Role of Hydrogen Bonding on Transport of Coadsorbed Gases in Metal-Organic Frameworks Materials.

Coadsorption of multicomponents in metal-organic framework (MOF) materials can lead to a number of cooperative effects, such as modification of adsorption sites or during transport. In this work, we explore the incorporation of NH3 and H2O into MOFs preloaded with small molecules such as CO, CO2, and SO2. We find that NH3 (or H2O) first displaces a certain amount of preadsorbed molecules in the outer portion of MOF crystallites, and then substantially hinders diffusion. Combining in situ spectroscopy with first-principles calculations, we show that hydrogen bonding between NH3 (or H2O) is responsible for an increase of a factor of 7 and 8 in diffusion barrier of CO and CO2 through the MOF channels. Understanding such cooperative effects is important for designing new strategies to enhance adsorption in nanoporous materials.

Novel Pd_{2}Se_{3} Two-Dimensional Phase Driven by Interlayer Fusion in Layered PdSe_{2}.

Two-dimensional (2D) materials are easily fabricated when their bulk form has a layered structure. The monolayer form in layered transition-metal dichalcogenides is typically the same as a single layer of the bulk material. However, PdSe_{2} presents a puzzle. Its monolayer form has been theoretically shown to be stable, but there have been no reports that monolayer PdSe_{2} has been fabricated. Here, combining atomic-scale imaging in a scanning transmission electron microscope and density functional theory, we demonstrate that the preferred monolayer form of this material amounts to a melding of two bulk monolayers accompanied by the emission of Se atoms so that the resulting stoichiometry is Pd_{2}Se_{3}. We further verify the interlayer melding mechanism by creating Se vacancies in situ in the layered PdSe_{2} matrix using electron irradiation. The discovery that strong interlayer interactions can be induced by defects and lead to the formation of new 2D materials opens a new venue for the exploration of defect engineering and novel 2D structures.

Rapid synthesis and antimicrobial activity of novel 4-oxazolidinone heterocycles.

The synoxazolidinone family of marine natural products bear an unusual 4-oxazolidinone heterocyclic core and promising antimicrobial activity against several strains of pathogenic bacteria. As part of our research program directed at the synthesis and chemical biology of this family of natural products we have developed a one-step method for the generation of variously substituted 4-oxazolidinone scaffolds from readily available materials. These studies revealed the importance of an electron deficient aromatic ring for antimicrobial activity and serve as the basis for future SAR studies around the 4-oxazolidinone core.

Structural band-gap tuning in g-C3N4.

g-C3N4 is a promising material for hydrogen production from water via photo-catalysis, if we can tune its band gap to desirable levels. Using a combined experimental and ab initio approach, we uncover an almost perfectly linear relationship between the band gap and structural aspects of g-C3N4, which we show to originate in a changing overlap of wave functions associated with the lattice constants. This changing overlap, in turn, causes the unoccupied pz states to experience a significantly larger energy shift than any other occupied state (s, px, or py), resulting in this peculiar relationship. Our results explain and demonstrate the possibility to tune the band gap by structural means, and thus the frequency at which g-C3N4 absorbs light.

Factors controlling the energetics of the oxygen reduction reaction on the Pd-Co electro-catalysts: insight from first principles.

We report here results of our density functional theory based computational studies of the electronic structure of the Pd-Co alloy electrocatalysts and energetics of the oxygen reduction reaction (ORR) on their surfaces. The calculations have been performed for the (111) surfaces of pure Pd, Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) alloys, as well as of the surface segregated Pd/Pd(0.75)Co(0.25) alloy. We find the hybridization of dPd and dCo electronic states to be the main factor controlling the electrocatalytic properties of Pd/Pd(0.75)Co(0.25). Namely the dPd-dCo hybridization causes low energy shift of the surface Pd d-band with respect to that for Pd(111). This shift weakens chemical bonds between the ORR intermediates and the Pd/Pd(0.75)Co(0.25) surface, which is favorable for the reaction. Non-segregated Pd(0.75)Co(0.25) and Pd(0.5)Co(0.5) surfaces are found to be too reactive for ORR due to bonding of the intermediates to the surface Co atoms. Analysis of the ORR free energy diagrams, built for the Pd and Pd/Pd(0.75)Co(0.25), shows that the co-adsorption of the ORR intermediates and water changes the ORR energetics significantly and makes ORR more favorable. We find the onset ORR potential estimated for the configurations with the O-OH and OH-OH co-adsorption to be in very good agreement with experiment. The relevance of this finding to the real reaction environment is discussed.

Orbital soft tissue composite lymphoma presenting as recurrence of a nodal lymphoma with mantle and follicular cell components: A case report, literature review and guideline for the treatment of patients.

Composite lymphoma with mantle and follicular cell components is a challenging diagnosis. Flow cytometry, immunohistochemistry and molecular genetics are required to distinguish the two components, as often the more aggressive one is predominant and masks the other. A 58-year-old man with history of nodal composite lymphoma presented with right exophthalmos and diplopia. A head CT scan showed an orbital tumor. A biopsy of the tumor revealed a mantle cell lymphoma predominating over a follicular lymphoma. Immunoglobulin heavy chain and light chain rearrangements analysis by PCR proved that both components of the orbital tumor were recurrences of the same nodal composite lymphoma diagnosed two years earlier. The nodal lymphoma was composed of a follicular lymphoma and an in situ mantle cell neoplasia. Consensus view is that dominant lymphoma should be treated when needed but taking into account if the mantle cell lymphoma is an in situ neoplasia and if it expresses CD5 and SOX11.

Anisotropic Ordering in 1T' Molybdenum and Tungsten Ditelluride Layers Alloyed with Sulfur and Selenium.

Alloying is an effective way to engineer the band-gap structure of two-dimensional transition-metal dichalcogenide materials. Molybdenum and tungsten ditelluride alloyed with sulfur or selenium layers (MX2xTe2(1-x), M = Mo, W and X = S, Se) have a large band-gap tunability from metallic to semiconducting due to the 2H-to-1T' phase transition as controlled by the alloy concentrations, whereas the alloy atom distribution in these two phases remains elusive. Here, combining atomic resolution Z-contrast scanning transmission electron microscopy imaging and density functional theory (DFT), we discovered that anisotropic ordering occurs in the 1T' phase, in sharp contrast to the isotropic alloy behavior in the 2H phase under similar alloy concentration. The anisotropic ordering is presumably due to the anisotropic bonding in the 1T' phase, as further elaborated by DFT calculations. Our results reveal the atomic anisotropic alloyed behavior in 1T' phase layered alloys regardless of their alloy concentration, shining light on fine-tuning their physical properties via engineering the alloyed atomic structure.

Design of Optimally Stable Molecular Coatings for Fe-Based Nanoparticles in Aqueous Environments.

Magnetic nanoparticles are widely used in biomedical and oil-well applications in aqueous, often harsh environments. The pursuit for high-saturation magnetization together with high stability of the molecular coating that prevents agglomeration and oxidation remains an active research area. Here, we report a detailed analysis of the criteria for the stability of molecular coatings in aqueous environments along with extensive first-principles calculations for magnetite, which has been widely used, and cementite, a promising emerging candidate. A key result is that the simple binding energies of molecules cannot be used as a definitive indicator of relative stability in a liquid environment. Instead, we find that H+ ions and water molecules facilitate the desorption of molecules from the surface. We further find that, because of differences in the geometry of crystal structures, molecules generally form stronger bonds on cementite surfaces than they do on magnetite surfaces. The net result is that molecular coatings of cementite nanoparticles are more stable. This feature, together with the better magnetic properties, makes cementite nanoparticles a promising candidate for biomedical and oil-well applications.

Comparación de secuencias volumétricas con técnicas convencionales en resonancia magnética de columna lumbar / Comparison of volumetric and conventional sequences for the evaluation in magnetic resonance of the lumbar spine

Objetivo: Comparar el protocolo que incluye la secuencia tridimensional SPACE-3D con el protocolo convencional en el estudio imagenológico por resonancia magnética (RM) del paciente con dolor lumbar. Metodología: Se realizó un estudio prospectivo de pruebas diagnósticas, en el que se tomaron imágenes por RM de la columna lumbar de 40 pacientes utilizando un protocolo convencional y otro protocolo que incluyera una secuencia volumétrica (SPACE-3D) en conjunto con secuencia axial con información T1 y sagital STIR, en un resonador de 1,5T. Las imágenes fueron interpretadas por dos radiólogos de manera independiente, empleando tanto el protocolo convencional como el protocolo que incluía la secuencia volumétrica, con un mes de diferencia. Se compararon ambos protocolos calculando la sensibilidad y la especificidad con el intervalo de confianza (IC 95 %), se consideró significación estadística un valor de p≤ 0,05 utilizando la prueba de Chi-cuadrado. Se evaluaron para ambas técnicas variables como presencia o no de artefactos, protrusión/extrusión discal, estrechez del canal neural central, receso lateral o foramen de emergencia radicular, radiculopatía. Se calculó la concordancia inter e intraobservador utilizando el índice Kappa con un IC 95 %. Resultados: Se encontró que el protocolo que incluye la secuencia SPACE-3D presenta rendimiento diagnóstico similar (no inferior) frente al protocolo con las secuencias convencionales para las variables evaluadas; igualmente, se detectaron los hallazgos anormales, lo cual permitió un estudio completo y un diagnóstico en menor tiempo. Conclusiones: El rendimiento diagnóstico del protocolo que incluye la secuencia volumétrica SPACE-3D es similar (no inferior) al protocolo con las secuencias convencionales utilizadas en RM de columna lumbar y acorta el tiempo total del estudio

Objective: To compare the protocol that includes the three-dimensional SPACE-3D sequence with the conventional protocol in the magnetic resonance imaging (MRI) study of patients with low back pain. Methods: A prospective study of diagnostic tests was carried out, in which MR images of the lumbar spine were taken from 40 patients using a conventional protocol and another protocol that included a volumetric sequence (SPACE-3D) in conjunction with axial T1 and sagittal STIR sequences, in a 1.5T resonator. The images were interpreted by two radiologists independently, both the conventional protocol and the protocol that included the volumetric sequence, one month apart. Both protocols were compared, calculating the sensitivity and specificity with the confidence interval (CI 95%), a value of p ≤0.05 using the Chi-square test was considered statistically significant. Variables such as the presence or absence of artifacts, disc protrusion/extrusion, narrowing of the central neural canal, lateral recess or root emergence foramen, and presence of radiculopathy, among others, were evaluated for both techniques. Inter- and intra-observer agreement was calculated using the Kappa index with a 95% CI. Results: it was found that the protocol that included the SPACE-3D sequence presents similar diagnostic performance (not inferior) when compared to the protocol with the conventional sequences for the variables evaluated, similarly, abnormal findings were detected, which allowed a complete study and diagnosis in less time. Conclusions: The diagnostic performance of the protocol that includes the SPACE-3D volumetric sequence is similar (not inferior) to the protocol with conventional sequences used in MRI of the lumbar spine and shortens the total study time.

Trapping gases in metal-organic frameworks with a selective surface molecular barrier layer.

The main challenge for gas storage and separation in nanoporous materials is that many molecules of interest adsorb too weakly to be effectively retained. Instead of synthetically modifying the internal surface structure of the entire bulk-as is typically done to enhance adsorption-here we show that post exposure of a prototypical porous metal-organic framework to ethylenediamine can effectively retain a variety of weakly adsorbing molecules (for example, CO, CO2, SO2, C2H4, NO) inside the materials by forming a monolayer-thick cap at the external surface of microcrystals. Furthermore, this capping mechanism, based on hydrogen bonding as explained by ab initio modelling, opens the door for potential selectivity. For example, water molecules are shown to disrupt the hydrogen-bonded amine network and diffuse through the cap without hindrance and fully displace/release the retained small molecules out of the metal-organic framework at room temperature. These findings may provide alternative strategies for gas storage, delivery and separation.

Synthesis of the Privileged 8-Arylmenthol Class by Radical Arylation of Isopulegol.

Hydrogen atom transfer (HAT) circumvents a disfavored Friedel-Crafts reaction in the derivatization of the inexpensive monoterpene isopulegol. A variety of readily prepared aryl and heteroaryl sulfonates undergo a formal hydroarylation to form 8-arylmenthols, privileged scaffolds for asymmetric synthesis, as typified by 8-phenylmenthol. High stereoselectivity is observed in related systems. This use of HAT significantly extends the chiral pool from the inexpensive monoterpene isopulegol.

Study of van der Waals bonding and interactions in metal organic framework materials.

Metal organic framework (MOF) materials have attracted a lot of attention due to their numerous applications in fields such as hydrogen storage, carbon capture and gas sequestration. In all these applications, van der Waals forces dominate the interaction between the small guest molecules and the walls of the MOFs. In this review article, we describe how a combined theoretical and experimental approach can successfully be used to study those weak interactions and elucidate the adsorption mechanisms important for various applications. On the theory side, we show that, while standard density functional theory is not capable of correctly describing van der Waals interactions, functionals especially designed to include van der Waals forces exist, yielding results in remarkable agreement with experiment. From the experimental point of view, we show examples in which IR adsorption and Raman spectroscopy are essential to study molecule/MOF interactions. Importantly, we emphasize throughout this review that a combination of theory and experiment is crucial to effectively gain further understanding. In particular, we review such combined studies for the adsorption mechanism of small molecules in MOFs, the chemical stability of MOFs under humid conditions, water cluster formation inside MOFs, and the diffusion of small molecules into MOFs. The understanding of these phenomena is critical for the rational design of new MOFs with desired properties.

Sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride photocatalyst: insights from first principles.

We present here results of our first-principles studies of the sulfur doping effects on the electronic and geometric structures of graphitic carbon nitride (g-C(3)N(4)). Using the ab initio thermodynamics approach combined with some kinetic analysis, we reveal the favorable S-doping configurations. By analyzing the valence charge densities of the doped and undoped systems, we find that sulfur partially donates its p(x)- and p(y)- electrons to the system with some back donation to the S p(z)-states. To obtain an accurate description of the excited electronic states, we calculate the electronic structure of the systems using the GW method. The band gap width calculated for g-C(3)N(4) is found to be equal to 2.7 eV, which is in agreement with experiment. We find the S doping causes a significant narrowing of the gap. Furthermore, the electronic states just above the gap become occupied upon doping, making the material a conductor. Analysis of the projected local density of states provides an insight into the mechanism underlying such changes in the electronic structure of g-C(3)N(4) upon S doping. Based on our results, we propose a possible explanation for the S-doping effect on the photocatalytic properties of g-C(3)N(4) observed in experiments.

Factors Controlling the Reactivity of Catalytically Active Monolayers on Metal Substrates.

The focus of this work is on the Pt/MS structures (MS = Au, Ir, Ru, or Pt substrate), as promising electrocatalysts and a prototype for more general systems: (active element monolayer)/(metal substrate) (AE/MS). We evaluate from first principles the effects of AE monolayer strain and the interlayer AE-MS electronic state hybridization on surface reactivity and reveal rationale for the interlayer hybridization to dominate over the strain effect in determining the AE/MS surface reactivity. We find, however, that, if AE is weakly bound to MS, the surface electronic structure does not suffice to characterize the surface reactivity, because of involvement of other factors related to lattice response to adsorption of a reaction intermediate. Guided by our findings, we trace surface reactivity to a newly introduced hybridization parameter that reflects important features of the electronic structure of the AE/MS surface, which are not taken into account in the original d-band center model.

First principles study of oxygen adsorption on Se-modified Ru nanoparticles.

We present here the results of our density-functional-theory-based calculations of the electronic and geometric structures and energetics of Se and O adsorption on Ru 93- and 105-atom nanoparticles. These studies have been inspired by the fact that Se/Ru nanoparticles are considered promising electrocatalysts for the oxygen reduction reaction (ORR) on direct methanol fuel cell cathodes and the oxygen binding energy is a descriptor for the catalyst activity toward this reaction. We find the character of chemical bonding of Se on a flat nanoparticle facet to be ionic, similar to that obtained earlier for the Se/Ru(0001) surface, while in the case of a low-coordinated Ru configuration there is an indication of some covalent contribution to the bonding leading to an increase in Se binding energy. Se and O co-adsorbed on the flat facet both accept electronic charge from Ru, whereas the adsorption on low-coordinated sites causes more complicated valence charge redistribution. The Se modification of the Ru particles leads to weakening of the oxygen bonding to the particles. However, overall, O binding energies are found to be higher for the particles than for Se/Ru(0001). The high reactivity of the Se/Ru nanoparticles found in this work is not favorable for ORR. We thus expect that larger particles with well-developed flat facets will be more efficient ORR catalysts than small nanoparticles with a large fraction of under-coordinated adsorption sites.

Aproximación diagnóstica de las fístulas perianales por resonancia magnética / Diagnostic Approach to Perianal Fistulas with Magnetic Resonance

La enfermedad fistulosa perianal es una entidad inflamatoria crónica que afecta el canal anal y los espacios perianales. Las fístulas anales presentan gran morbilidad y recurrencia. Para definir el tipo de tratamiento quirúrgico o médico, evitar recurrencias y complicaciones como la incontinencia fecal, es importante una adecuada caracterización y clasificación de las fístulas mediante la resonancia magnética (RM). Actualmente la RM es el estudio imaginológico con mayor sensibilidad diagnóstica debido a su alta resolución anatómica para definir las estructuras del canal anal y demostrar el trayecto fistuloso con sus complicaciones (abscesos y trayectos secundarios).

Fistulous perianal disease is an inflammatory entity that affects the anal canal and perianal spaces. Anal fistulas represent important morbidity and recurrence for patients. For the planning of surgical treatment, preventing recurrences and complications like fecal incontinence, a proper characterization and classification of fistulas with magnetic resonance must be done. Currently, magnetic resonance is the imaging modality with greatest diagnostic sensitivity due to its high anatomical resolution in defining structures like the anal canal and fistulous tracts with its complications (abscesses, secondary paths).

Anomalías congénitas y variantes anatómicas del seno coronario / Congenital Anomalies and Anatomical Variants of Coronary Sinus

El seno coronario (SC) es la estructura vascular que permite el acceso a las venas coronarias en procedimientos intervencionistas como el mapeo y la ablación de arritmias, la implantación de electrodos izquierdos en terapia de resincronización, anuloplastia mitral, tratamiento con células madre y cardioplejía retrógrada. El éxito de estos procedimientos depende del conocimiento de la anatomía del SC, del reconocimiento de sus variantes y anomalías. La tomografía multicorte permite obtener imágenes de la anatomía del SC sin necesidad de procedimientos invasivos de diagnóstico. La resonancia magnética, por su condición no invasiva y sin radiación, también es útil en la evaluación del seno coronario porque permite la valoración morfológica y funcional de diversas anomalías congénitas del corazón.

The coronary sinus (CS) is an important vascular structure that allows access to the coronary veins in multiple interventional procedures such as mapping and ablation of arrhythmias, implantation of left ventricular electrodes in resynchronization therapy, mitral annuloplasty, stem cells therapy, and retrograde cardioplegia. The success of these procedures is facilitated by the knowledge of the CS anatomy, in particular the recognition of its variants and anomalies. The widespread availability of multislice CT (MSCT) allows non-invasive image acquisition with excellent representation of the CS anatomy, avoiding thus the need for invasive diagnostic procedures. MRI is also useful for the non-invasive evaluation of the coronary sinus, without radiation, allowing the morphological and functional assessment of various congenital heart abnormalities.

Angiosarcoma de la mama: Presentación de dos casos / Angiosarcoma of the Breast: Report of Two Cases

Los angiosarcomas de la mama son tumores raros que conforman menos del 1 % de las neoplasias mamarias. Estos tumores pueden desarrollarse de forma primaria o secundaria y se han descrito 219 casos en la literatura mundial desde el primer caso informado por Schmidt en 1887. A continuación se presentan dos casos de angiosarcoma primario de la mama y sus principales características en los diferentes métodos diagnósticos.

Angiosarcomas are rare tumors that make up less than 1% of breast cancers. These tumors may develop in a primary or secondary form, and 219 cases have been reported in the literature since the first case described by Schmidt in 1887. Here we present two cases of primary angiosarcoma of the breast and its main features in different imaging modalities