Tumor Carbohydrate Associated Antigen Analogs as Potential Binders for Siglec-7

We investigated two recently synthesized and characterized sialyl derivatives, bearing the Neu5Ac-α-(2-6)-Gal epitope, as promising binders for Siglec-7, an inhibitory Siglec mainly found on natural killer cells. A variety of sialoglycan structures can be recognized by Siglec-7 with implications in the modulation of immune responses. Notably, overexpression of sialylated glycans recognized by Siglec-7 can be associated with the progression of several tumors, including melanoma and renal cell carcinoma. NOE-based NMR techniques, including Saturation Transfer Difference and transferred-NOESY NMR, together with molecular docking and dynamic simulations were combined to shed light on the molecular basis of Siglec-7 recognition of two conformationally constrained Sialyl-Tn antigen analogs. We, therefore, identify the ligands epitope mapping and their conformational features and propose 3D models accurately describing the protein-ligand complexes. We found that the binding site of Siglec-7 can accommodate both synthetic analogs, with the sialic acid mainly involved in the interaction. Moreover, the flexibility of Siglec-7 loops allows a preferred accommodation of the more rigid compound bearing a biphenyl moiety at position 9 of the sialic acid that contributed to the interaction to a large extent. Our findings provided insights for developing potential novel high affinity ligands for Siglec-7 to hinder tumor evasion.     

Surface-Modified Carbon Materials for CO2 Electroreduction

The electrochemical reduction of CO₂ to produce sustainable fuels and chemicals has attracted great attention in recent years. It is shown that surface-modified carbons catalyze the CO₂RR. This study reports a strategy to modify the surface of commercially available carbon materials by adding oxygen and nitrogen surface groups without modifying its graphitic structure. Clear differences in CO₂RR activity, selectivity and the turnover frequency between the surface-modified carbons were observed, and these differences were ascribed to the nature of the surface groups chemistry and the point of zero charge (PZC). The results show that nitrogen-containing surface groups are highly selective towards the formation of CO from the electroreduction of CO₂ in comparison with the oxygen-containing surface groups, and the carbon without surface groups. This demonstrates that the selectivity of carbon for CO₂RR can be rationally tuned by simply altering the surface chemistry via surface functionalization.     

Electrochemistry and Spin-Crossover Behavior of Fluorinated Terpyridine-Based Co(II) and Fe(II) Complexes

Due to their ability to form stable molecular complexes that have tailor-made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding Co^II and Fe^II complexes were synthesized and characterized by single-crystal X-ray structural analysis, electrochemistry and temperature-dependent SQUID magnetometry. Single crystal X-ray diffraction analyses at 100 K of these complexes revealed Co−N and Fe−N bond lengths that are typical of low spin Co^II and Fe^II centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis-NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction.     

Search for nematic biaxiality in bent-core mesogens: an X-ray diffraction perspective

ABSTRACT

Since its theoretical prediction in 1970, the search for the biaxial nematic phase in thermotropic systems has challenged generations of liquid crystal scientists. Over the last 10 years, bent-core mesogens have drawn much interest as promising candidates for nematic biaxiality. However, despite a number of disputed claims, conclusive evidence of proper (spontaneous and macroscopic) biaxial order in these materials is still missing. By contrast, it is now widely recognised that biaxiality exists on a local scale, in the form of nano-sized clusters of molecules (cybotactic groups) possessing smectic-like positional order and biaxial orientational order. This article provides a review of X-ray diffraction studies on biaxiality and cybotaxis in bent-core nematics, discussing the most relevant issues related to this research field.     

Viability of Biopolymers for Enhanced Oil Recovery

Xanthan gum and scleroglucan are assessed as environmentally friendly enhanced oil recovery (EOR) agents. Viscometric and interfacial tension measurements show that the polysaccharides exhibit favorable viscosifying performance, robust shear tolerance, electrolyte tolerance, and moderate interactions with surfactants. Non-ionic surfactants and anionic surfactants bind to xanthan gum and transform the backbone conformation from a strong helix to a more flexible structure, reducing the viscosifying efficacy of xanthan. In contrast, non-ionic surfactants and anionic surfactants bind to scleroglucan and increase the viscosifying efficacy by non-electrostatic interactions or imparted electrostatic effects. The two polysaccharides are technically viable as viscosifying agents in typical EOR injection fluid formulations.     

Investigation of the possible origins of sulfur in 19th century salted paper photographs by x‐ray fluorescence spectroscopy

An X‐ray fluorescence method to determine whether sulfur is present in 19th century photographs due to intentional toning or to environmental deterioration is proposed. In the 19th century salted paper print photographic process, AgCl formed on the surface of a sheet of paper was exposed to sunlight in contact with a negative, leading to the printing out of a Ag image that was fixed by immersing it in a sodium thiosulfate solution or hypo. The improper execution of the fixing in these photographs may result in the presence of sulfur, mostly manifested in image fading, irregular staining, and discoloration. Also, 19th century artists produced salted paper prints with a variety of image tonalities, for example, by using an artificially aged thiosulfate bath. The presence of sulfur in photographs may also be due to sulfur‐containing environmental pollutants. Therefore, knowledge about the location and amounts of sulfur is important to understand the artistic technique and/or the deterioration processes. In this study, the amounts of sulfur and the silver to sulfur signal ratios were determined for a salted paper print made in the laboratory following a 19th century procedure and for two artistic salted paper photographs using X‐ray fluorescence and standards prepared with different amounts of retained hypo and quantified by inductively coupled plasma atomic emission spectroscopy. The amounts of sulfur and the normalized silver to sulfur ratios for the artistic photographs were evaluated based on the results obtained in the samples prepared in the laboratory and in the context of the 19th century practices. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental Investigation on Transmission Control Protocol Throughput Behavior in Optical Fiber Access Networks

ABSTRACT

This article describes an experimental investigation on the behavior of transmission control protocol in throughput measurements to be used in the verification of the service-level agreement between the Internet service provider and user in terms of line capacity for ultra-broadband access networks typical of fiber-to-the-x architectures. It is experimentally shown different conditions in high bandwidth-delay product links where the estimation of the line capacity based on a single transmission control protocol session results are unreliable. Simple equations reported in this work, and experimentally verified, point out the conditions in terms of packet loss, time delay, and line capacity, that allow consideration of the reliability of the measurement carried out with a single transmission control protocol session test by adopting a suitable measurement time duration.     

Magnetically Induced Continuous CO2 Hydrogenation Using Composite Iron Carbide Nanoparticles of Exceptionally High Heating Power

The use of magnetic nanoparticles to convert electromagnetic energy into heat is known to be a key strategy for numerous biomedical applications but is also an approach of growing interest in the field of catalysis. The heating efficiency of magnetic nanoparticles is limited by the poor magnetic properties of most of them. Here we show that the new generation of iron carbide nanoparticles of controlled size and with over 80 % crystalline Fe_2.2C leads to exceptional heating properties, which are much better than the heating properties of currently available nanoparticles. Associated to catalytic metals (Ni, Ru), iron carbide nanoparticles submitted to magnetic excitation very efficiently catalyze CO₂ hydrogenation in a dedicated continuous‐flow reactor. Hence, we demonstrate that the concept of magnetically induced heterogeneous catalysis can be successfully applied to methanation of CO₂ and represents an approach of strategic interest in the context of intermittent energy storage and CO₂ recovery.     

Excitation Dynamics in Hetero‐bichromophoric Calixarene Systems

In this work, the dynamics of electronic energy transfer (EET) in bichromophoric donor–acceptor systems, obtained by functionalizing a calix[4]arene scaffold with two dyes, was experimentally and theoretically characterized. The investigated compounds are highly versatile, due to the possibility of linking the dye molecules to the cone or partial cone structure of the calix[4]arene, which directs the two active units to the same or opposite side of the scaffold, respectively. The dynamics and efficiency of the EET process between the donor and acceptor units was investigated and discussed through a combined experimental and theoretical approach, involving ultrafast pump–probe spectroscopy and density functional theory based characterization of the energetic and spectroscopic properties of the system. Our results suggest that the external medium strongly determines the particular conformation adopted by the bichromophores, with a direct effect on the extent of excitonic coupling between the dyes and hence on the dynamics of the EET process itself.     

A New Recurrence Relation and Related Determinantal form for Binomial Type Polynomial Sequences

For polynomial sequence of binomial type we propose a new recurrence formula equivalent to a determinantal form of the sequence, from which known and unknown properties are deducted. Relationships whit \({\delta}\)–functionals, \({\delta}\)–operators and generating function are pointed out. Finally, some classical examples are studied, highlighting interesting determinantal identities.