A bottom up method for the synthesis of unique tetracene‐based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were ...achieved through the formal 2+2 cycloaddition reaction of ortho‐functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra‐high vacuum scanning tunneling microscopy showed the occurrence of metal‐coordinated nanostructures at room temperature and their evolution into nanoribbons through formal 2+2 cycloaddition at 475 K. Frequency‐shift non‐contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so‐formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene‐based ribbons incorporating four‐membered rings. The reported findings will increase the understanding and availability of new graphene‐based nanoribbons with high potential in future spintronics.
Acene‐based nanoribbons: The on‐surface synthesis and characterization of the electronic and magnetic properties of unprecedented tetracene‐based nanoribbons was addressed by a combination of scanning probe microscopy (SPM) experimental techniques and theoretical calculations.
Utilizing spin‐orbit torque (SOT) to switch a magnetic moment provides a promising route for low‐power‐dissipation spintronic devices. Here, the SOT switching of a nearly compensated ferrimagnet ...Gdx(FeCo)1−x by the topological insulator Bi2Se3 and (BiSb)2Te3 is investigated at room temperature. The switching current density of (BiSb)2Te3 (1.20 × 105 A cm−2) is more than one order of magnitude smaller than that in conventional heavy‐metal‐based structures, which indicates the ultrahigh efficiency of charge‐spin conversion (>1) in topological surface states. By tuning the net magnetic moment of Gdx(FeCo)1−x via changing the composition, the SOT efficiency has a significant enhancement (6.5 times) near the magnetic compensation point, and at the same time the switching speed can be as fast as several picoseconds. Combining the topological surface states and the nearly compensated ferrimagnets provides a promising route for practical energy‐efficient and high‐speed spintronic devices.
Spin‐momentum locking in topological surface states promises ultrahigh spin‐orbit torque efficiency compared to bulk spin‐orbit coupling, where the energy dissipation can be reduced by one to two orders of magnitude. At the same time, near the magnetic compensation point of ferrimagnets, the spin‐orbit torque efficiency can be significantly enhanced.
Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption ...(TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of
2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a 5carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The 5helicene is responsible for the chiroptical activity while the push-pull geometry and the extended network of sp
carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results.
The continuous release of pharmaceuticals from WWTP effluents to freshwater is a matter of concern, due to their potential effects on non-target organisms. The occurrence of pharmaceuticals in WWTPs ...and their associated hazard have been scarcely studied in Latin American countries. This study aimed at monitoring for the first time the occurrence of 70 pharmaceutical active compounds (PhACs) in WWTPs across Costa Rica; the application of the hazard quotient (HQ) approach coupled to ecotoxicological determinations permitted to identify the hazard posed by specific pharmaceuticals and toxicity of the effluents, respectively. Thirty-three PhACs were found, with 1,7-dimethylxanthine, caffeine, acetaminophen, ibuprofen, naproxen, ketoprofen and gemfibrozil being the most frequently detected (influents/effluents). HQ for specific pharmaceuticals revealed 24 compounds with high/medium hazard in influents, while the amount only decreased to 21 in effluents. The top HQ values were obtained for risperidone, lovastatin, diphenhydramine and fluoxetine (influent/effluent samples), plus caffeine (influent) and trimethoprim (effluent). Likewise, the estimation of overall hazard in WWTP samples (sum of individual HQ, ∑HQ) demonstrated that every influent and 96% of the effluents presented high hazard towards aquatic organisms. Ecotoxicological analysis (Daphnia magna, Lactuca sativa and Microtox test) revealed that 16.7% of the effluents presented toxicity towards all benchmark organisms; the phytotoxicity was particularly frequent, as inhibition values ≥20% in the germination index for L. sativa were obtained for all the effluents. The ∑HQ approach estimated the highest hazard in urban wastewater, while the ecotoxicological results showed the highest toxicity in hospital and landfill wastewater. Likewise, ecotoxicological results and ∑HQ values showed a rather poor correlation; instead, better correlations were obtained between ecotoxicological parameters and HQ values for some individual pharmaceuticals such as cephalexin and diphenhydramine. Findings from this study provide novel information on the occurrence of pharmaceuticals and the performance of WWTPs in the tropical region of Central America.
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•Occurrence of 70 pharmaceutical compounds in WWTPs in Costa Rica.•High hazard estimated in every influent and 96% effluents towards aquatic organisms.•Risperidone, lovastatin and diphenhydramine exhibited the highest hazard in influents/effluents.•Toxicity of 16.7% effluents towards all benchmark organisms experimentally tested.•Phytotoxicity (inhibition in seed germination test) particularly critical in effluents.
Gold catalysis has emerged as a groundbreaking field in synthetic chemistry, revolutionizing numerous organic transformations. Despite the significant achieved advancements, the mechanistic ...understanding behind many gold‐catalyzed reactions remains elusive. This Concept article covers the so‐called “self‐activating” Au(I) complexes, sorting out their pivotal role in gold catalysis. We comment on how Au(I) complexes can undergo self‐activation, triggering diverse catalytic transformations without the need for external additives. The most important examples reported so far that underlie the catalytic activity of these species are discussed. This intrinsic reactivity represents a paradigm shift in gold catalysis, offering new avenues for the design of efficient and sustainable catalytic systems. Furthermore, we explore the factors influencing the stability, reactivity, and selectivity of these Au(I) complexes, providing insights into their synthetic utility and potential applications. This area of research not only advances our fundamental understanding of gold catalysis but also paves the way for the development of novel catalytic strategies with broad implications in organic synthesis and the chemical industry.
The multifaceted approaches discussed herein highlight the tremendous potential of self‐activating gold catalysis. Significant contributions have been made in the advancement of these catalysts through innovative ligand design and the discovery of novel modes of autoactivation. This knowledge holds promise for innovating organic transformations, including asymmetric catalysis, while mitigating the risk of reaction poisoning from traditional catalyst‐generating additives.
Solar radiation is affected by absorption and emission phenomena during its downward trajectory from the Sun to the Earth's surface and during the upward trajectory detected by satellite sensors. ...This leads to distortion of the ground radiometric properties (reflectance) recorded by satellite images, used in this study to estimate aboveground forest biomass (AGB). Atmospherically-corrected remote sensing data can be used to estimate AGB on a global scale and with moderate effort. The objective of this study was to evaluate four atmospheric correction algorithms (for surface reflectance), ATCOR2 (Atmospheric Correction for Flat Terrain), COST (Cosine of the Sun Zenith Angle), FLAASH (Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes) and 6S (Second Simulation of Satellite Signal in the Solar), and one radiometric correction algorithm (for reflectance at the sensor) ToA (Apparent Reflectance at the Top of Atmosphere) to estimate AGB in temperate forest in the northeast of the state of Durango, Mexico. The AGB was estimated from Landsat 5 TM imagery and ancillary information from a digital elevation model (DEM) using the non-parametric multivariate adaptive regression splines (MARS) technique. Field reference data for the model training were collected by systematic sampling of 99 permanent forest growth and soil research sites (SPIFyS) established during the winter of 2011. The following predictor variables were identified in the MARS model: Band 7, Band 5, slope ( beta ), Wetness Index (WI), NDVI and MSAVI2. After cross-validation, 6S was found to be the optimal model for estimating AGB (R2 = 0.71 and RMSE = 33.5 Mg times ha-1; 37.61% of the average stand biomass). We conclude that atmospheric and radiometric correction of satellite images can be used along with non-parametric techniques to estimate AGB with acceptable accuracy.
The combination of the ferrocene moiety with gold(I) catalysis remains a relatively unexplored field. In this article, we delve into the synthesis, characterization, and potential catalytic activity ...of four complexes utilizing both monodentate and bidentate ferrocenyl diphenylphosphane ligands (ppf and dppf), coordinated with two gold(I) metal centers, linked by either chloride or pentafluorophenylthiolate bridging ligands. This leads to the formation of cationic “self‐activated” precatalysts capable of initiating the catalytic cycle without the need for external additives. The catalytic activity of these complexes was assessed through a model reaction in gold(I) catalysis, specifically the cyclization of a N‐propargylbenzamide to produce an oxazole. In addition, we studied and compared the influence exerted by both the phosphane and the bridging ligand on the performance of these catalysts.
Dinuclear gold(I) complexes with ferrocenylphosphane and different bridging ligands such as, chloride or pentafluorophenylthiolate have a significant influence in their reactivity. Chloride‐bridged complexes excel as highly efficient catalysts, while thiolate‐bridged ones exhibit varied conversion rates. Additionally, the use of monophosphane or diphosphane ligands introduces intriguing performance differences, offering prospects for customized catalytic systems.
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