Novel properties of graphene have been well documented, whereas the importance of nanosheets of MoS2 and other chalcogenides is increasingly being recognized over the last two to three years. Borocarbonitrides, BxCyNz, with insulating BN and conducting graphene on either side are new materials whose properties have been attracting attention. These two-dimensional (2D) materials contain certain common features. Thus, graphene, MoS2, and borocarbonitrides have all been used in supercapacitor applications, oxygen reduction reactions (ORRs), and lithium-ion batteries. It is instructive, therefore, to make a comparative study of some of the important properties of these layered materials. In this article, we discuss properties related to energy devices at length. We examine the hydrogen evolution reaction facilitated by graphene, MoS2, and related materials. We also discuss gas and radiation sensors based on graphene and MoS2 as well as gas storage properties of graphene and borocarbonitrides. The article shou...

Comparative Study of Potential Applications of Graphene, MoS2, and Other Two-Dimensional Materials in Energy Devices, Sensors, and Related Areas

The highly refined organic chemistry in solid-phase synthesis has made it the method of choice not only to assemble peptides but also small proteins – mainly on a laboratory scale but increasingly also on an industrial scale. While conductive heating occasionally has been applied to peptide synthesis, precise microwave irradiation to heat the reaction mixture during coupling and Nα-deprotection has become increasingly popular. It has often provided dramatic reductions in synthesis times, accompanied by an increase in the crude peptide purity. Microwave heating has been proven especially relevant for sequences which might form β-sheet type structures and for sterically difficult couplings. The beneficial effect of microwave heating appears so far to be due to the precise nature of this type of heating, rather than a peptide-specific microwave effect. However, microwave heating as such is not a panacea for all difficulties in peptide syntheses and the conditions may need to be adjusted for the incorporation of Cys, His and Asp in peptides, and for the synthesis of, for example, phosphopeptides, glycopeptides, and N-methylated peptides. Here we provide a comprehensive overview of the advances in microwave heating for peptide synthesis, with a focus on systematic studies and general protocols, as well as important applications. The assembly of β-peptides, peptoids and pseudopeptides are also evaluated in this critical review (254 references).

Microwave heating in solid-phase peptide synthesis

Ion sources for molecular mass spectrometry are usually driven by direct current power supplies with no user control over the total charges generated. Here, we show that the output of triboelectric nanogenerators (TENGs) can quantitatively control the total ionization charges in mass spectrometry. The high output voltage of TENGs can generate single- or alternating-polarity ion pulses, and is ideal for inducing nanoelectrospray ionization (nanoESI) and plasma discharge ionization. For a given nanoESI emitter, accurately controlled ion pulses ranging from 1.0 to 5.5 nC were delivered with an onset charge of 1.0 nC. Spray pulses can be generated at a high frequency of 17 Hz (60 ms in period) and the pulse duration is adjustable on-demand between 60 ms and 5.5 s. Highly sensitive (∼0.6 zeptomole) mass spectrometry analysis using minimal sample (18 pl per pulse) was achieved with a 10 pg ml−1 cocaine sample. We also show that native protein conformation is conserved in TENG-ESI, and that patterned ion deposition on conductive and insulating surfaces is possible. The high output voltage of triboelectric nanogenerators enables well-controlled ion pulses for nanoelectrospray molecular mass spectrometry and surface modification.

Triboelectric nanogenerators for sensitive nano-coulomb molecular mass spectrometry.

Liquid extraction surface analysis mass spectrometry (LESA-MS) is a novel surface profiling technique that combines micro-liquid extraction from a solid surface with nano-electrospray mass spectrometry. One potential application is the examination of the distribution of drugs and their metabolites by analyzing ex vivo tissue sections, an area where quantitative whole body autoradiography (QWBA) is traditionally employed. However, QWBA relies on the use of radiolabeled drugs and is limited to total radioactivity measured whereas LESA-MS can provide drug- and metabolite-specific distribution information. Here, we evaluate LESA-MS, examining the distribution and biotransformation of unlabeled terfenadine in mice and compare our findings to QWBA, whole tissue LC/MS/MS and MALDI-MSI. The spatial resolution of LESA-MS can be optimized to ca. 1 mm on tissues such as brain, liver and kidney, also enabling drug profiling within a single organ. LESA-MS can readily identify the biotransformation of terfenadine to its major, active metabolite fexofenadine. Relative quantification can confirm the rapid absorption of terfendine after oral dosage, its extensive first pass metabolism and the distribution of both compounds into systemic tissues such as muscle, spleen and kidney. The elimination appears to be consistent with biliary excretion and only trace levels of fexofenadine could be confirmed in brain. We found LESA-MS to be more informative in terms of drug distribution than a comparable MALDI-MS imaging study, likely due to its favorable overall sensitivity due to the larger surface area sampled. LESA-MS appears to be a useful new profiling tool for examining the distribution of drugs and their metabolites in tissue sections.

Liquid extraction surface analysis mass spectrometry (LESA-MS) as a novel profiling tool for drug distribution and metabolism analysis: the terfenadine example

We predict the stability of an extended two-dimensional hydrocarbon on the basis of first-principles total-energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in $s{p}^{3}$ hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two-dimensional electronics.

Graphane: a two-dimensional hydrocarbon

Preparative mass spectrometry has become a diverse field that covers the spectrum of kinetic energy deposition. Of these methods, soft-landing mass spectrometry has many fundamental properties, which make it an advantageous technique for ion isolation and deposition. Its definition implies the preservation of ionic structural integrity after landing, which ensures the structure–function relationship of a molecule remains intact. Here the focus is on the instruments and applications of studying ion–surface landing in the hyperthermal and thermal kinetic energy regimes. Soft-landing preparative mass spectrometry covers the breadth of mass spectrometric ionization sources, instrumental configurations, and molecular families. Due to the diverse nature of soft landing, and to maximize readability, this review has been organized according to instrumental considerations and molecular families, with a discussion of theoretical work at the end.

Soft-landing preparative mass spectrometry

We report that hydrogenation of mono-, bi-, and trilayer graphene samples via exposure to H2 plasma occurs as a result of electron irradiation of H2O adsorbates on the samples, rather than H species in the plasma as reported by [Elias et al., Science 323, 610 (2009)]. We propose that the hydrogenation mechanism is electron-impact fragmentation of H2O adsorbates into H+ ions. At incident electron energies >60 eV, we observe hydrogenation that is significantly more stable at temperatures >200 °C than previously reported.

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On the mechanism for plasma hydrogenation of graphene

One-bead, one-compound peptide library sequencing via high-pressure ammonia cleavage coupled to nanomanipulation/nanoelectrospray ionization mass spectrometry.

Soft-landing ion mobility has been applied to the development of a reusable surface-enhanced Raman spectroscopic substrate. Sections of silicon wafers were cleaved and modified with 3-(mercaptopropyl) triethoxysilane. After modification, gold was deposited using a soft-landing ion mobility system at thermal kinetic energies. It was found that 30 min of deposition provided the optimal feature size for surface-enhanced Raman scattering, and thus deposition was completed in a pressure-dependent fashion. After gold deposition, caffeine was deposited from the solution phase and checked for Raman activity. The Raman spectroscopic signature for caffeine increased as an inverse function of pressure pertaining to surface coverage of captured Au particles. After Raman spectroscopic confirmation of caffeine, the 1 Torr surface was ultrasonically cleaned in deionized water and respotted with sodium bicarbonate solution. There was no interference on the sodium bicarbonate solution from residual caffeine on the surface.

William D. Hoffmann

Papers

Soft-landing preparative mass spectrometry

On the mechanism for plasma hydrogenation of graphene

One-bead, one-compound peptide library sequencing via high-pressure ammonia cleavage coupled to nanomanipulation/nanoelectrospray ionization mass spectrometry.

Toward a Reusable Surface-Enhanced Raman Spectroscopy (SERS) Substrate by Soft-Landing Ion Mobility

Sub-eV ion deposition utilizing soft-landing ion mobility for controlled ion, ion cluster, and charged nanoparticle deposition