Covalent polymeric modification of graphene nanosheets via surface‐initiated single‐electron‐transfer living radical polymerization

Graphene nanosheets offer intriguing electronic, thermal, and mechanical properties and are expected to find a variety of applications in high‐performance nanocomposite materials. Dispersal of graphene nanosheets in polymer hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia. Here, an efficient strategy is presented for growing polymers directly from the surface of reduced graphene oxide (GO). This method involves the covalent attachment of Br‐containing initiating groups onto the surface of hydrazine hydrate reduced GO via a diazonium addition and the succeeding linking of poly(tert‐butyl methacrylate) (PtBMA) chains (71.7 wt % grafting efficiency) via surface‐initiated single‐electron‐transfer living radical polymerization (SET‐LRP) to graphene nanosheets. The resulting materials were characterized by using a range of testing techniques and it was proved that polymer chains were successfully introduced to the surface of exfoliated graphene sheets. After grafting with PtBMA, the modified graphene sheets still maintained the separated single layers, and the dispersibility was improved significantly. The method is believed to offer possibilities for optimizing the processing properties and interface structure of graphene–polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Analytical progress for protein glycosylation in China

Glycosylation plays a key role in controlling various cellular processes; in diseases modifications of the glycans also highlight its clinical importance. However, ^glycosylation analysis remains a difficult task. In recent years, ^advances in sample preparation and mass spectrometry have greatly facilitated the analysis of glycoproteins. This review mainly covers five aspects of the improvements and advances on the research of protein glycosylation in China: 1) identification of glycoproteins, ^2) identification of glycosylation sites, ^3) new methods developed for glycopeptides enrichment, ^4) characterization of glycans, ^and 5) functional studies of protein glycosylation.     

Immobilization of enzyme on detonation nanodiamond for highly efficient proteolysis

Immobilization of enzyme on detonation nanodiamond (dND, 3-10 nm) and its application for efficient proteolysis have been demonstrated. By evaluation of the Michaelis constant (K_m) and maximum velocity (V_max) of immobilized enzyme, its activity was not impaired significantly by immobilization. And enzyme immobilized on dNDs exhibited much better thermal and chemical stabilities than its free counterpart and maintained high activity even after 10 times reuse. The efficient proteolysis by trypsin immobilized on dNDs (dND-trypsin) is demonstrated with the digestion of myoglobin (or other model protein) in a short time (5 min). Large numbers of identified peptides obtained by dNDs-trypsin enable a higher degree of sequence coverage and more positive identification of proteins than those obtained by in-solution digestion and the commercial immobilized trypsin beads, respectively. Moreover, immobilization of peptide-N-glycosidase F (PNGase F) on dNDs was realized and resulted in faster sequential glycosidase digestion of glycopeptides in less than 10 min.     

Ion-neutral complexes resulting from dissociative protonation: Fragmentation of <Emphasis Type="Italic">α</Emphasis>-furanylmethyl benzyl ethers and 4-<Emphasis Type="Italic">N,N</Emphasis>-dimethylbenzyl benzyl ethers

The loss of CH₂O during mass spectrometry in two series of α-aromaticmethyl benzyl ether compounds, namely, α-furanylmethyl p-substituted-benzyl ethers and 4-N,N-dimethylbenzyl p-substituted-benzyl ethers, is particularly interesting. The fragmentation mechanism is proposed to involve an ion-neutral complex-mediated pathway. Specifically, before the formation of an ion-neutral intermediate, the proton is transferred from the thermodynamically favored site at either the ether oxygen atom or the nitrogen atom to the dissociative protonation site at C_α position in either the furyl group or the 4-N,N-dimethylphenyl group. This transfer has been clarified via computational studies and isotopically labeled experiments. In addition, the decomposition of the intermediate may be affected by the substituent groups on the phenyl ring. This conclusion is indicated by the reasonably good correlation between ln[([M + H − CH₂O]⁺)/([M + H − CH₂O − C₆H₅R]⁺)] and the substituent constants.     

Specific enrichment methods for glycoproteome research

Glycosylation is, by far, one of the most common and important post-translational modifications and becomes a target for proteomic research. A key challenge in glycoproteome research is the development of fast and effective enrichment strategies for high-throughput glycosylation analysis. Different kinds of glycan-capturing anchors have been developed and successfully applied to glyco-specific enrichment in large-scale glycosylation identification in the past few years. In this paper, we highlight several examples on various types of enrichment methods that have been utilized to specifically capture glycopeptides/glycoproteins for subsequent mass spectrometric analysis.     

Interfacial organic synthesis in a simple droplet-based microfluidic system

A spherical liquid-liquid interface can be obtained by dispersing one liquid phase into another to form droplets, which will facilitate the two-phase reactions between the immiscible participating fluids. The phase transfer catalysts assembled at the droplet "wall" catalyze the reactions between the aqueous and organic phases. The study illustrates an interfacial synthetic approach which is ideal for the biphasic reaction by taking advantage of the droplet-based microdevice. The improved reaction efficiency can be attributed to the high surface-to-volume ratio and internal flow circulation in the droplets.     

A three-dimensionally adjustable amperometric detector for microchip electrophoretic measurement of nitroaromatic pollutants

A microchip capillary electrophoresis (CE)–amperometric detection (AD) system has been fabricated by integrating a two-dimensionally adjustable CE microchip and an amperometric detection cell containing a one-dimensionally adjustable disc detection electrode in a Plexiglas holder. It facilitates the precise three-dimensional alignment between the channel outlet and the detection electrode without a complicated three-dimensional manipulator. The performance of this unique system was demonstrated by separating four nitroaromatic pollutants (nitrobenzene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, and p-nitrobenzene). Factors influencing their separation and detection processes were examined and optimised. The four analytes have been well-separated within 120 s in a 75 cm long separation channel at a separation voltage of +2000 V using an electrophoretic separation medium containing 15 mM borax and 15 mM sodium dodecyl sulfate (pH 9.2). Highly linear response is obtained for the four analytes over the range of 0–5 ppm with the detection limits ranging from 12 to 52 ppb. The present system demonstrated long-term stability and reproducibility with relative standard deviations of less than 5% for the peak current (n = 9). The new approach for the microchannel–electrode alignment should find a wide range of applications in other microfluidic analysis systems.     

Rapid separation and determination of carbamate insecticides using isocratic elution pressurized capillary electrochromatography

An isocratic elution pressurized CEC (pCEC) system was used to separate and determine ten carbamate insecticides. It was found that introduction of the electrical field, supplementary pressure, and SDS in the proposed method greatly improved the speed, column efficiency, selectivity, and repeatability for separation and determination of carbamates. On a capillary column of 75 microm ID packed with 3 microm octadecyl silica, baseline separation and detection of ten analytes was performed by using a mobile phase consisting of 30% v/v ACN and 70% v/v of 5 mmol/L ammonium acetate (pH 6.5) containing 1 mmol/L SDS and 0.01% triethylamine (TEA). Under the optimum conditions ten carbamate insecticides could be completely separated within 20 min. For the real vegetable samples, an SPE procedure for the cleanup of matrices was carried out prior to pCEC analysis. The detection limits of 0.05-1.6 mg/kg for ten carbamates and mean recoveries of 51.3-109.2% for eight kinds of vegetable samples at different concentrations of carbamates with RSD less than 11.4% were obtained, respectively. The proposed method has been proved to be effective in the rapid analysis of carbamate residues in vegetables.     

Zeolite nanoparticle modified microchip reactor for efficient protein digestion

An enzymatic microreactor has been fabricated based on the poly(methyl methacrylate) (PMMA) microchchip surface-modified with zeolite nanoparticles. By introducing the silanol functional groups, the surface of PMMA microchannel has been successfully modified with silicalite-1 nanoparticle for the first time due to its large external surface area and high dispersibility in solutions. Trypsin can be stably immobilized in the microchannel to form a bioreactor using silica sol-gel matrix. The immobilization of enzyme can be realized with a stable gel network through a silicon-oxygen-silicon bridge via tethering to those silanol groups, which has been investigated by scanning electron microscopy and microchip capillary electrophoresis with laser-induced fluorescence detection. The maximum proteolytic rate constant of the immobilized trypsin is measured to be about 6.6 mM s(-1). Using matrix assisted laser desorption and ionization time-of-flight mass spectrometry, the proposed microreactor provides an efficient digestion of cytochrome c and bovine serum albumin at a fast flow rate of 4.0 microL min(-1), which affords a very short reaction time of less than 5 s.