Green Synthesis of 2-thioxothiazolidin-4-one Derivatives in Deep Eutectic Solvents via Knoevenagel Condensation

Recently, more and more researchers are resorting to green methods and techniques to avoid environmental pollution. Accordingly, many researchers have been working on the development of new green synthetic procedures trying to avoid the use of toxic organic solvents. A sustainable concept of green and environmentally friendly solvents in chemical synthesis nowadays encompasses a relatively new generation of solvents called deep eutectic solvents (DESs). DESs often have a dual role in the synthesis, acting as both, solvents and catalysts. In this study, DESs are used in the Knoevenagel synthesis of rhodanine derivatives, with no addition of conventional catalysts. A model reaction of rhodanine and salicylaldehyde was performed in 20 different DESs at 80 °C, in order to find the best solvent, which was further used for the synthesis of the series of desired compounds. A series of rhodanines was synthesized in choline chloride: acetamide (ChCl:acetamide) DES with good to excellent yields (51.4 – 99.7 %).

Performances of Homogeneous and Heterogenized Methylene Blue on Silica Under Red Light in Batch and Continuous Flow Photochemical Reactors

Methylene blue was efficiently immobilized on silica micro- and nanoparticles by electrostatic interactions and the performances of the heterogenized photocatalysts were compared against the homogeneous conditions using the photooxidation of citronellol as a model reaction under red light, in a batch and a continuous flow photochemical reactor. In batch, the heterogeneous photocatalyst outperforms the homogeneous one, presumably due to kinetic and stability effects. The two catalytic systems are also compared in a flow reactor displaying improved mass transfer properties. We demonstrate that this results in a dramatic enhancement in photocatalyst stability, reactivity and productivity. This study highlights the importance of photocatalyst stability under homogeneous versus heterogenized conditions and in batch versus flow photochemistry.

Electrogenerated BF3 From Tetrafluoroborate-Based Ionic Liquids: Theoretical And Experimental Studies Towards Selective Styrene Oxide Isomerization

The anodic oxidation of tetrafluoroborate anion yields the Lewis acid BF3. If this reaction is carried out in an imidazolium ionic liquid, a quite stable system containing BF3 is obtained, whose reactivity is similar to the one of BF3·Et2O, but less harmful. The two reagents’ stabilities were compared by computational analysis, strongly suggesting a higher stability for BF3/BMIm-BF4 system. The effect of substituents on the imidazolium ring and of the electrochemical configuration on BF3 reactivity were studied in a model reaction, styrene oxide isomerization. The experimental conditions were defined for the selective formation of phenylacetaldehyde or of 2-benzyl-4-phenyl-1,3-dioxolane. Moreover, the formation of N-heterocyclic carbene-BF3 adduct was confirmed when carrying out the electrolysis in an undivided cell. Electrogenerated BF3/BMIm-BF4 system demonstrated to be a valid alternative to commercial BF3·Et2O.

Effect of Stabilizers in the Synthesis of Silver Nanoparticles and Methylene Blue Oxidation

Metal nanocatalysts have received increasing attention in catalysis due to their higher reactivity and surface area-to-volume ratio at nano-size. Silver nanoparticle (AgNP) is among metal nanocatalysts that have been studied in various catalytic reactions (e.g., hydrogenation and oxidation). However, the high reactivity of AgNPs at nano-size caused instability and aggregation. Therefore, stabilizing molecules (or stabilizers) are always applied to maintain the nano size of AgNPs and prevent aggregation. Herein, the effects of different types and molar ratio of stabilizers-to-Ag precursor, to the synthesized AgNPs (i.e, size and concentration) were investigated. Two types of stabilizers, polyvinylpyrrolidone (PVP) and citrate were used in this study. The roles of stabilizers to the catalytic performance of synthesized AgNPs were then elucidated by using methylene blue oxidation as the model reaction. The UV-Vis absorption analyses showed that both stabilizers produced slightly different size and concentration of AgNPs based on the different wavelength and absorption intensity of the peak. We also found that the molar ratio of stabilizers-to-Ag precursor that produced better yield of AgNPs was 1:1 and 1:3 for PVP and citrate, respectively. Then, AgNPs stabilized by citrate was found having slightly higher catalytic activity in the methylene blue oxidation than AgNPs stabilized by PVP. This study provides insights to the roles of stabilizers for the synthesis of stable AgNPs with efficient catalytic reaction and can be used as guideline to other metal nanocatalysts.

Entropic Path Sampling: Computational Protocol to Evaluate Entropic Profile along a Reaction Path

Fleeting intermediates constitute dynamically-stepwise mechanisms. They have been characterized in molecular dynamics trajectories, but whether these intermediates form a free energy minimum to become entropic intermediate remains elusively defined. We developed a computational protocol known as entropic path sampling to evaluate the entropic variation of reacting species along a reaction path based on an ensemble of trajectories. Using cyclopentadiene dimerization as a model reaction, we observed a shallow entropic trap (–T∆S = –0.8 kcal/mol) along the reaction path which originates from an enhanced conformational flexibility as the reacting species enter into a flat energy region. As the reacting species further approach product formation, unfavorable entropic restriction fails to offset the potential energy drop, resulting in no free energy minimum along the post-TS pathway. Our results show that cyclopentadiene dimerization involves an entropic trap that leads to dynamic intermediates with elongated lifetime, but the reaction does not involve entropic intermediates.

On the road to percent accuracy V: The non-linear power spectrum beyond ΛCDM with massive neutrinos and baryonic feedback

In the context of forthcoming galaxy surveys, to ensure unbiased constraints on cosmology and gravity when using non-linear structure information, percent-level accuracy is required when modelling the power spectrum. This calls for frameworks that can accurately capture the relevant physical effects, while allowing for deviations from ΛCDM. Massive neutrino and baryonic physics are two of the most relevant such effects. We present an integration of the halo model reaction frameworks for massive neutrinos and beyond-ΛCDM cosmologies. The integrated halo model reaction, combined with a pseudo power spectrum modelled by HMCode2020 is then compared against N-body simulations that include both massive neutrinos and an f(R) modification to gravity. We find that the framework is 4 per cent accurate down to at least k ≈ 3 h Mpc−1 for a modification to gravity of |fR0| ≤ 10−5 and for the total neutrino mass Mν ≡ ∑mν ≤ 0.15 eV. We also find that the framework is 4 per cent consistent with EuclidEmulator2 as well as the Bacco emulator for most of the considered νwCDM cosmologies down to at least k ≈ 3 h Mpc−1. Finally, we compare against hydrodynamical simulations employing HMCode2020’s baryonic feedback modelling on top of the halo model reaction. For νΛCDM cosmologies we find 2 per cent accuracy for Mν ≤ 0.48 eV down to at least k ≈ 5h Mpc−1. Similar accuracy is found when comparing to νwCDM hydrodynamical simulations with Mν = 0.06 eV. This offers the first non-linear, theoretically general means of accurately including massive neutrinos for beyond-ΛCDM cosmologies, and further suggests that baryonic, massive neutrino and dark energy physics can be reliably modelled independently.

Radiosynthesis of 5-[18F]Fluoro-1,2,3-triazoles through Aqueous Iodine–[18F]Fluorine Exchange Reaction

In this report, a simple and efficient process to achieve fluorine-18-labeled 1,2,3-triazole is reported. The heteroaromatic radiofluorination was successfully achieved through an iodine–fluorine-18 exchange in an aqueous medium requiring only trace amounts of base and no azeotropic drying of fluorine-18. This methodology was optimized on a model reaction and further validated on multiple 1,2,3-triazole substrates with 18–60% radiochemical conversions. Using this strategy—the radiosynthesis of a triazole-based thiamin analogue—a potential positron emission tomography (PET) probe for imaging thiamin-dependent enzymes was synthesized with 10–16% isolated radiochemical yield (RCY) in 40 min (uncorrected, n > 5).

Free radical-mediated acetaldehyde formation by model reactions of dietary components: effects of meat, wine, cooking oil and coffee

Background Alcohol consumption and the ingestion of red meat and oxidized cooking oil are risk factors of gastric and colorectal cancers. We reported that acetaldehyde (AcAld) is generated from Heme/Mb/Meat-Linoleate-EtOH model reaction mixtures, and thus could be a new plausible mechanism for the carcinogenesis (Kasai and Kawai, ACS Omega, 2021). Results In this study, we investigated the effects of wine and coffee, in addition to meat components, on this reaction. Depending on the conditions, such as pH, reaction time and choice of free hemin, myoglobin (Mb), as well as meat extracts (raw meat, baked meat, salami), wine and coffee enhanced AcAld formation. Polyphenols in red wine and coffee may stimulate AcAld formation by acting as pro-oxidants in the presence of Heme/Mb/Meat. In a model reaction of Mb + EtOH + H2O2, we observed time-dependent AcAld formation. In support of these in vitro data, after the consumption of a red meat-rich diet with red wine, the fecal AcAld level significantly increased as compared to the levels associated with a diet of fish + wine, or red meat without alcohol. Conclusions These results suggested that AcAld generation from dietary components may be an important mechanism of gastrointestinal tract carcinogenesis.

Selenoxide Elimination Triggers Enamine Hydrolysis to Primary and Secondary Amines: A Combined Experimental and Theoretical Investigation

We discuss a novel selenium-based reaction mechanism consisting in a selenoxide elimination-triggered enamine hydrolysis. This one-pot model reaction was studied for a set of substrates. Under oxidative conditions, we observed and characterized the formation of primary and secondary amines as elimination products of such compounds, paving the way for a novel strategy to selectively release bioactive molecules. The underlying mechanism was investigated using NMR, mass spectrometry and density functional theory (DFT).