Disorder Induced Effects on the Critical Current Density of Iron Pnictide BaFe_1.8 Co_0.2 As_2 single crystals

Investigating the role of disorder in superconductors is an essential part of characterizing the fundamental superconducting properties as well as assessing potential applications of the material. In most cases, the information available on the defect matrix is poor, making such studies difficult, but the situation can be improved by introducing defects in a controlled way, as provided by neutron irradiation. In this work, we analyze the effects of neutron irradiation on a Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystal. We mainly concentrate on the magnetic properties which were determined by magnetometry. Introducing disorder by neutron irradiation leads to significant effects on both the reversible and the irreversible magnetic properties, such as the transition temperature, the upper critical field, the anisotropy, and the critical current density. The results are discussed in detail by comparing them with the properties in the unirradiated state.Comment: accepted for Ph

Необычные векторные сингулярности в неоднородно поляризованных оптических полях

Вводиться означення комплексного ступеня поляризації з представленням у стоксовому просторі й на цій основі визначається новий тип векторних сингулярностей у частково когерентних, неоднорідно поляризованих оптичних полях – U-контури, вздовж яких ступінь поляризації дорівнює нулю, і при перетині яких стан поляризації змінюється на ортогональний.The complex degree of polarization is defined and represented at the Stokes space, and on this base the new type of vector singularities in partially coherent, inhomogeneously polarized optical fields is determines, namely, the U-contours along which the degree of polarization equals zero, and by crossing of which the state of polarization changes by jump into orthogonal one.Вводится определение комплексной степени поляризации с представлением в стоксовом пространстве и на этой основе определяется новый тип векторных сингулярностей в частично когерентных, неоднородно поляризованных оптических полях – U-контуры, вдоль которых степень поляризации равняется нулю, и при пересечении которых состояние поляризации изменяется на ортогональное

Self-organized current transport through low angle grain boundaries in YBa2_2Cu3_3O7−δ_{7-\delta} thin films, studied magnetometrically

The critical current density flowing across low angle grain boundaries in YBa$_2$Cu$_3$O$_{7-\delta}$ thin films has been studied magnetometrically. Films (200 nm thickness) were deposited on SrTiO$_3$ bicrystal substrates containing a single [001] tilt boundary, with angles of 2, 3, 5, and 7 degrees, and the films were patterned into rings. Their magnetic moments were measured in applied magnetic fields up to 30 kOe at temperatures of 5 - 95 K; current densities of rings with or without grain boundaries were obtained from a modified critical state model. For rings containing 5 and 7 degree boundaries, the magnetic response depends strongly on the field history, which arises in large part from self-field effects acting on the grain boundary.Comment: 8 pages, including 7 figure

Oxidizing reactions of azines. 8. One-reactor oxidation of 4-aryl and 4-methyl-1,2,3,6-tetrahydropyridines to 1-formylamino-substituted alkan-3-ones

One-reactor oxidation by potassium permanganate has been carried out for a series of 4-aryl- and 4-methyl-l,2,3,6-tetrahydropyridines to give 1-formylamino-substituted 3-arylpropan-3-ones and butan-3-ones. The effect has been studied of the nature of the substrate, the temperature, and interphase transfer catalysts on the yield of amino alkanone. It is proposed that the reaction proceeds through the intermediate formation of 3,4-dihydroxypiperidin-2-ones which then undergo oxidative decyclization with elimination of one carbon atom

Synthesis and ethylene-promoted metathesis of adducts of tandem [4+2]/[4+2] cycloaddition between bis-furyl dienes and maleic acid derivatives

During this work, a series of 1,4:5,8-diepoxynaphthalenes, annellated with various carbo- and heterocycles, was synthesized based on the tandem intermolecular/intramolecular [4+2] cycloaddition of bis-furyl dienes with moderately to highly reactive cyclic dienophiles (maleic anhydride and maleinimides). The stereochemistry of the resulting adducts was established using 2D NMR and X-ray structural analysis, which showed that both successive Diels-Alder reactions led to single diastereoisomers of the target cycloadducts corresponding to the exo-transition state. The resulting hexacyclic compounds represent original polyfunctional synthons suitable for subsequent transformations, which has been demonstrated by the example of the ethylene-promoted ROCM reaction under new types of second-generation Hoveyda-Grubbs catalysts comprising a coordination N → Ru bond in a six-membered ring. As a result, the metathesis products, unsaturated 4,7-epoxyisobenzofurans, were obtained in satisfactory yields. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique

Influence of the N→Ru Coordinate Bond Length on the Activity of New Types of Hoveyda-Grubbs Olefin Metathesis Catalysts Containing a Six-Membered Chelate Ring Possessing a Ruthenium-Nitrogen Bond

An efficient approach to the synthesis of new types of Hoveyda-Grubbs catalysts containing an N→Ru bond in a six-membered chelate ring is proposed. The synthesis of the organometallic compounds is based on the interaction of ready accessible 2-vinylbenzylamines and 1,3-bis(2,4,6-trimethylphenyl)-2-trichloromethylimidazolidine ligands with dichloro(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphane)ruthenate, and it afforded the target ruthenium complexes in 70-80% yields. Areas of practical utility and potential applications of the obtained chelates were highlighted by tests of the catalysts in different olefin cross-metathesis (CM) and ring-closing-metathesis (RCM) reactions. These experiments revealed a high catalytic performance (up to 10-2 mol %) of all the synthesized structures in a broad temperature range. The structural peculiarities of the resultant ruthenium catalysts were thoroughly investigated by X-ray crystallography, which allowed making a reliable correlation between the structure of the metallo-complexes and their catalytic properties. It was proved that the bond length between ruthenium and nitrogen in the six-membered chelate ring has the greatest effect on the stability and efficiency of the catalyst. As a rule, the shorter and stronger the N→Ru bond, the higher the stability of the complex and the worse its catalytic characteristics. In turn, the coordination N→Ru bond length can be finely tuned and varied over a wide range of values by changing the steric volume of the cyclic substituents at the nitrogen atom, which will make it possible, as appropriate, to obtain in the future metal complexes with predictable stability and the required catalytic activity. Also, it was found that complexes in which the nitrogen atom is included in the morpholine or isoquinoline rings are the most efficient catalysts in this series. An attempt to establish a correlation between the N→Ru bond length and the 1H and 13C chemical shifts in the RuCH fragment has been made. © 2020 American Chemical Society

Application of New Efficient Hoveyda-Grubbs Catalysts Comprising an N→Ru Coordinate Bond in a Six-Membered Ring for the Synthesis of Natural Product-Like Cyclopenta[b]furo[2,3-c]pyrroles

The ring rearrangement metathesis (RRM) of a trans-cis diastereomer mixture of methyl 3-allyl-3a,6-epoxyisoindole-7-carboxylates derived from cheap, accessible and renewable furan-based precursors in the presence of a new class of Hoveyda-Grubbs-type catalysts, comprising an N→Ru coordinate bond in a six-membered ring, results in the difficult-to-obtain natural product-like cyclopenta[b]furo[2,3-c]pyrroles. In this process, only one diastereomer with a trans-arrangement of the 3-allyl fragment relative to the 3a,6-epoxy bridge enters into the rearrangement, while the cis-isomers polymerize almost completely under the same conditions. The tested catalysts are active in the temperature range from 60 to 120 °C at a concentration of 0.5 mol % and provide better yields of the target tricycles compared to the most popular commercially available second-generation Hoveyda-Grubbs catalyst. The diastereoselectivity of the intramolecular Diels-Alder reaction furan (IMDAF) reaction between starting 1-(furan-2-yl)but-3-en-1-amines and maleic anhydride, leading to 3a,6-epoxyisoindole-7-carboxylates, was studied as well

An IMDAF approach to annellated 1,4:5,8-diepoxynaphthalenes and their metathesis reaction leading to novel scaffolds displaying an antiproliferative activity toward cancer cells

A series of 1,4:5,8-diepoxynaphthalenes, annellated with six-membered carbo- A nd heterocycles, was obtained via the intramolecular Diels-Alder furan (IMDAF) cycloaddition approach from bis-furyl dienes and acetylenic dienophiles (dialkyl acetylenedicarboxylates and hexafluoro-2-butyne). To achieve a wide variety of different products for subsequent biotesting, ethylene-promoted ring-opening cross-metathesis (ROCM) reactions, Prilezhaev epoxidation, catalytic hydrogenation, and N-or O-deprotection reactions of pentacycles were performed. The polyfunctional scaffolds of the resulting diverse heterocycles were tested on cancer lines (PC3, DU-145, MDA-MB-231, HT-1080, and HCT116) and normal lung fibroblasts (WI-26 VA4), and it was found that some of the obtained compounds exerted a concentration-dependent antiproliferative action toward MDA-MB-231 human triple-negative breast cancer and especially PC3 human prostate cancer cell lines. It was demonstrated that compound 16f (hydrogenated 7-(tert-butyl)-4,5-dimethyl-2,8a-divinyl-3,5a-epoxyfuro[2,3,4-de]isoquinoline-4,5,7-tricarboxylate) possessed a time-dependent apoptosis induction activity associated with caspase 3/7 activation in prostate cancer cells, which clearly represents a viable lead for the further development of new-generation anticancer agents. © 2021 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique