Cost effective hydrogen evolution reaction (HER) catalyst without using precious metallic elements is a crucial demand for environment-benign energy production. Molybdenum sulfide is one of the promising candidates for such purpose, particularly in acidic condition, but its catalytic performance is inherently limited by the sparse catalytic edge sites and poor electrical conductivity. We report synthesis and HER catalysis of hybrid catalysts composed of amorphous molybdenum sulfide (MoSx) layer directly bound at vertical N-doped carbon nanotube (NCNT) forest surface. Owing to the high wettability of N-doped graphitic surface and electrostatic attraction between thiomolybdate precursor anion and N-doped sites, ∼2 nm scale thick amorphous MoSx layers are specifically deposited at NCNT surface under low-temperature wet chemical process. The synergistic effect from the dense catalytic sites at amorphous MoSx surface and fluent charge transport along NCNT forest attains the excellent HER catalysis with onset overpotential as low as ∼75 mV and small potential of 110 mV for 10 mA/cm(2) current density, which is the highest HER activity of molybdenum sulfide-based catalyst ever reported thus far.

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real-life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.

In the present investigation, we studied the modulating effects of several tea catechins and bioflavonoids on DNA methylation catalyzed by prokaryotic SssI DNA methyltransferase (DNMT) and human DNMT1. We found that each of the tea polyphenols [catechin, epicatechin, and (Ϫ)-epigallocatechin-3-O-gallate (EGCG)] and bioflavonoids (quercetin, fisetin, and myricetin) inhibited SssI DNMT-and DNMT1-mediated DNA methylation in a concentration-dependent manner. The IC 50 values for catechin, epicatechin, and various flavonoids ranged from 1.0 to 8.4 M, but EGCG was a more potent inhibitor, with IC 50 values ranging from 0.21 to 0.47 M. When epicatechin was used as a model inhibitor, kinetic analyses showed that this catecholcontaining dietary polyphenol inhibited enzymatic DNA methylation in vitro largely by increasing the formation of S-adenosyl-L-homocysteine (a potent noncompetitive inhibitor of DNMTs) during the catechol-O-methyltransferase-mediated Omethylation of this dietary catechol. In comparison, the strong inhibitory effect of EGCG on DNMT-mediated DNA methylation was independent of its own methylation and was largely due to its direct inhibition of the DNMTs. This inhibition is strongly enhanced by Mg 2ϩ . Computational modeling studies showed that the gallic acid moiety of EGCG plays a crucial role in its high-affinity, direct inhibitory interaction with the catalytic site of the human DNMT1, and its binding with the enzyme is stabilized by Mg 2ϩ . The modeling data on the precise molecular mode of EGCG's inhibitory interaction with human DNMT1 agrees perfectly with our experimental finding.DNA methylation at the C5-position of cytosine within the CpG dinucleotides represents an important mechanism for epigenetic control of gene expression and the maintenance of genome integrity. Although DNA hypermethylation is associated with inactivation of genes, global genomic hypomethylation is often associated with the induction of chromosomal instability (Chen et al., 1998). A number of recent studies have suggested that bioactive food components, including both essential and nonessential nutrients, can modify DNA methylation patterns in complex ways. For instance, consumption of a methyl-deficient diet led to hypomethylation of specific CpG sites within several oncogenes (such as c-myc, c-fos, and c-H-ras), resulting in elevated levels of mRNA for these genes (Wainfan and Poirier, 1992). A recent study showed that tea catechins are effective inhibitors of human DNA methyltransferase (DNMT)-mediated DNA methylation in vitro and in cultured cancer cells (Fang et al., 2003). DNA methylation is catalyzed by specific DNMTs. Multiple DNMTs are known to be present in humans, animals, and microorganisms, and they have varying degrees of specificity toward unmethylated and hemimethylated DNA substrates (Bestor and Ingram, 1983). S-Adenosyl-L-methionine (SAM) is the methyl donor in the DNMT-mediated DNA methylation, as in many other enzymatic methylation reactions [such as the catechol-O-methyltransferase (COMT)-med...

Substitutional heteroatom doping is a promising route to modulate the outstanding material properties of carbon nanotubes and graphene for customized applications. Recently, (nitrogen-) N-doping has been introduced to ensure tunable work-function, enhanced n-type carrier concentration, diminished surface energy, and manageable polarization. Along with the promising assessment of N-doping effects, research on the N-doped carbon based composite structures is emerging for the synergistic integration with various functional materials. This invited feature article reviews the current research progress, emerging trends, and opening opportunities in N-doped carbon based composite structures. Underlying basic principles are introduced for the effective modulation of material properties of graphitic carbons by N-doping. Composite structures of N-doped graphitic carbons with various functional materials, including (i) polymers, (ii) transition metals, (iii) metal oxides, nitrides, sulphides, and (iv) semiconducting quantum dots are highlighted. Practical benefits of the synergistic composite structures are investigated in energy and catalytic applications, such as organic photovoltaics, photo/electro-catalysts, lithium ion batteries and supercapacitors, with a particular emphasis on the optimized interfacial structures and properties.

We studied the modulating effects of caffeic acid and chlorogenic acid (two common coffee polyphenols) on the in vitro methylation of synthetic DNA substrates and also on the methylation status of the promoter region of a representative gene in two human cancer cells lines. Under conditions that were suitable for the in vitro enzymatic methylation of DNA and dietary catechols, we found that the presence of caffeic acid or chlorogenic acid inhibited in a concentration-dependent manner the DNA methylation catalyzed by prokaryotic M.SssI DNA methyltransferase (DNMT) and human DNMT1. The IC50 values of caffeic acid and chlorogenic acid were 3.0 and 0.75 microM, respectively, for the inhibition of M.SssI DNMT-mediated DNA methylation, and were 2.3 and 0.9 microM, respectively, for the inhibition of human DNMT1-mediated DNA methylation. The maximal in vitro inhibition of DNA methylation was approximately 80% when the highest concentration (20 microM) of caffeic acid or chlorogenic acid was tested. Kinetic analyses showed that DNA methylation catalyzed by M.SssI DNMT or human DNMT1 followed the Michaelis-Menten curve patterns. The presence of caffeic acid or chlorogenic acid inhibited DNA methylation predominantly through a non-competitive mechanism, and this inhibition was largely due to the increased formation of S-adenosyl-L-homocysteine (SAH, a potent inhibitor of DNA methylation), resulting from the catechol-O-methyltransferase (COMT)-mediated O-methylation of these dietary catechols. Using cultured MCF-7 and MAD-MB-231 human breast cancer cells, we also demonstrated that treatment of these cells with caffeic acid or chlorogenic acid partially inhibited the methylation of the promoter region of the RARbeta gene. The findings of our present study provide a general mechanistic basis for the notion that a variety of dietary catechols can function as inhibitors of DNA methylation through increased formation of SAH during the COMT-mediated O-methylation of these dietary chemicals.

Graphene is an atom-thick, two-dimensional material comprised of a monolayer hexagonal sp 2 -hybridized carbons. [1,2] It is flexible, has a large specific surface area, and exhibits excellent electrical and thermal conductivities and also good mechanical properties. Moreover, given the low cost of natural graphite, the potential for obtaining large quantities of graphene by a low-cost production process is high. As such, graphene and its chemically modified forms [3] are promising building blocks for accessing highly ordered assemblies that are suitable for nanoelectronics, energy storage/conversion, catalysis, composites, and other applications. [1][2][3][4][5][6][7][8] Although previous efforts have demonstrated that graphene-based platelets may be assembled into papers, thin films, or other two-dimensional constructs, [9][10][11][12][13] the ability to control the assembly such platelets into three-dimensional (3D) structures could result in the carbon materials that exhibit very large surface areas, unusual or novel physical and electronic properties, unsurpassed chemical functionality, and other attractive features that are necessary for the aforementioned applications. [3,[14][15][16] Herein we demonstrate the self-assembly of graphene oxide (GO) platelets into mechanically flexible, macroporous 3D carbon films with tunable porous morphologies. Selfassembly is the spontaneous bottom-up organization of preexisting components into patterned structures. [17,18] The intrinsic parallelism and scalability inherent to self-assembly can, in principle, enable low-cost, large-scale syntheses of highly ordered nanostructures. [19][20][21][22][23][24][25] Indeed, as will be described below, the self-assembly of chemically modified graphene platelets into a complex 3D morphology was achieved by the "breath-figure" method, which is a straightforward procedure for synthesizing large-area porous polymer films. [25][26][27][28][29][30][31][32][33][34] The breath-figure method as employed herein is illustrated in Figure 1 A. Briefly, polymer-grafted GO platelets were synthesized and dispersed in an organic solvent. The dispersion was then cast onto a suitable substrate and exposed to a stream of humid air. Endothermic evaporation of the volatile organic solvent resulted in the spontaneous conden- Figure 1. A) Procedure for the self-assembly of RGO into macroporous carbon films. B) A photograph of a mechanically flexible, semi-transparent macroporous RGO film on PET. C) A water contact angle of 1528 was measured for the superhydrophobic macroporous RGO film. D) Plane-view and E) 608-tilted SEM images of an RGO film. F,G) Plane-view SEM images of porous RGO film upon (F) and after (G) deformation.

Hybrid assembly of peptides and graphene into core/shell nanowires is presented here. Electroconductive nanowires comprised of multilayered graphene shells wrapped around peptide nanowire cores were readily assembled upon diluting peptide solution into an aqueous reduced graphene dispersion. Calcination of peptide cores generated a hollow graphene‐shell network with large surface area and high thermal/chemical stability.

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