Preparation and Characterization of Micronized Artemisinin via a Rapid Expansion of Supercritical Solutions (RESS) Method

The particle sizes of pharmaceutical substances are important for their bioavailability. Bioavailability can be improved by reducing the particle size of the drug. In this study, artemisinin was micronized by the rapid expansion of supercritical solutions (RESS). The particle size of the unprocessed white needle-like artemisinin particles was 30 to 1200 µm. The optimum micronization conditions are determined as follows: extraction temperature of 62 °C, extraction pressure of 25 MPa, precipitation temperature 45 °C and nozzle diameter of 1000 μm. Under the optimum conditions, micronized artemisinin with a (mean particle size) MPS of 550 nm is obtained. By analysis of variance (ANOVA), extraction temperature and pressure have significant effects on the MPS of the micronized artemisinin. The particle size of micronized artemisinin decreased with increasing extraction temperature and pressure. Moreover, the SEM, LC-MS, FTIR, DSC and XRD allowed the comparison between the crystalline initial state and the micronization particles obtained after the RESS process. The results showed that RESS process has not induced degradation of artemisinin and that processed artemisinin particles have lower crystallinity and melting point. The bulk density of artemisinin was determined before and after RESS process and the obtained results showed that it passes from an initial density of 0.554 to 0.128 g·cm<sup>−3</sup> after the processing. The decrease in bulk density of the micronized powder can increase the liquidity of drug particles when they are applied for medicinal preparations. These results suggest micronized powder of artemisinin can be of great potential in drug delivery systems

Effects of confinement on water structure and dynamics and on proton transport: a molecular simulation study

Classical molecular dynamics (MD) simulations are performed to study structural and dynamic properties of water confined within graphite surfaces. The surfaces are separated at distances varying between 7 and 14.5 Å and the water density is held constant at 1g/cc. Results at 298 K show the formation of a well-ordered structure constituted by water layers parallel to the graphite surfaces. The water molecules in the layers in contact with the surface have a tendency to orient their dipole parallel to the surface. Such ice-like structures may have different structural and dynamic properties than those of ice. The calculated mean square displacement reveals that the mobilities of the confined water at a separation of 8 Å become similar to that of low-temperature water (213 K) at the same density, although the structures of water are very different. The temperature at which the mobility of water confined at the separation of 7 Å would become similar to that of bulk low-temperature water was found to be 373K. With respect to the dynamics of confined water, a significant blue shift is observed in the intermolecular vibrational modes associated with the O×××O×××O bending and O×××O stretching of molecules linked by hydrogen bonds. The analysis of the geometry of water clusters confined between two graphite surfaces has been performed using ab initio methods. The ab initio calculations yield two preferential orientations of water molecules which are; 1) one O-H bond points to the surface and the other is parallel; 2) both O-H bonds are parallel to the surface. These orientations agree with those found in our MD simulation results. The calculated energy barriers for proton transfer of the confined H3O+-(H2O) complexes between two graphite model surfaces suggest that the confinement enhances the proton transfer at the separation 6-14.5 Å. When the confinement is high, at a separation of 4 Å, the barrier energies are extremely large. The confinement does not enhance proton transfer when the H3O+-(H2O) complexes are located further from the surfaces by more than 8 Å. As a result, the barrier energies start to increase at the separation of 20 Å

Oxygen Reduction Reaction on Dispersed and Core-Shell Metal Alloy Catalysts: Density Functional Theory Studies

Pt-based alloy surfaces are used to catalyze the electrochemical oxygen reduction reaction (ORR), where molecular oxygen is converted into water on fuel cell electrodes. In this work, we address challenges due to the cost of high Pt loadings in the cathode electrocatalyst, as well as those arising from catalyst durability. We aim to develop an increased understanding of the factors that determine ORR activity together with stability against surface segregation and dissolution of Pt-based alloys. We firstly focus on the problem of determining surface atomic distribution resulting from surface segregation phenomena. We use first-principles density functional theory (DFT) calculations on PtCo and Pt3Co overall compositions, as well as adsorption of water and atomic oxygen on PtCo(111) and Pt-skin structures. The bonding between water and surfaces of PtCo and Pt-skin monolayers are investigated in terms of orbital population. Also, on both surfaces, the surface reconstruction effect due to high oxygen coverage and water co-adsorption is investigated. Although the PtCo structures show good activity, a large dissolution of Co atoms tends to occur in acid medium. To tackle this problem, we examine core-shell structures which showed improved stability and activity compared to Pt(111), in particular, one consisting of a surface Pt-skin monolayer over an IrCo or Ir3Co core, with or without a Pd interlayer between the Pt surface and the Ir-Co core. DFT analysis of surface segregation, surface stability against dissolution, surface Pourbaix diagrams, and reaction mechanisms provide useful predictions on catalyst durability, onset potential for water oxidation, surface atomic distribution, coverage of oxygenated species, and activity. The roles of the Pd interlayer in the core-shell structures that influence higher ORR activity are clarified. Furthermore, the stability and activity enhancement of new shell-anchor-core structures of Pt/Fe-C/core, Pt/Co-C/core and Pt/Ni-C/core are demonstrated with core materials of Ir, Pd3Co, Ir3Co, IrCo and IrNi. Based on the analysis, Pt/Fe-C/Ir, Pt/Co-C/Ir, Pt/Ni-C/Ir, Pt/Co-C/Pd3Co, Pt/Fe-C/Pd3Co, Pt/Co- C/Ir3Co, Pt/Fe-C/Ir3Co, Pt/Co-C/IrCo, Pt/Co-C/IrNi, and Pt/Fe-C/IrNi structures show promise in terms of both improved durability and relatively high ORR activity

Catalytic valorization of glycerol in the absence of external hydrogen: Effect of the Cu/ZrO2 catalyst mass and solvent

The glycerol valorization by heterogeneous catalysis to produce high-value-added chemicals is mainly carried out in the presence of high pressures of molecular hydrogen, a highly flammable gas whose main production in our days depends on fossil fuels. Therefore, an attractive alternative to explore is hydrogen in-situ generation in the catalytic process. Herein, we investigated the liquid-phase catalytic valorization of 80% wt. glycerol in different solvents such as water, 2-propanol, and acetone using a Cu/ZrO2 catalyst in the absence of external hydrogen. Firstly, the mass effect of the Cu/ZrO2 in the glycerol aqueous medium was evaluated finding an optimum mass of 250 mg for glycerol conversion. At these conditions, an initial reaction rate value of 2.63 × 10−3 molgly·gcat−1·min−1 was observed while the main products were hydroxyacetone (HA) and 1,2-propanediol (1,2-PDO). The use of 2-propanol as solvent and hydrogen donor molecule in the glycerol conversion induced the hydrogenation of hydroxyacetone towards 1,2-PDO. The ratio between the selectivity of 1,2-PDO/HA was found to be higher than that observed for the catalytic experiment with water. For the conversion of glycerol in the presence of acetone as a solvent it was noted the occurrence of acetalization reaction of glycerol with acetone and the main product observed was 4-hydroxymethyl-2,2-dimethyl-1,3-dioxalane or solketal. Density functional theory (DFT) calculations were included to gain insight into the reaction mechanisms of the hydroxyacetone hydrogenation to the formation of 1,2-PDO on Cu/ZrO2 catalyst. Four possible pathways were considered. The elementary steps include several intramolecular hydrogen atom transfer steps and two hydrogen addition steps. The hydrogen sources would come from adsorbed hydroxyl species of the aqueous reaction medium on ZrO2 support. © 2023 Elsevier B.V.RJC, JCZ, JG, and GG gratefully acknowledge the financial support from the Chilean National Fund for Science and Technology, Fondecyt N◦ 1180243 and N◦1220355. JCZ acknowledges the support provided by ANID with the scholarship grant N◦21201413 and to Universidad de Concepcion by the internationalization program “UCO 1866″. AFP thanks FCT for the projects UIDB/50006/2020, UIDP/50006/2020; and for the contract funding through the Individual Call to Scientific Employment Stimulus (2020.01614. CEECIND/CP1596/CT0007).Peer reviewe

Electroreduction of Carbon Dioxide to Methane on Copper, Copper–Silver, and Copper–Gold Catalysts: A DFT Study

The electrochemical reduction of CO₂ is a promising process capable of efficiently recycling CO₂ waste and converting it into hydrocarbon fuel. To date, copper is the best metal catalyst; however the overpotential to achieve this reaction on Cu is excessively high. It follows that the development of a catalyst to efficiently catalyze the conversion with a low overpotential at a reasonable current density is needed. Many aspects of the molecular details of the reaction are still unclear. In this work, DFT calculations are applied to investigate CO₂ electroreduction to CH₄ over Cu₃Ag and Cu₃Au stepped surfaces (211) compared to that over Cu(211). In the resulting analysis, the Cu₃Ag surface shows a slightly lower overpotential and suppresses OH poisoning compared to the Cu surface, yet the selectivity toward H₂ increases. The Cu₃Au is not a good candidate due to higher overpotential and a relatively weak CO adsorption resulting in CO desorption rather than further reduction. The CO desorption can also be problematic on Cu₃Ag as well. The thermodynamics and kinetics of the nonelectrochemical hydrogenations are also examined to explore alternative paths which might result in an absence of formaldehyde intermediate production during CO₂ reduction on Cu

The Effect of Epoxy Group on Ethylene Carbonate Decomposition at Carbon Anode of Sodium Ion Batteries: Theoretical Study

Sodium-ion batteries (SIBs) have received much attention as promising alternatives to Li-ion batteries as large scale and low-cost energy storage systems owing to close electrochemical similarity between lithium and sodium, and the natural abundance of sodium resources. However, many challenges must be overcome to make SIBs well-positioned in commercialization such as low cyclability, and low stability of the solid-electrolyte interphase (SEI) formation, results from the decomposition of organic solvents in the electrolyte on the anode of SIBs. The SEI has a profound effect on cycle life and performance of the batteries. Therefore, understanding the SEI compositions and its formation mechanisms is crucial for SIBs development. Carbon-based anode materials are commonly used as the anode for SIBs because of their appropriate electrochemical properties, an abundance of carbon and safety. The oxygen-containing groups often present in the carbon-based anode and they usually actively involved in chemical reactions. In this work, we performed density functional theory (DFT) calculations to elucidate the effect of oxygen containing group of epoxy on decomposition mechanisms at the initial stages of sodiation of ethylene carbonate (EC) molecule which is one of common electrolytes applied in ion-battery. The calculation results indicated that EC decompositions on pristine graphene were initiated by CE-OE bond cleavage which is rate-limiting step followed by Cc-OE bond cleavage in the second step producing CO2 and acetaldehyde as products (Figure 1). The presence of an epoxy group on graphene does not directly change the mechanisms, however, it significantly increased the activation barriers on all decomposition pathways compared to those on pristine graphene. The strong electrostatic interaction between negatively charged epoxy group and positively charged Na ion weakens interaction between EC and carbon surface. Also, the presence of an epoxy group facilitates carbon surface to be more positively charged and electron transfer to EC is less favorable than that on pristine graphene. Furthermore, we investigated the solvation effect on the mechanisms by increase the number of EC molecules to model a solvation shell. The results showed that the inclusion of the electrolyte environment reveals other possible decomposition mechanisms including proton transfer from EC molecule to epoxy group producing hydroxyl group on carbon surface prior to the EC ring-opening reaction step. This work suggests that the presence of oxygenated functional group on anode carbon surface and solvent environment can have significant effects on EC decomposition mechanisms both thermodynamic and kinetic aspects. Including the electrolyte solvation shell is crucial for electrolyte decomposition investigation using molecular modeling. Figure 1 <jats:p /