Nitrogen-Doped Graphene with Pyridinic Dominance as a Highly Active and Stable Electrocatalyst for Oxygen Reduction

The nitrogen-doped graphene (NG) with dominance of the pyridinic-N configuration is synthesized via a straightforward process including chemical vapor deposition (CVD) growth of graphene and postdoping with a solid nitrogen precursor of graphitic C₃N₄ at elevated temperature. The NG fabricated from CVD-grown graphene contains a high N content up to 6.5 at. % when postdoped at 800 °C but maintains high crystalline quality of graphene. The obtained NG exhibits high activity, long-standing stability, and outstanding crossover resistance for electrocatalysis of oxygen reduction reaction (ORR) in alkaline medium. The NG treated at 800 °C shows the best ORR performance. Further study of the dependence of ORR activity on different N functional groups in these metal-free NG electrodes provides deeper insights into the origin of ORR activity. Our results reveal that the pyridinic-N tends to be the most active N functional group to facilitate ORR at low overpotential via a four-electron pathway

Responses of Murine and Human Macrophages to Leptospiral Infection: A Study Using Comparative Array Analysis

<div><p>Leptospirosis is a re-emerging tropical infectious disease caused by pathogenic <i>Leptospira</i> spp. The different host innate immune responses are partially related to the different severities of leptospirosis. In this study, we employed transcriptomics and cytokine arrays to comparatively calculate the responses of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HBMs) to leptospiral infection. We uncovered a series of different expression profiles of these two immune cells. The percentages of regulated genes in several biological processes of MPMs, such as antigen processing and presentation, membrane potential regulation, and the innate immune response, etc., were much greater than those of HBMs (>2-fold). In MPMs and HBMs, the caspase-8 and Fas-associated protein with death domain (FADD)-like apoptosis regulator genes were significantly up-regulated, which supported previous results that the caspase-8 and caspase-3 pathways play an important role in macrophage apoptosis during leptospiral infection. In addition, the key component of the complement pathway, C3, was only up-regulated in MPMs. Furthermore, several cytokines, e.g. interleukin 10 (IL-10) and tumor necrosis factor alpha (TNF-alpha), were differentially expressed at both mRNA and protein levels in MPMs and HBMs. Some of the differential expressions were proved to be pathogenic <i>Leptospira</i>-specific regulations at mRNA level or protein level. Though it is still unclear why some animals are resistant and others are susceptible to leptospiral infection, this comparative study based on transcriptomics and cytokine arrays partially uncovered the differences of murine resistance and human susceptibility to leptospirosis. Taken together, these findings will facilitate further molecular studies on the innate immune response to leptospiral infection.</p></div

The gene regulations of ECM components, synthesis enzymes, and degrading enzymes in murine peritoneal macrophages (MPMs) after 4-h <i>L. interrogans</i> infection.

<p>The gene regulations of ECM components, synthesis enzymes, and degrading enzymes in murine peritoneal macrophages (MPMs) after 4-h <i>L. interrogans</i> infection.</p

Comparison of cytokine regulation folds of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HBMs) at mRNA and protein levels.

<p>Hierarchical cluster analyses of the average microarray data and the average cytokine array data of 62 cytokines of murine peritoneal macrophages (MPMs) and 60 cytokines of human peripheral blood monocytes (HBMs) were performed using Cluster3.0 software and visualized by using TreeView software. MPMs and HBMs were infected by <i>L. interrogans</i> for 4-h or infected by <i>L. biflexa</i> for 4-h, respectively.</p

Comparisons of major regulated inflammatory cytokines and receptors in murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HBMs) infected by <i>L. interrogans</i>.

<p>MPM-1 h, -2 h, and -4 h show the gene expression fold changes of the leptospiral-infected MPMs at 1-, 2-, and 4-h, respectively; HBM-1 h, -2 h, and -4 h show the gene expression fold changes (Ln(microarray folds)) of the leptospiral-infected HBMs at 1-, 2-, and 4-h, respectively. Average fold changes are listed in the affiliated table below.</p

Comparisons of major regulated chemokines and receptors in murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HBMs) infected by <i>L. interrogans</i>.

<p>MPM-1 h, -2 h, and -4 h show the gene expression fold changes of the leptospiral-infected MPMs at 1-, 2-, and 4-h, respectively; HBM-1 h, -2 h, and -4 h show the gene expression fold changes (Ln(microarray folds)) of the leptospiral-infected HBMs at 1-, 2-, and 4-h, respectively. Average fold changes are listed in the affiliated table below.</p

The differences of up-regulated and down-regulated signaling pathways of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HBMs) infected by <i>L. interrogans</i>.

<p>The persistent regulations during the 4-h leptospiral infection, not the instantaneous regulations at the 1-h and the 2-h time points, were included in the statistical analysis using CapitalBio MAS (Molecule Annotation System version 3.0) software. The values above the bars show the percentages of total regulations, including up-regulations and down-regulations, of each KEGG signaling pathway.</p

The gene regulations of ECM components, synthesis enzymes, and degrading enzymes in human peripheral blood monocytes (HBMs) after 4-h <i>L. interrogans</i> infection.

<p>The gene regulations of ECM components, synthesis enzymes, and degrading enzymes in human peripheral blood monocytes (HBMs) after 4-h <i>L. interrogans</i> infection.</p

Toughening Graphene by Integrating Carbon Nanotubes

Perfect graphene is believed to be one of the strongest materials, yet its resistance to fracture is much less impressive. The modest fracture toughness is thought to be related to the general brittle nature in the fracture process of graphene and its two-dimensional (2D) analogous. The brittleness also makes it extremely difficult to assess mechanical properties of 2D materials. The introduction of carbon nanotubes (CNTs) into bulk materials has proven to be a widely accepted method for toughening and strengthening materials. To date, such toughening effect of CNTs on 2D materials is largely unknown. A unique material, rebar graphene, has been synthesized that consists of CNTs embedded in graphene. In this study, by implementing a “dry” transfer technique, the freely suspended rebar graphene was systematically tested under uniaxial tension mode inside a scanning electron microscope. Our combined experiments and molecular dynamics simulations confirm that the embedded CNTs divert and bridge the propagating crack and provide a toughening mechanism for the material. Our work identifies a promising extrinsic toughening strategy for 2D materials and provides mechanistic insights into the fracture process of graphene hybrid material

Toughening Graphene by Integrating Carbon Nanotubes

Perfect graphene is believed to be one of the strongest materials, yet its resistance to fracture is much less impressive. The modest fracture toughness is thought to be related to the general brittle nature in the fracture process of graphene and its two-dimensional (2D) analogous. The brittleness also makes it extremely difficult to assess mechanical properties of 2D materials. The introduction of carbon nanotubes (CNTs) into bulk materials has proven to be a widely accepted method for toughening and strengthening materials. To date, such toughening effect of CNTs on 2D materials is largely unknown. A unique material, rebar graphene, has been synthesized that consists of CNTs embedded in graphene. In this study, by implementing a “dry” transfer technique, the freely suspended rebar graphene was systematically tested under uniaxial tension mode inside a scanning electron microscope. Our combined experiments and molecular dynamics simulations confirm that the embedded CNTs divert and bridge the propagating crack and provide a toughening mechanism for the material. Our work identifies a promising extrinsic toughening strategy for 2D materials and provides mechanistic insights into the fracture process of graphene hybrid material