A Simple Biomimetic Receptor Selectively Recognizing the GlcNAc2 Disaccharide in Water

AbstractGlcNAc2 is the core disaccharide fragment present in N‐glycans exposed on the surface of enveloped viruses of high health concern, such as coronaviruses. Because N‐glycans are directly involved in the docking of viruses to host cells, recognition of GlcNAc2 by a biomimetic receptor may be a convenient alternative to the use of lectins to interfere with viral entry and infection. Herein, we describe a simple biomimetic receptor recognizing the methyl‐β‐glycoside of GlcNAc2 in water with an unprecedented affinity of 160 μM, exceeding that of more structurally complex receptors reported in the literature. The tweezers‐shaped acyclic structure exhibits marked selectivity among structurally related disaccharides, and complete discrimination between mono‐ and disaccharides. Molecular modelling calculations supported by NOE data provided a three‐dimensional description of the binding mode, shedding light on the origin of the affinities and selectivities exhibited by the receptor

Nanoparticulate Pd-Sn Compounds Supported on Metal Oxides: Synthesis, Material and Catalytic Properties

The manufacture of chemicals requires innovation at the catalyst frontier so that processes can be developed with higher energy efficiency and increased facility of separation and recovery of products. Catalysts with high selectivity and activity control the overall efficiency of a process by avoiding unwanted side-reactions and increasing the conversion per unit time. Although processes catalysed by homogeneous catalysts have the advantage of offering better control and understanding of the reaction mechanism, their frequent dependence on expensive metals which are difficult to recover, often precludes their employment in large-scale applications. Heterogeneously catalysed reactions on the other hand, are not associated with problems regarding recycling and reuse of catalyst, contamination of products or intermediates. This work reports the synthesis, characterization and testing of Pd-Sn nanoalloy catalyst in the selective hydrogenation of 2-methyl-3-butyn-2-ol. Our results show that the Pd-Sn nanoalloy, of composition Pd2.8Sn, supported on ZnO (Pd2.8Sn/ZnO), offers very high activity and selectivity in the semi-hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol in the liquid phase. Under identical reaction conditions, Pd2.8Sn/ZnO shows activity, both turnover frequency and activity normalized by Pd content, significantly higher than Pd/CaCO3 (the Lindlar catalyst), with TOF of 137.6 s−1 compared to 79.2 s−1 for Pd/CaCO3 with approximately equal selectivity. The preparation of Pd2.8Sn/ZnO is achieved using a one-pot polyol procedure with the addition of a capping agent (polyvinylpyrrolidone) to control the particle size distribution. TEM shows nanoparticles evenly dispersed on the support, with a size distribution of 4.06 ± 0.75 nm. Single phase Pd2.8Sn was also prepared without the ZnO support, via the polyol method. Powder X-Ray diffraction data from the unsupported nanoalloy shows that the unit cell of Pd2.8Sn is face centred cubic with the Pd and Sn atoms occupying randomly the same crystallographic position. The chemical formula was calculated from a combination of ICP and PXRD analyses

Stabilization of Pd3−xIn1+x polymorphs with Pd-like crystal structure and their superior performance as catalysts for semi-hydrogenation of alkynes

Selective hydrogenation (semi-hydrogenation) reactions of alkynes rely on Pd-based catalysts to provide the correct pathway to favour formation of double bonds and avoid full hydrogenation to single bonds. Here, we present the preparation and characterisation of "Pd3In"/TiO2 nanocatalysts, which show improved activity and selectivity compared to pure Pd catalysts, towards the liquid phase semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE), a fundamental step in the preparation of pharmaceuticals, and other industrially produced substances, as well as a model reaction for the semi-hydrogenation of alkynes. For both the supported and unsupported "Pd3In" alloys (later redefined as Pd3-xIn1+x), we stabilised two new cubic polymorphs with a Pd-like structure, instead of the tetragonal structure as reported so far in the literature. The stabilisation of these new polymorphs was made possible by using a solution-based synthesis and, thanks to the use of different solvents, the reaction was 2 carried out at different temperatures and the Pd/In ratio could be tuned. The same synthetic approach was adapted to prepare two "Pd3In"/TiO2 catalysts by adding the TiO2 support to the reaction mixture, in a practical one-step, one-pot reaction. HREM and X-Ray maps show that the cubic crystal structure of "Pd3In" is maintained when prepared in the presence of the support, however, the support seems to influence the Pd/In ratio

The density of states approach to the sign problem

1 + 11 pages, 6 figures. Invited talk presented by B. Lucini at the conference "XIIIth Quark Confinement and the Hadron Spectrum", Maynooth University, Ireland, 1-6 August 2018Approaches to the sign problem based on the density of states have been recently revived by the introduction of the LLR algorithm, which allows us to compute the density of states itself with exponential error reduction. In this work, after a review of the generalities of the method, we show recent results for the Bose gas in four dimensions, focussing on the identification of possible systematic errors and on methods of controlling the bias they can introduce in the calculation

Density of state method for complex action systems

While importance sampling Monte Carlo algorithms have proved to be a crucial tool for numerical studies in modern physics, they fail when we consider complex action systems. The density of states approach provides a way to simulate such systems and reduce the sign problem that afflicts them to a 1-dimensional oscillatory integral. In this work, we shall review the density of states approach as well as the Linear Logarithmic Relaxation algorithm and present some recent development concerning the control of systematics in this algorithm. The results of a benchmark study on the relativistic Bose gas shall be presented as well

Bi2WO6/C-dots/TiO2: A novel z-scheme photocatalyst for the degradation of fluoroquinolone levofloxacin from aqueous medium

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Photocatalytic materials and semiconductors of appropriate structural and morphological architectures as well as energy band gaps are materials needed for mitigating current environmental problems, as these materials have the ability to exploit the full spectrum of solar light in several applications. Thus, constructing a Z-scheme heterojunction is an ideal approach to overcoming the limitations of a single component or traditional heterogeneous catalysts for the competent removal of organic chemicals present in wastewater, to mention just one of the areas of application. A Z-scheme catalyst possesses many attributes, including enhanced light-harvesting capacity, strong redox ability and different oxidation and reduction positions. In the present work, a novel ternary Z-scheme photocatalyst, i.e., Bi2WO6/C-dots/TiO2, has been prepared by a facile chemical wet technique. The prepared solar light-driven Z-scheme composite was characterized by many analytical and spectroscopic practices, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption–desorption isotherm, Fourier-transform infrared spectroscopy (FT-IR), photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the Bi2WO6/C-dots/TiO2 composite was evaluated by studying the degradation of fluoroquinolone drug, levofloxacin under solar light irradiation. Almost complete (99%) decomposition of the levofloxacin drug was observed in 90 min of sunlight irradiation. The effect of catalyst loading, initial substrate concentration and pH of the reaction was also optimized. The photocatalytic activity of the prepared catalyst was also compared with that of bare Bi2WO6, TiO2 and TiO2/C-dots under optimized conditions. Scavenger radical trap studies and terephthalic acid (TPA) fluorescence technique were done to understand the role of the photo-induced active radical ions that witnessed the decomposition of levofloxacin. Based on these studies, the plausible degradation trail of levofloxacin was proposed and was further supported by LC-MS analysis

A hotspot of lichen diversity and lichenological research in the Alps: the Paneveggio-Pale di San Martino Natural Park (Italy)

A checklist of 916 lichenised taxa is reported from the Paneveggio-Pale di San Martino Natural Park and its surroundings (Trentino-Alto Adige, N Italy), based on 7351 records from: (a) 72 literature sources, (b) eight public and private herbaria and (c) field observations by some of the authors. The study area appears as a hotspot of lichen diversity, hosting 30.1% of the lichen biota of the Alps in a territory that has 0.064% of their total surface area. This is mainly due to its high climatical, geological and orographic heterogeneity, but also to the long history of lichenological exploration, that started in the 19th century with Ferdinand Arnold and is still ongoing. The present work highlights the importance of detailed species inventories to support knowledge of biodiversity patterns, taxonomy and ecology and to properly address conservation issues. Fuscidea mollis var. caesioalbescens, Hydropunctaria scabra, Protoparmelia badia var. cinereobadia and Variospora paulii are new to Italy, 18 other taxa are new to Trentino-Alto Adige

Efficient computations of continuous action densities of states for lattice models

Abstract The Logarithmic Linear Relaxation (LLR) algorithm is an efficient method for computing densities of states for systems with a continuous spectrum. A key feature of this method is exponential error reduction, which allows us to evaluate the density of states of a system over hundreds of thousands of orders of magnitude with a fixed level of relative accuracy. As a consequence of exponential error reduction, the LLR method provides a robust alternative to traditional Monte Carlo calculations in cases in which states suppressed by the Boltzmann weight play nevertheless a relevant role, e.g., as transition regions between dominant configuration sets. After reviewing the algorithm, we will show an application in U(1) Lattice Gauge Theory that has enabled us to obtain the most accurate estimate of the critical coupling with modest computational resources, defeating exponential tunneling times between metastable vacua. As a further showcase, we will then present an application of the LLR method to the decorrelation of the topological charge in SU(3) Lattice Gauge Theory near the continuum limit. Finally, we will review in general applications of the LLR algorithm to systems affected by a strong sign problem and discuss the case of the Bose gas at finite chemical potential.</jats:p

Pd₃Sn nanoparticles on TiO₂ and ZnO supports as catalysts for semi-hydrogenation : synthesis and catalytic performance

The two catalysts Pd₃Sn/TiO₂and Pd3Sn/ZnO were prepared via a one-pot procedure based on the “polyol method” with the addition of a capping agent (polyvinylpyrrolidone) to control the particle size distribution. The same procedure was used to prepare Pd/TiO2 and Pd/ZnO for comparison. All four catalysts showed high activity and selectivity for the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) in the liquid phase under identical conditions. However, Pd₃Sn/TiO₂and Pd₃Sn/ZnO show selectivities to alkene significantly higher than that of the Pd catalysts. Specifically, the selectivity increases from 96.4% to 97.4% on TiO₂support, and 96.2% to 97.6% on ZnO support, at 90% conversion. Transition electron microscopy shows nanoparticles evenly dispersed on the support, with mean particle sizes as low as 4.1 (±0.8) nm when Sn is incorporated into the catalyst. Unsupported Pd3Sn was prepared using the same method and characterised by powder X-Ray diffraction followed by the Rietveld refinement. Pd3Sn was found to be single-phase and isostructural to Pd metal with a face centred cubic unit cell