Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O 2 /butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene. For low O 2 /butane ratios, a high selectivity to alkenes was achieved for periods as long as 100 hours. This process is mildly catalyzed by ketonic C=O groups and occurs via a combination of parallel and sequential oxidation steps. A small amount of phosphorus greatly improved the selectivity by suppressing the combustion of hydrocarbons.Transition metal oxides have been widely used as catalysts for the conversion of butane to C 4 alkenes, important industrial precursors for producing synthetic rubbers, plastics, and a number of industrially important chemicals. Despite a great deal of research, alkene selectivity in the current butane-to-butadiene process is severely limited (1). One important reason is that the unsaturated products are much more readily oxidized to CO 2 than is the starting alkane. The chemical complexity of polyvalent metal oxides, although found to be necessary for catalytic activity, impedes satisfactory selectivity through isolation of active sites (2-6). For this reason, the origin of the catalytic activity is debated, and there is as yet no generally accepted picture of the reaction mechanism (7, 8).Carbon materials have been reported to catalyze the oxidative dehydrogenation (ODH) of an aromatic molecule, ethylbenzene. However, conventional carbons, in particular activated carbon, underwent unavoidable deactivations due to coking or combustion (9-12). Recently, it was shown that only wellnanostructured carbons are stable and coke-free catalysts for styrene synthesis (12, 13). Activation of C-H bonds in the ethyl group is considered to be coordinated by the ketonic carbonyl (C=O) group. Ethylbenzene has an aromatic moiety that enables relatively facile activation. Here, we report on surfacemodified carbon nanotubes (CNTs) as a high-performance catalyst for the ODH of the much less active butane. Relative to metal-based catalysts, CNTs displayed an enhanced selectivity to C 4 alkenes, especially butadiene.We conducted the reaction at 400° or 450°C with an O 2 /butane ratio of 2.0. The product mixture contained only 1-butene, 2-butene, butadiene, CO 2 , CO, and residual reactants; the resulting carbon balance was 100 ± 3% ( fig. S1A) (14). In a blank experiment without catalyst, the alkene yield was as low as 0.9%. Over pristine CNTs, 88.9% of the converted butane was burnt, yielding 1.6% alkenes (Fig. 1A). Considering the intensive stability of CNTs in O 2 ( fig. S1B) (14), we conclude that the CO 2 during the reaction mainly originated from the oxidation of the hydrocarbon feedstock and not from burning of t...

Metabolomics is the comprehensive assessment of endogenous metabolites and attempts to systematically identify and quantify metabolites from a biological sample. Small-molecule metabolites have an important role in biological systems and represent attractive candidates to understand disease phenotypes. Metabolites represent a diverse group of low-molecular-weight structures including lipids, amino acids, peptides, nucleic acids, organic acids, vitamins, thiols and carbohydrates, which makes global analysis a difficult challenge. The recent rapid development of a range of analytical platforms, including GC, HPLC, UPLC, CE coupled to MS and NMR spectroscopy, could enable separation, detection, characterization and quantification of such metabolites and related metabolic pathways. Owing to the complexity of the metabolome and the diverse properties of metabolites, no single analytical platform can be applied to detect all metabolites in a biological sample. The combined use of modern instrumental analytical approaches has unravelled the ideal outcomes in metabolomics, and is beneficial to increase the coverage of detected metabolites that can not be achieved by single-analysis techniques. Integrated platforms have been frequently used to provide sensitive and reliable detection of thousands of metabolites in a biofluid sample. Continued development of these analytical platforms will accelerate widespread use and integration of metabolomics into systems biology. Here, the application of each hyphenated technique is discussed and its strengths and limitations are discussed with selected illustrative examples; furthermore, this review comprehensively highlights the role of integrated tools in metabolomic research.

A self-powered pressure-sensor matrix based on ZnS:Mn particles for more-secure signature collection is presented, by recording both handwritten signatures and the pressure applied by the signees. This large-area, flexible sensor matrix can map 2D pressure distributions in situ, either statically or dynamically, and the piezophotonic effect is proposed to initiate the mechanoluminescence process once a dynamic mechanical strain is applied.

The peroxisome proliferator-activated receptor subtype ␥ (PPAR␥) ligands, namely the synthetic insulin-sensitizing thiazolidinedione (TZD) compounds, have demonstrated great potential in the treatment of type II diabetes. However, their clinical applicability is limited by a common and serious side effect of edema. To address the mechanism of TZD-induced edema, we generated mice with collecting duct (CD)-specific disruption of the PPAR␥ gene. We found that mice with CD knockout of this receptor were resistant to the rosiglitazone-(RGZ) induced increases in body weight and plasma volume expansion found in control mice expressing PPAR␥ in the CD. RGZ reduced urinary sodium excretion in control and not in conditional knockout mice. Furthermore, RGZ stimulated sodium transport in primary cultures of CD cells expressing PPAR␥ and not in cells lacking this receptor. These findings demonstrate a PPAR␥-dependent pathway in regulation of sodium transport in the CD that underlies TZD-induced fluid retention.roziglitazone ͉ Cre recombinase ͉ Evans blue technique T hiazolidinediones (TZDs), synthetic insulin-sensitizing drugs that include troglitazone, pioglitazone, and rosiglitazone (RGZ), are highly effective in the treatment of type II diabetes. TZDs are believed to mediate their antidiabetic effect via activation of peroxisome proliferator-activated receptor ␥ (PPAR␥) (1). In addition to lowering blood glucose, these drugs also benefit cardiovascular parameters, such as blood pressure and endothelial function (2, 3). However, fluid retention, presented as rapid weight gain, and peripheral and pulmonary edema have emerged as the most common and serious side effects of TZDs (4-6). Global awareness of this side effect has increased as a result of the growing number of reported cases. In a recent issue of Circulation (7), the American Heart Association and American Diabetes Association jointly issued a Consensus Statement commenting on the safety of TZD as related to edema. The mechanisms of fluid retention in patients treated with TZDs are poorly understood and may involve a number of factors, including reduction of urinary sodium excretion (8), alteration of endothelial permeability (9), increased sympathetic nervous system activity (10), or altered interstitial ion transport (11). To evaluate the relative contributions of these individual mechanisms, tissue-or cell-type-specific approaches are needed in carefully designed studies.PPARs are a group of zinc finger-containing transcription factors, representing a family of the nuclear hormone receptor gene superfamily. To date, three subtypes of PPARs encoded by different genes have been described from several species: PPAR␣, -␤͞␦, and -␥ (12, 13). They share a high degree of similarity in their overall amino acid sequences, particularly in the DNA-binding domain (14). The three isoforms of the PPARs heterodimerize with retinoid X receptor, bind to the same peroxisome proliferatorresponsive element in the promoter regions of their target genes, and modulate gene transcripti...

The ability to specifically attach chemical probes to individual proteins represents a powerful approach to the study and manipulation of protein function in living cells. It provides a simple, robust and versatile approach to the imaging of fusion proteins in a wide range of experimental settings. However, a potential drawback of detection using chemical probes is the fluorescence background from unreacted or nonspecifically bound probes. In this report we present the design and application of novel fluorogenic probes for labeling SNAP-tag fusion proteins in living cells. SNAP-tag is an engineered variant of the human repair protein O6-alkylguanine-DNA alkyltransferase (hAGT) that covalently reacts with benzylguanine derivatives. Reporter groups attached to the benzyl moiety become covalently attached to the SNAP tag while the guanine acts as a leaving group. Incorporation of a quencher on the guanine group ensures that the benzylguanine probe becomes highly fluorescent only upon labeling of the SNAP-tag protein. We describe the use of intramolecularly quenched probes for wash-free labeling of cell surface-localized epidermal growth factor receptor (EGFR) fused to SNAP-tag and for direct quantification of SNAP-tagged β-tubulin in cell lysates. In addition, we have characterized a fast-labeling variant of SNAP-tag, termed SNAPf, which displays up to a tenfold increase in its reactivity towards benzylguanine substrates. The presented data demonstrate that the combination of SNAPf and the fluorogenic substrates greatly reduces the background fluorescence for labeling and imaging applications. This approach enables highly sensitive spatiotemporal investigation of protein dynamics in living cells.

Metal-free nanostructured elemental carbons and carbonbased composites (e.g. C 3 N 4 ) have proven to be attractive alternatives to conventional metal-based catalysts for several important reactions, such as dehydrogenation of aromatic hydrocarbons or alkanes, Friedel-Crafts Reaction.[1] Carbon as the catalytic substance has significant advantages over the conventional metal-supported systems owing to the unique controllability of both its surface acidity/basicity and pelectron density through surface functionalization. In a carbon material it is the short-and long-range ordering of atomic carbon that essentially determines the macroscopic properties (e.g. thermal and electronic conductivities, combustibility) and thus its long-term performance in any potential industrial process. However, the lack of basic knowledge on the nature of carbonmediated reactions remains the most critical restriction for the development of carbon-based catalysis. For oxidative dehydrogenation (ODH) reactions, surface quinone-type oxygen functional groups have been proposed as the active sites and the reaction has been assumed to proceed by a redox mechanism.[2, 3] However, no quantitative description of the elementary steps, or kinetic data can be derived from the literature. The few mechanistic studies reported were conducted either with remarkable secondary oxidation and deactivation [4] or over "impure" surfaces, for example, Pd-or Fe-coordinated polynaphthoquinone[2] or pre-coked metal phosphates or oxides.[5] More detailed and reliable information is expected to be obtained over a pure carbon surface in the kinetic reaction region. Most importantly, the Mars-van Krevelen model for redox reactions is widely accepted based on previous work on the ODH of ethylbenzene. [4, 5] However, this model is incorrect and without physical relevance.[6] Therefore there is an urgent need to describe the reaction pathway by a physically relevant model. Ordered nanocarbon is chemically homogeneous and thus could be seen as the most suitable platform for a mechanistic investigation. To date, all such investigations have been confined to pure or mostly sp 2 -hybridized carbons. [4, 7] In particular, conventional activated carbon which has long-range disorder and high porosity

A conventional affinity protein purification system often requires a separate protease to separate the target protein from the affinity tag. This paper describes a unique protein purification system in which the target protein is fused to the C-terminus of a modified protein splicing element (intein). A small affinity tag is inserted in a loop region of the endonuclease domain of the intein to allow affinity purification. Specific mutations at the C-terminal splice junction of the intein allow controllable C-terminal peptide bond cleavage. The cleavage is triggered by addition of thiols such as dithiothreitol or free cysteine, resulting in elution of the target protein while the affinity-tagged intein remains immobilized on the affinity column. This system eliminates the need for a separate protease and allows purification of a target protein without the N-terminal methionine. We have constructed general cloning vectors and demonstrated single-column purification of several proteins. In addition, we discuss several factors that may affect the C-terminal peptide bond cleavage activity.

The p70 S6 kinase is activated by diverse stimuli through a multisite phosphorylation directed at three separate domains as follows: a cluster of (Ser/Thr) Pro sites in an autoinhibitory segment in the noncatalytic carboxyl-terminal tail; Thr-252 in the activation loop of the catalytic domain; and Ser-394 and Thr-412 in a segment immediately carboxyl-terminal to the catalytic domain. Phosphorylation of Thr-252 in vitro by the enzyme phosphatidylinositol 3-phosphate-dependent kinase-1 or mutation of Thr-412 3 Glu has each been shown previously to engender some activation of the p70 S6 kinase, whereas both modifications together produce 20 -30-fold more activity than either alone. We employed phospho-specific anti-peptide antibodies to examine the relative phosphorylation at several of these sites in wild type and various p70 mutants, in serum-deprived cells, and in response to activators and inhibitors of p70 S6 kinase activity.Substantial phosphorylation of p70 Thr-252 and Ser-434 was present in serum-deprived cells, whereas Thr-412 and Thr-444/Ser-447 were essentially devoid of phospho-specific immunoreactivity. Activation of p70 by insulin was accompanied by a coordinate increase in phosphorylation at all sites examined, together with a slowing in mobility on SDS-PAGE of a portion of p70 polypeptides. Upon addition of rapamycin or wortmannin to insulin-treated cells, the decrease in activity of p70 was closely correlated with the disappearance of anti-Thr-412(P) immunoreactivity and the most slowly migrating p70 polypeptides, whereas considerable phosphorylation at Ser-434 and Thr-252 persisted after the disappearance of 40 S kinase activity. The central role of Thr-412 phosphorylation in the regulation of kinase activity was further demonstrated by the close correlation of the effects of various deletions and point mutations on p70 activity and Thr-412 phosphorylation.In conclusion, although p70 activity depends on a disinhibition from the carboxyl-terminal tail and the simultaneous phosphorylation at both Thr-252 and Thr-412, p70 activity in vivo is most closely related to the state of phosphorylation at Thr-412.The p70 S6 kinase, an enzyme critical for cell cycle progression through G 1 , was among the first insulin/mitogen-activated protein (Ser/Thr) kinases to be identified, purified, and molecularly cloned. The enzyme was shown early on to be regulated by insulin/mitogen-stimulated (Ser/Thr) phosphorylation, and along with the kinases now known as Rsk provided the first evidence that insulin/mitogen signal transduction involved the recruitment of multiple, independently regulated cascades of protein (Ser/Thr) kinases (reviewed in Ref. 1). Nevertheless, whereas the in vitro activation of Rsk kinases by mitogenactivated protein kinase-catalyzed phosphorylation was accomplished early on (2), in vitro activation of p70 S6 kinase has proved much more difficult to reconstruct. During activation in vivo, p70 is phosphorylated at 10 or more sites by an array of independently regulated protein kinases. Enumeratin...