Chemical degradation of an uncrosslinked pure fluororubber in an alkaline environment

The chemical degradation of an uncrosslinked pure fluoroelastomer (FKM; Viton A) in an alkaline environment (10% NaOH and 80 °C) was investigated. Scanning electron microscopy images showed that on a microscopic level, significant degradation substantially increased the surface roughness after prolonged exposure (e.g., 12 weeks). The molecular mechanisms of the chemical degradation processes at the surface were evaluated with X‐ray photoelectron spectroscopy and attenuated total reflectance/Fourier transform infrared spectroscopy. The results revealed that the early degradation proceeded primarily via dehydrofluorination reactions, creating double bonds in the rubber backbone. This further accelerated the degradation after longer exposure times. Furthermore, the resulting double bonds underwent nucleophilic attack by an aqueous NaOH solution to form several oxygenated species. All these species ultimately recombined to form crosslinks, as evidenced by the increase in the gel fraction and surface hardness (Shore A). The pronounced effect of chemical degradation through a reduction in the thermal stability of the pure FKM rubber upon exposure was also evident from thermogravimetric analysis and differential thermogravimetry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6216–6229, 2004     

Acetylene diffusion in Na-Y zeolite

Study of diffusivity of acetylene adsorbed in Na-Y zeolite by quasi-elastic neutron scattering (QENS) measurements at temperatures of 300, 325 and 350 K is reported. A model in which the acetylene molecules undergo random-walk diffusion characterized by a Gaussian distribution of jump lengths inside zeolite cages describes the data consistently. The diffusion constant, residence time between jumps and root mean square jump length are determined.     

Base pairing in RNA structures: A computational analysis of structural aspects and interaction energies

The base pairing patterns in RNA structures are more versatile and completely different as compared to DNA. We present here results of ab-initio studies of structures and interaction energies of eight selected RNA base pairs reported in literature. Interaction energies, including BSSE correction, of hydrogen added crystal geometries of base pairs have been calculated at the HF/6-31G** level. The structures and interaction energies of the base pairs in the crystal geometry are compared with those obtained after optimization of the base pairs. We find that the base pairs become more planar on full optimization. No change in the hydrogen bonding pattern is seen. It is expected that the inclusion of appropriate considerations of many of these aspects of RNA base pairing would significantly improve the accuracy of RNA secondary structure prediction.     

SERS spectrum of the peptide thymosin‐β4 obtained with Ag nanorod substrate

Thymosin‐β4 is a peptide found at high concentrations in a wide range of mammalian cells. It has been shown to be elevated in metastatic cells. In this study, the surface‐enhanced Raman spectrum of thymosin‐β4 was obtained using a silver nanorod array surface‐enhanced Raman scattering substrate. Significant Raman peaks were found, and the corresponding vibrational modes were assigned based on previously published literature, with amide A–B, amide I, and amide III modes all identified. The majority of the remaining peaks were assigned modes based on the spectra of lysine and glutamic acid, the two most abundant amino acids in the thymosin‐β4 sequence. A standard Raman spectrum of thymosin‐β4 was also obtained and analyzed for comparison. Because thymosin‐β4 plays a significant role in regulating the formation of cellular cytoskeleton and other several biological processes, its Raman spectrum will be of use to researchers. Copyright © 2014 John Wiley & Sons, Ltd.     

Cordyceps militaris Fungus Extracts-Mediated Nanoemulsion for Improvement Antioxidant,Antimicrobial, and Anti-Inflammatory Activities

This study aimed to produce and optimize a Cordyceps militaris-based oil-in-water (O/W) nanoemulsion (NE) encapsulated in sea buckthorn oil (SBT) using an ultrasonication process. Herein, a nonionic surfactant (Tween 80) and chitosan cosurfactant were used as emulsifying agents. The Cordyceps nanoemulsion (COR-NE) was characterized using Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and field-emission transmission electron microscope (FE-TEM). The DLS analyses revealed that the NE droplets were 87.0 ± 2.1 nm in diameter, with a PDI value of 0.089 ± 0.023, and zeta potential of −26.20 ± 2. The small size, low PDI, and stable zeta potential highlighted the excellent stability of the NE. The NE was tested for stability under different temperature (4 °C, 25 °C, and 60 °C) and storage conditions for 3 months where 4 °C did not affect the stability. Finally, in vitro cytotoxicity and anti-inflammatory activity were assessed. The results suggested that the NE was not toxic to RAW 264.7 or HaCaT (human keratinocyte) cell lines at up to 100 µL/mL. Anti-inflammatory activity in liposaccharides (LPS)-induced RAW 264.7 cells was evident at 50 µg/mL and showed inhibition of NO production and downregulation of pro-inflammatory gene expression. Further, the NE exhibited good antioxidant (2.96 ± 0.10 mg/mL) activity and inhibited E. coli and S. aureus bacterial growth. Overall, the COR-NE had greater efficacy than the free extract and added significant value for future biomedical and cosmetics applications.     

Ag2Cr2O7 nanoparticles: An eco-friendly and reusable catalyst for synthesis of pyrano[c]chromenediones and [1,3]dioxolo[g]chromeneones in aqueous media at ambient temperature

An efficient and green protocol for the synthesis of 4-aryl-3,4-dihydro-2H,5H-pyrano[3,2-c]chromene-2,5-diones and 8-aryl-7,8-dihydro-6H-[1,3]dioxolo[4,5-g]chromene-6-ones through the Ag₂Cr₂O₇ nanoparticles catalyzed cyclocondensation reaction of active methylene compounds including 4-hydroxycoumarin or 3,4-methylenedioxyphenol, aromatic aldehydes, and meldrum's acid in water at ambient temperature was described. This method demonstrates several advantages compared with methods that are currently employed such as a mild reaction conditions, simple work-up, good to excellent yields, avoiding toxic catalyst and hazardous solvent, and recovery and reuse of the catalyst.     

Sol–gel synthesis and characterization of SiO2–Tac nanocomposites with controlled volume fraction

Nanocrystalline tantalum carbide (TaC) particles of average size ~15 nm dispersed in silica matrix, have been synthesized by the carbothermal reduction of Ta₂O₅ over a range of temperature 1,100–1,360 °C in Ar atmosphere. Investigation of the stability diagram of carbon saturated Ta–O–N system suggests that the TaC phase can be successfully synthesized within the SiO₂ matrix when the partial pressure of O₂ and N₂ are restricted to approximately lower than 1.25 and 0.0001 atm. respectively. Two different synthesis routes are investigated in the present study which differ fundamentally in the order of addition of the precursors, tetraethyl orthosilicate (TEOS) and tantalum isopropoxide (Ta-iso). Rietveld refinement analyses of the powder X-ray diffraction data are carried out for the quantitative estimation of the two phases in the samples. The yield of TaC increases from 18 to 52 % when both TEOS and Ta-iso are added simultaneously to the water compared to the process where TEOS is added first to the water followed by the delayed addition of Ta-iso. Samples are further characterized by field emission scanning electron microscopy and high resolution transmission electron microscopy.     

Scanning SQUID Microscopy of Local Superconductivity in Inhomogeneous Combinatorial Ceramics

Although combinatorial solid‐state chemistry promises to be an efficient way to search for new superconducting compounds, the problem of determining which compositions are strongly diamagnetic in a mixed‐phase sample is challenging. By means of reactions in a system of randomly mixed starting components (Ca, Sr, Ba, La, Y, Pb, Bi, Tl, and Cu oxides), samples were produced that showed an onset of diamagnetic response above 115 K in bulk measurements. Imaging of this diamagnetic response in ceramic samples by scanning SQUID microscopy (SSM) revealed local superconducting areas with sizes down to as small as the spatial resolution of a few micrometers. In addition, locally formed superconducting matter was extracted from mixed‐phase samples by magnetic separation. The analysis of single grains (d<80 μm) by X‐ray diffraction, elemental analysis, and bulk SQUID measurements allowed Tl₂Ca₃Ba₂Cu₄O₁₂, TlCaBaSrCu₂O_7?δ, BaPb_0.5Bi_0.25Tl_0.25O_3?δ, TlBa₂Ca₂Cu₃O₉, Tl₂Ba₂CaCu₂O₈, and YBa₂Cu₃O₇ phases to be identified. SSM, in combination with other diagnostic techniques, is therefore shown to be a useful instrument to analyze inhomogeneous reaction products in the solid‐state chemistry of materials showing magnetic properties.