Composition and thermal stability of SiO2-based hybrid materials TEOS-MTEOS system

Hybrid materials with different amounts of organics permanently bound on the inorganic network obtained in the TEOS-MTEOS (tetraethoxysilan-methyltriethoxysilan) system are used for obtaining coatings with different optical and mechanical properties. To study the thermal stability of the mentioned materials, compositions with different molar ratios of the precursors were prepared. The influence of the solvent and water amounts on the gelation process was also investigated. The gels obtained were characterised by IR spectrometry and their decomposition temperatures were determined by DTA/TG. Thermal stability of the gels is rather influenced by their composition than the conditions of the gelation process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Culture conditions dictate protease and tannase production in submerged and solid-state cultures of Aspergillus niger Aa-20

Undesirable protease production by Aspergillus niger Aa-20 in submerged culture and solid-state culture was evaluated using different concentrations of tannic acid as sole carbon source in a model system designed for tannase production. Protease production was found to be dependent on the culture system used (submerged culture or solid-state culture) and on the initial tannic acid concentration. Expression of protease activity in submerged culture was higher (up to 10 times) than activity obtained in solid-state culture, using identical culture medium composition. In submerged culture, the lowest final protease activity (0.13 IU) was obtained with the highest tannic acid concentration, while in solid-state culture protease activity was not affected by changes in initial substrate concentration. Absence of detectable proteolytic activity in solid-state culture is related to high production of tannase enzyme. Hence, the use of solid-state culture for fungal enzyme production may allow for higher and more stable enzyme titers present in culture extracts.     

Non-coherent visible and infrared radiation increase survival to UV (254 nm) in Escherichia coli K12

Interactions between visible or infrared (IR) and ultraviolet (UV, 254 nm) radiation have been studied in E. coli. Pre-illumination with non-coherent monochromatic 446, 466, 570 and 685 nm radiation, as well as with polychromatic red and IR radiation at room temperature, leads to increased cell survival after a subsequent irradiation with UV light. In the thermic range of the spectrum (red and IR), IR but not red light pre-treatment is able to increase cell survival to a subsequent lethal heat (51 degrees C) challenge, suggesting that increased UV survival may be due to IR-induced heat-shock response. On the other hand, visible-light-induced resistance may be due to a different mechanism, possibly involved with unknown bacterial light receptors.     

Evaluation of the residual stability of polyurethane automotive coatings by DSC

Degradation of poly(ester-urethanes), poly(ether-urethanes) and poly(acrylic-urethanes), as a base for automotive paintings in interior applications, has been studied by DSC. The samples were clearcoat and black-pigmented paints, unstabilized and stabilized with HALS Tinuvin 292, UV absorber Tinuvin 1130 and antioxidant Hostanox O3, exposed to weathering in Xenotest and in Arizona desert. From the dependences of oxidation onset temperature on the heating rate, the kinetic parameters enabling to calculate the oxidation induction time for a chosen temperature have been obtained. From the values of oxidation induction time, the protection factors of the additives and the residual stability of the polymer after an ageing stress has been evaluated. It has been shown that the equivalence between the two methods of weathering depends on the polymer composition. A new criterion for the evaluation of synergism/antagonism of additives in the stabilizing mixture has been proposed.     

A new approach to qualitative analysis of organophosphorus pesticide residues in cucumber using a double gas chromatographic system: GC-pulsed-flame photometry and retention time locking GC-mass spectrometry

A qualitative method for the screening of organophosphorus pesticides (OPs) that could present in different types of vegetables has been established and validated. A typical multi-residue extraction procedure of OPs using ethyl acetate and sodium sulphate has been applied. No clean-up was required after extraction, and concentrated extracts were analysed by gas chromatography with pulsed-flame photometric detection (GC-PFPD). Confirmation of compound identities was performed by gas chromatography with mass spectrometric detection (GC-MSD) in the electron impact (EI) mode with full scan acquisition. Retention time locking (RTL) software was used in order to improve the method capability of identification and confirmation. Spiked samples at pesticide concentrations equal to the maximum residue level (MRL) were used to check chromatographic performance and for validation studies. The proposed method allows a rapid and accurate identification of the studied OPs until the ng ml(-1) range for those whose use is forbidden, and above their MRL concentration for the rest.     

Mixtures of nonionic and anionic surfactants: interactions with low-molecular-mass homopeptides

The interaction between low molecular-mass homopeptides and mixtures of nonionic and anionic surfactants has been assessed by using reversed-phase thin-layer chromatography. The relative strength of interaction for mixtures of sodium dodecylsulfate and tridecylalcohol diglycolate (GNX) at the molar ratios of 8:2, 6:4, 4:6 and 2:8 has been calculated and its relationship with the physicochemical parameters (number of amino acid units, hydrophobicity, side chain bulkiness, electronic characteristics) of peptides has been computed by stepwise regression analysis. Each peptide interacted with each surfactant mixture the strength of interaction markedly depending on both the character of the peptide and the composition of the surfactant mixture. The hydrophobicity and electronic properties of the amino acid units exerted the highest influence on the strength of interaction at the highest concentration of the nonionic surfactant (GNX) whereas the number of amino acid units in the peptide molecule and the bulkiness of the amino acid side chain governed the strength of interaction at the lowest concentration of GNX.     

Atomic spectroscopy for detection in thermal analysis

An atomic absorption spectrophotometer is coupled to a conventional thermoanalytical quartz furnace as used for TG and DTG to detect the thermally evolved products. In this combined system, the dry aerosol (smoke) obtained by cooling the vapour evolved is transported from the furnace to the flame for metal-specific atomic absorption detection. The particular design of the furnace outlet promotes the formation of stable aerosols. Optimum experimental conditions were determined, using zinc chloride solution, by varying the specimen mass, the heating rate and the flow rate of the furnace gas at a linear temperature program. The absorbancevs. temperature curves obtained with this method for various zinc compounds are compared with the corresponding DTG curves. The applicability of the technique for studying heterogeneous reactions with carbon tetrachloride and hexane vapours is presented. The utilization of an atomic absorption spectrophotometer equipped with a quartz cuvette for detecting the thermal evolution of mercury vapours is described, as well as detection potentials by molecular absorption (for NO and NH₃) and light scattering (for smoke evolved from organic matter). The results obtained with the suggested methods may, in some respects, valuably complement the results achieved with DTG and with flame ionization detection.

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Zusammenfassung Ein Atomabsorptionsspektrometer wurde mit einem konventionellen thermoanalytischen Quarzofen gekoppelt um thermische Abspaltprodukte nachzuweisen. In diesem kombinierten System wird das durch Kühlung des entwickelten Dampfes erhaltene Aerosol (Rauch) vom Ofen in die Flamme für den metallspezifischen Atomabsorptionsnachweis übergeleitet. Die spezielle Ausbildung der Austrittsöffnung gewährleistet die Bildung eines stabilen Aerosols. Die optimalen Versuchsbedingungen wurden durch Zinkchloridlösungen bei Anderung der Probenmasse, der Aufheizgeschwindigkeit und der Strömungsgeschwindigkeit des Ofengases im linearen Temperaturprogramm ermittelt. Die mit dieser Methode für verschiedene Zinkverbindungen erhaltenen Absorptions—Temperatur-Kurven wurden mit den entsprechenden DTG-Kurven verglichen. Die Anwendbarkeit dieser Technik bei dem Studium heterogener Reaktionen mit Kohlenstofftetrachlorid und Hexandämpfen wird gezeigt. Der Einsatz eines mit einer Quarzküvette zum Nachweis der thermischen Entwicklung von Quecksilberdampf versehenen Atomabsorptionsspektrometers wird beschrieben, sowie die Nachweisgrenze durch molekulare Absorption (für NO und NH₃) und Lichtstreuung (für aus organischem Material entwickelten Rauch). Die bei den beschriebenen Methoden erhaltenen Ergebnisse können, in mancher Hinsicht, die durch DTG und Flammenionisationsnachweis erhaltenen Ergebnisse wertvoll ergänzen.

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- , , . (), , . . , . — , , -. . - , , , ( NO NH₃) ( , ). , , , - .

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Presented in part at the 24th Hungarian Conference on Analytical Sptecroscopy, Miskolc, June 15–18, 1981. Abstracts pp. 159–162.

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The authors wish to express their thanks to S. Gál for his assistance in the present application of the temperature programmer developed by him and his group, and for the valuable discussions on the subject. Thanks are also due to K. Tomor and J. Kmives who participated in the comparative thermoanalytical measurements and their analysis.     

Simple and rapid determination of the drug naproxen in pharmaceutical preparations by heavy atom-induced room temperature phosphorescence

A simple, selective and sensitive heavy atom-induced room temperature phosphorimetric method (HAI-RTP) is described for the determination of naproxen (NAP) in pharmaceutical preparations. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of a heavy atom salt and sodium sulfite as an oxygen scavenger to minimize RTP quenching. These variables selection constitute the basis of a HAI-RTP method for the determination of naproxen (detection limit 17.6 ng ml(-1); 1.71% relative standard deviation at 250 ng ml(-1)). The method has been applied satisfactorily to the analysis of pharmaceutical preparations.     

Distribution of mercury in soil organic matter fractions obtained by dissolution/precipitation method

Sequential multistep procedure, usually used for the fractionation and characterization of soil organic matter was tested for Hg content in the individual steps and fractions. Under general laboratory conditions serious problems have arosen during the attempt in the Hg mass balance calculation. Several sources of Hg contamination were recognized. The most serious was the background concentration of Hg even in research grade chemicals (what is in general not declared) and laboratory air. The work on operational Hg speciation as non-humic bound, humic acid, fulvic acid bound proceeds from the established status-quo on distribution of mercury of soil organic matter.     

Cyclodextrin Solubilization of the Antibacterial Agents Triclosan and Triclocarban: Effect of Ionization and Polymers

The natural β-cyclodextrin (βCD) and its complexes have limited solubility in aqueous solutions. This low aqueous solubility, as well as low aqueous solubility of the guest molecule (i.e. triclosan or triclocarban (TCC)), can result in low complexation efficiency (CE). The purpose of this study was to enhance the apparent intrinsic solubility (S ₀) of the guest molecule and its βCD complexes through ionization and addition of auxiliary compounds such as polymers, amino acids and metal ions. Both triclosan (pK _a 7.9) and TCC (pK _a 12.7) are weak acids. Addition of ethanol to the complexation medium enhanced S ₀ of both triclosan and TCC but at the same time ethanol lowered the stability constant (K _c ) of their βCD complexes resulting in overall lowering of CE. Addition of small amount of water-soluble polymers enhanced the βCD solubilization of both guests, and addition lysine enhanced the solubilization of TCC. Ionization of triclosan resulted in significant enhancement of CE and enhanced triclosan release from tablets containing triclosan/βCD complex. The effect of ionization was not as pronounced in the case of TCC.This revised version was published online in July 2005 with a corrected issue number.