A robust pathway to electrically conductive hemicellulose hydrogels with high and controllable swelling behavior

A robust pathway to synthesize electrically conductive hemicellulose hydrogels (ECHHs) based on O-acetyl-galactoglucomannan (AcGGM) and conductive aniline tetramer (AT) is presented. These ECHHs were obtained by functionalizing carboxylated AcGGM with glycidyl methacrylate (GMA) and subsequently covalently immobilizing AT onto GMA. Hydrogel swelling ratios (SRs) were regulated by the degree of substitution (DS) of the carboxylated AcGGM, the maximum varied as follows: SR_DS=1.14 < SR_DS=0.60 < SR_DS=0.24. The SR can also be tuned from 548% to 228% by changing the AT contents from 10% (w/w) to 40% (w/w) while simultaneously altering conductivities from 2.93 × 10⁻⁸ to 1.12 × 10⁻⁶ S/cm. Free-standing ECHHs with tunable conductivity and degree of swelling, as presented herein, have a broad potential for biomedical applications.     

Dissolution of alumina ceramics in HCl aqueous solution

Dissolution of a cold isostatically pressed high purity alumina ceramics in aqueous HCl solutions was studied as a function of immersion time and acid concentration. From the amounts of Al³⁺, Mg²⁺, Ca²⁺, Na⁺, Si⁴⁺ and Fe³⁺ ions released in the corrosive solution, a degree of dissolution χ_i for each component was calculated according to the equation χ_i = A/B, where A and B are respectively the amount of the element released in the corrosive solution and the amount of the element in the untreated material. The determination of the amounts of ions released in the corrosive solutions was carried out by means of atomic absorption spectrometry (AAS). The corrosion of alumina ceramics in the HCl aqueous solution is determined by the solubility of alumina and the solubility of grain-boundary impurities. Very low dissolution values of Al³⁺, Mg²⁺, Ca²⁺, Na⁺, Si⁴⁺ and Fe³⁺ ions after the corrosion test of alumina ceramics showed a very good corrosion resistance in the HCl aqueous solution.     

Measurement of carrier mobility in silicon nanowires

We report the first direct capacitance measurements of silicon nanowires (SiNWs) and the consequent determination of field carrier mobilities in undoped-channel SiNW field-effect transistors (FETs) at room temperature. We employ a two-FET method for accurate extraction of the intrinsic channel resistance and intrinsic channel capacitance of the SiNWs. The devices used in this study were fabricated using a top-down method to create SiNW FETs with up to 1000 wires in parallel for increasing the raw capacitance while maintaining excellent control on device dimensions and series resistance. We found that, compared with the universal mobility curves for bulk silicon, the electron and hole mobilities in nanowires are comparable to those of the surface orientation that offers a lower mobility.     

Ultra-Low Dark Current Organic–Inorganic Hybrid X-Ray Detectors

Organic-inorganic hybrid semiconductors are an emerging class of materials for direct conversion X-ray detection due to attractive characteristics such as high sensitivity and the potential to form conformal detectors. However, existing hybrid semiconductor X-ray detectors display dark currents that are 1000–10 000× higher than industrially relevant values of 1–10 pA mm⁻². Herein, ultra-low dark currents of <10 pA mm⁻², under electric fields as high as ≈4 V µm⁻¹, for hybrid X-ray detectors consisting of bismuth oxide nanoparticles (for enhanced X-ray attenuation) incorporated into an organic bulk heterojunction consisting of p-type Poly(3-hexylthiophene-2,5-diyl) (P3HT) and n-type [6,6]-Phenyl C71 butyric acid methyl ester (PC₇₀BM) are reported. Such ultra-low dark currents are realized through the enrichment of the hole selective p-type organic semiconductor near the anode contact. The resulting detectors demonstrate broadband X-ray response including an exceptionally high sensitivity of ≈1.5 mC Gy⁻¹ cm⁻² and <6% variation in angular dependence response under 6 MV hard X-rays. The above characteristics in combination with excellent dose linearity, dose rate linearity, and reproducibility over a broad energy range enable these detectors to be developed for medical and industrial applications.     

Structural studies of trimethoxysilane containing R'R"Im+I- ionic liquid and its nanocomposite with tetramethoxysilane (TMOS)

A dialkylsubstituted imidazolium iodide ionic liquid (1-methyl-3-[3-(trimethoxy-lambda4-silyl)propyl]imida-zolium iodide, MTMSPIm+I-) was prepared with the intention of using it as a quasi-solid-state electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of Gr?tzel design, while the analogous electrolyte in a gel state was made by the addition of tetramethoxysilane (TMOS) in the molar ratio MTMSPIm+I-:TMOS = 1:1. The structure of the MTMSPIm+I- in its non-hydrolyzed and hydrolyzed states and in its fully condensed form, obtained after ageing the sols for various times (from a few hours to a few weeks) and heating them at 200 degrees C (fully condensed form), was studied employing time-dependent infrared attenuated total reflection (ATR) and 29Si NMR spectroscopic measurements. The structure of the condensed species was correlated with the viscosity and the specific conductivity measurements of MTMSPIm+I- sols and TMOS/MTMSPIm+I- gels during their ageing. The final product of the condensation of MTMSPIm+I- sols was described as a positively-charged ladder-like polysilsesquioxane with Tn end groups exhibiting a single T3 signal in 29Si NMR spectra and characteristic doublet bands at 1138 and 1049 cm(-1) in IR. This structure was retained to a large extent in TMOS/MTMSPIm+I- gels, confirming their nanocomposite structure. The results of the ATR infrared time-dependent spectroscopic studies showed that in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to shifts in the vibrational band positions in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined and the results applied in this work.     

Determination of the adsorption character of cellulose fibres using surface tension and surface charge

The reactivity and adsorption properties of cellulose fibres are critical for successful treatment because behavior during the finishing process is determined by both structure and surface properties. The fine structure of natural cellulose fibres i.e. cotton, is different from the regular viscose, modal and new types of regenerated cellulose fibres i.e. lyocell, which are clarified by different hydrophilic/hydrophobic character of fibres and different adsorption properties. Tensiometry, seldom used in fibre characterization was used to obtain the differences in the adsorption properties of different cellulose fibres. The surface tension, contact angle and adsorption were measured, and then compared with various methods for determining water adsorption. Currently some additional methods especially sensitive to surface properties (electrokinetic properties of fibres) are being applied in order to characterize the adsorption character and reactivity of the fibre surfaces. The streaming potential was measured due to the fact that the interaction properties are strongly influenced by electric charges on the surface, and from these values the zeta potential (ζ) was calculated as a function of the pH and the surfactant concentration in the liquid phase. As with the results of fibre reactivity and adsorption properties obtained by conventional methods, the electrokinetic character of the materials and their adsorption ability determined using the tensiometry also show the same phenomena. The natural fibres have the smaller hydrophilic character and they are less reactive than the regenerated ones, so the ζ_max of cotton is the highest and the contact angle ϕ the greatest [1, 2, 3] Electronic Publication     

Electrochemical determination of antioxidant capacity of fruit tea infusions

Cyclic voltammograms (CV) taken to 800 mV at a scan rate 100 mV s⁻¹ were used to quantify electrochemical properties of antioxidants present in 10 fruit tea infusions as well as to deduce antioxidant capacity from the Q₆₀₀ parameter (charge passed to 600 mV). A pronounced anodic current peak observed at 440 mV in all analysed fruit teas indicated that ortho-dihydroxy-phenol and gallate groups are the major contributors to the antioxidant capacity of investigated teas. Antioxidant composite index (ACI) was determined for each tea employing antioxidant capacity values from previous spectrophotometric determinations as well as the Q₆₀₀ parameter derived from CV. A ranking of the most potent teas was obtained: the fruit tea containing a large portion of rose hip fruit exhibited the highest ACI and a CV with the most pronounced anodic current peak at 440 mV pointing to the presence of ortho-dihydroxy-phenol and gallate group containing compounds. Strong positive correlation was established between antioxidant capacities deduced from CVs with those previously determined using established spectrophotometric techniques (FRAP, ABTS and DPPH assays).     

Purification and characterization of an alkaline lipase from Pseudomonas aeruginosa isolated from putrid mineral cutting oil as component of metalworking fluid

Extracellular lipase was isolated and purified from the culture broth of Pseudomonas aeruginosa, an extremophile which naturally grows in water-soluble mineral cutting oil (pH 10) used as metalworking fluid (MWF) for cooling and lubrication in industrial metalworking processes. The molecular mass of the purified lipase was estimated by SDS-PAGE to be 54 kDa. The optimum pH and temperature were 11 and 70 degrees C, respectively. The enzyme is stabile over a broad pH range (pH 4-11.5). The lipase preferably acted on triacylglycerols with medium-chain fatty acids. The lipase was inhibited strongly by Zn(2+), Hg(2+), Cu(2+) and slightly by Ca(2+) and Mg(2+). Non-ionic detergents and sodiumdeoxycholate enhanced lipase activity. Alkaline lipase from P. aeruginosa, capable of growing in a water-restricted medium has excellent properties and good potential for biotechnological applications in the metal industry. Its marked stability and activity in organic solvents suggest that this lipase is highly suitable as a biotechnological tool in a water-restricted medium with a variety of applications including organosynthetic reactions and the control and prevention of MWF putrification in the metal industry.     

Determination of wine antioxidant capacity by derivative potentiometric titration with electrogenerated chlorine

The suitability of derivative potentiometric titration with electrogenerated chlorine for quantification of antioxidative capacity was investigated using catechin and gallic acid standards and a sample set of 11 Croatian wines. The investigation was motivated by advantages over other methods that include rapid measurements, inexpensive equipment, small sample volumes and reproducible results. The method was optimized with respect to various parameters including pH (in the range from 2 to 11), phenolic standard concentration and sample dilution. The chlorine scavenging antioxidant capacity obtained at pH 2 is in good agreement with the total phenolic content measured by Folin–Ciocalteau assay. The ranking order of antioxidant activity/total phenolic content is identical for both methods irrespective of the standard used.     

Leucine aminopeptidase from Streptomyces hygroscopicus is controlled by a low molecular weight inhibitor

In culture filtrate of Streptomyces hygroscopicus a producer of polyketide antibiotics, a leucine aminopeptidase and its autogenous inhibitor were detected. The leucine aminopeptidase was purified 4573-fold with yield of 82% by combination of ion exchange and hydrophobic chromatography. The enzyme is monomeric with a molecular mass of 51 kDa determined by gel chromatography and 67 kDa determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Optimal activity was at pH 8.0 and 40 degrees C. The pI of leucine aminopeptidase is 8.2. The enzyme is strongly inhibited by 1,10-phenantroline, amastatin and dithiothreitol. Atomic absorption spectrometry indicated 2 mols of ion zinc per mol of enzyme. The enzyme is stable at up to 70 degrees C. Leucine aminopeptidase prefers leucine and methionine as N-terminal amino acids. Activity of leucine aminopeptidase is strongly modulated by an autogenous low-molecular weight inhibitor during fermentation, especially during periods of intensive antibiotic production.