Integrated Leaching and Separation of Metals Using Mixtures of Organic Acids and Ionic Liquids

In this work, the aqueous phase diagram for the mixture of the hydrophilic tributyltetradecyl phosphonium ([P₄₄₄₁₄]Cl) ionic liquid with acetic acid (CH₃COOH) is determined, and the temperature dependency of the biphasic region established. Molecular dynamic simulations of the [P₄₄₄₁₄]Cl + CH₃COOH + H₂O system indicate that the occurrence of a closed “type 0” biphasic regime is due to a “washing-out” phenomenon upon addition of water, resulting in solvophobic segregation of the [P₄₄₄₁₄]Cl. The solubility of various metal oxides in the anhydrous [P₄₄₄₁₄]Cl + CH₃COOH system was determined, with the system presenting a good selectivity for CoO. Integration of the separation step was demonstrated through the addition of water, yielding a biphasic regime. Finally, the [P₄₄₄₁₄]Cl + CH₃COOH system was applied to the treatment of real waste, NiMH battery black mass, being shown that it allows an efficient separation of Co(II) from Ni(II), Fe(III) and the lanthanides in a single leaching and separation step.     

Chagas Disease: Perspectives on the Past and Present and Challenges in Drug Discovery

Chagas disease still has no effective treatment option for all of its phases despite being discovered more than 100 years ago. The development of commercial drugs has been stagnating since the 1960s, a fact that sheds light on the question of how drug discovery research has progressed and taken advantage of technological advances. Could it be that technological advances have not yet been sufficient to resolve this issue or is there a lack of protocol, validation and standardization of the data generated by different research teams? This work presents an overview of commercial drugs and those that have been evaluated in studies and clinical trials so far. A brief review is made of recent target-based and phenotypic studies based on the search for molecules with anti-Trypanosoma cruzi action. It also discusses how proteochemometric (PCM) modeling and microcrystal electron diffraction (MicroED) can help in the case of the lack of a 3D protein structure; more specifically, Trypanosoma cruzi carbonic anhydrase.     

Guido Beck,Alexandre Proca,and the Oporto Theoretical Physics Seminar

We describe the pioneering attempts made by Ruy Luís Gomes (1905–1984) and other Portuguese physicists to develop a research and teaching seminar in theoretical physics at the University of Oporto in 1942–1944 under the leadership first of the refugee Austrian theoretical physicist Guido Beck (1903–1988) and then of the Romanian-French theoretical physicist Alexandre Proca (1896–1955). These efforts failed, however, owing to lack of sustained financial support from the Portuguese government and to the political repression of the Salazar regime, which dismissed Gomes and other prominent Portuguese physicists and other scientists from their university positions.     

Silica-titania sol-gel hybrid materials: synthesis, characterization and potential application in solid phase extraction

The biphenilaminepropylsilica and biphenilaminepropylsilicatitania were synthesized by sol-gel method, in two steps: (a) biphenylamine reacts with chloropropyltrimethoxysilane and (b) the product of reaction was polycondensed with tetraethylorthosilicate (TEOS) or TEOS and titanium isopropoxide. The sol-gel materials were characterized using infrared spectroscopy and N₂ adsorption-desorption isotherms and they were employed as sorbents for carcinogenic N-containing compound retention, in aqueous solution, using the SPE technique. The N-containing compounds adsorption was influenced by the titania presence and the sorption process seems to happen in the pores with higher organic density.     

Semiempirical simulation of a theta‐class glutathione S‐transferase‐catalyzed glutathione attack to the allelochemical DIMBOA

We evaluated by the semiempirical method PM3 possible mechanisms of a putative interaction between a cereal allelochemical, the cyclic hydroxamic acid 2,4‐dihydroxy‐7‐metoxy‐2H‐1,4‐benzoxazin‐3(4H)‐one (DIMBOA), and the tripeptide glutathione (GSH) inside the active site of a theta‐class glutathione S‐transferase. Based on a preliminary study of transition states from DIMBOA reactions with methanethiolate as a simple model of GSH, we investigated the roles of catalytic residues of the enzyme during nucleophilic additions of GSH to the carbonyl groups of DIMBOA and of its phenol/aldehyde isomer inside the active site model. Our results suggest that a tyrosine residue, Tyr113, makes the most important contributions for the catalytic mechanism. In the modeled reaction steps, Tyr113 behaves as a double hydrogen bond donor catalyst for nucleophilic additions of GSH to substrates: It initially helps stabilize the strongly nucleophilic reduced GSH with a hydrogen bond intermediated by a water molecule; during substrate approach, small conformational changes enable the residue to make a direct hydrogen bond to the substrate group that develop negative charge after addition of reduced GSH. © 2002 Wiley Periodicals, Inc.; Int J Quantum Chem, 2002     

Synthesis of Purine-Based Ionic Liquids and Their Applications

Bio-based ionic liquids (ILs) are being increasingly sought after, as they are more sustainable and eco-friendly. Purines are the most widely distributed, naturally occurring N-heterocycles, but their low water-solubility limits their application. In this work, four purines (theobromine, theophylline, xanthine, and uric acid) were combined with the cation tetrabutylammonium to synthesize bio-based ILs. The physico–chemical properties of the purine-based ILs were characterized, including their melting and decomposition temperatures and water-solubility. The ecotoxicity against the microalgae Raphidocelis subcapitata was also determined. The ILs show good thermal stability (>457 K) and an aqueous solubility enhancement ranging from 53- to 870-fold, in comparison to their respective purine percursors, unlocking new prospects for their application where aqueous solutions are demanded. The ecotoxicity of these ILs seems to be dominated by the cation, and it is similar to chloride-based IL, emphasizing that the use of natural anions does not necessarily translate to more benign ILs. The application of the novel ILs in the formation of aqueous biphasic systems (ABS), and as solubility enhancers, was also evaluated. The ILs were able to form ABS with sodium sulfate and tripotassium citrate salts. The development of thermoresponsive ABS, using sodium sulfate as a salting-out agent, was accomplished, with the ILs having different thermosensitivities. In addition, the purine-based ILs acted as solubility enhancers of ferulic acid in aqueous solution.     

Nucleate and transition boiling in narrow horizontal spaces

Nucleate and transition boiling are performed in a horizontal narrow space between a heated upward-facing copper disk and an unheated surface for saturated n-pentane. The heat flux and the wall temperature are determined by mean of an inverse heat conduction method. The influence of the confinement on the boiling curves and the flow patterns are analysed. Characteristic instabilities are observed at low heat flux and during the transition regime.     

Profiling propolis flavonoids by means of micellar electrokinetic capillary chromatography, capillary gas chromatography and bactericidal action

Summary There is no proportional correlation between increasing organic solvent polarity from hexane to methanol and the extractability of propolis solids by the solvents or the bactericidal action of the propolis extracts obtained. Hexane (17.7%) and chloroform (62.1%) were the poorest and the best extractants, respectively, for propolis solids. The antibiotic activity of the extracts againstStaphylococcus strains decreased in the order hexane≥ethanol>methanol. Different capillary GC profiles were obtained for persilyl derivatives of propolis extracted with hexane and methanol and for propolis collected in different Brazilian provinces, suggesting the influence of flora variability on propolis composition. Wavelength-selected DAD detection revealed MEKC to be an innovative and sensitive method for monitoring the occurrence in propolis of the flavonoids and phenolcarboxylic acids thought to be responsible for the antimicrobial activity of propolis.     

Host–guest interactions and their role in enantioselective hydrogenation of α-keto esters: An analysis of model systems

The interaction between cinchonidine and methyl pyruvate has been proposed as the key step leading to enantiodifferentiation in the enantioselective hydrogenation of α-ketoesters. In the present work, we employ ab initio MP2/6-31G(d) and MP2/6-31G(d,p) methods to carry out an analysis of the most relevant kind of interactions operating in representative model systems. These interactions are discussed in terms of orbital superposition and dipolar interaction. When approaching H₂CO to NH₃ at distances lower than 3.4 Å, orbital superposition is the predominant interaction, while at distances above 3.4 Å, both orbital superposition and dipolar interactions may contribute to stabilization, with a small prevalence of dipolar interactions. The stabilization energy at large distances (above 4.5 Å) is very small (about 0.5 kcal mol⁻¹), probably not enough to be responsible for the enantiodifferentiation process. Semiempirical calculations on the parent systems were also unable to reveal any special interaction which could be attributed to the enantiodifferentiation process.     

Accuracy of the multipole expansion applied to a sphere in a creeping flow parallel to a wall

An example system is studied to discuss precision of the multipoleexpansion, applied to determine forces exerted on particlesby a viscous low-Reynolds-number fluid flow. A single spherein an ambient flow (pure shear, quadratic, and modulated shear)parallel to a close plane wall is considered. Forces and torquesexerted by the ambient flow on a motionless sphere are evaluated.Their precision is determined and related to a multipole orderof the truncation. Similar analysis is performed for a movingsphere with no ambient flow and for a freely moving sphere.Relative motion of the sphere with respect to the wall givesrise to strong lubrication interactions. It is analysed howthese interactions affect accuracy of the pure multipole expansion,and what are the smallest distances where it becomes insufficient.An alternative precise method is applied, in which lubricationexpressions are subtracted from the hydrodynamic forces andtorques, and the residue is evaluated as a fast-convergent seriesof inverse powers of the distance between the sphere centreand the wall. The accuracy of this procedure is carefully analysed.