Optical properties of a polyethylene dispersion with a luminescent silica prepared by surface grafting of a perylene derivative

A micrometric silica modified with perylene derivative (SiO₂–TES) has been prepared by hydrolysis–condensation reactions between silica and N,N’-bis-(3-triethoxysilylpropyl)-perylene-tetracarboxyldiimide (P-TES) and utilized as filler in LLDPE films together with a compatibilizer. Spectroscopic analyses on SiO₂–TES confirmed the grafting of P-TES on silica, while its amount was determined by thermogravimetric analysis. Solid state NMR provided information about the structure of silicon atoms involved in the condensation of SiO₂ and P-TES that resulted mainly in silicon atoms grafted with bi-dentate anchorages.UV–Vis and fluorescence analyses carried out on P-TES showed the ability of the dye to generate J-type aggregates in apolar solvents. The same analyses on SiO₂–TES revealed the presence of both isolated and aggregated dye molecules grafted on silica surface, while on polymeric dispersions of SiO₂–TES, they have shown only the presence of P-TES aggregates grafted to silica.Thanks to the direct correlation between optical properties (obtained both by UV–Vis and by fluorescence analyses) and the chemical environment of composites, the luminescent silica SiO₂–TES could be used to estimate the filler dispersion extent in different microcomposite polymer materials.     

Effect of head group size, temperature and counterion specificity on cationic micelles

The critical micelle concentration (cmc) and ionisation degree (α), of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltripropylammonium bromide (CTPABr) and cetyltripropylammonium chloride (CTPACl) have been measured over a narrow temperature range at 2 degree intervals using electrical conductivity. CTPACl and CTPABr are very soluble in water and were measured in the temperature range 275.15-323.15K. The Krafft temperatures for CTABr and for CTACl are 293.15K and 284.15K, respectively and established a lower temperature limit for our studies on these two surfactants. The cmc vs temperature curves have a smooth minimum near room temperature and α linearly increases with temperature. The changes of cmc and α with temperature are smaller than those associated with the modification of head group size or counterion nature. Using these results, basic thermodynamic quantities associated with the phenomena of micellization have been evaluated. Thermodynamic properties of the surfactant solutions were discussed in terms of temperature dependence of the free energy, enthalpy and entropy of micellization. A close similarity between the effects of change in temperature on protein folding and micellization process appears from the data.     

TG–FTIR analysis applied to the study of thermal behaviour of some edible mushrooms

The article is devoted to the study on the thermal behaviour of three species of edible mushrooms: Boletus edulis (foot and cap), Pleurotus ostreatus (foot and cap), Lactarius deterrimus (cap) by the TG–FTIR-coupled technique, in air, over the 30–900 °C temperature range. The analysis of the TG–DTG–DTA curves reveals the thermal degradation mechanism to be complex and specific to every species under the recording conditions applied. A similar degradation mechanism is noticed for the foot and cap of Pleurotus ostreatus in comparison with the Boletus edulis and Lactarius deterrimus species where the mechanisms are different. The TG–FTIR analysis, combustion heats and IR spectra of the starting samples also support these results. The initial degradation temperatures from TG–DTG indicate the temperature range where these species are thermally stable and their nutrient features maintained making them proper for food. The TG–FTIR analysis gives information on the gaseous species evolved by the thermal degradation bringing thus a contribution to the elucidation of the changes developing by processing the edible mushrooms (industrialization, conservation, culinary preparations, etc.) at temperatures above the initial degradation temperature. At the same time, the environmental impact, when the mushroom failed cultures are burned, is also important.     

The effect of composition of solid silver amalgam electrodes on their electrochemical response

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag₂Hg₃), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.     

Anthraquinone profile, antioxidant and antimicrobial properties of bark extracts of Rhamnus catharticus and R. orbiculatus

The anthraquinone profile, antioxidant and antimicrobial activities as well as the total phenol and total flavonoid contents were determined in methanol extracts of the barks of Rhamnus catharticus L. and R. orbiculatus Bornm. The most abundant anthraquinone derivatives in R. catharticus were physcion (67.8%) and emodin (26.2%), while R. orbiculatus contained mostly physcion (81.3%) and chrysophanol (14.6%). R. catharticus displayed better activity in the beta-carotene-linoleic acid assay, as well as chelating activity, whereas its activity in the reducing power assay was significantly lower than that of R. orbiculatus. Both methanol extracts showed antimicrobial activity against all microbial species tested (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, Aspergillus niger, Microsporum gypseum) with MIC values either equal to or lower than 2.50 mg/mL. R. catharticus and R. orbiculatus contained several anthranoid aglycones and their bark extracts demonstrated notable antioxidant and antimicrobial properties. The results obtained indicate the medicinal potential of these two species.     

Worms,gaps, and hydras

We define a direct translation from finite rooted trees to finite natural functions which shows that the Worm Principle introduced by Lev Beklemishev is equivalent to a very slight variant of the well‐known Kirby‐Paris' Hydra Game. We further show that the elements in a reduction sequence of the Worm Principle determine a bad sequence in the well‐quasi‐ordering of finite sequences of natural numbers with respect to Friedman's gapembeddability. A characterization of gap‐embeddability in terms of provability logic due to Lev Beklemishev is also presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermoeconomic analysis of an irreversible Stirling heat pump cycle

In this paper an analysis of the Stirling cycle in thermoeconomic terms is developed using the entropy generation. In the thermoeconomic optimization of an irreversible Stirling heat pump cycle the F function has been introduced to evaluate the optimum for the higher and lower sources temperature ratio in the cycle: this ratio represents the value which optimizes the cycle itself. The variation of the function F is proportional to the variation of the entropy generation, the maxima and minima of F has been evaluated in a previous paper without giving the physical foundation of the method. We investigate the groundwork of this approach: to study the upper and lower limits of F function allows to determine the cycle stability and the optimization conditions. The optimization consists in the best COP at the least cost. The principle of maximum variation for the entropy generation becomes the analytic foundation of the optimization method in the thermoeconomic analysis for an irreversible Stirling heat pump cycle.     

Optimized polymer-enzyme electrostatic interactions significantly improve penicillin G amidase efficiency in charged PEGA polymers

Hydrolytic yields as high as 80% were obtained by using penicillin G amidase (PGA) on substrates anchored on optimized positively charged PEGA polymers. By increasing the amount of permanent charges inside the polymer, electrostatic interactions between the positively charged PEGA⁺ and the negatively charged PGA (pI=5.2-5.4) were strengthened, thus favouring the accessibility of the bulky enzyme (MW=88 kDa) inside the pores. The effect of different amounts of charges on polymer swelling and protein retention inside the polymer was investigated and correlated to the enzyme efficiency demonstrating that electrostatic interactions predominate over swelling properties in determining enzyme accessibility.     

on submicron rings and their application for coherent nanoelectronic devices

Electron-phase modulation in magnetic and electric fields will be presented in In_0.75Ga_0.25As Aharonov–Bohm (AB) rings. The zero Schottky barrier of this material made it possible to nanofabricate devices with radii down to below 200 nm without carrier depletion. We shall present a fabrication scheme based on wet and dry etching that yielded excellent reproducibility, very high contrast of the oscillations and good electrical gating. The operation of these structures is compatible with closed-cycle refrigeration and suggests that this process can yield coherent electronic circuits that do not require cryogenic liquids. The InGaAs/AlInAs heterostructure was grown by MBE on a GaAs substrate [F. Capotondi, G. Biasiol, D. Ercolani, V. Grillo, E. Carlino, F. Romanato, L. Sorba, Thin Solid Films 484 (2005) 400], and in light of the large effective g-factor and the absence of the Schottky barrier is a material system of interest for the investigation of spin-related effects [W. Desrat, F. Giazotto, V. Pellegrini, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, D.K. Maude, Phys. Rev. B 69 (2004) 245324; W. Desrat, F. Giazotto, V. Pellegrini, M. Governale, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, Phys. Rev. B 71 (2005) 153314; J. Nitta, T. Akazaki, H. Takayanagi, T. Enoki, Phys. Rev. Lett. 78 (1997) 1335] and the realization of hybrid superconductor/semiconductor devices [Th. Schäpers, A. Kaluza, K. Neurohr, J. Malindretos, G. Crecelius, A. van der Hart, H. Hardtdegen, H. Lüth, Appl. Phys. Lett. 71 (1997) 3575].