Fast and Clean Synthesis of Nylon-6/Synthetic Saponite Nanocomposites

Nylon/saponite nanocomposites were synthesized and characterized. The nanocomposites were prepared by means of a fast, efficient, low cost, and environmentally friendly method. All of the tested preparations resulted in the pre-designed nanocomposites. To this end, delaminated saponites were directly synthesized to be used as a filler in a polymer matrix formed by nylon-6 by the in situ intercalation polymerisation of an ε-caprolactam monomer without the use of surfactants or other organic reagents to organophilise the clay, thus avoiding the drawbacks of contamination. The efficiency of the preparation method increased, and significant savings were achieved in terms of both energy reaction time, savings of 60% and 70%, respectively, by using microwave radiation as an energy source during the synthesis of the nanocomposites. In addition, given that the method that was followed avoids the use of contaminating organophilic agents, it is important to highlight the savings in reagents and the fact that there was zero environmental contamination.

Production cross–section and reaction yield calculations for 123-126I isotopes on 123Sb(α,xn) reactions

Most of the radioisotopes used in the medical fields, like examination and treatment studies, were produced by employing nuclear reactions. Within the process of a nuclear reaction, one of the most important parameters is the cross-section data, which help reveal the reaction phenomenon's mechanisms. The main intention of this study is to investigate the efficiencies of producing iodine isotopes via 123Sb(α,xn) reactions. For this, optical and level density models of TALYS 1.8 code have been used. Production cross-section, the alpha beam energy, reaction yields, and total activation of radioisotopes have been computed. It has been figured out that a 45 MeV cyclotron could be enough for producing 123-126I radioisotopes with reaction yields of 39.3372, 5.5685, 0.2410, and 0.0796 GBq/mAh, respectively.

Promotion in solid phase reaction of Pt/SiOx bilayer film by electron-orbital-selective-excitation

A thermally impossible positive free energy reaction can proceed by electron-orbital-selective excitation.

Substituição nucleofílica alifática: qual o mecanismo preferencial? Estudo computacional dos efeitos da estrutura do substrato e solvente

Nucleophilic aliphatic substitution reactions constitute important steps in the synthesis of substances with biological activity and industrial appeal, beyond to participating in steps in biosynthetic routes of natural products. Unimolecular (SN1) and bimolecular (SN2) pathways can be understood as limiting cases of a mechanistic continuum. In between them, borderline mechanisms are proposed. The preference for one path over another depends on several factors, such as the structure of the substrate, the nucleophile and the solvent used. This plurality is still a topic of discussion and needs further understanding. In this context, the present work aims to rationalize the preferential reaction pathway for nucleophilic aliphatic substitutions, whose substrates do not fit only in the uni- and bimolecular models, by identifying lower energy reaction pathways due to the structural and electronic characteristics. The evaluation was carried out by molecular modeling at the Density Functional Theory (DFT) level, simulating substrates with the nucleofuge (Cl and NH3 + ) connected to secondary carbon atoms, with the computational method M06-2X/aug-cc-pVTZ, previously validated according to geometrical and energetic parameters. Besides, we checked the effect of a polar solvent with high dielectric constant in the reaction pathways. The analyzed substrates demonstrated preference for the bimolecular mechanism and the influence of a solvent in these reactions was evident.

Photocatalytic selective oxidation of methane by quantum sized bismuth vanadate

Selective oxidation of methane to desirable C1 oxygenates has long been the major challenge in catalysis. Here we report photocatalytic oxidation of methane by using quantum-sized bismuth vanadate nanoparticles as catalyst and oxygen as mild oxidant. A high selectivity towards methanol (1.1 mmol g-1 yield and 96.6% selectivity) and formaldehyde (13.1 mmol g-1 yield and 86.7% selectivity) products is successfully realized by simply controlling the light wavelength, light energy, reaction time and the amount of water solvent. Comprehensive characterizations disclose that the radical reaction mechanism is responsible for this efficient photocatalytic methane conversion.

Novel Insights into the Thioesterolytic Activity of N-Substituted Pyridinium-4-oximes

The pyridinium oximes are known esterolytic agents, usually classified in the literature as catalysts, which mimic the catalytic mode of hydrolases. Herein, we combined kinetic and computational studies of the pyridinium-4-oxime-mediated acetylthiocholine (AcSCh+) hydrolysis to provide novel insights into their potential catalytic activity. The N-methyl- and N-benzylpyridinium-4-oximes have been tested as oximolytic agents toward the AcSCh+, while the newly synthesized O-acetyl-N-methylpyridinium-4-oxime iodide was employed for studying the consecutive hydrolytic reaction. The relevance of the AcSCh+ hydrolysis as a competitive reaction to AcSCh+ oximolysis was also investigated. The reactions were independently studied spectrophotometrically and rate constants, koxime, kw and kOH, were evaluated over a convenient pH-range at I = 0.1 M and 25 °C. The catalytic action of pyridinium-4-oximes comprises two successive stages, acetylation (oximolysis) and deacetylation stage (pyridinium-4-oxime-ester hydrolysis), the latter being crucial for understanding the whole catalytic cycle. The complete mechanism is presented by the free energy reaction profiles obtained with (CPCM)/M06–2X/6–311++G(2df,2pd)//(CPCM)/M06–2X/6–31+G(d) computational model. The comparison of the observed rates of AcSCh+ oximolytic cleavage and both competitive AcSCh+ and consecutive pyridinium-4-oxime-ester hydrolytic cleavage revealed that the pyridinium-4-oximes cannot be classified as non-enzyme catalyst of the AcSCh+ hydrolysis but as the very effective esterolytic agents.

An Evaluation of Energy-loss Straggling Calculation of the LISE++ Code

Energy loss straggling was found to be critical in evaluating the energy reaction using heavy-ion beams during the early stage of experiments at accelerator facilities. Despite a significant attempt in simulating this quantity using computer codes such as LISE++ and SRIM, there still exists a discrepancy between experimental data and computed results. In this study, we provide a greatly improved precision of estimations using the LISE++ code by evaluating the energy loss straggling of the alpha particles at 5.486 MeV in Tb, Ta, and Au materials. After comparing with the observables, it was found that the ratio of the energy loss straggling computed by the LISE++ code to that measured in experiments has a fairly large range of 1.5 - 3.0. For this reason, the so-called modified LISE++ calculation is constructed by adding the adjusting parameters into the original estimation to minimize the uncertainty of the straggling prediction. The modified calculation has shown dramatic improvements in computed energy loss straggling, which are almost similar to those obtained in the measurements, of 5.486-MeV alphas in the aforementioned materials with the atomic numbers in a range of Z = 65 – 79.