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This study delves into the intriguing properties of the 1H/1T-TaS2 van der Waals heterostructure, focusing on the transparency of the 1H layer to the charge density wave of the underlying 1T layer. Despite the sizable interlayer separation and metallic nature of the 1H layer, positive bias voltages result in a pronounced superposition of the 1T charge density wave structure on the 1H layer. The conventional explanation relying on tunneling effects proves insufficient. Through a comprehensive investigation combining low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, non-contact atomic force microscopy, and first-principles calculations, we propose an alternative interpretation. The transparency effect arises from a weak yet substantial electronic coupling between the 1H and 1T layers, challenging prior understanding of the system. Our results highlight the critical role played by interlayer electronic interactions in van der Waals heterostructures to determine the final ground states of the systems.
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BACKGROUND: While mechanical thrombectomy (MT) is proven to be lifesaving and disability sparing, there remains a disparity in its access in low- to middle-income countries. We hypothesized that team-based MT workshops would improve MT knowledge and skills. METHODS: We designed a 22-hour MT workshop, conducted as 2 identical events: in English (Jamaica, January 2022) and in Spanish (Dominican Republic, May 2022). The workshops included participating neurointerventional teams (practicing neurointerventionalists, neurointerventional nurses, and technicians) focused on acute stroke due to large vessel occlusion. The course faculty led didactic and hands-on components, covering topics from case selection and postoperative management to device technology and MT surgical techniques. Attendees were evaluated on stroke knowledge and MT skills before and after the course using a multiple choice exam and simulated procedures utilizing flow models under fluoroscopy, respectively. Press conferences for public education with invited government officials were included to raise stroke awareness. RESULTS: Twenty-two physicians and their teams from 8 countries across the Caribbean completed the didactic and hands-on training. Overall test scores (n=18) improved from 67% to 85% (P<0.002). Precourse and postcourse hands-on assessments demonstrated reduced time to completion from 36.5 to 21.1 minutes (P<0.001). All teams showed an improvement in measures of good MT techniques, with 39% improvement in complete reperfusion. Eight teams achieved a Thrombolysis in Cerebral Infarction score of 3 on pre-course versus 15 of 18 teams on post-course. There was a significant reduction in total potentially dangerous maneuvers (70% pre versus 20% post; P<0.002). Universally, the workshop was rated as satisfactory and likely to change practice in 93% Dominican Republic and 75% Jamaica. CONCLUSIONS: A team-based hands-on simulation approach to MT training is novel, feasible, and effective in improving procedural skills. Participants viewed these workshops as practice-changing and instrumental in creating a pathway for increasing access to MT in low- to middle-income countries.
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Competência Clínica , Países em Desenvolvimento , Trombectomia , Humanos , Trombectomia/educação , Acidente Vascular Cerebral/terapia , Acidente Vascular Cerebral/cirurgia , Equipe de Assistência ao PacienteRESUMO
Kondo lattices are systems with unusual electronic properties that stem from strong electron correlation, typically studied in intermetallic 3D compounds containing lanthanides or actinides. Lowering the dimensionality of the system enhances the role of electron correlations providing a new tuning knob for the search of novel properties in strongly correlated quantum matter. The realization of a 2D Kondo lattice by stacking a single-layer Mott insulator on a metallic surface is reported. The temperature of the system is steadily lowered and by using high-resolution scanning tunneling spectroscopy, the phase transition leading to the Kondo lattice is followed. Above 27 K the interaction between the Mott insulator and the metal is negligible and both keep their original electronic properties intact. Below 27 K the Kondo screening of the localized electrons in the Mott insulator begins and below 11 K the formation of a coherent quantum electronic state extended to the entire sample, i.e., the Kondo lattice, takes place. By means of density functional theory, the electronic properties of the system and its evolution with temperature are explained. The findings contribute to the exploration of unconventional states in 2D correlated materials.
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Polymorphic phases and collective phenomena-such as charge density waves (CDWs)-in transition metal dichalcogenides (TMDs) dictate the physical and electronic properties of the material. Most TMDs naturally occur in a single given phase, but the fine-tuning of growth conditions via methods such as molecular beam epitaxy (MBE) allows to unlock otherwise inaccessible polymorphic structures. Exploring and understanding the morphological and electronic properties of new phases of TMDs is an essential step to enable their exploitation in technological applications. Here, scanning tunneling microscopy (STM) is used to map MBE-grown monolayer (ML) TaTe2 . This work reports the first observation of the 1H polymorphic phase, coexisting with the 1T, and demonstrates that their relative coverage can be controlled by adjusting synthesis parameters. Several superperiodic structures, compatible with CDWs, are observed to coexist on the 1T phase. Finally, this work provides theoretical insight on the delicate balance between Te Te and Ta-Ta interactions that dictates the stability of the different phases. The findings demonstrate that TaTe2 is an ideal platform to investigate competing interactions, and indicate that accurate tuning of growth conditions is key to accessing metastable states in TMDs.
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Molecular functionalization of MoS2 has attracted a lot of attention due to its potential to afford fine-tuned hybrid materials that benefit from the power of synthetic chemistry and molecular design. Here, we report on the on-surface reaction of maleimides on bulk and molecular beam epitaxy grown single-layer MoS2, both in ambient conditions as well as ultrahigh vacuum using scanning probe microscopy.
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The synthesis of a novel type of branched iminosugars is described. This synthetic strategy is based on two key reactions: first, an aldol reaction with formaldehyde in order to introduce selectively the hydroxymethyl branch, and second, a tandem ß-fragmentation-intramolecular cyclization reaction. The combination of both reactions afforded a battery of compounds exhibiting a great structural complexity, with the concomitant formation of a quaternary center, starting from readily available aldoses. With this approach we have demonstrated the usefulness of the fragmentation of anomeric alkoxyl radicals (ARF) promoted by the PhIO/I2 system for the preparation of new compounds with potential interest for both medicinal and synthetic chemists.
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Álcoois/química , Imino Açúcares/síntese química , Iodo/química , Imino Açúcares/química , Estrutura MolecularRESUMO
In this work we fabricate and characterize a functionalized superconducting (SC) Nb tip of a scanning tunnelling microscope (STM). The tip is functionalized with a Tetracyanoquinodimethane molecule (TCNQ) that accepts charge from the tip and develops a magnetic moment. As a consequence, in scanning tunnelling spectroscopy (STS), sharp, bias symmetric sub-gap states identified as Yu-Shiba-Rusinov (YSR) bound states appear against the featureless density of states of a metallic graphene on Ir(111) sample. Although the coupling regime of the magnetic impurity with the SC tip depends on the initial absorption configuration of the molecule, the interaction strength between the SC tip and the charged TCNQ molecule can be reversibly controlled by tuning the tip-sample distance. The controlled transition from one coupling regime to the other allows us to verify the relation between the energy scales of the two competing many-body effects for the functionalized tip. Quenching the SC state of the Nb tip with a magnetic field switches abruptly from a tip dominated by the YSR bound states to a Kondo tip.
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The on-surface photogeneration of nonacene from α-bisdiketone precursors deposited on nanostructured epitaxial graphene grown on Ru(0001) has been studied by means of low temperature scanning tunneling microscopy and spectroscopy. The presence of an unoccupied surface state, spatially localized in the regions where the precursors are adsorbed, and energetically accessible in the region of the electromagnetic spectrum where n-π* transitions take place, allows for a 100% conversion of the precursors into nonacenes. With the help of state-of-the-art theoretical calculations, we show that such a high yield is due to the effective population of the surface state by the incoming light and the ensuing electron transfer to the unoccupied states of the precursors through an inelastic scattering mechanism. Our findings are the experimental confirmation that surface states can play a prominent role in the surface photochemistry of complex molecular systems, in accordance with early theoretical predictions made on small molecules.
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The ability of the guanidinylating reagent N',N''-diBoc-N-triflyl-guanidine (GN-Tf) to react with in situ formed free amines from azides in carbohydrate scaffolds was explored. This reaction proved to be an efficient method to prepare guanidine derivatives in a one-pot manner with good to excellent yields, either with primary or secondary azides with different substitution patterns. Labile protecting groups such as benzyl ethers are not removed under these hydrogenolytic conditions.
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Azidas/química , Carboidratos/química , Guanidinas/síntese química , Guanidinas/química , Espectroscopia de Ressonância Magnética , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
The development of graphene (Gr) spintronics requires the ability to engineer epitaxial Gr heterostructures with interfaces of high quality, in which the intrinsic properties of Gr are modified through proximity with a ferromagnet to allow for efficient room temperature spin manipulation or the stabilization of new magnetic textures. These heterostructures can be prepared in a controlled way by intercalation through graphene of different metals. Using photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we achieve a nanoscale control of thermally activated intercalation of a homogeneous ferromagnetic (FM) layer underneath epitaxial Gr grown onto (111)-oriented heavy metal (HM) buffers deposited, in turn, onto insulating oxide surfaces. XPS and STM demonstrate that Co atoms evaporated on top of Gr arrange in 3D clusters and, upon thermal annealing, penetrate through and diffuse below Gr in a 2D fashion. The complete intercalation of the metal occurs at specific temperatures, depending on the type of metallic buffer. The activation energy and the optimum temperature for the intercalation processes are determined. We describe a reliable method to fabricate and characterize in situ high-quality Gr-FM/HM heterostructures, enabling the realization of novel spin-orbitronic devices that exploit the extraordinary properties of Gr.
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The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (HAT) reaction between the two pyranose units in a (1-->4)-O-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with alpha-D-Glcp-(1-->4)-beta-D-Glcp, alpha-L-Rhamp-(1-->4)-alpha-D-Galp or alpha-D-Manp-(1-->4)-beta-L-Gulp skeletons led exclusively to the abstraction of the hydrogen from H--C-5' and the formation, through a nine-membered transition state, of a 1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of alpha-L-Rhamp-(1-->4)-alpha-D-Glcp or alpha-D-Manp-(1-->4)-alpha-D-Galp exclusively abstract the hydrogen from H--C-1' through a seven-membered transition state and, therefore, lead to an interglycosidic spiro ortho ester.
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Dissacarídeos/química , Hidrogênio/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Estrutura Molecular , EstereoisomerismoRESUMO
[reaction: see text]. The beta-fragmentation of 2,2-difluoro-saccharide anomeric alkoxyl radicals, generated under oxidative condition by treatment of the respective alcohols with (diacetoxyiodo)benzene (DIB) and iodine, afforded 1,1-difluoro-1-iodo alditols in high yield. The reactivity of the fluorinated radical generated by rupture of the C-I bond has been preliminarily assessed by reductive deiodination with tributyltin hydride/AIBN and intermolecular allylation using the Keck reaction.
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Álcoois/química , Hidrocarbonetos Halogenados/síntese química , Monossacarídeos/química , Álcoois Açúcares/síntese química , Flúor/química , Iodo/química , Espectroscopia de Ressonância Magnética , Estrutura MolecularRESUMO
[reaction: see text] The alkoxy radical generated by reaction of 3,7-anhydro-2-deoxyoctitols with (diacetoxyiodo)benzene (DIB) and iodine abstracts regioselectively either the proton at C7 or that at C4 depending on the electronegativity of the substituent at C4. The correct election of this substituent can switch the reaction to give 2,9-dioxabicyclo[3.3.1]nonane or hexahydro-2H-furo[3,2-b]pyran ring systems.
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Carboidratos/química , Radicais Livres/química , Hidrogênio/química , Indicadores e Reagentes , Modelos MolecularesRESUMO
The present study described the frequency of animal bites and attacks in the municipality of San Juan, Puerto Rico between the fiscal years 1996 through 1998. A total of 275 cases were reported to the San Juan Local Office of Environmental Health. The distribution of cases by gender was equal, and persons aged 18 years or older had the highest frequency of animal bites and attacks (52.9%). The animal species reported to be involved in the majority of animal bites was the dog (81.1%). Upper extremities were involved in 43% of these injuries. Animal bites caused by dogs were more often reported among male victims (87.4%) (p = 0.031). Approximately 41% of dog bites and attacks and 75% of bites and attacks caused by other animal species were documented as provoked (p = 0.002). More than 75% of the injuries in the head, face or neck involved children < 13 years whereas 65.9% of the injuries in the upper extremities involved adults (> 18 years) (p = 0.001). Animal bites and attacks in the upper extremities were more prominent among injuries caused by an animal species different to the dog (71%) (p < 0.001). We conclude that animal bites and attacks is a public health concern in light of the increasing pet population. Therefore, educational strategies towards the general population must stress careful supervision of the human-animal interaction as well as the general procedures to follow in case of an injury.
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Mordeduras e Picadas/epidemiologia , Gatos , Cães , Adolescente , Adulto , Fatores Etários , Animais , Traumatismos do Braço/epidemiologia , Traumatismos do Braço/etiologia , Criança , Estudos de Coortes , Traumatismos Craniocerebrais/epidemiologia , Traumatismos Craniocerebrais/etiologia , Traumatismos Faciais/epidemiologia , Traumatismos Faciais/etiologia , Feminino , Humanos , Masculino , Lesões do Pescoço/epidemiologia , Lesões do Pescoço/etiologia , Porto Rico/epidemiologia , Estações do Ano , Fatores SexuaisRESUMO
The fragmentation of anomeric alkoxyl radicals (ARF) and the subsequent intramolecular cyclization promoted by hypervalent iodine reagents provide an excellent method for the synthesis of tetrazolo-sugars. This new reaction offers additional advantages for the synthesis of these compounds, including the ready availability of the starting materials, experimental simplicity, mild conditions, and good yields.
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Álcoois/química , Glicosídeos/síntese química , Tetrazóis/química , Ciclização , Glicosídeos/química , Estrutura MolecularRESUMO
A new general methodology for the synthesis of 1,1,1-trihaloalditols by starting from 1,5-anhydro-2-deoxy-hex-1-enitol derivatives (glycals) is described. The halogens are introduced sequentially in each of the three different steps of the process. The fluorine is introduced in the first step by electrophilic fluorination of the starting glycal; next, hydroxyhalogenation of the resulting vinyl fluoride allows the addition of any halogen (F, Cl, Br or I) at will, and finally, an iodine atom is inserted through an alkoxyl radical fragmentation reaction. This methodology allows the preparation of diverse types of 1,1,1-trihalogenated compounds (R--CF(2)I, R--CFI(2), R--CFClI and R--CFBrI) under mild conditions compatible with sensitive substituents. In some cases, the diastereomeric mixtures generated from R--CFClI and R--CFBrI can be chromatographically separated, and their configuration determined by X-ray crystallographic analysis. The synthetic usefulness of these compounds has been preliminarily assessed by examining the reactivity of the fluorinated radical generated by rupture of the C--I bond.
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Álcoois Açúcares/síntese química , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Estrutura Molecular , Espectrometria de Massas por Ionização por Electrospray , Estereoisomerismo , Álcoois Açúcares/químicaRESUMO
The reaction of phenyl and benzyl amidophosphates and alkyl and benzyl carbamate derivatives of aminoalditols with (diacetoxyiodo)benzene or iodosylbenzene and iodine is a mild and selective procedure for the synthesis of chiral 7-oxa-2-azabicyclo[2.2.1]heptane and 8-oxa-6-azabicyclo[3.2.1]octane ring systems under neutral conditions. This reaction can be considered to be an intramolecular N-glycosidation that goes through an intramolecular 1,5-hydrogen abstraction promoted by an N-amido radical followed by oxidation of the transient C-radical intermediate to an oxycarbenium ion. This methodology proved to be useful not only as a suitable strategy for the preparation of these bicyclic arrays but also for the selective oxidation of specific carbons of the carbohydrate skeleton, constituting a good procedure for the synthesis of protected N,O-uloses.
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Carboidratos/química , Heptanos/síntese química , Octanos/síntese química , Carboidratos/síntese química , Heptanos/química , Hidrogênio/química , Indicadores e Reagentes , Modelos Moleculares , Estrutura Molecular , Octanos/química , Oxirredução , EstereoisomerismoRESUMO
The reaction of specifically protected anhydroalditols with (diacetoxyiodo)benzene or iodosylbenzene and iodine is a mild and selective procedure for the synthesis of chiral 6,8-dioxabicyclo[3.2.1]octane and 2,7-dioxabicyclo[2.2.1]heptane ring systems under neutral conditions. This reaction can be considered to be an intramolecular glycosidation that goes through an intramolecular hydrogen abstraction promoted by an alkoxy radical followed by oxidation of the transient C-radical intermediate to an oxycarbenium ion. This methodology is useful not only for the preparation of chiral synthons but also for the selective oxidation of specific carbons of the carbohydrate skeleton, constituting a good procedure for the synthesis of protected uloses.