AFM substantiation of the fracture behavior and mechanical properties of sol–gel derived silica packed epoxy networks

Silica packed epoxy networks are prepared in two steps via in situ, solvent free sol–gel processing of tetraethoxysilane in liquid epoxy monomer and curing the mixture with a flexible diamine afterwards. The influence of filler content and processing conditions on the mechanical properties and the fracture behavior is studied by means of the static mechanical analysis and AFM characterization of the pristine and the fractured polymer surfaces, and a mechanism to enhance polymer strength and toughness is proposed. The in–situ evolution and packing of silica nanostructures into epoxy networks influences the overall morphology and performance of polymers under high stress. It is found that smaller silica domains distributed at the molecular level cause efficient crack distribution by absorbing energy and thus improve the strength and toughness of silica packed epoxy polymers.     

Micelle directed synthesis of (C19H42N)4H3(PW11O39) nanoparticles and their catalytic efficiency for oxidative degradation of azo dye

The nanoparticles of monovacant lacunary keggin-type polyoxometalate (C₁₉H₄₂N)₄H₃(PW₁₁O₃₉) has been successfully synthesized by Micelle Directed Method using hexadecyltrimthyl ammonium bromide (CTAB) as a template. Non-ionic copolymer Pluronic F127 was used as a capping agent that helps in formation of nanoparticles by preventing the aggregation during the coating of H₃(PW₁₁O₃₉)^4- onto the counter ion (C₁₉H₄₂N)⁺. The synthesized material was characterized by Scanning electron microscope (SEM), TGA, DSC and FT-IR techniques. SEM images indicated that (C₁₉H₄₂N)₄H₃(PW₁₁O₃₉) nanoparticles possess spherical structure. FTIR results revealed that the structural integrity of monovacant lacunary keggin-type polyoxometalates (POM) was not affected when reducing the size. TGA–DSC results showed that the material was thermally stable (with 37 % weight loss) and POM encapsulates CTAB. The efficiency of synthesized material was checked by applying it as a catalyst for the oxidation of toxic mordant yellow dye i.e., potentially hazardous and non-biodegradable azo dye. The (C₁₉H₄₂N)₄H₃(PW₁₁O₃₉) nanoparticles gave 96 % dye degradation in 60 min at 60 °C temperature. Moreover, on recycling POM nanoparticles demonstrate 92 % oxidative degradation of mordant yellow dye.     

Pulsed supersonic beams with nucleobases

The dissolution of the primary nucleobases in supercritical fluids has been investigated using pulsed molecular beam mass spectrometry. Due to the low critical temperatures of ethylene and carbon dioxide, their adiabatic jet expansion permits transferring thermally sensitive solutes into the gas phase. This feature is particularly attractive for pharmaceutical and biomedical applications. In this study, adenine, guanine, cytosine, thymine, and uracil have been dissolved in supercritical ethylene with a few percent of ethanol as cosolvent. At source temperatures of 313?K, these solutions have been expanded from supercritical pressures into high vacuum using a customized pulsed nozzle. A mass spectrometer was used to monitor the relative amounts of solute, solvent, and cosolvent in the supersonic beam. The results suggest a paramount influence of the cosolvent.     

Synthesis and Characterization of High Surface Area Tin Oxide Nanoparticles via the Sol‐Gel Method as a Catalyst for the Hydrogenation of Styrene

A systematic study on the preparation of SnO₂ nanoparticles using a simple sol‐gel technique has been conducted by varying reaction parameters such as concentration of ammonia, ammonia feed rate and reaction temperature. The tin oxide obtained was characterized by using FTIR, BET, XRD and TEM. Particles size was obtained in the range of 4 to 5.6 nm and the surface area was found to be between 76 to 114 m² g^?1 depending on the reaction parameters. Meanwhile, the catalytic activity of SnO2 was first time investigated for the hydrogenation reaction of styrene using ethanol as the solvent at 70 °C and 1 atmospheric pressure. It is found that SnO2 acts as a good catalyst in this hydrogenation process. The product conversions in the presence of catalysts prepared at different conditions were between 37 to 72%.     

Role of deliquescence lowering in enhancing chemical reactivity in physical mixtures

Mixtures of deliquescent solids are susceptible to deliquescence lowering, where water vapor condensation occurs in mixtures at a lower critical relative humidity (RH(0mix)) than individual component critical relative humidities (RH(0)s). The purpose of this study was to evaluate the effect of deliquescence lowering on chemical reactivity. Sucrose, citric acid and their physical mixtures were characterized using vapor sorption analysis to determine RH(0) and RH(0mix). Acid-catalyzed sucrose hydrolysis kinetics was determined using polarimetric analysis. Physical mixtures of sucrose and citric acid crystals were prepared and stored at various relative humidities at 22 degrees C. For these physical mixtures, sucrose hydrolysis was found to occur only when the environmental RH exceeded RH(0mix). Degradation kinetics correlated with the storage RH, being fastest at higher RH. In addition, a lag period was initially observed, which was most prominent for samples stored close to RH(0mix). With exposure to RHs below RH(0mix), no sucrose degradation was detected over the experimental time period. In conclusion, mixtures of deliquescent solids showed increased water sorption at lower RHs, which caused solid dissolution and subsequently led to an increase in the chemical reactivity.     

Wrapped weighted exponential distributions

We have developed a new class of circular distributions named wrapped weighted exponential distributions. The estimation of unknown parameters along with some characteristics of these distributions is also investigated. Some theorems that relate the distribution to some other circular distributions are established and we clarify their modeling potential using a classical data set on movements of sea stars.     

An online nano-LC-ESI-FTICR-MS method for comprehensive characterization of endogenous fragments from amyloid β and amyloid precursor protein in human and cat cerebrospinal fluid

Amyloid precursor protein (APP) is the precursor protein to amyloid β (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD). Endogenous Aβ peptides reflect the APP processing, and greater knowledge of different APP degradation pathways is important to understand the mechanism underlying AD pathology. When one analyzes longer Aβ peptides by low-energy collision-induced dissociation tandem mass spectrometry (MS/MS), mainly long b-fragments are observed, limiting the possibility to determine variations such as amino acid variants or post-translational modifications (PTMs) within the N-terminal half of the peptide. However, by using electron capture dissociation (ECD), we obtained a more comprehensive sequence coverage for several APP/Aβ peptide species, thus enabling a deeper characterization of possible variants and PTMs. Abnormal APP/Aβ processing has also been described in the lysosomal storage disease Niemann-Pick type C and the major large animal used for studying this disease is cat. By ECD MS/MS, a substitution of Asp7 → Glu in cat Aβ was identified. Further, sialylated core 1 like O-glycans at Tyr10, recently discovered in human Aβ (a previously unknown glycosylation type), were identified also in cat cerebrospinal fluid (CSF). It is therefore likely that this unusual type of glycosylation is common for (at least) species belonging to the magnorder Boreoeutheria. We here describe a detailed characterization of endogenous APP/Aβ peptide species in CSF by using an online top-down MS-based method.     

Photostability of lasing process from water solution of Rhodamine 6G with gold nanoparticles

We report the lasing performance and photobleaching of gain material containing a water solution of Rhodamine 6G dye and gold nanoparticles (NPs). In comparison to a pure dye solution, the investigated material demonstrated both enhancement and quenching of the lasing output, depending on the relative concentration of the gold NPs. Although the presence of NPs with an optimized concentration looks preferable in terms of the lasing output enhancement, such additives deteriorate the operational resource of the gain material; i.e., the photobleaching rate speeds up.     

Orbital optimization techniques: Comparative study in a semiempirical framework

In this paper, MC-SCF and CI methods have been explored for the calculation of ground- and excited-state energies of some aromatic heterocycles in the PPP framework. A new algorithm for solving the orbital equations in MC-SCF theory has been suggested and its performance has been compared with the conventional gradient optimization technique. Energies of first few transitions have been calculated and compared with rather extensive CI results.     

UV-Induced Electrical and Optical Changes in PVC Blends

 2-Chloro-polyaniline (2-Cl-PANI) in its non-conducting (emeraldine base, EB) form, prepared by a chemical route, was dissolved together with poly-(vinylchloride) (PVC) in THF for casting into thin (10–50 μm) films. Upon exposure to UV radiation, the electrical conductivity of these films increased by more than 4 orders of magnitude (from 10⁻⁶ to 10⁻²S/cm). This is attributed to the dehydrochlorination of PVC by exposure to energetic photons and subsequent doping of 2-Cl-PANI (i.e. conversion to emeraldine salt, ES) by in situ created HCl. The doped films could be returned to their undoped form by exposure to NH₃ vapours. The UV-induced doping/NH₃ undoping cycles could be repeated several times. Various spectroscopic techniques were employed to follow the changes in the films upon exposure to UV radiation. The same photo-dehydrochlorination process has also been utilized for optical and/or lithographic purposes by preparing PVC blends containing methyl violet, and acid-base indicator dye. The photo-dehydrochlorination can be effectively sensitized by incorporating hydroquinone into the PVC blends containing methyl violet.