Diphenylacetylene hydrogenation on a PdAg/Al2O3 single-atom catalyst: an experimental and DFT study
The hydrogenation of diphenylacetylene (DPA) on palladium–silver catalysts with a single-atom structure was investigated. It has been shown experimentally that the reaction rate of alkene to alkane hydrogenation is substantially lower than the rate of DPA semi-hydrogenation. The kinetic barriers of all stages of hydrogenation were calculated by the DFT method.
The Diels-Alder reaction is a cornerstone of modern organic synthesis. Despite this, it remains essentially inaccessible to biosynthetic approaches. Only a few natural enzymes catalyze even a formal [4+2] cycloaddition, and it remains uncertain if any of them proceed via the Diels-Alder mechanism. In this study, we focus on the [4+2] cycloaddition step in the biosynthesis of spinosyn A, a reaction catalyzed by SpnF enzyme—one of the most promising “true Diels-Alderase” candidates. The four currently proposed mechanisms (including the Diels-Alder one) for this reaction in water (as a first-order approximation of the enzymatic reaction) are evaluated by an exhaustive quantum mechanical search for possible transition states (728 were found in total). We find that the line between the recently proposed bis-pericyclic [J. Am. Chem. Soc. 2016, 138 (11), 3631] and Diels-Alder routes is blurred, and favorable transition states of both types may coexist. Application of the Curtin-Hammett principle, however, reveals that the bis-pericyclic mechanism accounts for ≈83% of the reaction flow in water, while the classical Diels-Alder mechanism contributes only ≈17%. The current findings provide a route for modeling this reaction inside the SpnF active site and inferring the catalytic architecture of possible Diels-Alderases.
Ozonolysis of furocoumarins followed by reductive work-up yields not only common symmetrical dialdehydes, but also o-for- mylumbelliferones with moderate-to-high yields. Simultaneous formation of both products accounts for the transformation of carbonyl oxides – products of primary ozonide ring opening
This article explores the internal and external factors influencing the compliance performance of the Group of 20 (G20) and the BRICS. The authors start with an overview of the G20 and BRICS compliance patterns using comparative data onthe number of commitments made by the two institutions, the level of institutional compliance, and distribution of commitments and compliance across issue areas. G20 compliance is traced since the leaders’ first 2008 summit in Washington. The BRICS compliance performance record includes data since the third stand alone summit in Sanya in 2011.The study then takes stock of compliance catalysts embedded in the summits’ discourse: priority placements, numerical targets, timelines, self-accountability pledges and mandates to implement and/or monitor implementation. The authors review trends in the use of catalysts in different years and issue areas and identify commonalities and differences.The analysis then turns to external causes of compliance and focuses on demand for collective actions and members’ collective power to respond and deliver on their pledges. Here the study explores whether the self-accountability mechanisms created by the institutions in response to the demand for effectiveness and legitimacy facilitate compliance.The article concludes by highlighting catalysts, causes of compliance and their combinations with the greatest power to encourage implementation, explaining trends in G20 and BRICS compliance performance. The data sets on G20 and BRICS differ in terms of scale. The G20 data set contains 1,511 commitments of which 114 have been monitored, and the BRICS data set contains 231 commitments of which 23 have been monitored.
The New Russian Encyclopedia is a fundamental reference publication in 18 volumes that characterizes nature, population, economy, history, science, art, technology and other important aspects. Contains about 60,000 articles, about 30,000 biographies, about 15,000 color illustrations, maps, charts, diagrams, tables. Leaves since 2003.
Rigid amphipathic fusion inhibitors are potent broad-spectrum antivirals based on the perylene scaffold, usually decorated with a hydrophylic group linked via ethynyl or triazole. We have sequentially simplified these structures by removing sugar moiety, then converting uridine to aniline, then moving to perylenylthiophenecarboxilic acids and to perylenylcarboxylic acid. All these polyaromatic compounds, as well as antibiotic heliomycin, still showed pronounced activity against tick-borne encephalitis virus (TBEV) with limited toxicity in porcine embryo kidney (PEK) cell line. 5-(Perylen-3-yl)-2-thiophenecarboxylic acid (5a) showed the highest antiviral activity with 50% effective concentration of approx. 1.6 nM.
This volume, being the 55th of this Series, contains a wealth of information on bioactive natural products. In Chapter 1, Watson and colleagues have discussed the synthesis of monoterpene indole alkaloids, an important class of structurally diverse natural products, with respect to conventional and biomimetic synthetic approaches.
Titanocene(III) has been widely used in the synthesis of complex organic molecules and natural products including polyketides, phenylpropanoids, antibiotics, and alkaloids. Oltra and coworkers have provided a review on the stereoselective synthesis of natural products facilitated by titanocene(III) in Chapter 2.
About 70 biologically active macrocyclic bisbibenzyls (MBBs) have been isolated and structurally elucidated during the last 30 years. Song and Zhao, in Chapter 3, have provided a review on the synthesis of MBBs with diverse pharmacological properties.
Diabetes mellitus is the most common endocrine/metabolic disorder that poses a global health concern. Reyes and colleagues have discussed the hypoglycemic activity of some terrestrial and marine bioactive compounds with potential for treating type 2 diabetes in Chapter 4. In Chapter 5, Pietruszka and coworkers have highlighted the importance of some marine oxylipins that exhibit different bioactive properties.
Depression has become a psychiatric disorder, which leads to various disabilities. Natural compounds like polyphenols and terpenoids have antioxidant and neuroprotective properties and can be used for the treatment of depression. In Chapter 6, Rodrigues et al. review the clinical studies and trials on polyphenols and terpenoids for the treatment of various psychiatric disorders. The lipid A phosphate and their phosphorylated analogues found in Gram-negative bacteria are of major importance because they provide the host with defense against infections from various microorganisms. Paradies and Zimmermann have discussed physical characteristics, isolation, and bioactivity of lipopolysaccharides (lipid A) for developing new vaccines and therapeutics in Chapter 7.
Hydroxycinnamic acids (HCAs) are a group of phytonutrients with numerous beneficial effects on human health that are largely derived from plants. HCAs play important roles like defense against UV rays or pathogenic attack during growth and development of plants. In Chapter 8, El-Seedi and colleagues present a review focusing on the therapeutic effects of HCAs for the treatment of cancer, diabetes, pulmonary, hepatic, neuro-, and cardiovascular diseases. In Chapter 9, Pomilio and Mercader have presented the study of natural anthocyanins and other related flavonoids for the readers, highlighting their possible and preferable uses as health-protecting food dyes over synthetic ones. They have also discussed the anthocyanins isolated from Ipomoea cairica along with their QSAR studies.
Cardiovascular diseases are considered to be a major threat to health. Polyphenols and carotenoids are structurally diverse groups of bioactive compounds isolated from fruits and vegetables, carrying protective effects against endothelial dysfunction. These therapeutic effects have been explored by Yamagata in Chapter 10.
The roots of licorice and ivy leaves have been used in folk medicine and drugs since long. The biological activity of these complexes has been discussed by Yakovishin and Grishkovets in Chapter 11. In Chapter 12, the chemical and biological characteristics of amicoumacins and xenocoumacins are reviewed by Korshun et al. with reference to the preparation of antibiotics.
I hope that this volume will be received with the same enthusiasm as the earlier volumes of this long-standing series the first volume of which was published under my Editorship in 1988. I would like to express my gratitude to Ms. Taqdees Malik and Mr. Mahmood Alam for their assistance in the preparation of this volume.
Composite materials based on homogeneous perfluorinated cation exchange membranes MF-4SK and sulfonated zirconium oxide were obtained by in situ and casting methods and their transport properties and gas permeability were studied. With the introduction of sulfonated zirconia, the conductivity of in situ and casting membranes increases at room temperature by more than 1.5 and 4 times, respectively. The anion transfer numbers characterizing the undesirable anion transfer for composite membranes obtained by the in situ and casting methods decrease by more than 1.5 times (from 0.026 to 0.020 and from 0.020 to 0.014, respectively). For samples based on MF-4SK membranes and zirconium oxide, a significant (more than 3 times) decrease in hydrogen permeability was noted. The differences in the observed values of moisture content, conductivity and mutual diffusion of the obtained composite membranes are discussed.
Hybrid membranes were prepared by incorporating silica with propyl-imidazoline groups in polybenzimidazoles (phthalide-containing PBI or PBI based on 2,6- or 2,5-pyridinedicarboxylic acids). The influence effects of the silica precursor hydrolysis conditions on the conductivity of the hybrid membranes are studied. Ionic conductivity, water uptake, phosphoric acid doping, and gas permeability of the obtained materials were found to depend on the preparation method and the silica loading. The materials with 10 wt% of functionalized silica present the highest conductivity. A decrease of hydrogen permeability is observed for low silica loadings.