Roman Brukh

Production of Graphene Sheets by Direct Dispersion with Aromatic Healing Agents

Graphene exhibits remarkable properties for various novel applications. One of many appealing applications of graphene would be to fabricate transparent conductive films to replace indium tinoxide (ITO).Theuseof graphene is promisingdue to its high optical transmittance, low resistance, high chemical stability, and high mechanical strength. This, as well as other applications, requires a large quantity of high-quality graphene as the basic component. Among the reported methods to prepare graphene, liquid-phase methods have drawn tremendous attention due to their scalability and ease of functionalization. Compared to chemical vapor deposition (CVD) approaches, which produce graphene films with the highest conductivity yet obtained, one advantage of liquid-phase methods is that the produced graphene can be conveniently deposited on any substratewith simple processing, such as spincoating or inkjet-printing on plastic substrates. Therefore, liquid-based techniqueshave thepotential to realize large-scale organic devices including photovoltaic cells.

Kinetics of carbon nanotube oxidation

Carbon nanotubes, graphite and amorphous carbon are structurally different, which is reflected in their reactivity and the resistance to oxidation. This paper reports the stability of single- and multi-walled nanotubes, and their true oxidation rates based on conversion to CO2 when heated in the presence of oxygen. Non-isothermal techniques were employed to determine the kinetic parameters for the oxidation of nanotubes, amorphous carbon and graphite. Single-walled nanotubes were found to be the most reactive, followed by multi-walled nanotubes, amorphous carbon and graphite. The oxidation rates of different single-walled tubes samples containing different residual catalysts were also found to vary significantly.

Structure and Function of the Catalytic Domain of the Dihydrolipoyl Acetyltransferase Component in Escherichia coli Pyruvate Dehydrogenase Complex

Background: The E. coli pyruvate dehydrogenase complex catalyzes conversion of pyruvate to acetyl-CoA and comprises E1p, E2p, and E3 components. Results: The structure of the E2 core domain was solved and shown to efficiently catalyze acetyl transfer between domains. Conclusion: Mass spectrometry revealed hitherto unrecognized domain-induced interactions between E1 and E2 core domain. Significance: A multifaceted approach is required to understand communication between intact multidomain components. The Escherichia coli pyruvate dehydrogenase complex (PDHc) catalyzing conversion of pyruvate to acetyl-CoA comprises three components: E1p, E2p, and E3. The E2p is the five-domain core component, consisting of three tandem lipoyl domains (LDs), a peripheral subunit binding domain (PSBD), and a catalytic domain (E2pCD). Herein are reported the following. 1) The x-ray structure of E2pCD revealed both intra- and intertrimer interactions, similar to those reported for other E2pCDs. 2) Reconstitution of recombinant LD and E2pCD with E1p and E3p into PDHc could maintain at least 6.4% activity (NADH production), confirming the functional competence of the E2pCD and active center coupling among E1p, LD, E2pCD, and E3 even in the absence of PSBD and of a covalent link between domains within E2p. 3) Direct acetyl transfer between LD and coenzyme A catalyzed by E2pCD was observed with a rate constant of 199 s−1, comparable with the rate of NADH production in the PDHc reaction. Hence, neither reductive acetylation of E2p nor acetyl transfer within E2p is rate-limiting. 4) An unprecedented finding is that although no interaction could be detected between E1p and E2pCD by itself, a domain-induced interaction was identified on E1p active centers upon assembly with E2p and C-terminally truncated E2p proteins by hydrogen/deuterium exchange mass spectrometry. The inclusion of each additional domain of E2p strengthened the interaction with E1p, and the interaction was strongest with intact E2p. E2p domain-induced changes at the E1p active site were also manifested by the appearance of a circular dichroism band characteristic of the canonical 4′-aminopyrimidine tautomer of bound thiamin diphosphate (AP).

Process modeling and on-line monitoring of benzene and other species during the two-stage combustion of ethylene in air

Abstract The on-line measurement of combustion effluents is important in the study of reaction mechanisms, process control, and environmental monitoring and impact. Microtrap gas chromatography for real-time analysis of volatile organics preconcentrates the sample, and uses rapid desorption to yield low detection limits with a relatively rapid analysis. This technique is used here for the on-line monitoring of low levels of benzene, a known precursor to polyaromatics and dioxins, produced during the combustion of ethylene in air. In addition, several other species are monitored by more conventional on-line methods. Process modeling with detailed reaction mechanisms of the combustion runs provided reasonably good simulations of the observed concentrations.

A Novel Small-Molecule Inhibitor of the Mycobacterium tuberculosis Demethylmenaquinone Methyltransferase MenG Is Bactericidal to Both Growing and Nutritionally Deprived Persister Cells

ABSTRACT Active tuberculosis (TB) and latent Mycobacterium tuberculosis infection both require lengthy treatments to achieve durable cures. This problem has partly been attributable to the existence of nonreplicating M. tuberculosis “persisters” that are difficult to kill using conventional anti-TB treatments. Compounds that target the respiratory pathway have the potential to kill both replicating and persistent M. tuberculosis and shorten TB treatment, as this pathway is essential in both metabolic states. We developed a novel respiratory pathway-specific whole-cell screen to identify new respiration inhibitors. This screen identified the biphenyl amide GSK1733953A (DG70) as a likely respiration inhibitor. DG70 inhibited both clinical drug-susceptible and drug-resistant M. tuberculosis strains. Whole-genome sequencing of DG70-resistant colonies identified mutations in menG (rv0558), which is responsible for the final step in menaquinone biosynthesis and required for respiration. Overexpression of menG from wild-type and DG70-resistant isolates increased the DG70 MIC by 4× and 8× to 30×, respectively. Radiolabeling and high-resolution mass spectrometry studies confirmed that DG70 inhibited the final step in menaquinone biosynthesis. DG70 also inhibited oxygen utilization and ATP biosynthesis, which was reversed by external menaquinone supplementation. DG70 was bactericidal in actively replicating cultures and in a nutritionally deprived persistence model. DG70 was synergistic with the first-line TB drugs isoniazid, rifampin, and the respiratory inhibitor bedaquiline. The combination of DG70 and isoniazid completely sterilized cultures in the persistence model by day 10. These results suggest that MenG is a good therapeutic target and that compounds targeting MenG along with standard TB therapy have the potential to shorten TB treatment duration. IMPORTANCE This study shows that MenG, which is responsible for the last enzymatic step in menaquinone biosynthesis, may be a good drug target for improving TB treatments. We describe the first small-molecule inhibitor (DG70) of Mycobacterium tuberculosis MenG and show that DG70 has characteristics that are highly desirable for a new antitubercular agent, including bactericidality against both actively growing and nonreplicating mycobacteria and synergy with several first-line drugs that are currently used to treat TB. IMPORTANCE This study shows that MenG, which is responsible for the last enzymatic step in menaquinone biosynthesis, may be a good drug target for improving TB treatments. We describe the first small-molecule inhibitor (DG70) of Mycobacterium tuberculosis MenG and show that DG70 has characteristics that are highly desirable for a new antitubercular agent, including bactericidality against both actively growing and nonreplicating mycobacteria and synergy with several first-line drugs that are currently used to treat TB.

Synergy of oxygen and a piranha solution for eco-friendly production of highly conductive graphene dispersions

A variety of strategies for the synthesis of solution processable graphene sheets has been developed so far. However, no approach has been reported to directly produce highly conductive, low-oxygen-containing graphene sheets without relying on toxic reagents and metal containing compounds and without generating toxic by-products. With an aim of developing such an eco-friendly approach, for the first time, this work studied solution phase oxidation of graphite particles and reversible graphite intercalation compounds using molecular oxygen and piranha etching solutions. We found that the synergy of the piranha etching solution and the intercalated molecular oxygen enables controlled oxidation of graphite particles assisted by microwave heating. The controlled oxidation leads to the rapid and direct generation of highly conductive, “clean”, and low oxygen containing graphene sheets without releasing toxic gases or aromatic by-products as detected by gas chromatography-mass spectrometry (GC-MS). These highly conductive graphene sheets have unique molecular structures, different from both graphene oxide and pristine graphene sheets. It is even different from chemically reduced graphene oxide, while combining many of its merits. They can be dispersed in both aqueous and common organic solvents without surfactants/stabilizers, producing “clean” solution phase graphene sheets. “Paper-like” graphene films are generated via simple filtration, resulting in films with a conductivity of 2.3 × 104 S m−1, the highest conductivity observed so far for graphene films assembled via vacuum filtration from solution processable graphene sheets. After 2 hours of low temperature annealing at 300 °C, the conductivity further increased to 7.4 × 104 S m−1. This eco-friendly and rapid approach for the production of highly conductive and “clean” solution-phase graphene sheets would enable a broad spectrum of applications at low cost.

PATHWAYS TO METHYLENE CHLORIDE DESTRUCTION AT LOW AND HIGH CONCENTRATIONS

A two-stage combustor facility is used to investigate methylene chloride (CH2Cl2) incineration and formation of products of incomplete combustion (PIC). For measuring low concentrations of CH2Cl2, on-line microtrap gas chromatography is employed. Destruction efficiency of CH2Cl2 over a wide range of feed concentrations was investigated under fuel-lean and fuel-rich ethylene/air combustion conditions. The impact of CH2Cl2 on the formation of PICs such as methane, ethylene, ethane, and acetylene is investigated. The combustion process is simulated using an ideal reactor model and a detailed chemical reaction mechanism. Rate-of-production analyses based on modeling results show that there are different pathways for the destruction of CH2Cl2 under fuel-lean and fuel-rich conditions. As shown by experimental results, the destruction efficiency is lower at lower inlet concentrations. Simulations of experimental results have shown that the significance of various radicals and destruction channels varies with combustion conditions and concentration of organics, and that atoms and fragments of destroyed molecules play an important role in further destruction of parent species.