Capture and Activation of Carbon Dioxide Using Guanidine Superbases

<p>Due to its abundance and low-cost, carbon dioxide is a desirable C₁-building block within organic transformations. However, the thermodynamic and kinetic stability of CO₂ often necessitates preliminary activation before it can be inserted into organic molecules. This prompts the need for compounds that can effectively promote the activation of CO₂. This research investigates the capture and activation of carbon dioxide using a class of superbases that incorporate the bicyclic guanidine unit, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (hppH, 1). A series of compounds containing multiple hpp-units assembled around a phenyl ring scaffold were synthesized and investigated in the functionalization of CO₂. The work presented in this study has demonstrated the ability of protonated superbasic hppH derivatives to efficiently and effectively capture and activate carbon dioxide from ambient air to form the corresponding guanidinium bicarbonate salts. A series of optimization reactions was carried out, and showed that addition of substoichiometric concentrations of a proton source activates these guanidine compounds to their fully protonated cationic forms, and results in CO₂ capture through bicarbonate formation. A series of protonation studies were employed to fully characterize the cationic species. The tetraphenylborate and hydrochloride guanidinium salts were synthesized, isolated, and characterized by ¹H NMR and ¹³C NMR spectroscopic analysis. Molecular structures of relevant crystals were obtained through single crystal X-ray diffraction. These structures revealed a complex hydrogen-bonding network within these ionic species, and showed efficient delocalization of the formal positive charge within the protonated guanidinium units. The guanidine superbases were implemented in a series of reactions attempting the functionalization of CO₂ and an alcohol to form corresponding alkylcarbonate products. However, the synthesis of these carbonate products was not achieved under the reaction conditions employed. This lack of success has been attributed to the hygroscopic nature of this class of compounds, resulting in the preferential capture of ambient water.</p>

Capture and Activation of Carbon Dioxide Using Guanidine Superbases

<p>Due to its abundance and low-cost, carbon dioxide is a desirable C₁-building block within organic transformations. However, the thermodynamic and kinetic stability of CO₂ often necessitates preliminary activation before it can be inserted into organic molecules. This prompts the need for compounds that can effectively promote the activation of CO₂. This research investigates the capture and activation of carbon dioxide using a class of superbases that incorporate the bicyclic guanidine unit, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (hppH, 1). A series of compounds containing multiple hpp-units assembled around a phenyl ring scaffold were synthesized and investigated in the functionalization of CO₂. The work presented in this study has demonstrated the ability of protonated superbasic hppH derivatives to efficiently and effectively capture and activate carbon dioxide from ambient air to form the corresponding guanidinium bicarbonate salts. A series of optimization reactions was carried out, and showed that addition of substoichiometric concentrations of a proton source activates these guanidine compounds to their fully protonated cationic forms, and results in CO₂ capture through bicarbonate formation. A series of protonation studies were employed to fully characterize the cationic species. The tetraphenylborate and hydrochloride guanidinium salts were synthesized, isolated, and characterized by ¹H NMR and ¹³C NMR spectroscopic analysis. Molecular structures of relevant crystals were obtained through single crystal X-ray diffraction. These structures revealed a complex hydrogen-bonding network within these ionic species, and showed efficient delocalization of the formal positive charge within the protonated guanidinium units. The guanidine superbases were implemented in a series of reactions attempting the functionalization of CO₂ and an alcohol to form corresponding alkylcarbonate products. However, the synthesis of these carbonate products was not achieved under the reaction conditions employed. This lack of success has been attributed to the hygroscopic nature of this class of compounds, resulting in the preferential capture of ambient water.</p>

Demonstration of TNSA proton radiography on the National Ignition Facility Advanced Radiographic Capability (NIF-ARC) laser

Proton radiography using short-pulse laser drivers is an important tool in high-energy density (HED) science for dynamically diagnosing key characteristics in plasma interactions. Here we detail the first demonstration of target-normal sheath acceleration (TNSA)-based proton radiography the NIF-ARC laser system aided by the use of compound parabolic concentrators (CPCs). The multi-kJ energies available at the NIF-ARC laser allows for a high-brightness proton source for radiography and thus enabling a wide range of applications in HED science. In this demonstration, proton radiography of a physics package was performed and this work details the spectral properties of the TNSA proton probe as well as description of the resulting radiography quality.

Dosimetric Optimization of a Laser-Driven Irradiation Facility Using the G4-ELIMED Application

ELIMED has been developed and installed at ELI beamlines as a part of the ELIMAIA beamline to transport, monitor, and use laser-driven ion beams suitable for multidisciplinary applications, including biomedical ones. This paper aims to investigate the feasibility to perform radiobiological experiments using laser-accelerated proton beams with intermediate energies (up to 30 MeV). To reach this goal, we simulate a proton source based on experimental data like the ones expected to be available in the first phase of ELIMED commissioning by using the G4-ELIMED application (an application based on the Geant4 toolkit that simulates the full ELIMED beamline). This allows the study of transmission efficiency and the final characteristics of the proton beam at the sample irradiation point. The Energy Selector System is used as an active energy modulator to obtain the desired beam features in a relatively short irradiation time (around 6 min). Furthermore, we demonstrate the capability of the beamline to filter out other ion contaminants, typically co-accelerated in a laser-plasma environment. These results can be considered as a detailed feasibility study for the use of ELIMED for various user applications such as radiobiological experiments with ultrahigh dose rate proton beams.

Multilayer radiation shield for satellite electronic components protection

In this paper, various multi-layer shields are designed, optimized, and analyzed for electron and proton space environments. The design process is performed for various suitable materials for the local protection of sensitive electronic devices using MCNPX code and the Genetic optimization Algorithm. In the optimizations process, the total ionizing dose is 53.3% and 72% greater than the aluminum shield for proton and electron environments, respectively. Considering the importance of the protons in the LEO orbits, the construction of the shield was based on designing a proton source. A sample shield is built using a combination of Aluminum Bronze and molybdenum layers with a copper carrier to demonstrate the idea. Comparisons of radiation attenuation coefficient results indicate a good agreement between the experimental, simulation, and analytical calculations results. The good specifications of the proposed multi-layer shield prove their capability and ability to use in satellite missions for electronic device protection.

Selective Catalytic Conversion of Acetylene to Ethylene Powered by Water and Visible Light

The production of polymer-grade ethylene requires the purification of ethylene feed from acetylene contaminant. Accomplishing this task by state-of-the-art thermal hydrogenation requires high temperature, external feed of H2 gas, and noble metal catalysts, and is not only expensive and energy-intensive but also prone to overhydrogenate to ethane. We report a photocatalytic system to reduce acetylene to ethylene with >99% selectivity for ethylene under both non-competitive (no ethylene co-feed) and competitive (ethylene co-feed) conditions, and near 100% conversion under the latter industrially relevant condition. Our system uses a molecular catalyst based on earth-abundant cobalt operating under ambient conditions and sensitized by either [Ru(bpy)3]2+ or an inexpensive organic semiconductor (mpg-CN) under visible light. These features and the use of water as a proton source offer substantial advantages over current hydrogenation technologies with respect to selectivity and sustainability.