while Si atoms enrich the T sites within them. Decomposition of the total energy into site and bond energy terms provides a rationale for the observed distribution, which can be explained by symmetry and electronegativity arguments. For any composition in Gd5(SixGe(1-x))4, a structure map is presented that will allow for a rapid assessment of the specific structure type.     

Phase transformation driven by valence electron concentration: tuning interslab bond distances in Gd5GaxGe4-x

X-ray single crystal and powder diffraction studies on the Gd(5)Ga(x)()Ge(4)(-)(x)() system with 0 < or = x < or = 2.2 reveal dependence of interslab T-T dimer distances and crystal structures themselves on valence electron concentration (T is a mixture of Ga and Ge atoms). While the Gd(5)Ga(x)()Ge(4)(-)(x)() phases with 0 < or = x < or = 0.6 and valence electron concentration of 30.4-31 e(-)/formula crystallize with the Sm(5)Ge(4)-type structure, in which all interslab T-T dimers are broken (distances exceeding 3.4 A), the phases with 1 < or = x < or = 2.2 and valence electron concentration of 28.8-30 e-/formula adopt the Pu(5)Rh(4)- or Gd(5)Si(4)-type structures with T-T dimers between the slabs. An orthorhombic Pu(5)Rh(4)-type structure, which is intermediate between the Gd(5)Si(4)- and Sm(5)Ge(4)-type structures, has been identified for the Gd(5)GaGe(3) composition. Tight-binding linear-muffin-tin-orbital calculations show that substitution of three-valent Ga by four-valent Ge leads to larger population of the antibonding states within the dimers and, thus, to dimer stretching and eventually to dimer cleavage.     

Long-lived excited electronic states of the dichloroethylene cation isomers probed by charge exchange ionization

Charge exchange technique has been used to detect the presence of long-lived excited electronic states of trans-, cis-, and 1,1-C₂H₂Cl ₂ ^+· . The \(\tilde B\) states of the three cations which are formed by removal of an electron from an in-plane chlorine nonbonding orbital of the corresponding neutrals have been found to have long lifetimes (tens of microseconds or longer). Whether the à states formed by removal of an electron from the other in-plane chlorine nonbonding orbitals are long-lived also can not be determined by the present experiments. Cations in the excited electronic states above the \(\tilde B\) states were not detected because of their prompt dissociation following intramolecular relaxation or radiative decay.     

Multiquark picture for Σ (1620)

In this work we report on a new QCD sum rule analysis to predict masses of the excited baryon states (e.g. Σ (1620) and Λ (1405)) by using multiquark interpolating fields ((qˉq)(qqq)). For the Σ (1620) we consider the ˉKN, πΣ, and πΛ (I = 1) multiquark interpolating fields. The calculated mass from those multiquark states is about 1.592 GeV. For the Λ (1405) we first show the result using the π⁺Σ⁻+π⁰Σ⁰+π⁻Σ⁺ (I = 0) multiquark interpolating field, and compare the calculated mass to that of our previous result using the π⁰Σ⁰ multiquark state. We then show that the mass 1.405 GeV is well reproduced when using the ˉKN (I = 0) multiquark state. The uncertainties in our sum rules are also discussed. Received: 7 September 1998 / Revised version: 5 January 2000     

Expression, High Cell Density Culture and Purification of Recombinant EC-SOD in Escherichia coli

Superoxide dismutase (SOD) catalyzes the dismutation of the biologically toxic superoxide anion into oxygen and hydrogen peroxide and is deployed by the immune system to kill invading microorganisms. Extracellular SOD (EC-SOD) is a copper- and zinc-containing glycoprotein found predominantly in the soluble extracellular compartment that consists of ～30-kDa subunits. Here, we purified recombinant EC-SOD3 (rEC-SOD) from Escherichia coli BL21(DE3) expressing a pET-SOD3-1 construct. Cells were cultured by high-density fed-batch fermentation to a final OD₆₀₀ of 51.8, yielding a final dry cell weight of 17.6 g/L. rEC-SOD, which was expressed as an inclusion body, comprised 48.7% of total protein. rEC-SOD was refolded by a simple dilution refolding method and purified by cation-exchange and reverse-phase chromatography. The highly purified rEC-SOD thus obtained was a mixture of monomers and dimers, both of which were active. The molecular weights of monomeric and dimeric rEC-SOD were 25,255 and 50,514 Da, respectively. The purified rEC-SOD had 4.3 EU/mg of endotoxin and the solubility of rEC-SOD was more than 80% between pH 7 and 10. In 2 L of fed-batch fermentation, 60 mg of EC-SOD (99.9% purity) could be produced and total activity was 330.24 U. The process established in this report, involving high-cell-density fermentation, simple dilution refolding, and purification with ion-exchange and reverse-phase chromatography, represents a commercially viable process for producing rEC-SOD.     

Implication of phosphorylation of the myosin II regulatory light chain in insulin-stimulated GLUT4 translocation in 3T3-F442A adipocytes

In adipocytes, insulin stimulates glucose transport primarily by promoting the translocation of GLUT4 to the plasma membrane. Requirements for Ca(2+)/calmodulin during insulin-stimulated GLUT4 translocation have been demonstrated; however, the mechanism of action of Ca(2+) in this process is unknown. Recently, myosin II, whose function in non-muscle cells is primarily regulated by phosphorylation of its regulatory light chain by the Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK), was implicated in insulin-stimulated GLUT4 translocation. The present studies in 3T3-F442A adipocytes demonstrate the novel finding that insulin significantly increases phosphorylation of the myosin II RLC in a Ca(2+)-dependent manner. In addition, ML-7, a selective inhibitor of MLCK, as well as inhibitors of myosin II, such as blebbistatin and 2,3-butanedione monoxime, block insulin-stimulated GLUT4 translocation and subsequent glucose transport. Our studies suggest that MLCK may be a regulatory target of Ca(2+)/calmodulin and may play an important role in insulin-stimulated glucose transport in adipocytes.     

Chromatographic biopanning for the selection of peptides with high specificity to Pb from phage displayed peptide library

Toxic heavy metal pollution is a global problem occurring in air, soil as well as water. There is a need for a more cost effective, renewable remediation technique, but most importantly, for a recovery method that is selective for one specific metal of concern. Phage display technology has been used as a powerful tool in the discovery of peptides capable of exhibiting specific affinity to various metals or metal ions. However, traditional phage display is mainly conducted in batch mode, resulting in only one equilibrium state hence low-efficiency selection. It is also unable to monitor the selection process in real time mode. In this study, phage display technique was incorporated with chromatography procedure with the use of a monolithic column, facilitating multiple phage-binding equilibrium states and online monitoring of the selection process in search of affinity peptides to Pb²⁺. In total, 17 candidate peptides were found and their specificity toward Pb²⁺ was further investigated with bead-based enzyme immunoassay (EIA). A highly specific Pb²⁺ binding peptide ThrAsnThrLeuSerAsnAsn (TNTLSNN) was obtained. Based on our knowledge, this is the first report on a new chromatographic biopanning method coupled with monolithic column for the selection of metal ion specific binding peptides. It is expected that this monolith-based chromatographic biopanning will provide a promising approach for a high throughput screening of affinity peptides cognitive of a wide range of target species.     

Performance of ionic liquid as catalyst in the copolymerization of phenyl glycidyl ether with carbon dioxide

Summary Selective ammoxidation of ethylene over Co-ZSM-5 prepared by aqueous and solid-state ion exchange has been studied. The catalyst prepared using solid-state exchange showed higher activity and selectivity to acetonitrile. Catalysts tested in the ammoxidation of ethylene were previously characterized by chemical analysis, XRD, N₂-BET measurements and FTIR. TPD of ammonia and FTIR of pyridine used as probe molecule showed that solid-state ion exchange of H-ZSM-5 with cobalt generates new Lewis acid sites which seem to play a role in the ammoxidation reaction.