Messai A. Mamo

Improved electronic and magnetic properties of reduced graphene oxide films

We demonstrate semi-metallic transport in graphene oxide layers treated with an organic acid through a nearly linear current-vs.-voltage relationship and the weak temperature dependence of resistance from high temperatures down to 20 K. Additionally an energy gap was observed below 17 K due to the formation of local barriers by residual oxygen groups and disorder in reduced graphene oxide (RGO) sheets. At higher temperatures resistance shows a negative T2 temperature dependence. Temperature dependent magnetization measurements showed a phase transition from diamagnetic to ferromagnetic at around 10 K, in agreement with the electronic transport properties of the RGO films.

Ring‐opening Metathesis Co‐polymerization of a C60‐cyclopentadiene Cycloadduct and Norbornene with the Grubbs Second‐generation Catalyst

Abstract A series of C60‐containing polymers were synthesized by the co‐polymerization of a C60‐cyclopentadiene cycloadduct and norbornene in varying ratios. The polymerization was facilitated by a catalytic amount of Grubbs second generation catalyst and the co‐polymers formed were investigated by spectroscopic and thermal techniques.

The In Vitro Antitumour Activity of Novel, Mitochondrial-Interactive, Gold-Based Lipophilic Cations

In this study we compared the effects of two previously described antimitochondrial gold complexes, that is, [A] [Au(dppe)2]Cl and [B] [Au(d4pype)2]Cl with two novel lipophilic cations, that is, [C] [Au(dpmaaH2)(dpmaaSnMe2)]Cl and [D] [Au(dpmaaSnMe2)2]Cl as antimitochondrial agents. The results of this study indicate that [C] and [D] have intermediate partition coefficients and exhibited a selective uptake by cells. They exhibited a higher selectivity for the various cell lines than [A] but were more cytotoxic than [B]. There is a significant correlation between the cytotoxic potential of [A], [B], [C], and [D] and their octanol/water partition coefficients in both MCF-7 (breast cancer) and MCF-12A (nonmalignant breast) cells, whereas their cytotoxic potential and ability to induce the release of cytochrome c correlated only in the case of the MCF-12A cells. Complexes [C] and [D] are promising new chemotherapeutic drugs. These compounds target the mitochondrial membranes of certain cancer cells exploiting the differences between the mitochondrial membrane potential of these cells and normal cells. Although the concentrations of these compounds necessary to eradicate cancer cells are very high, the results provide a basis for the synthesis of a new family of compounds with intermediate partition coefficients compared to [A] and [B] but with increased activity against cancer cells.

Synthesis of C60-containing Polymers by Ring-opening Metathesis Co-polymerization of a C60-cyclopentadiene Cycloadduct and N-(cycloheptyl)-endo-norbornene-5,6-dicarboximide and their Application in a Photovoltaic Device

A C60-cyclopentadiene cycloadduct and N-(cycloheptyl)-endo-norbornene-5,6-dicarboximide were utilized as co-monomers in ring-opening metathesis polymerization (ROMP) reactions to afford a series of polymers containing C60 in varying ratios. The polymerization reactions were catalyzed by the Grubbs second-generation ruthenium catalyst, and the co-polymers formed were investigated by spectroscopic and thermal techniques. The photovoltaic behavior of the new materials was studied by the construction of a simple sandwich-type photovoltaic cell. Under irradiation we concluded that the C60 in the copolymers simultaneously accelerated both the charge separation in the polymer and the charge recombination between the electrons in the TiO2 and the electrolyte.

The anti-tumour properties and biodistribution (as determined by the radiolabeled equivalent) of Au-compounds intended as potential chemotherapeutics

The anti-tumour activity of the Au (I) phosphine complex [Au(dppe(2)]Cl was first discovered in the mid 1980s although promising results were obtained it did not pass clinical studies because of its toxicity to organs such as the liver and heart. The aim of this study was to determine whether the two novel gold compounds (MM5 and MM6), selected for this study, have higher selectivity for cancer cells with less toxicity towards normal cells than [Au(dppe)(2)]Cl, and also to determine whether they have improved bio distribution compared to [Au(dppe)(2)]Cl. The Au-compounds as potential chemotherapeutic drugs were evaluated by using radioactive tracers in the in vitro and in vivo studies. Results obtained from these experiments showed that the uptake of these experimental compounds was dependent on their octanol/water partition coefficient. However; the inhibition of cell growth did not correlate with the uptake of these compounds by the cells that were tested. In terms of the total uptake it was found that the compounds that were less lipophilic (MM5, MM6) were taken up less efficiently in cells than those that are more lipophilic. Therefore hydrophilic drugs are expected to have a limited biodistribution compared to lipophilic drugs. This might imply a more selective tumour uptake.

Phenolic Compounds in Water: Sources, Reactivity, Toxicity and Treatment Methods

Phenolic compounds exist in water bodies due to the discharge of polluted wastewater from industrial, agricultural and domestic activities into water bodies. They also occur as a result of natural phenomena. These compounds are known to be toxic and inflict both severe and long‐lasting effects on both humans and animals. They act as carcino‐ gens and cause damage to the red blood cells and the liver, even at low concentrations. Interaction of these compounds with microorganisms, inorganic and other organic com‐ pounds in water can produce substituted compounds or other moieties, which may be as toxic as the original phenolic compounds. This chapter dwells on the sources and reactivity of phenolic compounds in water, their toxic effects on humans, and methods of their removal from water. Specific emphasis is placed on the techniques of their removal from water with attention on both conventional and advanced methods. Among these methods are ozonation, adsorption, extraction, photocatalytic degradation, biological, electro‐Fenton, adsorption and ion exchange and membrane‐based separation.

Electronic Detection of Drechslera sp. Fungi in Charentais Melon (Cucumis melo Naudin) Using Carbon-Nanostructure-Based Sensors

The development of chemical sensor technology in recent years has stimulated an interest regarding the use of characteristic volatiles and odors as a rapid and early indication of deterioration in fruit quality. The fungal infestation by Drechslera sp. in melons is a severe problem, and we demonstrate that electronic sensors based on carbon nanostructures are able to detect the presence of these fungi in melon. The responses of sensor conductance G and capacitance C at 27 kHz were measured and used to calculate their ΔG and ΔC variation over the full melon ripening process under shelf conditions with proliferation of Drechslera sp. fungi. The sensor response showed that these fungi can be electronically identified in charentais melon, constituting an effective and cheap test procedure to differentiate between infected and uninfected melon.

Hydrostatic pressure sensors based on carbon spheres dispersed in polyvinyl alcohol prepared using hexadecyltrimethylammonium bromide as surfactant and water as solvent

We report on hydrostatic pressure sensors based on carbon spheres–polyvinyl alcohol composites prepared in aqueous medium. The carbon spheres were dispersed in water applying a surfactant (hexadecyltrimethylammonium bromide) and deposited onto interdigitated electrodes of tin. The pressure dependence of the conductance of the devices is investigated. An almost linear behavior of the sensitivity of 6.8% between 90–135 kPa is observed for the composite prepared from a solution of 15 mg mL−1 of undoped-carbon spheres, representing a significant improvement with respect to devices based on composites with non-dispersed carbon spheres.

The effects of two–dimensional TiSe2 on the thermoelectric, electronic and optical response of Yb14MnSb11/AlSb9Yb11 heterostructures – A theoretical study

Two-dimensional TiSe2, with Yb14MnSb11 and AlSb9Yb11 thermoelectric materials, were used to generate heterostructures. The electronic and optical calculations were done using the Materials Studio 2018 modelling software package, employing the Cambridge Serial Total Energy Package code and using the generalised gradient approximation with Perdew-Burke-Ernzerhof exchange-correlation functionals. However, the electronic results obtained revealed a reduction in the calculated band gap and an increase in the slope of the density of state at the Femi level, as well as the energy bands of the generated heterostructures was reported. Partial density of states showed that various orbitals were present in the thermoelectric materials. The thermal transport and electronic properties are compared using the Boltzmann transport theory and Mott derived equations, which were expressed in the maximum attainable figure of merit. A variation in the electric potential of the layers is observed. The dielectric function is found to decrease in both thermoelectric layers generated and far more than the Yb14MnSb11-TiSe2 layer, which was more negative. The reduction in reflectivity of AlSb9Yb11TiSe2 layer and elevation of the Yb14MnSb11-TiSe2 layer is observed. Upon forming heterostructures with TiSe2, the conductivity reduced in the high frequency, due to the generated complex multicomponent compounds.

A first-principles study of half-Heusler intermetallic compound MgAgAs with 2D-TiC/2D-Mo2TiC composite material

The world reliance on non-renewable and depleted energy resources has made the search for renewable and sustainable energy more significant. However, a theoretical study is necessary to give a more elaborate investigation of the electronic and optical properties since the role of the heterostructures is still deficient. Furthermore, no first-principles studies have been reported on 2D thermoelectric heterostructures comprising of MgAgAs, 2D-TiC and 2D-Mo2TiC material. Our calculated electronic results show no bandgap induction in the heterostructures compared to pure intermetallic MgAgAs, 2D-TiC and 2D-Mo2TiC material, which favours the separation and transfer of charge carriers and visible-light-driven activity. Based on the analysis of the electronic properties, band structure, projected density of state and spin-polarised contributions from the spin-down and spin-up eigenstates, the Mo2TiC–MgAgAs–Mo2TiC layer was found to have improved conductivity at the infrared region. This makes the electrons move easily from the surface of the thermoelectric material once generated and stored in the heterostructures. The proposed theoretical design offers a new way for the effective and large-scale fabrication of 2D-based thermoelectric materials for application in solar energy conversion and storage.