Theoretical Exploitation of 1,2,3,4,5,6-Hexachloro- and 1,2,3,4,5,6-Hexafluorocyclohexane Isomers as Biologically Active Compounds

Hexachlorocyclohexanes (HCHs) have been widely explored as biological compounds during the last century. However, most of them were banned due to their potential toxicity in humans, animals, and the environment. Revisiting HCHs to explore their biological activity while improving key features is valuable and may lead to a new class of pesticides that utilizes the biological response of HCHs without their toxic characteristics. In this sense, the fluorine atom can be a possible alternative since a large number of therapeutics and agrochemicals have been developed with this halogen in their structure. We have evaluated herein the conformational behavior of HCHs and their bioisosteric fluorinated compounds, namely, hexafluorocyclohexanes (HFHs), through quantum-chemical calculations. We also explored the potential of the HCH and HFH isomers as biological compounds by docking them inside three possible targets. It was demonstrated that HCH and HFH have similar ligand-protein interactions with three pockets: the picrotoxin and barbiturate sites of the GABA_A receptor and the ryanodine receptor. The results support HFHs as possible alternatives for HCHs since the replacement of Cl with F does not forfeit the main ligand-protein interactions. Finally, we demonstrated that HFHs have a lower log P than HCHs by almost two logarithmic units. This result highlights the role of fluorine in distribution and bioaccumulation.     

The effects of ZnO coating on the photoluminescence properties of porous silicon for the advanced optoelectronic devices

In the present work we investigate, the role of zinc oxide (ZnO) thin films passivating layer deposited by rf magnetron sputtering at room temperature on low (18%) and high (80%) porosity porous silicon (PS). The micro-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) analysis have been carried out to understand the effect of ZnO films coating on PS. A systematic investigation from Raman spectroscopy suggests the formation of a good quality ZnO wurtzite structure on PS. The photoluminescence (PL) measurements on PS and ZnO coated PS shows a red, blue and UV emission bands at around ～1.8, ～2.78 and ～3.2 eV. An enhancement of all PL emission bands have been achieved after ZnO films deposition on high porosity PS.     

Dielectric properties of ternary melt processed blends

Thermal, morphological and dielectric properties of conductive thermoplastic blends based on polystyrene, styrene–butadiene–styrene block copolymer and doped polyaniline have been investigated with special emphasis on the effect of doped polyaniline concentration. Blends were prepared by melt blending using an internal mixer. Morphological studies by scanning electron microscopy of cryofractured surfaces indicated that thermoplastic matrix had a better miscibility with the presence of copolymer as compatibilizer and also good dispersability and structuring of doped polyaniline particles within polystyrene. A reduction in impedance from 26 to 2 MΩ at 10 Hz, with the increasing polyaniline content is also observed. The blends can be used for antistatic applications. From the fit to the impedance spectroscopy data we obtained the relaxation strength, the depression angle and the relaxation.     

Chemical Kinetic Strategies for High‐Throughput Screening of Protein Aggregation Modulators

Insoluble aggregates staining positive to amyloid dyes are known histological hallmarks of different neurodegenerative disorders and of type II diabetes. Soluble oligomers are smaller assemblies whose formation prior to or concomitant with amyloid deposition has been associated to the processes of disease propagation and cell death. While the pathogenic mechanisms are complex and differ from disease to disease, both types of aggregates are important biological targets subject to intense investigation in academia and industry. Here we review recent advances in the fundamental understanding of protein aggregation that can be used on the development of anti‐amyloid and anti‐oligomerization drugs. Specifically, we pinpoint the chemical kinetic aspects that should be attended during the development of high‐throughput screening assays and in the hit validation phase. The strategies here devised are expected to establish a connection between basic research and pharmaceutical innovation.     

ss‐NMR and single‐crystal X‐ray diffraction in the elucidation of a new polymorph of bischalcone (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one

We report a new polymorph of (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one, C₁₇H₁₂F₂O. Contrary to the precedent literature polymorph with Z′ = 3, our polymorph has one half molecule in the asymmetric unit disordered over two 50% occupancy sites. Each site corresponds to one conformation around the single bond vicinal to the carbonyl group (so‐called anti or syn). The other half of the bischalcone is generated by twofold rotation symmetry, giving rise to two half‐occupied and overlapping molecules presenting both anti and syn conformations in their open chain. Such a disorder allows for distinct patterns of intermolecular C—H…O contacts involving the carbonyl and anti‐oriented β‐C—H groups, which is reflected in three ¹³C NMR chemical shifts for the carbonyl C atom. Here, we have also assessed the cytotoxicity of three symmetric bischalcones through their in vitro antitumour potential against three cancer cell lines. Cytotoxicity assays revealed that this biological property increases as halogen electronegativity increases.     

Effect of Polymer Strengtheners on the Local Environment of Biocompatible Glass as Probed by Fluorescence

Mixed silica–calcite matrices were prepared by developing a “low” temperature (sol–gel) method in presence of several biocompatible polymers, thus providing samples with adequate porosity for the flow of biological fluids and also mechanically robust. In order to analyse and characterise the sample’s microenvironments, the highly solvatochromic probe Nile red was used, which enabled the role of polymer addition upon local environmental effects in the host media to be elucidated. The polymers used were polyethylene glycol, polymethylmethacrylate and polyethylene. Each matrix was also characterized with respect to microstructure, morphology and pore size via the use of X-ray diffractometry and scanning electron microscopy. The results show that is was possible to obtain, in a controlled way, mixed silica–calcite matrices with a wide range of porosities (important if the material is to be used for scaffold or drug release applications, for example). The spectroscopic behaviour of Nile red when incorporated has confirmed the existence of distinct and specific local polarities within each type of matrix that may determine to a large extent the mechanism of interaction between these matrices and biological molecules. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A novel source of atomic hydrogen for passivation of defects in silicon

Palladium membranes have been used for decades for the separation of hydrogen from other gasses. In this letter the use of thin palladium leaves to act as sources of atomic hydrogen for silicon samples is explored. It has been assumed in the past that although hydrogen diffuses through palladium in atomic form, the atoms recombine to form molecular hydrogen at the surface. In this letter it is shown that hydrogen supplied to one surface of a palladium leaf can result in atomic hydrogen being released from the opposite surface at low pressure. This is demonstrated through the use of a palladium leaf in a direct plasma system which allows for atomic hydrogen to be supplied to a sample while avoiding exposure to UV radiation from the plasma and high energy charged particles. This method is shown to provide significant atomic hydrogen to silicon samples and improve passivation of silicon surfaces. Method of Shielded Hydrogen Passivation: Schematic of direct plasma chamber with a shield inserted between the plasma and the silicon sample.     

Study of graded Ni-Ti shape memory alloy film growth on Si(100) substrate

In-situ X-ray diffraction (XRD) was employed to study the effect of the deliberate change of the Ti/Ni ratio during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (XTEM), and electrical resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film (thickness of ≈ 420 nm) with a Ti-rich composition in the central part (ranging from 50 to ≈60 at. %) and near-equiatomic composition in the extremities, following four distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2–3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti₂Ni. When stopping the Ti co-sputtering, Ti₂Ni dissolves and, thus, plays the role of a Ti reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the morphology of the interface has shown the presence of NiSi₂ silicides (A-NiSi₂ and B-NiSi₂), Ti₄Ni₄Si₇, Ti₂Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, ER measurements revealed phase transitions associated with the B2, R-phase and B19^′ phases. These type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation. PACS 81.15.Cd; 61.10.Nz; 68.55.Jk